Preparation Of Modified SrTiO₃ And Cd_0.5Zn_0.5S Composites And Their Photocatalytic Properties For Hydrogen Production

With population growth and the gradual depletion of fossil fuels,coupled with environmental issues,it is imperative to look for renewable environmentally friendly clean energy.Hydrogen is the most common element in nature and it is mainly stored in water as a compound.It is estimated that if all of the hydrogen in seawater is extracted,it will generate 9000 times more heat than all the fossil fuels on earth.While 3/4 of the earth is covered by the ocean,hydrogen energy is the best candidate for energy.SrTiO₃ has become a promising photocatalyst due to its unique electronic and optical properties,photochemical stability,lower cost and higher catalytic efficiency.However,due to its wide bandgap（3.2 eV）,it responds only to the UV region,limiting its photocatalytic activity.Therefore,many research efforts are devoted to narrowing the band gap and broadening their spectral counterparts.For example,metal and non-metal doping,forming heterojunction composite materials with other semiconductor materials,introducing defects and the like.In this paper,the sol-gel method was used to synthesize SrTiO₃ with nano-sheet morphology.By using H₂ hydrogenated SrTiO₃（abbreviated as STO）directly and NaBH₄ solid reduced SrTiO₃（abbreviated as STO-T）,a colored SrTiO₃ with surface oxygen vacancies was successfully prepared.SrTiO₃ with oxygen vacancies was hydrothermally synthesized with Cd_0.5Zn_0.5S（abbreviated CZS）to form a composite material.The photocatalytic hydrogen production performance of composites obtained by two methods was compared.Among them,the formation of heterojunction structures of the original Sr TiO₃/CZS and STO/CZS nanocomposites and their photoelectrochemical properties were also compared.HRTEM shows that STO has the core-shell structure of crystalline core and amorphous shell of SrTiO₃@SrTiO_3-x,and surface oxygen vacancies contribute to the formation of good heterojunction structure.X-ray photoelectron spectroscopy（XPS）discloses that S^2-enters the oxygen vacancy on the（110）plane of STO and interacts with the adjacent Ti in the van der Waals force to form the Ti-O-S group,which results in the formation of excellent heterojunctions and makes the CZS nanoparticles growth evenly on the STO nanoplates.Due to the electron trap effect of oxygen vacancies and the synergistic effect of good heterojunction structure,the effective separation of its photogenerated carriers is promoted.For the STO-T/CZS composites obtained by NaBH₄ reduction and hydrothermal treatment,the influence of oxygen vacancy concentration on the photocatalytic activity of the composites was also investigated.STO-325/CZS shows the best photocatalytic activity under visible light.Its photocatalytic rate of hydrogen production can reach 25.008mmol·g^-1·h^-1,which is twice that of pure CZS.In addition,a Cd_x Zn_yNi_1-x-yS solid solution composite was synthesized by a one-step hydrothermal method and its photocatalytic hydrogen production property was explored.Compared with pure CZS,its photocatalytic activity has been significantly improved.The photocatalytic activity of 0.5%CZNS was 25.339 mmol·g^-1·h^-1.