Cu and Ni dual-doped ZnO nanostructures templated by cellulose nanofibrils for the boosted visible-light photocatalytic degradation of wastewater pollutants

In this study, cellulose nanofibrils (CNF) and transition metals (Cu and Ni) were used as the matrix and doping agents, respectively, for the controllable synthesis of ZnO@CNF nanocomposites with adjustable visible-light photocatalytic properties. All samples were elaborately characterized by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller, X-ray diffraction, scanning electron microscopy-energy dispersive spectrometry, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance and photocurrent response. Several nano-ZnO particle morphologies, including plate, nanorod, sphere, and star, were produced and anchored on the CNFs by controlling the ZnO loading ratio. The as-produced ZnO@CNF nanocomposites exhibited a remarkable photocatalytic degradation of methyl orange under visible-light irradiation. The plate-like ZnO0.6@CNF exhibited the best photodegradation efficiency (53.1%) for methyl orange under blue light (λmax = 450 nm, 50 W) irradiation. Furthermore, when doped with transition metals, Cu or/and Ni–ZnO0.6@CNF exhibited better photocatalytic efficiency than pristine ZnO0.6@CNF. Under blue light irradiation, the preferred Cu/Ni–ZnO0.6@CNF nanocomposite sample demonstrated an enhanced degradation efficiency for various wastewater pollutants, including methyl orange (96.6%), tetracycline hydrochloride (96.6%), rhodamine B (99.0%), 4-nitrophenol (94.7%), bromocresol green (92.9%), bromothymol blue (88.3%), methylene blue (87.7%), 2-chlorophenol (27.5%), and aniline (19.5%), with the recyclability of more than ten times. This study provides new insights into the regulation of ZnO morphology for synthesizing efficient ZnO@CNF photocatalysts for wastewater pollutant degradation under visible-light irradiation.