Synthesis of novel reduced graphene oxide decorated β-cyclodextrin epichlorohydrin composite and its application for Cr(VI) removal: Batch and fixed-bed studies

Abstract

• The novel RGO-βCD-ECH composite was synthesized as a new adsorbent by wet chemical method. • The Cr(VI) adsorption was pH-dependent, equilibrium time was 75 min and the optimum temperature is 30 °C. • The data were fitted by Langmuir Isotherm and maximum capacity was 1321.01 mg/g. • The rate of adsorption was in good agreement with the pseudo-second-order kinetic model. • From FBAC study it was confirmed that at low flow rate and at higher bed height the performance was maximum. A novel ternary composite was synthesized comprising reduced graphene oxide (RGO), beta-cyclodextrin (βCD), and epichlorohydrin (RGO-βCD-ECH). The electrical and structural properties of the composite were analyzed by using Zeta potential, RAMAN, XRD, FTIR, BET, and SEM. It was encouraging to find out that the composite shows exceptional adsorption performance for Cr(VI) removal from water both in batch as well as Fixed bed adsorption column (FBAC) study. The optimized adsorption parameters were: adsorbent dosage 0.2 g/L, initial Cr(VI) concentration 300 mg/L, contact time 75 min, temperature 30 °C, and solution pH 1.0. Among the isotherm models, the Langmuir model proved to be a better fit, and maximum capacity ( q m ) can reach up to 1321.01 mg/g, whereas kinetic data follows the pseudo-second-order kinetic model. From the Boyd plot, it was confirmed that the rate-limiting step was controlled by intra-particle diffusion. The thermodynamic analysis confirmed that the adsorption process was an endothermic, entropy-driven, and spontaneous process. From the FBAC study, it was observed that with an increase in bed height, the parameters like bed capacity ( q bed ), breakthrough time ( t b ), and exhaustion time ( t e ) of the composite increase, and as the Cr(VI) flow rate increases the value decreases. To fit experimental data of the FBAC study, Thomas, Yoon-Nelson, and BDST model was used. Besides, it can easily and efficiently regenerate with a small effect on removal percentage. In binary solution, the results showed that coexisting ions like S O 4 2 - , N O 3 - , C l - , C u 2 + , C o 2 + , and, N i 2 + had no such substantial effect on Cr(VI) adsorption. These characteristics implied the applicability of these novel composites in the application of Cr(VI) contaminated groundwater or industrial wastewater in both batch and continuous mode.