Mingbo Wu

Cu–N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon Dots

The broadband light-absorption ability of carbon dots (CDs) has inspired their application in photocatalysis, however this has been impeded by poor electron transfer inside the CDs. Herein, we report the preparation of Cu-N-doped CDs (Cu-CDs) and investigate both the doping-promoted electron transfer and the performance of the CDs in photooxidation reactions. The Cu-N doping was achieved through a one-step pyrolytic synthesis of CDs with Na2 [Cu(EDTA)] as precursor. As confirmed by ESR, FTIR, and X-ray photoelectron spectroscopies, the Cu species chelates with the carbon matrix through Cu-N complexes. As a result of the Cu-N doping, the electron-accepting and -donating abilities were enhanced 2.5 and 1.5 times, and the electric conductivity was also increased to 171.8 μs cm(-1) . As a result of these enhanced properties, the photocatalytic efficiency of CDs in the photooxidation reaction of 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate is improved 3.5-fold after CD doping.

Graphene enhanced carbon-coated tin dioxide nanoparticles for lithium-ion secondary batteries

A one-step, scalable method has been developed to prepare SnO2 based carbon materials. Their performances as anodes for lithium-ion batteries can be improved through simultaneous growth of SnO2 nanoparticles, a carbonaceous polymer coating and “doping” of graphene oxide (GO) by thermal treatment. Detailed characterization of the resulting composite materials using transmission electron microscopy and X-ray diffraction suggests that “doping” a certain amount of GO could clearly change the crystallinity and distribution of SnO2 nanoparticles in the mixture. The SnO2 based carbon material exhibits a stable reversible capacity of 720 mA h g−1 after 70 cycles as the anode of lithium-ion batteries, indicating that the composites might have a promising future application in Li-ion batteries.

Pt Nanocatalysts Supported on Reduced Graphene Oxide for Selective Conversion of Cellulose or Cellobiose to Sorbitol

Pt nanocatalysts loaded on reduced graphene oxide (Pt/RGO) were prepared by means of a convenient microwave-assisted reduction approach with ethylene glycol as reductant. The conversion of cellulose or cellobiose into sorbitol was used as an application reaction to investigate their catalytic performance. Various metal nanocatalysts loaded on RGO were compared and RGO-supported Pt exhibited the highest catalytic activity with 91.5 % of sorbitol yield from cellobiose. The catalytic performances of Pt nanocatalysts supported on different carbon materials or on silica support were also compared. The results showed that RGO was the best catalyst support, and the yield of sorbitol was as high as 91.5 % from cellobiose and 58.9 % from cellulose, respectively. The improvement of catalytic activity was attributed to the appropriate Pt particle size and hydrogen spillover effect of Pt/RGO catalyst. Interestingly, the size and dispersion of supported Pt particles could be easily regulated by convenient adjustment of the microwave heating temperature. The catalytic performance was found to initially increase and then decrease with increasing particle size. The optimum Pt particle size was 3.6 nm. These findings may offer useful guidelines for designing novel catalysts with beneficial catalytic performance for biomass conversion.

Synthesis of nanocomposites with carbon–SnO2 dual-shells on TiO2 nanotubes and their application in lithium ion batteries

Through the introduction of well-distributed tin oxide nanocrystals on the surface of pre-prepared TiO2 nanotubes and carbon coating, novel TiO2/SnO2–C double-shell nanotubes have been synthesized. As an anode material of Li-ion batteries (LIBs), DSNTs exhibit excellent long-term cycling stability (256.0 mA h g−1 at 1 A g−1 after 710 cycles) and satisfactory rate capability, which are ascribed to the synergetic effects of a unique combination of material properties in the well-designed conductive matrix: high volume stable titanium dioxide to form a one-dimensional (1D) core section to maintain the structure, large theoretical capacity tin oxide as a functional layer to increase capacity and highly conductive carbon as a buffer layer to accelerate charging rate.

Lamellar Metal Organic Framework-Derived Fe–N–C Non-Noble Electrocatalysts with Bimodal Porosity for Efficient Oxygen Reduction

Developing highly efficient and stable non-Pt electrocatalysts for the oxygen reduction reaction (ORR) to replace the state-of-the-art noble metal is essential for commercialization of fuel cells. Fe-N-C-based electrocatalysts are considered as a promising alternative to commercial Pt/C. An efficient electrocatalyst commonly requires large density of active site, high surface area, and desirable porosity, especially multimodal porosity with both large pores for efficient mass transfer and small pores for exposing as many active sites as possible. Herein, a lamellar metal organic framework (MOF) was developed as a precursor to directly achieve such a highly active Fe-N-C electrocatalyst with high surface area and desirable bimodal porosity. The mesopores arising from the special lamellar morphology of MOF benefits efficient mass transfer, and the nanopores resulting from pyrolysis of the MOF makes the majority of active sites accessible to electrolyte and thus effective for ORR. Uniform distribution of active elements N, C, and Fe at the molecular level in MOF precursor ensures abundant well-dispersed highly active sites in the catalyst. As a result, the catalyst exhibited superior ORR electrocatalytic activity and stability to commercial Pt/C. This strategy, using rarely reported lamellar MOF to prepare ORR catalysts with the merits mentioned, could inspire the exploration of a wide range of electrocatalysts from lamellar MOF precursors for various applications.

Self-templating synthesis of nitrogen-decorated hierarchical porous carbon from shrimp shell for supercapacitors

Nitrogen-doped hierarchical porous carbon (HPC) was prepared from shrimp shell using its intrinsic mineral scaffold (CaCO3) as the self-template combined with KOH activation. The roles of the template removal and KOH activation on the hierarchical porous structure of the obtained HPC were discussed in detail. The as-made HPC with abundant micropores, mesopores and interconnected macropores exhibits high electrochemical performance when used as the supercapacitor electrode. The specific surface area of HPC can be easily controlled via changing the activation temperature, and the natural nitrogen in shrimp shell can be preserved, which favor the final electrochemical property. Attributing to the synergetic electrochemical activity of the accessible porosity and the heteroatom, the hierarchical porous carbon pyrolyzed at 700 °C displays the largest specific capacitance of 348 F g−1 in a 6 M KOH electrolyte. The hierarchical porosity of the obtained carbon provides a well-defined ion pathway and electrolyte reservoir, allowing for rapid ionic transportation. This self-templating method represents a very attractive approach for the scalable production of hierarchical porous carbons from natural biomass containing both nitrogen/carbon sources and intrinsic templates.

Facile hydrothermal synthesis of SnO2/C microspheres and double layered core–shell SnO2 microspheres as anode materials for Li-ion secondary batteries

SnO2/C microspheres and double layered core–shell SnO2 microspheres have been synthesized by a facile hydrothermal method with a post heat-treatment. The soluble starch used as carbon source and the mass ratio of starch to SnCl4·5H2O play key roles in the formation of SnO2/C microspheres, and the hydrothermal synthesis mechanism of SnO2/C microspheres has been proposed. SnO2/C-1.0 microspheres (the mass ratio of soluble starch to SnCl4·5H2O is 1:1) with good spherical shape and 34.91 wt% of SnO2 exhibit superior rate capability and cyclic stability, while double layered core–shell SnO2 microspheres show improved electrochemical performance compared to SnO2 particles. The electrode based on SnO2/C-1.0 microspheres delivers a reversible discharge capacity of 568 mA h g−1 at a constant current density of 100 mA g−1 in the second cycle, and 379 mA h g−1 (67% retention) is retained after the 50th cycle, suggesting SnO2/C microspheres are promising candidates for energy storage.

Enteromorpha based porous carbons activated by zinc chloride for supercapacitors with high capacity retention

Porous carbons were prepared from enteromorpha overrunning in China Sea with ZnCl2 as an active agent. The obtained porous carbons were used as electrode materials to make supercapacitors. In order to make enteromorpha based supercapacitors with high performance, the effects of preparation parameters, including impregnation weight ratio of ZnCl2 to enteromorpha, activation time and temperature on pore structure and electrochemical performances of enteromorpha based porous carbons (EBPCs) were investigated. The specific area and porous structure were characterized by nitrogen adsorption. Galvanostatic charge–discharge and cyclic voltammetry analysis were used to investigate the electrochemical properties of EBPCs. The results show that activation temperature of 700 °C, the impregnation weight ratio of 2/1 and activation time of 1.5 h are the optimal preparation parameters. The prepared EBPC with a specific surface area of 1651 m2 g−1 exhibited a specific capacitance of 206 F g−1 and capacity retention of 93% even after 5000 cycles, showing excellent electrochemical properties of EBPC and good future utilization of enteromorpha.

Monodispersed Hollow SO3H-Functionalized Carbon/Silica as Efficient Solid Acid Catalyst for Esterification of Oleic Acid

SO3H-functionalized monodispersed hollow carbon/silica spheres (HS/C-SO3H) with primary mesopores were prepared with polystyrene as a template and p-toluenesulfonic acid (TsOH) as a carbon precursor and -SO3H source simultaneously. The physical and chemical properties of HS/C-SO3H were characterized by N2 adsorption, TEM, SEM, XPS, XRD, Raman spectrum, NH3-TPD, element analysis and acid-base titration techniques. As a solid acid catalyst, HS/C-SO3H shows excellent performance in the esterification of oleic acid with methanol, which is a crucial reaction in biodiesel production. The well-defined hollow architecture and enhanced active sites accessibility of HS/C-SO3H guarantee the highest catalytic performance compared with the catalysts prepared by activation of TsOH deposited on the ordered mesoporous silicas SBA-15 and MCM-41. At the optimized conditions, high conversion (96.9%) was achieved and no distinct activity drop was observed after 5 recycles. This synthesis strategy will provide a highly effective solid acid catalyst for green chemical processes.

The roles of polycarboxylates in Cr(VI)/sulfite reaction system: Involvement of reactive oxygen species and intramolecular electron transfer

In this study, the effects of polycarboxylates on both Cr(VI) reduction and S(IV) consumption in Cr(VI)/S(IV) system was investigated in acidic solution. Under aerobic condition, the productions of reactive oxygen species (ROS), i.e., SO4(-) and OH, have been confirmed in S(IV) reducing Cr(VI) process by using electron spin resonance and fluorescence spectrum techniques, leading to the excess consumption of S(IV). However, when polycarboxylates (oxalic, citric, malic and tartaric acid) were present in Cr(VI)/S(IV) system, the affinity of polycarboxylates to CrSO6(2-) can greatly promote the reduction of Cr(VI) via expanding the coordination of Cr(VI) species from tetrahedron to hexahedron. Besides, as alternatives to S(IV), these polycarboxylates can also act as electron donors for Cr(VI) reduction via intramolecular electron transfer reaction, which is dependent on the energies of the highest occupied molecular orbital of these polycarboxylates. Notably, the variant electron donating capacity of these polycarboxylates resulted in different yield of ROS and therefore the oxidation efficiencies of other pollutants, e.g., rhodamine B and As(III). Generally, this study does not only shed light on the mechanism of S(IV) reducing Cr(VI) process mediated by polycarboxylates, but also provides an escalated, cost-effective and green strategy for the remediation of Cr(VI) using sulfite as a reductant.