| Summary: | 碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系博碩士班 === 106 === Bismuth vanadate (BiVO4) and silver vanadate (Ag3VO4) are prepared by hydrothermal method in this study. BiVO4 and Ag3VO4 were modified by Bi2O3 permeation liquid-liquid one-step process and solid-liquid two-step process. This study employed the Bi2O3/BiVO4 and Bi2O3/Ag3VO4 molar ratios 1 to synthesize various photocatalysts and the prepared photocatalysts were denoted as BB-1 to BB-6 and BA-1 to BA-8. C.I. Reactive Red 2 (RR2) was selected as the target compound. The surface characteristics and photocatalytic activities of prepared photocatalysts were determined and compared in this study.
The surface properties of Bi2O3/BiVO4 and Bi2O3/Ag3VO4 were characterized by X-ray diffraction (XRD), brunauer Emmett teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis spectroscopy (UV-Vis), photoluminescence (PL), inductively coupled plasma optical emission spectrometry (ICP-OES), zeta potential meter and X-ray photoelectron spectroscopy (XPS).
The used Ag3VO4 was characterized by SEM and found the structure of used Ag3VO4 collapsed. Through SEM and TEM observation, the used Bi2O3/Ag3VO4 was found that Ag3VO4 was still immobilized on the surface of Bi2O3 and the structure was not destroyed. Through PL analysis, the recombination rate of electrons and holes of 1BB (overdose) (BB-1)、Bi2O3(s) (solvothermal)/BiVO4(l) (BB-6) and 1BA (overdose) (BA-1) were lower than that of BiVO4 and Ag3VO4. The critical absorption wavelengths of Bi2O3/BiVO4 and Bi2O3/Ag3VO4 were in the visible range. The specific surface area of BB-1 and BB-6 was increased from 0.03 m2/g to 8.42 m2/g and 2.87 m2/g after Bi2O3 modification. BiVO4 was synthesized by a hydrothermal method herein.
Trisodium citrate dehydrate (TCD) was added as a chelating agent during the preparation, and a 460 W xenon lamp was used as the UV light source for photocatalytic experiments. After 180 minutes of visible light irradiation, the RR2 removal efficiency of BiVO4 was 43% and the RR2 removal percentage of BB-1 and BB-6 was 89% and 69%, respectively. The photocatalytic efficiency of BB-1 and BB-6 only decreased 10% after three times reuse. After 60 minutes of visible light irradiation, the RR2 removal efficiency of Ag3VO4 was 23% and the RR2 removal percentage of 1BA (overdose) (BA-1) and Bi2O3(s) (solvothermal)/Ag3VO4(l) (BA-8) was 50% and 30%, respectively. The ICP-OES results showed that Ag3VO4 almost dissolved completely after the photodegradation. Under visible light irradiation, BA-1 and BA-8 showed the RR2 removal efficiency after three times reuse was 50% and 30%, respectively, and the used powder recovery percentage was 85%.
The experimental results of active oxidation species trapping revealed that the role of hydroxyl radicals could be ignored in Bi2O3/BiVO4 system, conversely, hydroxyl radical played a major role in Bi2O3/Ag3VO4 system. The photogenerated hole (h+) played a major role and photoinduced electrons played a minor role in the Bi2O3/BiVO4 system. The BB-1, BB-6, BA-1 and BA-8 showed a better photocatalytic efficiency than TiO2 (P25) under visible light irradiation.
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