Preparation And Application Of Black N-doped TiO 2 Nanospheres

With the rapid development of social economy and people's living standard,the problem of energy shortage and environmental pollution has become an increasing serious situation,more and more people are searching the useful means to solve this problem.Among various kinds of ways,semiconductor photocatalysis is one of the most effective methods.Many semiconductor catalysts have been researched and applied in photocatalytic degration of organic pollutants.Among all the semiconductor catalysts,TiO₂ has attracted the most widely attention due to its series of properties,such as nontoxicity,environmentally friendly,low price,and high efficiency.However,it has two obvious drawbacks,which greatly restrain its photocatalytic performance,thus limiting the practical application.One is that it can only absorb the UV light because of its wide band gap?3.2 eV?,while the UV light merely account for 5%of the whole sunlight.The other is the high recombination rate of electrons and holes,which means the short lifetime of photon-generated carriers.To solve these problems,different 3D N doped TiO₂ had been synthesized through two diverse ways.The prepared catalysts were analyzed by XRD,Raman,BET,XPS,UV-Vis,and so on.Then,the performance of the as-prepared materials were tested,and the photocatalytic mechanisms of them had been discussed.The main results of the paper are as follows:?1?The N doped Ti O₂ nanospheres were synthesized by an evaporation induced self-assembly?EISA?process and an in-situ solid-state chemical reduction method,of which titanium isopropoxide and urea were used as raw materials.During the synthetic process,it was found that the best calcination temperature was 450^oC and the optimum source amount was 1 mL.The performance of the resultant catalyst for degradation of MO and phenol were 96%and 95%,respectively,the photocatalytic reduction efficiency was 95%,and the hydrogen production was 149.65?mol h^-1 g^-1.?2?Considering the light use ratio of solid spheres is not high enough,the hollow spheres were carried out and prepared through a template method,a NaOH etch process and an in-situ solid-state chemical reduction with tetrabutyl titanate and urea as raw materials and SiO₂ as template.The optimum calcination temperature and optimum amount of titanium source were 350 ^oC and 0.7 mL.The obtained material had excellent photocatalytic activity with a MO degradation efficiency of 96%,a phenol degradation efficiency of 95%,a Cr?VI?reduction rate of 96%,and a hydrogen production efficiency of 158?mol h^-1 g^-1.?3?To compare the catalytic performance of solid and hollow spheres,the initial concentration of phenol and Cr?VI?were increased,the results showed that the performance of hollow spheres were apparently higher than that of solid spheres,suggesting the hollow nanospheres structure indeed have better utilization efficiency of visible light.According to the above analyzes,the possible mechanism of photocatalytic reaction had been proposed.The improved photocatalytic activity could be mainly attributed to the N and Ti³⁺co-doping and the unique 3D structure.The co-doping could efficiently narrow the band gap and widen the photo response to visible light area,thus enhancing the photocatalytic activity.Meanwhile,the 3D mesoporous hollow nanospheres had played an important role in improving the photocatalytic performance,its high BET specific surface area could not only absorb contaminant more effectively,but also provide more active sites during the process of catalytic reaction.Meanwhile,its hollow cavity could make use of light scattering and refraction,thus improving the utilization of sunlight and enhancing the catalytic performance.