Synthesis, Characterization And Photocatalytic Activity Of TiO₂-based Nanocomposites

Titanium dioxide?TiO₂?attracts extensive attention in the past several decades,due to its high stability,easy preparation,benign environment friendliness,etc.However,TiO₂ shows a wide bandgap?3.0-3.4 eV?so that the absorption is limited to ultra-violet light,resulting in a low utilization of sunlight?-4%?.This issue greatly reduces its values as photocatalysts.Thus,how to modify/construct TiO₂-related composites for superior performance under visible light is desired.In this work,several composites have been synthesized,characterized and examined as photocatalysts for hydrogen evolution under visible light.Compared to TiO₂,these composites exhibit better performances.The underlying mechanisms are proposed based on controlled experiments,transient photocurrent tests,or electrochemical impedance spectra.The main results are listed as follows.1.Self-doping of TiO₂ by Ti³⁺ on gold to improve photocatalytic performances.Here,gold nanorods/nanospheres were used as a scaffold for the coating of oxygen-deficient TiO₂,which was synthesized by a slow hydrolysis and followed with a high-temperature annealing in Ar/H₂.The formation of Ti³⁺ and Ti-OH was verified by XPS spectra.Compared with Au@TiO₂?without thermal treatment?and Au@A-TiO₂?annealed in air?,Au@H-TiO₂?annealed in Ar/H₂?showed higher activity in photocatalytic hydrogen generation and photodegradation of methylene orange.The enhanced performances were attributed to the synergistic effect of Ti³⁺ species,oxygen vacancies and Au,which significantly reduced charge recombination and promoted charge-transfer across the interface.2.MoSe₂ nanosheets supported TiO₂ to improve photocatalytic performances.Here,TiO₂ grown on MoSe₂ nanosheets was synthesized by a simple process and explored as a photocatalyst for hydrogen generation.In visible light,hydrogen generation rate of MoSe₂/TiO₂ was 468.2 ?mol·h-1·g-1,much higher than those of MOSe2,TiO₂ and their mixture.It was believed that the good absorption of MoSe,to visible light and improved charge separation by the interface of MoSe₂/TiO₂ greatly promoted the hydrogen generation rate,as supported by transient photocurrent responses and electrochemical impedance spectra.In different ratios of MoSe₂ and TiO₂,MoSe₂/TiO₂-0.3 showed the best performance.3.Self-doping of TiO₂ or coupling with rGO for MoSe₂/TiO₂,to improve photo-catalytic performances.MoSe₂/H-TiO₂ and MoSe₂/rGO/TiO₂ exhibited the better performances than MoSe₂/TiO₂,not only in photocatalytic hydrogen evolution,but also in electrocatalytic hydrogen evolution.The enhanced performances were attributed to the improved separation efficiency of photogenerated charges and the reduced charge transfer resistance,as evidenced by transient photocurrent response,and electrochemical impedance spectra.4.Growth-doping of Cu in ZnSe quantum rods and their optical properties.Cu-doped ZnSe quantum rods?Cu:ZnSe?were obtained by a growth-doping process.The one-dimensional morphology,small size?diamter?3 nm?,and cubic phase were confirmed by TEM,HRTEM,SAED and XRD analysis.Compared with ZnSe,Cu:ZnSe showed enhanced light absorption and PL efficiency.The reaction process was monitored by UV-Vis absorption spectra and PL spectra,where the absorption peak shifted to the red in the region of visible light.The as-obtained nanorod had a significant quantum size effect with a tunable PL 'peak between 480 to 520 nm.These results offer the opportunities for us to investigate Cu:ZnSe/TiO₂ for photocatalytic reactions.