Preparation of a Coal-Based MoS2/SiO2/GO Composite Catalyst and Its Performance in the Photocatalytic Degradation of Wastewater and Hydrogen Production.

Photocatalytic degradation of wastewater and the simultaneous production of hydrogen (H2) is a green and efficient method to solve energy and environmental problems. In this paper, coal-based SiO2/GO with a stable structure was prepared by a modified Hummers oxidation method, and then, a lotus-shaped composite photocatalyst, MoS2/SiO2/GO, was prepared by in situ loading of flower cluster MoS2 from sodium molybdate reduction onto SiO2/GO. Its photocatalytic degradation of wastewater and H2 production properties were investigated while characterizing the material structure. The results show that SiO2/GO as a carrier not only ensures adequate dispersion of MoS2 but also enhances the visible-light response of the composite catalyst. In addition, it can also hinder the recombination of photogenerated electrons and holes in MoS2 and act as an electron transport channel in composite catalysts. MoS2/SiO2/GO exhibits much higher photocatalytic degradation of wastewater and H2 production capacity than MoS2: after 180 min of reaction, the CODcr removal of wastewater increased from 45.6% for MoS2 to 84.2% for MoS2/SiO2/GO and the H2 yield reached 233.4 µmol. The goal of degrading wastewater while producing H2 more economically has been tentatively achieved, although not to the extent required for industrialization.

Boron nitride nanomaterials for thermal management applications.

Hexagonal boron nitride nanosheets (BNNs) are analogous to their two-dimensional carbon counterparts in many materials properties, in particular, ultrahigh thermal conductivity, but also offer some unique attributes, including being electrically insulating, high thermal stability, chemical and oxidation resistance, low color, and high mechanical strength. Significant recent advances in the production of BNNs, understanding of their properties, and the development of polymeric nanocomposites with BNNs for thermally conductive yet electrically insulating materials and systems are highlighted herein. Major opportunities and challenges for further studies in this rapidly advancing field are also discussed.

Photo-derived fixation of dinitrogen into ammonia at ambient condition with water on ruthenium/coal-based carbon nanosheets.

Photocatalytic synthesis of ammonia is a kind of compelling and challenging nitrogen fixation method. In this paper, we extract the small-sized graphite-like carbon layer in the coal by organic solvent extraction method using HNO3 pretreated coal as a precursor. Then the coal-based carbon nanosheets (CNs) containing with Ca2+, Ti4+, Fe2+, Al3+, Si4+, C, N, O and other metal/non-metal ions was obtained under the assistance of the ultrasonication. The composite catalyst Ru/CNs was prepared by in situ loading the ruthenium (Ru) nanoparticles reduced from RuCl3·3H2O onto the as prepared CNs. The structure was characterized and the photocatalytic nitrogen fixation into ammonia performance under ambient temperature and atmospheric pressure was studied. The results show that the composite catalyst Ru/CNs with uniform dispersion of Ru nanoparticles on CNs has excellent photocatalytic nitrogen fixation activity, and the NH3 yield reaches 221.3 µmol/L after the reaction for 4 h. At the same time, the as prepared catalyst had quite good stability, and the NH3 yield remained substantially unchanged in 5 cycle experiments.

Synthesis and photocatalytic CO2 reduction performance of aminated coal-based carbon nanoparticles.

To obtain high-efficiency, low-cost, environmentally friendly carbon-based photocatalytic material, we synthesized coal-based carbon dots with sp2 carbon structure and multilayer graphene lattice structure by the hydrogen peroxide (H2O2) oxidation method to strip nano-scale crystalline carbon in the coal structure and link with oxygen-containing groups such as the hydroxyl group. N, S co-doped aminated coal-based carbon nanoparticles (NH2-CNPs) were then obtained by thionyl chloride chlorination and ethylenediamine passivation. The physical properties and chemical structure of the synthesized NH2-CNPs were studied and the photocatalytic CO2 reduction performance was tested. The results show that NH2-CNPs are vesicle-type spherical particles with particle size of 42.16 ± 7.5 nm and have a mesoporous structure that is capable of adsorbing CO2. A defect structure was formed on the surface of the NH2-CNPs due to the doping of N and S elements, thereby significantly improving the ability to photogenerate electrons under visible light along with the ability to efficiently separate the photo-generated carriers. The photocatalytic reduction products of CO2 over NH2-CNPs were CH3OH, CO, C2H5OH, H2 and CH4. After 10 hours of reaction, the total amount of products was 807.56 µmol g-1 cat, the amount of CH3OH was 618.7 µmol g-1 cat, and the calculated selectivity for conversion of CO2 to CH3OH was up to 76.6%.

Enhanced Fluorescence Properties of Carbon Dots in Polymer Films.

Carbon dots of small carbon nanoparticles surface-functionalized with 2,2'-(ethylenedioxy)bis(ethylamine) (EDA) were synthesized, and the as-synthesized sample was separated on an aqueous gel column to obtain fractions of the EDA-carbon dots with different fluorescence quantum yields. As already discussed in the literature, the variations in fluorescence performance among the fractions were attributed to the different levels and/or effectiveness of the surface functionalization-passivation in the carbon dots. These fractions, as well as carbon nanoparticles without any deliberate surface functionalization, were dispersed into poly(vinyl alcohol) (PVA) for composite films. In the PVA film matrix, the carbon dots and nanoparticles exhibited much enhanced fluorescence emissions in comparison with their corresponding aqueous solutions. The increased fluorescence quantum yields in the films were determined quantitatively by using a specifically designed and constructed film sample holder in the emission spectrometer. The observed fluorescence decays of the EDA-carbon dots in film and in solution were essentially the same, suggesting that the significant enhancement in fluorescence quantum yields from solution to film is static in nature. Mechanistic implications of the results, including a rationalization in terms of the compression effect on the surface passivation layer (similar to a soft corona) in carbon dots when embedded in the more restrictive film environment resulting in more favorable radiative recombinations of the carbon particle surface-trapped electrons and holes, and also potential technological applications of the brightly fluorescent composite films are highlighted and discussed.

Flexible graphene-graphene composites of superior thermal and electrical transport properties.

Graphene is known for high thermal and electrical conductivities. In the preparation of neat carbon materials based on graphene, a common approach has been the use of well-exfoliated graphene oxides (GOs) as the precursor, followed by conversion to reduced GOs (rGOs). However, rGOs are more suitable for the targeted high electrical conductivity achievable through percolation but considerably less effective in terms of efficient thermal transport dictated by phonon progression. In this work, neat carbon films were fabricated directly from few-layer graphene sheets, avoiding rGOs completely. These essentially graphene-graphene composites were of a metal-like appearance and mechanically flexible, exhibiting superior thermal and electrical transport properties. The observed thermal and electrical conductivities are higher than 220 W/m · K and 85000 S/m, respectively. Some issues in the further development of these mechanically flexible graphene-graphene nanocomposite materials are discussed and so are the associated opportunities.