Preparation,Modification And Photoelectrochemical Properties Of TiO₂ Nanocrystal Arrays

The conversion of solar energy into chemical energy based on photocatalytic reaction has attracted increasing attention from scientists,and has shown good application prospects.TiO₂is one of the first semiconductor materials used for photocatalytic hydrogen production.It has a wide range of sources and good chemical stability.However,the forbidden band width of TiO₂is 3.2 e V,and its light absorption range is limited to the ultraviolet light region(only 4%of the total energy of luminescence).Therefore,as a photocatalytic hydrogen production material,TiO₂cannot efficiently utilize solar energy,and its photoelectric efficiency is very low.One-dimensional nanostructured TiO₂has better charge transport performance than TiO₂particulate catalyst,and TiO₂nanorods(TiO₂NRs)arrays have fewer defects and superior photoelectrocatalytic activity.In this paper,the modification of various aspects based on the structure of TiO₂NRs have been studied.The details are as follows:1.Ultrafine titanium dioxide nanocrystalline arrays(TiO₂-F NRs)were prepared by solvothermal method combined with alkaline solution chemical etching.The electrochemical properties of the nanocrystalline arrays(TiO₂-F NRs)were studied by using different etching concentrations and optimal etching concentrations.The morphology,structure and element valence of TiO₂NRs were characterized.The photoelectrochemical properties and electrochemical active areas of TiO₂-F NRs prepared under different etching conditions were compared and analyzed.The results show that alkaline liquid etching can be performed.The TiO₂nanocrystals were effectively refined without causing the destruction of the nanocrystal array structure.The etched TiO₂-F NRs showed higher photocurrent intensity than the as-prepared TiO₂NRs.TiO₂-F(0.025/2h)NRs has photocurrent up to 0.45 m A/cm²,which is five times that of TiO₂NRs.Large electrochemical active areas and charge transport rates are key to improving photoelectrochemical performance.2.Co-doped titanium dioxide nanocrystalline arrays(TiO₂-Co(n)%NRs)were prepared by adding solvothermal method with different molar ratios of cobalt nitrate as cobalt source.The morphology,structure,elemental valence,compositional analysis and elemental distribution after doping by using different concentrations of cobalt nitrate were characterized.The photoelectrochemical properties,light absorption properties and photogenerated electrons of TiO₂-Co(n)%NRs prepared under different concentrations of doping conditions were compared and analyzed.The probability of photogenerated electron and hole recombination shows that the doping can uniformly dope the Co ion in the TiO₂nanocrystal,without forming the Co compounds or second phases.The TiO₂-Co(n)%NRs photocurrent prepared under optimized conditions has the higher photocurrent intensity,which is up to 0.253m A/cm²and equals to 2.5 times that of TiO₂NRs.The main reason for increasing the photoelectrochemical performance is induced by the smaller photogenerated electron and hole recombination probability and higher charge transfer rate,as well as reduced band gap.3.Titanium dioxide nanocrystalline arrays(Co/TiO₂-n NRs)deposited by nano-Co particles were prepared by solvothermal method,and then photo-reduction of different concentrations of cobalt nitrate as cobalt source.The electrochemical properties of the nanoparticles were studied by using different concentrations of cobalt nitrate on TiO₂NRs.The morphology,structure,element valence,composition analysis and element distribution after deposition were characterized.The photoelectrochemical properties,light absorption properties and photogenerated electron and hole recombination of Co/TiO₂-n NRs prepared under different deposition conditions were compared and analyzed.The results show that the deposition can uniformly deposit Co ions on the surface of TiO₂nanocrystals without causing damage to the nanocrystal array structure.The deposited Co/TiO₂-n NRs phase has the higher photocurrent intensity compared with the as-prepared TiO₂NRs,which(Co/TiO₂-40 NRs)equals to 0.206 m A/cm²as 1.1 times that of TiO₂NRs.The smaller photogenerated electron and hole recombination probability and charge transfer rate,as well as the reduction of the band gap,is the main reason leading to the improved photoelectrochemical performance.