Studies On The Preparation,Compositing And Properties Of BCN Nanosheets

Boron carbon nitride(BCN)nanosheets have been gaining increasing attention as a novel semiconductor because of their controllable band-gap and good stability property.This work focuses on the preparation and the properties of BCN nanosheets.We present seveal facile methods for preparing BCN nanosheets and the corresponding morphology and chemical structure are well analyzed.We find that BCN nanosheets have great application prospect in dilute magnetic semiconductor,photocatalysis,nonlinear optical and supercapacitor.The concrete research content is as follows:(1)Na intercalation method for the preparation of BCN nanosheets with ferromagnetismThe mixture of graphene and h-BN nanosheets(BNNSs)can be exfoliated using Na intercalation method.The overlapped graphene and BNNSs are used to prepare BCN nanosheets under a calcination process.BCN nanosheets are obtained after the C elements into the lattices of BNNSs.The proposed method features mild reaction conditions,brief reaction steps,relatively high yield and low cost.The as-prepared BCN nanosheets possess not only favourable 2D structures but also adjustable C content.The BCN nanosheets have an even morphology,and are almost transparent,indicating their ultrathin nature.The thickness of BCN nanosheets is?3 nm.It is noteworthy that the electronic states induced by C in BCN nanosheets are spin-polarized.Owing to the novel atomic arrangement and electron characteristics of BCN nanosheets,the intensive ferromagnetism(FM)emerges.No trace of FM behavior was observed in the BNNSs and graphene.However,the maximum saturation magnetizations of BCN nanosheets can be up to 0.134 emu/g at 300 K and 0.3 emu/g at 5 K,and the Curie temperature reached 463K.In addition,the BCN nanosheets can keep alignment in polymer under an imposed magnetic field.These results not only open up new possibilities for the manipulation of FM in metal-free nanomaterials but also provide a new candidate for optoelectronic devices.(2)Substitution method for the preparation of BCN nanosheets with nonlinear optical performancesBCN nanosheets were synthesised by substituting C atoms into the lattice of BNNSs.This work is inspired by the thermolability of 2D graphene and BNNSs at high temperatures.Compared with the above Na intercalation method,the proposed method features mild reaction conditions,brief reaction steps,relatively high yield and low cost.The as-prepared BCN nanosheets possess not only favourable 2D structures but also adjustable C content.BCN nanosheets show enhanced NLO properties as a result of the introduction of C atoms.After irradiation by laser pulses under 1064 and 532 nm,the as-obtained BCN nanosheets exhibit excellent nonlinear optical(NLO)performance.The NLO absorption properties of the nanosheets shift from saturable absorption to reverse saturable absorption.The corresponding NLO performance can be adjusted by controlling the carbon content in the BCN nanosheets.The developed BCN nanosheets can be utilised as a new and advanced NLO material for sensitive optical components and laser protection.(3)Solid-phase synthesis method for the preparation of BCN nanosheets with supercapacitor applicationsTo further improve the C concentration in BCN nanosheets,we use a solid-phase synthesis method to prepare BCN nanosheets.Using this method,we find that porous BCN nanosheets with 60 at%C concentration can be obtained.The porous BCN nanosheets have nice crystal structure and ultrathin thickness less than 2 nm.Based on the excellent electrical conductivity and huge specific surface area,the porous BCN nanosheets are suitable for supercapacitor applications.We make the BCN nanosheets as working electrode,and measure the capacitance with a 3-electrode system.BCN nanosheets show a specifc capacitance of 407 F/g at 0.1 A/g.This result shows the BCN nanosheets can act as a new kind of supercapacitor materials,and have wide application prospect.(4)Photocatalytic performances of BCN nanosheets,0D/2D CdS/BCN nanocomposites and 0D/2D CdS/MoS2 nanocompositesThe substitutional occupation of C dopants,as revealed by X-ray absorption spectrum,in BCN nanosheets induce tunable band gap reduction.Using the XPS and Mulder schottky curve results,we find that the BCN nanosheets can be used as a new kind of photocatalytic materials.The photocatalytic performances of BCN nanosheets are studied and the rate of H2 evolution can be up to 400 ?mol h-1 g-1 when using Pt as co-catalyst.Except for the photocatalytic performances of BCN nanosheets,the 0D/2D CdS/BCN nanocomposites also show excellent photocatalytic performances.The in-situ growth method was conducted to prepare 0D/2D CdS/BCN nanocomposites.The photocatalytic performance of the nanocomposites was studied comparing with pure CdS nanoparticles,and the results showed that BCN nanosheets played an important role in improving the photocatalytic performance.Under optimum conditions,the rate of H2 evolution can be up to 2.39 mmol h-1 g-1.During the experimental process,it is found that the barriers about electronic transport still exist between CdS nanoparticles and BCN nanosheets.This is not conducive to the photocatalytic performance.Based on this point,MoS2 nanosheets were used to displace BCN nanosheets and novel 0D/2D CdS/MoS2 nanocomposites were fabricated.The photocatalytic results showed that the H2 evolution rate of 0D/2D CdS/MoS2 nanocomposites can be up to 35.6 mmol h-1 g-1.Besides,the evolution of hydrogen presents no notable activity losses for up to 400 h.