Preparation of hydrogel reinforced with bentonite by gamma irradiation for metal absorption

Nội dung text: Preparation of hydrogel reinforced with bentonite by gamma irradiation for metal absorption

1. Nuclear Science and Technology, Vol.10, No. 4 (2020), pp. 48-55 Preparation of hydrogel reinforced with bentonite by gamma irradiation for metal absorption 1 1 1* 2 Tran To Uyen , Trinh Thi Tu Anh , Tamikazu Kume , Cao Dong Vu , Nguyen Minh Hiep2, Le Xuan Cuong2, Nguyen Ngoc Hoan1 1Dalat University, 01 Phu Dong Thien Vuong, Dalat, Lam Dong, Vietnam 2Dalat Nuclear Research Institute, 01 Nguyen Tu Luc, Dalat, Lam Dong, Vietnam *Corresponding author: tami.kume@gmail.com (Received 26 October 2020, accepted 07 December 2020) Abstract: A natural-based sodium carboxymethyl cellulose (CMC) hydrogel reinforced with bentonite was prepared by using gamma irradiation technology. This is a novel hydrogel that uses natural polymer to absorb metal ions in wastewater. The influence of dose, concentration of CMC and bentonite on the sorption of hydrogels was investigated by atomic absorption spectrometry (AAS) method. According to the Langmuir isotherm model, the maximum adsorption capacities of CMC/bentonite hydrogel for Cu2+ and Pb2+ were 181.82 mg/g and 204.08 mg/g at room temperature, respectively. The pseudo-second-order model which describes the adsorption process of Cu2+ and Pb2+ was also studied. Keywords: carboxymethyl cellulose, bentonite, hydrogel, Cu2+ and Pb2+. I. INTRODUCTION been investigated in several studies. Ozay et al. used p(AMPS)t hydrogel networks to adsorb Currently, the problem of removing magnetic iron particles [6]; Wasikiewicz et al. metals from wastewater solutions is investigated the adsorption efficiency of investigated in many researches [1-4]. One carboxymethyl chitin (CM-chitin) and of the methods used for this purpose is carboxymethylchitosan (CM-chitosan) on using materials of natural or man-made scandium and gold [7]. The adsorption of lead polymers that have been treated like by hydrolysis lignin-g-poly-(acrylic acid) hydrogel materials. hydrogel was studied by Sun et al. [8]. Hydrogel are defined as hydrophilic polymers with three-dimensional structure, Carboxymethyl cellulose is a natural capable of swelling in water and will not polymer with numerous carboxylic and dissolve in water. This ability of swelling hydroxyl groups which is suitable to prepare makes hydrogel an ideal material used in drug heavy metal adsorption materials. Bentonite is transportation, tissue technology, a natural clay mineral with a layer structure of agriculture, [5]. In addition, hydrogels are 2:1 consisting of 2 tetrahedra layers and an also capable of responding to many physical octahedral layer in the middle so it has a stimuli such as temperature, pressure, and porous structure and has a large specific chemical stimulation. It was used for surface that can absorb large amounts of adsorption, enrichment, separation and substances [9]. There are some studies using recovery of metal ions, recovery of dyes and polymer/clay hydrogel such as chitosan- removal of harmful components in wastewater. PVA/bentonite (10%) nanocomposites [10], Adsorption of heavy metals using hydrogel has CMC-g-poly(NIPAm-co-AA)/MMT [11] to â2020 Vietnam Atomic Energy Society and Vietnam Atomic Energy Institute
2. TRAN TO TUYEN et al. adsorb metals in wastewater. However, by the bentonite in distilled water and further stirred authors understanding, until now, there is no at room temperature for an hour for dispersion. research on preparation of CMC/bentonite The mixture was sealed in polyethylene bags hydrogel for adsorption purposes. The aim of for air-free irradiation. According to the ratios this work is to prepare a new adsorption of CMC/bentonite, the prepared hydrogels material which is simple and eco-friendly for were named as CMCB/0 (20:0, removing heavy metals from wastewater. The CMC:bentonite), CMCB/1 (20:1, efficiency of the CMC/bentonite hydrogel for CMC:bentonite),CMCB/3 (20:3, the removal of Cu2+ and Pb2+ from aqueous CMC:bentonite), CMCB/5 (20:5, solution was investigated. CMC:bentonite), correspondingly. Gamma irradiation was carried out by a II. CONTENT 60Co gamma source irradiation dose of 20 kGy at A. Material and methods room temperature at the Radiation Technology Center, Dalat Nuclear Research Institute. 1. Materials 3. Absorption studies Sodium Carboxymethyl cellulose (CMC) 1380, degree of substitution of 1.34 The adsorption experiments were carried was purchased from Daicel Co., Ltd., Japan. out using solutions of CuSO4, Pb(NO3)2 with Bentonite clay was provided by Hiep Phu JSC, concentrations of metal ions from 50 ppm to Lam Dong, Viet Nam. CuSO4.5H20 and 400 ppm. The dried hydrogel samples (0.2 g) Pb(NO3)2 were purchased from National were soaked in 100 ml of aqueous metal ions Pharmaceutical Group Chemical Reagent Co., for 8 hours at room temperature. Ltd., China. After the adsorption, the remaining Metal ion standard solutions were solutions were filtered out and diluted to provided from Merck, Germany. proportions as shown in Table I. The dilution factor depends on the measuring 2. Sample preparation and irradiation limit of the instrument. The metal ions Solutions of 5% (w/w) of CMC and 0, 1, concentration in solution was measured by 3, 5% (w/w) of bentonite were prepared by atomic absorption spectrometer model AA- dissolving 20 g CMC and 0, 0.2, 0.6, 1.0 (g) 6800, Shimazu, Japan. Table I. Concentration and the dilution of metal ions solution Concentration 50 100 200 300 400 (ppm) Dilution factor 10 25 50 100 100 (times) The efficiency of hydrogel was Whereas, Co and Ci are the calculated according to Eq. (1) [12]: concentrations of metal ions in mg/L before Removal (%) = (1) and after the adsorption, respectively. 49
3. PREPARATION OF HYDROGEL REINFORCED WITH BENTONITE BY GAMMA IRRADIATION The value for qe (mg/g) is the maximum bentonite increases from 1% to 3%, the adsorption capacity at equilibrium was absorption increases with the increasing of gel calculated as [12]: faction. However, when the concentration of bentonite is more than 3%, the adsorption q = (2) e efficiency of metal ions decreases. This is Where V is the solution volume (L) and because bentonite act as a multifunctional m is the mass of the hydrogel (g). crosslinker in which the more of its content in hydrogel, the tighter the carbon network B. Result and discussion between CMC and bentonite [13]. When the 1. Effect of clay content on metal ions sorption bentonite concentration reached 5%, the 2+ As seen in Fig. 1, the sorption of Cu bonding network becomes too tight which 2+ and Pb ions onto CMC/bentonite hydrogel prevents the penetration of metal ions. The increased by the increasing of bentonite metal ions in solutions can not bind to hydrogel concentration in hydrogel. The sorption as well as in CMCB/3 sample. As a result, the efficiency reaches to the maximum value at 3% hydrogel based on CMC/Bentonite with the of bentonite in the hydrogel, 81.26% and ratio of 20% CMC and 3% bentonite 2+ 2+ 68.24% for Cu and Pb , respectively. It can (CMCB/3) was selected for further heavy be explained that when the concentration of metal ions adsorption investigation. Fig. 1. Sorption efficiency of Cu2+ and Pb2+ on four hydrogels CMCB/0, CMCB/1, CMCB/3, CMCB/5 2. Effect of contact time surface are available to interact with metal The effect of adsorption time on metal ions. When the adsorption time increases, the ions adsorption has also been investigated. adsorption rate decreases when the active The effect of contact time on the adsorption sites are exhausted and it finally reaches a of Cu2+ and Pb2+ ions is shown in Fig. 2. The state of dynamic equilibrium. Therefore, the metal ions uptake is found to be rapid for the optimal vibration time was determined to be 2+ 2+ first 240 min. When adsorption begins, all about 240 min for Cu , 360 min for Pb active adsorbent sites on the adsorbent (Fig. 2). 50
4. TRAN TO TUYEN et al. Fig. 2. The sorption of Cu2+ and Pb2+ onto hydrogel at various adsorption time 3. Adsorption kinetics t 1 t = 2 + (4) q k q q The time adsorption of metal ions to t 2 e e CMC/bentonite hydrogel was investigated with Where qt and qe are the amount adsorbed initial concentration of 100 mg/L for each at time t and at equilibrium (mg/g), metal solution. Common mathematical models respectively. The fitting parameters k1 and k2 used to describe adsorption kinetics included in Eq. (3) and (4) represent the pseudo-first- Lagergren's pseudo-first-order kinetic equation, order (1/min) and the pseudo-second-order rate pseudo-second-order kinetic equation. The coefficients (g mg-1min-1), respectively. pseudo-first-order kinetics is described by [14]: The fitting of pseudo-first-order and pseudo-second-order kinetic models to ln(qe – qt) = ln(qe) – k1t (3) experimental data is displayed in Fig. 3 and 4 The pseudo-second-order kinetic model and the fitting parameters (k and qe) of both is given by Eq 4: models are shown in Table II. Fig. 3. Pseudo-first-order kinetic models Fig. 4. Pseudo-second-order kinetic model It can be seen that the coefficients (R2) of suitable than the pseudo-first-order kinetic the pseudo-second order kinetic model are more model. When comparing experimental (Qe,exp) 51
5. PREPARATION OF HYDROGEL REINFORCED WITH BENTONITE BY GAMMA IRRADIATION and theoretical values (Qe,cal) as shown in Table sharing or electron exchange between the I, the pseudo-second order kinetic model is also adsorbent and metal ions in solution. The more appropriate. The pseudo-second order pseudo-second order kinetic model kinetic model suggests that the adsorption demonstrates that the combination of bentonite mechanism governs the adsorption process, and particles gives a structure and a higher number the adsorption rate of metal ions onto the gel can of available adsorption positions on the surface be controlled by chemical process through of the hydrogel for metal ions. Table II. Kinetic parameters of metal sorption onto CMC/bentonite hydrogel Metal Qe,exp Pseudo-first-order kinetic Pseudo-second-order kinetic ions (mg/g) 2 2 R Qe,cal k1 R Qe,cal k2 (mg/g) (min -1) (mg/g) (mg/g min -1) Cu2+ 40.16 0.9885 18.94 0.0099 0.9987 43.48 0.0008 Pb2+ 35.95 0.977 24.94 0.0087 0.9962 40.65 0.0004 4. Sorption isotherm The linearized form of this model represented by Equation 5: We used Langmuir isotherm models to analyze the sorption data. Langmuir isotherm (5) is usually used to describe monolayer adsorption where all reactive sites on the Where: sorbent’s surface are energetically homogenous where there is no lateral interaction and steric + KL is Langmuir equilibrium constant (l/mg). hindrance between the adsorbed molecules. + qmax (mg/g) is maximum sorption capacity. Fig. 5. Adsorption isotherm of metal ions by CMC/bentonite hydrogel 52
6. TRAN TO TUYEN et al. Table III. Isotherm parameters of metal sorption onto CMC/bentonite hydrogel metals Langmuir 2 R KL Qmax Cu 0.9797 0.013 181.82 Pb 0.9521 0.007 204.08 Fig. 5 shows the Langmuir isotherm found to be from 70 to 170 mg/g for Cu [11, obtained by plotting Ce and Ce/qe, and the 15] or 76.70 - 84.9 for lead [11, 16]. Compared 2 values of KL, Qmax, and R are listed in Table to their data, it can be seen that crosslinked 3. Based on these coefficients obtained, it can CMC/bentonite hydrogel can be efficiently be concluded that the Langmuir equation (R2 > used as adsorbent for the removal of Pb2+ and 0.90) gives a good fit to the experimental data Cu2+ ions. of lead and copper ions. From the slope and Table IV lists the qmax values of some intercept of Langmuir isotherm, the values of 2+ 2+ 2+ materials for removal Pb and Cu . The qmax qmax were calculated to be 181.82mg/g for Cu value of the CMC/bentonite hydrogel was and 204.08 mg/g for lead adsorption. Some higher than that of most absorbents. carboxymethylated CMC-based adsorbents are Table IV. Comparison of maximum adsorption capacity of some materials Materials Cu2+ Pb2+ Reference Kind of materials CTS-PVA/BT (10%) 24.97 18.00 [10] Polymer/clay Nanocomposites CMC-g-poly (NIPAm-co-AA)/MMT 70.5 84.9 [11] Polymer/clay CMC/Chitosan hydrogel 169.5 [15] Polymer/polymer Graphene oxide/carboxymethyl monoliths 82.93 76.70 [16] Polymer/graphite Chitosan/cellulose 26.50 26.31 [17] Polymer/cellulose Chitosan/PVC 87.9 [18] Polymer/polymer Thiosemicarbazide modified green CMC 144.92 [19] Modify Polymer CMC/bentonite hydrogel 181.82 204.08 This work Polymer/clay III. CONCLUSIONS hydrogel with the ratio of 20:3 (CMCB/3) is the most suitable for the Pb2+ and Cu2+ A natural-based sodium carboxymethyl adsorption, which are 181.82 and 204.08 mg/g cellulose (CMC) hydrogel reinforced with for Cu2+ and Pb2+ at room temperature, bentonite was successfully prepared by respectively. The prepared CMC/bentonite irradiation of a mixture of CMC and bentonite hydrogel can be efficiently used as an clay. The prepared hydrogel showed a good adsorbent for the removal of Pb2+ and Cu2+ adsorption ability for heavy metal ions. The ions and has a potential application for removal obtained result showed that CMC/bentonite of heavy metal ions from wastewater. 53
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