Study On Preparation Of Nano-BaTiO3and MnTiO3Powders And Their Photocatalytic Properties For Degradation Of Humic Acid In Water

Humic acid (HA), as part of natural organic matters, represents90%of dissolved organic carbon in surface water and has extremely complicated molecular structures. In chlorination process of drinking water, it has been confirmed that HA could react with major disinfectants (chlorine dioxide and chlorine) to form organic halogenated compounds like trihalomethanes, which is very harmful to human health owing to its carcinogenicity. Therefore, it is very necessary to remove HA before the chlorination of drinking water. The traditional ways used to eliminate HA mainly contain active carbon absorption method, coagulation process, ultrafiltration membranes techniques, oxidation and ultrasonic method. In recent years, photocatalytic degradation techniques have received great attention in organics treatment since the degradation reaction is complete and no secondary pollution. TiO2, Fe2O3, ZnO, ZnTiO3and NiTiO3photocatalysts have been used in HA treatment study, however there are still no literatures mentioning about the HA decomposition by BaTiO3or MnTiO3as the photocatalyst. In this paper, a dual chelating sol-gel method was used to synthesize BaTiO3nanoparticles by using acetylacetone and citric acid as chelating agents. The samples calcined at different temperatures were analyzed by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscope (SEM) and UV-vis diffuse reflectance spectra (UV-vis). The results indicated that cubic phase BaTiO3nanoparticles about19.6nm can be obtained at600℃and changed into tetragonal phase at900℃about97.1nm. The phase transformation temperature from cubic to tetragonal is much lower than1000℃or higher in the reported references. The photocatalytic activities of the samples were investigated by the removal of humic acid (HA) from water under UV light (λ=365nm) irradiation. The processing parameters such as the concentration of photocatalyst and the initial concentration of HA have important influence on the degradation rate of HA. All the BaTiO3nanoparticles showed the photocatalytic activities on the removal of HA. Among them, the tetragonal phase BaTiO3calcined at900℃showed the best photocatlytic activity, especially when the concentration of the photocatalyst was0.6g/L and the initial concentration of HA was10mg/L, the degradation rate of HA can be reached to100%after reaction for120min. This could be associated to the higher light absorbance at365nm, spontaneous polarization of itself, Ti3+ions existence and smaller particle size. A comparison of single (acetylacetone or citric acid) and dual chelating (acetylacetone and citric acid) synthetic processes was also studied and the results demonstrated that the dual chelating agents indeed reduce phase transformation temperature from cubic to tetragonal BaTiO3.In this paper, another photocatalyst MnTiO3powders were successfully prepared by sol-gel method using tetrabutyl titanate and manganese acetate as the raw materials, absolute ethyl alcohol as solvent and citric acid as chelating agent. The composition, crystal morphology and absorbance of the samples were characterized by XRD, SEM and UV-vis. Then, the effects of calcination temperature and concentration of photocatalyst were also discussed under UV light (λ=365nm) irradiation. The results showed that the morphology of MnTiO3prepared at900℃for4h was sheet, and the photocatalytic activity was much better than another two samples, especially when the concentration of the photocatalyst was0.4g/L and the initial concentration of HA was10mg/L, the degradation rate of HA can be reached to80%after UV light irradiation for150min. The contrasts of degradation rates of HA among photolysis, adsorption and photocatalysis further indicated that MnTiO3powders have a better photocatalytic activity.