Catalytic and photocatalytic activity of Urtica dioica-mediated Ud-ZnO nanoparticles

Abstract Due to their pollution-free process, low-cost, and high-quality products, plant-mediated synthesis routes have been increasingly integrated and extended for preparing a different kind of nanomaterials particularly metals/metal oxides nanoparticles (NPs). In this work, Urtica dioica (U. dioica) ethanolic leaf extract mediated ZnO NPs (Ud-ZnO NPs) were synthesized and applied for photodegradation of methyl orange (MO, C14H14N3NaO3S) and rhodamine B (RhB, C28H31ClN2O3) dyes under ultraviolet (UV) light irradiation. Also, the catalytic activity of the prepared Ud-ZnO NPs was examined for catalytic reduction of toxic 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The chemical structure, surface morphology, crystalline structure, elemental composition, and light properties of the prepared Ud-ZnO NPs investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and UV–visible diffuse reflectance spectroscopy (DRS) analyses, respectively. The SEM analysis illustrated the hexagonal phase structure with no significant agglomerations. The particle size of synthesized Ud-ZnO NPs was ranging between 26.5 and 73.7 nm with a mean particle size of 44.9 nm. The optical band gap (Eg) of the synthesized Ud-ZnO NPs estimated via DRS spectroscopy using Tauc plot was found to be 3.14 eV. The quantitative photocatalytic activity of prepared Ud-ZnO NPs indicated that 73.4 % of MO and 85 % of RhB were degraded photochemically within 90 and 140 min, respectively, indicating high photocatalytic activity. The kinetics of the photodegradation MO and RhB reactions, and also, rapid catalytic reduction 4NP reaction was analyzed based on the Langmuir-Hinshelwood (L-H) model, indicating a pseudo-first-order reaction with the reaction rate constants of 0.0155 min−1, 0.0121 min−1, and 0.0158 s−1, respectively. The results verified the effectiveness of the U. dioica leaf extract as an active reducing and capping agent for preparing Ud-ZnO NPs.