Improved photocatalytic activity for phenol degradation using a p-n junction photocatalyst composite in the presence of visible light: [GeO2 + B2O3] particles-doped ZnO oxygen vacancy

An excellent method to harvest a wider range of the solar-spectrum and enhance electron-hole pair separation is synthesizing a composite-photocatalyst. A series of ZnO oxygen vacancy (ZnO ov), and its photocatalyst composites including GeO2 + B2O3 (GB)-doped ZnO ov, were synthesized using thermal-precipitation, annealing, and impregnation methods. Raman spectroscopy and electron spin resonance were employed to verify the creation of the oxygen vacancies on the surface of the synthesized ZnO. The X-ray photoelectron spectroscopy (XPS), Powder X-ray diffraction (XRD), scanning-electron microscopy (SEM), and energy dispersive spectroscopy (EDS) demonstrated the presence of GB and ZnO ov particles, with upgrowth of successful doping process. Highresolution transmission electron microscopy and Mott-Schottky analysis illustrated a successful production of a p-n junction composite between the GB and ZnO ov. Photocatalytic-activity for GB, ZnO ov, 50 wt% B2O3/ZnO ov, 50 wt% GeO2/ZnO ov, and X wt% GB/ZnO ov, had been studied. This work revealed that 50 wt% GB/ZnO ov is the best photocatalyst with 80.37 % of phenol degradation under 180 min of visible-light, with 4-times recycling capacity. Photoluminescence (PL) and UV-vis spectra, affirmed that the increase in photocatalytic activity was caused by a decrease in electron-hole recombination and a wider absorption of light, while surface area had less impact on the photocatalytic activity. It was determined by process parameters studies for phenolcontent and pH-reaction values that phenol with a concentration of 10 ppm and pH of 4.79 provides the highest degradation by the 50 wt% GB/ZnO ov. According to the quenching test, hydroxide-radical (& sdot;OH) had the highest impact on phenol degradation using the p-n junction pathway.