Preparation And Photocatalysis Of Porous TiB₂-TiC/TiO₂ Heterostructure

With the double intensification of global pollution and crisis of resources,photocatalytic technology has attracted widespread attention for its application in clean energy and wastewater treatment.Finding an environmentally friendly,cost-effective catalytic material has become one of the major research directions of materials science.Porous materials are structural and functional materials widely used in the environment and energy fields.Especially,porous TiB2-TiC composites have the characteristics of corrosion resistance,thermal shock resistance,good stability,and have broad application prospects in filtration and adsorption degradation.By preparing a porous material with a high specific surface area and obtaining a heterostructure with photocatalytic properties on the surface,it is an effective way to increase the photocatalyst efficiency,prolong the service life,and realize the encapsulation of the device agent.In this study,porous TiB2-TiC composites were prepared by photocatalytic degradation of organic dyes and water splitting of hydrogen and hydrogen production.Then,TiB2-TiC/TiO2 and TiB2-TiC/Na2Ti3O7 heterostructures were prepared by using hydrothermal synthesis method using porous TiB2-TiC composites as precursors.It is a new type of three-dimensional porous B and C elements doping material;non-metallic elements are used.Doped and synthesized a variety of TiO2 heterostructure photocatalysts,through the adjustment of composition,morphology and electronic structure to optimize its photocatalytic degradation of organic dye,electrochemical performance and water splitting of hydrogen and oxygen production properties.The main contents include the following aspects:(1)Firstly,porous TiB2-TiC composites were prepared by using Ti and B4C powders as raw materials by using vacuum sintering and laser heating methods.Then,TiB2-TiC/TiO2 heterostructures were prepared using porous TiB2-TiC composites as precursors.After hydrothermal reaction,Na2Ti3O7 was formed.After ion exchange and calcination treatment,the TiO2 was formed.The morphology of the original porous structure still remains,while the nanowires,nanobelts,nanosheets,and nanorods structure that change with different hydrothermal times are presented.The TiB2-TiC/TiO2 heterostructures prepared by two kinds of methods:laser heating and vacuum sintering.Their specific surface areas of TiB2-TiC/TiO2 heterostructures are 24.9 m2·g-1 and 22.1 m2·g-1,respectively.In addition,the growth process of TiO2 nanorods with "sweet roll" shape gradually crosses or joins into nanosheets with the hydrothermal reaction time,and then the nanosheets follow certain rules to curl into nanorods.The formation mechanism is that the bending caused by the excess surface energy and the driving force of the curling process may be the energy asymmetry of both sides of the single-layer nanosheets,resulting in the nanosheets curled into nanorods to compensate for the mechanical tension generated during the change process.(2)Compared with the porous TiB2-TiC composite and P25,the TiB2-TiC/TiO2 heterostructure exhibited significantly excellent photocatalytic activity.After 3 h of irradiation with UV light,MO and RhB are almost entirely decomposed by the TiB2-TiC/TiO2 heterostructures prepared via laser heating method,in which all sides of the nanorod structure are high energy.The high-energy facets of TiB2-TiC/TiO2 heterostructures prepared by laser heating constitute all the side faces,so exposing them to the reagent in a radial and arc surface distribution is the ideal morphology in terms of photoactivity.The electron transfer also slows the recombination of photo-induced charge carriers and prolongs the electron lifetime and provide more active sites for the adsorption and degradation of pollutant molecules,which may be an important reason of the favorable photoactivity of the TiB2-TiC/TiO2 heterostructures.In addition,the TiB2-TiC/Na2Ti3O7 samples prepared by the self-propagation method have a maximum battery capacity of 300 mA·h·g-1,exhibiting good cycle stability and conductivity,and the resistance is 82 ?.The sodium titanate grows on the porous TiB2-TiC with more active sites for the insertion of sodium to make its structure stable,and the network of TiB2-TiC structure greatly enhances the conductivity of sodium titanate and has more pore structure.It also promotes the migration of sodium ions.(3)The co-doped TiO2 heterostructures with boron,carbon,and boron and carbon were prepared by hydrothermal synthesis method.Compared with single-doped samples and pure TiO2,the TiO2-B-C heterostructure with three-dimensional network has more excellent photocatalytic activity,and has the highest degradation rate for CR and MB.There are two-stage heterostructures in the TiO2-B-C sample,the first layer is porous TiB2-TiC composites covered with whiskers of TiO2-B-C in 3D network.The second layer is the TiB2 and TiC scattered sporadically on TiO2-B-C nanobelts.The specific surface area of the TiO2-B-C is greatly increased because of the special heterostructures.Therefore,the electrons can transport into TiB2-TiC with porous structure in 3D networks,and the holes in the TiO2 can participate in photocatalysis under light irradiation as a result of better separation of the photogenerated carriers,which can react with O2 and H2O to form·O2-and-OH and directly oxidize pollutants In addition,without co-catalyst,the photocatalytic hydrogen and oxygen release rate of TiO2-B-C were 191.9 ?mol· h-1·g-1 and 687.8 ?mol· h-l·g-1.The B and C elements in the TiO2 heterostructure plays a key role in promoting the separation of electrons and holes during the photocatalytic water splitting,resulting in a low rate of charge recombination and a high light absorption rate,thereby increasing the photocatalytic activity.In particular,the TiO2-C sample presents the greatest photocatalytic activity,with 54831.0 ?mol· h-1·g-1 photogenerated O2.