Cu、C共负载ZnO光催化剂固氮性能及机理

为提高ZnO催化剂光催化固氮性能,克服其光生电子-空穴复合率高、可见光响应能力差以及易光腐蚀等缺点,本研究采用Cu、C共负载方式对ZnO催化剂进行改性(以下简称CuCZ催化剂)。结果显示,CuCZ?3%(Cu占ZnO质量的3%)催化剂的光催化固氮速率最大,达到4.96 mmol·g_cat^-1·h^-1,为ZnO(0.612 mmol·g_cat^-1·h^-1)的8.10倍、CZnO(C负载ZnO,3.00 mmol·g_cat^-1·h^-1)的1.65倍。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV?Vis DRS)、光致发光光谱(PL)以及电化学阻抗谱(EIS)对CuCZ催化剂进行表征以探究其光催化固氮效果提高的机理。结果表明,Cu、C共负载产生的界面电荷转移机制和C的“电子桥梁”作用提高了ZnO催化剂的光催化固氮性能,降低了光生电子-空穴复合率。CuCZ?3%催化剂的4次光催化循环固氮速率稳定于4.61~4.96 mmol·g_cat^-1·h^-1之间,这说明C层的包覆削弱了CuCZ催化剂的光腐蚀过程,增强了其稳定性。

Performance and Mechanism of Cu, C Co-loaded ZnO Photocatalyst for Nitrogen Fixation

Herein, Cu, C co-loaded ZnO photocatalyst was synthesized to promote its photocatalytic nitrogen fixation properties and overcome its disadvantages of high photoelectron-hole recombination rate, poor response to visible light and photocorrosion. The results indicated that CuCZ-3% (the weight of Cu loaded was 3% of the weight of ZnO) photocatalyst achieved the highest nitrogen fixation rate (4.96 mmol·g_cat^-1·h^-1), which was 8.10 times higher than that of ZnO (0.612 mmol·g_cat^-1·h^-1) and 1.65 times higher than that of CZnO (C-loaded ZnO, 3.00 mmol·g_cat^-1·h^-1). To explore possible mechanism for the promoted nitrogen fixation efficiency of CuCZ photocatalyst, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL), and electrochemical impedance spectroscopy (EIS) were applied. The results indicated that the interfacial charge transfer mechanism induced by the transition metal Cu and the electronic bridging function of C enhanced nitrogen fixation efficiency and inhibited photoelectron-hole recombination of ZnO photocatalyst. CuCZ-3% photocatalyst exhibited excellent stability with the nitrogen fixation rate ranged between 4.61 and 4.96 mmol·g_cat^-1·h^-1 in four cycles. The main reason is that the coating effect of C weakens the photocorrosion of CuCZ photocatalyst.