查看更多>>摘要：? 2022Mecury(II) ions (Hg2+) detection based on fluorescence quenching of quantum dots is a research hotspot, however, the underlying physical mechanisms leading to their highly efficient quenching remains a mystery. Here, the fluorescence quenching mechanism of the colloidal carbon dots (CDs) by Hg2+ is studied using experiments and time-dependent density functional theory calculations. The results reveal that Hg2+ is attracted by the polarized fluorophores on the CD surface due to the strong attraction force between them. As a result, there arises a Hg2+-dominated unoccupied electron orbital lying below the HOMO of CD by 0.17 eV, which induces efficient electron transfer from HOMO to it and results in formation of charged and slightly separated CD+ and Hg+. This electron transfer along with diminished quantum transition rate accounts for the observed strong fluorescence quenching. These findings highly improve our understanding of the quenching mechanisms of metal ion in solution.
查看更多>>摘要：? 2022This work explains the synergistic effects of graphene nanosheets (GNS) and functionalized nanodiamonds (FNDs) on the pitch derived carbon foam (CF) composite to improve its electrical, mechanical, and thermal properties. Two different types of (1, 2 and 4 wt%) CF/GNS and CF/GNS-FNDs hybrid composites were prepared via pretreatment, foaming, carbonization and graphitization from coal tar pitches. The additive role of GNS and FNDs was studied by varying their amounts in CF matrix. The structure and morphological investigations of the composite reveal that pore size and cellular structure are significantly improved with the addition of additives amount. Moreover, electrical, mechanical and thermal properties of CF/GNS-FNDs hybrid composites are much higher than CF/GNS and pure CFs. Maximum in-plane electrical (20.20 × 103 Sm?1) and thermal (29.95 W m?1 K?1 at 800 °C) conductivities were revealed by 4 wt% CF/GNS-FND hybrid composite. Similarly, optimum values of 19.22 and 46.08 MPa of compressive strength and Young's modulus were represented by 2 wt% CF/GNS-FND hybrid composites which effectively suggests the role and importance of FNDs in the CF composites.
查看更多>>摘要：? 2022The reduction of nitroaromatics to corresponding anilines in the presence of the metal catalyst is an important and useful synthetic way in various applications. Silver nanoparticles have recently attained very interest as effective catalysts in the reduction of nitroaromatics by NaBH4. In this study, in situ sulfur-doped graphitic carbon nitride, exhibited as S-g-C3N4, was prepared, employing thiourea as an inexpensive precursor via a simple thermal method and applied as ideal catalyst support. Ag nanoparticles were stabilized on magnetic S-g-C3N4 modified with starch (S-g-C3N4/starch-Fe3O4-Ag). Several spectroscopic and microscopic methods approved the formation of S-g-C3N4/starch-Fe3O4-Ag nanocatalyst and the results have been well interpreted in this context. S-g-C3N4/starch-Fe3O4-Ag presented a good catalytic activity for the reduction of aromatic compounds bearing the nitro group when NaBH4 was employed as the reductive agent. The reduction efficiency of 4-nitroaniline in an aqueous medium was obtained at 99% in the presence of 5 mg of catalyst at 50 °C for 90 min. This prepared nanocatalyst's good catalytic potency and stability can be attributed to the synergistic interaction between very dispersed Ag nanoparticles and support.
查看更多>>摘要：? 2022 Elsevier B.V.Carbon nanofibers (CNFs) with high specific surface area and flexible lap structure are highly desirable for numerous applications such as adsorption films, supercapacitors, heat dissipation elements, and composites. In this work, CNFs were prepared using two major categories of pitches, isotropic pitch (IP) and mesophase pitch (MP), as raw materials to compare their molecular structure effects on the morphology and properties of CNFs. The analysis of scanning electron microscopy results found that some fusions among nanofibers easily formed in IP-derived electrospun nanofibers (IP-SNFs) while an independent and smooth nanofiber morphology were observed in MP-derived electrospun nanofibers (MP-SNFs). Besides, composed of high aromatic molecules content and appropriate aliphatic components, MP-SNFs showed a mitigating exothermic reaction and MP-CNFs exhibited higher specific surface area, conductivity and thermal diffusion coefficient. While with too abundant aliphatic components in IP, there was a violent exothermic reaction of IP-SNFs during the stabilization process, endowing the corresponding IP-CNFs with poor performances. Therefore, thermal behavior of SNFs varied with the molecular structure differences of IP and MP, which had a significant influence on the microstructure and properties of their CNFs.
查看更多>>摘要：? 2022 Elsevier B.V.The use of renewable and environmentally friendly biomass to prepare carbon materials with a hierarchical porous structure and large specific surface area has attracted great attention in energy storage devices (Supercapacitors, SCs). Here, a succulent-leaf-derived carbon material with a hierarchical porous structure (N-S-HPC) was prepared through a one-step carbonization strategy using Mg(NO3)2·6H2O and ZnCl2 as double activation agents and CH4N2S as S and N source. The N-S-HPC specific capacitance reached 455.3 F g?1 at 1 A g?1, and with 1 M Na2SO4 electrolyte. The assembled N-S-HPC//N-S-HPC symmetric SCs could enhance the voltage window to 1.8 V. Meanwhile, N-S-HPC exhibited the specific energy of 19.89 Wh kg?1 (450 W kg?1) and highly stable cycling performance. Compared with previously reported biomass-derived carbon materials, N-S-HPC has the advantages of i) hierarchical porous sturcture and 2136.2 m2 g?1 maximal specific surface area, allowing accommodation of more ions; ii) 1177.5 m2 g?1 specific surface area for mesopores and macropores, providing shorter diffusion pathways; iii) rich co-doping of N (9.5 at.%) and S (2.21 at. %), increasing pseudocapacitive contribution and improving surface wettability. All these data indictae the great potential application prospect of N-S-HPC, suggesting the importance of biomass-derived carbon materials for symmetric SCs.
查看更多>>摘要：? 2022 Elsevier B.V.This work reports on deoxygenation thermokinetics involved in preparing freestanding deoxygenated graphene oxide paper (DGOP) and the degree of deoxygenation-electrical transport correlation. The differential scanning calorimetry (DSC) and thermomechanical analyzer (TMA) for dimensional change study revealed that the manifestation of graphene oxide paper (GOP) into DGOP is associated with the activation energy of 153.8 kJ/mol with releasing gaseous moieties in the range of 210–230 °C. With variation in deoxygenation temperature ranging from 50 to 250 °C, DGOP is altered from dark brown to black, indicating the thermal reduction of DGOP. Upon increasing the annealing temperature, the hydrophobicity and electrical conductivity of DGOP are significantly increased. DGOP-250 exhibited superhydrophobicity and electrical conductivity of 102.2° and 4.5 S/cm, respectively. Understanding the underlying controlled-thermokinetics in converting GOP into DGOP with DSC and TMA helps in fine-tuning the structural modification associated electrical transport and hydrophobicity, which is desirable for practical applications.
查看更多>>摘要：? 2022 Elsevier B.V.The current study investigates the intercalation of the alkaline metal Sr atom in the AB stacked bilayer graphene system and their effect on the structural, electronic and optical properties using density functional theory (DFT) calculations. The results indicate that the intercalated structure crystallizes in the hexagonal system with the SrC6 structure type, and it is energetically more stable than the pure structure. The electronic behavior of AB stacked bilayer graphene is semi-metallic. In contrast, the behavior of the Sr-intercalated AB stacked bilayer graphene changes to metallic with a Dirac point is located about 1.33 eV under the Fermi level. Optical properties have been calculated under electric fields polarized both parallel and perpendicular to the z-axis. The calculated optical properties show the anisotropic behavior for the dielectric function, absorption coefficient, refractive and extinction coefficients. After the intercalation of the Sr atom, the static refractive index increase in the perpendicular polarization. In addition, the photoluminescence phenomenon was assured for the pure and intercalated bilayer graphene. The research results provide a basis for developing graphene intercalation compounds in optoelectronic nanodevices.
查看更多>>摘要：? 2022 Elsevier B.V.Determining and controlling the mechanical response of carbon nanomaterials under different physical and chemical conditions is a crucial challenge for their implementation in new nanotechnologies. In this sense, knowing and comparing the mechanical properties between carbon nanomaterials, such as the stretching bond force constant (Kr), contributes to its early technological implementation as specific nanosensors. Therefore, the average values for equilibrium bond length (Lr) and Kr of 0-, 1-, 2-, and 3-dimensional carbon nanostructures, spanning from sp to sp3 hybridization were calculated and analyzed under density functional theory (DFT) framework, leaving for first time to determine the effect and differences between Lr and Kr due to the dimensionality and hybridization type. Furthermore, DFT calculations suggest a range of allowable Kr values for carbon nanomaterials, delimited by the diamond and linear carbon chain values.
查看更多>>摘要：? 2022Fluorination of the silicon terminated (100) diamond surface under ultra-high vacuum using a molecular fluorine source (C60F48) is investigated with a combination of high resolution photoelectron spectroscopy and low energy electron diffraction. The C60F48 fluorinates the dangling bonds of the silicon-termination on contact, resulting in an inhomogeneous fluorine termination, which remains when the C60F48 is removed by a 550 °C anneal. Despite removing approximately 50% of the surface silicon in the process, the two domain (3 × 1) surface symmetry of the silicon-terminated (100) surface is retained. When exposed to ambient conditions, while some fluorine is displaced by atmosphere exposure, partial fluorination remains. While further optimsation of this process is required for fluorinating diamond in cases where homogeniety and minimised surface damage are desirable, this work demonstrates the potential of the silicon-terminated (100) diamond surface for enabling engineering of the surface properties of diamond.
查看更多>>摘要：? 2022The effect of H+ implantation and annealing of diamond (100) monocrystalline substrates has been studied by ToF-SIMS, cathodoluminescence, transmission spectroscopy and TEM. Blistering conditions suitable for the Smart Cut? technology have been identified in monocrystalline diamond, using two sets of hydrogen implantation and annealing. A first hydrogen implantation followed by a first annealing leads to amorphization of a buried layer without hydrogen exodiffusion. Blisters and exfoliations appear at the surface of the diamond samples, after a second hydrogen implantation inside the pre-amorphized diamond layer and a final annealing, as evidenced by TEM and optical microscopy. Demonstration of hydrogen-induced blistering is a major step to adapt the Smart Cut? process on diamond material. This process is compatible with wafer bonding before the second annealing and therefore open the way for thin diamond layer transfer on a bonded receiver wafer, still not achieved to date.
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