Preparation And Selective Degradation Toward Organic Pollutant Of Molecular Imprinted Codoped TiO₂ Catalysts

With the rapid development of industry and agriculture, organic pollutants in wastewater increase, leading to seriously threat to the ecological environment and human health. Titanium dioxide (TiO2) is used to degrade organic pollutants due to high redox potential, nontoxicity, long-term chemical stability and inexpensiveness. However, owing to large energy band gap of TiO2 (3.0 eV for rutile,3.2 eV for anatase), TiO2 can be activated by ultraviolet light, which just takes about 5% of the solar light. Therefore, in order to improve effective utilization of the solar light, a lot of researches have been made to extend its photocatalytic activity to visible light region. Among various modification strategies, doping with other elements is an efficient, stable, low-cost way. However, the highly toxic and lowly toxic organic pollutants in wastewater are coexistence in general. When codoped TiO2 deals with this wastewater, its photocatalytic efficiency is relatively low. As molecular imprinted polymers have molecular recognition ability and specific adsorption for organic pollutants, the problem concerning enhancement of photocatalytic degradation of codoped TiO2 toward target pollutants could be resolved by molecular imprinting technique.Preparation and photocatalytic properties of codoped TiO2 were firstly carried out in this paper. Details are as follows:1. Synthesis and Photocatalytic Activity of Mo/N-TiO2. Mo/N-TiO2、N-TiO2、Mo-TiO2 and TiO2 were synthesized by hydrolysis precipitation method. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM). UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of catalysts was evaluated by degrading methylene blue (MB) under simulate sunlight. The results indicated the light absorbance of Mo/N-TiO2 extend from the UV to the visible light range due to the doping of N and Mo element. The final degradation rates of MB were found to be 94.7%、80.8%、57.7% and 40.6% within 120 min. When Mo doping ratio was 0.07%, photocatalytic activity of the obtained Mo/N-TiO2 is highest in all samples.2. Synthesis and Photocatalytic Activity of N/F-TiO2. N/F-TiO2 and TiO2 were synthesized by solvothermal method. The obtained samples were characterized by XRD, SEM, UV-vis DRS and XPS. Photocatalytic activity of catalysts was evaluated by degrading MB under simulate sunlight. The results indicated the light absorbance of N/F-TiO2 extended from the UV to the visible light range due to the doping of N and F element. The final degradation rates of MB were found to be 98.1% and 25.6% within 120 min. When ratio of NH4F and tetrabutyl orthotitanate was 2:1, photocatalytic activity of the obtained N/F-TiO2 was highest in all samples.Molecular imprinted codoped TiO2 had high photocatalytic degradation and selectivity toward target pollutants. Details are as follows:1. Preparation and properties of molecular imprinted Mo/N-TiO2 (MIP-MNTs). MIP-MNTs were synthesized by hydrolysis precipitation method using rhodamine B (RhB) as template molecules. Non-imprinted Mo/N-TiO2 (denoted as NIP-MNTs) were prepared using the same procedure except the addition of template molecules. The obtained samples were characterized by XRD, SEM, BET and UV-vis DRS. The adsorption and degradation ability of the samples toward RhB were evaluated by adsorption and degradation experiments of target pollutants (RhB) and non-target pollutants (Rh6G) under simulate sunlight. In order to investigate reuse of MIP-MNTs, cycle test were conducted. The results indicated particle size of MIP-MNTs was less than that of NIP-MNTs. The specific surface area of MIP-MNTs was greater than that of NIP-MNTs. The absorption spectrum of MIP-MNTs showed red shift. MIP-MNTs had high adsorption. Photocatalytic degradation of RhB over MIP-MNTs is 97.19% after 180 min. The degradation rate of RhB was found no change in MIP-MNTs cycle test.2. Preparation and properties of molecular imprinted N/F-TiO2 (MIP-NFTs). MIP-NFTs were synthesized by simple solvothermal method using 2-nitrophenol (2NP) or 4-nitrophenol (4NP) as template molecules (denoted as 2NP/MIP-NFTs or 4NP/MIP-NFTs). Non-imprinted N/F-TiO2 (denoted as NIP-NFTs that said N/F-TiO2) were prepared using the same procedure but without the addition of template molecules. The obtained samples were characterized by XRD, SEM, BET and UV-vis DRS. The adsorption and degradation ability of the samples toward target pollutants were evaluated by adsorption and degradation experiments of target pollutants and non-target pollutants under simulate sunlight. In order to investigate reuse of MIP-NFTs, cycle test were conducted. The results indicated the specific surface area of MIP-NFTs was greater than that of NIP-NFTs. MIP-NFTs had high adsorption. Photocatalytic degradation of 2NP and 4NP over corresponding MIP-NFTs were 97.66% and 95.41% respectively after 75 min.The degradation rate of target pollutants was found no change in MIP-NFTs cycle test.