428 Journal of Scientific & Industrial Research J SCI IND RES VOL 72 JULY 2013 Vol. 72, July 2013, pp. 428-434 Biosorption of methylene blue on chemically modified Chaetophora Elegans algae by carboxylic acids Farah Mikati and Mouhiaddine El Jamal* Chemistry Department, Faculty of Sciences (I), Lebanese University, El Hadath, Lebanon Received 20 July 2012; revised 28 December 2012; accepted 02 April 2013 Chemical modification of Chaetophora Elegans algae with carboxylic acids were undertaken in order to improve the methylene blue adsorption. The modified algae with 1 M acetic and formic acid showed an increase in the maximum uptake, but the modified algae with 1M oxalic acid showed an important decrease in the uptake from 143 mg g-1 to 20 mg g-1. The type and concentration of acid used in the chemical modification (0.1 M -1 M) is the major parameter affecting the maximum uptake. The carboxylic acids having more than one –COOH lead to cross-linking effect and so to decrease in qmax. Langmuir-Freundlich isotherm model fitted better the isotherm adsorption data for modified and unmodified algae. Pseudo second order model was well in line with the experimental data. The adsorption rate constant (K2) is higher for modified algae with acetic acid than that of raw algae. The maximum uptake is independent of isotherm adsorption temperature in the range studied. Keywords: Modified algae, acetic acid, formic acid, oxalic acid, methylene blue, isotherm adsorption, kinetic. Introduction The extensive use of dyes poses pollution problems. They reduce light penetration and photosynthesis; in addition, some dyes are carcinogenic1. Several methods exist for reducing the color in textile effluent streams: adsorption, oxidation–ozonation, biological treatment, coagulation–flocculation and membrane processes. The adsorption process is one of the most effective and attractive processes for wastewaters tr eatment. Adsorption using activated carbon is certainly one of the most suitable techniques for treating wastewater containing toxic pollutants; however, it is not economical due to its expensive cost 2-4 . Therefore, research is directed toward the development of low-cost adsorbents alternative to activated carbon. In the past years, many low cost materials have been tested for the removal of dyes and transition metals5-12.The sorption capacities of a raw biosorbents are generally low, but chemical modification can improve it31. The chemical treatment increases the number of the active sites or replaces the existing sites by more attractive ones. Many chemical reagents, organic or inorganic are used for this purpose. The reagents used for this modification are citric acid13-19, HCl20- 21, oxalic acid22, tartaric acid23, NaOH24, KMnO425, formaldehyde26, 27, CaCl2 21, 26, 28, methanol27, 29, 30. Citric acid is the mostly reagent used since it introduces carboxylate group at the surface of the biomass13, 14, but sometimes the chemical modification has a negative effect on the uptake, due to decrease in the available number of active sites: increase in crosslinking degree leads to accessibility problem to the active sites15, 19. Previous work, in our laboratory, showed a dramatic decrease in MB uptake after chemical treatment of Chaetophora Elegans alga with citric acid31 . The uptake decreased with the increase in citric acid concentration used. Similar results are obtained after treatment of the brown macroalga, S. marginatum with several organic compounds such as formic acid, methanol, and formaldehyde30. The authors explained the decrease as a result of blocking carboxyl, hydroxyl and amine groups. To understand better the cross-linking effect observed with citric acid (with 3 -COOH) on the uptake of methylene blue (MB), a chemical modification with similar car boxylic acids such as acetic acid (CH3-COOH), formic acid (H-COOH) and oxalic acid (HCOO-COOH) is undertaken. Materials and Methods Dye Solution Preparation. *Author for correspondence E-mail: [email protected] Methylene blue was purchased from Sigma (C.I. 52015, 82 %). Stock aqueous solution of the dye MIKATI & JAMAL: BIOSORPTION OF METHYLENE BLUE ON C E ALGAE (500 mg L-1) was prepared, without further purification, and then eight working solutions were prepared by dilution in order to draw the adsorption isotherm. Surface Modification The chemical modification was carried out with different carboxylic acids, different acid concentrations, and temperature of the chemical reaction. The acids used for this purpose were acetic, formic and oxalic acid. The concentrations of the acid were 0.1, 0.5 and 1 M. The chemical reaction between the acid and the raw algae (RG) in the water bath shaker was 25, 40, 50 and 60 oC. Chaetophora elegans algae (collected in June 2010, and prepared as described in a previous work32 was mixed with acid solution at a ratio of 5.0 g biomass to 50 mL of a selected acid concentration and stirred for 4 h at a selected water bath temperature. The acid/biomass was then heated at 110 oC for 4 h, afterward; the dried powder was washed and filtered several times with distilled water (~ 500 ml) until the pH and color of drain water became neutral and clear respectively. The washed biomass was finally dried in an oven at 110 oC for 4 h. Three samples of raw algae were treated in the same manner at 40, 50 and 60 oC by replacing the acid solution with distilled water in order to use them as references. The biomass weight loss was determined after each treatment. For simplicity the samples treated with oxalic acid are called aOX b, where a represents the concentration of the acid used and b the temperature of the water bath. The abbreviation aFO b and aAC b are used for the samples treated with formic and acetic acid. Batch Mode Adsorption Studies Batch adsorption experiments were conducted to evaluate the MB adsorption capacities of the raw and modified algae. The different parameters affecting the adsorption such as pH, mass of algae, equilibrium time, are already determined in a previous work33. 0.1 g of modified biomass was added to 100 ml plastic erlnmeyer, containing 50 mL of MB solutions of different concentration and agitated in the water bath shaker at 200 rpm at 25±1 oC for 3h 30 min, which was sufficient to attain equilibrium. Several initial MB concentrations (Co: 62.5, 125, 150, 250, 300, 350, 400, 450 and 500 mg L-1) were used in order to draw the adsorption isotherm and deduce qmax. After equilibrium being attained, the samples were centrifuged and the remaining concentrations (Ce) in the supernatant solutions were analyzed at 666 nm, lmax of MB, using a double beam UV – Visible 429 spectrophotometer (Specord 200, Analytical Jena). Isotherm experiments were carried out in duplicate. For the kinetic study, several samples were prepared in the same conditions (0.1 g of biomass, 50 mL of MB of fixed concentration). Then 2 ml was withdrawn at a selected time in order to determine the adsorption rate constant and the order of adsorption. Characterization of the Modified Algae The raw and the modified algae were characterized by FTIR (spectrophotometer Thermo, Nicolet IR 200, dilution with KBr) to know the functional groups that might intervene in the adsorption process. XR diffraction is carried out with D8 Focus Bruker (Cu K a 1.54 Ao at 50 KV) to observe any change in the modified biomass with respect to raw algae. Results and Discussion FTIR and XR Diffraction Analysis The IR spectrum of raw algae (RG) displays a number of absorption peaks: at 3350 cm-1 (-OH or – NH2), 2915 cm-1 (-CH or COOH), 1620 cm-1 (>C=O) and 1060 cm-1 (C-O or >S=O) (Fig.1a) 31, 33. Effervescence is observed immediately after addition of acid to raw algae, but it is stronger with formic acid. Chemical reaction occurred between the acid and the carbonate already presents in the protective wall of algae, leading to the formation of CO2 and a dramatic decrease in algae weight. The weight loss is more affected by the acid concentration used and by its nature rather than by the temperature of the chemical treatment: ~ 20 %, ~ 40% and ~ 60 % with 0.1 M, 0.5 M and 1 M of acid (formic or acetic) respectively. A decrease in the amount of biomass was found by Lodeiro et al., after treatment by HCl/ HCOH34. The authors explained the decrease by the replacement of Ca2+, and Mg2+ bound to active sites by H+. The IR spectrum of modified algae with acetic acid is similar to that of raw algae with few differences decrease in the strong peak at 1430 cm-1 and in the peak at 866 cm-1 . These two peaks are characteristic bands of carbonate. The decrease in the peak’s intensities and in the weight of algae after chemical treatment is proportional to acid concentration used. So the chemical modification with acetic acid decreases the amount of carbonate in the raw biomass and let the algae more pure. Thermal analysis (TG-DSC) on Carolina algae showed a sharp decrease at 786 o C (endothermic) attributed to the conversion of CaCO3 to CaO (s) and CO 2(g)26 . 430 J SCI IND RES VOL 72 JULY 2013 12 0 120 T % 10 0 100 80 80 1AC 60 1 FO 40 I% RG 60 60 0 .1 F O 60 RG 0 .5 F O 60 40 40 20 0 4 00 20 0 900 140 0 1 90 0 24 00 2 900 -1 W avenu m be r (cm ) 3 40 0 39 00 10 15 20 25 2 q? 30 35 40 Fig. 1(a)—IR spectra of raw algae and of modified algae with formic acid treated at 60 oC. Fig. 1(b)—XR diffraction spectra of raw algae (RG) and of modified algae with acetic and formic acid. After treatment with formic acid, the broad band at 3350 cm-1 is divided into several bands and the intensity of the band at 1400 cm-1 is function of the formic acid concentration used Fig. 1(a).The crystalline state of raw algae is good as shown by its XR diffraction spectrum. The XR diffraction spectra of algae before and after treatment with acetic and formic acid are different with respect to the peaks’ intensities Fig. 1(b). The three peaks at 2 q :14.64, 17.1, and 22.92 became more intense, and the intense peak in RG at 29.54 remained the intense one after treatment (100 %). The IR spectrum and the XR diffraction spectrum of algae after treatment with acetic acid are similar to those obtained with HCl31. The IR spectrum of algae after treatment with oxalic acid is different from that of raw algae: the broad band of OH at 3365 cm-1 is divided into several bands (OH of COOH and OH of alcohol). The intensity of the band at 2914 cm-1 which corresponds to COOH increases dramatically. New bands appeared at 1615 and 1336 cm-1, which can be assigned to C=O stretching vibration of COOH and COO- indicating the introduction of a new COOH sites15. Other bands appeared also for wavenumber < 900 cm-1. The same behavior is observed with the other treated samples (0.1 M and 0.5 M), but it is more pronounced with 1 M of oxalic acid. The IR spectrum of algae after treatment with oxalic acid is similar to that obtained with citric acid31. The XR diffraction spectra of algae before and after treatment with oxalic acid are very different. For example, the sample 1OX 25 showed the appearance of new intense peaks (2 q : 14.9, 15.22, 24.38 and 30.1) and the disappearance of that at 29.52 (100 % in the raw algae). We thought that an important chemical reaction occurred between the raw algae and oxalic acid. Isotherm Modeling Analysis Several isotherm models are used to find the relationship between qe and Ce .The experimental data related to the adsorption of MB molecules onto the algal biomass at 25 o C were fitted using Langmuir 35,33 , Freundlic36,33 , Temkin37,33 , and combined LangmuirFreundlich equations38,33. In this study, the theoretically predicted isotherm data were determined using a nonlinear regression analysis via the Origin 7 software. Raw Algae The experimental isotherm adsorption data of raw algae fitted better Langmiur-Freundlich isotherm than the other models listed above. The untreated raw algae and the treated with distilled water at 40, 50 and 62 oC showed an average of qmax equal to 143 ± 5 mg g-1. The raw biomass (organic compounds) looses its adsorption property with storage time. In a previous work, the maximum uptake of MB onto fresh collected algae was much higher (300 mg g-1)33. The decrease in qmax is related to deterioration of the external surface. According to the IR spectrum of raw algae and the effect of initial pH on the adsorption of crystal violet32 and methylene blue33, it is seemed that the functional groups –COOH are responsible of this adsorption. Modified Algae with Formic and Acetic Acids The formic and acetic modified algae showed an increase in the qmax. The increase in the maximum uptake is more related to acid concentration than to the reaction temperature (Fig. 2a and 2b). The maximum uptake passed from 143 mg g-1 (for RG) to 297 and 254 mg g-1 for 1FO 25 and 1AC 25 respectively. In general the algae treated with formic acid have qmax higher than those 431 MIKATI & JAMAL: BIOSORPTION OF METHYLENE BLUE ON C E ALGAE 0.1M F O 350 0.5M F O 1M FO 300 300 0.1M AC 0.5 M AC 1 M AC 250 200 -1 q (mg g ) -1 q (mg g ) 250 200 150 150 100 100 50 50 0 0.1M F O 0.5M F O 1M F O 25 oC 40 oC 60 oC 159 223 297 152 220 310 149 219 300 0 0.1M AC 0.5 M AC 1 M AC 25 oC 40 oC 60 oC 161 193 254 170 185 250 174 180 240 T ( o C) o T ( C) Fig. 2(a)—Effect of formic acid concentration and temperature, used in the chemical modification of algae on the maximum uptake according to non linear Langmuir- Freundlich model. (0.1g of algae, T: 24 oC, pH: 6) Fig. 2(b)—Effect of acetic acid concentration and temperature, used in the chemical modification of algae on the maximum uptake according to non linear Langmuir- Freundlich model. (0.1 g of algae, T: 24 oC, pH: 6) 300 250 was the case with Sargassum muticum biomass treated with acetone (elimination of lipid)21. 1AC 60 1 FO 60 Modified Algae with Oxalic Acid q raw -1 q (mg g ) 200 1OX 60 150 100 50 0 0 20 40 60 Ce (mg L-1) 80 100 Fig. 3—Isotherm adsorption of several modified algae (0.1 g of algae, T: 24 oC, pH: 6). obtained with acetic acid. The difference in the uptake between the raw algae and the treated algae is manifested for high initial MB concentration ([MB]o > 150 mg L-1 ). The remained concentration of MB in contact with 500 mg L-1 of MB is 10.8 mg L-1 for 1FO 25 and 19.4 for 1AC 25 against 144.4 mg L-1 for the raw algae (RG). The increase in the uptake of RG after treatment with formic acid is similar to that treated with HCl (320 mg g-1)31. Qmax increases with the increase in acid strength (Acetic acid < Formic acid < HCl), in other way it is related to the ability of the acid the remove carbonate from the raw algae. The increase in the uptake, is not always related to the cross-linking between the algae and the chemical reagent, but sometimes it is related to a change in the chemical composition of the algae as Concerning, the isotherm adsorption of modified algae with oxalic acid, Langmiur - Freundlich model remained the best model. All the samples showed a decrease in the uptake (Fig. 3). The lowest qmax (20 mg g-1) is obtained with 1 M of oxalic acid (1OX 60). The concentration of oxalic acid is the important factor which governs the decrease in the uptake. The decrease in qmax may be due to increase in the cross-linking degree which would hamper the adsorption of MB15 . Similar results are obtained with citric acid31. It seems that in our case the chemical modification with high concentration of carboxylic acid having more than 1 -COOH such as oxalic acid and citric acid leads to increase in the crosslinking degree, preventing the MB adsorption. As the cross-linking degree decreased with the decrease in acid concentration, the modified algae with 0.1 M citric or oxalic acid have approximately the same qmax as RG. The increase in the uptake with acid such as HCl31, acetic acid and formic acid is explained in majority by the elimination of a high percent of carbonate already present in the protective cell walls of algae (proved by effervescence effect). In the case of oxalic acid, in addition to the elimination of a part of carbonate, there is also cross-linking effect causing steric hindrance and make against the adsorption of basic dyes. 432 J SCI IND RES VOL 72 JULY 2013 Table 1—Pseudo first and pseudo second order adsorption kinetic parameters at 24 oC and error estimation deduced at different initial dye concentrations for 1AC 25 and raw algae (values between ()) [MB] o (mg L-1) 62.5 100 150 qe calc. (mg g-1) 29.9 (28.5) 48.15 (47.0) 72.1 (72.3) Pseudo-first order (Non linear) K1 R2 -1 (min ) 2.5 0.995 (1.52) (0.98) 2.47 0.994 (1.4) (0.983) 2.03 0.994 (0.79) (0.993) χ2 qe (mg g-1) 30.5 (29.7) 49.0 (48.0) 73.80 (73.80) 0.46 (1.79) 1.56 (3.93) 3.78 (3) Pseudo-second order (Non linear) K2 R2 -1 -1 (g mg .min ) 0.293 1 (0.111) 0.998 0.174 0.999 (0.077) (0.995) 0.078 1 (0.024) (0.999) χ2 0.06 (0.2) 0.30 (1.11) 0.19 (0.31) Table 2—The activation kinetic parameters for modified algae with 1M acetic acid (1AC 25) and raw algae (values between ()) [MB]o(mg L-1) 62.5 100 Ea (kJ.mol-1) 23.9 (48.6) 6.7 (48) DH# (kJ.mol-1) 21.36 (46) 4.2 (46.1) Kinetic Study The modified algae with acetic acid were selected for the kinetic study. Non-linear regression method has been used to predict the best sorption kinetic model (Lagergren first order and pseudo-second order) and also to obtain reliable kinetic parameters33, 39, 40. For initial MB concentrations (60 mg L-1 - 150 mg L-1), the uptake of modified algae with acetic acid and the raw algae as a function of time is quite similar Table 1. The adsorption rate of both kinds of algae is very fast in the first five minutes, then decreases to become negligible after 30 min. The dynamic sorption behavior of MB onto Chaetophora elagans’ surface under several initial dye concentrations was monitored and modeled. The related kinetic parameters and error derivation values are presented in Table 1. The first and the second adsorption models can be used to interpret the results, but according to R2 values, the pseudo-second order model fit better the kinetic data. In this range of initial MB concentrations the maximum uptake increased linearly (R2:1), but the rate constant K 2 decreased linearly with [MB] o (R2: 0.978). Effect of Temperature The activation parameters associated with the adsorption of 62.5 and 100 mg L-1 MB onto 1AC 25 are calculated as follow: plot of ln K2 vs. 1/T gives the value of the activation energy (Ea), according to Arrhenius equation. The DH# and DS# value can be calculated from Eyring equation31.The rate constant K2 increased with the increase in temperature for the acetic acid modified DS# (kJ.mol-1.K-1) -0.19 (-0.11) -0.25(-0.12) DG#298 (kJ.mol-1) 78 (78.8) 78.7(81.9) algae and for unmodified algae. The rate constants k2 obtained with 1AC 25 are higher than those obtained with the unmodified algae in the range of temperature studied (25 oC-35 oC). The kinetics parameters are listed in Table 2. The activation energies for modified algae are less than those of raw algae, but the free energies are approximately the same Table 2. Conclusions Chemical modification of Chaetophora Elegans algae with acetic and formic acids showed an increase in the maximum uptake. The increase is proportional to acid concentration used. Modified algae with 1 M of acetic and formic acids gave the best uptake (qmax increased from 143 mg g-1 to 254 and 297 mg g-1 at 24 o C respectively). The modified algae with oxalic acid showed an important decrease in the uptake. The decrease in qmax is inversely proportional to oxalic acid concentration used. Modified algae with 1 M oxalic acid gave the worst uptake (qmax decreased from 143 mg g-1 to 20 mg g-1). Acid concentration used in the chemical modification is the major parameter affecting the maximum uptake. The decrease is related to increase in the cross-linking degree. It seems that the carboxylic acids having more than one –COOH lead to cross-linking effect. The temperature of the chemical modification has a small effect on the uptake (25 oC – 60 oC). Langmuir-Freundlich isotherm model fitted better the isotherm adsorption data for all samples studied. 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