Cotrolled Synthesis Of Ultrathin Organic Nanosheets For Heterogeneous Catalysis

Since the discovery of graphene,two-dimensional(2D)nanomaterials with atomic or molecular thickness have received broad interest in recent years such as transition-metal dichalcogenides,black phosphorus and noble-metal nanosheets.These 2D nanosheets have unique physicochemical properties compared with their counterparts.However,there still exist several major technical issues that hinder their further development,such as large-scale production and easy to restack.Our research mainly focus on how to solve those problems.On the one hand,we demonstrate a novel intercalation and chemical exfoliation approach to obtain MOF nanosheets from intrinsically layered MOF crystals.This novel strategy relies on the incorporation of a chemically scissable intercalating agent,4,4'-dipyridyl disulfide,into the intrinsically layered MOF crystals through the linker insertion process.The cleavage of predesigned disulfide groups using phosphorus nucleophiles occurs rapidly and,to a certain degree,is capable of controlling the thickness of exfoliated MOF nanosheets.This chemical exfoliation process can proceed efficiently at room temperature to produce ultrathin 2D MOF nanosheets(?1 nm)with-57%overall yield without assistance of the external mechanical force.The obtained ultrathin MOF nanosheets exhibit efficient and far superior heterogeneous photocatalysis performance to the corresponding bulk MOF.On the other hand,we provide a general approach for the exfoliation of CNx(g-C3N4,C2N and Aza-CMP)assisted by mineral acid through the hydrothermal method.The exfoliation route is simple,efficient and inexpensive due to the cyclic utilization of mineral acid.It is worth emphasizing that the developed method is suitable for the exfoliation of carbon nitride with different C/N ratio.Additionally,the as-prepared g-C3N4 nanosheets are used for photocatalytic hydrogen production and shows superior catalytic performance compared with the bulk counterpart.Besides,the increasing global energy crisis and environmental issues caused by the heavy reliance on fossil fuels have stimulated a great interest in developing renewable energy generation and storage systems,such as rechargeable metal-air batteries and regenerative fuel cells.Metal-air batteries which can offer extremely high theoretical energy densities have become a promising technology for future electronic vehicles and other advanced electronic devices.In particular,rechargeable zinc-air batteries are environmental benign,safe and affordable,making them ideal energy sources for various applications.Our research is involved in the synthesis of metal complex and its application in electrocatalysis.Nowadays electrochemical research mainly focus on how to reduce the amount of noble-metal loadings such as Pt and Ru or Ir,and findings in other electrochemical materials to replace precious metals while keeping up the electrochemical activities of electrocatalyst.Among them,it is highly desirable to develop low-cost,efficient and durable catalysts.Usually,there are two strategies for the design of electrocatalyst:1)Heteroatom-doped porous carbons.Theoretical stimulation and experimental data results indicate that electron distribution of carbonous materials would be changed after heteroatoms replace the carbon atoms of hybridization in sp2 in carbon matrix.Heteroatom dopants would also improve the electron donating ability of electrocatalysts and supply more active sites for oxygen absorption and reduction,both of which ultimately boost the catalytic performance of electrocatalysts.2)Carbonous composites with metal oxides,metal nitrides/carbides.Take graphene as an example,it is known that the surface area of graphene is very large and its corresponding structure is stable.If graphene is doped with metal nanoparticals,the composite material would combine both advantages to exhibit more superior catalytic performance of electrocatalysts.Based on these strategies above,we have developed an efficient bifunctional electrocatalyst for both ORR and OER successfully.The bifunctional electrocatalyst could be used to build a three-electrode zinc-air rechargeable battery.Compared with the commercial electrocatalyst(Pt/C or RuO2),the developed electrocatalyst is superior in energy efficiency.Our bifunctional electrocatalyst holds great promise for large scale application of zinc-air battery in future due to its efficient electrochemical performance and its accessible preparation approach from low-cost biological sources.