Graphene Oxide Based Z-Scheme Photo-catalyst

Environmental pollution and energy shortages are the major challenges of humanity, and it is also a major issue must be prioritized in the sustainable development strategy of our country. Photocatalyst can efficiently convert solar energy into chemical energy, and split water to acquire clean and renewable Hydrogen energy, which is significant to solve Environmental pollution and energy shortages problem. But Traditional photocatalytic materials can hardly split water into hydrogen and oxygen at the same time. So sacrificial reagents are always used in the photocatalytic reaction to ensure hydrogen production can stably work. The adding of sacrificial reagents improves the cost and also restricts the application of photocatalyst. Especially, graphene offers an excellent mobility of charge carriers at room temperature, exhibits an extremely high theoretical specific surface area. Notably, graphene oxide based semiconductor photocatalysts have attracted extensive attention because of their promising potential for conversion of solar to chemical energy. Using graphene oxide as the conductive medium to interface the H2 and O2 photocatalysts, form a Z-scheme system, and separate the hydrogen production and oxygen production happen in two different photocatalysts. However, graphene can hardly connect with photocatalyst effective. This made the way how photocatalyst load on graphene significant for the enhancement of transfer of charge carriers. To spilt pure water under visible light is still a challenge issue.This paper research synthesis the various Z-scheme systems with graphene oxide in different state, and photocatalyst load on graphene in different way. The main results are showed follows:(1) Cd/GO was synthesized via a simple hydrothermal process. Cd2+ iron and graphene can keep stable in DMF solution, which disperse Cd S particles uniform on graphene oxide sheets. Graphene oxide sheets wrinkles by Cd2+ iron and DMF solution in hydrothermal process, which reduced the Contact resistance between graphene oxide and Cd S nano particles and enhanced the connection between graphene oxide and Cd S nano particles. The enhancement of connection improved the utilization efficiency of photogenerated electrons. The activity of Cd S/GO synthesized in situ approximately 1.3 times higher than Cd S/GO mixed mechanically. The results also showed the activity of Cd S/GO were synthesized at a solution DMF: water is 4:1, and loaded on 5wt% graphene oxide.(2) Cd/GO synthesized by hydrothermal process was mixed respectively with BiVO4,WO3,Ag3PO4 to achieve a Z-scheme system. The photocatalytic activity and performance were characterized by split water to hydrogen and oxygen. The result showed Ag3PO4 has a highest photocatalytic activity, but very unstable. BiVO4 showed a higher photocatalytic activity than WO3. The Z-scheme system used different electron mediators showed very diverse performance activity. Graphene oxide photo catalytically reduced provided a great improvement in the activity for water splitting by efficiently transferring photo excited electrons from the O2 photocatalyst to the H2 photocatalyst. Graphene oxide had a higher degree of reduction while iron electron mediators were add as co- electron mediators. The content of electron mediator had an effect on the activity of Z-scheme system either.(3) Cd S-G core shell structure was synthesized by graphitized the phenolic resin absorbed on Cd S surface. The characteristic and activity of H2 evolution and O2 evolution had researched by compound Cd S-G and BiVO4 to achieve a Z-scheme system. 2-4nm thick graphene were synthesized on Cd S surface. The graphene graphitized in situ proved a continuous flow of electrons between Cd S and graphene. Cd S-G/BiVO4 can split water without any other electron mediator, and showed a more efficient activity for split water to hydrogen and oxygen than Cd S/GO/ BiVO4 with I-/IO3- as co- electron mediator. The graphene synthesized by graphitized the phenolic resin absorbed on Cd S surface had a high degree of graphitization, low concentration of defect, and can transfer electron between Cd S and BiVO4 efficient without a photo-reduced process. This Z-scheme system exhibit a remarkable catalytic stability.