查看更多>>摘要：? 2022 Elsevier B.V.Based on density functional theory, two novel sp2-hybridized cubic boron nitride (cP128 BN and cP144 BN) structures are proposed. Analysis of phonon spectra, elastic constants and molecular dynamics simulation energy changes at 800 K indicates that cP128 BN and cP144 BN have dynamical stability, mechanical stability and thermodynamic stability. The bulk to shear modulus ratios for cP128 BN and cP144 BN are calculated to be 2.28 and 2.26, and the Poisson's ratios are calculated to be 0.31 and 0.31, respectively, indicating that both novel BN polymorphs are ductile. Compared with the anisotropy of cP128 BN, c-BN, P213 BN and Pm-3n BN in the primary plane, cP144 BN has large anisotropy in the primary planes. Moreover, both cP128 BN and cP144 BN are wide band gap semiconductors, in which cP128 BN has a direct band gap with a band gap of 3.297 eV, and cP144 BN can be regarded as an indirect band gap semiconductor with a band gap of 2.824 eV. Through the design and study of these two novel electronic materials, it can be found that they have good prospects for application in the industry for optoelectronic devices, as well as high temperature, high power and other electronic devices.
查看更多>>摘要：? 2022A SiO2-C composite (SC) was prepared via sol-gel method using industrial raw materials: commercial partially hydrolysed tetraethyl orthosilicate as an ethoxylated silica precursor (ESP) and phenolic-formaldehyde resin as a carbon precursor. The synthesized composite, constituted by a silica network cross-linked with a carbon network, resulted in a material with a sharp pore size distribution (pore size diameter ~ 32 nm) and a high specific surface area (~350 m2/g). In a subsequent step, it was possible to isolate each network: Carbon (C) and Silica (S). In this work, the composite synthesis, and the isolation paths to obtain the individual structures are described. In addition, the composite and the isolated structures were mineralogically and structurally characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (laser of 785 nm = 1.58 eV) (RS), nuclear magnetic resonance (NMR) and thermogravimetric analyses (TGA). The textural characterization was performed by nitrogen adsorption (SBET), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM-EDS). The three materials exhibited properties suitable for applications such as catalysis, immobilization of bioactive molecules and dyes, drug delivery, among others. In particular, the carbonaceous network had a pseudo graphene structure and microdomains of high activity, which would enhance its use as a low-cost material in new green technologies for wastewater treatment and drinking water purification.
查看更多>>摘要：? 2022 Elsevier B.V.Development of high-performance photothermal agent plays a decisive role in photothermal therapy of tumor. Herein, carbon spheres are rapidly synthesized by pyrolysis of pyrogallol-formaldehyde spheres at 400–1000 °C under nitrogen atmosphere. As-prepared carbon spheres exhibit strong absorption in near-infrared region and good photothermal effect. The results reveal that the photothermal conversion efficiency of carbon spheres has a tight association with carbon defects caused by pyrolysis. The carbon defects serve as the nonradiative recombination centers of the excited electrons to promote photothermal conversion efficiency. Strikingly, carbon spheres after calcination at 700 °C exhibit the photothermal conversion efficiency of 54.2% under 808 nm laser irradiation, which is superior to the reported carbon-based photothermal agents. The prepared carbon spheres have good cell biocompatibility and can ablate the tumor tissues in tumor-bearing mice through the conversion of near-infrared laser energy into thermal energy.
查看更多>>摘要：? 2022 Elsevier B.V.The vibrational behaviour of the germanium-vacancy (GeV) in diamond is studied through its photoluminescence spectrum and first-principles modelled partial phonon density of states. The former is measured in a region below 600 cm?1. The latter is calculated for the GeV center in its neutral, charged, and excited state. The photoluminescence spectrum presents a previously unobserved feature at 248 cm?1 in addition to the well-known peak at 365 cm?1. In our calculations, two localized modes, associated with the GeV center and six nearest carbon atoms (GeC6 cluster) are identified. These correspond to one vibration of the Ge ion along with the [111] orientation of the crystal and one perpendicular to this direction. We propose these modes to be assigned to the two features observed in the photoluminescence spectrum. The dependence of the energies of the localized modes on the GeV-center and their manifestation in experimental optical spectra is discussed.
查看更多>>摘要：? 2022Spheroidal carbon particles are touted as excellent additives in lubricants for reduction in friction and wear. Herein 50–100 nm-sized spheroidal carbon soot particles with heliocentric graphitic layers are prepared by controlled decomposition of wasted rubber and subsequent heat-treatment of wasted rubber derived soot. Thermogravimetric analysis showed that the on-set degradation temperature of the soot particles was representative of a material constituted by amorphous and crystalline phases complementing well with x-ray diffraction studies. The soot particles are dispersed in an additive-free base oil (BO), and the soot particles added oil was used as a lubricant. At room temperature, a reduction in coefficient of friction (CoF) and wear scar diameter (WSD) of ~9% and 16.55% were recorded. At a higher temperature of 70 °C, a reduction in CoF and WSD of as high as 48.93% and 28.12% were recorded. Based on the observations, it is theorized that the soot particles acted like nano-bearings between the contacting surfaces producing a rolling effect that efficiently reduced friction and wear concerning the contacting surfaces. Also, the dispersion of soot particles improved the viscosity retention of BO at higher temperatures indicating its multifunctional ability.
查看更多>>摘要：? 2022 Elsevier B.V.We studied the noncovalent interactions of yttrium bisphthalocyanine YPc2 with graphene sheet models with and without topological defects. The density functional theory results obtained for the cluster models containing Stone-Wales defect (SW), isolated pentagon (5) and pyracylene unit (5665) were compared to those for defect-free graphene sheet (G). The optimized geometry for adsorption complexes, bonding strength and some electronic parameters were analyzed. In all cases YPc2 molecule suffers considerable distortion, whose direction and degree depend on a particular model and site of adsorption (‘exo’ and ‘endo’, in the case of conical 5 and 5665 models); also, it is more pronounced for Pc ligand directly contacting graphene surface. In the case of 5_exo and 5665_exo complexes, the bending follows the direction of already existing curvature of Pc ligand, whereas for 5_endo and 5665_endo its direction changed. For G and SW models, the changes in curvature result in almost flat geometry of contacting Pc. The interactions are strong for all the noncovalent complexes analyzed, increasing in the following order: 5665_endo <5665_exo < 5_exo < 5_endo < G < SW. The plots of HOMO, LUMO and spin density are analyzed, as well as the changes in HOMO-LUMO gap energy.
查看更多>>摘要：? 2022 Elsevier B.V.The presence of defects has a significant effect on the mechanical and vibrational properties of carbon nanotubes (CNTs) and graphene. The vibrational properties of single-layered graphene sheets (SLGS) and single-wall carbon nanotubes (SWCNT) have been investigated in this research. Molecular dynamics simulations have been conducted on pristine and defective zigzag and armchair CNTs, with clamped-free (C-F) boundary conditions as well as pristine and defective armchair graphene sheets with different boundary conditions to investigate the effect of various parameters such as chirality, aspect ratio, boundary conditions, and types and number of defects on the longitudinal and transverse vibrational behavior of CNTs and graphene sheets. It was observed that for the cantilever boundary condition, shorter tubes give better vibrational sensitivity as compared to the larger ones for a constant diameter of the tube. The chirality has not a considerable effect on the natural frequency of CNTs. Regarding graphene sheets, it was observed that increasing the size of the graphene sheet decreased the fundamental natural frequency of SLGS. As compared to Stone-Wales defects, the vacancy defects were found to have more impact on the degradation of the natural frequency of CNTs and GS.
查看更多>>摘要：? 2022 Elsevier B.V.A lot of humidity sensors cannot accurately measure humidity of air containing NH3 gas due to reaction of NH3 gas with sensor materials. A guanidyl group is a strong hydrophilic group, moreover, guanidyl groups do not adsorb NH3 molecules via hydrogen or chemical bonds. In this paper, moroxydine moieties were grafted on surfaces of graphene oxide (GO) materials to synthesize N-[4-morpholinecarboximidamidoyl]carboximidamidoylated graphene oxide (MCGO) for fabricating humidity sensors. When RH increased from 11% to 95%, impedance value of the sensor decreased from 5.41 × 108 to 2.25 × 104 Ω at testing frequency 100 Hz. The change of impedance was much higher than that fabricated by GO. The sensors also exhibited short response/recovery time (2 s/20 s). Their good humidity sensing properties would be attributed to the fact that those N atoms in guanidyl groups at moroxydine moieties on the surfaces MCGO may strong interact with H atom in H2O molecules to form intermolecular hydrogen bonds and generate OH? ions to increase ionic conductivities. The impedance change of the humidity sensor at a low or high relative humidity was due to electronic or ionic conductivities, respectively.
查看更多>>摘要：? 2022 Elsevier B.V.Nowadays, high-performance electromagnetic wave (EMW) absorption materials derived from low-cost biomass materials have attracted widespread attention. Herein, a novel biomass?carbon with porous array structures derived from waste soybean dregs is prepared by a hydrothermal method combined with heat treatment using formaldehyde and KOH as activators. The as-prepared biomass?carbon with significantly enhanced specific surface area can possess more charge transmission paths, increased multiple reflections and scattering, multiple loss modes, and improved impedance matching, leading to the improvement of EMW absorption performances. The obtained single-component biomass?carbon without any functional fillers exhibits an effective EMW absorption capability with a wide absorption bandwidth of 4.8 GHz at a thickness of 3.5 mm. This study will provide a valuable approach for the preparation of biomass?carbon based EMW absorption materials with controllable porous structures by the activation process.
查看更多>>摘要：? 2022In this study, the electronic structure and thermodynamic parameters of titanium doping at different locations of carbon nanotubes (6-6) have been investigated using density functional theory computational methods. The Ti prefers to be located near to vertex of the nanotube sidewall and at the central axis and leads to better structural stability and thermodynamic parameters than other sites. Then, the most stable and active structure for carbon monoxide adsorption was examined from two directions of oxygen and carbon atom, which is accompanied by hybridization and spatial repulsion. The results obtained from the energy level of the highest occupied HOMO orbital and the lowest occupied LUMO one and also NBO analysis indicated that the electron-accepting titanium metal (Mulliken charge for titanium atom above 0.5) has an empty orbital. Carbon monoxide gas is a donor of electron pairs. The adsorption of carbon monoxide from the oxygen atom side in the vertical state (IVA) on the surface of the nanotube doped with titanium was found to be the best.
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