| Energy and environmental issues are two major problems that affect the sustainable development of human beings.Photocatalytic technology based on the utilization of solar energy has pointed out the direction for people to solve the energy problem and eliminate the negative impact on the environment caused by the use of traditional fossil energy.Among them,the use of TiO2 for photo-splitting water for hydrogen production and photo-degradation of harmful pollutants has become the favored object of many scientific researchers.In this paper,TiO2 nanocrystals with exposed(001)and(101)crystal planes and TiO2 nanotubes are used as the basis,and they are modified by noble metals and metal oxides such as Pt、Pd and Au.It is expected to improve the shortcomings of TiO2,such as wide band gap and high carrier recombination rate.Its catalytic performance and reaction mechanism were studied through photo-splitting water for hydrogen production and photoreduction of 4-NP.It is beneficial for the development and application of this type of catalyst.The main contents of this article are as follows:(1)TiO2 nanocrystals(TNC)with exposed(001)and(101)planes were synthesized by hydrothermal method with Ti powder as the titanium source.The noble metals were directionally deposited on the(101)plane of TNC by photoreduction method to obtain M-TNC(M=Pt、Pd、Au)series catalysts.The three catalysts 0.5%-Au-TNC,1%-Pd-TNC and 1%-PtTNC were screened out by photolysis of water for hydrogen production.Using these three catalysts as carriers,and further selectively depositing PbO2 on the(001)crystal plane of TNC by photoreduction method to obtain PbO2-M-TNC(M=Pt、Pd、Au)composite catalyst.The hydrogen production performance of the modified catalyst was significantly improved compared with pure TiO2,which was attributed to the coordinated effect of noble metals and metal oxides with TiO2 crystal planes.(2)P25 was used as the titanium source,a multi-layer coiled TiO2 nanotube(TNT)with a length of about 100-300 nm and a diameter of about 8-12 nm was synthesized by hydrothermal method.Then Au-TiO2 and Pt-TiO2 composite catalyst were synthesized by deposition and precipitation method.Through the characterization results such as spherical aberration electron microscopy,it is found that Au and Pt are uniformly distributed on the surface of TiO2 in the form of single atoms.The experiments of photo-splitting water for hydrogen production and photo-reduction of 4-NP show that such single-atom supported modified catalysts have excellent catalytic performance,and the presence of atomically dispersed metals is indeed beneficial to the adsorption of reaction substrates and their photogenerated electrons and holes separation.At the same time,the single-atom noble metal loading also reduces the production cost of such catalysts,which is beneficial for large-scale synthesis and application in future industries.(3)The CM-TNT(CM=Pd,Ag)catalyst supported by homogeneous metal nanoclusters was synthesized by the molten salt method using the synthesized TNT as the carrier.The characterization results such as TEM show that the metal clusrers are uniformly dispersed on the surface of TiO2.The experimental results of photo-splitting water for hydrogen production and photo-reduction of 4-NPs show that all composite catalysts exhibit excellent photocatalytic performance,which is mainly due to the uniform loading of noble metal nanoclusters enhances more proton reduction sites for the reaction and reduces recombination of electrons and holes.At the same time,the difference in metal loading also has a significant effect on the photocatalytic performance.(4)Combined with catalyst characterization and related experimental results,the catalytic reaction mechanism of photo-splitting water for hydrogen production and reduction of 4-NP is proposed.The modified TiO2 composite catalyst effectively improves the separation efficiency of electrons and holes,increases the reactive sites,and improves the photocatalytic reaction efficiency. |
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