Degradation Of Organic Pollutant By Mesoporous Nano-Photocatalyst

Photocatalytic technique, which is taken as an advanced oxidation process (AOP), have many virtues, such as strong oxidation, little secondary pollution and no selectivity upon mineralization of pollutant into inorganic ions. Among the catalysts studied presently, TiO₂ has shown great potential in organic wastewater treatment for its stability, low price, no poison and high photoactivity. However, the photoactivity of normal TiO₂ nanoparticles do not suffice the requirement of the practical application because of its wide band gap and high combination ratio of electron-hole pair. The photoactivity of TiO₂ nanoparticles can be improved by microstructure amendment and rare earth doping.At present, most previous researches on the photodegradation of organic pollutant in water have mainly focused on the investigation and optimization of the photoreaction conditions. However, majority of organic pollutant degradation contains many complicated processes with intermediate generation. Therefore, it is necessary to determine the intermediates and mineralization products and obtain photocatalytic degradation mechanism finally.The dissertation have synthesized and characterized La doped/undoped mesoporous TiO₂ nanoparticles through hythrothermal method. Their photoactivities were investigated upon photocatalytic degradation of dye and organophosphorus pesticides in solution. The main results are summarized as follows:1. La doped/undoped mesoporous anatase TiO₂ nanoparticles with high thermal stability can be obtained from Ti(SO₄)₂ and ta(NO₃)₃ through hythrothermal method under a low temperature, while surfactant cetyltrimethyl ammonium bromide (CTAB) was taken as the template agent. The synthesized TiO2 nanoparticles possess stable mesoporous structure and high temperature of phase transformation; 1% La doped TiO₂ nanoparticles exhibited a higher temperature of phase transformation than undoped samples, which is because the doping La restrain the phase transformation of TiO₂. Moreover, the doped La maintains a stable state in the synthesized mesoporous materials.2. Photocatalytic degradation of methyl orange in suspension was investigated by using mesoporous TiO₂ nanoparticles as the catalyst. Effects of reaction conditons, such as lamp power, initial pH and catalyst concentration, were investigated and optimized. 98% MO (20 mg/L) can be degraded in the 1.0 g/L TiO₂ suspension (pH 2.0) after 45min illumination of 250W Hg lamp. Under these conditions, photodegradation of MO mainly involves three intermedial processes: demethylation, methylation and hydroxylation. Among those processes, demethylation is more favorable than the hydroxylation, but the hydroxylation results in the largest number of intermediates.3. Photocatalytic degradation of methamidophos in suspension containing mesoporous TiO₂ nanoparticles was investigated by determination of the product PO₄^3- through optimized molybdenum blues photometric method. Effects of initial pH, catalyst concentration and methamidophos concentration to the photocatalytic degradation rate were investigated and these conditions were optimized. The experimental results show that 71.8 % methamidophos can be mineralized under the optimal photocatalytic conditions (20 mg/L methamidophos, 0.5 g/L TiO2 suspension (pH 4.02), 3h UV illumination). Besides, nearly all methamidophos can be decomposed and mineralized into nontoxic inorganic constituents. Photodegradation pathways of methamidophos are proposed after computative simulation of the methamidophos molecule.4. Photocatalytic degradation of methyl parathion (MP) and phoxime in suspension were investigated by using La doped mesoporous TiO2 nanoparticles as the catalyst. Effects of La doping amount, calcination temperature, initial pH, and catalyst concentration to the photocatalytic degradation rate were investigated and these conditions were optimized. All MP (20 mg/L) can be degraded in the 2.0 g/L 1% La doped 500℃calcined TiO₂ suspension (pH 6.38) after 3h illumination. All phoxime (20 mg/L) can be degraded in the 0.5 g/L 1% La doped 700℃calcined TiO₂ suspension (pH 4.43) after 3h illumination. After 3h illumination, although all organophosphorus pesticides in solution were removed, complete mineralizations were not observed through ion chromatography analysis, which is due to the intermediates generated during the photocatalytic degradation.