Synthesis of reduced graphene oxide - Cu₀.₅Ni₀.₅Fe₂O₄ - Prussian blue nanocomposite materials for cesium adsorption from aqueous solution

Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 5 SYNTHESIS OF REDUCED GRAPHENE OXIDE - Cu0.5Ni0.5Fe2O4 - PRUSSIAN BLUE NANOCOMPOSITE MATERIALS FOR CESIUM ADSORPTION FROM AQUEOUS SOLUTION Tran Quang Dat, Nguyen Tran Ha, Nguyen Vu Tung, Pham Van Thin* Le Quy Don Technical University Abtract Adsorbents composed of reduced graphene oxide, Cu0.5Ni0.5Fe2O4 ferrite and prussian blue (RGO-CNF-PB nanocomposites) were fabricated for the adsorption of cesium and rapid magnetic separation of absorbent from contaminated water. The morphology, structure and magnetic properties of samples were characterized by SEM, XRD, FTIR, VSM. The effect of pH, contact time and adsorption isotherms were conducted in batch experiments. It was found that reduced graphene oxide was exfoliated and decorated homogeneously with ferrite nanoparticles. Cu0.5Ni0.5Fe2O4 has the average particle diameter of about 15 nm and prussian blue has been covered smoothly onto RGO-CNF surfaces. The remanences (Mr) and coercive forces (Hc) are near to zero, indicating that obtained material is superparamagnetic. The adsorption of cesium could be suitably described by the pseudo- second-order and the Langmuir models. The highest adsorption capacity of the composites for cesium was evaluated to be 125 mg/g at pH = 7 and 25°C. Keywords: Adsorption; ferrite; prussian blue; reduced graphene oxide; cesium. 1. Introduction Nuclear power is viewed as a reasonable option to meet future energy demands and reduce the consistently developing worries of global warming. At present, nuclear power represents around 10% of the world’s energy, in spite of the fact that this rate is foreseen to increment [1]. Notwithstanding, nuclear energy can also present environmental concerns with inheritance waste and unintentional release of radionuclides through incident, such as that was happening in Chernobyl (1986) and Fukushima (2011), undermining environments and human lives [2]. Among the radionuclides, radioactive cesium (137Cs) is a strong gamma emitter, which has been distinguished as a tricky radionuclide because of its long half-life (30.1 years), and dangerous radiological hazard to nature and human. Additionally, cesium is a group I alkali metal and is extremely dissolvable in water, so making it hard to be removed from waste water [3]. Accordingly, it is imperative to create a suitable and efficient technique to * Email: thinpv.hvkt@gmail.com Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 6 separate cesium from an aqueous solution. Along with other methods to remove cesium from aqueous solutions, adsorption has pulled in the most interest in light of its cost- practicality, adaptability, and straightforwardness of activity to isolate cesium [4]. Prussian blue (PB) has been tried effectively as a sustenance supplement given to cattle to diminish radiocesium contamination in animal products. It works by binding to accessible radiocesium in a creature’s gastrointestinal tract and expands Cs discharge through feces. In 2003, the insoluble type of PB has been endorsed for treatment of radioactive Cs harming in people by the U.S. Food and Drug Administration (FDA), making it liable to be alright for utilizations in the both people and the nature [5]. In our previous reports, reduced graphene oxide - ferrite - polyaniline composites have been prepared for the feasibility of adsorption of uranium [6, 7, 8]. Graphene is an abundant carbon-based material that is chemically and mechanically consistent and has large operative surface area. Furthermore, it has some functional groups (epoxide, phenol, hydroxyl and carboxyl groups) on the surface of GO and expansive π-stacking that gives suitable interaction through hydrogen bonding, π-π, and electrostatic interactions. Magnetic composites are easy to isolate from aqueous solution after the adsorption process, which may reduce the cost of industrial application. In this study, we report the uncomplicated synthesis method of ternary nanocomposite made out of RGO-CNF-PB. The synthesized nanocomposite was utilized as an adsorbent for effective adsorption of cesium ions from aqueous solution. 2. Experimental 2.1. Synthesis of RGO-CNF-PB material RGO-CNF composite was received following previous report [7]. To synthesize RGO-CNF-PB composite, first, RGO-CNF powder were re-dispersed with the aid of ultrasonication in potassium hexacyanoferrate (K4[Fe(CN)6], 99.9%) solution. Then, the pH of the solution mixture was adjusted to 2 by the addition of HCl 0.1 M solution. The solution was vigorously mechanical stirred for 1 h at 25oC at about 400 ÷ 500 rpm. After that, RGO-CNF-PB composite was separated from the reaction mixture and repeatedly washed with water and ethanol using magnetic decantation. Finally, the obtained powder was dried in vacuum at 50oC for 24 h. 2.2. Characterization of materials The morphologies and crystal structures of the composites were characterized using scanning electron microscopy (SEM - S4800), X-ray diffraction (XRD, Bruker D5 with Cu Kα1 radiation λ = 1.54056 Å), and Fourier transform infrared spectroscopy Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 7 (FTIR, Perkin Spectrum Two). Magnetic measurements were done with a vibrating sample magnetometer (VSM, DMS 880 in magnetic fields of up to 13.5 kOe). 2.3. Adsorption experiments A batch technique was performed to study the adsorption of cesium ion from aqueous solutions by RGO-CNF-PB. Cesium solutions used in all adsorption experiments were prepared by dissolving cesium chloride in deionized water. All the adsorption experiments were carried out at 25ºC with 20 mg of adsorbent and 50 mL of solution. After the adsorption reached the equilibrium, the adsorbent was separated from solution by a magnet. Then, the samples were filtered and the cesium concentration of the effluent was measured by inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7500). The pH values ranging from 4 to 10 were adjusted by adding 0.1 mol/L NaOH or 0.1 mol/L HNO3 solution. The contact time was varied from 15 to 90 min. In the adsorption equilibrium isotherm studies, the initial concentrations of cesium were varied and the other parameters were kept constant (contact time = 60 min and pH = 7). The amount of cesium adsorbed per unit mass of the adsorbent was calculated according to the following equation:  o ee C CQ V m (1) where Qe (mg/g) is the adsorption capacity, Co and Ce (mg/L) are the concentrations of the cesium at initial and equilibrium states, respectively, m is the weight of sorbent (g), and V is the volume of the solution (L). 3. Results and discussion 3.1. Morphology, structure characterization and magnetic properties of composites FTIR spectra of RGO-CNF-PB composite is shown in Fig. 1. The peak at 2081, 1624, 986, 544 cm-1 could be assigned corresponding to the vibrations of CN stretching, C=C stretching, C-N stretching and Fe-O bond, respectively [9, 10]. These peaks show the interactions that appear in the material. This result confirms the formation of RGO-CNF-PB composite. The morphology of RGO-CNF is shown in Fig. 2. The CNF particles were dispersed well and cover almost totally the whole surface of the RGO, so that the RGO leaves cannot be seen except only at the boundaries between the RGO-CNF blocks. The CNF particle size distribution is shown in Fig. 3, where could be seen that the particle sizes range from 11 to 21 nm in diameter. The distribution curve has a typical bell-shape with the maximum in the range of 15 ÷ 16 nm. Fig. 4 shows the surface morphology of Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 8 the composite RGO-CNF-PB. After RGO-CNF composite was coated with PB, PB should cover on the surface of the RGO-CNF. 3500 3000 2500 2000 1500 1000 500 70 75 80 85 90 95 RGO-CNF-PB Tr an sm itt an ce (% ) Wavenumber (cm-1) Fig. 1. FTIR spectra of RGO-CNF-PB Fig. 2. SEM image of RGO-CNF 10 12 14 16 18 20 22 0 5 10 15 20 25 Pe rc en ta ge ( % ) Diameter (nm) RGO-CNF Fig. 3. Particle size distribution of CNF Fig. 4. SEM image of RGO-CNF-PB In the XRD pattern of the RGO-CNF-PB (Fig. 5), a broad peak corresponding to RGO at about 24.4º, with an interlayer spacing of 0.54 nm. We also can see peaks corresponding to (220), (311), (400), (422), (511), and (440) crystal planes, respectively. XRD data identified that the CNF particles have a face-centered cubic trevorite structure. The crystallite size of the CNF nanoparticles was evaluated by using the Scherrer formula. The results obtained by calculation with (311) peak display that the crystallite size of CNF in RGO-CNF-PB composite is 17 nm. Room temperature magnetization of the RGO-CNF-PB composite was studied and the result is presented in Fig. 6. The VSM measurement demonstrated that achieved materials were generally superparamagnetic-like with remanences and coercive forces near zero. The maximum magnetization value of the RGO-CNF-PB is about 45 emu/g. In our experiments, the RGO-CNF-PB sample have 56 wt% of Cu0.5Ni0.5Fe2O4, and the saturated magnetization of Cu0.5Ni0.5Fe2O4 is 80 emu/g [7]. The present results are in good agreement with the previous experiments. Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 9 10 20 30 40 50 60 70 0 40 80 120 160 In te ns ity (a .u ) 2 (degrees) RGO-CNF-PB (r G O ) (2 20 ) (3 11 ) (4 00 ) (4 22 ) (5 11 ) (4 40 ) -15 -10 -5 0 5 10 15 -60 -40 -20 0 20 40 60 M (e m u/ g) H (kOe) RGO-CNF-PB Fig. 5. XRD patterns of RGO-CNF-PB Fig. 6. Room temperature magnetic hysteresis loops of the RGO-CNF-PB 3.2. Adsorption kinetics The pH of the sample solution is an important factor to control the cesium sorption efficiency. The effect of pH on the amount of cesium adsorbed on the RGO- CNF-PB composite is carried out in Fig. 7. The cesium adsorption percentage was calculated by the following equation: Adsorption percentage (%) .100%o e o C C C   (2) The amount of cesium is augmented when the pH increases from 4 to 7. As the pH value is reliably extended from 7 to 10, the amount of adsorbed cesium diminishes. This result demonstrates that the sorption capacity of RGO-CNF-PB for cesium reaches its best value when pH = 7. The decrease of adsorption capacity in acidic medium was ascribed to a competition effect between H+ and Cs+. Furthermore, the slight decomposition of PB in alkaline solution was making the decrease of adsorption capacity [11]. 4 5 6 7 8 9 10 60 65 70 75 80 85 pH A ds or pt io n pe rc en ta ge (% ) @ 25 0C; t = 60 min, C0= 50 mg/L, m = 20 mg, V = 50 mL 15 30 45 60 75 90 0 40 80 120 @ 25 0C; C 0 = 50 mg/L, pH = 7, m = 20 mg, V = 50 mL t (min) Q t ( m g/ g) Fig. 7. Effect of pH on cesium adsorption Fig. 8. Effect of contact time on the adsorption Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 10 0 20 40 60 80 -2 0 2 4 6 t (min) Ln (Q e-Q t) Pseudo-first order: Qe (cal) = 200 (mg/g) k1 = 0.056 (min -1) R = 95.8% (a) 0 15 30 45 60 75 90 0.4 0.6 0.8 (b) t/Q t ( m in .g /m g) t (min) Pseudo-second order: Qe (cal) = 167 (mg/g) k 2 = 1.3.10-4(g.mg-1.min-1) R = 98.1% Fig. 9. Pseudo-first-order (a), pseudo-second-order (b) plot for the adsorption Effect of contact time on adsorption is shown in Fig. 8. The adsorption of cesium on composite reaches equilibrium within 60 min and it is kept almost constant thereafter. Therefore, the contact time of 60 min was chosen for all adsorption experiments to confirm that equilibrium was set up in each adsorption process. To determine the kinetic parameters and models which well fit these experimental data, the experimental data was treated in terms of the pseudo-first-order or pseudo-second-order kinetic models [6, 8]. The evaluated values of kinetic parameters for both models are displayed in Fig. 9. The correlation coefficient value of the pseudo-second-order kinetic model is higher than that of pseudo-first-order kinetic model. Furthermore, adsorption capacity calculated by the pseudo-second-order kinetic model is in good agreement with the experimental values. It could be concluded that the cesium adsorption kinetics of this adsorbent can be well explained in terms of the pseudo-second-order kinetic model due to the chemical adsorption. 3.3. Adsorption Isotherms of Cesium The adsorption isotherms of cesium on RGO-CNF-PB are shown in Fig. 10. The results indicated that the cesium adsorption amount increased with the increasing of equilibrium concentration and reached 108 mg/g in this experimental condition. This adsorption process did not approach the saturated state, so this value was not the maximum adsorption capacity of cesium on RGO-CNF-PB. To determine the cesium adsorption pattern and capacity, the experimental data was analyzed by Langmuir, Freundlich and Dubinin-Radushkevich isotherms. The plots of these isotherms are delineated in Fig. 11 - Fig. 13. On comparing the adsorption isotherms, the Langmuir isotherm could be more suitable to characterize the cesium adsorption behavior of the RGO-CNF-PB composite because of the high correlation coefficient value. According to the Langmuir isotherm, the maximum adsorption Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 11 capacity of cesium on RGO-CNF-PB was calculated 125 mg/g at 25oC, and the adsorption process can be a homogeneously monolayer. The removal of cesium in the presence of materials can be allocated to the interaction between material surface and cesium species presented in the solution. The special cesium ions adsorption of PB composites are caused by typical lattice spaces encircled by cyanide-bridged metal [15]. It is considered that RGO-CNF-PB has high capacity of cesium adsorption exhibited a potential of utilization in removal and recovery of cesium from aqueous solutions. 0 5 10 15 20 25 30 40 60 80 100 120 @ 25 0C; t = 60 min, pH = 7, m = 20 mg, V = 50 mL Q e ( m g/ g) Ce (mg/L) 0 10 20 30 0.0 0.1 0.2 0.3 Langmuir model: Qm = 125 (mg/g) R = 98.9% KL = 0.30 (L/mg) C e/Q e ( g/ L) Ce (mg/L) Fig. 10. Effect of equilibrium concentration on the adsorption Fig. 11. The Langmuir model for the adsorption 0 1 2 3 4 3 4 5 Freundlich model: n = 2.9 R = 87.1% K F = 37.8 (L/g) Ln Q e Ln Ce 0 4 8 12 3.0 3.5 4.0 4.5 5.0 Dubinin-Radushkevich model: Qm = 95.6 (mg/g) R = 77% K D-R = 8.0x10-7 (mol2/J2) Ln Q e   (105) Fig. 12. The Freundlich model for the adsorption Fig. 13. The Dubinin-Radushkevich model for the adsorption The results for the adsorption capacity of different adsorbents for Cs+ from previous studies are listed in Tab. 1. The adsorption capacity of the RGO-CNF-PB composite is not the best among those adsorbents but its conditions are more favourable (short contact time, closer neutral solution). Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 12 Tab. 1. Maximum adsorption capacity of different adsorbents for cesium Adsorbents Capacity (mg/g) pH Contact time Ref. PB coated Fe3O4 96 - 24 h [2] MHPVA 82.8 8 6 h [3] PB@Fe3O4 46 - 6 h [12] PSMGPB 219 7 24 h [13] NaCuHCF@PEI-Fe3O4 167 4-10 4 h [14] RGO-CNF-PB 125 7 60 min This work 4. Conclusion In this work, ternary composite RGO-CNF-PB was synthesized and used as an adsorbent for adsorption of cesium from polluted water. The nanocomposites were characterized by SEM, FTIR, XRD, and VSM. The isotherm and kinetic studies indicated that the Langmuir isotherm and pseudo-second-order models well described the experimental data. The maximum cesium adsorption capacity of RGO-CNF-PB composite was estimated to be 125 mg/g at pH = 7 and 25oC within the Langmuir model. The RGO-CNF-PB composite appears as an effective cesium-adsorbent holding promising application in cesium segregation from aqueous solution because of their simplicity of magnetic separation and high adsorption capacity. References 1. H.J. Yang, H.Y. Li, J.L. Zhai, L. Sun, Y. Zhao, H.W. Yu. (2014). Magnetic prussian blue/graphene oxide nanocomposites caged in calcium alginate microbeads for elimination of cesium ions from water and soil. Chemical Engineering Journal, 246, pp. 10-19. 2. C. Thammawong, P. Opaprakasit, P. Tangboriboonrat, P. (2013). Sreearunothai, Prussian blue-coated magnetic nanoparticles for removal of cesium from contaminated environment, Journal of Nanoparticle Research, 15(6), pp. 1-10. 3. Y.K. Kim, T. Kim, Y. Kim, D. Harbottle, J.W. Lee (2017). Highly effective Cs+ removal by turbidity-free potassium copper hexacyanoferrate-immobilized magnetic hydrogels. Journal of Hazardous Materials, 340, pp. 130-139. 4. X. Liu, G. Chen, D. Lee, T. Kawamoto, H. Tanaka, M. Chen, Y. Luo (2014). Adsorption removal of cesium from drinking waters: A mini review on use of biosorbents and other adsorbents. Bioresource Technology, 160, pp. 142-149. 5. H.A. Alamudy, K. Cho (2018). Selective adsorption of cesium from an aqueous solution by a montmorillonite-prussian blue hybrid, Selective adsorption of cesium from an aqueous solution by a montmorillonite-prussian blue hybrid. Chemical Engineering Journal, 349, pp. 595-602. 6. T.Q. Dat, P.T. Hung, D.Q. Hung (2017). Efficient removal of uranium from aqueous solution by reduced graphene oxide - Zn0.5Ni0.5Fe2O4 ferrite - polyaniline nanocomposite. Journal of Electronic Materials, 46, pp. 3273-3278. 7. T.Q. Dat, N.T. Ha, D.Q. Hung (2017). Reduced graphene oxide - Cu0.5Ni0.5Fe2O4 - polyanilinenanocomposite: Preparation, characterization and microwave absorption properties. Journal of Electronic Materials, 46, pp. 3707-3713. Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 13 8. T.Q. Dat, N.T. Ha, P.V. Thin, N.V. Tung, D.Q. Hung (2018). Synthesis of RGO/CF/PANI magnetic composites for effective adsorption of uranium. IEEE Transactions on Magnetics, 54(6), pp. 1-6. 9. K.S. Hwang, C.W. Park, K.W. Lee, S.J. Park, H.M. Yang (2017). Highly efficient removal of radioactive cesium by sodium-copper hexacyanoferrate-modified magnetic nanoparticles. Colloids and Surfaces, 516, pp. 375-382. 10. X. Hong, B. Zhang, E. Murphy, J. Zou, F. Kim (2017). Three-dimensional reduced graphene oxide/polyaniline nanocomposite film prepared by diffusion driven layer-by-layer assembly for high-performance supercapacitors. Journal of Power Sources, 343, pp. 60-66. 11. Y. Zhu, W. Wang, H. Wang, X. Ye, Z. Wu, A. Wang (2017). Fast and high-capacity adsorption of Rb+ and Cs+ onto recyclable magnetic porous spheres. Chemical Engineering Journal, 327, pp. 982-991. 12. H. Yang, S. Jang, S. Hong, K. Lee, C. Roh, Y. Huh, B. Seo (2016). Prussian blue- functionalized magnetic nanoclusters for the removal of radioactive cesium from water. Journal of Alloys and Compounds, 657, pp. 387-393. 13. A. Kadam, J. Jang, D. Lee (2016). Facile synthesis of pectin-stabilized magnetic graphene oxide Prussian blue nanocomposites for selective cesium removal from aqueous solution. Bioresource Technology, 216, pp. 391-398. 14. H. Yang, K. Hwang, C. Park, K. Lee (2017). Sodium-copper hexacyanoferrate- functionalized magnetic nanoclusters for the highly efficient magnetic removal of radioactive caesium from seawa