Traditional thermally conductive materials are gradually losing their advantages as the electronics industry develops rapidly. Polymers are in urgent need of a material with high thermal conductivity, stable structure, good mechanical properties and oxidation resistance, which makes hexagonal boron nitride (h-BN) an excellent heat transfer filler for polymer composites. Boron nitride nanosheets (BNNS) are monolayers of hexagonal boron nitride, and theoretical studies have shown that BNNS have a higher thermal conductivity than h-BN (up to 400 Wm⁻¹K⁻¹, in-plane). This paper provides a comprehensive review of various methods for preparing BNNS, including mechanical exfoliation, liquid phase sonication exfoliation and chemical vapor deposition (CVD). In addition, various factors affecting the thermal conductivity of BNNS, including grain boundary, grain size and defects, are also discussed. Then, the influence of BNNS as filler on the thermal conductivity of the polymer was further discussed. Finally, this paper summarizes the existing BNNS applications and lists the application scenarios of BNNS in various fields. The purpose of this review is to summarize the previous work and put forward the prospect and future development direction of preparing high thermal conductivity BNNS-included polymer composites, so as to stimulate the research and improvement of new preparation methods for BNNS and promote its practical application as heat transfer materials.

As a new type of dielectric material, the low dielectric constant and corona resistance life of fluorene polyester (FPE) restricts the range of its applications. In order to simultaneously achieve a high dielectric constant and the long corona aging lifetime of FPE, SiO₂ nanoparticles were chosen as additive to prepare FPE-based composite films. The microstructure of the composite film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and small-angle X-ray scattering (SAXS). The dielectric performances of the composites, including the dielectric constant, breakdown strength and corona resistance lifetime, were investigated. The results show that the introduced SiO₂ does not destroy the structure of the FPE molecular chain and that it increases the thickness of the filler-matrix interface. The dielectric constant of SiO₂/FPE composites increased from 3.54 to 7.30 at 1 Hz. Importantly, the corona resistance lifetime increased by about 12 times compared with the pure FPE matrix. In brief, this work shows what possibilities there might be when considering the potential applications of high-strength insulating materials.

First-principle calculations are used to study the electronic structures, electronic and optical properties of pure, phosphorus-doped, aluminum-doped, and co-doped graphene with phosphorus and aluminum. The results show that the band gap of graphene can be effectively opened as the carbon atoms were replaced by P and Al atoms, and a large band gap of 0.45 eV could be opened when the P and Al atoms co-replaced carbon atoms. In addition, the band gap could be also reached 0.40 eV when an Al atom replaces a carbon atom. When P is doped into graphene, the band gap value is only 0.12 eV. For co-doped graphene with phosphorus and aluminum, the lost number of the electrons which are around the aluminum (2.10 e) is smaller than that of the Al-doping graphene (2.27 e). However, the phosphorus atom loses less electrons (0.43 e) than that in P-doping graphene (1.40 e). Furthermore, the optical parameters of pure graphene and several other doped graphene systems were studied, including refractive index, dielectric function and absorption coefficient have been also calculated. These crucial results confirm existence of P, Al and P–Al doping induced in graphene is an effective method in band gap engineering. Our research provides the theoretical foundation of using the chemical doping with heteroatoms approach to improve the electronic and optical performances of graphene, expected to benefit the practical application of graphene in tunable optoelectronic devices.

Research on the effect of alternative doping on the photoelectric properties of boron nitride is still at an early stage. In particular, research on hexagonal boron nitride’s diatomic co-doping is still rarely studied. In this work, first-principles calculations are selected as the main method to investigate the electronic structure and optical properties of different atoms used to dope hexagonal boron nitride (h-BN). The band gap value of intrinsic h-BN is 4.66 eV. The band gap was changed after Cs, Br, and Cs-Br doping. The results show that the band gap is 4.61 eV when the Br atom replaces the N atom, while the band gap of h-BN doped with Cs is 3.52 eV. Additionally, the band gap width can be reduced to a typical narrower band gap width of 3.19 eV when Cs-Br is used for doping. At the same time, the complex dielectric function representing the optical properties is calculated after Cs, Br, and Cs-Br doping. The optical absorption peaks of Cs-Br-doped h-BN are weaker at low-frequency conditions. The optical absorption of h-BN can be modified by Cs doping, Br doping, and Cs-Br co-doping in the near-infrared, visible, or portion of the near-ultraviolet bands, which makes the doped material more suited for photoelectric detectors in the relevant frequency bands.