Preparation And Properties Of Lanthanum Cerium Doped TiO₂ Photocatalysts

Along with the development of society,it will inevitably lead to the environmental pollution problems.The government work report points out that we must continue to prevent the pollution and develop the new energy vigorously at this year's Two Sessions.TiO₂ is applied to the photocatalytic degradation of polluted wastewater on account of its low cost,environmental friendliness,non-toxicity and stable photochemical properties.However,TiO₂ has a wide band gap so that it can only be excited in the wavelength range of ultraviolet light.The utilization rate of solar energy is extremely low.In addition,the photogenerated electron-hole pairs of TiO₂ are easy to recombine after being excited which results in its low catalytic efficiency under visible light.These greatly limit the extensive application of TiO₂.Therefore,it is great important to improve the photocatalytic performance of TiO₂under visible light.In this paper,TiO₂ was doped by the rare earth elements lanthanum and cerium to improve the utilization of visible light.And the related characterization tests and performance analysis were also carried out.Firstly,Ti?SO₄?₂ and La₂O₃ were used as raw materials to prepare the La-doped TiO₂ photocatalysts by hydrothermal method.The effects of precursor concentration,hydrothermal temperature,time,pH and La doping amount on the TiO₂ performance were investigated.The experimental result shows that hydrothermal La is only surface doping that La³⁺is combined with Ti⁴⁺and the Ti-O-La chemical bond is formed at the interface of TiO₂.It can accelerate the separation of TiO₂ photogenerated electron-hole pairs,reduce the recombination probability and improve the photocatalytic performance of TiO₂.Under the preferred conditions?precursor concentration 0.3 mol/L,hydrothermal 120°C,12 h,pH=6,La doping 1.5%?,the visible photocatalytic performance of TiO₂ was improved to more than 50%and the degradation efficiency of the methyl orange was just reduced by 6%after the 1.5%La-TiO₂ was reused for 5 times.And then,compared to hydrothermal method,the La-doped TiO₂ catalyst was synthesized through the hydrolysis precipitation method.The hydrolysis precipitated La is bulk doped that La is embedded in the lattice of TiO₂ to form the Ti-O-La chemical bond.Under the optimal conditions?calcination temperature 400°C?,the visible light catalysis level of 1.5%La-TiO₂ is comparable to that of the hydrothermal method.The recyclability is superior that the degradation efficiency is only reduced by 0.6%.Subsequently,Ti?SO₄?₂ and Ce?NO₃?₃×6H₂O were used as raw materials to prepare Ce-doped TiO₂ photocatalyst by the hydrolysis precipitation method.The effects of hydrolysis pH value,the calcination temperature of precipitation products,time and Ce doping amount on the properties of TiO₂ were investigated.Ce doping can form the 4f impurity level in the energy band of TiO₂,which can reduce the forbidden bandwidth of TiO₂ and improve the utilization of visible light.Under the optimal conditions?pH=1,calcination temperature 550°C,4 h,Ce doping 0.5%?,the degradation efficiency of 0.5%Ce-TiO₂ was 95.30%,which was much larger than52.43%of the pure TiO₂ after 8 h visible light irradiation.In addition,this paper also carried out a preliminary exploration of the co-doping.La and Ce co-doped TiO₂catalysts were prepared by the hydrolysis precipitation method.The photocatalytic performance of co-doped samples improved observably due to the synergistic effect of La and Ce.Under the optimal conditions?pH=1,calcination temperature 600°C,2h,La doping 1.5%,Ce doping 0.5%?,the degradation efficiency under visible light after 6 h can reach the equivalent level as that after 8 hours of single La and Ce doping,or even more better.