The Research Of Photocatalytic Degradation Of Refractory Organics Over Nano-TiO₂

From the perspective of the water treatment development in recent years, refractory pollutants are a major problem. The photocatalytic oxidation of organic pollutant removal method is the more promising methods, and the general reaction can be achieved complete mineralization, no secondary pollution. In this paper, UV and TiO₂ catalysts are used to photocatalytic degradation of refractory organic pollutants: nitrobenzene, PAEs and PCBs. Sol-gel method using tetra butyl titanate, ethanol, acetic acid, distilled water as raw materials were make into nano-TiO₂ particles,30 40nm diameter, good dispersion and photocatalytic activity. By the research on nano-TiO₂ loaded in activated carbon, zeolite, ceramic, the most cost-effective is load material -zeolite, which can make a certain amount of methylene blue solution completely bleaching. Experiment determine the affection law of removal rate of nitrobenzene in the appropriate magnetic stirring speed, light intensity, distance from light source to the reaction surface; Carry on a series of experiments by changing the solution pH, initial concentration, TiO₂ content, the results as follows: (1) As pH increases, the degradation rate of nitrobenzene decreased gradually ,and then increased again, in acidic and alkaline conditions, the treatment results are better than neutral conditions. Removal rate under the conditions of amount of nano-TiO₂ 0.1g/L, nitrobenzene concentration of 40mg/L is best ,can reach 63.81%; nitrobenzene in the initial has a rapid degradation rate, then degradation rate in the late phase decline, the nitrobenzene removal can meet the kinetic equation.(2) by adding nano-TiO₂ quantity was 0.1g/L, the concentration of 40mg/L, removal efficiency of the best light one hour of the removal rate reached 63.81%; nitrobenzene in the rapid degradation of the initial rate , the degradation rate decreased gradually later stage, the removal of nitrobenzene to satisfy a kinetic equation. (3) TiO₂ content impact on nitrobenzene removal rate greatly, and the optimum ratio of TiO₂: nitrobenzene is equal to 1:5. In this study, nano-TiO₂ photocatalytic oxidation was used to treatment the four phthalates and seven polychlorinated biphenyls mixture, according to the effects of system TiO₂ dosage, initial concentration, pH, and removal of such factors effect , the results obtained: (1) pH on the photocatalytic degradation has significant influence, and pH on the degradation of different reagents have different effects ,on the whole PAEs and PCBs are easily degradable in the polar conditions; (2)With the increase of initial concentration of the removal rate also increased, when the initial concentration in the PAEs were 1.0mg/L,DMP (dimethyl phthalate), DBP (deputy phthalate), DEHP (o-acid -2-ethylhexyl ester) and DOP (dioctyl phthalate), respective removal rates after 30 min was reached 70.93%, 62.09%, 69.22%, 67.81%; when in the initial PCB concentrations were 0.2mg / L, PCB₂₈, PCB₅₂, PCB₁₀₁, PCB₁₁₈, PCB₁₅₃, PCB₁₃₈, PCB₁₈₀ ,the respective removal rate after 30 min was reached: 93.42%, 64.27%, 80.35%, 85.63%, 75.94%, 96.92%. 96.17%.(3) The removal rate of PAEs and PCBs increase with the TiO₂ dosage, when the dosage of TiO₂ reached a certain value, little effect on the removal rate, then this study identified such a mixture of refractory organic nano-TiO₂ 0.5mg/L as the best. These studies not only can improve the reactor on the natural environment of great theoretical significance adaptation, but also can have a certain value to control the degradation of toxic organic pollutants.