Comprehensive kinetic and mass transfer modeling for methylene blue dye adsorption onto CuO nanoparticles loaded on nanoporous activated carbon prepared from waste coconut shell

Abstract

Abstract The waste coconut shell (WCS) was used for the preparation of nanoporous activated carbon (NPAC) by chemical and physical activation method. The synthesized CuO nanoparticles were successfully loaded on the NPAC by the physical adsorption method. Different characterization techniques such as XRD, FT-IR, BET surface area, point of zero charge (pHpzc), SEM, TEM, SADE pattern, particle size distribution, and XPS were used to determine the physical-chemical properties of the CuO-NPAC nanocomposite. Thus, the prepared nanocomposites were used for methylene blue (MB) dye adsorption from aqueous solution by varying batch experimental parameters, such as initial MB dye concentration, initial pH, contact time, temperature, SDS concentration and amount of nanocomposite. In this work, a kinetic model was developed, and the developed kinetic equation was fitted with experimental data, and compared with several traditional models, such as the pseudo-second-order and Elovich models. The mass transfer mechanism was described by four diffusion models, such as Weber-Morris, liquid diffusion, Bangham's and Burt, and McKay et al. models. Adsorption equilibrium data were fitted to non-linear form of conventional isotherm models such as Langmuir, Freundlich, and Sips models, and according to high R2 values, the Sips model was best fitted followed by Langmuir and Freundlich. The possible reaction mechanism for the adsorption of MB onto the CuO-NPAC nanocomposite has also been suggested. The thermodynamic studies confirmed spontaneous adsorption of MB onto CuO-NPAC nanocomposites and showed suitability at high temperatures. The regeneration study of nanocomposite was accomplished by HCl, H2SO4, ethanol, double distilled water, and NaOH to determine the suitable reagent for the same.