Designing And Synthetizing Of Highly Stable Copper Nanoparticle Encapsulated By Carbon Cage And Its Performance Study Via Visible-light Water Splitting H₂ Evolution

With the development of human society,the increasing demand for energy and the shortage of fossil fuels make people eager to find a clean energy.Photocatalytic technology can effectively convert solar energy into hydrogen energy or other forms of chemical energy,so it has significant advantages in solving energy and environmental problems.However,semiconductor photocatalytic materials widely used in traditional research,such as TiO₂ and SrTiO₃,can only utilize 5%of solar energy due to their wide bandgap.Therefore,the visible light response of photocatalyst is very important.In recent years,it has been found that the absorption of light by metal nanoparticles can be used to induce the photocatalytic process（MIP）.This provides a new idea for the development of visible-light responsive photocatalysts,which has gradually become an important direction of visible-light photocatalysis research.In the current research,Au is still the main metal used in metal sensitization,but the high price limits its wide application.At the same time,we found that the main driving force of Au-sensitized semiconductor for photocatalytic water splitting is not the localized surface plasmon resonance（LSPR）,but the interband transition of Au.Compared with Au,Cu nanoparticles have smaller interband transition threshold.Therefore,Cu nanoparticles should have better semiconductor sensitization effect.However,Cu nanoparticles are facing the problem of instability and oxidative deactivation in the catalytic system.Therefore,it is undoubtedly of great significance to solve the stability of Cu nanoparticles while realizing Cu-sensitized semiconductors.With the development of graphene two-dimensional materials,people gradually understand the excellent properties of graphene,and master its preparation methods.In recent studies,there have also emerged some reports of the use of metal-organic frameworks（MOF）pyrolysis at high temperatures to obtain carbon layers to protect transition metal nanoparticles.However,this top-down synthesis inevitably results in carbon deposition on semiconductor materials,and the surface of semiconductor materials is often the surface reaction center of MIP or the adsorption site in the process of thermal catalysis.Therefore,it is necessary to develop a carbon material protection method which can achieve selectively coating and control thickness conveniently.Therefore,in this work,we used chemical vapor deposition（CVD）method to coat Cu nanoparticles supported on SrTiO₃ with thin carbon cages.The selective encapsulation of carbon cages was realized by the catalysis of Cu nanoparticles.In addition,by adjusting different process conditions,we have further realized the regulation of the thickness of carbon cage.The catalyst samples were also characterized by X-ray diffraction（XRD）and transmission electron microscopy（TEM）,which proved that the expected core-shell structure was successfully synthesized.The highest hydrogen evolution rate of 102μmol g^-1 h^-1 was achieved over Cu@C/SrTiO₃ with carbon layer of about 1 nm,and excellent stability was maintained in cyclic and placement oxidation experiments.In addition,to further expand the potential application of this coating strategy,we use the reduction of4-nitrophenol（4-NP）to 4-aminophenol（4-AP）by Na BH₄ as the probe reaction.The coated sample also showed good activity and stability in this reaction,and the reaction rate constant k=0.0068 S^-1 was obtained.After three cycles,there was no significant activity decrease obtained towards the coated sample.X-ray photoelectron spectroscopy（XPS）and Raman spectroscopy（Raman）showed that the presence of graphene carbon layer protects the copper nanoparticles from oxidation during reaction and placement,which makes the catalyst exhibit excellent activity and stability.