Dual-Functional Silver Nanoparticles Supported on ZnO Nanoparticles Catalyst from Plant Extract: High-TOF Hydrogen Generation and Fast Photocatalytic Tetracycline Removal

A green synthesized 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 (Ea) 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.

本研究以香附子（Cyperus scariosus）根提取物作为天然还原与稳定剂，制备了绿色合成的银纳米颗粒@氧化锌复合纳米材料（AgNPs@ZnO NC）。通过紫外-可见分光光度法（UV-Vis）、傅里叶变换红外光谱（Fourier Transform Infrared Spectroscopy, FTIR）、X射线衍射（X-ray Diffraction, XRD）、扫描电子显微镜（Scanning Electron Microscope, SEM）、能量色散X射线光谱（Energy Dispersive X-ray Spectroscopy, EDS）、热重分析（Thermogravimetric Analysis, TGA）以及布鲁诺尔-埃米特-特勒（Brunauer–Emmett–Teller, BET）分析对所制备的纳米结构进行了全面表征，证实了银的成功负载，以及该介孔载体具有显著增大的比表面积与优异的稳定性。本研究还测试了AgNPs@ZnO的双功能催化活性：以甲酸（Formic Acid, FA）为氢源，在低温下开展析氢反应（hydrogen evolution reaction, HER）；同时在太阳光下催化降解四环素（Tetracycline, TC）。系统探究了Ag@ZnO NC上甲酸的催化脱氢反应在不同实验条件下的表现。该催化剂在pH=4的条件下展现出优异的催化性能，周转频率（TOF）可达3935 h⁻¹，这归因于体系中充足的质子以及热力学上有利的Ag-ZnO界面协同效应。研究优化了甲酸/甲酸钠（Sodium Format, SF）的摩尔比（3:1）与催化剂用量（15 mg），并证实水相较于N,N-二甲基甲酰胺（DMF）或甲醇具有更优的反应效果。上述结果表明，在最优反应条件下，Ag@ZnO NC作为催化剂可高效、高选择性且可循环地从甲酸中制备氢气，具备优异的应用潜力。采用AgNPs@ZnO开展四环素光催化降解实验，结果显示该材料可在45分钟内实现约99%的降解率，降解动力学符合准一级动力学模型，且表观活化能（Activation Energy, Ea）仅为4.94 kJ·mol⁻¹，热力学参数表现优良（焓变ΔH=2.32 kJ·mol⁻¹，吉布斯自由能变ΔG≥27 kJ·mol⁻¹）。猝灭实验与能带边分析表明，超氧自由基（·O₂⁻）与羟基自由基（·OH）是体系中的主要活性氧物种（Reactive oxygen species, ROS），且Ag-ZnO的协同效应可增强这两种自由基的生成。该纳米催化剂具备良好的循环稳定性，证实了复合纳米材料在能源与环境领域的实际应用潜力。