Removal of Cd(II) from aqueous solutions by crumpled graphite oxide - Ha Xuan Son

Vietnam Journal of Science and Technology 55 (4C) (2017) 8-13 REMOVAL OF Cd(II) FROM AQUEOUS SOLUTIONS BY CRUMPLED GRAPHITE OXIDE Ha Xuan Son 1 , Hac Van Vinh 1 , Nguyen Thanh Hai 1 , Dang Thi Hong Phuong 2 , Nguyen Thi Kim Ngan 3 , Pham Van Hao 4 , Dang Nhat Minh 5 , Dang Van Thanh 1,* , Phan Ngoc Hong 5,6,* , Phan Ngoc Minh 6 1 TNU - University of Medicine and Pharmacy, 284 Luong Ngoc Quyen, Thai Nguyen, Viet Nam 2 TNU - University of Agriculture and Forestry, Quyet Thang ward, Thai Nguyen, Viet Nam 3 TNU - University of Science, Thai Nguyen University, Tan Thinh, Thai Nguyen, Viet Nam 4 TNU - University of Information and Communication Technology, Tan Thinh ward, Thai Nguyen City, Viet Nam 5 Institute of Materials Science, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Viet Nam 6 Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Viet Nam * Email: hongpn@ims.vast.ac.vn, thanhdv@tnmc.edu.vn Received: 8 August 2017; Accepted for publication: 15 October 2017 ABSTRACT In this study, crumpled graphite oxides (CGOs) were fabricated from graphite electrode of exhausted dry batteries (RG) by cathodic plasma electrolysis method (CPE) and applied for removing Cd(II) from aqueous solutions. The effects of pH, contact time, and initial concentrations on the removal of Cd(II) ions were studied. A removal efficiency of ∼98 % was obtained after 120 min, via the dispersion of 15 mg of CGO in Cd(II) solutions (40 mL, 1 ppm) at pH 6. The maximum adsorption capacity (qmax) was calculated to be 40.82 mg/g. Results showed that CGO is an effective adsorbent for the removal of Cd(II) from aqueous environment and acts as a promising adsorbent for the removal of other heavy metals from the polluted water. Keywords: adsorption; cadmium, graphite oxides, plasma electrolysis. 1. INTRODUCTION Cadmium is a highly toxic heavy metal, which is usually found in sewage sludge, industrial wastes from metallization, and production of batteries, pesticides, paints, colored powders and plastics [1]. It is bio-accumulated in living body, which disrupts the activity of internal organs such as liver, kidneys, and lungs. It also causes bone degeneration, cancer, hypertension, and acute respiratory distress syndrome, and kidney diseases. Thus, it is necessary for removing Cd(II) in industrial wastes before releasing to environment [2]. Recently, the adsorption of Cd(II) using few layered graphene oxide nanosheets (FGOs) or functionalized graphene has Removal of Cd(II) from aqueous solutions by crumpled graphite oxide 9 been shown to be a simple and efficient method for the removal of Cd(II) from aqueoussolutions [3, 4]. However, the preparation of these materials is time consumption and uses some hazardous chemicals (e.g., H2SO4, HNO3, and KMnO4) which are environmentally harmful. In addition, RG is considered as industrial wastes and need to be treated or modified before discharging. Therefore, it is desirable to find a sorbent material with high adsorption capacity, low cost, and suitable to Vietnam's conditions. In the present work, we recycled the graphite electrode of exhausted dry batteries for producing of crumpled graphite oxide (CGO) and employ it for removing of cadmium (Cd(II)) from aqueous solution. 2. EXPERIMENTAL METHODS 2.1. Reagents and materials Graphite rods were collected from exhausted dry battery. KOH, (NH4)2SO4, and stock Cd(II) solutions (1000 mg/L) were purchased from Sigma-Aldrich. All the reagents are of analytical grade. 2.2. Synthesis of GO In previous work, we report on producing of crumpled graphite oxides by cathodic plasma electrolysis along with the characterization of their morphology and crystal structure [5]. The as- synthesized CGOs were dried at 100 o C in vacuum oven for 24 hours and stored in a drying box at 50 o C. 2.3. Characterization of adsorbents The structures of the CGOs powders were examined by a D2 X-ray diffractometer equipped with a Cu Ka tube and a Ni filter (ʎ = 0.1542 nm). High resolution transmission electron microscopy (HRTEM) images were recorded using a JEOL 2100F apparatus operated at 200 kV. Scanning electron microscopy (SEM) was done using a JEOL JSM-6500F scanning electron microscope working at 15 kV. 2.4. Adsorption experiments The Cd(II) removal tests were conducted in batch adsorption experiments at room temperature. Cd(II) solutions were prepared from stock solution (1000 ppm, Sigma Aldrich Dilutions). Investigated influence factors included contact time (0 to 300 min), initial Cd(II) concentration (0.25, 0.5, 2, 4, 5, 10 and 20 mg/L), and initial pH of solution (from 2.0 to 12.0). Equilibrium isotherms were determined with different initial concentrations of Cd(II) (0.25, 0.5, 2, 4, 5, 10 and 20 mg/L) at room temperature, pH 6, adsorbent dosage 15 mg and 40 mL of solution. To evaluate the removal efficiency of Cd(II) in real conditions, the real water samples were collected from Suoi Cat Spring, Dai Tu District, Thai Nguyen Province, Vietnam (metallic and mining industries). These samples were filtered, acidified with HNO3 (0.5 % v/v) and stored in polyethylene bottles. The Cd(II) concentration and pH value of the samples was measured at 0.128 mg/L and 6.5, respectively. During the Cd(II) removal experiment, the suspension was magnetically stirred at 300 rpm to for well dispersion of CGO (15 mg) in Cd(II) contaminated Hà Xuan Son, et al 10 solution (40 ml, pH 6.5, 25 o C). The concentration of Cd(II) was determined by inductively coupled plasma optical emission spectrometry (ICP-OES, OPTIMA DV7300). The adsorption capacity and removal efficiency were calculated using following equations: q = (1) H % = x 100% (2) ưhere: V: the volume of the solution (L); M: the adsorbent amount (g); C0: the initial concentration (mg/L); Ce: the equilibrium concentration (mg/L); q: the adsorption capacity at equilibrium time (mg/g); H: the removal efficiency of Cd(II). pHpzc for the CGO was determined according to the method published in the literature [6]. In this study, the equilibrium data were calculated using the Freundlich and Langmuir isotherm expressions given by the equations, respectively, Freundlich: qe=Kf. (3) Langmuir: qe= (4) where Kf and n are Freundlich constants related to sorption capacity and sorption intensity of adsorbents. The value of n falling in the range of 1–10 indicates favorable sorption. qe is the adsorption capacity at equilibrium condition and Ce is the equilibrium concentration of Cd(II) in solution. q0 is the monolayer adsorption capacity and b is the Langmuir constant related to the free energy of adsorption. 3. RESULT AND DISCUSSION 3.1. Characterization of CGO Figure 1. (a) XRD of GR and CGO, SEM image of (b) RG; (c) CGO; and (d) TEM image of CGO; inset in (d) is the XRD of CGO. Figure 1b and 1c display the SEM images of RG and CGO, indicating their significant difference in morphology. RG contained thickened and dispersed flakes and ordered layer structure while CGO was crumpled ball-like structure particles, which may be preferable for the adsorption process. This morphology can be further observed via TEM image (Fig 1d), where the CGO comprised of many ridges with dimensions of 0.5–2 µm, consistent with the FESEM observations. Notably, XRD patterns of CGO (inset in TEM image), reveal a broad-diffraction peak at a value of 2 of 9.8°, corresponding to the (001) diffraction peak of graphite oxide [7, 8], Removal of Cd(II) from aqueous solutions by crumpled graphite oxide 11 as a result of the structure expansion as oxygen-containing groups incorporate between the carbon sheets during the condition of strong oxidation [5, 9]. 3.2. Cd(II) adsorption Figure 2a presents isoelectric point (pHpzc) of the CGO, revealing pHpzc = 7.02. It is observed that the adsorption process was significantly affected by its pHpzc (pzc: point of zero charge). When solution pH is higher than pHpzc (pH > pHpzc), the GO surface is negatively charged because of the deprotonation of carboxyl and hydroxyl groups. Therefore, the electrostatic interaction with metal ions (positively charged) was favorable, result in an improvement in adsorption capacity, and vice versa. As can be seen from Fig. 2b, Cd(II) adsorption was favored under basic conditions (i.e. pH 10) with a maximum uptake of 98.5 % at pH 12. In weak acidic environment (pH ≥ 5), free electron pairs form more complexes with Cd(II) ion, which lead to higher ability of adsorbing Cd(II). On the other, in strong acidic environment, CGO transforms into non-electron-pairs form, which was unable to form complex with metal and resulted in a reduction in adsorption ability. Notably, at pH = 6, about 98 % Cd(II) was adsorbed on CGO. Thus, we chose optimum solution pH 6 for further experiments. Figure 2c shows the effect of contact time on the removal efficiency of Cd(II) on CGO. The removal efficiency of CGO for Cd(II) rapidly increased at the first 100 min, and was then relative stable after 120 min when it its equilibrium was reached. Therefore, optimum contact time for all further experiments was set at 120 min. Figure 2. (a) The isoelectric point (pHpzc) of the CGO, (b) The effect of pH on removal efficiency of Cd(II) on CGO, (c) The effect of contact time on removal efficiency of Cd(II) on CGO, (d) The removal efficiency of Cd(II) with different initial metal concentration. Hà Xuan Son, et al 12 Figure 2d presents the influence of initial metal concentration on the removal efficiency of Cd(II) on the CGO. When the initial concentration of Cd(II) increased, the removal efficiency decreased. Figure 3. (a) The dependence of Ccb/q (g/l) on Ccb (mg/l) of Cd(II) and (b) the dependence of logq on logCcb of Cd(II). Figure 3 displays Cd(II) adsorption isotherms on CGO and two adsorption models, Langmuir (Eq. 4) and Freundlich (Eq. 3) isotherms, for experimental curve fitting. Clearly, Langmuir model was fitted better than Freundlich model for expressing the adsorption of Cd(II), demonstrated by the higher regression coefficient. Additionally, the qmax of Cd(II) was predicted as qmax=40.82 and Langmuir constant is b = 3.88, which compares favorably with previous results [4, 9]. Table 1. Characteristics of the wastewater sample from Suoi Cat spring. Water sample Concentration Cd(II) (mg/L) Real water sample 0.128 Treated sample 0.003 Table 1 represents effective removal of Cd(II) of water samples from Suoi Cat spring using CGO adsorbent. Due to recent industrial pollution by Nui Phao Company (Dai Tu District, Thai Nguyen Province, Vietnam), this spring was seriously contaminated by metal ions, such as Cd(II). The results showed that the Cd(II) effectively removed from 0.128 mg/L to 0.003 mg/L with efficiency of 97.6 % after 120 min at near neutral pH environment (pH 6.5). The effluent quality in terms of Cd(II) concentration met well Vietnam National Technical Regulation on Surface Water Quality (Collumn A1, QCVN 08-MT:2015/BTNMT). 4. CONCLUSION Crumpled graphite oxides were effectively utilized as an effective low-cost adsorbent for the removal of Cd(II) via adsorption from aqueous solution. The SEM pictures show that the CGO possesses a crumpled morphology. The adsorption of Cd(II) followed the Langmuir adsorption model with the maximum adsorption capacity of 40.82 mg/g. Removal of Cd(II) from aqueous solutions by crumpled graphite oxide 13 Acknowledgments. This research is funded by grant number B2017-TNA-47. We would also thank Dr Nguyen Van Chien at Department of Material Science and Engineering, National Chiao Tung University, Taiwan for helps with SEM measurements. REFERENCES 1. Yu Xi, Luo Yiting, Luo Jinming, and Luo Xubiao, Removal of cadmium (II) from wastewater using novel cadmium ion-imprinted polymers, Journal of Chemical & Engineering Data 60 (11) (2005) 3253-3261. 2. Monika Jain, Garg V. K., and Kadirvelu K. - Cadmium (II) sorption and desorption in a fixed bed column using sunflower waste carbon calcium–alginate beads, Bioresource technology 129 (2013) 242-248. 3. Guixia Zhao, Li Jiaxing, Ren Xuemei, Chen Changlun, and Wang Xiangke - Few-layered graphene oxide nanosheets as superior sorbents for heavy metal ion pollution management, Environmental science & technology 45 (24) (2011) 10454-10462. 4. Xiaojiao Deng, Lü Lili, Li Hongwei, and Luo Fang - The adsorption properties of Pb (II) and Cd (II) on functionalized graphene prepared by electrolysis method, Journal of hazardous materials 183 (1) (2010) 923-930. 5. Thanh D., Chen H. C., Li L. J., Chu C. W., and Wei K. H. - Plasma electrolysis allows the facile and efficient production of graphite oxide from recycled graphite, RSC ADVANCES 3 (38) (2013) 17402-17410. 6. PCC Faria, Orfao J. J. M., and Pereira M. F. R. - Adsorption of anionic and cationic dyes on activated carbons with different surface chemistries, Water Research 38 (8) (2004) 2043-2052. 7. Alexandra Buchsteiner, Lerf Anton, and Pieper Jörg - Water dynamics in graphite oxide investigated with neutron scattering, The Journal of Physical Chemistry B 110 (45) (2006) 22328-22338. 8. Hui Wang and Hu Yun Hang - Effect of oxygen content on structures of graphite oxides, Industrial & Engineering Chemistry Research 50 (10) (2011) 6132-6137. 9. James Guo Sheng Moo, Khezri Bahareh, Webster Richard D., and Pumera Martin - Graphene Oxides Prepared by Hummers’, Hofmann’s, and Staudenmaier’s Methods: Dramatic Influences on Heavy‐Metal‐Ion Adsorption, Chem. Phys. Chem. 15 (14) (2014) 2922-2929.