Preparation Of Magnetically Separable Sr²⁺ Doped TiO₂ And Their Utilization For The Degradation Of Bisphenol A

With the rapid development of the domestic industrialization and society, industrial and urban waste discharge were increased accordingly, which resulted in the water pollution problem increasingly severe. Some traces of persistent organic pollutants such as EDCs, POPs and PPCPs cannot be effectively removed by the traditional water treatment system, along with the sewage discharged into the natural water bodies, causing a potential threat to human survival. Traditional wastewater treatment technologies usually are not effective and easy enough to handle it, and may produce secondary pollution to the environment. Among the semiconducting photocatalysts, titanium dioxide(TiO2) has received greatest interest in research and development of photocatalysis technology due to its chemical stability, non-toxicity, low-cost and its photogenerated holes and electrons are highly oxidizing and reducing, respectively. Whereas, three obvious drawbacks of untreated TiO2 impeded the wide application in sewage treatment(i) owning to its wide band gap(the band gap of TiO2 is generally a range of 3.0-3.2eV), photocatalytic processes can only be activated by ultraviolet light, which accounts for only about 4% and(ii) it is difficult to separate the catalyst from the treated water in the photocatalytic reactor and(iii) failing to recycle the photocatalyst not only increases the cost but also brings potential genotoxicity. We designed this integrated photocatalyst/magnetical material given several advantages:(1) easy separation from solution for reuse,(2) prohibiting the charge recombination,(3) visible light response, and(4) scaleable and reusable. For the photocatalytic activity of as-synthesized photocatalyst, the commercialized TiO2(Degussa P25) was involved as comparison matrix. The possible formation mechanism of mesoporous Sr2+ doped TiO2 was discussed and their photocatalytic activity for the degradation of bisphenol A(BPA) was also investigated in this paper. The specific research contents were as follows:1. Sol-gel method was employed to synthesize the Sr2+ doped TiO2 photocatalyst. Ni0.6Zn0.4Fe2O4 was employed as magnetic core given it not only absorb visible light but also has a magnetically property for facile separation. Besides, soluble starch was also applied as pore-form agent given the hypothesis to synthesize mesoporous anatasae particles with high photocatalytic activity. The prepared photocatalysts were characterized by X-ray Diffraction(XRD), Field Emission Scanning Electron Miccroscopy(FESEM), High Resolution Transmission Electron Microscopic(HRTEM), N2 adsorption/desorption isotherm, UV-vis diffuse reflectance and Vibrating Sample Magnetometer(VSM) different methods. the HRTEM and FESEM images of as-synthesized magnetically separable Sr2+ doped TiO2 photocatalyst shown that they are spherical shape uniformly with crystallite size of 18 nm. While from the XRD patterns, we can clearly recognize the plane of anatase phase of TiO2 and the plane of spinel phase of Ni0.6Zn0.4Fe2O4, which reveals that TiO2/Ni0.6Zn0.4Fe2O4 photocatalysises are parepared. Compared with the analysis of FESEM, HRTEM and XRD data, it can be observed that the crystallite size of the as-synthesized photocatalyst is under controled and could be tailored via adding the starch during the preparing procedure. All the as-synthesized photocatslysts demonstrate high optical absorption capacity in the range of visible light as compared to P25, suggesting their potential photocatalytic activity under visible light.2. Bisphenol A(BPA) was involved as target pollutant to exam the photocatalytic activity of the as-synthesized TiO2/Ni0.6Zn0.4Fe2O4 photocatalysises. The removal efficiency of BPA by mesoporous anatasae particles could reached 100% after 240 min UV-254 nm irradiation and 83% after visible light irradiation, at the catalyst dosage of 0.5g/L, initial BPA concentration of 10 ppm and neutral pH value. Evidently, the as-synthesized Sr2+ doped TiO2/Ni0.6Zn0.4Fe2O4 photocatalytic activities were much increased compared to that of P25. Lower or higher initial pH value conditions were favorable for the photocatalytic degradation of BPA, and the p H value of the reaction solution trended to neutral and mild during the photoreation process. The Sr2+ doped TiO2/Ni0.6Zn0.4Fe2O4 photocatalysises could separated from the slurry conveniently by means of applying an appropriate magnetic field.3. Magnetic NiZn ferrite was designed to separate the photocatalyst from the slurry solution. Magnetization(M)- magnetic field(H) loop of the S2 sample indicates that the Sr2+ doped TiO2/Ni0.6Zn0.4Fe2O4 photocatalysis inherits the magnetic property from the Ni0.6Zn0.4Fe2O4 with the saturated magnetization(Ms) of 19.04 emu/g and exhibits typical soft ferrite behavior. The dispersion of the S2 in water(photocatalyst dosage is 0.5 g/L) appears to be a turbid suspension but becomes in close proximity to transparent quickly within about 30 seconds after applied an external magnet(made of NdFeB). The photocatalytic degradation of BPA by S1 sample over from cycle 1 to cycle 3 under visible irradiation and UV-254 nm irradiation still reached 78% and 84%, respectively. By means of applying an appropriate magnetic field to separate the photocatalysis from the slurry, the nanocomposites could fortify their durability and minimize the potential genotoxicity to nature. The as-synthesized Sr2+ doped TiO2/Ni0.6Zn0.4Fe2O4 photocatalysis shows potential value in applying in industry to remove the POPs in sewage.