Dual-function silver nanoparticles catalyst supported on ZnO nanoparticles from plant extract: high-TOF hydrogen generation and fast photocatalytic tetracycline removal

Abstract

A green hybrid AgNPs@ZnO nanocomposite (NC) was prepared, employing Cyperus scariosus root extract as a natural reducing and stabilizing agent. The prepared nanostructure was thoroughly investigated via UV-vis, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Thermogravimetric Analysis (TGA), and Brunauer–Emmett–Teller (BET) analyses and confirmed the success of Ag deposition and the mesoporous support with considerably increased surface area and stable nature. The dual-functional catalytic activity of AgNPs@ZnO was also tested for hydrogen evolution reaction (HER) at low temperature with Formic Acid (FA) as a hydrogen source and the photo-catalytic degradation of Tetracycline (TC) under solar light. The catalytic dehydrogenation of formic acid (FA) on Ag@ZnO NCs was systematically investigated under various experimental conditions. The catalyst exhibited outstanding efficiency at pH 4 with a TOF of 3935 h⁻¹ owing to abundant protons and a thermodynamically favorable Ag–ZnO interfacial synergy. The FA/Sodium Format (SF) molar ratio (3 : 1) and the catalyst amount (15 mg) were optimized, whereas water was evaluated as being more effective than DMF or methanol. These results reveal that Ag@ZnO NCs are highly active catalysts for the efficient, selective, and recyclable hydrogen generation from FA under an optimal reaction condition. Photocatalytic degradation of TC was carried out using AgNPs@ZnO, showing an efficient and fast removal (∼99% over 45 min) following pseudo-first-order kinetics, with a low Activation Energy (E_a) value (4.94 kJ mol⁻¹) and favorable thermodynamic parameters (ΔH = 2.32 kJ mol⁻¹ and ΔG ≥ 27 kJ mol⁻¹). The studies of scavenger and band-edge showed that superoxide (˙O₂⁻) and hydroxyl (˙OH) radicals were major Reactive oxygen species (ROS) in the system, and were enhanced by the synergistic Ag–ZnO effects. The good recyclability of the nano catalyst revealed the potential of NCs for practical applications toward energy and the environment.