Design And Photocatalytic Performance Of Transition Metal Sulfide/three-dimensional Nanoporous Graphene Heterojunctio

As an effective approach for solar energy conversion,photocatalytic hydrogen evolution technique via semiconductor presents excellent application potential in solving energy crisis and environmental optimization.Transition metal sulfides have been overwhelmingly attractive to be explored due to their good visible light utilization capacity,suitable band location and band gap structure.However,unmodified single photocatalyst still has problems such as insufficient intrinsic active sites and rapid recombination of photocarriers,which explicitly limit its photocatalytic activity.Surface modification of photocatalyst or the construction of heterojunction with other three-dimensional nanoporous matrix can be used as effective strategies to overcome the above limitations.In this paper,three-dimensional nanoporous heterojunctions for transition metal sulfides are constructed and shallow defect levels with intrinsic vacancy are introduced to achieve efficient separation of photogenerated carriers.The main research contents are as follows:（1）The internal electric field at the heterointerface promotes the separation and migration of photogenerated carriers by the rational design of interfacial energy level locations.3D bicontinuous nanoporous reduced graphene oxide（np-r GO）is served as a free-standing supporting matrix for the anchorage of Cd S nanoparticles to obtain the highly efficient photocatalysis system for hydrogen production.The bicontinuous internal ligament and open nanopores in 3D nanoporous heterojunction are conducive to multiple reflecting and scattering of the incident light,leading to improved light absorption and utilization capacity.Moreover,the construction of p-n heterojunction with staggered band alignment is achieved in Cd S/np-r GO to accelerate the transport of photo-excited carriers.The constructed Cd S/np-r GO p-n heterojunction achieves a corresponding hydrogen generation rate of 2171.23μmol·g^-1·h^-1,which is 3.6 times in comparison with bare Cd S.DFT calculations also indicate the preferable photocatalytic performance of Cd S/np-r GO could be assigned to the ideal interfacial charge rearrangement on the heterointerface,which optimizes the H*adsorption kinetic energies and leads to a remarkable enhancement of the photocatalytic hydrogen evolution performance.（2）The efficient bidirectional carrier separation can be realized by the anisotropic design of migration paths for photogenerated electrons and holes.S-vacancies riched Zn In₂S₄（V_S-ZIS）nanosheets are integrated on 3D bicontinuous nitrogen-doped nanoporous graphene（N-npG）,forming 3D hierarchical heterostructures with well-matched geometric configuration（V_S-ZIS/N-npG）.The V_S-ZIS/N-npG presents ultrafast interfacial photo-generated holes capture and electron self-trapping behaviors during photocatalysis,which are systematically manifested by in-situ XPS,transient-state SPV（TS-SPV）spectra and femtosecond transient absorption（fs-TA）spectroscopy.Photo-generated electrons are captured by S vacancies in V_S-ZIS efficaciously to participate in hydrogen evolution reaction,while electron-rich N-npG is presented as electron donors to promote interfacial holes neutralization.Efficient visible-light utilization and sufficient active site exposure are guaranteed by well-matched nanoporous heterostructure.The optimized 3D hierarchical heterojunction（V_S-ZIS/N-npG 1.0）exhibits a comparably high hydrogen production speed of 3974.7μmol g^-1h^-1,which is 5.9-fold the V_S-ZIS and 12.6-fold the bare ZIS.