activated carbon nano-composites: Synthesis and application in sulphide ion removal from water

Accepted Manuscript Title: Alumina/Activated Carbon Nano-composites: Synthesis and Application in Sulphide Ion Removal from Water Authors: Ushadevi Balasubramani, Ranjithkumar Venkatesh, Sangeetha Subramaniam, Gayathri Gopalakrishnan, Vairam Sundararajan PII: DOI: Reference:

S0304-3894(17)30505-8 http://dx.doi.org/doi:10.1016/j.jhazmat.2017.07.006 HAZMAT 18698

To appear in:

Journal of Hazardous Materials

Received date: Revised date: Accepted date:

15-3-2017 9-6-2017 4-7-2017

Please cite this article as: Ushadevi Balasubramani, Ranjithkumar Venkatesh, Sangeetha Subramaniam, Gayathri Gopalakrishnan, Vairam Sundararajan, Alumina/Activated Carbon Nano-composites: Synthesis and Application in Sulphide Ion Removal from Water, Journal of Hazardous Materialshttp://dx.doi.org/10.1016/j.jhazmat.2017.07.006 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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Alumina/Activated Carbon Nano-composites: Synthesis and Application in Sulphide Ion Removal from Water Ushadevi Balasubramania, Ranjithkumar Venkateshb, Sangeetha Subramaniama Gayathri Gopalakrishnanc, Vairam Sundararajana* a

Department of Chemistry, Government College of Technology, Coimbatore, India. Department of Chemistry, Kongunadu Arts and Science College, Coimbatore, India c Department of Nanotechnology, Anna University-Regional Centre, Coimbatore, India b

Corresponding author @: Department of Chemistry, Government College of Technology, Coimbatore, India 641 013 [email protected]; [email protected]

Graphical abstract

Highlights  Controlled pyrolysis of aluminium carboxylates/carbon mixture results in nano alumina embedded carbon composite.  The composites have the capacity of adsorptive oxidation of sulphide ions in water.  Sulphide removal efficacy in acidic, neutral, alkaline, sodium chloride and surfactant media is analysed thoroughly.  Composites show high sulphide removal efficiency in sodium chloride and surfactant media, following II order kinetics.  Composites may be applied to sulphide removal in tannery effluents.

Abstract An investigation of adsorption of sulphide ion (S2-) in water onto carbon/alumina nano-composites synthesized from aluminium carboxylate precursors, in presence of HCl, NaOH, NaCl and surfactant is reported in this paper. A controlled oxygen free pyrolytic technique has been adopted for the synthesis of nano-composites, using acetate, acetyl acetonate, lactate and distearate of aluminium and activated carbon. XRD, SEM and TEM studies of the composites show that they contain clusters made of nano carbon particles of size 50-130 nm into which nano alumina particles of size around 10 nm are dispersed. While applying the adsorption data in Langmuir, Freundlich, Temkin and Dubinin-Raduskevich isotherm models, the data fit well with Langmuir model. All composites have increased porosity and decreased surface area compared to bare carbon. The adsorption capacity of composites obtained from acetate and lactate are higher and are found to be in the range of 71 to 200 mg/g.

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Key words: Alumina, Aluminium carboxylates, Adsorption isotherms, Carbon nanocomposite, Sulphide, TEM.

1. Introduction Alumina, owing to high surface area, mechanical strength and thermal stability, finds a wide application as adsorbent and catalyst [1-3]. Its common presence and inherent amphoteric nature make it suitable for the use as catalyst in industries and water technology [4]. It is well understood that chemistry of aluminium ion plays a vital role in capturing the ions present in water resulting in their elimination. Al3+, as a hard Lewis acid, associates with OH-, PO43-, F-, SO42- and CO32-, which are hard bases. However, sulphide ions (S2-) have reluctance in association with Al3+, and its removal from water is unlikely by simple processes. The main source of sulphides in waste water originates from the use of sodium sulphide in tanneries as dehairing agents for hides [5]. The bacterial reduction of sulphates and thermal degradation of organosulphur compounds also contributes to the elevation of sulphide concentration in water [6, 7]. A report indicates that the pollution level of sulphide is 265 ppm [5] in tannery effluents. Sulphide is a highly toxic producing offensive odour and is hazardous at elevated concentrations. It causes physiological disorders to aquatic organisms and in humans it causes irritation and nausea initially, and serious illness which is even fatal at higher concentration. Moreover, it also causes pipeline corrosion and catalytic poisoning. The presence of sulphides is not permitted in drinking water [8] and the permissible limit of sulphide ions in inland waters and sewer discharge should be in the range of 0 to 10 ppm [9]. A common practice is removal of sulphides from effluents after oxidation by adding substances like hydrogen peroxide, sodium meta bisulphite, etc. The remaining sulphide is subsequently removed by iron (II) salts and aeration [10, 11]. In this process, the main disadvantages encountered are the generation of sludge, inclusion of undesirable anions into sewer and increase in dosage of iron salts more than stoichiometric amounts, due to its reaction with phosphorous compounds [12]. Activated carbons from different sources are being used for the adsorption of gaseous sulphides due to their surface characteristics such as specific surface area, pore size and surface functional groups. Several kinds of carbon based adsorbents have been employed to capture H2S which include agro-based carbon, coal based, chemically activated carbon, fly ash [13-15], etc. In most of the studies, removal of H2S by carbonaceous materials usually follows adsorption/oxidation mechanism [16, 17]. With a view to find the alternative method avoiding chemicals, it was intended to prepare a new nontoxic composite. Generally, composites have unique properties of the blended materials. Carbon metal oxide composites have combined properties of the ingredients, porosity and surface area of carbon, and the catalytic activity of alumina. Hence, in the present work a carbon composite containing nano alumina was chosen for the removal of the sulphide ions from water. In this work, nano-composites comprising nano alumina into activated carbon, have been synthesized using aluminium carboxylates (acetate, acetyl acetate, lactate, distearate) as precursors and characterized by IR, XRD, SEM and TEM techniques, and BET isotherm studies. Adsorption isotherm and kinetic studies have been carried out, and data have been evaluated using Langmuir, Freundlich, Temkin and Dubinin Radushkevich isotherms to find the mechanism. Further, since the tannery effluent also includes sodium chloride and detergents, the efficiency of the synthesized composites for the removal of sulphides in presence of sodium chloride and a commercial surfactant has also been studied. 2. Materials and Methods 2.1. Materials The materials used in this study were activated carbon, aluminium acetate, aluminium acetyl acetonate, aluminium lactate, aluminium distearate, sodium sulphide nonahydrate, N,N’-dimethyl-p-phenylenediamine sulphate, zinc acetate, ferric ammonium chloride,

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hydrochloric acid, sodium chloride and sodium hydroxide procured from Sigma Aldrich and Merck. 2.2. Experimental 2.2.1. Synthesis of Composites The composites (Al3+/C = 1/10 by mass), ANC1, ANC2, ANC3, and ANC4 were prepared by mixing aluminium acetate (7.6 g), acetyl acetonate (12.02 g), lactate (10.89 g), and distearate (22.62 g) respectively with 10 g of activated carbon (AC) in 50 ml of water and stirred for 4 hours using a magnetic stirrer. The slurry obtained in each case was air dried and heated in a closed furnace in the absence of oxygen at 450°C for 2 hours. The synthesized composites were characterized by IR (SHIMADZU-IR PRESTIGE 21), XRD (SHIMADZU XRD 6000), SEM (JOEL JFM 6390), EDX (OXFORD INSTRUMENT), BET isotherm study (QUANTACHROME NOVA 1200E-Surface area and Pore analyser), Simultaneous TG-DTA (Shimadzu DTA-60) and HR-TEM (JEOL/JEM 2100). 2.2.2. Adsorption studies For all adsorption studies, a stock solution of sulphide of 500 ppm was prepared daily by dissolving Na2S. 9H2O crystals in double distilled water and solutions of other electrolytes hydrochloric acid, sodium chloride and sodium hydroxide of 0.1 M, and surfactant of 1%. The residual sulphide present after adsorption was measured colorimetrically by methylene blue method at 670 nm [18] in a UV-visible spectrophotometer (HACH 5000). The data collected were evaluated by isotherm studies, Langmuir, Freundlich, Temkin and DubininRadushkevich models. The adsorption experiments were conducted using 50 ml of varying concentrations from 20 -100 ppm added with different adsorbent dosages ranging from 0.01 to 0.2 g in the increments of 0.05 g, in 100 ml sealed glass bottles kept in an incubator shaker for 1h at 30˚C. In the batch studies, 50 ml portions of 50 ppm of sulphide solutions were agitated with 0.01 g of adsorbents for 1 hour, and the residual concentration of sulphide at different time intervals 10, 20, 30, 40, 50, and 60 minutes were noted for kinetic studies. 3. Results and Discussion 3.1. Characterization of adsorbents 3.1.1 IR analysis The IR spectra of AC and ANCs are shown in Fig.1. The spectrum of AC shows narrow bands in the range 3600- 3640 cm-1 and 1700 -1740 cm-1 due to non-bonded υO-H and υC=O of –COOH group respectively. The bands appearing at 2924, 2226 and 1500 cm-1 are due to alkyl CH, aromatic C=C and alkene C=C implying aromatic and aliphatic groups present in carbon. The spectra of nano-composites (ANCs) exhibit blue shift of bands from 3640 cm-1(υO-H) to the range of 3450 – 3520 cm-1. This may be due to the interaction of hydroxy group with alumina particles, and this shift appears to be more prominent in ANC2. Further, the band around 1700 cm-1 vanished in the spectra of composites substantiates the decarboxylation making composite porous. In addition, a band observed at 950 cm-1 in AC exhibits a red shift attributable to the interaction of metal oxide with carbon. The presence of the bands around 470- 524 cm-1 and 690 cm-1 (υAl-O) supports the presence of alumina in carbon matrix. 3.1.2 XRD analysis The XRD patterns of AC and the nano-composites (ANC1-4) are depicted in Fig. 2. All the patterns show a prominent broad peak at 2θ values 26.6˚ (111) and 43.4˚ (010) corresponding to graphitic carbon (JCPDS card no. 75-2078). This means that the nature of carbon is not much affected due to the insertion of alumina. In addition, comparing the pattern of carbon with that of composites, it is observed that the later has additional sharp peaks at 2θ values 25˚ (012), 43˚ (113), 68˚ (300), and 77˚ (119) (JCPDS card no. 10-0173) implying the insertion of alumina particles in between the graphitic layers. FWHM values applied in Scherrer’s formula, D=kλ/βcosθ, where λ is x-ray wavelength (0.154 nm), β, FWHM of a diffraction peak, θ, diffraction angle and k, Scherrer’s constant of the order of

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0.89, indicate that both carbon and alumina are in nano range. It is calculated that the average crystallite size of metal oxides is in the range of 10-50 nm. 3.1.3. SEM analysis The presence of alumina is further substantiated by electron microscopic analysis. The SEM micrographs shown in Fig. 3 indicate that bare carbon (AC) has hard shell structures with tubular morphology here and there. But after the treatment with aluminium carboxylates, the carbon has been baked into spongy porous structures. The EDX spectra show that the atomic ratio of aluminium to oxygen corresponds to Al2O3. From this observation, it is understood that heating with carboxylates helps increase in number of pores in carbon due to outcoming CO2 through the matrix, giving room to occupation of Al2O3 particles ultimately decreasing the surface area. 3.1.4. TEM analysis In order to confirm the size and the presence of Al2O3 particles inside carbon shell TEM analysis was carried out (Fig. 4). The images and their corresponding SAED pattern of the nano composites are displayed. The light shade region and dark spherical shape particles are carbon and alumina respectively. From the figure, the diameter of nano-composites is observed in the range of 10 – 50 nm, which agrees well with the results obtained in XRD. The SAED pattern shows Bragg spots with diffusion rings for ANCs depicting that the composites were predominantly amorphous. Analysing the pattern indicates that ANC1 and ANC3 were in γ-Al2O3 phase (ICDD no. 10-0425) and ANC2 and ANC3 were in αAl2O3phase (ICDD no. 10-0173). 3.1.5. BET isotherm analysis The pore size, pore volume and the surface area of the nano-composites were calculated from nitrogen adsorption and desorption curves, and the values are tabulated (Table 1). The analysis indicates that pore size increases in the case of nano-composites (in the range of 6 to 25 nm) when compared to AC (2nm). The pore volume and surface area are found to be less than that of AC. This may be due to the occupation of alumina nano particles into many of the pores of activated carbon. While comparing the pore size among the ANCs, it increases from ANC1 to ANC3 and decreases in ANC4. The same trend is observed in pore volume as well. The surface area decreases ANC1 to ANC4. These observations may be attributed to the quantity of the carbon content and the nature of carbon in the organic moiety in precursors. While the distearate precursor having more number of carbon atoms yielded composite of smallest surface area, the acetate precursor resulted in the composite of largest surface area. The lactate and acetyl acetonate precursors yielded composites with medium surface area. 3.1.6. Simultaneous TG-DTA The sulphide adsorption on the composites is further confirmed by TG-DTA analysis. The residues of the decomposition of composites end up with alumina particles which show a residual percentage to about 10% (Fig. 5). This observation is found to be rational for the alumina formation from carboxylates (precursors) taken with carbon. Further, all TG curves show the exothermic decomposition with a sudden weight loss in the case of unadsorbed composites. But sulphur adsorbed composites show an inflection in the exothermic decomposition in the range of 480-500˚C, evidencing the oxidation of sulphide ion. 3.2. Adsorption study 3.2.1. Adsorption kinetics Kinetic studies were carried out in order to explain the adsorption process over the mesoporous surfaces. The equilibrium time was determined, and the mechanism of adsorption for the removal of S2- ions in aqueous system was proposed by studying the adsorption kinetics. A comparison of pseudo first order and pseudo second order kinetic studies of adsorption of sulphide ions by the adsorbents (ANC1-4) is shown in Fig. 6 a & b. The kinetic equations [19] used are: Pseudo-first order kinetic equation: log (qe-qt) = log qe-k1t/2.303 (1)

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Pseudo-second order kinetic equation: t/qt = 1/k2qe2 + t/qt (2) 2where qe and qt are the amounts of S ions adsorbed at equilibrium and at time t (min), t is the adsorption time (min), and k1 (min-1) and k2 (g mg-1min-1) are pseudo-first order and pseudo-second order rate constants, respectively. The kinetic constants obtained by linear regression for the two models are summarized in Table 2. The correlation coefficients R2 values for pseudo-second order model are found to be closer to unity, and the calculated qe values agree well with the experimental values. 3.2.2. Adsorption isotherms The aim of studying the adsorption isotherm is to reveal the specific relation between the equilibrium concentration of adsorbate in the bulk and the adsorbed amount at the surface. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich equations [19] were used to suggest the nature of S2- adsorption onto the nano-composites at constant temperature of 30˚ C. Values of the various constants and R2 calculated from the linear forms of these isotherm models are given in Table 3. The linear form of Langmuir, Freundlich, Temkin and Dubinin-Radushkevich equations are represented as, 1 1 1 = 𝑞 + 𝑏𝑞 𝑐 (3) 𝑞 𝑒

𝑚

𝑚 𝑒

where ce (mg/L) is the equilibrium concentration of S2- ions in solution, qe (mg/g), maximum amount of S2- ions adsorbed at equilibrium, qm (mg/g), maximum amount of S2- ions adsorbed per unit mass of adsorbent required for monolayer coverage of the surface and b (L/mg) is the Langmuir constant. log qe= log KF + (1/n) log ce (4) where KF is the Freundlich constant indicative of adsorption capacity of the adsorbent, and n is another constant related to the surface homogeneity. Using the slope and intercept of linear plots of log qe against log ce, the values of 1/n and log KF obtained, are also given in Table 3. qe = B ln A + B ln ce (5) where B = RT/b, T is the absolute temperature (K), R is the universal gas constant (8.314 J/mol/K), A is the equilibrium binding constant (L/mg) and B is related to the heat of adsorption. ln (qe) = ln (qs) – β ε2 (6) where qe is the amount of adsorbate adsorbed per unit dosage of adsorbent (mg/g), qs, the theoretical isotherm saturation capacity(mg/g), β, Dubinin-Radushkevich isotherm constant(mol2/J2), ε, Dubinin isotherm constant. The value of ε was calculated using the equation, ε = RT ln (1+1/ ce) (7) where R, T and ce represents the gas constant (8.314 J/mol/K), absolute temperature (K), and adsorbate equilibrium concentration (mg/L) respectively. The linear plots of ln qe against ε2yield the values of qm and β. The value of mean adsorption energy E (KJ/mol), was calculated using D-R parameter β in the equation, E=1/√2β (8) As seen in Table 3, Langmuir isotherm fits quite well for the experimental data, with correlation co-efficient around 0.99 and the fitness of other models is found to be less satisfactory. This indicates that the Langmuir model is more suitable for describing the sorption equilibrium of S2- onto the nano-composites, substantiating homogenous distribution of active sites on the surface of the adsorbents and the monolayer adsorption of S2- ions. The qm value in Langmuir isotherm shows the adsorption capacity of the adsorbents, the values were 71.42, 71.42, 90.90, 142.00 and 83.00 mg/g for AC, ANC1, ANC2, ANC3, and ANC4 respectively, indicating high capacities of the synthesized nano-composites. 3.3. Effect of pH The effect of adsorption of S2- with pH was examined at acidic, basic and neutral medium, 5, 12 and 7 respectively (Fig. 7). The study of adsorption at these pH values is significant, since the possibility of removal of sulphide as hydrogen sulphide is in acidic medium and stabilization of sulphide in basic medium are more.

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As concentration of sulphide increases, the percentage removal is found to decrease, irrespective of pH of the medium for all adsorbents. But the percentage is lesser for composites (47.5 to 64 for 20 ppm) than that of AC (69 %). This may be due to the decrease in surface area. When pH is 12, the percentage of removal for the adsorbents, AC, ANC1, ANC2, and ANC3 are found to be similar, whereas at pH 5 the removal percentage is lower. This is because of the continuous elimination of sulphide as hydrogen sulphide rather than adsorption onto the absorbents. In both the pH values, ANC4 shows lower adsorption compared to other composites. This is attributed to the nature of carbon produced by linear lengthy hydrocarbon chain of distearate. Comparing all the values altogether, it is inferred that ANC3 has better percentage removal at pH 12. Analysing the stability behaviour of composites, they are stable in pH range of 4 to 12. In lower pH, alumina gets dissolved partly resulting in reduction of the mass of the composites (Table 4). 3.4. Effect of addition of sodium chloride The percentage removal of sulphide in presence of sodium chloride is presented (Fig. 8). It indicates that the values are better than those of neutral (without NaCl), acidic and alkaline medium. The reason cannot be attributed due to the involvement of various factors such as hydration enthalpy, surface activation of carbon by chloride ions, etc. Generally, tannery effluents contain sodium chloride. Thus, these adsorbents can be prominent materials for the removal of sulphide ions in tannery effluents. 3.5. Effect of addition of Surfactant Surfactants are amphiphilic molecules consisting of a non-polar, hydrophobic tail and a polar, hydrophilic head group. When a surfactant is dissolved in an aqueous environment, the hydrophobic tail interacts weakly with water molecules using van dar Waals forces. On the other hand, the hydrophilic head interacts with the water molecules using dipole-dipole forces. Though sulphide ion being hydrophobic interacts with alkyl groups of surfactants and SO3- being hydrophilic, it attaches to the functional group present in carbon. Nevertheless, these interactions lead to formation of a big molecule preventing more adsorption on carbon surface. This is revealed in the observation of removal of sulphides onto carbon and other ANCs in the presence of surfactants. In addition, the percentage removal due to adsorption appears higher in ANCs than that of bare carbon (Fig. 9). This may be because of interaction of surfactant ion with alumina particles which adds up with the interaction of sulphonyl group with the functional group of carbon through hydrogen bonding. 3.6. Role of surface area and Porosity The surface area and porosity of the adsorbents play a vital role in sulphide adsorption. As the specific surface area increases, an increase in the percentage removal of sulphide ions is observed. In order to compare the effects of surface area and the pore size of the adsorbents AC and ANCs on sulphide ion adsorption, the adsorption capacity with BET surface area and the pore size were plotted (Fig.10). As noted in the figure, adsorbent AC having a surface area of 473.87 m2/g adsorbs higher, whereas ANC4 with a surface area of 58.28 m2/g adsorbs less. But this trend is not followed for all the environments studied as we analyzed earlier. Concerning the pore diameter of the adsorbents, adsorbent with a narrow pore diameter is favourable for the adsorption of hydrogen sulphide [20]. But in this case, an incongruity of adsorption is observed with respect to pore diameter. ANC3 with larger pore diameter of 25.19 nm adsorbs almost equally with AC with a very low pore diameter of 2.48 nm. Hence, it is inferred that there are other factors which contribute the adsorption of sulphide ions onto the adsorbents apart from the surface area and porosity. 3.7. Role of surface functional groups The adsorption of sulphide increases with increase in the surface groups such as C-O and C=O in the form of hydroxyl and carbonyl functionalities [20]. Among acidic groups, hydroxyl group showed the highest content on activated carbons irrespective of the activation conditions. In addition, the lactonic group content does not change with temperature of activation, while carboxyl group content decreases significantly with increase in temperature.

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In the present work, AC has -OH, -CH, –NH and -C=O groups (as revealed from IR spectrum) have the highest adsorption in all the environments under study (except in surfactant medium). Similarly, the ANCs synthesized at a temperature of 450˚C, also show characteristic absorption bands for –OH and -C=O. The mechanism of sulphide adsorption is revealed from the IR spectra of sulphide adsorbed composites (Fig. 1b). They show adsorption bands around 1270 cm-1 and 970 cm-1 (υC=S) indicating that there may be reduction of carbonyl groups by adsorbed sulphide ions. Further, the spectra of sulphide adsorbed nano-composites exhibit a shift of bands 3450 cm1 (υO-H), and the appearance of bands near 2500-2600 (υS-H) cm-1 may be due to the interaction of sulphide ions with hydroxyl groups present in the composites. ANC3, synthesized from lactate of aluminium, shows the highest adsorption which may be due to presence of lactonic functional group. ANC1 with carbonyl group also shows good adsorption, whereas the adsorbent ANC2 also shows better adsorption, which was synthesized from acetyl acetonate of aluminium. ANC4, which was a composite from distearate precursor, with low surface area also shows better adsorption only in presence of surfactants. It is worth mentioning here that the nature of alumina formed in carbon matrix depends on the type of precursor.ANC2 and ANC4 formα-Al2O3, whereas ANC1 and ANC3 form γ-Al2O3 (as evident from SAED pattern). It is a well-known fact that γ-Al2O3shows higher adsorption than α-Al2O3. These observations imply that the presence of functional groups in carbon surface also play a crucial role in adsorption of sulphide ions. 3.8. Evaluation of adsorption system From the above discussion, it is clear that the dynamic adsorption of sulphide ions onto the adsorbents involves more multifaceted phenomena in aqueous medium which includes pH, adsorption environment, surface area, pore diameter, surface functional groups and alumina nano-particles, and not a mere simple pore filling. The fate of sulphide ions adsorbed on the composites was identified as they undergo improved oxidation catalysed by alumina. It is worth mentioning that sulphide undergoes oxidation at 516˚C for activated carbon and 491 ˚C and 467 ˚C for ANC1 and ANC3 respectively as noticed in the thermograms. The probable reactions that might have undergone are [21], Na2S S2-+ 2Na+ (9) O2 gas O2 ads (10) 22S + 2O2 ads SO4 (11) This was confirmed by the precipitation of the leachate with barium chloride solution. In case of acidic medium when there is formation of HS- ions, the oxidative decomposition on the carbon surface would be following the reaction series [16], in which case also sulphate ions are introduced into leachates. Na2S + H3O+ HS- + 2Na+ + H2O (12) HS ads + C(O*)ads → Sads + OH(13) HS ads + 3C(O*)ads →SO2 + OH (14) SO2ads+ C(O*)ads → SO3ads (15) + 2SO3ads + H2O → 2 H + SO4 (16) 3.9 Regeneration studies The regeneration of the nanocomposite is an important economic aspect for the adsorption process. Most of sulphide ions adsorbed are removed as sulphate, and the remaining loaded sulphide ions are eliminated using 2M HCl. The regeneration was studied for two cycles after which there is no significant change in adsorption. The percentage of recovery of ANC2 (62% & 41%), ANC4 (56% & 36%), whereas ANC1 (80% & 64%) and ANC3 (88 & 69%) are successfully recycled for two cycles. 3.10 Field study of sulphide adsorption The field application of the adsorption of sulphide by the synthesized nanocomposites was carried by collecting the sample from a tannery near Erode, Tamil Nadu, India. The samples collected were found to have sulphide concentration in the range of 300- 400 ppm and hence they were diluted to 100ppm. The diluted solution (50 ml) was stirred with 0.01 g

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of nanocomposites for 1h, and the supernatant solution was estimated using methylene blue method. A comparison of the removal percentage of sulphide from synthetic solution and the actual effluent is given in Fig. 11. The results indicate that the composites may be used to remove sulphide from tannery effluent. 4. Conclusion Carbon/alumina nano composites were successfully synthesized from aluminium carboxylate precursors, with alumina incorporation of 10-50 nm inside the carbon matrix by simple pyrolysis. They act as good adsorbents of sulphides from waste water and nanocomposite ANC3, prepared from lactate precursor adsorbs 142.85 mg of sulphide at pH 7. Adsorption follows Langmuir adsorption isotherm with second order kinetics. The efficiency of the synthesized nano-composites is higher even in the presence of surfactants than bare carbon. The adsorbed sulphides undergo oxidation on the surface of carbon catalysed by nano alumina particles. The results suggest that combination of surface functional groups, pore diameter, pore volume and the incorporated alumina nano particles contribute to the adsorption process. Further study is needed to evaluate the nature of adsorption to understand the utility of composites in sulphide removal for combined environments. Acknowledgement The authors wish to acknowledge Centre of Excellence, Environmental Science, TEQIP- Phase-II, Government College of Technology, Coimbatore for the financial assistance. References [1] Caiyun Han, Hongping Pu, Hongying Li, Lian Deng, Si Huang, Sufang He, The optimization of As(V) removal over Mesoporous alumina by using response surface methodology and adsorption mechanism, J. of Hazard. Mater. 254-255 (2013) 301-309. http://dx.doi.org/10.1016/j.jhazmat.2013.04.008 [2] Raka Mukherjee, Sirshendu De, Adsorptive removal of phenolic compounds using cellulose acetate phthalate-alumina nanoparticle mixed matrix membrane, J. of Hazard. Mater. 265 (2014) 8-19. http://dx.doi.org/10.1016/j.jhazmat.2013.11.021 [3] Mohammadreza Esmaeilirad, Mohammed Zabihi, Jalal Sheyegan, Farhad Khorasheh, Oxidation of Toluene in humid air by Metal Oxides Supported on γ-alumina, J. of Hazard. Mater. (2017) Accepted manuscript. http://dx.doi.org/10.1016/j.jhazmat.2017.03.038 [4] Barbara Kasprzyk-Hordern, Maria Ziolek, Jacek Nawrocki, Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment, Appl. Catal. B. 46 (4) (2003) 639-669. http://dx.doi.org/10.1016/S0926-3373(03)00326-6 [5] S. Balasubramanian, V. Pugalenthi, A comparative study of the determination of sulphide in tannery waste water by ion selective electrode (ISE) and iodometry, Water Res. 34(17) (2000) 4201-4206. http://dx.doi.org/10.1016/S0043-1354(00)00190-1 [6] K.L. Londry, J.M.Suflita, Use of nitrate to control sulphide generation by sulphatereducing bacteria associated with oily waste, J. Ind. Microbiol. Biotechnol. 22 (1999) 582-589. http://dx.doi.org/10.1038/sj.jim.2900668 [7] Alon Amrani, Organosulfur compounds: Molecular and Isotopic evolution from biota to oil and gas, Annual Review of Earth and Planetary Sciences. 42 (2014) 733-68. http://dx.doi.org/10.1146/annurev-earth-050212-124126 [8] Guidelines for Drinking-Water Quality, First Addendum to third edition, Volume I, Recommendations, World Health Organization, 2006. [9] B.I. Islam, A.E.Musa, E.H. Ibrahim, Salma A.A.Sharafa, Babiker M. Elfaki, Evaluation and characterization of Tannery wastewater, Journal of Forest Products and Industries, 3(3), (2014) 141-150. [10] N. A. Padivel, W. A. Kimbell, J. A. Redner, Use of iron salts to control dissolved sulphide in trunk sewers, J. Environ. Eng. 121(11) (1995) 824-829. http:// ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9372(1995)121:11(824)

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[11] P. Jameel, The use of ferrous chloride to control dissolved sulphides in interceptor sewers, Journal (Water Pollution Control Federation) 61(2) (1989) 230-236 [12] Simon W.Poulton, Michael D. Krom, Jaap van Rijn, Robert Raiswell, The use of hydrous iron (II) oxides for the removal of hydrogen sulphide in aqueous systems, Water Res. 36 (2002) 825-834. http://dx.doi.org/10.1016/S0043-1354(01)00314-1 [13] J. Kazmierczak, P. Nowicki, R. Pietrzak, Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation, Adsorption 19 (2013) 273-281. http://dx.doi.org/10.1007/s10450-012-9450-y [14] Andrey Bagreev, J. Angel Menendez, Irina Dukhno, Yuriy Tarasenko, Teresa J. Bandosz, Bituminous coal-based activated carbons modified with nitrogen as adsorbents of hydrogen sulphide. Carbon 42 (2004) 469-476. http://dx.doi.org/10.1016/j.carbon.2003.10.042 [15] Guofeng Shang, Liang Liu, Ping Chen, et al. Kinetics and the mass transfer mechanism of hydrogen sulphide removal by biochar derived from rice hull, J. Air Waste Manage. Assoc. 66(5) 2016 439-445. http://dx.doi.org/10.1080/10962247.2015.1122670 [16] L. M. Le Leuch, A. Subrenat, P. Le Cloirec, Hydrogen Sulfide, Adsorption and Oxidation onto Activated Carbon Cloths: Applications to Odorous Gaseous Emission Treatment, Langmuir 19 (2003) 10869-10877. http://dx.doi.org/10.1021/la035163q [17] Yonghou Xiao, Shudong Wang, Diyong Wu, et al. Catalytic oxidation of hydrogen sulphide over unmodified and impregnated activated carbon, Sep. Purif. Technol. 59 2008 326-332. http://dx.doi.org/10.1016/j.seppur.2007.07.042 [18] T.D. Rees, A.B. Gyllenspetz, A.C Docherty, The determination of trace amounts of sulphide in condensed steam with NN-Diethy-p-phenylenediamine, Analyst 96 (1971) 201-208. http://dx.doi.org/10.1039/AN9719600201 [19] Hardiljeet K Boparai, Meera Joseph, Denis M O’Caroll. Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles, J. of Hazard. Mater. 186 (2011) 458-465. http://dx.doi.org/10.1016/j.jhazmat.2010.11.029 [20] Takunya Mochizuki, Mitsuhiro Kubota, Hitoki Matsuda, Luis F.D’Elia Camacho, Adsorption behaviour of ammonia and hydrogen sulphide on activated carbon prepared from petroleum coke by KOH chemical activation, Fuel Process. Technol. 144 (2016) 164-169. http://dx.doi.org/10.1016/j.fuproc.2015.12.012 [21] A. T. Kuhn, G.H. Kelsall, M.S. Chana, A review of the air oxidation of aqueous Sulphide solutions, J. Chem. Technol. Biotechnol. 33A (1983) 406-414. http://dx.doi.org/10.1002/jctb.504330804 Figure Captions Fig. 1 IR spectra of (a) Activated carbon and composites

10

(b) Sulphide adsorbed composites (ANC1 & ANC4)

Fig. 2 XRD patterns of activated carbon and composites

Fig. 3 SEM and EDS images of the activated carbon and composites

11

Fig. 4 TEM image and SAED patterns of composites

12

13

Fig. 5 Thermograms of unadsorbed (a & b) and sulphide adsorbed composites (c & d) and carbon (e)

Fig. 6 Pseudo-first order (a) and pseudo- second order kinetics (b), for S2- adsorption 1.500

1.6

6a

1.2

0.500

1

t/qt

log(qe-qt)

6b

1.4

1.000

0.000 0

20

40

60

0.8 0.6

-0.500

0.4

-1.000

0.2 0

-1.500 AC



0

Time (min) ANC 1

ANC 2

ANC 3

ANC 4

AC

20 ANC 1

40 Time (min)

ANC 2

ANC 3

60 ANC 4

14

Fig. 7 Removal % of sulphide ions in acidic (a) alkaline (b) and neutral medium (c) 80

100

(a)

(b)

90

70

80

60 AC

40

ANC1

30

ANC2

20

% Removal

% Removal

70 50

60

AC

50

ANC1

40

ANC2

ANC3

30

ANC3

ANC4

20

ANC4

10

10

0

0 20

40

60

80

100

20

Concentration (ppm)

100

(c)

90 80

% Removal

70 60

AC

50

ANC1

40

ANC2

30

ANC 3

20

ANC4

10 0 20

40

60

80

100

Concntration (ppm)

Fig. 8 Removal % of sulphide ions in NaCl medium 100 90 80

% Removal

70 60 50 40

AC

30

ANC1

20

ANC2

10

ANC3 ANC4

0 20



40 60 80 Concentration (ppm)

100

40 60 80 Concentration (ppm)

100

15

Fig. 9 Removal % of Sulphide ions in surfactant Medium 70 60

% Removal

50 40 30 AC 20

ANC1 ANC2

10

ANC3 ANC4

0 20

40 60 80 Concentration (ppm)

100

Fig. 10 Sulphide ion removal % as a function of surface area and porosity 500

30 Surface area Pore diameter

Surface area (m2/g)

20 300 15 200 10 100

Pore diameter (nm)

25

400

5

0

0 0

20

40 60 % Removal

80

100



Fig. 11 Removal % of Sulphide ions in tannery effluent 90

Synthetic Effluent

80

% Removal

70 60 50 40 30 20 10 0 AC



ANC1 ANC2 ANC3 ANC4 Composite

16

Table 1. Surface area, Porosity of AC and ANCs Adsorbent Surface area Pore size (m2/g) (nm) AC ANC1 ANC2 ANC3 ANC4

473 342 278 297 58

2.48 6.21 22.42 25.19 15.86

Pore volume (cc/g) 0.293 0.099 0.174 0.189 0.056

Table 2. Kinetic parameters for adsorption of Sulphide Pseudo-first order k1 qe cal (min-1) (mg/g)

Composite

AC ANC1 ANC2 ANC3 ANC4

Pseudo-second order k2 qe cal (g/mg min) (mg/g)

R2

qe exp R2

(mg/g)

0.0767

1.72

0.7504

0.0592

48.07

1.00

47.8

0.1255 0.0451 0.1432 0.0336

53.71 30.98 51.28 20.51

0.8891 0.8757 0.9679 0.9152

0.0038 0.0022 0.0065 0.0035

51..28 48.78 50.76 38.31

0.9983 0.9666 0.9989 0.9825

47.5 46.9 47.7 37.8

Table 3. Isotherm constants for adsorption of Sulphide onto AC and ANCs Medium

Composite AC ANC 1

Neutral

ANC 2 ANC 3 ANC 4 AC ANC 1

HCl

NaOH

ANC 2

R2

71.42

0.35

0.991

17.86

71.42 90.90 142.85 83.33 52.63 100.00 90.90

0.14 0.02 0.05 0.02 0.06 0.02 0.02

0.987 0.995 0.998 0.997 0.961 0.969 0.951

10.56 3.54 9.46 2.85 6.75 3.68 3.15

2.05 1.77 1.47 1.48 1.46 2.23 1.48 1.46

DR constants

R2

A

B

R2

qs

β

0.980

1.91

19.89

0.913

57.85 52.61

0.979 0.985 0.984 0.992 0.909 0.948 0.929

0.85 0.25 0.65 0.22 0.59 0.27 0.23

21.02 18.43 26.77 16.54 11.26 18.43 17.64

0.897 0.951 0.982 0.968 0.921 0.928 0.905

40.77 61.37 36.3 35.69 41.92 39.88

E

R2

4x10-07

1.12

0.764

1x10

-06

0.71

0.748

1x10

-05

0.22

0.878

2x10

-06

0.50

0.888

1x10

-05

0.22

0.884

7x10

-06

0.26

0.907

1x10

-05

0.22

0.891

1x10

-05

0.22

0.897

-05

0.22

0.857

90.90

0.02

0.996

3.24

1.42

0.994

0.24

18.95

0.948

40.28

1x10

ANC 4

71.42

0.01

0.972

2.28

1.53

0.949

0.21

12.56

0.974

29.84

2x10-05

0.16

0.944

AC

111.11

0.11

0.995

13.86

1.68

0.985

1.08

24.57

0.964

62.8

1x10-06

0.71

0.878

ANC 1

100.00

0.17

0.994

17.10

1.88

0.978

1.55

22.44

0.978

63.56

7x10-07

0.85

0.889

54.92

8x10

-07

0.80

0.815

6x10

-07

0.91

0.878

8x10

-06

0.25

0.805

5x10

-07

1.00

0.912

6x10

-07

0.91

0.918

1x10

-06

0.71

0.959

7x10

-07

0.85

0.974

4x10

-06

0.35

0.934

2x10

-05

0.16

0.872

8x10

-06

0.25

0.759

ANC 2 ANC 4 AC ANC 1 ANC 2 ANC 3 ANC 4

Surfactant

b

Temkin constants

ANC 3

ANC 3

NaCl

qm

Freundlich constants Kf n

Langmuir constants

AC ANC 1

76.92 100.00 52.63 142.85 166.66 166.66 200.00 111.11 29.41 37.03

0.19 0.19 0.05 0.16 0.10 0.08 0.09 0.04 0.03 0.07

0.981 0.995 0.997 0.996 0.994 0.893 0.920 0.981 0.973 0.980

14.86 18.70 4.71 21.37 18.07 17.06 20.46 7.76 2.17 5.02

2.1 1.97 1.82 1.62 1.53 1.70 1.64 1.69 1.89 2.19

0.977 0.955 0.977 0.968 0.975 0.883 0.903 0.939 0.954 0.982

1.42 1.87 0.34 1.88 1.44 1.36 1.71 0.53 0.24 0.43

18.34 21.55 13.84 28.14 29.33 26.11 28.19 20.25 7.14 9.79

0.935 0.941 0.957 0.983 0.98 0.935 0.987 0.968 0.927 0.938

63.62 34.53 72.31 71.8 74.36 78.57 53.09 18.69 27.99

17 ANC 2 ANC 3 ANC 4

30.25 41.66 31.25

0.06 0.07 0.06

0.876 0.992 0.939

3.97 6.19 4.21

2.12 2.38 2.27

0.88 0.974 0.925

0.34 0.59 0.39

9.02

0.794

9.38

0.975

8.09

0.861

24.45

1x10-05

0.22

0.677

30.29

7x10

-06

0.27

0.895

1x10

-05

0.22

0.783

23.71

Units: qm(mg/g), b(L/mg), Kf (mg/g(L/mg) ), A(L/g), qs(mol/g), β (mol /J ), E (kJ/mol) 1/n

2

Table 4. Stability percentage of the synthesized ANCs pH Composite 3 10 80 84 ANC1 62 76 ANC2 96 94 ANC3 ANC4

56

68

2