Study On Photocatalytic Degradation Of Organophosphorous Pesticides With TiO₂ Nanometer Powder

The organophosphorous pesticides wastewater is thick and poisonous. The toxicants inhibit the reproduction of bacterium, so the pollutant degradation by microbe is poor. The organic pollutants can be effectively degraded into inorganic ions by photocatalysis, and there is no secondary' pollution. The photocatalysis is a potential treatment for organophosphorous pesticides wastewater.The photocatalytic degradation of methamidophos is influenced greatly by the adsorption of methamidophos on the TiO₂ surface. The Langmuir adsorption isotherm equation of methamidophos on the TiO₂ surface C_e/q_e = 0.1095 C_e +0.06347 is put forward on the basis of the experimental results. A phosphoryl oxygen-titanium bond is formed via O of P=O with TiO₂ when methamidophos is adsorbed on the TiO₂ surface. According to the experimental results, the process of photocatalytic degradation is proposed.The influence factors on the photocatalytic degradation of methamidophos are investigated, such as the optimum amount of TiO₂. The degradation of methamidophos is more efficient in acidic medium and basic medium. The degradation efficiency of methamidophos increases with a decrease of the initial concentration of methamidophos or an increase of the light intensity and airflow. The degradation efficiency of methamidophos increases greatly when the electron acceptor H₂O₂ or Fe³⁺ is added.The kinetic equation, which is expressed by the products of organic pollutant degradation, is given. The photocatalytic degradation is a zero order reaction when the initial concentration of methamidophos is in the range of 7.06-70.56 mg.L^-1 . CH₃-SO₂-SCH₃ and CH₃S-SCH₃ are detected by GC-MS during the photocatalytic degradation of methamidophos. SO₄²- NH₄⁺ NO₃^- ion are determined by ion-chromatography. N in methamidophos is photocatalyzed into NH₄⁺ , and then NH₄⁺ is oxidized into NO₃^- . The proposed pathway of photocatalytic degradation of methamidophos is put forward on the basis of experimental results. The reaction rate constant of zero order of methamidophos is 0.02132 mg.L^-1 .min^-1 when the sunlight intensity is 18.2W.m^-2 . It is showed that the photocatalytic degradation of methamidophos is easier than that of isocarbophos by the experimental results.Fe2O3/ TiO2 is prepared by adding TiO2 in Fe(OH)3 colloid. DRS shows that the absorption property of light is improved and the red shift of excitation wavelength occurs after TiO2 is coupled with Fe2O3. According to XRD results, iron enters the TiO2 lattice;The Ti-O-Fe is confirmed by XPS, so ion doping is existing when TiO2 is coupled with Fe2O3. When the light illuminates Fe2O3/ TiO2, the electron moves from TiO2 to Fe2O3. At the same time, the defect in the crystal lattice acts as the trap, so the electron-hole pair on the TiO2 surface is separated effectively and the activity of Fe2O3/ TiO2 increases. Ti3+ surface state decreases the activity of Fe2O3/ TiO2, and the photocatalytic activity of Fe2O3/ TiO2 isn't proportional to the amount of surface hydroxyl radical. The particle size and specific surface area aren't the main influence factors on the activity of Fe2O3/ TiO2, and the effective separation of electron-hole pair is the main reason.Nano-sized TiO2 with good dispersion, high purity and high activity in the aqueous solution is prepared by the improved hydrolysis. The optimum preparation conditions are investigated. The degradation efficiency of photocatalytic degradation of methamidophos for 1 h is 61.3% by prepared TiO2, and 35.9% by TiO2 made in Japan. The characterization of nano-sized TiO2 is studied using TEM, XRD, TG, DTA, BET, IR and XPS, indicating that the photocatalytic activity of the photocatalyst must be evaluated by crystallite patterns, crystallinity, crystal size, specific surface area, surface state and surface hydroxyl radical. The single parameter is not proportional to the photocatalytic activity. The main reasons influencing the photocatalytic activity are the crystallite patterns and crystallinity.