ZnO-functionalized sugarcane bagasse biochar for enhanced photocatalytic removal of paracetamol: structural, optical, and interfacial charge-transport properties

Abstract Functionalized semiconductor/carbon nanocomposites offer promising opportunities for photocatalytic environmental remediation by combining pollutant adsorption with enhanced charge separation and transport. In this work, we synthesized a ZnO-functionalized biochar composite (ZnO@BC) by thermally converting zinc hydroxychloride anchored onto a sugarcane bagasse-derived carbonaceous framework. X-ray diffraction and scanning electron microscopy coupled with energy-dispersive spectroscopy confirmed the formation of crystalline hexagonal wurtzite ZnO nanostructures, with an average crystallite size of approximately 28.9 nm, distributed throughout the porous biochar matrix. Nitrogen adsorption–desorption analysis revealed a predominantly microporous structure with a specific surface area of 74.15 m² g⁻¹. The optical band gap decreased slightly from 3.22 eV for commercial ZnO to 3.18 eV for ZnO@BC, while the Urbach energy decreased from 110.3 ± 1.6 to 49.3 ± 0.8 meV, indicating reduced optical disorder in the composite. Electrochemical impedance spectroscopy revealed an 11.7% increase in low-frequency conductance under illumination, consistent with enhanced photoinduced charge transport through the ZnO/biochar interface. The ZnO@BC composite achieved 78.5% paracetamol removal after 60 min of irradiation, with an apparent pseudo-first-order rate constant of 0.0207 min⁻¹, compared with 43% removal and 0.0079 min⁻¹ for commercial ZnO. Radical-scavenging experiments indicated relevant contributions from hydroxyl and superoxide radicals, with a secondary contribution from photogenerated holes. The results demonstrate that integrating ZnO with sugarcane bagasse biochar provides a functional hybrid interface with enhanced photocatalytic performance and promising potential for pharmaceutical-contaminant removal.