A free-standing 3D nano-composite photo-electrode—Ag/ZnO nanorods arrays on Ni foam effectively degrade berberine

Berberine is a widely used antibiotic in China, its photocatalytic degradation is not well understood nor its efficient treatment reported. In this study, it is most quickly and efficiently degraded (97.9% under UV and 98.9% under visible light) using a free-standing 3D composite photo-electrode, with well dispersed Ag nanoparticles (Ag NPs) over well-aligned ZnO nanorods arrays (ZnO NAs) on Ni foam (NiF), compared to ZnO NAs/NiF, ZnO powder and P25. The composite photo-electrode was prepared by first directly growing ZnO NAs on NiF hydrothermally, followed by photo-deposition of Ag NPs, without any inactive binders or non-conductive substrates. It was characterized using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), ultraviolet–visible spectrophotometry (UV–Vis) and electrochemical analysis (I-t, EIS). The highest activity of Ag NPs/ZnO NAs/NiF in degrading the target pollutant, is due to the synergy of easy pollutants diffusion and fast reaction on active sites, from suppressed electron-hole recombination by Ag NPs/ZnO NAs heterojunctions, extended light absorption by surface plasmon resonance (SPR) of Ag NPs and accelerated electron transport on the conductive macro-porous NiF. The reactive oxidizing species (•OH, •O₂⁻, h^±), degradation intermediates and possible degradation pathways of berberine over Ag NPs/ZnO NAs/NiF were examined respectively. This free-standing whole piece photo-electrode with UV–visible light response, is easy to recycle and assemble, that not only degrades pollutant, but also generates electricity as photo-anode in a photo-catalytic fuel cell reactor using carbon fiber cloth as cathode.