Arsenic removal by highly efficient MnFe2O4/TiO2/g-C3N4 and MnFe2O4/TiO2/GO adsorbents from a groundwater sample, Bardsir, Iran

Abstract

In this study, MnFe2O4/TiO2/GO and MnFe2O4/TiO2/g-C3N4 spinel ferrites nanoparticles were used, and synthesized via the co-precipitation method, for the removal of arsenic from groundwater in the Bardsir region, Iran. The magnetic adsorbents were characterized by XRD, VSM, BET, FE-SEM, EDS, RAMAN, and FTIR analyses. The effects of pH, adsorbent dosage, contact time, initial arsenic concentration, and temperature on the adsorption process were investigated. MnFe2O4/TiO2/GO and MnFe2O4/TiO2/g-C3N4 were utilized to minimize the concentration of arsenic. The arsenic concentration was reduced from the initial amount of 17.8 mg/l to 197 µg/l and 177 µg/l using MnFe2O4/TiO2/GO and MnFe2O4/TiO2/g-C3N4, which indicates the adsorption capacity of 331 (mg/g) and 332 (mg/g), and the removal efficiency of 98.89% and 99.01%, respectively. Moreover, the adsorption rate for MnFe2O4/TiO2/GO and MnFe2O4/TiO2/g-C3N4 was very fast and occurred in 5 (min) and 15 (min), respectively. The results of kinetics studies were well correlated with the pseudo-second-order model, with the coefficient of determination values of 1 for both adsorbents. These nanoparticles could remove arsenic by following the Freundlich isotherm model. The thermodynamics studies showed that arsenic adsorption was an exothermic and spontaneous process. This article also presents a numerical simulation containing the second-order kinetic expression using COMSOL Multiphysics software. The experimental data and the numerical modeling results were in solid agreement. Furthermore, after five adsorption–desorption cycles, the adsorption capacity of the adsorbents remained constant as in the first cycle. Overall, a simple synthesis method, high adsorption capacity, fast kinetics, easy magnetic separation, and reusability demonstrate that MnFe2O4/TiO2/GO and MnFe2O4/TiO2/g-C3N4 are high-performance adsorbents for arsenic removal from aqueous systems.