Toward safer bisphenols remediation: Range-Corrected DFT study of zero-valent metal-mediated bisphenols reduction

The environmental persistence and health implications of bisphenol A (BPA) and its structural analogues, aided by the shortfalls of existing remediation techniques, necessitate the development of safer and more efficient degradation strategies. In this study, density functional theory (DFT) calculations were employed to investigate the reductive degradation of BPA, bisphenol F (BPF), bisphenol E (BPE), and bisphenol AP (BPAP) initiated by zero-valent metals (Zn⁰, Mg⁰, and Ca⁰) in vacuum and simulated aqueous media. Geometry optimizations, transition-state searches, intrinsic reaction coordinate analyses, and thermochemical evaluations were performed at the ωB97XD/cc-pVTZ level of theory. The degradation proceeds through a two-step deoxygenation mechanism involving formation of an organometallic intermediate followed by protonation-assisted cleavage to yield monophenolic and fully reduced products. Kinetic and thermodynamic analyses reveal that Zn⁰-mediated reduction is highly endothermic and non-spontaneous, whereas Mg⁰ exhibits moderate facilitation of reductive degradation in aqueous phase. Ca⁰-mediated reduction offers the lowest activation barriers and exhibits strongly exothermic, and spontaneous behavior, indicating the most feasible bisphenol degradation. Substituent variation and number of phenolic hydroxyl groups exert minimal influence on the overall degradation tendency. Toxicity assessment using experimental endocrine-disruption data and QSAR-predicted aquatic toxicity and mutagenicity indicates that the degradation products are significantly less toxic than their parent bisphenols. Overall, zero-valent calcium emerges as the most promising reductive agent for efficient and environmentally safer degradation of BPA and related analogues, highlighting the potential of zero-valent metal-mediated reduction as an alternative to conventional advanced oxidation processes.