Preparation Of CeO₂-based Nanocomposite Materials And Environment And Energy Photocatalytic Applications

Solar-driven photocatalysis as a green and sustainable technology is regarded as one of the most effective ways to address the energy-and environment-related issues.Particularly,the photocatalytic H₂ evolution from water splitting driven by solar energy is highly attractive for converting solar energy to clean and renewable fuel.In this regard,the key lies in the design and synthesis of suitable photocatalysts that can harvest sunlight,facilitate photo-generated charge carrier separation,and thus accelerate surface redox reaction.As a typical rare earth oxide semiconductor material,CeO₂ possesses many excellent physical and chemical properties,including nontoxic,controlled morphology,unique electronic structure and high oxygen storage capacity,thus deeply concerned by the majority of scientists.However,the photocatalytic activity of CeO₂ in the visible-light region is still unsatisfactory due to its large band gap?E_g=2.9 eV?,poor activity,low quantum efficiency,and high recombination rate of photoinduced electro-hole pairs.Hence,it is highly desirable to design and modification of CeO₂ for effectively enhances the photocatalytic activity.In this paper,the highly efficient and stable CeO₂-based nanocomposite materials photocatalyst has been successfully fabricated by appropriate design of hollow sphere structure,doping of exteral element sulfur and modification of sensitized material CdS.The specific research contents are as follows:?1?Shape-dependent CeO₂ nanostructures were successfully fabricated by a facile ethanol?EtOH?assisted hydrothermal method.It was found that the morphology and crystalline structure of CeO₂ can be tuned by simply adjusting the EtOH/H₂O.Moreover,we compared our results with those reported for octahedral and spherial CeO₂ nanoparticles generated using EtOH/H₂O volume ratios of 1:4 and4:1,respectively.Spindle CeO₂ nanoparticles generated using distilled water exhibited a remarkable adsorption capacity for Congo red(162.4 mg g^-1),almost three times higher compared to octahedral CeO₂ and two times higher than spherical CeO₂.The superior adsorption performance mainly attributed to the peculiar structure,large surface and presence of electrostatic interactions between the sample surface and dye molecules.?2?A shape-controlled binary hollow photocatalyst consisting of S-doped CeO₂hollow spheres sensitized with ultrathin CdS shells were successfully synthesized using a simple template-assisted method followed by anion-exchange and chemical bath deposition processes.The core-shelled CeO₂-_xS_x@CdS nanocomposite exhibits superior photocatalytic activity for hydrogen evolution(1147.2?mol g^-1 h^-1)under visible-light illumination,which is 4.4,11.1 and 94.8 times higher than that of CdS(258.2?mol g^-1 h^-1),CeO_2-xS_x(103.0?mol g^-1 h^-1)and CeO₂(12.1?mol g^-1 h^-1),respectively.The superior photocatalytic activity mainly attributed to the following aspects:i)the hollow sphere structure ont only reduce the material resistance but also provide a large surface area and abundant active sites for the adsorption of reactants;ii)the doping of sulfur species into the CeO₂ crystal structure can create oxygen vacancies and reduce the electronic band gap of the semiconductor;iii)the coating of the ultrathin CdS shell not only leads to the sensitization effect but also provides a large surface area and abundant active sites for the adsorption of reactants;iiii)the composite structure of CeO₂-_xS_x@CdS can promote the transfer of photogenerated electrons of CeO₂-_xS_x to the surface of CdS,thus hindering the recombination of the generated electron–hole pairs.