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Integrating chloroethyl phosphate with biopolymer cellulose and assessing their potential for absorbing brilliant green dye
Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
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Integrating chloroethyl phosphate with biopolymer cellulose and assessing their potential for absorbing brilliant green dye Fabrícia de Castro Silvaa , Marcia Maria Fernandes da Silvab , Luciano Clécio Brandão Limaa , Josy Anteveli Osajimaa , Edson Cavalcanti da Silva Filhoa,* a Programa de Pós-Graduação em Ciência dos Materiais, Laboratório Interdisciplinar de Materiais Avançados–LIMAV, Centro de Ciências da Natureza-CCN, Universidade Federal do Piauí-UFPI, Teresina, PI, CEP 64049-550, Brazil b Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Norte-IFRN, Campus Currais Novos, Currais Novo, RN, CEP 59380000, Brazil
A R T I C L E I N F O
Article history: Received 23 April 2016 Received in revised form 21 June 2016 Accepted 11 July 2016 Available online 12 July 2016 Keywords: Biopolymer Cellulose Modified Adsorption Dye
A B S T R A C T
Cellulose is vastly used in the adsorption of dyes. It can be used in its natural formor with modified surface. This present study aimed at integrating phosphate cellulose with chloroethyl phosphate, value their potential as adsorbents of brilliant green dye, and compare suchresults to those of pure cellulose (Pure-Cel). The phosphatic material (Phosp-Cel) was characterized by XRD, where it was found that the crystallinity of the material was kept; by IV, which showedtwo bands in 1059 and 1027 cm1 that indicated the presence of the COP link; by 31P NMR, which showed a broad signal in 1.86 ppm O C); and by indicating the presence of a single species of phosphorus in material (P thermogravimetry, where Phosp-Cel proved to be more thermally stable than cellulose forerunner. A time of 20 and 120 min was obtained to reach the equilibrium, through the tests of adsorption, for Pure-Cel and Phosp-Cel, respectively. In both cases the system follows the pseudo second order model. The largest removal occurred at pH 10 and the maximum adsorption was 46.7, 58.42 and 90.5 mg g1for Pure-Cel, and 113.6, 114.2 and 112.1 mg g1 for Phosp-Cel at 25 C, 35 C and 45 C, respectively. Pure-Cel experimental isotherms were best fit to the Langmuir model, and Phosp-Cel at 25 C best fit the Langmuir model; while at 35 C and 45 C it best fit the Freundlich model. ã 2016 Elsevier Ltd. All rights reserved.
1. Introduction Aquatic ecosystems are of utmost ecological importance, besides being used for various purposes, such as: leisure, recreation and fishing activities, it is an important livelihood activity of coastal communities [1]. The growths of industrial activity and population have contributed to significant increase of various pollutants in the aquatic environment [2,3]. Water is considered the universal solvent and, by its extraordinary ability to dissolve, it transports a large part of impurities, and if it does not receive the proper treatment, it will have its physical, chemical and ecological characteristics substantially modified [4]. The water used in textile industries serves as vehicle for dyes used in the dyeing process, generating highly colored effluents [5]. Discoloration of such effluents can be made by coagulation,
* Corresponding author. E-mail address: edsonfi[email protected] (E.C. da Silva Filho). http://dx.doi.org/10.1016/j.jece.2016.07.010 2213-3437/ã 2016 Elsevier Ltd. All rights reserved.
precipitation, reverse osmosis, adsorption and many other techniques. However, the adsorption excels the other, because it is a simple technique, one of the most effective processes for the removal of color and textile effluent treatment, where low-cost materials are used, such as cellulose [6–9]. Cellulose is the most abundant modifiable and renewable biopolymerin nature. It is thus a promising raw material available, in terms of cost for adsorption and synthesis of new materials [10,11]. The presence of hydroxyl groups in cellulose surface can under go typical reactions of primary and secondary alcohols, which are the possible active sites for polymer modification [12– 14]. Cellulose chemistry modification is an efficient method for the production of materials with properties improved in relation to precursor polymer [15]. Cellulose phosphorylation is under explored, but very promising in ion-exchange processes [16], inhibitor of the activation
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
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yellow powder which has a yield of 11.0475 g, was labeled as Phosp-Cel (yellow powder).
proteins in the blood that are harmful in hemodialysis after incorporation in the membranes in separation and purification of proteins, vitamins and other important natural products [16], in addition to being used in the adsorption of drugs, metals and dyes. Adsorption can be defined as a process of transferring one or more constituents, which occurs at the interface between two phases. Compound (pollutant) that sticks or adheres to the solid surface is called an adsorbate and the solid surface is known as an adsorbent. When adsorption equilibrium is established, the concentrations of pollutants adsorbed and in the water become constant. The relationship, at a given temperature, between the equilibrium amounts of pollutant adsorbed and in the water is called an adsorption isotherm. Langmuir, Freundlich, Temkin and other models are well known and can explain the adsorption efficiency of a pollutant systematically and scientifically. Parameters as temperature, the nature of the adsorbate and adsorbent and atmospheric and experimental conditions (pH, concentration of pollutants, contact time) can affect the adsorption process. Thus, the adsorption parameters can be optimized in search for maximum decontamination capacity as well as having extensive knowledge of the system to possible large-scale extrapolations [17–21]. Thus, this work aimed at adding chloroethyl phosphate to cellulose phosphorylation to formulate a product with higher adsorption properties of precursor polymer, in order to compare both in brilliant green dye adsorption, by evaluating the parameters: time, pH, temperature and concentration.
2.3. Characterization The techniques used to characterize the materials were X-ray diffraction, infrared, nuclear magnetic resonance 31P and thermogravimetry. The X-ray diffraction was performed on a diffractometer (Shimadzu XRD600A) in 2u range between 5 and 75 . This rate was 5 min1, using the CuKa radiation source, with a wavelength of 154.06 p.m. The infrared spectra were obtained using a Varian FTIR spectrophotometer by the method of the tablet, using 1% of sample in KBr, with 100 scans in the region between 4000 and 400 cm1 with resolution of 4 cm1. The 31PNMR spectrum of the modified solid was obtained by cross-polarization (CP) with magic angle spin of rotation (MAS) technique in a Bruker AC300 spectrometer at room temperature. The relaxation time used was 3 s, with acquisition time of 50 ms, contact 3 ms, a rotation frequency of about 4 MHz and resonance frequence of 75 MHz. Thermogravimetric analyzes were obtained on a TA instrument brand and SDTQ-600 V20.9 Build 20 model, at a temperature range of 25–1000 C, at a heating rate of 10 C min1, under constant flow of nitrogen. Dye solution concentrations were determined on a Varian CARY300 spectrometer.
2. Experimental part 2.4. Adsorption 2.1. Reagents 2.4.1. Adsorption kinetics Kinetics equilibrium was carried out in batches using a range of contact time between 0 and 180 min, where 20 mL of dye solution at a concentration of 100.0 mg L1. They were then put in contact with 20.0 mg of adsorbent material under mechanical agitation to 150 rpm at different time intervals at 25 C. Followed by centrifugation, dilution and the analysis of the final concentrations of solutions. The concentration of the adsorbed dye in the adsorbent phase was quantified according to Eq. (1):
Cellulose microcrystalline (White powder, CAS: 9004-34-6, Fagron), chloroethyl phosphate ((ClCH2CH2O)3P(O), Molecular Weight: 285.49 g mol1, Dinâmica), acetone 99.5% (Isofar), brilliant green dye (Aldrich), NaOH (Impex), HCl (Impex), KNO3 (Impex) and deionized water. All of which were analytical grade reagents and were usedwith no further purification. 2.2. Synthesis of cellulose with chloroethyl phosphate The sample was prepared by reaction of 3.0 g of microcrystalline cellulose (Cel) with 7 mL of chloroethyl phosphate under mechanical stirring or 4 h at 95 C. After reaction, the sample was filtered and washed with deionized water and acetone. The solid was dried at 60 C for 48 h [22,23]. The final material, a dark
ðC o C e Þ V m
ð1Þ
Intensity / a.u.
q¼
0
10
20
30
2θ
40
50
60
70
80
0
10
20
30
2θ Fig. 1. X-Ray diffraction of Pure-Cel(a) and Phosp-Cel (b).
40
50
60
70
80
3350
Transmittance / a.u.
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
b) a)
4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number / cm
100
0
Che m ical shift / pp m
Fig. 2. Infrared Spectra with Fourier transform of Pure-Cel(a) and of Phosp-Cel (b). Fig. 3.
where C0 and Ce are the initial concentrations and equilibrium in solution in mg L1, m the mass of the material in g and V the volume of the solution used in mL. The results obtained with the experiments were studied with the kinetic models of pseudo-first order adsorption, pseudosecond order, intraparticle diffusion and Elovich [24–27]. The pseudo-first order model of Lagergen, represented by Eq. (2), perhaps is the first example reported in the literature that investigates and describes the rate of adsorption in a liquid phase. ln(qe qt)=lnqt K1t
(2)
With qe and qt (mg g1) the values of the quantity adsorbed per unit mass at equilibrium and in any moment t, qt (mg g1) is the amount adsorbed per gram of adsorbent at time t (min) and k1 (min1) is the adsorption rate constant of pseudo-first order, which is obtained from the slope of the line when the graph is plotted of ln (qe-qt) vs t [24]. The pseudo-second order model of Ho and Mckay, is represented by Eq. (3), where the initial velocity of adsorption, represented by h (mg g1 min1) when t = 0 is obtained using
100
31
P NMR Spectrum of Phos-Cel.
Eq. (4) [25]: t 1 1 ¼ þ t qt K 2 qe 2 qe
ð3Þ
h ¼ K 2 qe 2
ð4Þ 1
where qe (mg g ) is the amount adsorbed per gram of adsorbent in equilibrium condition, qt (mg g1) is the amount adsorbed per gram of adsorbent at time t (min) and k2 the pseudo-second order rate constant (g mg1 min1), this equation provides that the ratio between the amount adsorbed in function of time must be linear. The intraparticle diffusion was evidenced by Weber and Morris, whose in their experiments observed that in many cases of adsorption, the solute varied almost proportionately with t1/2 instead of with the contact time t [26]. Its expression is represented by Eq. (5): qt ¼ K p t1=2 þ C
ð5Þ 1
1/2
where Kp the intraparticle diffusion constant (mg g min ), C is a constant related to the diffusion resistance (mg g1) and qt the
Table 1 IR assignments of the main vibrations in the FTIR spectra of Pure-Cel and Phosp-Cel. Pure-Cel
Phosp-Cel
Vibrations (cm1) Assignments
Vibrations (cm1)
Assignments Absorption band presented wider y(CHOH) y(CH2OH) Absorption band more intense CH and CH2 asymmetrical and symmetrical stretching OH deformation CHOH deformation Absorption region more intense due the phosphate ester P¼O stretch contribuction structure of the glucopyranoside CO stretching COP alcoholicgroups Shift absorption with OH substitution COH
3340
y(CHOH) y(CH2OH)
3384
2885
CH and CH2 asymmetrical and symmetrical stretching OH deformation CHOH deformation
2906
1170–1060
structure of the glucopyranoside CO stretching
1170–1060
<1000 894
alcoholicgroups COH
1655 1451–1319
1662 1451 e 1319
1059 e 1027 <1000 888
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3,0 100
1,4
100 2,5
1,2
80
40
1,0
0,8
Mass / %
Mass / %
1,5
60
0,5
0
0,0
0,4
-1
-1
20
0,6
Derivative / % K
60
1,0
80
Derivative / % K
2,0
40 0,2 0,0
20
-0,2 0
200
400
600
800
0
1000
200
Temperature / C
400
600
800
1000
Temperature / C
Fig. 4. TG/DTG Curves of Pure-Cel (a) and Phosp-Cel (b) under dynamic atmosphere of N2 (100 mL me1).
where b the desorption constant (g mg1), a the initial adsorption rate (mg g1 min1) and qt the quantity adsorbed (mg g1) at time t (min) [27].
quantity adsorbed (mg g1) at time t (min). In case of intraparticle diffusion the graph of qt as a function of t1/2 must be linear. The Elovich Eq. (6) is suitable for systems whose adsorption surfaces are heterogeneous: qt ¼ bðlnabÞ þ bðlntÞ
ð6Þ
Cel
OH
OCH2CH2OCl
+
O
P O C H2 C H2 O C l O C H2 C H 2 O C l
OH
OH
OH HO O
O
O HO
OH HO O
O
OH
OH
O
O HO
OH HO O
OH
O OH
O
O
O
O
P O
O
O OH HO O OH
O HO
O
OH HO O
O
OH
O HO
O
OH HO O
OH
OH
+ 3 HCl Fig. 5. Proposal reaction of pure cellulose with chloroethyl phosphate.
O OH
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F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356 Table 2 Linear kinetic parameters calculated for pure cellulose and Phosp-Cel in brilliant green dye.
2.4.2. Effect of pH To adjust the initial pH of the dye solution was used solutions of HCl and NaOH. The solutions were prepared using 20.0 mg of adsorbent in 20.0 mL of dye solution (100.0 mg L1) varying the pH value between 3 and 10. The dye solution was in contact with the adsorbent under stirring (150 rpm) for 1 h at a temperature of 25 C. The samples were centrifuged, diluted and the final concentration of the supernatant solution was determined by UV–vis spectroscopy. The optimal pH value for adsorption was determined.
Kinetic Models
Pure-Cel
Phosp-Cel
qe(mg g1) K1 (min1) qt(mg g1) R2 qe(mg g1) K2 (g mg1 min1)
15.8140 0.0287 0.4939 0.4838 15.8140 0.0819
64.5000 0.0173 18.5478 0.9454 64.5000 0.0020
Pseudo- second order
qt(mg g1) R2 h (mg g1 min1) KP (g mg1 min1/2)
15.8730 0.9842 20.6355 0.1376
66.6667 0.9996 8.8889 1.4555
intraparticle diffusion
C (mg g1) R2 a (g mg1 min1)
14.9323 0.2888 –
44.9911 0.8338 23.8761
Elovich
b (g mg1)
0.1973 0.4992
6.3162 0.9499
Pseudo- first order
2.4.3. Experimental isotherms In the same way described above the experimental isotherms of adsorption were obtained, however by using the range of concentration of 20–200 mg L1, pH and a predetermined time period. Then they were centrifuged, diluted and analyzed. The experimental isotherms of adsorption were conducted at 25, 35 and 45 C for both materials. To establish the most appropriate correlation for the equilibrium curves in all temperatures for each dye, three theoretical models of isotherms were used: Langmuir, Freundlich and Temkin [28–30]. The adsorption data were adjusted by the Langmuir linear model [28]. The Langmuir linear expression is given by Eq. (7): Ce 1 Ce ¼ þ qe K L qm qm
Parameters
R2
where Ce dye concentration at equilibrium (mg L1), qe the amount adsorbed at equilibrium (mg g1), qm the constant related to the maximum adsorption capacity (mg g1) and KL the constant related to the energy adsorption (L mg1). The essential characteristic of the Langmuir isotherm can be expressed by a dimensionless
ð7Þ
18 16 14 12 10 8 6 4 2 0 -2 -2 0
0
20
40
60
80
100
120
140
160
180
200
70 60 50 40 30 20 10 0 -1 0 -2 0
0
20
40
60
80
100
120
140
Fig. 6. Study of contact time in brilliant green dye adsorption on Pure-Cel and Phosp-Cel.
160
180
200
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
change the crystallinity of synthesized material, even after incorporation of chloroethyl phosphate in the structure. The infrared spectra of natural cellulose and phosphate are shown in Fig. 2. Fig. 2a showed the specter of pure cellulose, which features around 3430 cm1, the band refers to the primary and secondary stretch of hydroxyl OH vibration, y( CH OH) and y( CH2OH), respectively. Around 2885 cm1 is referring to the band stretch vibration of CH and CH2. The band in 1655 cm1 refers to the deformation vibration group OH. The bands around 1451– 1319 cm1 are caused by deformation of the Group CH OH. The bands around 1170–1060 cm1 are related to the stretching of the C O bond, regarding the structure of the glucopyranoside and the bands present in the region below 1000 cm1 are assigned to absorption of alcoholic groups, also in the ring [32]. The modified cellulose kept the intrinsic bands of cellulose, containing some changes, as noted in Fig. 2. The absorption band at 3384 cm1 corresponding to the OH stretching wider presented with decreasing wavelength compared to cellulose precursor, due to changes that occurred in the C6 hydroxyl, referring to the hydroxyl carbons 2 and 3, of the 6 carbon hydroxyl not replaced. And for the same reason there is modification in the band due to the vibration of deformation of the OH group around 1662 cm1. The band in 2906 cm1 is assigned to the CH2 group stretch, which unlike pure cellulose, whose band is more intense due to the incorporation of chloroethyl phosphate, incorporates new CH2 groups in biopolymer. The adjusting of bands in between 1448 and 1322 cm1 refers to the CHOH group deformation and, in this region, the phosphate ester P¼O stretch occurs for that reason they were more intense and with the emergence of a new band in 1240 cm1. Another set between 1162 and 1053 cm1 are the C O bonds. Two bands of 1059 and 1027 cm1 indicate the presence of C O P connection, therefore suggesting a phosphating reaction [33,34]. There is still a difference in band in 894 cm1 of pure cellulose, which caused a decrease in intensity and offset for 888 cm1, after modification, regarding Group COH, indicating that the incorporation occurred in the OH group. Table 1 shows the important IR assignments in FTIR specters. Fig. 3 shows the spectrum of 31P NMR of cellulose phosphate, such technique was performed in order to confirm the presence of phosphorus in the solid modified.
constant called equilibrium parameter (RL) according to Eq. (8): RL ¼
1 1 þ K L Ce
ð8Þ
where Ce the highest initial concentration (mg L1) and KL constant of Langmuir. If 0
ð9Þ
where qe is the amount of adsorbed ions per unit of adsorbent in mg g1, Ce the concentration of ions in the fluid phase at equilibrium in mg L1, n and KF are empirical parameters of Freundlich, and the magnitude of their constants provide an indication of the affinity and ability of adsorption of adsorbent system-adsorbate, respectively [29]. The isotherm of Temkin contains a factor that shows how the interactions occur between the adsorbate and the adsorbent. This isotherm assumes that the heat of adsorption of all molecules that cover the adsorbent decreases linearly as a function of the coating, due to adsorbate–adsorbate interactions. The adsorption is characterized by a uniform distribution of binding energies [30,31]. The isotherm of Temkin is represented by Eq. (10): qe ¼
1 1 1nK T þ 1nC e nT nT
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ð10Þ
where nT indicates, quantitatively, the reactivity of energetic material sites and KT is the bonding equilibrium constant (L mg1). 3. Results 3.1. Characterizations Fig. 1 shows the X-ray diffraction of Pure-Cel and of Phosp-Cel. Significant changes were not found after the phosphorylation reaction, in which X-ray diffraction peaks exhibited 15.77, 22.56 and 34.55, indicating that it has a structure similar to pure cellulose microcrystalline, which showed characteristic peaks at approximately 15.68, 22.40 and 34.55 , so, there were no significant changes in intramolecular interactions of compound that could
40 55
35
50
25
qt / mg g
-1
qt / mg g
-1
30
( a)
20 15 10
45
40
(b) 35
5 30 2
3
4
5
6
7
pH
8
9
10
11
2
3
4
5
6
7
pH
Fig. 7. Study of pH for brilliant green dye adsorption in Pure-Cel (a) and Phosp-Cel (b).
8
9
10
11
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F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
100
130
90
120 110
80
100 70
90
60
80
50
70 60
40
50
30
40
25 35 45
20 10
30
25 35 45
20 10
0
0
-10
-10 -10
0
10
20
30
40
(c)
50
60
70
80
-5
0
OH
O
10
15
20
OH
OH HO
5
O
O HO
OH HO O
O
OH
OH
O
O HO
25
30
35
40
OH HO O
OH
O OH
O
N
N
O
N
N
O
O
P O
O
O OH HO O OH
O HO
O
OH HO O
O
OH OH
O HO
O
OH
OH HO O
O OH
Fig. 8. Adsorption Isotherm at different temperatures for the Pure-Cel system (a) and Phosp-Cel inbrilliant green dye (b) and interaction scheme of modified cellulose and brilliant green dye (c).
The occurrence of a 1.86 ppm signal is associated with the presence of the phosphate group, confirming that a phosphorylation reaction occurred. The two symmetrical side bands in 85.6 and 81.2 ppm are bands resulting from the rotation of the anisotropy powder [35]. Unlike other NMR spectra of 31P for the other pulps in phosphate material, a broad peak occurs, indicating the presence of a single species of phosphorus in material (P OC), since the incorporated Group has an organic group, this causes the enlargement, unlike other surfaces that have been modified with inorganic phosphors. Fig. 4 shows the thermogravimetric curves of pure cellulose (a) and (b) the modified cellulose. The Pure-Cel presented two mass loss events and the Phosp-Cel three events. The first being related to water loss, occurring between 25 and 70 C and 29–100 C, with 7 and 5% mass loss, respectively. Such waste is not valid for the evaluation of thermal
stability because it is attributed to the release of the water simply physically adsorbed on the surface of materials. The second event, in the temperature range of 269–391 C is for cellulose degradation, which in pure caused almost 100% of decomposition. To modified cellulose, the second event occurs in the temperature range from 222 to 304 C with decomposition near 50%, related to the groups of superficial hidroxyl condensation and the beginning of the degradation of carbonic structure, that remains almost continuous at temperatures greater than 304 C, with a total degradation at about 76% of its mass. That keepsthe degradation of the structure of the polysaccharide, resulting a mass related to phosphorus oxide that does not suffer from degradation from the phosphate group incorporated. Once characterizations had been understood and analyzed, it was possible to develop a suggestion of the proposed reaction, shown in Fig. 5.
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356 Table 3 Parameters obtained for different models of isotherms for brilliant green dye adsorption in Pure-Cel and Phosp-Cel at different temperatures, pH 10. Models
25 C
35 C
45 C
Langmuir
PureCel
PhospCel
PureCel
PhospCel
PureCel
Phosp-Cel
qm (mg g1) KL (L mg1) RL R2
56.9476 0.0931 0.3043 0.9523
149.9250 0.1213 0.3457 0.8825
68.4462 0.0743 0.1477 0.9901
193.4235 0.0412 0.4060 0.6003
98.9119 0.2882 0.2654 0.9677
161.2903 0.0681 0.2967 0.8698
Freundlich N KF (mg g1) R2
1.8106 6.4010 0.8241
1.5154 17.1945 0.7792
1.9925 7.5101 0.9792
1.5787 12.2597 0.9082
2.1739 22.7101 0.6028
1.6901 14.8823 0.9712
Temkin nT KT (L mg1) R2
0.0799 0.9989 0.9307
0.0277 1.1687 0.8430
0.0793 1.1949 0.9633
0.0338 0.8621 0.7743
0.0528 4.9472 0.8329
0.0349 1.1372 0.8628
3.2. Adsorption Fig. 6 shows the analysis of the period of time when dye remained in contact with absorbents. Equilibrium time study results (Fig. 6) show that the adsorption speed is greater for pure cellulose. It has been observed that a longer time with contact is needed, superior to 100 min, to achieve the equilibrium of the new biopolymer, despite the variation being very small after 90 min, and during this period the quantity of dye removed is far superior, four times the value of removal, when compared to pure cellulose, indicating the presence of phosphate group in the synthesized material. Pure cellulose has reached equilibrium in 20 min, with adsorption capacity of 15.81 mg g1. Phosp-Cel reached its equilibrium in 120 min, with maximum adsorption of 64.5 mg g1. Although it is most necessary contact time in the adsorption process using the modified material was obtained a value removal capacity 4 times higher than that presented by pure cellulose, even though it has not yet been optimized all parameters. Through the data in Table 2, it can be seen that the kinetic behaviors adjusted better to the pseudo-second order model for both materials, since the linear correction coefficient was 0.9842 and 0.9996, for Pure-Cel and Phosp-Cel, respectively, besides the value of the sorbed amount per gram of adsorbent, obtained experimentally, qe, near to the calculated values, qt [36,37]. The pH of the solution affects the load on the surface of the adsorbents and affects the level of ionization of different pollutants. The change of pH affects the adsorption process for the dissociation of functional groups in actives from the adsorbent surface sites [38]. The values of pH 1.0, 2.0, 11.0 and 12.0 spectral changes, for the dye in study, occur according to changes in the wavelength of maximum absorption. Consequently, the effect of the variation of initial pH of dye stuff solutions was evaluated only with pH values between 3.0 and 10.0, as shown in Fig. 7. Pure-Cel and Phosp-Cel showed maximum adsorption capacity at pH 10, with the difference that Pure-Cel showed a rapid increase in pH 6 and then removing capacity showed a minor increase over the previous pH, while Phosp-Cel increased gradually from pH 5 to pH of maximum removal. These behaviors are explained using the point of zero charge of the materials (pHpzc evaluates the behavior of charges on the surface of materials, due the change in solution pH) and the dye pKa. For Pure-Cel, it found that the pHpzc value was 6.35 whereas for modified material, pHpzc found was 4.96, over these pH values
3355
materials showed negative charges on its surface due to the release proton to the medium. Once the pKa values of brilliant green dye are 2.63 and 4.93 [39], thereby the adsorption of dye is favored by electrostatic attraction at pH > 6 to pure cellulose and at pH > 4.96 for Phosp-Cel (pH > pHpzc) due the surfaces of materials are negatively charged and dye is positively charged (pH > pKa) [40,41]. Fig. 8 shows the experimental data of equilibrium of brilliant green dye for the biopolymers under study. It was observed in Fig. 8 that the equilibrium curves have two stages, the first characterized by an increase in adsorption capacity, due to high affinity materials and the dye; and the second stage is characterized by a plateau, that represents the maximum capacity of saturation in the monolayer. The maximum capacity of adsorption of the dye per gram of adsorbent on the surface of materials were 46.7, 58.42 and 90.5 mg g1 in pure cellulose, and 113.6, 114.2 and 112.1 mg g1 in Phosp-Cel to 25 C, 35 C and 45 C, respectively. The considerable increase in material adsorption capacity, after its modification, is explained by favoring the formation of attraction forces type hydrogen bonding between the surface of material and dye. An illustrative scheme for the interaction between material and dye can be foundin Fig. 8c. It is worth mentioning that temperature increase favored the process of adsorption of Pure-Cel, evidencing an endothermic process. The same is not noted for Phosp-Cel, because the maximum capacities of no significant show variation in adsorption with temperature increase. To establish the most appropriate correlation for the equilibrium curves in all temperatures, three models were used: Langmuir isotherms, Freundlich, and Temkin. Table 3 presents the parameters of the isotherms and the quality of fit for adsorption under study. Based on data contained in Table 3, it can be noticed that the experimental isotherm of Pure-Cel fits the Langmuir modelbetter, because it presents the highest values of the coefficient of linear correlation in the three temperatures. In addition, comparing the values of qm calculated from the Langmuir isotherm and the experimental values is possible to note that the same are quite close indicating that Langmuir isotherm is appropriate to describe the adsorption process. For Phosp-Cel at 25 C, its experimental isotherm was best adjusted to the Langmuir model, because its coefficient of linear correlation presents higher value when compared to other models, in addition having the qe value closer to the value of q calculated from the model only at this temperature. However at 35 C and 45 C it best fit the Freundlich model, because of its better linearity, characterizing an adsorption in multilayers. The RL values calculated from the Langmuir equation suggest that the adsorption is favorable (0 < RL < 1) in all cases in which was obtained a good fit to this model. In face of what has been exposed, the necessary parameters for applying the adsorption technique making use of Phosp-Cel as adsorbent (contact time, concentration pH and temperature) support the proposal the economic viability of the system, even if it is necessary wide scale tests to prove efficiency in this condition, for the cellulose modification reaction has promoted a return of 11,0475 g of the modified material, therefore an average cost of US$ 7,00 in the proposed reaction, in this sense obtaining a 114 mg removal of the dye in solution it is spent less than US$ 1,00 taking into account the amount of reagent used in the adsorption tests. 4. Conclusion In this work, a phosphate pulp was synthesized with chloroethyl phosphate and compared with the cellulose precursor as adsorbents for the adsorption of brilliant green dye.
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F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
The characterization techniques that were used contributed to prove the efficiency of the incorporation of the phosphate group on the surface of cellulose. Through DRX it was observed that the crystallinity of the material was kept after synthesis. In IV, two bands in 1059 and 1027 cm1 appeared for the sample, indicating the presence of the link C-O-P, in 31NMR P. It ocurred the presence of a broad signal cornering thermogravimetric 1.86 ppm and the Phosp-Cel proved itself thermally more stable than the precursor cellulose. Through adsorption tests, it was possible to determine that the time of equilibrium was 20 and 120 min, for the pure Cel and Phosp-Cel, respectively, and that in both cases the experimental data are better adjusted to the pseudo-second order model. The best removal occurred in pH 10, considering that the cationic dye is desprotoned in this condition. The removal increased significantly after the phosphatizing of cellulose being evidenced by the adsorption capacity of 46.7, 58.42 and 90.5 mg g1 of pure cellulose and 113.6, 114.2 and 112.1 mg g1 of Phosp-Cel to 25 C, 35 C and 45 C, respectively. The experimental isotherms of Pure-Cel were best adjusted to the Langmuir model; and the Phosp-Cel in 25 C to the Langmuir model; and at 35 C and 45 C both best fit the Freundlich model. Therefore, the chemically modified cellulose presented maximum removal capacity of brilliant green greater than that pure cellulose, which provides to this paper a useful applicability. Acknowledgments CAPES, FAPESP and CNPq are grateful thankfully acknowledged for financial support, UFPI and LIMAv. References [1] N. Zaitsev, S. Dror, Water quality function deployment, Qual. Eng. 25 (2013) 356–369. [2] E.C. Silva Filho, L.C.B. Lima, F.C. Silva, K.S. Sousa, M.G. Fonseca, S.A.A. Santana, Immobilization of ethylene sulfide in aminated cellulose for removal of the divalent cations, Carbohydr. Polym. 92 (2012) 1203–1210. [3] I. Ali, H.Y. Aboul-Enein, Instrumental Methods in Metal Ions Speciation: Chromatography, Capillary Electrophoresis and Electrochemistry, Taylor & Francis Ltd., New York, 2006. [4] A. Pohorille, L.R. Pratt, Is water the universal solvent for life? Orig. Life Evol. Biosph. 42 (2012) 405–409. [5] L.S. Silva, L.C.B. Lima, F.C. Silva, J.M.E. Matos, M.R.M.C. Santos, L.S. Santos Júnior, K.S. Sousa, E.C.D. Silva Filho, Dye anionic sorption in aqueous solution onto a cellulose surface chemically modified with aminoethanethioll, Chem. Eng. J. 218 (2013) 89–98. [6] S. Kumari, D. Mankotia, G.S. Chauhan, Crosslinked cellulose dialdehyde for congo red removal from its aqueous solutions, J. Environ. Chem. Eng. 4 (2016) 1126–1136. [7] N.B. Douissa, S. Dridi-Dhaouadi, M.F. Mhenni, Spectrophotometric investigation of the interactions between cationic (C.I. basic blue 9) and anionic (C.I. acid blue 25) dyes in adsorption onto extracted cellulose from posidonia oceânica, J. Text. Sci. Eng. 6 (2016) 240–249. [8] L. Liu, Z.Y. Gao, X.P. Su, X. Chen, L. Jiang, J.M. Yao, Adsorption removal of dyes from single and binary solutions using a cellulose-based bioadsorbent, Chem. Eng. 3 (2015) 432–442. [9] A. El Ghali, B.M. Hassen, R.M. Sadok, Surface functionalization of cellulose fibers extracted from juncus acutus L plant: application for the adsorption of anionic dyes from wastewaters, J. Eng. Fiber Fabr. 10 (2015) 52–62. [10] L.V.A. Gurgel, O. Karnitz Júnior, R.P.F. Gil, L.F. Gil, Adsorption of Cu(II) Cd(II), and Pb(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with succinic anhydride, Bioresour. Technol. 99 (2008) 3077–3083. [11] R.D.S. Bezerra, M.M.F. Silva, A.I.S. Morais, M.R.M.C. Santos, C. Airoldi, E.C. Silva Filho, Natural cellulose for ranitidine drug removal from aqueous solutions, J. Environ. Chem. Eng. 2 (2014) 605–611. [12] D.M. Suflet, G.C. Chitanu, V.I. Popa, Phosphorylation of polysaccharides: new results on synthesis and characterisation of phosphorylated cellulose, React. Funct. Polym. 66 (2006) 1240–1249.
[13] Y. Zhou, S. Fu, H. Liu, S. Yang, H. Zhan, Removal of methylene blue dyes from wastewate using cellulose-based superadsorbent hydrogels, Polym. Eng. Sci. 10 (2011) 2417–2424. [14] F. Aloulou, S. Boufi, J. Labidi, Modified cellulose fibres for adsorption of organic compound in aqueous solution, Sep. Purif. Technol. 52 (2006) 332–342. [15] D.R. Mulinari, M.L.C.P. Da Silva, Adsorption of sulphate ions by modification of sugarcane bagasse cellulose, Carbohydr. Polym. 74 (2008) 617–620. [16] E.E. Nifant'ev, The phosphorylation of cellulose, Russ. Chem. Rev. 34 (1965) 942–947. [17] I. Ali, V.K. Gupta, Advances in water treatment by adsorption technology, Nat. Protoc. 1 (2007) 2661–2667. [18] I. Ali, The quest for active carbon adsorbent substitutes: inexpensive adsorbents for toxic metal ions removal from wastewater, Sep. Purif. Rev. 39 (2010) 95–171. [19] I. Ali, New generation adsorbents for water treatment, Chem. Rev. 112 (2012) 5073–5091. [20] I. Ali, M. Asim, T.A. Khan, Low cost adsorbents for removal of organic pollutants from wastewater, J. Environ. Manage. 113 (2012) 170–183. [21] I. Ali, Water treatment by adsorption columns: evaluation at ground level, Sep. Purif. Rev. 43 (2014) 175–205. [22] S.A.A. Santana, A.P. Vieira, E.C. da Silva Filho, J.C.P. de Melo, C. Airoldi, Immobilization of ethylenesulfide on babassu coconut epicarp and mesocarp for divalent cation sorption, J. Hazard. Mater. 174 (2010) 714–719. [23] K.S. Sousa, E.C. da Silva Filho, C. Airoldi, Ethylenesulfide as a useful agent for incorporation into the biopolymer chitosan in a solvent-free reaction for use in cation removal, Carbohydr. Res. 344 (2009) 1716–1723. [24] S. Lagergren, Zurtheorie der sogenannten adsorption gelosterstoffe, K. Vet. Akad. Handl. 24 (1898) 1–39. [25] Y.S. Ho, G. Mckay, Pseudo-second order model for sorption processes, Process Biochem. 34 (1999) 451–465. [26] W.J. Weber Júnior, J.C. Morris, Kinetics of adsorption on carbon from solution, J. Sanit. Eng. Div. 89 (1963) 31–59. [27] C. Aharoni, F.C. Tompkins, Kinetics of adsorption and desorption and the Elovich equation, Adv. Catal. 21 (1970) 1–49. [28] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. Soc. 40 (1918) 1361–1403. [29] H.M.F. Freundlich, Uber die adsorption in lösungen, Z. Phys. Chem. 57A (3) (1907) 85–470. [30] M.J. Temkin, V. Pyzhev, Recent modifications to Langmuir isotherms, Acta Phys. Chim. 12 (1940) 217–222. [31] O. Hamdaoui, E. Naffrechoux, Modeling of adsorption isotherms of phenol and chlorophenols onto granular activated carbon: part I. Two-parameter models and equations allowing determination of thermodynamic parameters, J. Hazard. Mater. 147 (2007) 381–394. [32] Y. Hao, J. Peng, Y. Ao, J. LI, M. Zhai, Radiation effects on microcrystalline cellulose in 1-butyl-3-methylimidazolium chloride ionic liquid, Carbohydr. Polym. 90 (2012) 1629–1633. [33] P.L. Granja, L. Pouységu, M. Pétraud, B. De Jéso, C. Baquey, M.A. Barbosa, Cellulose phosphates as Biomaterials. I. synthesis and characterization of highly phosphorylated cellulose gels, J. Appl. Polym. Sci. 82 (2001) 3341–3353. [34] I.S. Skorynina, S.S. Gusev, N.K. Vorob'yeva, I.N. Yermolenko, Phosphorylation of cellulose by polyphosphoric acids, Polym. Sci. U. S. S. R. 12 (1970) 2452–2456. [35] W.D. Wanrosli, R. Rohaizu, A. Ghazali, Synthesis and characterization of cellulose phosphate from oil palm empty fruit brunches microcrystalline cellulose, Carbohydr. Polym. 84 (2011) 262–267. [36] E.C. Lima, B. Royer, J.C.P. Vaghetti, N.M. Simon, B.M. Cunha, F.A. Pavan, E.V. Benvenutti, R.C. Veses, C. Airoldi, Application of Brazilian pine-fruit shell as a biosorbent to removal of reactive red 194 textile dye from aqueous solution Kinetics and equilibrium study, J. Hazard. Mater 155 (2008) 536–550. [37] M.A.M. Salleh, D.K. Mahmoud, W.A.W.A. Karim, A. Idris, Cationic and anionic dye adsorption by agricultural solid wastes: a comprehensive review, Desalination 280 (2011) 1–13. [38] D.I. Mall, V.C. Srivastava, N.K. Agarwal, Removal of Orange- G and methyl violet dyes by adsorption onto bagasse fly ash- kinetic study and equilibrium isotherm analyses, Dyes Pigm. 69 (2006) 210–223. [39] M.S.U. Rehman, M. Munir, M. Ashfaq, N. Rashid, M.F. Nazar, M. Danish, J. Há, Adsorption of Brilliant Green dye from aqueous solution onto red clay, Chem. Eng. J. 228 (2013) 54–62. [40] M.A. Salem, R.G. Elsharkawy, M.F. Hablas, Adsorption of brilliant green dye by polyaniline/silver nanocomposite: kinetic, equilibrium, and thermodynamic studies, Eur. Polym. J. 75 (2016) 577–590. [41] R. Kobiraj, N. Gupta, A.K. Kushwaha, M.C. Chattopadhyaya, Determination os equilibrium, kinetic and thermodynamic parameters for the adsorption of brilhant green dye from aqueous solutions ont eggshell powder, Indian J. Chem. Technol. 19 (2012) 26–31.
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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Integrating chloroethyl phosphate with biopolymer cellulose and assessing their potential for absorbing brilliant green dye Fabrícia de Castro Silvaa , Marcia Maria Fernandes da Silvab , Luciano Clécio Brandão Limaa , Josy Anteveli Osajimaa , Edson Cavalcanti da Silva Filhoa,* a Programa de Pós-Graduação em Ciência dos Materiais, Laboratório Interdisciplinar de Materiais Avançados–LIMAV, Centro de Ciências da Natureza-CCN, Universidade Federal do Piauí-UFPI, Teresina, PI, CEP 64049-550, Brazil b Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Norte-IFRN, Campus Currais Novos, Currais Novo, RN, CEP 59380000, Brazil
A R T I C L E I N F O
Article history: Received 23 April 2016 Received in revised form 21 June 2016 Accepted 11 July 2016 Available online 12 July 2016 Keywords: Biopolymer Cellulose Modified Adsorption Dye
A B S T R A C T
Cellulose is vastly used in the adsorption of dyes. It can be used in its natural formor with modified surface. This present study aimed at integrating phosphate cellulose with chloroethyl phosphate, value their potential as adsorbents of brilliant green dye, and compare suchresults to those of pure cellulose (Pure-Cel). The phosphatic material (Phosp-Cel) was characterized by XRD, where it was found that the crystallinity of the material was kept; by IV, which showedtwo bands in 1059 and 1027 cm1 that indicated the presence of the COP link; by 31P NMR, which showed a broad signal in 1.86 ppm O C); and by indicating the presence of a single species of phosphorus in material (P thermogravimetry, where Phosp-Cel proved to be more thermally stable than cellulose forerunner. A time of 20 and 120 min was obtained to reach the equilibrium, through the tests of adsorption, for Pure-Cel and Phosp-Cel, respectively. In both cases the system follows the pseudo second order model. The largest removal occurred at pH 10 and the maximum adsorption was 46.7, 58.42 and 90.5 mg g1for Pure-Cel, and 113.6, 114.2 and 112.1 mg g1 for Phosp-Cel at 25 C, 35 C and 45 C, respectively. Pure-Cel experimental isotherms were best fit to the Langmuir model, and Phosp-Cel at 25 C best fit the Langmuir model; while at 35 C and 45 C it best fit the Freundlich model. ã 2016 Elsevier Ltd. All rights reserved.
1. Introduction Aquatic ecosystems are of utmost ecological importance, besides being used for various purposes, such as: leisure, recreation and fishing activities, it is an important livelihood activity of coastal communities [1]. The growths of industrial activity and population have contributed to significant increase of various pollutants in the aquatic environment [2,3]. Water is considered the universal solvent and, by its extraordinary ability to dissolve, it transports a large part of impurities, and if it does not receive the proper treatment, it will have its physical, chemical and ecological characteristics substantially modified [4]. The water used in textile industries serves as vehicle for dyes used in the dyeing process, generating highly colored effluents [5]. Discoloration of such effluents can be made by coagulation,
* Corresponding author. E-mail address: edsonfi[email protected] (E.C. da Silva Filho). http://dx.doi.org/10.1016/j.jece.2016.07.010 2213-3437/ã 2016 Elsevier Ltd. All rights reserved.
precipitation, reverse osmosis, adsorption and many other techniques. However, the adsorption excels the other, because it is a simple technique, one of the most effective processes for the removal of color and textile effluent treatment, where low-cost materials are used, such as cellulose [6–9]. Cellulose is the most abundant modifiable and renewable biopolymerin nature. It is thus a promising raw material available, in terms of cost for adsorption and synthesis of new materials [10,11]. The presence of hydroxyl groups in cellulose surface can under go typical reactions of primary and secondary alcohols, which are the possible active sites for polymer modification [12– 14]. Cellulose chemistry modification is an efficient method for the production of materials with properties improved in relation to precursor polymer [15]. Cellulose phosphorylation is under explored, but very promising in ion-exchange processes [16], inhibitor of the activation
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
3349
yellow powder which has a yield of 11.0475 g, was labeled as Phosp-Cel (yellow powder).
proteins in the blood that are harmful in hemodialysis after incorporation in the membranes in separation and purification of proteins, vitamins and other important natural products [16], in addition to being used in the adsorption of drugs, metals and dyes. Adsorption can be defined as a process of transferring one or more constituents, which occurs at the interface between two phases. Compound (pollutant) that sticks or adheres to the solid surface is called an adsorbate and the solid surface is known as an adsorbent. When adsorption equilibrium is established, the concentrations of pollutants adsorbed and in the water become constant. The relationship, at a given temperature, between the equilibrium amounts of pollutant adsorbed and in the water is called an adsorption isotherm. Langmuir, Freundlich, Temkin and other models are well known and can explain the adsorption efficiency of a pollutant systematically and scientifically. Parameters as temperature, the nature of the adsorbate and adsorbent and atmospheric and experimental conditions (pH, concentration of pollutants, contact time) can affect the adsorption process. Thus, the adsorption parameters can be optimized in search for maximum decontamination capacity as well as having extensive knowledge of the system to possible large-scale extrapolations [17–21]. Thus, this work aimed at adding chloroethyl phosphate to cellulose phosphorylation to formulate a product with higher adsorption properties of precursor polymer, in order to compare both in brilliant green dye adsorption, by evaluating the parameters: time, pH, temperature and concentration.
2.3. Characterization The techniques used to characterize the materials were X-ray diffraction, infrared, nuclear magnetic resonance 31P and thermogravimetry. The X-ray diffraction was performed on a diffractometer (Shimadzu XRD600A) in 2u range between 5 and 75 . This rate was 5 min1, using the CuKa radiation source, with a wavelength of 154.06 p.m. The infrared spectra were obtained using a Varian FTIR spectrophotometer by the method of the tablet, using 1% of sample in KBr, with 100 scans in the region between 4000 and 400 cm1 with resolution of 4 cm1. The 31PNMR spectrum of the modified solid was obtained by cross-polarization (CP) with magic angle spin of rotation (MAS) technique in a Bruker AC300 spectrometer at room temperature. The relaxation time used was 3 s, with acquisition time of 50 ms, contact 3 ms, a rotation frequency of about 4 MHz and resonance frequence of 75 MHz. Thermogravimetric analyzes were obtained on a TA instrument brand and SDTQ-600 V20.9 Build 20 model, at a temperature range of 25–1000 C, at a heating rate of 10 C min1, under constant flow of nitrogen. Dye solution concentrations were determined on a Varian CARY300 spectrometer.
2. Experimental part 2.4. Adsorption 2.1. Reagents 2.4.1. Adsorption kinetics Kinetics equilibrium was carried out in batches using a range of contact time between 0 and 180 min, where 20 mL of dye solution at a concentration of 100.0 mg L1. They were then put in contact with 20.0 mg of adsorbent material under mechanical agitation to 150 rpm at different time intervals at 25 C. Followed by centrifugation, dilution and the analysis of the final concentrations of solutions. The concentration of the adsorbed dye in the adsorbent phase was quantified according to Eq. (1):
Cellulose microcrystalline (White powder, CAS: 9004-34-6, Fagron), chloroethyl phosphate ((ClCH2CH2O)3P(O), Molecular Weight: 285.49 g mol1, Dinâmica), acetone 99.5% (Isofar), brilliant green dye (Aldrich), NaOH (Impex), HCl (Impex), KNO3 (Impex) and deionized water. All of which were analytical grade reagents and were usedwith no further purification. 2.2. Synthesis of cellulose with chloroethyl phosphate The sample was prepared by reaction of 3.0 g of microcrystalline cellulose (Cel) with 7 mL of chloroethyl phosphate under mechanical stirring or 4 h at 95 C. After reaction, the sample was filtered and washed with deionized water and acetone. The solid was dried at 60 C for 48 h [22,23]. The final material, a dark
ðC o C e Þ V m
ð1Þ
Intensity / a.u.
q¼
0
10
20
30
2θ
40
50
60
70
80
0
10
20
30
2θ Fig. 1. X-Ray diffraction of Pure-Cel(a) and Phosp-Cel (b).
40
50
60
70
80
3350
Transmittance / a.u.
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
b) a)
4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number / cm
100
0
Che m ical shift / pp m
Fig. 2. Infrared Spectra with Fourier transform of Pure-Cel(a) and of Phosp-Cel (b). Fig. 3.
where C0 and Ce are the initial concentrations and equilibrium in solution in mg L1, m the mass of the material in g and V the volume of the solution used in mL. The results obtained with the experiments were studied with the kinetic models of pseudo-first order adsorption, pseudosecond order, intraparticle diffusion and Elovich [24–27]. The pseudo-first order model of Lagergen, represented by Eq. (2), perhaps is the first example reported in the literature that investigates and describes the rate of adsorption in a liquid phase. ln(qe qt)=lnqt K1t
(2)
With qe and qt (mg g1) the values of the quantity adsorbed per unit mass at equilibrium and in any moment t, qt (mg g1) is the amount adsorbed per gram of adsorbent at time t (min) and k1 (min1) is the adsorption rate constant of pseudo-first order, which is obtained from the slope of the line when the graph is plotted of ln (qe-qt) vs t [24]. The pseudo-second order model of Ho and Mckay, is represented by Eq. (3), where the initial velocity of adsorption, represented by h (mg g1 min1) when t = 0 is obtained using
100
31
P NMR Spectrum of Phos-Cel.
Eq. (4) [25]: t 1 1 ¼ þ t qt K 2 qe 2 qe
ð3Þ
h ¼ K 2 qe 2
ð4Þ 1
where qe (mg g ) is the amount adsorbed per gram of adsorbent in equilibrium condition, qt (mg g1) is the amount adsorbed per gram of adsorbent at time t (min) and k2 the pseudo-second order rate constant (g mg1 min1), this equation provides that the ratio between the amount adsorbed in function of time must be linear. The intraparticle diffusion was evidenced by Weber and Morris, whose in their experiments observed that in many cases of adsorption, the solute varied almost proportionately with t1/2 instead of with the contact time t [26]. Its expression is represented by Eq. (5): qt ¼ K p t1=2 þ C
ð5Þ 1
1/2
where Kp the intraparticle diffusion constant (mg g min ), C is a constant related to the diffusion resistance (mg g1) and qt the
Table 1 IR assignments of the main vibrations in the FTIR spectra of Pure-Cel and Phosp-Cel. Pure-Cel
Phosp-Cel
Vibrations (cm1) Assignments
Vibrations (cm1)
Assignments Absorption band presented wider y(CHOH) y(CH2OH) Absorption band more intense CH and CH2 asymmetrical and symmetrical stretching OH deformation CHOH deformation Absorption region more intense due the phosphate ester P¼O stretch contribuction structure of the glucopyranoside CO stretching COP alcoholicgroups Shift absorption with OH substitution COH
3340
y(CHOH) y(CH2OH)
3384
2885
CH and CH2 asymmetrical and symmetrical stretching OH deformation CHOH deformation
2906
1170–1060
structure of the glucopyranoside CO stretching
1170–1060
<1000 894
alcoholicgroups COH
1655 1451–1319
1662 1451 e 1319
1059 e 1027 <1000 888
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
3351
3,0 100
1,4
100 2,5
1,2
80
40
1,0
0,8
Mass / %
Mass / %
1,5
60
0,5
0
0,0
0,4
-1
-1
20
0,6
Derivative / % K
60
1,0
80
Derivative / % K
2,0
40 0,2 0,0
20
-0,2 0
200
400
600
800
0
1000
200
Temperature / C
400
600
800
1000
Temperature / C
Fig. 4. TG/DTG Curves of Pure-Cel (a) and Phosp-Cel (b) under dynamic atmosphere of N2 (100 mL me1).
where b the desorption constant (g mg1), a the initial adsorption rate (mg g1 min1) and qt the quantity adsorbed (mg g1) at time t (min) [27].
quantity adsorbed (mg g1) at time t (min). In case of intraparticle diffusion the graph of qt as a function of t1/2 must be linear. The Elovich Eq. (6) is suitable for systems whose adsorption surfaces are heterogeneous: qt ¼ bðlnabÞ þ bðlntÞ
ð6Þ
Cel
OH
OCH2CH2OCl
+
O
P O C H2 C H2 O C l O C H2 C H 2 O C l
OH
OH
OH HO O
O
O HO
OH HO O
O
OH
OH
O
O HO
OH HO O
OH
O OH
O
O
O
O
P O
O
O OH HO O OH
O HO
O
OH HO O
O
OH
O HO
O
OH HO O
OH
OH
+ 3 HCl Fig. 5. Proposal reaction of pure cellulose with chloroethyl phosphate.
O OH
3352
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356 Table 2 Linear kinetic parameters calculated for pure cellulose and Phosp-Cel in brilliant green dye.
2.4.2. Effect of pH To adjust the initial pH of the dye solution was used solutions of HCl and NaOH. The solutions were prepared using 20.0 mg of adsorbent in 20.0 mL of dye solution (100.0 mg L1) varying the pH value between 3 and 10. The dye solution was in contact with the adsorbent under stirring (150 rpm) for 1 h at a temperature of 25 C. The samples were centrifuged, diluted and the final concentration of the supernatant solution was determined by UV–vis spectroscopy. The optimal pH value for adsorption was determined.
Kinetic Models
Pure-Cel
Phosp-Cel
qe(mg g1) K1 (min1) qt(mg g1) R2 qe(mg g1) K2 (g mg1 min1)
15.8140 0.0287 0.4939 0.4838 15.8140 0.0819
64.5000 0.0173 18.5478 0.9454 64.5000 0.0020
Pseudo- second order
qt(mg g1) R2 h (mg g1 min1) KP (g mg1 min1/2)
15.8730 0.9842 20.6355 0.1376
66.6667 0.9996 8.8889 1.4555
intraparticle diffusion
C (mg g1) R2 a (g mg1 min1)
14.9323 0.2888 –
44.9911 0.8338 23.8761
Elovich
b (g mg1)
0.1973 0.4992
6.3162 0.9499
Pseudo- first order
2.4.3. Experimental isotherms In the same way described above the experimental isotherms of adsorption were obtained, however by using the range of concentration of 20–200 mg L1, pH and a predetermined time period. Then they were centrifuged, diluted and analyzed. The experimental isotherms of adsorption were conducted at 25, 35 and 45 C for both materials. To establish the most appropriate correlation for the equilibrium curves in all temperatures for each dye, three theoretical models of isotherms were used: Langmuir, Freundlich and Temkin [28–30]. The adsorption data were adjusted by the Langmuir linear model [28]. The Langmuir linear expression is given by Eq. (7): Ce 1 Ce ¼ þ qe K L qm qm
Parameters
R2
where Ce dye concentration at equilibrium (mg L1), qe the amount adsorbed at equilibrium (mg g1), qm the constant related to the maximum adsorption capacity (mg g1) and KL the constant related to the energy adsorption (L mg1). The essential characteristic of the Langmuir isotherm can be expressed by a dimensionless
ð7Þ
18 16 14 12 10 8 6 4 2 0 -2 -2 0
0
20
40
60
80
100
120
140
160
180
200
70 60 50 40 30 20 10 0 -1 0 -2 0
0
20
40
60
80
100
120
140
Fig. 6. Study of contact time in brilliant green dye adsorption on Pure-Cel and Phosp-Cel.
160
180
200
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
change the crystallinity of synthesized material, even after incorporation of chloroethyl phosphate in the structure. The infrared spectra of natural cellulose and phosphate are shown in Fig. 2. Fig. 2a showed the specter of pure cellulose, which features around 3430 cm1, the band refers to the primary and secondary stretch of hydroxyl OH vibration, y( CH OH) and y( CH2OH), respectively. Around 2885 cm1 is referring to the band stretch vibration of CH and CH2. The band in 1655 cm1 refers to the deformation vibration group OH. The bands around 1451– 1319 cm1 are caused by deformation of the Group CH OH. The bands around 1170–1060 cm1 are related to the stretching of the C O bond, regarding the structure of the glucopyranoside and the bands present in the region below 1000 cm1 are assigned to absorption of alcoholic groups, also in the ring [32]. The modified cellulose kept the intrinsic bands of cellulose, containing some changes, as noted in Fig. 2. The absorption band at 3384 cm1 corresponding to the OH stretching wider presented with decreasing wavelength compared to cellulose precursor, due to changes that occurred in the C6 hydroxyl, referring to the hydroxyl carbons 2 and 3, of the 6 carbon hydroxyl not replaced. And for the same reason there is modification in the band due to the vibration of deformation of the OH group around 1662 cm1. The band in 2906 cm1 is assigned to the CH2 group stretch, which unlike pure cellulose, whose band is more intense due to the incorporation of chloroethyl phosphate, incorporates new CH2 groups in biopolymer. The adjusting of bands in between 1448 and 1322 cm1 refers to the CHOH group deformation and, in this region, the phosphate ester P¼O stretch occurs for that reason they were more intense and with the emergence of a new band in 1240 cm1. Another set between 1162 and 1053 cm1 are the C O bonds. Two bands of 1059 and 1027 cm1 indicate the presence of C O P connection, therefore suggesting a phosphating reaction [33,34]. There is still a difference in band in 894 cm1 of pure cellulose, which caused a decrease in intensity and offset for 888 cm1, after modification, regarding Group COH, indicating that the incorporation occurred in the OH group. Table 1 shows the important IR assignments in FTIR specters. Fig. 3 shows the spectrum of 31P NMR of cellulose phosphate, such technique was performed in order to confirm the presence of phosphorus in the solid modified.
constant called equilibrium parameter (RL) according to Eq. (8): RL ¼
1 1 þ K L Ce
ð8Þ
where Ce the highest initial concentration (mg L1) and KL constant of Langmuir. If 0
ð9Þ
where qe is the amount of adsorbed ions per unit of adsorbent in mg g1, Ce the concentration of ions in the fluid phase at equilibrium in mg L1, n and KF are empirical parameters of Freundlich, and the magnitude of their constants provide an indication of the affinity and ability of adsorption of adsorbent system-adsorbate, respectively [29]. The isotherm of Temkin contains a factor that shows how the interactions occur between the adsorbate and the adsorbent. This isotherm assumes that the heat of adsorption of all molecules that cover the adsorbent decreases linearly as a function of the coating, due to adsorbate–adsorbate interactions. The adsorption is characterized by a uniform distribution of binding energies [30,31]. The isotherm of Temkin is represented by Eq. (10): qe ¼
1 1 1nK T þ 1nC e nT nT
3353
ð10Þ
where nT indicates, quantitatively, the reactivity of energetic material sites and KT is the bonding equilibrium constant (L mg1). 3. Results 3.1. Characterizations Fig. 1 shows the X-ray diffraction of Pure-Cel and of Phosp-Cel. Significant changes were not found after the phosphorylation reaction, in which X-ray diffraction peaks exhibited 15.77, 22.56 and 34.55, indicating that it has a structure similar to pure cellulose microcrystalline, which showed characteristic peaks at approximately 15.68, 22.40 and 34.55 , so, there were no significant changes in intramolecular interactions of compound that could
40 55
35
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25
qt / mg g
-1
qt / mg g
-1
30
( a)
20 15 10
45
40
(b) 35
5 30 2
3
4
5
6
7
pH
8
9
10
11
2
3
4
5
6
7
pH
Fig. 7. Study of pH for brilliant green dye adsorption in Pure-Cel (a) and Phosp-Cel (b).
8
9
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F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356
100
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80
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90
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20 10
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-10
-10 -10
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(c)
50
60
70
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-5
0
OH
O
10
15
20
OH
OH HO
5
O
O HO
OH HO O
O
OH
OH
O
O HO
25
30
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40
OH HO O
OH
O OH
O
N
N
O
N
N
O
O
P O
O
O OH HO O OH
O HO
O
OH HO O
O
OH OH
O HO
O
OH
OH HO O
O OH
Fig. 8. Adsorption Isotherm at different temperatures for the Pure-Cel system (a) and Phosp-Cel inbrilliant green dye (b) and interaction scheme of modified cellulose and brilliant green dye (c).
The occurrence of a 1.86 ppm signal is associated with the presence of the phosphate group, confirming that a phosphorylation reaction occurred. The two symmetrical side bands in 85.6 and 81.2 ppm are bands resulting from the rotation of the anisotropy powder [35]. Unlike other NMR spectra of 31P for the other pulps in phosphate material, a broad peak occurs, indicating the presence of a single species of phosphorus in material (P OC), since the incorporated Group has an organic group, this causes the enlargement, unlike other surfaces that have been modified with inorganic phosphors. Fig. 4 shows the thermogravimetric curves of pure cellulose (a) and (b) the modified cellulose. The Pure-Cel presented two mass loss events and the Phosp-Cel three events. The first being related to water loss, occurring between 25 and 70 C and 29–100 C, with 7 and 5% mass loss, respectively. Such waste is not valid for the evaluation of thermal
stability because it is attributed to the release of the water simply physically adsorbed on the surface of materials. The second event, in the temperature range of 269–391 C is for cellulose degradation, which in pure caused almost 100% of decomposition. To modified cellulose, the second event occurs in the temperature range from 222 to 304 C with decomposition near 50%, related to the groups of superficial hidroxyl condensation and the beginning of the degradation of carbonic structure, that remains almost continuous at temperatures greater than 304 C, with a total degradation at about 76% of its mass. That keepsthe degradation of the structure of the polysaccharide, resulting a mass related to phosphorus oxide that does not suffer from degradation from the phosphate group incorporated. Once characterizations had been understood and analyzed, it was possible to develop a suggestion of the proposed reaction, shown in Fig. 5.
F. de Castro Silva et al. / Journal of Environmental Chemical Engineering 4 (2016) 3348–3356 Table 3 Parameters obtained for different models of isotherms for brilliant green dye adsorption in Pure-Cel and Phosp-Cel at different temperatures, pH 10. Models
25 C
35 C
45 C
Langmuir
PureCel
PhospCel
PureCel
PhospCel
PureCel
Phosp-Cel
qm (mg g1) KL (L mg1) RL R2
56.9476 0.0931 0.3043 0.9523
149.9250 0.1213 0.3457 0.8825
68.4462 0.0743 0.1477 0.9901
193.4235 0.0412 0.4060 0.6003
98.9119 0.2882 0.2654 0.9677
161.2903 0.0681 0.2967 0.8698
Freundlich N KF (mg g1) R2
1.8106 6.4010 0.8241
1.5154 17.1945 0.7792
1.9925 7.5101 0.9792
1.5787 12.2597 0.9082
2.1739 22.7101 0.6028
1.6901 14.8823 0.9712
Temkin nT KT (L mg1) R2
0.0799 0.9989 0.9307
0.0277 1.1687 0.8430
0.0793 1.1949 0.9633
0.0338 0.8621 0.7743
0.0528 4.9472 0.8329
0.0349 1.1372 0.8628
3.2. Adsorption Fig. 6 shows the analysis of the period of time when dye remained in contact with absorbents. Equilibrium time study results (Fig. 6) show that the adsorption speed is greater for pure cellulose. It has been observed that a longer time with contact is needed, superior to 100 min, to achieve the equilibrium of the new biopolymer, despite the variation being very small after 90 min, and during this period the quantity of dye removed is far superior, four times the value of removal, when compared to pure cellulose, indicating the presence of phosphate group in the synthesized material. Pure cellulose has reached equilibrium in 20 min, with adsorption capacity of 15.81 mg g1. Phosp-Cel reached its equilibrium in 120 min, with maximum adsorption of 64.5 mg g1. Although it is most necessary contact time in the adsorption process using the modified material was obtained a value removal capacity 4 times higher than that presented by pure cellulose, even though it has not yet been optimized all parameters. Through the data in Table 2, it can be seen that the kinetic behaviors adjusted better to the pseudo-second order model for both materials, since the linear correction coefficient was 0.9842 and 0.9996, for Pure-Cel and Phosp-Cel, respectively, besides the value of the sorbed amount per gram of adsorbent, obtained experimentally, qe, near to the calculated values, qt [36,37]. The pH of the solution affects the load on the surface of the adsorbents and affects the level of ionization of different pollutants. The change of pH affects the adsorption process for the dissociation of functional groups in actives from the adsorbent surface sites [38]. The values of pH 1.0, 2.0, 11.0 and 12.0 spectral changes, for the dye in study, occur according to changes in the wavelength of maximum absorption. Consequently, the effect of the variation of initial pH of dye stuff solutions was evaluated only with pH values between 3.0 and 10.0, as shown in Fig. 7. Pure-Cel and Phosp-Cel showed maximum adsorption capacity at pH 10, with the difference that Pure-Cel showed a rapid increase in pH 6 and then removing capacity showed a minor increase over the previous pH, while Phosp-Cel increased gradually from pH 5 to pH of maximum removal. These behaviors are explained using the point of zero charge of the materials (pHpzc evaluates the behavior of charges on the surface of materials, due the change in solution pH) and the dye pKa. For Pure-Cel, it found that the pHpzc value was 6.35 whereas for modified material, pHpzc found was 4.96, over these pH values
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materials showed negative charges on its surface due to the release proton to the medium. Once the pKa values of brilliant green dye are 2.63 and 4.93 [39], thereby the adsorption of dye is favored by electrostatic attraction at pH > 6 to pure cellulose and at pH > 4.96 for Phosp-Cel (pH > pHpzc) due the surfaces of materials are negatively charged and dye is positively charged (pH > pKa) [40,41]. Fig. 8 shows the experimental data of equilibrium of brilliant green dye for the biopolymers under study. It was observed in Fig. 8 that the equilibrium curves have two stages, the first characterized by an increase in adsorption capacity, due to high affinity materials and the dye; and the second stage is characterized by a plateau, that represents the maximum capacity of saturation in the monolayer. The maximum capacity of adsorption of the dye per gram of adsorbent on the surface of materials were 46.7, 58.42 and 90.5 mg g1 in pure cellulose, and 113.6, 114.2 and 112.1 mg g1 in Phosp-Cel to 25 C, 35 C and 45 C, respectively. The considerable increase in material adsorption capacity, after its modification, is explained by favoring the formation of attraction forces type hydrogen bonding between the surface of material and dye. An illustrative scheme for the interaction between material and dye can be foundin Fig. 8c. It is worth mentioning that temperature increase favored the process of adsorption of Pure-Cel, evidencing an endothermic process. The same is not noted for Phosp-Cel, because the maximum capacities of no significant show variation in adsorption with temperature increase. To establish the most appropriate correlation for the equilibrium curves in all temperatures, three models were used: Langmuir isotherms, Freundlich, and Temkin. Table 3 presents the parameters of the isotherms and the quality of fit for adsorption under study. Based on data contained in Table 3, it can be noticed that the experimental isotherm of Pure-Cel fits the Langmuir modelbetter, because it presents the highest values of the coefficient of linear correlation in the three temperatures. In addition, comparing the values of qm calculated from the Langmuir isotherm and the experimental values is possible to note that the same are quite close indicating that Langmuir isotherm is appropriate to describe the adsorption process. For Phosp-Cel at 25 C, its experimental isotherm was best adjusted to the Langmuir model, because its coefficient of linear correlation presents higher value when compared to other models, in addition having the qe value closer to the value of q calculated from the model only at this temperature. However at 35 C and 45 C it best fit the Freundlich model, because of its better linearity, characterizing an adsorption in multilayers. The RL values calculated from the Langmuir equation suggest that the adsorption is favorable (0 < RL < 1) in all cases in which was obtained a good fit to this model. In face of what has been exposed, the necessary parameters for applying the adsorption technique making use of Phosp-Cel as adsorbent (contact time, concentration pH and temperature) support the proposal the economic viability of the system, even if it is necessary wide scale tests to prove efficiency in this condition, for the cellulose modification reaction has promoted a return of 11,0475 g of the modified material, therefore an average cost of US$ 7,00 in the proposed reaction, in this sense obtaining a 114 mg removal of the dye in solution it is spent less than US$ 1,00 taking into account the amount of reagent used in the adsorption tests. 4. Conclusion In this work, a phosphate pulp was synthesized with chloroethyl phosphate and compared with the cellulose precursor as adsorbents for the adsorption of brilliant green dye.
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The characterization techniques that were used contributed to prove the efficiency of the incorporation of the phosphate group on the surface of cellulose. Through DRX it was observed that the crystallinity of the material was kept after synthesis. In IV, two bands in 1059 and 1027 cm1 appeared for the sample, indicating the presence of the link C-O-P, in 31NMR P. It ocurred the presence of a broad signal cornering thermogravimetric 1.86 ppm and the Phosp-Cel proved itself thermally more stable than the precursor cellulose. Through adsorption tests, it was possible to determine that the time of equilibrium was 20 and 120 min, for the pure Cel and Phosp-Cel, respectively, and that in both cases the experimental data are better adjusted to the pseudo-second order model. The best removal occurred in pH 10, considering that the cationic dye is desprotoned in this condition. The removal increased significantly after the phosphatizing of cellulose being evidenced by the adsorption capacity of 46.7, 58.42 and 90.5 mg g1 of pure cellulose and 113.6, 114.2 and 112.1 mg g1 of Phosp-Cel to 25 C, 35 C and 45 C, respectively. The experimental isotherms of Pure-Cel were best adjusted to the Langmuir model; and the Phosp-Cel in 25 C to the Langmuir model; and at 35 C and 45 C both best fit the Freundlich model. Therefore, the chemically modified cellulose presented maximum removal capacity of brilliant green greater than that pure cellulose, which provides to this paper a useful applicability. Acknowledgments CAPES, FAPESP and CNPq are grateful thankfully acknowledged for financial support, UFPI and LIMAv. References [1] N. Zaitsev, S. Dror, Water quality function deployment, Qual. Eng. 25 (2013) 356–369. [2] E.C. Silva Filho, L.C.B. Lima, F.C. Silva, K.S. Sousa, M.G. Fonseca, S.A.A. Santana, Immobilization of ethylene sulfide in aminated cellulose for removal of the divalent cations, Carbohydr. Polym. 92 (2012) 1203–1210. [3] I. Ali, H.Y. Aboul-Enein, Instrumental Methods in Metal Ions Speciation: Chromatography, Capillary Electrophoresis and Electrochemistry, Taylor & Francis Ltd., New York, 2006. [4] A. Pohorille, L.R. Pratt, Is water the universal solvent for life? Orig. Life Evol. Biosph. 42 (2012) 405–409. [5] L.S. Silva, L.C.B. Lima, F.C. Silva, J.M.E. Matos, M.R.M.C. Santos, L.S. Santos Júnior, K.S. Sousa, E.C.D. Silva Filho, Dye anionic sorption in aqueous solution onto a cellulose surface chemically modified with aminoethanethioll, Chem. Eng. J. 218 (2013) 89–98. [6] S. Kumari, D. Mankotia, G.S. Chauhan, Crosslinked cellulose dialdehyde for congo red removal from its aqueous solutions, J. Environ. Chem. Eng. 4 (2016) 1126–1136. [7] N.B. Douissa, S. Dridi-Dhaouadi, M.F. Mhenni, Spectrophotometric investigation of the interactions between cationic (C.I. basic blue 9) and anionic (C.I. acid blue 25) dyes in adsorption onto extracted cellulose from posidonia oceânica, J. Text. Sci. Eng. 6 (2016) 240–249. [8] L. Liu, Z.Y. Gao, X.P. Su, X. Chen, L. Jiang, J.M. Yao, Adsorption removal of dyes from single and binary solutions using a cellulose-based bioadsorbent, Chem. Eng. 3 (2015) 432–442. [9] A. El Ghali, B.M. Hassen, R.M. Sadok, Surface functionalization of cellulose fibers extracted from juncus acutus L plant: application for the adsorption of anionic dyes from wastewaters, J. Eng. Fiber Fabr. 10 (2015) 52–62. [10] L.V.A. Gurgel, O. Karnitz Júnior, R.P.F. Gil, L.F. Gil, Adsorption of Cu(II) Cd(II), and Pb(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with succinic anhydride, Bioresour. Technol. 99 (2008) 3077–3083. [11] R.D.S. Bezerra, M.M.F. Silva, A.I.S. Morais, M.R.M.C. Santos, C. Airoldi, E.C. Silva Filho, Natural cellulose for ranitidine drug removal from aqueous solutions, J. Environ. Chem. Eng. 2 (2014) 605–611. [12] D.M. Suflet, G.C. Chitanu, V.I. Popa, Phosphorylation of polysaccharides: new results on synthesis and characterisation of phosphorylated cellulose, React. Funct. Polym. 66 (2006) 1240–1249.
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