| Due to their excellent properties,boron nitride nanosheets are widely applied in many fields,such as detectors,sensors,electronic devices and energy storage.Among these methods for the preparation of boron nitride nanosheets,the liquid phase exfoliation method is considered to be one of the most effective methods for the mass production of boron nitride.However,for this method,the exfoliation yield is still low,and the layers number of the nanosheets is difficult to control.Therefore,the development of a low-cost,large-scale and high-quality liquid-phase method for the preparation of boron nitride nanosheets remains a challenge.In viewe of the current problems,we have studied the liquid phase exfoliation of boron nitride nanosheets in pure organic solvents,organic solvent-water mixed solvents and organic electrolyte solutions.The main research contents are as follows:?1?The boron nitride nanosheets were prepared by liquid phase ultrasonic exfoliation method in different organic solvents,such as TMU,NMP,IPA,EtOH and DMF.The morphology,structure and thickness of boron nitride nanosheets were characterized by TEM,SEM,Raman,AFM and other means.It was found that the exfoliated boron nitride nanosheets are hexagonal,and more than 90%of boron nitride nanosheets were 1-4 layers nanosheets.The effect of solvent on the exfoliation efficiency is determined by many properties of the solvent.?2?Five organic solvent/water mixed solvents were developed to the exfoliation of boron nitride nanosheets by liquid phase method.It is shown that the concentration of the dispersion prepared in TMU/H2O?7:3?and NMP/H2O?8:2?mixed solvents is 2.9 and 3.6 times higher than that in pure solvent,respectively.89%of the nanosheetse prepared in a TMU/H2O?7:3?mixed solvent are few layers,while93%of the nanosheets prepared in a NMP/H2O?8:2?mixed solvent are few layers.Their lateral dimensions are 20-30nm.Moreover,the mechanism research suggested that formed aggregates?TMU·3H2O?n and?NMP·2H2O?n,are decisive factors in the liquid phase exfoliation of boron nitride.?3?Boron nitride nanosheets are prepared by liquid phase exfoliation in organic electrolyte solutions where N-methyl-pyrrolidinone is used as an organic solvent,and disodium edetate?EDTA?,sodium tartrate?SDTT?,sodium citrate?SDCT?,sodium pyrophosphate,sodium potassium tartrate and ammonium oxalate as intercalate agents.The results shwon that the concentration of boron nitride nanosheets dispersion prepared in organic electrolyte solutions assisted with intercalation agents EDTA,SDCT and SDTT was 1.8,1.08 and 0.56 mg/ml,and the corresponding yields were 15,9 and 4.7%,respectively.Compared with pure NMP,the concentration of the dispersion was increased by 35,21 and10 times,and the yield was increased by 36.5,21.5 and10.8 times,respectively.The boron nitride nanosheets have high purity,and integrated crystal structure.The layer of boron nitride nanosheets is mainly concentrated in 1-4 layers.The Lewis acid-base theory was used to explain the mechanism of boron nitride nanosheet exfoliation.The results shown that the alkalinity of the anion and the size of the cation in salts have directe affect on the concentration of the dispersion and the yield. |
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