Synthesis And Photocatalytic Activity Of Nanostructured TiO₂ And Ag/AgCl-based Photocatalysts

Oriented growth of different crystal facets in anatase TiO₂ can largely improve the separation efficiency of photo-excited charge carriers.In this dissertation,anatase TiO₂ with different nanostructures were synthesized by one-step solvothermal method.The morphologies,structures,compositions,formation processes and photocatalytic properties were investigated.The photocatalytic mechanisms were also analyzed in detail.On the other hand,Ag/AgCl plasmonic photocatalyst has attracted considerable attention due to its excellent photocatalytic activity under visible light irradiation.In this dissertation,Ag/AgCl-based plasmonic photocatalysts were synthesized as well using natural geothermal water as a raw material by a deposition-precipitation method.The visible-light-driven photocatalytic performance and charge separation were carefully discussed.The main contents are as follows:1.Synthesis of mesoporous silica-embedded TiO₂ nanocrystals and their photocatalytic activityMesoporous silica-embedded TiO₂ nanocrystals were successfully synthesized via a solvothermal method using Ti?OC₄H₉?₄ as precursor,acetic acid as solvent and Si?OC₂H₅?₄?TEOS?as stabilizer.When the molar ratio of Si/Ti was 1:5.5,the nanocrystals exhibited rhombic or truncated rhombic morphology and the nanocrystals assembled to form a chain-like structure.The high-energy?001?facets were exposed at the two ends of the truncated rhombic nanocrystals.The maximum photocatalytic activity was obtained on the silica-embedded titania nanoparticles with Si/Ti molar ratio of 5.5,which was 6.7 times that achieved on the pure titania sample.This was mainly attributed to the large surface area,high crystallinity,and exposed high-energy?001?facets.2.Synthesis of anatase TiO₂ mesocrystals along[001]orientation with high photocatalytic activity.Anatase TiO₂ mesocrystals were successfully fabricated by a one-step solvothermal method in the mixed system of Ti?OC₄H₉?₄,Si?OC₂H₅?₄,acetic acid and sodium acetate trihydrate.The as-synthesized anatase TiO₂ mesocrystals showed the spindle-like shape along[001]orientation.The addition of Si?OC₂H₅?₄ and sodium acetate trihydrate promoted the formation of TiO₂ mesocrystals.The anatase TiO₂ mesocrystals showed the excellent photocatalytic activity for the degradation of methylene blue and high hydrogen production rate from photocatalytic water splitting due to the high crystallinity,large surface area and fast spacial separation of photoinduced charge carriers.3.Synthesis of CdS sensitized elongated TiO₂ nanocrystals along[001]oritentation for efficient visible-light photocatalytic hydrogen evolution from water splittingElongated Ti02 nanocrystals along[001]oritentation with stepped?101?surface were prepared by a solvothermal method in the mixed system of Ti?OC₄H₉?₄,Si?OC₂H₅?₄,acetic acid and cadmium acetate dihydrate.Subsquently,CdS sensitized TiO₂ nanocrystals could be obtained by the sulfuration of Cd²⁺.When the molar ratio of Cd/Ti was 0.17,the CdS sensitized TiO₂ nanocrystals had the highest hydrogen production rate of 3.85 mmol·h-1·g-1 with a apparent quantum yield?AQY?of 7.8%,which was attributed to the narrow band gap of CdS and the efficient transfer of photoexcited electrons between CdS nanoparticles and the?101?surfaces of elongated TiO₂ nanocrystals.4.Synthesis of Ag/AgCI@SiO₂ core-shell photocatalyst in natural geothermal water with enhanced photocatalytic activity under visible light irradiationAg/AgCl@SiO₂ core-shell structures were synthesized by a deposition-precipitation method with silver nitrate?AgNO₃?as silver source and geothermal water as chlorine and silica source.The praparation of Ag/AgCl@SiO₂ largely decreased the SiO₂ amount in geothermal water,and the SiO₂ layer could prevent the Ag from oxidation.The Ag/AgCl@SiO₂ samples exhibited excellent photocatalytic performance and stability for the degradation of organic pollutants under visible light irradiation.This work might open up new insights into the application of cheap geothermal water resources and provide new opportunities for the fabrication of visible-light-driven Ag/AgCl-based photocatalyst.5.Synthesis of cube-like Ag/AgCl photocatalysts in natural geothermal water with enhanced photocatalytic activity under visible light irradiationCube-like Ag/AgCl plasmonic photocatalyst was synthesized through a similar deposition-precipitation method by adding an aqueous solution of AgNO₃ into the geothermal water.The cube-like Ag/AgCl with a size of 0.5-0.9 ?m exhibited enhanced visible-light photocatalytic performance for the degradation of methyl orange and 4-chlorophenol.The·O₂-and h+ were the main active species during photocatalytic process.6.Synthesis of ternary Ag₂CO₃/Ag/AgCl photocatalyst in geothermal water with enhanced photocatalytic activity under visible light irradiationTernary Ag₂CO₃/Ag/AgCl photocatalyst was prepared via a precipitation method in geothermal water.The Ag/AgCl nanoparticles were anchored on the surface of polyhedral Ag₂CO₃.The Ag₂CO₃/Ag/AgCl photocatalyst exhibited high photocatalytic performance for the degradation of methylene blue.The holes and ·O₂-were the two main active species in the photocatalytic process.Finally,a possible Z-scheme photocatalytic mechanism of the charge transfer was proposed for the enhanced photocatalytic performance.7.Synthesis of Ag/AgCl/g-C₃N₄ composites in geothermal water with enhanced photocatalytic activity under visible light irradiationNovel Ag/AgCl/g-C₃N₄ composites were synthesized by a simple precipitation method in geothermal water.The formed Ag/AgCl nanoparticles were highly dispersed on the surface of g-C₃N₄.The 50 wt%Ag/AgCl/g-C₃N₄ exhibited the highest photocatalytic activity for the degradation of organic dyes under visible light irradiation.The holes and ·O₂-were the two main active species in the photocatalytic process,and a possible photocatalytic mechanism of the charge transfer was proposed.