Liquid Exfoliation Of Two-dimensional Materials(Borophene And Halides Nanosheets) And Their Properties

Since the discovery of graphene in 2004,research on two-dimensional(2D)nanomaterials has been made explosive progress.Researchers can control the structures and properties of two-dimensional nanosheets through different synthetic methods,which can be widely used in electronics,photonics,energy storage,drug delivery and barrier coating.However,the two-dimensional materials that have been experimentally studied so far are still very limited(less than 100),and theoretical calculations show that there are more than 2,000 layered compounds with weak Van der Waals forces between layers that can be exfoliated.Different two-dimensional nanomaterials may have some unique physical and chemical properties which are expected to be applied in various fields.In addition,quality control,large-scale preparation,and long-term stability of two-dimensional materials are still difficult to be solved.This project is dedicated to find efficient dispersion systems in order to prepare a large number of stable two-dimensional nanosheets.The research substances are divided into the following two parts:(1)Boron nanosheets were prepared by sonication-assisted liquid phase exfoliation,and the effects of different exfoliation conditions were discussed.A series of characterizations were carried out to investigate their properties,and it was applied as catalyst to electrochemical reduction of nitrogen.(2)Preparation of two-dimensional lead iodide nanosheets by sonication-assisted liquid phase exfoliation.The stripping mechanism and influencing factors were studied.Finally,we characterized the properties of PbI2 nanosheets which was expected to be applied to optical devices such as Q-switches and mode lockers.The content of this paper as follows:(1)Two-dimensional boron nanosheets were exfoliated by using 21 different solvents and 6 unexplored organic molecules afforded more efficient exfoliation.In particular,benzyl benzoate has a significantly higher exfoliating capability than the others.The average thickness of boron nanosheets was 7.5 nm and the highest concentration was 0.2 mg mL-1.The stabilities of boron nanosheets in benzyl benzoate can last for at least 30 days.(2)Two-dimensional boron nanosheets exhibit excellent electrochemical reduction of nitrogen.The maximum NH3 yield is 3.12 μg h-1 mg-1 cat,and the NH3 Faraday efficiency is 4.84%,which is twice and nearly four times of bulk boron.This is because(021)and(003)facets which are removed in the exfoliation process are less active in nitrogen reduction performance.(3)It was found that cyclopentanone had a good effect on exfoliation two-dimensional lead iodide nanosheets.The exfoliation kinetics accorded with the pseudo first-order kinetic equation.In cyclopentanone,lead iodide nanosheets are stable for at least six hundred hours and have no significant settling at low temperatures.(4)The PbI2 nanosheets exhibited excellent saturable absorption properties both at 515 fs pulse and 532 ns pulse excitations in the visible region.