Photoelectrocatalysis Removal Of Typical Environmenttal Pollutants And Mechanism Research

Over the past decades, the rapid development of technology and social economy have greatly improved the qualities of people’s life. But in the same time, the increasing population, emissions of industrial and domestic sewage as well as the emission of motor vehicle exhaust, brought serious pollutions to our living environment. How to deal with environmental pollutions became a focus of global concern. The disposal of toxic and hazardous materials requires new technologies. Advanced oxidation technologies (AOTs), involving an in situ generation of highly potent chemical oxidants such as hydroxyl radicals (OH), are regarded as promissing technologies for non-selective oxidation of hazardous pollutants.Among AOTs, photocatalysis has been entensively studied as one of the most effective solutions in water and gas pollution treatment because of its facility, high efficiency, as well as its potential applications in both aquatic and atmospheric purification. However, the application of photocatalysts still suffers from their low efficency of solar energy utilization. In addition, Fenton oxidation exibited superior performance in treatment of high concentrational, toxic and hardly decomposed wastewater in comparison with other methods. Howerer, the restriction of acid condition and high cost of H2O2 utilization also hampered the large scale application of Fenton oxidation. Hence, how to improve the efficiency of photocatalysis and Fenton oxidation is always the emphasis and difficulty in pollution contoling.This dissertation aims to explore high efficient visible-light-driven photocatalysts through simple synthesis method and designe novel promising oxidation system by coupling visible light driven photorelectrochemical oxidation (PEC) and electro-Fenton oxidation (EF). The reaction mechanism of these different oxidation system in gas and water pollutant removal are also studied in detail through a series of analytic method. This disssertation first introduced the environmental problems, the highlighted pollution of solid, gas and water, the current atmospheric and water control technology as well as AOTs. Then we elaborated the synthesis of visible-light-driven photocatalysts (self-doped Bi2WO6 and Bi2MoO6) and the designing of promising BDD| Fe@Fe2O3/ACF electrochemical oxidation system and Bi2WO6/FTO| Fe@Fe2O3/ACF photoelectro-chemical/electon-Fenton oxidation system. The crystal structure, composition, morphology, activity, and mechanism of these resulting photocatalysts and oxidation systems in pollutant degradation were characterized and evaluated by XRD, XPS, SEM, TEM, HPLC, TOC, IC, NO analyzer and GC/MS.The results were summarized as follows.1. A simple soft-chemical method was developed to realize bismuth self doping of Bi2WO6 for efficient PCP removal under visible light irradiation. Density functional theory (DFT) calculations and systematical characterizations (XRD, SEM, TEM, XPS and so on) were applied to investigate the influence of bismuth self doping on the electronic band structures, optical properties, the separation and transfer of photogenerated electron-hole pairs of Bi2WO6 as well as the reactive species generation during photocatalysis. To clarify the interaction of photogenerated reductive and oxidative species with NaPCP, ion chromatography (IC), gas chromatography-mass spectrometry (GC/MS) and total organic carbon analyses (TOC) were used to check the dechlorination and the benzene ring cleavage as well as the final mineralization of sodium pentachlorophenate (NaPCP) during Bi2+xWO6 photocatalysis. It was found that more superoxide ions can promote the dechlorination process and thus favor the subsequent benzene ring cleavage and the final mineralization of sodium pentachlorophenate during bismuth self-doped Bi2WO6 photocatalysis.2. The reactive species generation of Bi2MoO6 under visible light can be regulated by Bi self-doping via a simple soft-chemical method. Density functional theory calculations and systematical characterization results revealed that Bi self-doping could not only promote the separation and transfer of photogenerated electron-hole pairs of Bi2M0O6 but also alter the position of valence and conduction band without changing its preferential crystal orientations, morphology, visible light absorption as well as band gap energy. The photocatalytic removal of NO and product determination revealed that the enhanced generation of superoxide could improve the oxidation of NO to NO2 while · OH and photogenerated holes mainly contributed to the further oxidation of NO2 to NO3-. Photostability and NO absorbtion tests demonstrated that NO3- on the surface of catalysts took up the NO absorption sites and caused the deactivation of catalysts. This study provides new insight into the different effects of photogenerated reactive species on NO removal and sheds light on the design of highly efficient visible light-driven photocatalysts for NO removal.3. An electrochemical/electro-Fenton oxidation (EC/EF) system was designed by utilizing a boron-doped diamond (BDD) and Fe@Fe2O3 core-shell nanowires supported activated carbon fiber as the anode and cathode, respectively. Interestingly, this system exhibited much higher activity than the electrochemical (EC) and electrochemical/traditional electro-Fenton (EC/TEF) oxidation system on degradation of atrazine in aqueous solution at pH of 3. Total organic carbon (TOC) and ionic chromatography were applyed here in order to evaluate the mineralization and the decholorination efficiency of the treated aqueous solutions. A higher mineralization rate of 87% and decholorination rate of 87.5%was obtained in fours hours under a low current of 30 mA. After determine the difference of intermediates during the decomposition of atrazine by High Performance Liquid Chromatography and Gas chromatography-Mass spectrometry technology, it can be revealed that Fe@Fe2O3 can promote the E-Fenton process to decompose the intermediates like atrazine-desethyl, atrazine-despropyl and so on and thus accelerate the mineralization consequently. Besides, this novel system realized the circulation of Fe (Ⅱ) and Fe (Ⅲ) make the recycle of system be feasible.4. A photo-electrochemical/electro-Fenton oxidation (PEC/EF) system was designed by coupling visible light driven photo-electrochemical oxidation (PEC) and electro-Fenton oxidation (EF) in a single and double cells. Bi2WO6 nanoplates deposited on FTO glass (Bi2WO6/FTO) and Fe@Fe2O3 core-shell nanowires supported on activated carbon fiber (Fe@Fe2O3/ACF) were used as the anode and the cathode respectively in the PEC/EF system. This novel PEC/EF system showed much higher activity than the single PEC and EF systems on degradation of rhodamine B at natural pH. Moreover, the degradation and the instantaneous current efficiencies of the PEC/EF system were increased by 154% and 26% in comparison with the sum of those of single PEC and EF systems, respectively. These significant enhancements could be attributed to the synergetic effect from better separation of photo-generated carriers in the photo-anode and the transfer of photo-electrons to the oxygen diffusion cathode to generate more electro-generated H2O2 and ·OH on the Fenton cathode. The better separation of photo-generated carriers contribute more to the overall degradation enhancement than the photo-electrons generated H2O2 and the subsequent Fenton reaction on the cathode during the PEC/EF process. Besides, the two separated cells could degrade rhodamine B (RhB) simultaneously and thus enhance the degradation efficiency and the TOC removal significantly in comparison with that of counterpart single-cell PEC-EF system (S-PEC-EF) because of more H2O2 electro-generated on the Fe@Fe2O3/ACF cathode by photo-generated electrons transferred from the Bi2WO6/FTO anode and less H2O2 consumed by anodic oxidation owing to the partition of two cells, which enhanced both PEC and EF oxidation ability and improved both photocatalytic quantum efficiency and overall current efficiency significantly. DOCTORAL DISSERTATION...