Enhancement of surface area of iron oxide modified by natural moieties towards defluoridation from water and antibacterial properties

Abstract

A novel adsorbent has been developed by modifying iron oxide (Fe2O3) surface using humic acid (HA) biopolymer and reduced graphene oxide (rGO), resulting in a highly efficient composite rGO/HA-Fe2O3 with magnetic property for removal of fluoride. The surface area of the composite is found to be 455.6 m2/g which has been enhanced around five times after modification with rGO and HA. Batch adsorption experiments were conducted to determine the optimal conditions for fluoride adsorption. The study found that the maximum fluoride adsorption occurred at adsorbent dose of 0.3 g/L, pH 7, contact time of 120 min. Equilibrium adsorption study data best fitted for the freundlich isotherm model, whereas, kinetic studies follow second-order kinetics which demonstrates multilayer adsorption on a heterogeneous surface with chemisorption type interaction. The adsorption process was found to be feasible, spontaneous, endothermic in nature and also the adsorbent was capable of removing around 99% of fluoride at 100 ppm initial fluoride concentration. The composite demonstrated a fluoride removal capacity of 376.46 and 395.32 mg/g at 30 and 50 °C, respectively, at pH 7, and also exhibited antibacterial properties. The composite was successfully regenerated using a 0.1 M alkaline solution with 98% efficiency and can be reused up to four cycles with an efficiency of 83.1%. The antibacterial property of the composite was assessed using solutions of Escherichia coli in water. This study is unique in its use of humic biopolymer in fluoride adsorption studies with graphene oxide, incorporating iron oxide to maintain a neutral pH during the adsorption process. The high surface area of the rGO/HA-Fe2O3 facilitates for removal of fluoride up to a very high-level fluoride concentration broadening its practical applications in various aspects. Moreover, this adsorbent is cost-effective as the precursors are easily and abundantly available in the natural environment.