Fluoride and bromide removal from synthetic and real water utilizing biocompatible graphene oxide composites: Evaluating linear and nonlinear modeling

Access to clean water remains a critical global challenge. Accordingly, there is an urgent demand for efficient, cost-effective, and environmentally sustainable sorbents for anion removal from water. In this study, biocompatible functionalized graphene oxide (GO) composites were synthesized and evaluated for their performance in removing fluoride and bromide from water. Methionine-functionalized GO (Meth@GO) and β-cyclodextrin-functionalized GO (BCD@GO) with three different loading ratios were prepared for comparison. The influence of co-anions on the removal of both target anions was investigated, with negligible competitive effects observed in water samples. The optimal composites were selected based on application performance and further used to optimize anion removal from simulated and real water samples. Linear and nonlinear models were employed to interpret the adsorption behavior. Nonlinear pseudo-second-order models suitably described the removal of fluoride and bromide by Meth@GO and BCD@GO. The maximum adsorption capacities for fluoride and bromide were 6.57 mg/g and 4.48 mg/g for BCD@GO, and 4.73 mg/g and 3.53 mg/g for Meth@GO, respectively, as determined by nonlinear models. Model results indicated differences between linear and nonlinear findings based on error functions. The reusability of Meth@GO and BCD@GO was effective over four consecutive cycles, with BCD@GO demonstrating higher performance of BCD@GO. The removal of both anions from real water samples exceeded 97.31%, highlighting the practical potential of the sustainably synthesized composites.