Modifing Synthesis Of TiO₂ And Photocatalytic Degradation Mechanism Of Diazinon By P25

In the 21 st century, environmental pollution and shortage of energy have become the limited factors of the development of human society. Photocatalytic technology attract extensive attention worldwide as the hopeful means to solve these two issues. Titanium dioxide is one of the most promising catalysts due to its high efficiency, stability, non-toxic, superior performance. But how to improve the visible light utilization of TiO2, the effect of condition on mechanism of degradation of pesticides by TiO2 attract people’s strong attention. In this study, different morphologies of titanium dioxide was synthesized by changing the solvothermal experimental conditions, and using a variety of characterization methods to characterize crystalline phase, surface composition, light absorption capacity, carrier separation and its photocatalytic activity. degradation pollution actives. And a detailed study was carried out about the effect of pH on adsorption kinetics, thermodynamics and mechanism during the photocatalytic degradation of diazinon. We can get the following conclusions:1. TiO2 nanobelts precursor was synthesized in glycerol solvent. XRD, TGA, IR and other instruments were used to investigated crystalline phase, surface composition and structural analysis of the precursor. After calcination the catalyst surface was modified by noble metal Pt. We used DRS, PL, TEM to study light absorption ability, the carrier separation efficiency and morphology of catalyst composites and photocatalytic activity was evaluated through degradation of Rhodamine B and diazinon under the visible and ultraviolet light respectively. The results showed that: glycerol coordinated Ti generating titanium glycerolate precursor. High-temperature calcination of the precursor structure loses organic ingredients and transformed into anatase polycrystalline titanium dioxide nanobelts. The more Pt loaded on the surface of nanobelts, the stronger visible light absorption ability, and the narrower band gap. But when loaded amount of Pt is 1%, catalyst composites has the optimum catalytic activity. Catalyst calcined at 250℃ has the best degradation activity for sulfathiazole, and the degradation rate is 86.5 times of P25.2. Regular morphology of the solid TiO2 microspheres was synthesized in hexanoic acid solvent, and we studied the effects of reaction conditions on the crystal phase and morphology. XRD, SEM, DRS, TGA, IR and other technology was used to investigate crystalline phase, morphology size, light absorption ability and surface composition calcined catalysts; and their photocatalytic activity was evaluated through degradation of sulfathiazole under visible light irradiation. The results show that: trace of water in the system or reaction time extension caused titania microspheres from mixed phase by the TiO2(B) and anatase mixed turned into more stable anatase phase, and excessive water will destroy the morphology of microspheres. TiO2 microspheres has bandwidth reduction to 2.39 e V after 200℃ calcination, and 2.61 e V after 250℃ calcination, which had great absorption in the visible region, it has the best visible degradation activity. Infrared Characterization shows some organic material on the catalyst before calcined, and specific surface area increased to 141.4 m2/g after calcined at 250 ℃. XPS also indicates that the bond Ti-O-C formation on the surface of the product after calcination.3. Organophosphorus pesticide diazinon was degraded by P25 photocatalyst. HPLC, LC-MS technology measured degradation kinetics and intermediates of diazinon at different pH environments, speculating degradation routes. Isothermal Titration Calorimetry technique measured heat flow in the diazinon adsorped process at different pH system to give deep understanding of the adsorption process. The results showed that: diazinon declined fastest in near- neutral conditions and system pH also decreased duringdegradation; a variety of OH- adducts intermediates were detected by LC-MS. Moreover, diazinon molecule P-O-N is easily broken, P = S double bond tends to formed P = O. Intermediate species are different in the acidic, neutral and alkaline conditions, indicating pH changes diazinon degradation route. The adsorption between P25 and diazinon is in accordance with Langmuir isotherm. Diazinon is more easily adsorbed under neutral conditions than acidic conditions. The adsorption process is spontaneous, meanwhile adsorption in acidic and alkaline solution is exothermic and endothermic reaction in neutral condition. pH affects the different active species in the solution is the real cause of different photocatalytic degradation mechanisms of diazinon.