Fundamental Research On Preparation And Functional Application Of Low-dimensional Hexagonal Boron Nitride

Low-dimensional materials,especially two-dimensional layered materials represented by graphene,have attracted a great deal of interest over the past decades.Different from bulk materials,low-dimensional materials will possess many novel optical,electrical and magnetic properties with the reduction of dimensions,which make them widely applied in electronics,optoelectronics,energy conversion and storage,and thermal electronics.Due to its light weight,large specific surface area,high thermal conductivity,excellent oxidation resistance and chemical inertness,low-dimensional hexagonal boron nitride(h-BN)is considered to be one of the most promising new functional materials in the current low-dimensional material systems,which is expected to be widely used in the fields of high-performance electronic devices,composite materials,energy storage and conversion,etc.In this work,the low-dimensional functional h-BN with different dimensions has been effectively synthesized by designing and developing novel reaction routes.The special dimensional effects of low-dimensional h-BN will give it special physical and chemical properties.Combining the special physical and chemical properties with its intrinsic properties makes it applied in the fields of optics,electricity and adsorption.The main contents and results are listed as follows:(1)An improved ultrasonic assisted solvothermal method using h-BN nanosheets(BNNSs)with 4-8 layers as precursors for effectively preparing h-BN quantum dots(BNQDs)was reported.The size and properties of BNQDs can be tuned by controlling the preparation conditions of their precursors.When the synthesis temperature of precursors is 900?,the precursor displays graphene-like sheet structure,which is more suitable for the preparation of BNQDs.The average size of BNQDs is 4.6 nm.Based on the quantum confinement effect,the photoluminescence(PL)properties of BNQDs were studied.In addition,the temperature-dependent PL of BNQDs was investigated for the first time and its luminescent mechanism was also explored.Meanwhile,BNQDs were used to construct temperature sensors and its potential application in temperature monitoring was discussed.The results show that BNQDs can emit blue-green light under the UV-light and the PL origins from the defect states.There is a good linear relationship between the PL intensity and temperature,indicating the BNQDs can be exploited for temperature sensors.Besides,the BNQDs exhibit excellent photostability and reversibility,which render the as-prepared BNQDs great potential in temperature sensor application.(2)The method of precursor nitridation was adopted to synthesize h-BN fibers at 900? in nitrogen/hydrogen(5%hydrogen)using H3BO3 and C3N6H6 as raw materials.The structural analysis indicates that h-BN fibers exhibit highly-density defects in structure and large specific surface area(964.4 m2/g),indicating h-BN fibers are very promising adsorption materials.Besides,the adsorption performance of h-BN fibers for rhodamine-B(RhB)was investigated.The results show that h-BN fibers exhibit valuable adsorption capacity reaching 210.1 mg/g.From thermodynamic viewpoint,the adsorption process of RhB on h-BN fibers is physisorption,spontaneous and exothermic.In addition,due to its excellent thermal stability,h-BN fibers containing dyes can be regenerated by a simple thermal treatment at 400? for 2 h in air,revealing the h-BN fibers exhibit good regeneration performance.Above results demonstrate h-BN fibers are expected to be widely used in environmental purification.(3)Flake h-BN was synthesized by combining low temperature combustion synthesis and nitridation methods at 900? in NH3 using H3BO3,C6H12O6 H2O,HNO3 and CO(NH2)2 as raw materials.The obtained h-BN is characterized as layered structure with many surface groups(-OH/NH2),large specific surface area(936 m2/g)and pore volume(0.705 cm3/g),which suggests the flake h-BN has been functinalized and its conductivity has been also improved.Meanwhile,due to its unique two-dimensional structure,the electrochemical properties of the flake h-BN were studied.The results show that h-BN modified glassy carbon electrode exhibits excellent electrocatalytic activity and high selectivity for AA,DA and UA.Compared with other electrode materials,flake h-BN exhibit higher sensitivity,wider detection range and lower detection limit,which indicating flake h-BN can be used in the field of electrochemistry.(4)On the basis of(3),due to the large specific surface area and porous structure,the photocatalytic performance of flake h-BN as catalyst TiO2 supporters was investigated.Firstly,the first principle calculations were performed as guides to study the influence of h-BN introducing TiO2 on the band gap of the composites,the change of adsorption energy and charge density during the degradation of RhB.The results show that the introduction of h-BN can bend and upshift the VBM of composites caused by N-P orbits and the band gap is reduced,which further improves the utilization of visible light and the photocatalytic activity.Based on the theoretical analysis,2D/2D h-BN/TiO2 heterostructures were prepared by solvothermal method using glycol as solvents,TiC13 as titanium sources and h-BN as support materials.The effect of the amount of h-BN on the crystal structure and micromorphology of TiO2 was studied.In addition,the photocatalytic properties of h-BN/TiO2 heterostructures were investigated.The effect of h-BN on the photocatalytic enhancement of the composites and the possible photocatalytic mechanism were disscussed.The results show that the morphology and dispersion of TiO2 can be tuned by controlling the amount of flake h-BN,which is favor of the improvement photocatalytic performance.Besides,12 wt%h-BN/TiO2 composites show 3.5 and 6.9 times higher degradation rate than the synthesized TiO2 and commercial TiO2(P25),respectively,and the excellent repeatability and stability are also obtained.