Preparation And Photocatalytic Activity Of MXene-based Composite Materials

With the development of human industrialization,the excessive use of limited fossil fuels will lead to energy shortage,environmental pollution and abnormal climate change.Therefore,it is necessary to develop an environmentally friendly and sustainable technology to solve these problems.Solar energy is a clean,efficient and renewable new energy source that can be converted into chemical energy by semiconductor photocatalysis,demonstrating great potential for applications in the areas such as decomposing water to produce hydrogen,CO₂ reduction to organic fuels,and degrading organic pollutants.Recently,MXenes similar to graphene with two-dimensional layered materials have been widely used in electrocatalysis,lithium-ion batteries,supercapacitors and electronic devices due to their superior physical and chemical properties.In this paper,we have investigated the factors affecting the preparation process of MXene（Ti₃C₂）nanosheets,which are used to modify two common semiconductor photocatalysts,bismuth tantalate（Bi₃TaO₇）and titanium dioxide（TiO₂）nanofibers to construct 0D/2D Bi₃TaO₇/MXene and 1D/2D TiO₂/MXene composites.Their photocatalytic degradation and photocatalytic hydrogen production performance have further been investigated,respectively,as follows:（1）MXene（Ti₃C₂）samples with a sandwich-like structure were prepared by etching in HF solution using MAX titanium aluminum carbide（Ti₃Al C₂）as the precursor.The MXene was then intercalated by dimethyl sulfoxide（DMSO）and finally exfoliated into Ti₃C₂ nanosheets with few or single layers by ultrasonic exfoliation.The structures and morphologies of Ti₃Al C₂ before etching and multilayer Ti₃C₂ nanosheets after etching were investigated.（2）The 0D/2D Bi₃TaO₇/Ti₃C₂ composite photocatalytic materials were in-situ prepared on the surface of 2D Ti₃C₂ by electrostatic adsorption and solvothermal methods using bismuth nitrate pentahydrate and tantalum pentachloride as the Bi and Ta sources,respectively.The effects of 2D Ti₃C₂ nanosheets on the microstructure of0D/2D Bi₃TaO₇/Ti₃C₂ samples were investigated by various physicochemical characterizations.The photocatalytic properties of the prepared samples were evaluated by visible light degradation of sodium sulfadiazine solution（SD-Na）.The experimental results showed that the photocatalytic performance of the 0D/2D Bi₃TaO₇/Ti₃C₂ composites was significantly enhanced.Under the optimal conditions（Ti₃C₂ to Bi₃TaO₇ mass ratio of 0.02）,the sample BT2 sample exhibited the highest photocatalytic activity for degrading the sodium sulfadiazine solution and the apparent rate constant k value was 2.8 times higher than that of the pure Bi₃TaO₇sample.The significant improvement in the performance of the 0D/2D Bi₃TaO₇/Ti₃C₂composite photocatalytic material was attributed to the formation of heterojunction structure on the interface of the 0D/2D Bi₃TaO₇/Ti₃C₂,resulting in the rapid transfer and separation of photogenerated carriers.（3）The 1D TiO₂ nanofibers were firstly prepared by electrostatic spinning method using tetrabutyl titanate（TBOT）,glacial acetic acid,polyvinylpyrrolidone（PVP）and methanol as precursor materials.And then the mixture containing Ti₃C₂and 1D TiO₂ was calcined under nitrogen atmosphere to obtain the 1D/2D TiO₂/Ti₃C₂composite photocatalytic materials.The effects of 2D Ti₃C₂ nanosheets on the microstructure of 1D/2D TiO₂/Ti₃C₂ composite photocatalytic materials were investigated by various physicochemical characterizations.The photocatalytic hydrogen production performance was evaluated by using triethanolamine as a sacrificial agent under simulated sunlight.The experimental results showed that the addition of Ti₃C₂ significantly promoted the photocatalytic performance of 1D/2D TiO₂/Ti₃C₂ composites.When the mass ratio of Ti₃C₂ to TiO₂ was 0.02,the 1D/2D TiO₂/Ti₃C₂ composite had the highest photocatalytic hydrogen production performance,and the corresponding hydrogen production was 4821μmol·h^-1·g^-1,which was 2.2 times higher than that of pure TiO₂ nanofibers.