Fabrication And Photocatalytic Performance Of Highly Efficient Stable Metal Photosensitized Semiconductor Composite Materials

With the increasing need for energy and shortage of fossil fuels in the world,there is a growing desire to develop effective strategies for the conversion of solar energy into hydrogen gas,hydrocarbon fuels or other energy forms.The superiority of photocatalysis over this issue has attracted an enormous amount of research efforts.Various semiconductors with large band gaps have been proven to be effective under UV light,such as TiO₂ and SrTiO₃.Nevertheless,UV light only accounts for 4%while visible light occupies 43%of total sunlight energy.So,developing visible-light responsive photocatalysts is of great importance.Though various strategies,including metal-ion and nonmetal doping,have been proposed to extend absorption of semiconductors into visible regions,these approaches generally face the challenges of instability,photocorrosion and fast electron/hole recombination rates.Over the past several years,coinage metal?Au,Ag,Cu?photosensitized semiconductors via their visible-light absorption offer a promising strategy for this issue.Visible-light photocatalysis achieved through coinage metal photosensitization or solely plasmonic metals has found applications in various fields.However,the efficiencies of these composite materials are relatively low,particularly for water splitting which requires relatively high redox potentials.Much efforts have been made from the perspective of reaction environment modulation,cocatalyst optimizing,and morphology manipulation of metal nanoparticles.However,study from the point of promoting the intrinsic driving force has seldom been reported.For gold photosensitization,more and more studies indicate that Au interband transitions?from the d-band to the sp-band?play an important and even critical role particularly in harsh photocatalytic processes.In our previous work,visible-light water oxidation over Au/SrTiO₃ was experimentally demonstrated to be driven by the interband transitions of Au.Therefore,promoting interband transitions is an attractive approach for achieving efficient Au photosensitized semiconductors.As another important coinage metal,Cu attracts less attention than Au in semiconductor photosensitization,which is mainly caused by the easy oxidization of Cu.Nevertheless,the interband transition threshold of Cu?1.9 eV?is much lower than that of Au?2.4 eV?,suggesting that incorporation of Cu potentially enhances the metal interband transitions.Inspired by these,herein,for the first time,an Au–Cu alloy strategy is explored in effective enhancement of visible-light photocatalytic H₂ evolution via promoting metal interband transitions.First,five Au-Cu alloy samples with different Au/Cu molar ratios were prepared through deposition-precipitation method.The XRD and TEM patterns indicated changing Au/Cu molar ratios can effectively control the composition,size distribution and lattice spacing of Au-Cu alloy nanoparticles.Meanwhile,the UV-vis diffusion reflectance spectra of these five samples suggested interband absorption can be effectively enhanced by forming Au–Cu alloys.Subsequently,photocatalytic water splitting under visible light was carried out,Au₃Cu/SrTiO₃ showed the highest visible-light hydrogen evolution activity(29.5?mol·g^-1·h^-1),the rate of which was about one time and three times higher than that of Au/SrTiO₃ and Cu/SrTiO₃,respectively.Meanwhile,the restraint of Cu oxidation in Au-Cu alloys is another key factor for achieving effective metal photosensitization as suggested by XPS analysis.In conclusion,activity enhancement,simulation and the characterization results indicated that incorporation of Cu effectively enhanced the metal interband transitions,and ultimately promoted visible-light photocatalytic H₂ evolution.