Study On The Construction Of High-performance TiO₂ Heterojunction Nanomaterials And Their Photocatalytic Performance

Semiconductor photocatalysis technology,for its advantages of green,environmental protection as well as sustainable development,has received wide attention.Among them,TiO₂ semiconductor materials are widely studied in the field of photocatalysis by virtue of their low price,nontoxicity,and chemical stability,and have been commercially used now.Yet,the performance of this material in photocatalysis still needs to be improved due to its narrow photoresponse range and high photogenerated carrier complexation rate.Among many improvement strategies,the construction of heterojunctions plays an important role in improving the photoresponse range and optimizing carrier transport.In this work,TiO₂ with different microscopic morphologies is used as a substrate to construct heterojunctions by compounding with graphitic carbon nitride（g-C₃N₄）,Ag₂O,and Ag₃PO₄ to investigate the ability of these substances to improve the defects of TiO₂ itself,and then to develop new semiconductor materials with high photocatalytic performance.The main research is divided into three parts as follows.1,We have synthesized P-g-C₃N₄/TiO₂ heterojunction photocatalytic materials with hollow sphere structure by high-temperature calcination and secondary hydrothermal method（P-g-C₃N₄ represents graphitic carbon nitride after protonation）.To obtain highly efficient heterojunction catalytic materials with more uniform surface compounding,we further protonated and ultrasonically exfoliated the prepared g-C₃N₄ before compounding,changed its morphology while retaining its semiconductor properties and optical band gap unchanged,and finally obtained ultrathin nanosheet structures.On this basis,a variety of binary composites with different ratios were synthesized,and an optimum ratio among the two materials was explored by degrading RHB.As a result,the material exhibited the best catalytic activity under the same conditions with the weight ratio of P-g-C₃N₄ to TiO₂ of 0.1.Complete degradation of RHB was achieved at 110 min.Subsequently,to further explore its optical properties,various characterizations were made and a suitable catalytic mechanism of the Z-scheme was proposed for its excellent catalytic performance.2,Several kinds of ternary heterojunction composites with different ratios of TiO₂@g-C₃N₄-Ag/Ag₂O（TCNA）have been prepared by water thermal method,elevated temperature calcination method,ultrasonic exfoliation,and wet chemical precipitation.It was analyzed by several tests such as XRD,SEM,TEM,FT-IR,DRS,and XPS.The prepared multivariate heterojunction catalysts showed excellent photodegradation of RHB under the modified catalytic device,among which TCNA-2 reached 99%degradation at 90 min with a photodegradation rate constant 4.7 times higher than that of TiO₂.In addition,tests to revel the influence of external conditions on the catalytic activity indicated that the activity of the catalyst was significantly inhibited in an acidic environment.Subsequently,the main active substances as well as the stability of the materials involved in catalysis were investigated through scavenger studies and stability tests,and their catalytic mechanisms were discussed.3,The biphasic TiO₂/Ag₃PO₄ nanofiber photocatalytic materials（TPA）with different ratios were prepared by combining with the electrostatic spinning technique and in-situ growth.The morphology,crystal structure,and microscopic composition were characterized by several tests such as SEM,TEM,XPS,and DRS.A systematic experimental study confirmed that the highest photocatalytic activity of the biphasic composite was achieved when the proportion of Ag₃PO₄ and TiO₂ was 2.5:10.The degradation rate of RHB reached 98.6%in 40 min and 80.9%in 90 min for MO.Moreover,we analyzed the main reasons for the high photocatalytic activity in the composite and proposed a rational photocatalytic mechanism based on the associated characterization outcomes.