Low-temperature synthesis of a multifunctional NiO/Ni(OH)2 decorated sulfonated bentonite for sustainable and enhanced visible-light-driven degradation and mineralization of bisphenol-A in water

The persistence of endocrine-disrupting compounds (EDCs) such as bisphenol A (BPA) in aquatic environments necessitates the development of efficient, sustainable, and cost-effective treatment strategies. In this study, a multifunctional photocatalyst composed of nickel oxide (NiO), nickel hydroxide [Ni(OH) 2 ], and metallic nickel (Ni 0 ) supported on sulfonated carbon-rich bentonite (SB) was synthesized via a low-temperature, calcination-free route. The fabrication process—comprising acid activation, ion exchange, and mild chemical reduction—preserves hydroxide-layered structures while integrating redox-active and light-responsive phases within a hierarchically porous clay matrix. The resulting NiO/Ni(OH) 2 @SB composite demonstrated outstanding photocatalytic performance under visible light. Complete degradation and mineralization of BPA (5 mg/L) were achieved within 20 and 60 minutes, respectively using 0.5 g/L catalyst. Kinetic modeling confirmed pseudo-first-order behavior (k 1 = 0.2177 min -1 ), while quantum yield analysis indicated high photon-to-reactivity efficiency (Φ = 3.32 × 10 -7 ). Mechanistic studies revealed that photogenerated •OH and •O 2 - radicals—amplified by Ni 2+ /Ni 3+ redox cycling and Ni 0 /NiO Schottky junctions—drive the oxidative degradation pathway. The sulfonated bentonite support enhances pollutant adsorption, interfacial contact, and dispersion of the active phases. The catalyst exhibited remarkable structural integrity and reusability, maintaining >90% of its initial activity after six consecutive cycles, with negligible Ni leaching (<0.001 mg/L). This work offers a scalable and environmentally benign strategy for solar-assisted remediation of phenolic micropollutants. The design principles established herein provide a blueprint for developing next-generation clay-supported photocatalysts targeting a wide range of emerging contaminants in real-world wastewater matrices.