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Mango stone biocomposite preparation and application for crystal violet adsorption: A mechanistic study
Accepted Manuscript Mango stone biocomposite preparation and application for crystal violet adsorption: A mechanistic study Sidra Shoukat, Haq Nawaz Bhatti, Munawar Iqbal, Saima Noreen PII:
S1387-1811(16)30464-4
DOI:
10.1016/j.micromeso.2016.10.004
Reference:
MICMAT 7944
To appear in:
Microporous and Mesoporous Materials
Received Date: 7 April 2016 Revised Date:
27 September 2016
Accepted Date: 7 October 2016
Please cite this article as: S. Shoukat, H.N. Bhatti, M. Iqbal, S. Noreen, Mango stone biocomposite preparation and application for crystal violet adsorption: A mechanistic study, Microporous and Mesoporous Materials (2016), doi: 10.1016/j.micromeso.2016.10.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Mango stone biocomposite preparation and application for crystal violet adsorption: A mechanistic study
a
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Sidra Shoukata, Haq Nawaz Bhattia,*, Munawar Iqbalb,* and Saima Noreena
Department of Chemistry, University of Agriculture, Faisalabad 38000, Pakistan b
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Department of Chemistry, The University of Lahore, Lahore, Pakistan
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*Corresponding author(s) E-mail: [email protected] (H. N. Bhatti); [email protected] (M. Iqbal)
Abstract
Mango stone biocomposite (MSBC) was prepared and employed for the adsorption of crystal violet (CV) dye. Process variables were optimized and maximum dye adsorption of 352.79 mg/g
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was achieved at pH 8, 0.05 g adsorbent dose, 30 min contact time, 33 0C for dye initial concentration of 400 mg/L onto MSBC. Salt and surfactants pre-treatments of MSBC did not affect the CV adsorption. The CV equilibrium adsorption data followed pseudo second order
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kinetic model and Langmuir adsorption isotherm. Thermodynamic parameters (∆Go, ∆Ho and ∆So) revealed that the CV adsorption onto MSBC was an exothermic and spontaneous process.
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SEM analysis revealed that the surface morphology of dye loaded MSBC was changed significantly and hydroxyl and carbonyl groups were main functional group responsible for CV adsorption onto MSBC. The prepared MSBC also showed recyclable nature and might be potential candidate for dyes removal form textile effluents. Keywords: Mango stone biocomposite; Crystal violet; Adsorption; Kinetics; Thermodynamics; Isotherms; Desorption
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1. Introduction Water pollution has been increased to alarming level and dyes are one of the major sources from textiles and dying sector, which is a serious threat to ecological balance. Recent
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reports revealed the toxic and carcinogenic nature of dyes [1-21]. More than 100,000 dyes are synthesized with 700,000 metric tons production annually. Among many classes of synthetic dyes, triphenylmethane class of dyes is most versatile due to their diverse applications. Crystal
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violet dye (basic violet 3, gentian violet, and methyl violet 10B) is a member of triarylmethane dyes [22]. Other than dying and printing, it is also used in biological studies, dermatology,
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veterinary and poultry feed etc. The CV is a mutagenic, carcinogenic and poisonous to mitotic division process [23, 24], which is also non-biodegradable and persists in the environment for longer time. Other than cytogenetic effects, eye irritation, skin irritation, digestive tract irritation, respiratory and kidney failures have been reported in response of CV exposure [25-27]. In view
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of toxic nature of dyes, management of wastewater from textile industry before thronging out in water sheds is necessary. Various methods have been applied with positive outcomes for the adsorption of pollutant form simulated solution as well as effluents [1, 2, 5-8, 10, 28-36].
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Adsorption using agriculture waste biomasses have been used potentially for dyes adsorption as these are easy-to-handle, recyclable, available round the year, less expensive and more efficient
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[37-40] i.e., garlic waste [41], coir pith [42], baggase pith [43], pineapple waste [44], rice waste [45], rice husk [46], plant waste and bark [47], okra waste [48], fly ash, powdered activated carbon [49, 50], bagasse [51], activated carbon, coal-based bottom ash [52], modified zeolite and clay [53], powdered peanut hull [54], orange peel [55], soy waste biomass [56], palm fiber-based activated carbon [57], bamboo dust-based, coconut shell-based, groundnut shell-based activated
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carbon [58] commercial activated carbon [59] and eucalyptus angophoroides bark [40] showed promising efficiencies for dyes adsorption (Table 1). The composites technology advanced the applications of adsorbents for pollutant
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adsorption and is proved to be highly efficient versus native biomasses [60-62]. Mango is the plump stony fruit, belongs to genus Mangifera and family Anacardiaceae and national fruit of Philippines, India and Pakistan. The Food and Agriculture Organization (FAO) of the United
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Nations reported mango production of 35 million tons (MT) worldwide in 2009 including India (13.6 MT), Mexico (1.9 MT), Thailand (2.5 MT), Indonesia (2.2 MT), China (4.2 MT), Pakistan
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(1.7 MT) and Brazil (1.2 MT) as major growers [62, 63]. As a result of mango processing a considerable amount of waste materials i.e., mango stones (seed), peel and kernel is produced and wasted [2, 64]. Previously, mango stone has been reported as efficient adsorbent for different types of pollutants [65], however, mango stone composites have not been investigated for the
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adoption of CV [37, 66].
Therefore, mango stone was used for composite preparation and employed for CV dye adsorption. As-prepared MSBC adsorption capacity was studied as function of medium pH, dye
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initial concentration, contact time and adsorbent dose. Salt and surfactants pre-treatments effect on dye adsorption was also studied. Kinetic, thermodynamics and isotherms models were
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employed to understand CV adsorption mechanism onto MSBC. Desorption behavior of prepared MSBC was also checked. FTIR and SEM techniques were used to monitor the dye loaded and un-loaded MSBC. 2. Material and Methods 2.1.Reagents, Chemicals and Instruments
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The chemical and reagents such as HCl, NaOH, acetone, ferric chloride and sodium borohydride, HNO3, H2SO4 and CH3COOH were purchased from Fluka and Merck. Potassium dihydrogen phosphate/disodium hydrogen phosphate, citric acid/sodium hydroxide/sodium chloride solution
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and boric acid/sodium hydroxide solution/potassium chloride (Sigma-Aldrich) were used to prepare buffers of pH 4, 7 and 11, respectively. The surfactants such as C-TAB, Tween-80, SDS were purchased from Sigma-Aldrich, whereas Surf Excel and Rim were purchased from local
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market. Ultra-pure water with a resistivity of 18.2 MΩ cm from Milli-Q system (Millipore) was used for the preparation of dye and other solutions. The instruments such as octagon siever
(Moulinex,
France),
FTIR
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(OCT-DIGITAL 4527-OI), shaker (PA 250/25.H), pH meter (HI-8014 Hanna), grinder (Beaconfield
Buckinghamshire
HP9
1QA)
and
SEM
(JSM5910, JEOL, Japan) were used throughout the study. 2.2.Solution preparation
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Crystal violet dye was purchased from local textile market, Faisalabad, Pakistan. Dye stock solution was prepared by dissolving respective amount of dye in ultra-pure water and the
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working concentrations were prepared by diluting stock solution. 2.3.Biomass collection and preparation
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The mango stone was collected from student market, University of Agriculture, Faisalabad, Pakistan. Preliminary, the mango stone was cleaned and dried in open air followed by oven drying at 50°C for 72 h. Dry mango stone was chopped, grinded and sieved through Octagon siever to obtained uniform particle size (0.25 mm), which was used for MSBC preparation. 2.4. Mango stone biocomposite preparation Mango stone powder (6 g) was mixed with 0.45 M ferric chloride solution (15 mL), stirred and 4
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0.25 M sodium borohydride (15 mL) was added slowly with continuous stirring. After an additional stirring of 20 min, the mixture was filtered (2.5 µm), washed with ethanol thrice and
airtight plastic bags until adsorption experiments. 2.5.Point of zero charge (pHpzc)
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dried in desiccators for 48 h. The dried composite was again grinded (0.25 mm) and stored in
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For pHpzc determination, 0.1 M KNO3 concentration series (50 mL) were prepared and pH was adjusted between 1.0-12.0. The adsorbent (0.1 g) was mixed with solution, shaken and left for 48
determination. 2.6. Adsorption procedure
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h with intermit mixing [67]. Final pH was noted and data was plotted for the pHpzc
Process variables i.e., solution pH, dye concentration, contact time, MSBC dose were studied and optimized. The pH (2-8), adsorbent dose (0.05 - 0.30 g), contact time (5-120 min),
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temperature (33-54 °C) ranges were studied. NaCl salt (0.2-1.0 M) and surfactants pre-treatments (CTAB, SDS, Tween-80, Rim and Surf Excel) (5% solution) effect on CV adsorption onto composite was also studied. For adsorption experiments, 100 mL solution was taken in flasks,
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covered with aluminum foil and set on shaker at 120 rpm. After stipulated time period, flasks
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were removed and the contents were filtered (2.5 µm) to separate the adsorbent from dye solution. Residual dye concentration was determined and amount of CV adsorbed on unit mass was estimated (Eq. 1).
=
(Eq. 1)
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Where, qe (mg/g) is dye adsorption capacity, Ci (mg/L) and Cf (mg/L) are representing the crystal violet initial and concentration at equilibrium. V (L) and m (g) are volume and adsorbent dose,
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respectively. 2.7. Desorption study
Desorption was carried out using 0.1 M HCl, HNO3, H2SO4 and CH3COOH. Among all
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desorbing agents, CH3COOH showed better desorption capacity and then, 0.2-1.0 M CH3COOH solution was used to desorb dye from MSBC. For desorption study, CV loaded MSBC was dried
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and placed in contact with CH3COOH solution and stirred for 2 h at 120 rpm. MSBC was separated and dye desorbed was estimated (Eq. 2).
(%) = 100
(Eq. 2)
(desorbed), respectively.
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Where, qd (%), D and R are representing desorption capacity, dye adsorbed and dye recovered
2.8.SEM and FTIR analysis
elsewhere [68].
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The loaded and un-loaded MSBC was characterized using FTIR and SEM as precisely reported
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3. Results and discussion
3.1. Point of zero charge of native and mango stone biocomposite The pHpzc is important to evaluate the charge on adsorbent surface since surface charge depends upon pHpzc. pHpzc was checked in KNO3 solutions in the pH the range of 1.0 to 12.0. pH difference (∆pH = pHi - pHf) was estimated and response was plotted between pH and ∆pH and pHpzc was estimated. The pHpzc of native mango stone biomass was found to be 6.5, whereas it
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was 6.3 for MSBC (Fig. 1A) (point of zero charge of mango stone native biomass versus mango stone biocomposite). It is reported that adsorption depends upon the pHpzc since charges on
present investigation did not reveal significant difference in pHpzc. 3.2. Screening of native and mango stone biocomposite
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adsorbent surface vary according to pHpzc [67]. However, native and composite adsorbents in
As-prepared MSBC and native mango stone adsorbents were screened for CV adoption
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capacities and MSBC showed considerably higher CV uptake as compared to native mango stone biomass (Fig. 1B), which revealed that MSBC offers favorable environment for dye
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adsorption. This enhanced adsorption is attributed to change in surface characteristics in response of composite preparation since MSBC provides reinforcement and compatible matrix that may enhanced the adsorption capacity. It is reported that functional groups on MSBC surface are modified and accommodate dyes molecule efficiently [61]. Similar trend have also
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been reported previously that composites showed more dye uptake capacity as compared to native biomasses and this enhanced adsorption capacity of have been correlated favorable physico-chemical properties of composites [37, 40, 61, 62, 69].
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3.3. Effect of pH on dye adsorption
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The medium pH affects charges on adsorbent surface, ionization and the speciation of adsorbate species, which play important role in dye adsorption [40, 61]. The pH effect on adsorption was studied in the pH range of 2-10 using 0.10 g adsorbent dose, 1 h contact time, 50 mg/L dye initial concentration and 33 0C were fixed. The solution pH affects the CV adsorption considerably. The CV adsorption increased gradually and maximum adsorption was observed at pH 8.0 and further increase in pH, the CV adsorption capacity decreased (Fig. 1C). This behavior of CV adsorption as a function of pH is due to changed active sites binding capacity since MSBC 7
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surface can be protonated/de- protonated under acidic/basic conditions, which may affect the dye adsorption depending on dye nature (cationic/anionic). At optimum pH (mild basic condition), the binding sites remained available hence CV uptake was higher. The possible explanation of
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this behavior could be the involvement of functional groups that may expose under specific conditions (acidic/basic) and resultantly, negative/positive charge density on the adsorbent surface attracted/repel dye ions [70]. The decreasing trend of dye adsorption under basic
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condition (pH > 8) was due to the formation of hydroxyl species [71]. On the other hand, under acidic condition, the ligands on cell wall are closely related to H3O+ ions that might hinders CV
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dye approach to the adsorbent surface due to repulsive forces. Therefore, the H3O+ ions compete with CV ions for adsorption. Since under acidic condition, the H3O+ ions concentration is likely to increase and can cover the active sites leaving the dye ions un-adsorbed. As the pH of the medium increased, the competition between dye ions and H3O+ ions decreased and resultantly,
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dye adsorption increased [40]. Similar trend regarding pH effect on dyes adsorption have been reported previously i.e., bark adsorbent [72] and apple shell waste adsorbent [73]. Both authors correlated low dye adsorption with deprotonation under acidic pH.
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3.4. Effect adsorbent dosage on dye adsorption Since surface area available for dye ions has direct effect on adsorption, So for the effect of
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adsorbent dose in the range of 0.05 to 0.3 g was studied for 1 h contact time, 50 mg/L dye initial concentration, pH 8 at 33 0C. At low adsorbent dose, considerably higher CV adsorption was observed, which decreased linearly as the adsorbent dose increased (Fig. 1D). The adsorption capacity of 49.0 mg/g at 0.05 g adsorbent dose was achieved, which decreased to 9 mg/g for the adsorbent dose of 0.3 g. This decreasing adsorption capacity at higher adsorbent dose was due to low surface area [40, 69, 74]. An increase in adsorbent amount using same solution volume and
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dye concentration lead to occupation of available binding sites and due to particles interaction, aggregation may occur and resultantly, surface area may decreased [37-39, 60-62, 75]. The decreasing trend of dye adsorption at higher adsorbent dose can be attributed to decreased
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adsorbent surface area and unavailability of adsorption sites [54]. Sonawane and Shrivastava [76] reported the optimum dose of maize cob 12 g/L for maximum dye adsorption, which
3.5. Effect Contact time on dye adsorption
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indicates that composite are efficient for dye adsorption at very low dose versus native biomass.
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To find out the time required for equilibrium attainment for CV adsorption on to MSBC, the contact time in the range of 5-120 min was investigated. Other variables i.e., 50 mg/L dye initial concentration, pH 8, 0.05 g adsorbent dose and 33 0C were constant and results thus obtained are represented in Fig. 2(A). The MSBC dye adsorption efficiency was very fast initially followed by slow adsorption and then, equilibrium was reached within 30 min of contact time, which
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indicates that MSBC is highly efficient for CV adsorption because equilibrium was attained in shorter duration. The CV adsorption trend as a function of contact time revealed that adsorption occurred in two distinct steps i.e., initial fast phase remained for very shorter duration followed
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by slow adsorption phase remained for comparatively longer duration. After attaining the
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equilibrium, further adsorption was insignificant as a function of contact time. From this trend, it can be concluded that initially the binding sites were freely available and fast adsorption was occurred, whereas in second phase the slow CV adsorption was due to the saturation of binding sites and dye ions occupy the remaining vacant sites slowly due to repulsive forces between the dye ions and ions already adsorbent on adsorbent. Secondly, slow adsorption with the passage of time may also be due to intraparticle diffusion process dominating over adsorption [37, 77]. These finding are in line with previous studies for different adsorbents as a function of contact 9
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time i.e., adsorption of direct red 75 and direct red 80 onto calcined bone [78], pineapple waste biomass [44] and cationic dye removal from aqueous solution by rice bran [45]. However, native biomass took longer time to reach the equilibrium i.e., equilibrium for dye adsorption was
3.6. Effect initial dye concentration on dye adsorption
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reached in 129 min for coniferous pinus bark powder [72] and in case of wood apple shell [73].
Dye initial concentration in the range of 20 to 500 mg/L was studied since dye initial
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concentration acts as a driving force in transferring the dyes ions from aqueous media to solid surface. The contact time of 1 h, pH 8.0, 0.05 g adsorbent dose and 33 0C conditions were
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constant and response thus obtained is depicted in Fig. 2(B). CV adsorption increased gradually with initial concentration and reached 352.79 mg/g for initial dye concentration of 400 mg/L. Beyond this concentration, the adsorption capacity was insignificant. Similar trend in adsorption capacity as a function of dye initial concentration have been reported previously for different
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adsorbents [79]. It is noted that dye initial concentration is important in adsorption process since concentration provides driving force to overcome mass transfer resistance between solid and solution phases [30, 37-40, 61, 62, 69, 74]. At higher concentration, the ratio of the initial CV
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ions to the available surface area was high and the fractional adsorption subsequently becomes dependent to the initial concentration. However, at extremely high concentration, the available
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sites exhausted and resultantly, the CV adsorption decreased. Previously, similar dyes adsorption behaviour have been reported as a function of dyes initial concentrations for different adsorbent types [25, 38, 45, 46, 49, 54, 80, 81]. 3.7. Effect of temperature on dye adsorption The effect of temperature was studied in the range of 33-54 0C on CV adsorption on to MSBC, whereas 50 mg/L dye initial concentration, 1 h contact time, pH 8.0, 0.05 g adsorbent dose were
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constant and adsorption response is depicted in Fig. 2(C). The maximum CV adsorption of 48.0 mg/g was observed at 33 0C, which reduced to 40.0 mg/g at 54 0C. The decreasing adsorption trend at higher temperature indicates that the CV adsorption was an exothermic process, which
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might be due to the deteriorating of binding forces on surface at higher temperature [82]. The dye adsorption as a function of temperature indicates that adsorbent surface activity decreased by increasing temperature and CV adsorption is mainly controlled by physical forces [83].
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Therefore, the CV adsorption process was exothermic in nature because as temperature increased, the CV adsorption decreased. However, some researchers reported higher CV
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adsorption onto different adsorbents at higher temperature for activated carbon and groundnut shell [23, 84] and difference might be due to stable nature of adsorbents at elevated temperature.
3.8. NaCl and surfactants pre-treatment effect on dye adsorption
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To study the pre-treatment effect of NaCl on CV adsorption is important since the wastewater discharged from industries has different salts. Salt effect was studied in the range of 0.2-1.0 M (Fig. 2D). While studying the effect of salt on CV adsorption, 50 mg/L CV initial concentration,
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1 h contact time, pH 8.0 and 0.05 g adsorbent dose at 33 0C were kept constant. Interestingly, the MSBC treated with NaCl did not affect the CV adsorption. It has been reported that salt affects
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the enthalpy of adsorption process along with pH change of medium and hydrophobic and electrostatic interactions between adsorbent surface and dye ions may change [61, 69]. The salt addition may also affect the forces such as van der Waals, ion-dipole, and dipole-dipole among ions in the solution and low removal of dye can also be correlated with co-ion competition for binding sites on to the adsorbent surface [85]. However, NaCl treated MSBC revealed insignificant effect on CV adoption. Similarly, the MSBC was also pre-treated with surfactants
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i.e., Surf Excel, Rim, C-TAB, Tween-80 and SDS and employed for CV adsorption. A 5% solution of each surfactant was used and 50 mg/L CV initial concentration, 1 h contact time, pH 8.0 and 0.05 g adsorbent dose and 33 0C were constant and results, thus obtained are shown in
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Fig. 2(E). Surfactants pretreatments of MSBC decreased the CV adsorption slightly in following order Excel > Rim > C-TAB > SDS > Tween-80. Previously, adsorbent pre-treated with surfactants showed significant effect on dye adsorption [69], but present investigation revealed
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that surfactants effect was insignificant for MSBC. A slight decrease of CV adsorption might be due to coverage of active sites and resultantly [86]. Previously, it have also been reported that the
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dyes adsorption may decrease in the presence of surfactants, which was correlated with coverage of acidic groups on adsorbent surface and resultantly, the hydrophilic end of surfactants behave like base and repulsive forces was generated between dye ions and adsorbent surface [61, 69],
3.9.Kinetic modeling
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which reduced the CV adsorption slightly.
Pseudo-first-order and pseudo-second-order kinetic models were employed to study the CV adsorption behavior as a function of contact time [40]. The pseudo-first-order kinetic model is
= ( − )
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shown in Eq. 4 and the integrated can be seen in Eq. 5 [37].
log ( − ) = log −
#
$.&'&
(
(Eq. 4)
(Eq. 5)
Where, k1(min−1), qe (mg/g), and q (mg/g) are the rate constant, dye adsorbed at equilibrium, dye adsorbed at time t, respectively and t is time. The k1 was determined from the slope of plot log (qe−q) versus t.
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The integrated and linear forms of pseudo second order kinetic model are shown in Eqs. 6-7, respectively [87]. = $ ( − )$
=
)
#* +*
+
(Eq. 6)
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(Eq. 7)
+
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Where, k2 (g−1min−1) and qe (mg/g) are the constant and adsorption capacity at equilibrium, which were determined from the slope and intercept of plot t/qt versus time. The kinetic data is
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presented in Table 2 and plots are shown in Figs. 3(AB), respectively. The qe estimated values from experimental data did not correlate with the pseudo first order kinetic model and the R2 values (0.86, 0.54 and 0.41 for 25, 50 and 75 mg/g dye concentration, respectively) were also not acceptable, leading to the assumption that the experimental data did not fit well with the pseudo-
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first order kinetics model. In case of pseudo second order kinetic model, the qe values coincided well with the modeled values (23.26, 50.00 and 76.92 for 25, 50 and 75 mg/g concentration, respectively) and the R2 values (0.99, 1.0 and 1.0 for 25, 50 and 75 mg/g concentration,
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respectively) were also higher versus pseudo first order kinetic model. Therefore, CV adsorption on to MSBC followed pseudo second order kinetic model. A similar kinetic behavior of CV have
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also been reported previously for different types of biomasses i.e., peanut waste [54], citric acid treated wheat straw adsorbent [24] and NaOH pre-treated rice waste [25], coir pith [88] and sawdust [81]. Findings revealed that CV adsorption onto composite was chemisorption process, which requires valence forces through the sharing or exchange of electrons between the adsorbent and the adsorbate [89]. 3.10.
Intraparticle diffusion model
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Weber-Morris intraparticle diffusion model was employed [90] and model is shown in Eq. 8. = -. ( './ + 0
(Eq. 8)
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Where, qt is the adsorption capacity at time t and kid is the intraparticle diffusion rate constant and C is the film thickness, which was calculated from the plot between qt and t0.5. Intraparticle diffusion model presumed that first adsorbate is transferred on the surface of adsorbent and then,
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transported within the available pores by diffusion process [40], boundary layer is formed and finally, adsorbate interacts with binding sites. The data for intraparticle diffusion model fitting is
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shown in Table 2 and plot is depicted in Fig. 3(C). Data revealed that the intraparticle diffusion was not only the rate controlling step for CV adsorption [91]. This trend of CV adsorption was in line with reported observation [92] regarding intraparticle diffusion modeling as well as dye adsorption onto different adsorbents [69, 93-96].
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3.11. Adsorption isotherms
Langmuir, Freundlich and Harkins-Jura isotherms were employed to understand the forces governing interaction between CV ions and MSBC [61, 62, 69]. The linear form of Langmuir
+
=
1
+
21 +
(Eq. 9)
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isotherm is expressed in Eq. 9.
Where, qe (mg/g), Ce (mg/L), Qo (mg/g) and b (L/mg) are representing amount of dye adsorbed at equilibrium/unit mass of adsorbent, equilibrium dye concentration, maximum dye adsorbed per unit mass of adsorbent to form a monolayer at higher Ce values, respectively, where b is related to the energy of the adsorption. A plot of Ce/qe versus Ce yielded a straight line with slope 1/bQo
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and intercept 1/Qo (Fig. 3(D)). The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless constant called separation factor (RL) (Eq. 10)
(Eq. 10)
52
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34 =
Where, C0 is the initial concentration of dye (mg/L), and b (L/mg) is the Langmuir constant. The RL is used to assess the adsorption behaviour of adsorbate on to adsorbent i.e., the RL > 1, RL = 1,
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0 < RL < 1 and RL represent unfavourable, linear, favourable and irreversible adsorption,
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respectively and based on RL value CV adsorption was favourable onto MSBC. The Freundlich isotherm exponential form is shown in Eq. 11 [61]. /8
= -6 0
(Eq. 11)
Where, KF (mg/g) and n are the constants, and KF is representing the adsorption capacity/unit
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mass of adsorbent. The 1/n value reveals the favourability of adsorption and its value > 1 indicates the favourable adsorption of adsorbate onto adsorbent surface [37, 39]. The logarithmic form of Freundlich is shown in Eq. 6. The KF and n are calculated from the intercept and slope of
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the plot of log qe versus log Ce (Fig. 3(E)).
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Harkins–Jura isotherm is presented in Eq. 12 [97]. Where, A and B are constants. This isotherm accounts multilayer adsorption system and existence of heterogeneous pore distribution. The Harkins–Jura isotherm curve is shown in Fig. 3(F).
+*
=
9 :
− log 0
(Eq. 12)
:
The Freundlich, Langmuir and Harkin-Jura constants with R2 values are given in Table 3 and plots can be seen in Figs. 3(D-F), respectively. The R2 and equilibrium experimental data revealed that the R2 value for the Langmuir model was high and acceptable to explain the CV 15
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equilibrium adsorption onto MSBC, whereas the R2 values in case of Freundlich and HarkinsJura isotherms were not acceptable. The Freundlich isotherm model described the adsorption on heterogeneous surface and is not restricted to the formation of monolayer and 1/n suggests the
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favorable adsorption of CV dye onto MSBC. The Langmuir isotherm assumes monolayer coverage of adsorbate over a homogenous adsorbent surface. A saturation point is reached after attaining equilibrium and further adsorption is not possible at same site [40, 61, 62, 69].
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Similarly to present investigation, the adsorption of CV onto grapefruit peel was better explained by the Langmuir versus Freundlich isotherm [98]. In another study, almond skin waste also
3.12.
Thermodynamic study
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followed Langmuir isotherm for CV adsorption [80].
Thermodynamic parameters i.e., enthalpy (∆H°), entropy (∆S°) and Gibbs free energy (∆G°)
<+
(Eq. 13)
+
∆> ' = −3?@A-; ∆B
−
∆C D
(Eq. 15)
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@A-; =
(Eq. 14)
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-; =
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were computed to understand the nature and were measurd using Eqs. 13-15 [61, 69].
Where, Kc, qe and Ce are representing the equilibrium constant, adsorption at equilibrium (mg/g) and dye concentration at equilibrium (mg/L). The thermodynamic data for CV adsorption onto MSBC is shown in Table 4 and plot of lnKc versus 1/T is shown in Fig. 4(A). The ∆G° value indicates that the adsorption process was spontaneous in nature. ∆H° negative value verifies the exothermic nature of CV adsorption onto MSBC. The negative ∆S° value revealed decrease in randomness at the solid/solution interface as a result of CV adsorption [87]. The ∆G0 value in the 16
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range of -0.34 to -0.40 revealed that CV process was physisorption. A value between -20 and 0 kJ/mol favors physiosorption, whereas chemisorption mechanism is involved when ∆Go is in the range of -80 to -400 kJ/mol [99]. The ∆Go values for CV adsorption onto MSBC were in the
physisorption nature of CV adsorption on to MSBC [100, 101]. Desorption studies
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3.13.
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range of -0.34 to -0.40 kJ/mol for temperature range of 33 0C to 54 0C. These results revealed the
Desorption of CV was performed using 0.2-1.0 M CH3COOH solution. Dye loaded MSBC was
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mixed with CH3COOH solution and agitated for 120 min at 100 rpm and desorbed dye was estimated. Results showed that desorption capacities for 1.0, 0.8, 0.6, 0.4, 0.2 M CH3COOH solutions were 5.0%, 11.0%, 17.0%, 15.0% and 10.5%, respectively (Fig. 4(B)) and CH3COOH 0.6 M showed maximum desorption capacity. Desorption yields concentrated adsorbate and adsorbent cab be regenerated using suitable S/L ratio. The CH3COOH solution (50 mL) was
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mixed with 0.1 g with dried MSBC. The S/L ratio were found to be 50:0.10, 50:0.22, 50:0.34, 50:0.30, 50:21 for 1.0, 0.8, 0.6, 0.4 and 0.2 M CH3COOH, respectively. Desorption of CV dye was maximum for 0.6 M CH3COOH; hence S/L ratio of 50:0.34 is best to desorbs CV from
FTIR and SEM studies
AC C
3.14.
EP
MSBC for the regeneration of the adsorbent.
Un-loaded and dye loaded MSBC surface morphology was monitored by SEM analysis. The SEM image of un-loaded MSBC is shown in Fig. 5(A). The surface morphology indicates that un-loaded MSBC has spaces, pores and surface was also un-even in un-loaded adsorbent. The dye loaded SEM image is shown in Fig. 5(B). It can be seen that the surface of dye loaded MSBC is changed considerably, which is more even than un-loaded adsorbent. The CV dye absorbed on the cell wall matrix and created stronger crosslinking and uniformity on the surface 17
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of the adsorbent. Further confirmation of the adsorption of CV onto MSBC was confirmed by FTIR analysis. The FTIR analysis is an important tool to identify the functional groups involved in the adsorption. The FTIR spectra of un-loaded and loaded MSBC are shown in Fig. 5(CD),
RI PT
respectively. The characteristics peaks were found at 1015 (C-O stretch-Ester), 1216 (C-O stretch-acid/ether), 1324, 1435 (C═C stretch-aromatic), 1511 (C═C stretch), 1631 (N-H bending-carbonyl), 1728 (C═O- stretch-aromatic), 2131 (-C≡C-), 2924 (C-H stretch) and 3123
SC
(OH-stretch-alcohol) (cm−1) for un-loaded adsorbent, whereas CV loaded MSBC showed characteristics peaks at 480, 610, 1033, 1326, 1435, 1511, 1631, 1718, 1890, 2033-2400 and
M AN U
2924 (cm−1). Few peaks changed slightly (shift/intensity) after adsorption i.e., peaks at 1324 to 1326, 1728 to 1718 and 1890 to 2114 (cm−1) and others were vanished, which indicates that specific groups i.e., -C-O, C═O -C-N, C═C, N-H, -C≡C- functional group were involved actively in the adsorption of CV [74] and these groups belong to alcohol, amine, ester and
TE D
carbonyl functional group. However, some FTIR characteristics peaks did not change after adsorption and are not involved in the adsorption of CV dye. The strong band at 3800– 3400 cm−1 before adsorption indicates the presence of hydroxyl (O―H) functional group, the
EP
adsorption bands at 1700–1200 cm−1 was due to carbonyl group (C═O) of aldehyde or ketone and 1022-1033 cm−1 (C―O) is assigned to esters. Furthermore, peaks at 600–500 cm−1 attributed
AC C
to the presence of silica/sulphate group. From the FTIR analysis, it is concluded that functional groups such as hydroxyl (O―H) and carbonyl group (C═O) mainly participated in the adsorption of CV onto MSBC. 4. Conclusions Mango stone composite was prepared and employed for the adsorption of CV dye. The process variables were optimized and maximum CV adsorption of 352.79 mg/g was achieved at pH 8.0, 18
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contact time 30 min, 0.05 g MSBC dose, CV initial concentration 400 mg/L and 33 0C. MSBC pre-treatments (NaCl salt and surfactants) did not affect the dye adsorption significantly. The Langmuir isotherm and pseudo-second-order kinetic model fitted well to the CV adsorption. The
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CV adsorption process was spontaneous and exothermic in nature. The intraparticle diffusion model was not the main mechanism involved in the adsorption of CV. The MCBC is recyclable and can be used in multiple adsorption cycles. In view of promising adsorption capacity, the
SC
MSBC could be used as potential adsorbent for dyes adsorption from industrial effluents.
M AN U
Acknowledgements
The Director CRL Laboratories, University of Peshawar is acknowledged for assistance in sample analysis. References
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[1] B. Adesola, K. Ogundipe, K.T. Sangosanya, B.D. Akintola, A. Oluwa, E. Hassan, Chem. Int. 2 (2016) 89-102. [2] A. Babarinde, G.O. Onyiaocha, Chem. Int. 2 (2016) 37-46. [3] H.G. Mokri, N. Modirshahla, M. Behnajady, B. Vahid, Int. J. Environ. Sci. Technol. 12 (2015) 1401-1408. [4] H. Shindy, Chem. Int. 2 (2016) 29-36. [5] K. Qureshi, M.Z. Ahmad, I.A. Bhatti, M. Iqbal, A. Khan, Chem. Int. 1 (2015) 53-59. [6] W. Abbas, T.H. Bokhari, I.A. Bhatti, M. Iqbal, Asian J. Chem 27 (2015) 282-286. [7] M. Bilal, M. Asgher, M. Iqbal, H. Hu, X. Zhang, Int. J. Biol. Macromol. 89 (2016) 181-189. [8] M. Bilal, M. Iqbal, H. Hu, X. Zhang, Biochem. Eng. J. 109 (2016) 153-161. [9] U.C. Peter, U. Chinedu, Chem. Int. 2 (2016) 80-88. [10] C. Ukpaka, Chem. Int. 2 (2016) 19-28. [11] C.P. Ukpaka, Chem. Int. 2 (2016) 128-135. [12] C.P. Ukpaka, Chem. Int. 3 (2016) 8-18. [13] C.P. Ukpaka, Chem. Int. 2 (2016) 267-278. [14] S.A.A.a.C.P. Ukpaka, Chem. Int. 2(2016) 103-114. [15] S. Jafarinejad, Curr. Sci. Perspect. 2 (2016) 78-82. [16] B.K. Pandey, S. Vyas, M. Pandey, A. Gaur, Curr. Sci. Perspect. 2 (2016) 52-56. [17] B.K. Pandey, S. Vyas, M. Pandey, A. Gaur, Curr. Sci. Perspect. 2 (2016) 39-46. [18] C. Ukpaka, E. Wami, S. Amadi, Curr. Sci. Perspect. 1 (2015) 107-111. [19] C.P. Ukpaka, I. Collins, Curr. Sci. Perspect. 2 (2016) 69-77. [20] S. Jafarinejad, Chem. Int. 2 (2016) 242-253. [21] M. Iqbal, Chemosphere, 144 (2016) 785-802. 19
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Tables 1: Comparison of dyes adsorption capacities of various reported adsorbents and mango stone biocomposite (present study) Dyes
Adsorbent
Reactive Black 5
Coal fly ash (high lime) Powdered activated carbon
7.94 58.8
[49]
Reactive dye
Bagasse fly ash
16.42
Reactive Blue 222
Granular activated carbon (250–2000 µm) Coal-based bottom ash (>590 µm)
6.53 4.02
[51] [52]
Biomass fly ash
4.38
RI PT
----
---
[50] ----
88.5 169.1
[53]
----
13.99
[60]
10.72, 21.5, 19.18
[55]
SC
3.65
Modified zeolite Modified clay (sepiolite) Powdered peanut hull
Orange peel
Banana peel Rice husk Eucalyptus bark
Methylene blue
TE D
Acid yellow 36 Remazol BB Acid blue 25, Acid red 114, Basic blue 69, Basic red 22 Direct re d 80, Direct re d 81, Acid blue 92, Acid Red 14
EP
Sunset Yellow Direct red 23, Direct red 80, Acid violet 17 Methyl orange, Methylene blue, Rhodamine B, Congo red, Methyl violet, Amido black 10B
References
----
M AN U
Reactive Black 5 Reactive Yellow 176
qe (mg/g)
Baggase pith
Soy meal hull
21.0, 20.8, 20.6, 18.8, 12.2, 6.5 86.9 90.0
17.5, 20.0, 152, 75.0 478.57, 120.48, 114.94, 119.89
[61] [46] [47] [43]
[57] [58]
277.78
Bamboo dust-based activated carbon Coconut shell-based activated carbon
143.20 277.90
Groundnut shell-based activated carbon
164.90
---
312.50
---
AC C
Palm fiber-based activated carbon
Methylene blue
---
Methylene blue
Commercial activated carbon
240.0
Crystal violet
Sulfuric acid activated rice husk carbon grapefruit peel
64.875 249.68
[59] [23] [62]
---
zinc chloride activated rice husk carbon
61.575
----
-----
NaOH-modified rice husk Citric acid esterifying wheat straw
44.87 227.27
---
Coniferous pinus bark powder
32.78
---
Coniferous pinus bark powder
42.25
[24] [63] [64]
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Calotropis procera leaf
---
Orange peel
14.3
-----
Jute fiber carbon Skin almond waste
27.99 85.47
---
Neem sawdust
3.8
-----
Sugarcane dust Treated coir pith
3.8 94.7
---
Sawdust
37.83
[68] [27]
-----
Sugarcane fiber Biocomposite (mango stone)
10.44 352.79
---Present study
----
AC C
EP
TE D
M AN U
SC
RI PT
4.14
[26] [61] [65] [66] [67]
---
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Table 2: Pseudo-first, pseudo-second order kinetic parameters and Intraparticle diffusion model for the adsorption of crystal violet onto mango stone composite Kinetic models
Parameter values 25 mg/L -0.04376
50 mg/L 0.000169
75 mg/L 0.02303
qe (mg/g)
-0.29843
-0.47237
-0.57675
0.835
0.539
0.413
Pseudo-second order K2 (g/mg min)
0.04741
0.048326
0.092756
qe (mg/g)
23.25581
50
76.92308
R2
0.999
1
Intraparticle diffusion model Kid (mg/g min1/2)
0.552
13.15
C
42.99
R2
0.592
EP AC C
SC 1
M AN U
0.45
35.02
69.24
0.962
0.591
TE D
R2
RI PT
Pseudo-first order K1(l/ min)
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Table 3: Freundlich, Langmuir and Harkins-Jura isotherms comparison for crystal violet adsorption onto mango stone composite
Kf (mg/g)
qm (mg/g)
0.52
500
B (L/mg)
26
Harkins-Jura isotherm R2
0.94
A
5.6x 10-4
EP
TE D
M AN U
SC
6.098
R2
AC C
1.007
n
Langmuir isotherm
RI PT
Freundlich isotherm
B
5.2x 10-6
R2
0.47
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Table 4: Thermodynamic parameters for the adsorption of crystal violet dye onto mango stone composite ∆Ho(kJ/mole)
33
-0.40646
-176.772
40
-0.36395
47
-0.34512
54
- 0.34006
∆So (kJ/moleK) -5.39662
RI PT
∆Go (kJ/mole)
AC C
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TE D
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SC
Temperature (0C)
AC C
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TE D
M AN U
SC
RI PT
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26
(C)
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25
qe (mg/g)
24
23
SC
22
21
2
4
M AN U
20 6
8
pH
(D)
TE D
50
40
30
EP
qe (mg/g)
10
20
AC C
10
0.05
0.10
0.15
0.20
0.25
0.30
Adsorbent dose (g)
Fig. 1: (A) The point of zero charge of mango stone native biomass versus mango stone biocomposite (B) Crystal violet dye adsorption onto mango stone native biomass versus mango stone biocomposite (Conditions; 0.10 g adsorbent dose, 1 h contact time, 50 mg/L dye initial concentration), (C) Effect of pH on crystal violet adsorption onto mango stone biocomposite (Conditions; 0.10 g adsorbent dose, 1 h contact time, 50 mg/L dye initial concentration at 33 0C in the pH range of 2-10) (D) Effect of biosorbent dose on crystal violet adsorption onto mango stone biocomposite (Conditions; 1 h contact time, 50 mg/L dye initial concentration, pH 8, 0.05 to 0.3 g adsorbent dose, 33 0C).
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80
(A)
70
50 40 30 20
20
40
60
Time (min)
400
(B)
350
250
120
200 150
EP
qe (mg/g)
100
TE D
300
80
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0
SC
qe (mg/g)
RI PT
25 mg/L 50 mg/L 75 mg/L
60
100
AC C
50 0
0
100
200
300
Concentration (mg/L)
400
500
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(C) 50
RI PT
qe (mg/g)
48 46 44
SC
42 40
30
40
M AN U
38 35
40 45 0 Temperature ( C)
(D)
50
TE D
35
25 20 15
EP
qe (mg/g)
30
10
AC C
5 0
0.2
0.4
0.6
NaCl (M)
0.8
1.0
55
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45
(E)
40 35
RI PT
25 20 15 10 5 0 Surf Excel
Rim
C-TAB
SDS
Tween-80
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Surfactants
SC
qe (mg/g)
30
AC C
EP
TE D
Fig. 2: Crystal violet adsorption onto mango stone composite (A) Effect of contact time (Conditions; 5-120 min contact time, 50 mg/L dye initial concentration, pH 8, 0.05 g adsorbent dose, 33 0C) (B) Effect of dye initial concentration (Conditions; dye initial concentration 20 to 500 mg/L, 1 h contact time, pH 8, 0.05 g adsorbent dose, 33 0C) (C) Effect of temperature (Conditions; 33-54 0C, 50 mg/L dye initial concentration, 1 h contact time, pH 8, 0.05 g adsorbent dose) (D) Effect of NaCl addition (Conditions; 0.2-1.0 M salt concentration, 50 mg/L dye initial concentration, 1 h contact time, pH 8, 0.05 g adsorbent dose, 33 0C) (E) Effect of surfactants pre-treatment on dye adsorption (Conditions; 5% surfactant solution concentrations, 50 mg/L dye initial concentration, 1 h contact time, pH 8, 0.05 g adsorbent dose, 33 0C).
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1.0
(A)
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
1.51575
Adj. R-Square
0.39702
log(qe-qt)
Intercept
Value Standard Error 0.3186 0.43949
log(qe-qt)
Slope
-0.01299
0.00627
log(qe-qt)
0.0
-0.5
-1.0
-1.5 0
20
40
60
80
100
120
M AN U
Time
(B) 2.5
2.0
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
2.07666E-4
Adj. R-Square
0.99994 Value
Standard Error
t/qt
Intercept
0.00925
0.00419
t/qt
Slope
0.02082
6.35449E-5
t/qt
TE D
1.5
1.0
0.0 0
20
EP
0.5
40
60
AC C
Time
SC
RI PT
0.5
Equation
80
100
120
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75
(C)
74
71 70
Equation
y = a + b*x
Weight Residual Sum of Squares Pearson's r
No Weightin 8.0255 0.76927 0.51013
Adj. R-Squar
Value
69
Standard Err
qt
Intercept
69.2404
1.22539
qt
Slope
0.45073
0.16742
68 2
4
6
8
10
12
0.5
(D)
0.4
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
0.00721
Adj. R-Square
0.92845 Value
Standard Error
ce/qe
Intercept
0.05264
0.01098
ce/qe
Slope
0.00241
2.21753E-4
Ce/qe
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t1/2
0.1
0
20
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0.2
40
60
80
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Ce
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qt
72
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100
120
140
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(E)
2.6
2.0
Equation
y = a + b*x
Weight
No Weighting 0.93448
Residual Sum of Squares
1.8
0.38375
Adj. R-Square
Value
1.6 0.0
Standard Erro
log qe
Intercept
1.65235
0.18519
log qe
Slope
0.42672
0.16604
1.5
2.0
0.5
1.0
2.5
(F)
0.0030 0.0025
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
6.64653E-6
Adj. R-Square
-0.0446
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log Ce
Value 1/qe2
Intercept
1/qe2
Slope
Standard Error
5.69955E-4
3.33606E-4
-5.28469E-6
6.73482E-6
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1/qe2
0.0020
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log qe
2.2
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2.4
0.0015 0.0010
0.0000 0
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0.0005
20
40
60
80
100
120
140
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Ce log
Fig 3: Plots of crystal violet adsorption onto mango stone composite; (A) Pseudo-first-order (B) Pseudo-secondorder, (C) Intraparticle diffusion model (D) Langmuir isotherm (E) Freundlich isotherm and (F) Harkin-Jura model
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(A) Equation
y = a + b*x
Weight
No Weighting 57.28556
40
0.92616
Adj. R-Square
Value Intercept
lnKc lnKc
Slope
Standard Error
-649.16836
108.18722
212623.01929
34209.8419
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Residual Sum of Squares
lnKc
30
20
10
0 0.00306
0.00312
0.00318
0.00324
0.00330
18
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1/T
(B)
16 14
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12
dq (%)
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50
10 8
4 0.2
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6
0.4
0.6
0.8
1.0
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CH3COOH (M)
Fig. 4: (A) Plot of lnKc versus 1/T for 50 mg/L crystal violet initial concentration, (B) Desorption of crystal violet dye using 0.2-1.0 M CH3COOH
100
(C) 2400
(D)
90
90
Transmettence (%)
Transmettence (%)
100
2131
80 1511 3123
70
1728 1631
60
1015 1324, 1435
50 1216
40 30 4000
1890
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80
2300-2400
70
2900
1511 1718 1326 610 1631 1435 1033
60 50 40
3500
3000
2500
2000
1500
1000
-1
500
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
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Wavenumber (cm )
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Fig. 5: Scanning electron microscopy micrographs of mango stone biocomposite (A) un-loaded composite SEM image (B) dye loaded composite SEM image (C) un-loaded composite FTIR and (D) dye loaded composite FTIR (Conditions: 0.1 g adsorbent dose, 50 mg/L ye concentration, 120 min contact time, 33 0C temperature and pH 8.0).
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Highlights
Mango stone biomass was modified using ferric chloride and sodium borohydride
•
Prepared composite was employed for crystal violet adsorption
•
Pseudo-second order kinetic model exhibited the best fit with the experimental results
•
Langmuir isotherm was found most appropriate model for this study
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Composite showed significantly higher affinity for crystal violet adoption versus native biomass
•
Mango stone composite proved to be potential candidate for dyes adsorption from wastewater
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•
S1387-1811(16)30464-4
DOI:
10.1016/j.micromeso.2016.10.004
Reference:
MICMAT 7944
To appear in:
Microporous and Mesoporous Materials
Received Date: 7 April 2016 Revised Date:
27 September 2016
Accepted Date: 7 October 2016
Please cite this article as: S. Shoukat, H.N. Bhatti, M. Iqbal, S. Noreen, Mango stone biocomposite preparation and application for crystal violet adsorption: A mechanistic study, Microporous and Mesoporous Materials (2016), doi: 10.1016/j.micromeso.2016.10.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Mango stone biocomposite preparation and application for crystal violet adsorption: A mechanistic study
a
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Sidra Shoukata, Haq Nawaz Bhattia,*, Munawar Iqbalb,* and Saima Noreena
Department of Chemistry, University of Agriculture, Faisalabad 38000, Pakistan b
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Department of Chemistry, The University of Lahore, Lahore, Pakistan
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*Corresponding author(s) E-mail: [email protected] (H. N. Bhatti); [email protected] (M. Iqbal)
Abstract
Mango stone biocomposite (MSBC) was prepared and employed for the adsorption of crystal violet (CV) dye. Process variables were optimized and maximum dye adsorption of 352.79 mg/g
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was achieved at pH 8, 0.05 g adsorbent dose, 30 min contact time, 33 0C for dye initial concentration of 400 mg/L onto MSBC. Salt and surfactants pre-treatments of MSBC did not affect the CV adsorption. The CV equilibrium adsorption data followed pseudo second order
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kinetic model and Langmuir adsorption isotherm. Thermodynamic parameters (∆Go, ∆Ho and ∆So) revealed that the CV adsorption onto MSBC was an exothermic and spontaneous process.
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SEM analysis revealed that the surface morphology of dye loaded MSBC was changed significantly and hydroxyl and carbonyl groups were main functional group responsible for CV adsorption onto MSBC. The prepared MSBC also showed recyclable nature and might be potential candidate for dyes removal form textile effluents. Keywords: Mango stone biocomposite; Crystal violet; Adsorption; Kinetics; Thermodynamics; Isotherms; Desorption
1
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1. Introduction Water pollution has been increased to alarming level and dyes are one of the major sources from textiles and dying sector, which is a serious threat to ecological balance. Recent
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reports revealed the toxic and carcinogenic nature of dyes [1-21]. More than 100,000 dyes are synthesized with 700,000 metric tons production annually. Among many classes of synthetic dyes, triphenylmethane class of dyes is most versatile due to their diverse applications. Crystal
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violet dye (basic violet 3, gentian violet, and methyl violet 10B) is a member of triarylmethane dyes [22]. Other than dying and printing, it is also used in biological studies, dermatology,
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veterinary and poultry feed etc. The CV is a mutagenic, carcinogenic and poisonous to mitotic division process [23, 24], which is also non-biodegradable and persists in the environment for longer time. Other than cytogenetic effects, eye irritation, skin irritation, digestive tract irritation, respiratory and kidney failures have been reported in response of CV exposure [25-27]. In view
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of toxic nature of dyes, management of wastewater from textile industry before thronging out in water sheds is necessary. Various methods have been applied with positive outcomes for the adsorption of pollutant form simulated solution as well as effluents [1, 2, 5-8, 10, 28-36].
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Adsorption using agriculture waste biomasses have been used potentially for dyes adsorption as these are easy-to-handle, recyclable, available round the year, less expensive and more efficient
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[37-40] i.e., garlic waste [41], coir pith [42], baggase pith [43], pineapple waste [44], rice waste [45], rice husk [46], plant waste and bark [47], okra waste [48], fly ash, powdered activated carbon [49, 50], bagasse [51], activated carbon, coal-based bottom ash [52], modified zeolite and clay [53], powdered peanut hull [54], orange peel [55], soy waste biomass [56], palm fiber-based activated carbon [57], bamboo dust-based, coconut shell-based, groundnut shell-based activated
2
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carbon [58] commercial activated carbon [59] and eucalyptus angophoroides bark [40] showed promising efficiencies for dyes adsorption (Table 1). The composites technology advanced the applications of adsorbents for pollutant
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adsorption and is proved to be highly efficient versus native biomasses [60-62]. Mango is the plump stony fruit, belongs to genus Mangifera and family Anacardiaceae and national fruit of Philippines, India and Pakistan. The Food and Agriculture Organization (FAO) of the United
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Nations reported mango production of 35 million tons (MT) worldwide in 2009 including India (13.6 MT), Mexico (1.9 MT), Thailand (2.5 MT), Indonesia (2.2 MT), China (4.2 MT), Pakistan
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(1.7 MT) and Brazil (1.2 MT) as major growers [62, 63]. As a result of mango processing a considerable amount of waste materials i.e., mango stones (seed), peel and kernel is produced and wasted [2, 64]. Previously, mango stone has been reported as efficient adsorbent for different types of pollutants [65], however, mango stone composites have not been investigated for the
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adoption of CV [37, 66].
Therefore, mango stone was used for composite preparation and employed for CV dye adsorption. As-prepared MSBC adsorption capacity was studied as function of medium pH, dye
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initial concentration, contact time and adsorbent dose. Salt and surfactants pre-treatments effect on dye adsorption was also studied. Kinetic, thermodynamics and isotherms models were
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employed to understand CV adsorption mechanism onto MSBC. Desorption behavior of prepared MSBC was also checked. FTIR and SEM techniques were used to monitor the dye loaded and un-loaded MSBC. 2. Material and Methods 2.1.Reagents, Chemicals and Instruments
3
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The chemical and reagents such as HCl, NaOH, acetone, ferric chloride and sodium borohydride, HNO3, H2SO4 and CH3COOH were purchased from Fluka and Merck. Potassium dihydrogen phosphate/disodium hydrogen phosphate, citric acid/sodium hydroxide/sodium chloride solution
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and boric acid/sodium hydroxide solution/potassium chloride (Sigma-Aldrich) were used to prepare buffers of pH 4, 7 and 11, respectively. The surfactants such as C-TAB, Tween-80, SDS were purchased from Sigma-Aldrich, whereas Surf Excel and Rim were purchased from local
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market. Ultra-pure water with a resistivity of 18.2 MΩ cm from Milli-Q system (Millipore) was used for the preparation of dye and other solutions. The instruments such as octagon siever
(Moulinex,
France),
FTIR
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(OCT-DIGITAL 4527-OI), shaker (PA 250/25.H), pH meter (HI-8014 Hanna), grinder (Beaconfield
Buckinghamshire
HP9
1QA)
and
SEM
(JSM5910, JEOL, Japan) were used throughout the study. 2.2.Solution preparation
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Crystal violet dye was purchased from local textile market, Faisalabad, Pakistan. Dye stock solution was prepared by dissolving respective amount of dye in ultra-pure water and the
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working concentrations were prepared by diluting stock solution. 2.3.Biomass collection and preparation
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The mango stone was collected from student market, University of Agriculture, Faisalabad, Pakistan. Preliminary, the mango stone was cleaned and dried in open air followed by oven drying at 50°C for 72 h. Dry mango stone was chopped, grinded and sieved through Octagon siever to obtained uniform particle size (0.25 mm), which was used for MSBC preparation. 2.4. Mango stone biocomposite preparation Mango stone powder (6 g) was mixed with 0.45 M ferric chloride solution (15 mL), stirred and 4
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0.25 M sodium borohydride (15 mL) was added slowly with continuous stirring. After an additional stirring of 20 min, the mixture was filtered (2.5 µm), washed with ethanol thrice and
airtight plastic bags until adsorption experiments. 2.5.Point of zero charge (pHpzc)
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dried in desiccators for 48 h. The dried composite was again grinded (0.25 mm) and stored in
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For pHpzc determination, 0.1 M KNO3 concentration series (50 mL) were prepared and pH was adjusted between 1.0-12.0. The adsorbent (0.1 g) was mixed with solution, shaken and left for 48
determination. 2.6. Adsorption procedure
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h with intermit mixing [67]. Final pH was noted and data was plotted for the pHpzc
Process variables i.e., solution pH, dye concentration, contact time, MSBC dose were studied and optimized. The pH (2-8), adsorbent dose (0.05 - 0.30 g), contact time (5-120 min),
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temperature (33-54 °C) ranges were studied. NaCl salt (0.2-1.0 M) and surfactants pre-treatments (CTAB, SDS, Tween-80, Rim and Surf Excel) (5% solution) effect on CV adsorption onto composite was also studied. For adsorption experiments, 100 mL solution was taken in flasks,
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covered with aluminum foil and set on shaker at 120 rpm. After stipulated time period, flasks
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were removed and the contents were filtered (2.5 µm) to separate the adsorbent from dye solution. Residual dye concentration was determined and amount of CV adsorbed on unit mass was estimated (Eq. 1).
=
(Eq. 1)
5
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Where, qe (mg/g) is dye adsorption capacity, Ci (mg/L) and Cf (mg/L) are representing the crystal violet initial and concentration at equilibrium. V (L) and m (g) are volume and adsorbent dose,
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respectively. 2.7. Desorption study
Desorption was carried out using 0.1 M HCl, HNO3, H2SO4 and CH3COOH. Among all
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desorbing agents, CH3COOH showed better desorption capacity and then, 0.2-1.0 M CH3COOH solution was used to desorb dye from MSBC. For desorption study, CV loaded MSBC was dried
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and placed in contact with CH3COOH solution and stirred for 2 h at 120 rpm. MSBC was separated and dye desorbed was estimated (Eq. 2).
(%) = 100
(Eq. 2)
(desorbed), respectively.
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Where, qd (%), D and R are representing desorption capacity, dye adsorbed and dye recovered
2.8.SEM and FTIR analysis
elsewhere [68].
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The loaded and un-loaded MSBC was characterized using FTIR and SEM as precisely reported
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3. Results and discussion
3.1. Point of zero charge of native and mango stone biocomposite The pHpzc is important to evaluate the charge on adsorbent surface since surface charge depends upon pHpzc. pHpzc was checked in KNO3 solutions in the pH the range of 1.0 to 12.0. pH difference (∆pH = pHi - pHf) was estimated and response was plotted between pH and ∆pH and pHpzc was estimated. The pHpzc of native mango stone biomass was found to be 6.5, whereas it
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was 6.3 for MSBC (Fig. 1A) (point of zero charge of mango stone native biomass versus mango stone biocomposite). It is reported that adsorption depends upon the pHpzc since charges on
present investigation did not reveal significant difference in pHpzc. 3.2. Screening of native and mango stone biocomposite
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adsorbent surface vary according to pHpzc [67]. However, native and composite adsorbents in
As-prepared MSBC and native mango stone adsorbents were screened for CV adoption
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capacities and MSBC showed considerably higher CV uptake as compared to native mango stone biomass (Fig. 1B), which revealed that MSBC offers favorable environment for dye
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adsorption. This enhanced adsorption is attributed to change in surface characteristics in response of composite preparation since MSBC provides reinforcement and compatible matrix that may enhanced the adsorption capacity. It is reported that functional groups on MSBC surface are modified and accommodate dyes molecule efficiently [61]. Similar trend have also
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been reported previously that composites showed more dye uptake capacity as compared to native biomasses and this enhanced adsorption capacity of have been correlated favorable physico-chemical properties of composites [37, 40, 61, 62, 69].
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3.3. Effect of pH on dye adsorption
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The medium pH affects charges on adsorbent surface, ionization and the speciation of adsorbate species, which play important role in dye adsorption [40, 61]. The pH effect on adsorption was studied in the pH range of 2-10 using 0.10 g adsorbent dose, 1 h contact time, 50 mg/L dye initial concentration and 33 0C were fixed. The solution pH affects the CV adsorption considerably. The CV adsorption increased gradually and maximum adsorption was observed at pH 8.0 and further increase in pH, the CV adsorption capacity decreased (Fig. 1C). This behavior of CV adsorption as a function of pH is due to changed active sites binding capacity since MSBC 7
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surface can be protonated/de- protonated under acidic/basic conditions, which may affect the dye adsorption depending on dye nature (cationic/anionic). At optimum pH (mild basic condition), the binding sites remained available hence CV uptake was higher. The possible explanation of
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this behavior could be the involvement of functional groups that may expose under specific conditions (acidic/basic) and resultantly, negative/positive charge density on the adsorbent surface attracted/repel dye ions [70]. The decreasing trend of dye adsorption under basic
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condition (pH > 8) was due to the formation of hydroxyl species [71]. On the other hand, under acidic condition, the ligands on cell wall are closely related to H3O+ ions that might hinders CV
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dye approach to the adsorbent surface due to repulsive forces. Therefore, the H3O+ ions compete with CV ions for adsorption. Since under acidic condition, the H3O+ ions concentration is likely to increase and can cover the active sites leaving the dye ions un-adsorbed. As the pH of the medium increased, the competition between dye ions and H3O+ ions decreased and resultantly,
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dye adsorption increased [40]. Similar trend regarding pH effect on dyes adsorption have been reported previously i.e., bark adsorbent [72] and apple shell waste adsorbent [73]. Both authors correlated low dye adsorption with deprotonation under acidic pH.
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3.4. Effect adsorbent dosage on dye adsorption Since surface area available for dye ions has direct effect on adsorption, So for the effect of
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adsorbent dose in the range of 0.05 to 0.3 g was studied for 1 h contact time, 50 mg/L dye initial concentration, pH 8 at 33 0C. At low adsorbent dose, considerably higher CV adsorption was observed, which decreased linearly as the adsorbent dose increased (Fig. 1D). The adsorption capacity of 49.0 mg/g at 0.05 g adsorbent dose was achieved, which decreased to 9 mg/g for the adsorbent dose of 0.3 g. This decreasing adsorption capacity at higher adsorbent dose was due to low surface area [40, 69, 74]. An increase in adsorbent amount using same solution volume and
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dye concentration lead to occupation of available binding sites and due to particles interaction, aggregation may occur and resultantly, surface area may decreased [37-39, 60-62, 75]. The decreasing trend of dye adsorption at higher adsorbent dose can be attributed to decreased
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adsorbent surface area and unavailability of adsorption sites [54]. Sonawane and Shrivastava [76] reported the optimum dose of maize cob 12 g/L for maximum dye adsorption, which
3.5. Effect Contact time on dye adsorption
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indicates that composite are efficient for dye adsorption at very low dose versus native biomass.
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To find out the time required for equilibrium attainment for CV adsorption on to MSBC, the contact time in the range of 5-120 min was investigated. Other variables i.e., 50 mg/L dye initial concentration, pH 8, 0.05 g adsorbent dose and 33 0C were constant and results thus obtained are represented in Fig. 2(A). The MSBC dye adsorption efficiency was very fast initially followed by slow adsorption and then, equilibrium was reached within 30 min of contact time, which
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indicates that MSBC is highly efficient for CV adsorption because equilibrium was attained in shorter duration. The CV adsorption trend as a function of contact time revealed that adsorption occurred in two distinct steps i.e., initial fast phase remained for very shorter duration followed
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by slow adsorption phase remained for comparatively longer duration. After attaining the
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equilibrium, further adsorption was insignificant as a function of contact time. From this trend, it can be concluded that initially the binding sites were freely available and fast adsorption was occurred, whereas in second phase the slow CV adsorption was due to the saturation of binding sites and dye ions occupy the remaining vacant sites slowly due to repulsive forces between the dye ions and ions already adsorbent on adsorbent. Secondly, slow adsorption with the passage of time may also be due to intraparticle diffusion process dominating over adsorption [37, 77]. These finding are in line with previous studies for different adsorbents as a function of contact 9
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time i.e., adsorption of direct red 75 and direct red 80 onto calcined bone [78], pineapple waste biomass [44] and cationic dye removal from aqueous solution by rice bran [45]. However, native biomass took longer time to reach the equilibrium i.e., equilibrium for dye adsorption was
3.6. Effect initial dye concentration on dye adsorption
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reached in 129 min for coniferous pinus bark powder [72] and in case of wood apple shell [73].
Dye initial concentration in the range of 20 to 500 mg/L was studied since dye initial
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concentration acts as a driving force in transferring the dyes ions from aqueous media to solid surface. The contact time of 1 h, pH 8.0, 0.05 g adsorbent dose and 33 0C conditions were
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constant and response thus obtained is depicted in Fig. 2(B). CV adsorption increased gradually with initial concentration and reached 352.79 mg/g for initial dye concentration of 400 mg/L. Beyond this concentration, the adsorption capacity was insignificant. Similar trend in adsorption capacity as a function of dye initial concentration have been reported previously for different
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adsorbents [79]. It is noted that dye initial concentration is important in adsorption process since concentration provides driving force to overcome mass transfer resistance between solid and solution phases [30, 37-40, 61, 62, 69, 74]. At higher concentration, the ratio of the initial CV
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ions to the available surface area was high and the fractional adsorption subsequently becomes dependent to the initial concentration. However, at extremely high concentration, the available
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sites exhausted and resultantly, the CV adsorption decreased. Previously, similar dyes adsorption behaviour have been reported as a function of dyes initial concentrations for different adsorbent types [25, 38, 45, 46, 49, 54, 80, 81]. 3.7. Effect of temperature on dye adsorption The effect of temperature was studied in the range of 33-54 0C on CV adsorption on to MSBC, whereas 50 mg/L dye initial concentration, 1 h contact time, pH 8.0, 0.05 g adsorbent dose were
10
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constant and adsorption response is depicted in Fig. 2(C). The maximum CV adsorption of 48.0 mg/g was observed at 33 0C, which reduced to 40.0 mg/g at 54 0C. The decreasing adsorption trend at higher temperature indicates that the CV adsorption was an exothermic process, which
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might be due to the deteriorating of binding forces on surface at higher temperature [82]. The dye adsorption as a function of temperature indicates that adsorbent surface activity decreased by increasing temperature and CV adsorption is mainly controlled by physical forces [83].
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Therefore, the CV adsorption process was exothermic in nature because as temperature increased, the CV adsorption decreased. However, some researchers reported higher CV
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adsorption onto different adsorbents at higher temperature for activated carbon and groundnut shell [23, 84] and difference might be due to stable nature of adsorbents at elevated temperature.
3.8. NaCl and surfactants pre-treatment effect on dye adsorption
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To study the pre-treatment effect of NaCl on CV adsorption is important since the wastewater discharged from industries has different salts. Salt effect was studied in the range of 0.2-1.0 M (Fig. 2D). While studying the effect of salt on CV adsorption, 50 mg/L CV initial concentration,
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1 h contact time, pH 8.0 and 0.05 g adsorbent dose at 33 0C were kept constant. Interestingly, the MSBC treated with NaCl did not affect the CV adsorption. It has been reported that salt affects
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the enthalpy of adsorption process along with pH change of medium and hydrophobic and electrostatic interactions between adsorbent surface and dye ions may change [61, 69]. The salt addition may also affect the forces such as van der Waals, ion-dipole, and dipole-dipole among ions in the solution and low removal of dye can also be correlated with co-ion competition for binding sites on to the adsorbent surface [85]. However, NaCl treated MSBC revealed insignificant effect on CV adoption. Similarly, the MSBC was also pre-treated with surfactants
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i.e., Surf Excel, Rim, C-TAB, Tween-80 and SDS and employed for CV adsorption. A 5% solution of each surfactant was used and 50 mg/L CV initial concentration, 1 h contact time, pH 8.0 and 0.05 g adsorbent dose and 33 0C were constant and results, thus obtained are shown in
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Fig. 2(E). Surfactants pretreatments of MSBC decreased the CV adsorption slightly in following order Excel > Rim > C-TAB > SDS > Tween-80. Previously, adsorbent pre-treated with surfactants showed significant effect on dye adsorption [69], but present investigation revealed
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that surfactants effect was insignificant for MSBC. A slight decrease of CV adsorption might be due to coverage of active sites and resultantly [86]. Previously, it have also been reported that the
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dyes adsorption may decrease in the presence of surfactants, which was correlated with coverage of acidic groups on adsorbent surface and resultantly, the hydrophilic end of surfactants behave like base and repulsive forces was generated between dye ions and adsorbent surface [61, 69],
3.9.Kinetic modeling
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which reduced the CV adsorption slightly.
Pseudo-first-order and pseudo-second-order kinetic models were employed to study the CV adsorption behavior as a function of contact time [40]. The pseudo-first-order kinetic model is
= ( − )
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shown in Eq. 4 and the integrated can be seen in Eq. 5 [37].
log ( − ) = log −
#
$.&'&
(
(Eq. 4)
(Eq. 5)
Where, k1(min−1), qe (mg/g), and q (mg/g) are the rate constant, dye adsorbed at equilibrium, dye adsorbed at time t, respectively and t is time. The k1 was determined from the slope of plot log (qe−q) versus t.
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The integrated and linear forms of pseudo second order kinetic model are shown in Eqs. 6-7, respectively [87]. = $ ( − )$
=
)
#* +*
+
(Eq. 6)
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(Eq. 7)
+
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Where, k2 (g−1min−1) and qe (mg/g) are the constant and adsorption capacity at equilibrium, which were determined from the slope and intercept of plot t/qt versus time. The kinetic data is
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presented in Table 2 and plots are shown in Figs. 3(AB), respectively. The qe estimated values from experimental data did not correlate with the pseudo first order kinetic model and the R2 values (0.86, 0.54 and 0.41 for 25, 50 and 75 mg/g dye concentration, respectively) were also not acceptable, leading to the assumption that the experimental data did not fit well with the pseudo-
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first order kinetics model. In case of pseudo second order kinetic model, the qe values coincided well with the modeled values (23.26, 50.00 and 76.92 for 25, 50 and 75 mg/g concentration, respectively) and the R2 values (0.99, 1.0 and 1.0 for 25, 50 and 75 mg/g concentration,
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respectively) were also higher versus pseudo first order kinetic model. Therefore, CV adsorption on to MSBC followed pseudo second order kinetic model. A similar kinetic behavior of CV have
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also been reported previously for different types of biomasses i.e., peanut waste [54], citric acid treated wheat straw adsorbent [24] and NaOH pre-treated rice waste [25], coir pith [88] and sawdust [81]. Findings revealed that CV adsorption onto composite was chemisorption process, which requires valence forces through the sharing or exchange of electrons between the adsorbent and the adsorbate [89]. 3.10.
Intraparticle diffusion model
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Weber-Morris intraparticle diffusion model was employed [90] and model is shown in Eq. 8. = -. ( './ + 0
(Eq. 8)
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Where, qt is the adsorption capacity at time t and kid is the intraparticle diffusion rate constant and C is the film thickness, which was calculated from the plot between qt and t0.5. Intraparticle diffusion model presumed that first adsorbate is transferred on the surface of adsorbent and then,
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transported within the available pores by diffusion process [40], boundary layer is formed and finally, adsorbate interacts with binding sites. The data for intraparticle diffusion model fitting is
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shown in Table 2 and plot is depicted in Fig. 3(C). Data revealed that the intraparticle diffusion was not only the rate controlling step for CV adsorption [91]. This trend of CV adsorption was in line with reported observation [92] regarding intraparticle diffusion modeling as well as dye adsorption onto different adsorbents [69, 93-96].
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3.11. Adsorption isotherms
Langmuir, Freundlich and Harkins-Jura isotherms were employed to understand the forces governing interaction between CV ions and MSBC [61, 62, 69]. The linear form of Langmuir
+
=
1
+
21 +
(Eq. 9)
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isotherm is expressed in Eq. 9.
Where, qe (mg/g), Ce (mg/L), Qo (mg/g) and b (L/mg) are representing amount of dye adsorbed at equilibrium/unit mass of adsorbent, equilibrium dye concentration, maximum dye adsorbed per unit mass of adsorbent to form a monolayer at higher Ce values, respectively, where b is related to the energy of the adsorption. A plot of Ce/qe versus Ce yielded a straight line with slope 1/bQo
14
ACCEPTED MANUSCRIPT
and intercept 1/Qo (Fig. 3(D)). The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless constant called separation factor (RL) (Eq. 10)
(Eq. 10)
52
RI PT
34 =
Where, C0 is the initial concentration of dye (mg/L), and b (L/mg) is the Langmuir constant. The RL is used to assess the adsorption behaviour of adsorbate on to adsorbent i.e., the RL > 1, RL = 1,
SC
0 < RL < 1 and RL represent unfavourable, linear, favourable and irreversible adsorption,
M AN U
respectively and based on RL value CV adsorption was favourable onto MSBC. The Freundlich isotherm exponential form is shown in Eq. 11 [61]. /8
= -6 0
(Eq. 11)
Where, KF (mg/g) and n are the constants, and KF is representing the adsorption capacity/unit
TE D
mass of adsorbent. The 1/n value reveals the favourability of adsorption and its value > 1 indicates the favourable adsorption of adsorbate onto adsorbent surface [37, 39]. The logarithmic form of Freundlich is shown in Eq. 6. The KF and n are calculated from the intercept and slope of
EP
the plot of log qe versus log Ce (Fig. 3(E)).
AC C
Harkins–Jura isotherm is presented in Eq. 12 [97]. Where, A and B are constants. This isotherm accounts multilayer adsorption system and existence of heterogeneous pore distribution. The Harkins–Jura isotherm curve is shown in Fig. 3(F).
+*
=
9 :
− log 0
(Eq. 12)
:
The Freundlich, Langmuir and Harkin-Jura constants with R2 values are given in Table 3 and plots can be seen in Figs. 3(D-F), respectively. The R2 and equilibrium experimental data revealed that the R2 value for the Langmuir model was high and acceptable to explain the CV 15
ACCEPTED MANUSCRIPT
equilibrium adsorption onto MSBC, whereas the R2 values in case of Freundlich and HarkinsJura isotherms were not acceptable. The Freundlich isotherm model described the adsorption on heterogeneous surface and is not restricted to the formation of monolayer and 1/n suggests the
RI PT
favorable adsorption of CV dye onto MSBC. The Langmuir isotherm assumes monolayer coverage of adsorbate over a homogenous adsorbent surface. A saturation point is reached after attaining equilibrium and further adsorption is not possible at same site [40, 61, 62, 69].
SC
Similarly to present investigation, the adsorption of CV onto grapefruit peel was better explained by the Langmuir versus Freundlich isotherm [98]. In another study, almond skin waste also
3.12.
Thermodynamic study
M AN U
followed Langmuir isotherm for CV adsorption [80].
Thermodynamic parameters i.e., enthalpy (∆H°), entropy (∆S°) and Gibbs free energy (∆G°)
<+
(Eq. 13)
+
∆> ' = −3?@A-; ∆B
−
∆C D
(Eq. 15)
AC C
@A-; =
(Eq. 14)
EP
-; =
TE D
were computed to understand the nature and were measurd using Eqs. 13-15 [61, 69].
Where, Kc, qe and Ce are representing the equilibrium constant, adsorption at equilibrium (mg/g) and dye concentration at equilibrium (mg/L). The thermodynamic data for CV adsorption onto MSBC is shown in Table 4 and plot of lnKc versus 1/T is shown in Fig. 4(A). The ∆G° value indicates that the adsorption process was spontaneous in nature. ∆H° negative value verifies the exothermic nature of CV adsorption onto MSBC. The negative ∆S° value revealed decrease in randomness at the solid/solution interface as a result of CV adsorption [87]. The ∆G0 value in the 16
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range of -0.34 to -0.40 revealed that CV process was physisorption. A value between -20 and 0 kJ/mol favors physiosorption, whereas chemisorption mechanism is involved when ∆Go is in the range of -80 to -400 kJ/mol [99]. The ∆Go values for CV adsorption onto MSBC were in the
physisorption nature of CV adsorption on to MSBC [100, 101]. Desorption studies
SC
3.13.
RI PT
range of -0.34 to -0.40 kJ/mol for temperature range of 33 0C to 54 0C. These results revealed the
Desorption of CV was performed using 0.2-1.0 M CH3COOH solution. Dye loaded MSBC was
M AN U
mixed with CH3COOH solution and agitated for 120 min at 100 rpm and desorbed dye was estimated. Results showed that desorption capacities for 1.0, 0.8, 0.6, 0.4, 0.2 M CH3COOH solutions were 5.0%, 11.0%, 17.0%, 15.0% and 10.5%, respectively (Fig. 4(B)) and CH3COOH 0.6 M showed maximum desorption capacity. Desorption yields concentrated adsorbate and adsorbent cab be regenerated using suitable S/L ratio. The CH3COOH solution (50 mL) was
TE D
mixed with 0.1 g with dried MSBC. The S/L ratio were found to be 50:0.10, 50:0.22, 50:0.34, 50:0.30, 50:21 for 1.0, 0.8, 0.6, 0.4 and 0.2 M CH3COOH, respectively. Desorption of CV dye was maximum for 0.6 M CH3COOH; hence S/L ratio of 50:0.34 is best to desorbs CV from
FTIR and SEM studies
AC C
3.14.
EP
MSBC for the regeneration of the adsorbent.
Un-loaded and dye loaded MSBC surface morphology was monitored by SEM analysis. The SEM image of un-loaded MSBC is shown in Fig. 5(A). The surface morphology indicates that un-loaded MSBC has spaces, pores and surface was also un-even in un-loaded adsorbent. The dye loaded SEM image is shown in Fig. 5(B). It can be seen that the surface of dye loaded MSBC is changed considerably, which is more even than un-loaded adsorbent. The CV dye absorbed on the cell wall matrix and created stronger crosslinking and uniformity on the surface 17
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of the adsorbent. Further confirmation of the adsorption of CV onto MSBC was confirmed by FTIR analysis. The FTIR analysis is an important tool to identify the functional groups involved in the adsorption. The FTIR spectra of un-loaded and loaded MSBC are shown in Fig. 5(CD),
RI PT
respectively. The characteristics peaks were found at 1015 (C-O stretch-Ester), 1216 (C-O stretch-acid/ether), 1324, 1435 (C═C stretch-aromatic), 1511 (C═C stretch), 1631 (N-H bending-carbonyl), 1728 (C═O- stretch-aromatic), 2131 (-C≡C-), 2924 (C-H stretch) and 3123
SC
(OH-stretch-alcohol) (cm−1) for un-loaded adsorbent, whereas CV loaded MSBC showed characteristics peaks at 480, 610, 1033, 1326, 1435, 1511, 1631, 1718, 1890, 2033-2400 and
M AN U
2924 (cm−1). Few peaks changed slightly (shift/intensity) after adsorption i.e., peaks at 1324 to 1326, 1728 to 1718 and 1890 to 2114 (cm−1) and others were vanished, which indicates that specific groups i.e., -C-O, C═O -C-N, C═C, N-H, -C≡C- functional group were involved actively in the adsorption of CV [74] and these groups belong to alcohol, amine, ester and
TE D
carbonyl functional group. However, some FTIR characteristics peaks did not change after adsorption and are not involved in the adsorption of CV dye. The strong band at 3800– 3400 cm−1 before adsorption indicates the presence of hydroxyl (O―H) functional group, the
EP
adsorption bands at 1700–1200 cm−1 was due to carbonyl group (C═O) of aldehyde or ketone and 1022-1033 cm−1 (C―O) is assigned to esters. Furthermore, peaks at 600–500 cm−1 attributed
AC C
to the presence of silica/sulphate group. From the FTIR analysis, it is concluded that functional groups such as hydroxyl (O―H) and carbonyl group (C═O) mainly participated in the adsorption of CV onto MSBC. 4. Conclusions Mango stone composite was prepared and employed for the adsorption of CV dye. The process variables were optimized and maximum CV adsorption of 352.79 mg/g was achieved at pH 8.0, 18
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contact time 30 min, 0.05 g MSBC dose, CV initial concentration 400 mg/L and 33 0C. MSBC pre-treatments (NaCl salt and surfactants) did not affect the dye adsorption significantly. The Langmuir isotherm and pseudo-second-order kinetic model fitted well to the CV adsorption. The
RI PT
CV adsorption process was spontaneous and exothermic in nature. The intraparticle diffusion model was not the main mechanism involved in the adsorption of CV. The MCBC is recyclable and can be used in multiple adsorption cycles. In view of promising adsorption capacity, the
SC
MSBC could be used as potential adsorbent for dyes adsorption from industrial effluents.
M AN U
Acknowledgements
The Director CRL Laboratories, University of Peshawar is acknowledged for assistance in sample analysis. References
AC C
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22
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Tables 1: Comparison of dyes adsorption capacities of various reported adsorbents and mango stone biocomposite (present study) Dyes
Adsorbent
Reactive Black 5
Coal fly ash (high lime) Powdered activated carbon
7.94 58.8
[49]
Reactive dye
Bagasse fly ash
16.42
Reactive Blue 222
Granular activated carbon (250–2000 µm) Coal-based bottom ash (>590 µm)
6.53 4.02
[51] [52]
Biomass fly ash
4.38
RI PT
----
---
[50] ----
88.5 169.1
[53]
----
13.99
[60]
10.72, 21.5, 19.18
[55]
SC
3.65
Modified zeolite Modified clay (sepiolite) Powdered peanut hull
Orange peel
Banana peel Rice husk Eucalyptus bark
Methylene blue
TE D
Acid yellow 36 Remazol BB Acid blue 25, Acid red 114, Basic blue 69, Basic red 22 Direct re d 80, Direct re d 81, Acid blue 92, Acid Red 14
EP
Sunset Yellow Direct red 23, Direct red 80, Acid violet 17 Methyl orange, Methylene blue, Rhodamine B, Congo red, Methyl violet, Amido black 10B
References
----
M AN U
Reactive Black 5 Reactive Yellow 176
qe (mg/g)
Baggase pith
Soy meal hull
21.0, 20.8, 20.6, 18.8, 12.2, 6.5 86.9 90.0
17.5, 20.0, 152, 75.0 478.57, 120.48, 114.94, 119.89
[61] [46] [47] [43]
[57] [58]
277.78
Bamboo dust-based activated carbon Coconut shell-based activated carbon
143.20 277.90
Groundnut shell-based activated carbon
164.90
---
312.50
---
AC C
Palm fiber-based activated carbon
Methylene blue
---
Methylene blue
Commercial activated carbon
240.0
Crystal violet
Sulfuric acid activated rice husk carbon grapefruit peel
64.875 249.68
[59] [23] [62]
---
zinc chloride activated rice husk carbon
61.575
----
-----
NaOH-modified rice husk Citric acid esterifying wheat straw
44.87 227.27
---
Coniferous pinus bark powder
32.78
---
Coniferous pinus bark powder
42.25
[24] [63] [64]
ACCEPTED MANUSCRIPT
Calotropis procera leaf
---
Orange peel
14.3
-----
Jute fiber carbon Skin almond waste
27.99 85.47
---
Neem sawdust
3.8
-----
Sugarcane dust Treated coir pith
3.8 94.7
---
Sawdust
37.83
[68] [27]
-----
Sugarcane fiber Biocomposite (mango stone)
10.44 352.79
---Present study
----
AC C
EP
TE D
M AN U
SC
RI PT
4.14
[26] [61] [65] [66] [67]
---
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Table 2: Pseudo-first, pseudo-second order kinetic parameters and Intraparticle diffusion model for the adsorption of crystal violet onto mango stone composite Kinetic models
Parameter values 25 mg/L -0.04376
50 mg/L 0.000169
75 mg/L 0.02303
qe (mg/g)
-0.29843
-0.47237
-0.57675
0.835
0.539
0.413
Pseudo-second order K2 (g/mg min)
0.04741
0.048326
0.092756
qe (mg/g)
23.25581
50
76.92308
R2
0.999
1
Intraparticle diffusion model Kid (mg/g min1/2)
0.552
13.15
C
42.99
R2
0.592
EP AC C
SC 1
M AN U
0.45
35.02
69.24
0.962
0.591
TE D
R2
RI PT
Pseudo-first order K1(l/ min)
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Table 3: Freundlich, Langmuir and Harkins-Jura isotherms comparison for crystal violet adsorption onto mango stone composite
Kf (mg/g)
qm (mg/g)
0.52
500
B (L/mg)
26
Harkins-Jura isotherm R2
0.94
A
5.6x 10-4
EP
TE D
M AN U
SC
6.098
R2
AC C
1.007
n
Langmuir isotherm
RI PT
Freundlich isotherm
B
5.2x 10-6
R2
0.47
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Table 4: Thermodynamic parameters for the adsorption of crystal violet dye onto mango stone composite ∆Ho(kJ/mole)
33
-0.40646
-176.772
40
-0.36395
47
-0.34512
54
- 0.34006
∆So (kJ/moleK) -5.39662
RI PT
∆Go (kJ/mole)
AC C
EP
TE D
M AN U
SC
Temperature (0C)
AC C
EP
TE D
M AN U
SC
RI PT
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26
(C)
RI PT
25
qe (mg/g)
24
23
SC
22
21
2
4
M AN U
20 6
8
pH
(D)
TE D
50
40
30
EP
qe (mg/g)
10
20
AC C
10
0.05
0.10
0.15
0.20
0.25
0.30
Adsorbent dose (g)
Fig. 1: (A) The point of zero charge of mango stone native biomass versus mango stone biocomposite (B) Crystal violet dye adsorption onto mango stone native biomass versus mango stone biocomposite (Conditions; 0.10 g adsorbent dose, 1 h contact time, 50 mg/L dye initial concentration), (C) Effect of pH on crystal violet adsorption onto mango stone biocomposite (Conditions; 0.10 g adsorbent dose, 1 h contact time, 50 mg/L dye initial concentration at 33 0C in the pH range of 2-10) (D) Effect of biosorbent dose on crystal violet adsorption onto mango stone biocomposite (Conditions; 1 h contact time, 50 mg/L dye initial concentration, pH 8, 0.05 to 0.3 g adsorbent dose, 33 0C).
ACCEPTED MANUSCRIPT
80
(A)
70
50 40 30 20
20
40
60
Time (min)
400
(B)
350
250
120
200 150
EP
qe (mg/g)
100
TE D
300
80
M AN U
0
SC
qe (mg/g)
RI PT
25 mg/L 50 mg/L 75 mg/L
60
100
AC C
50 0
0
100
200
300
Concentration (mg/L)
400
500
ACCEPTED MANUSCRIPT
(C) 50
RI PT
qe (mg/g)
48 46 44
SC
42 40
30
40
M AN U
38 35
40 45 0 Temperature ( C)
(D)
50
TE D
35
25 20 15
EP
qe (mg/g)
30
10
AC C
5 0
0.2
0.4
0.6
NaCl (M)
0.8
1.0
55
ACCEPTED MANUSCRIPT
45
(E)
40 35
RI PT
25 20 15 10 5 0 Surf Excel
Rim
C-TAB
SDS
Tween-80
M AN U
Surfactants
SC
qe (mg/g)
30
AC C
EP
TE D
Fig. 2: Crystal violet adsorption onto mango stone composite (A) Effect of contact time (Conditions; 5-120 min contact time, 50 mg/L dye initial concentration, pH 8, 0.05 g adsorbent dose, 33 0C) (B) Effect of dye initial concentration (Conditions; dye initial concentration 20 to 500 mg/L, 1 h contact time, pH 8, 0.05 g adsorbent dose, 33 0C) (C) Effect of temperature (Conditions; 33-54 0C, 50 mg/L dye initial concentration, 1 h contact time, pH 8, 0.05 g adsorbent dose) (D) Effect of NaCl addition (Conditions; 0.2-1.0 M salt concentration, 50 mg/L dye initial concentration, 1 h contact time, pH 8, 0.05 g adsorbent dose, 33 0C) (E) Effect of surfactants pre-treatment on dye adsorption (Conditions; 5% surfactant solution concentrations, 50 mg/L dye initial concentration, 1 h contact time, pH 8, 0.05 g adsorbent dose, 33 0C).
ACCEPTED MANUSCRIPT
1.0
(A)
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
1.51575
Adj. R-Square
0.39702
log(qe-qt)
Intercept
Value Standard Error 0.3186 0.43949
log(qe-qt)
Slope
-0.01299
0.00627
log(qe-qt)
0.0
-0.5
-1.0
-1.5 0
20
40
60
80
100
120
M AN U
Time
(B) 2.5
2.0
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
2.07666E-4
Adj. R-Square
0.99994 Value
Standard Error
t/qt
Intercept
0.00925
0.00419
t/qt
Slope
0.02082
6.35449E-5
t/qt
TE D
1.5
1.0
0.0 0
20
EP
0.5
40
60
AC C
Time
SC
RI PT
0.5
Equation
80
100
120
ACCEPTED MANUSCRIPT
75
(C)
74
71 70
Equation
y = a + b*x
Weight Residual Sum of Squares Pearson's r
No Weightin 8.0255 0.76927 0.51013
Adj. R-Squar
Value
69
Standard Err
qt
Intercept
69.2404
1.22539
qt
Slope
0.45073
0.16742
68 2
4
6
8
10
12
0.5
(D)
0.4
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
0.00721
Adj. R-Square
0.92845 Value
Standard Error
ce/qe
Intercept
0.05264
0.01098
ce/qe
Slope
0.00241
2.21753E-4
Ce/qe
TE D
0.3
M AN U
t1/2
0.1
0
20
EP
0.2
40
60
80
AC C
Ce
SC
qt
72
RI PT
73
100
120
140
ACCEPTED MANUSCRIPT
(E)
2.6
2.0
Equation
y = a + b*x
Weight
No Weighting 0.93448
Residual Sum of Squares
1.8
0.38375
Adj. R-Square
Value
1.6 0.0
Standard Erro
log qe
Intercept
1.65235
0.18519
log qe
Slope
0.42672
0.16604
1.5
2.0
0.5
1.0
2.5
(F)
0.0030 0.0025
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of Squares
6.64653E-6
Adj. R-Square
-0.0446
M AN U
log Ce
Value 1/qe2
Intercept
1/qe2
Slope
Standard Error
5.69955E-4
3.33606E-4
-5.28469E-6
6.73482E-6
TE D
1/qe2
0.0020
SC
log qe
2.2
RI PT
2.4
0.0015 0.0010
0.0000 0
EP
0.0005
20
40
60
80
100
120
140
AC C
Ce log
Fig 3: Plots of crystal violet adsorption onto mango stone composite; (A) Pseudo-first-order (B) Pseudo-secondorder, (C) Intraparticle diffusion model (D) Langmuir isotherm (E) Freundlich isotherm and (F) Harkin-Jura model
ACCEPTED MANUSCRIPT
(A) Equation
y = a + b*x
Weight
No Weighting 57.28556
40
0.92616
Adj. R-Square
Value Intercept
lnKc lnKc
Slope
Standard Error
-649.16836
108.18722
212623.01929
34209.8419
RI PT
Residual Sum of Squares
lnKc
30
20
10
0 0.00306
0.00312
0.00318
0.00324
0.00330
18
M AN U
1/T
(B)
16 14
TE D
12
dq (%)
SC
50
10 8
4 0.2
EP
6
0.4
0.6
0.8
1.0
AC C
CH3COOH (M)
Fig. 4: (A) Plot of lnKc versus 1/T for 50 mg/L crystal violet initial concentration, (B) Desorption of crystal violet dye using 0.2-1.0 M CH3COOH
100
(C) 2400
(D)
90
90
Transmettence (%)
Transmettence (%)
100
2131
80 1511 3123
70
1728 1631
60
1015 1324, 1435
50 1216
40 30 4000
1890
M AN U
110
SC
RI PT
ACCEPTED MANUSCRIPT
80
2300-2400
70
2900
1511 1718 1326 610 1631 1435 1033
60 50 40
3500
3000
2500
2000
1500
1000
-1
500
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
TE D
Wavenumber (cm )
AC C
EP
Fig. 5: Scanning electron microscopy micrographs of mango stone biocomposite (A) un-loaded composite SEM image (B) dye loaded composite SEM image (C) un-loaded composite FTIR and (D) dye loaded composite FTIR (Conditions: 0.1 g adsorbent dose, 50 mg/L ye concentration, 120 min contact time, 33 0C temperature and pH 8.0).
ACCEPTED MANUSCRIPT
Highlights
Mango stone biomass was modified using ferric chloride and sodium borohydride
•
Prepared composite was employed for crystal violet adsorption
•
Pseudo-second order kinetic model exhibited the best fit with the experimental results
•
Langmuir isotherm was found most appropriate model for this study
•
Composite showed significantly higher affinity for crystal violet adoption versus native biomass
•
Mango stone composite proved to be potential candidate for dyes adsorption from wastewater
AC C
EP
TE D
M AN U
SC
RI PT
•