Study On Preparation And Properities Of Nano-TiO₂ Photo-catalyst Coated On Magnetic Particles

In recent years, TiO2 has been studied extensively in the photocatalytic field because of its advantages comparing to other semiconductor photocatalysts, such as inexpensive, non-toxic, high photocatalytic activity, chemical inertness, strong oxidizing power. However, the practical application of TiO2 is limited due to its low quantum yield, narrow range of light responding, low utilization rate of solar energy, difficulty in separation and recovery. In this paper, aiming at the disadvantages of TiO2 powder, such as difficulty in separation and recovery and low utilization rate of solar energy, magnetic photocatalysts have been prepared by the sol-gel processing using magnetic nano-powder with a large surface area and easy magnetic separation property as the carrier. Through the doping of alkaline-earth metal ions expands the scope of TiO2 the spectral response and improves the utilization of sunlight. Magnetic composite materials of titanate nanotubes were prepared by a hydrothermal method using TiO2 coated on magnetic nanoparticles as the precursor. The relationship between the magnetic photocatalyst structure and catalytic properties was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibration sample magnetometer (VSM), transmission electron microscopy (TEM) and diffuse reflectance spectra (DRS). Photocatalytic activities of the products were evaluated by measuring the decolorization rates of methylene blue(MB) solution.The magnetic nanocomposite photocatalysts TiO2/SiO2/NiFe2O4(TSN),TiO2/SiO2/CoFe2O4(TSC) and Ti02/Si02/Co0.64Zn0.36Fe2O4(TSCZ) was prepared by the sol-gel processing with the magnetic particles SiO2/MeFe2O4 (SM, Me= Ni, Co, Co0.64Zn0.36) as the carrier. TSN, TSC and TSCZ are ferrimagnetism, easy to recycle through the magnetic separation and with good recovery performance and reusability. The thin SiO2 layer gave rise to the increase in photocatalytic activity. The photocatalytic results showed that the TSN has the best Photocatalytic activity under the UV irradiation and The TSCZ has the best Photocatalytic activity under visible light.Alkaline earth metal ions (M2+) doped magnetic photo-catalyst Ba2+-TSN was prepared by the sol-gel method. The effect of M2+ on photo-catalytic activity of TSN was systematic studied. It was found that the doping of M2+ causes the absorption spectrum to red-shift, leads to the distortion of lattice and restrains the increase of the particle size of TiO2. The optimum doping of Ca2+, Mg2+, Sr2+ and Ba2+is 1.0%,1.0%,0.8%, and 0.8%. The photocatalytic results show that the doping of M2+ remarkably gives rise to the remarkable increase in visible-light photo-catalytic activity. The decolorization rate of MB improved near two times using the Ba2+-TSN as the catalyst in the visible area.Magnetic composite materials of titanate nanotubes coated on magnetic particles (MTNT) were prepared by a hydrothermal method using TSN as the precursor. The effects of preparation conditions on their properties of MTNT were studied. The results show that the hydrothermal temperature and concentration of NaOH has a significant impact on the formation of the products. The main components of MTNT are Na0.8H1.2Ti3O7. The magnetism of MTNT has improved than raw materials because the SiO2 was dissolved by NaOH solution. MTNT was changed to TiO2 when it was calcined at high temperature with the heat-stable range of 400-500℃. The photocatalytic results show that the catalytic activity of MTNT was enhanced after calcined. In the visible-light photo-catalytic degradation of MB, the pH value of the system has little effect. The decolorization rate of MB improved near two times when the dosage of MTNT is only 1/3 of raw materials.Ba2+ dopeded magnetic composite materials of titanate nanotubes coated on magnetic particles (Ba2+-MTNT) were prepared by a hydrothermal method using Ba2+-TSN as the precursor. Doping of Ba2+ had no obvious impact on the morphology of MTNT. Doping of Ba2+ accelerated the reaction rate and improved the thermal stability of MTNT. Doping of Ba2+ increased the specific surface area and enhanced the visible-light catalytic properties of MTNT. In the visible-light photo-catalytic degradation of MB, the pH value of the system has little effect, catalyst dosage is less. Ba2+-MTNT had good recovery, reuse performance and good applied outlook.