Preparation And H₂-evolution Performance Of Cobalt Sulfide Modified Titanium Dioxide Based Photocatalyst

Nowadays,energy crisis and environmental pollution have become two major issues to be solved urgently in the development of human society.Semiconductor photocatalytic materials represented by TiO₂ have unique advantages in the development of clean energy due to their good chemical properties,stability,non-toxicity and low cost.However,researchers have found that the TiO₂ material has a problem of the rapid recombination of photogenerated electron-hole pairs,limited its further commercial applications.There are several strategies to effectively enhance the photocatalytic performance of TiO₂,such as semiconductor coupling,cocatalyst modification,element doping,and dye sensitization.Among them,cocatalyst modification is currently considered as one of the most effective methods of transferring photo-generated electrons.So it is necessary to find a simple method to synthesize a kind of low price and efficient cocatalysts to improve the photocatalytic performance of new-type TiO₂ material.Based on the above definite research purpose,we carried out experimental research work by using titanium dioxide as the main photocatalytic material and amorphous CoS_x as a cocatalyst.The main experimental methods and the final results were summarized as follows:First,the amorphous CoS_x/TiO₂ composite photocatalyst was synthesized by one-step in situ photo-deposition of CoSx on the surface of TiO2 photocatalyst.The results show that the photocatalytic hydrogen evolution performance of amorphous CoSx modified TiO2 photocatalyst is significantly improved.The hydrogen production performance of the composite sample with the optimal mass ratio of 10%amorphous CoS_x/TiO₂ is higher than that of pure TiO₂ by a factor of 16.7 times,indicating that amorphous CoS_x can be used as an efficient cocatalyst to improve the photocatalytic activity of titanium dioxide.Based on the above experimental results,the basic mechanism that amorphous cobalt sulfide enhances the activity of hydrogen production of photocatalytic materials is proposed.Compared with crystalline cobalt sulfide,amorphous cobalt sulfide has more unsaturated S atoms as the efficient active sites to rapidly capture protons from solution,and then promote the direct reduction of H⁺to H₂ by photogenerated electrons.Second,graphene and TiO₂ were first synthesized by hydrothermal method,and then the amorphous cobalt sulphate was successfully modified on rGO-TiO₂ by in situ photo-deposition method to prepare amorphous CoSx/rGO-TiO2 composite material.The results of photocatalytic experiments show that the photocatalytic hydrogen evolution of CoSx/rGO-TiO2?10%?photocatalyst reaches the optimal value(256?mol h^-1),which is higher than that of pure phase TiO₂,rGO-TiO₂,CoS_x/TiO₂?10%?by factors of 58,13 and 2 times,respectively.Based on the above experimental results,the basic mechanism of photocatalytic hydrogen production of the ternary system material is proposed:Amorphous cobalt sulfide as a cocaalyst can provide more active sites for hydrogen production,but its conductivity is poor.Therefore,the introduction of graphene can facilitate the rapid transfer of photogenerated electrons,which can offset the defect of cobalt sulfide.So the synergistic effect of the two cocatalysts effectively inhibits the recombination of photogenerated electrons and holes in the TiO₂ so as to remarkably increase the hydrogen production rate of splitting water.