Visible-light photocatalytic mineralization of 4-Chlorophenol over ZnO-loaded sulfonated carbonaceous bentonite:...

4-Chlorophenol (4-CL) is a toxic and persistent industrial pollutant resistant to conventional treatment, making its removal from wastewater a major environmental challenge. Visible-light photocatalysis provides a clean and efficient route for its complete mineralization. This study introduces a novel ZnO-functionalized sulfonated carbonaceous bentonite (ZnO@SB) nanohybrid, designed to enhance visible-light absorption, charge separation, and surface reactivity. The composite was synthesized via controlled sulfonation of organic-rich bentonite followed by uniform ZnO nanoparticle deposition. Structural and spectroscopic analyses confirmed successful functionalization and high ZnO dispersion across the sulfonated matrix. Under visible light, ZnO@SB (0.5 g/L, pH 8) achieved 100% degradation of 4-CL (5 mg/L) in 30 min and 100% TOC removal in 60 min (complete mineralization), following pseudo-first-order kinetics (k₁ = 0.1657 min⁻¹, R² > 0.98). The quantum yield increased from 7.39 × 10⁻⁸ to 2.96 × 10⁻⁷ with higher catalyst loading. The photocatalyst retained > 90% activity after five cycles, with Zn²⁺ leaching below 0.005 mg/L, indicating excellent chemical stability. Mechanistic studies confirmed the dominant roles of superoxide (O₂•⁻) and hydroxyl (•OH) radicals in driving hydroxylation, dechlorination, and aromatic ring cleavage. The novelty of this work lies in the synergistic integration of sulfonated carbonaceous bentonite with ZnO, which simultaneously enhances adsorption, charge transfer, and visible-light response. This multifunctional hybrid provides a low-cost, stable, and highly efficient photocatalyst for scalable visible-light-driven degradation and mineralization of chlorinated phenolic pollutants.