Wenzhong Shen

Nitrogen-containing porous carbons: synthesis and application

Nitrogen-containing porous carbon materials are ubiquitous with a wide range of technologically important applications, including separation science, heterogeneous catalyst supports, water purification, electrochemistry, as well as the developing areas of energy generation and storage applications. To date, a variety of approaches has been developed and applied to introduce nitrogen into the carbon matrix. It is important and necessary to design and control a hierarchical porous structure and the surface chemical groups of nitrogen-containing porous carbons for their applications. In this work, we summarize and compare recently reported routes for the preparation of nitrogen-containing porous carbon materials and the effect of nitrogen groups on its applications in adsorption, electrochemistry, catalysis/catalyst supports and hydrogen storage properties.

Effect of Fe-doped TiO2 nanoparticle derived from modified hydrothermal process on the photocatalytic degradation performance on methylene blue

Anatase Fe-doped TiO2 nanoparticles with 10-15 nm particles sizes were directly prepared with amorphous TiO2 nanoparticles and Fe(NO3)3.9H2O by hydrothermal method. The TiO2 crystallite grain sizes decreased with the increase of Fe contents. When Fe contents increased, the diffuse reflectance spectra of Fe-doped TiO2 nanoparticles displayed a red shift in the band gap transition. And the absorbing band edge moved to visible range when the Fe contents were more than 2 mol%. XPS analysis showed that Fe3+ was not on the surface of TiO2 nanoparticles, but inserting into the matrix interior. As a result, the photoactivity degradation of MB on Fe-doped TiO2 nanoparticles decreased.

Hierarchical porous polyacrylonitrile-based activated carbon fibers for CO2 capture

Hierarchical porous activated carbon fibers with a BET surface area of 2231 m2 g−1 and a pore volume of 1.16 cm3 g−1 were made from polyacrylonitrile through pre-oxidation and chemical activation. This type of material contains a large amount of nitrogen-containing groups (N content > 8.1 wt%) and consequently basic sites, resulting in a faster adsorption rate and a higher adsorption capacity for CO2 than pure carbon materials with analogous structures under the same conditions. Moreover, its adsorption capacity for CO2 was more than 3.3-times higher than that for N2. In particular, it showed a much higher CO2 adsorption capacity than zeolite 13X, which is conventionally used to capture CO2, in the presence of H2O.

Fe3O4@Carbon Nanosheets for All-Solid-State Supercapacitor Electrodes

Fe3O4@carbon nanosheet composites were synthesized using ammonium ferric citrate as the Fe3O4/carbon precursor and graphene oxide as the structure-directing agent under a hydrothermal process. The surface chemical compositions, pore structures, and morphology of the composite were analyzed and characterized by nitrogen adsorption isotherms, TG analysis, FT-IR, X-ray photoelectron energy spectrum, transmission electron microscopy, and scanning electron microscopy. The composites showed excellent specific capacitance of 586 F/g, 340 F/g at 0.5 A/g and 10 A/g. The all-solid-state asymmetric supercapacitor device assembled using carbon nanosheets in situ embedded Fe3O4 composite and porous carbon showed a largest energy density of 18.3 Wh/kg at power density of 351 W/kg in KOH/PVA gel electrolyte. The synergism of high special surface to volume ratio, mesoporous structure, graphene-based conduction paths, and Fe3O4 nanoparticles provided a high surface area of ion-accessibility, high electric conductivity, and the utmost utilization of Fe3O4 and resulted in excellent specific capacitance, outstanding rate capability and cycling life as all-solid-state supercapacitor electrodes.

Facile one-pot synthesis of bimodal mesoporous carbon nitride and its function as a lipase immobilization support

Bimodal mesoporous carbon nitride is synthesized using Triton X-100 as a template and melamine and glutaraldehyde as precursors through polymerization and carbonization. The structures and surface chemical properties of carbon nitrides are characterized and compared by nitrogen adsorption isotherms, TG, FT-IR spectra and SEM images. The results show that the mesopore sizes in the carbon nitride are centered at 3.8 nm and 10–40 nm. The pyrolysis and decomposition of the polymer to form the condensation cross-linking ring structures takes place at 350–700 °C. The nitrogen atom in the carbon nitride exists in C–N and N–H states. As a Candida rugosalipase immobilization support, the mesoporous carbon nitride displays a higher amount of immobilization and improves the thermal stability of Candida rugosalipase, which still displays higher catalytic activity after 4 runs.

Yeast‐Based Microporous Carbon Materials for Carbon Dioxide Capture

A hierarchical microporous carbon material with a Brunauer-Emmett-Teller surface area of 1348 m(2) g(-1) and a pore volume of 0.67 cm(3) g(-1) was prepared from yeast through chemical activation with potassium hydroxide. This type of material contains large numbers of nitrogen-containing groups (nitrogen content >5.3 wt%), and, consequently, basic sites. As a result, this material shows a faster adsorption rate and a higher adsorption capacity of CO(2) than the material obtained by directly carbonizing yeast under the same conditions. The difference is more pronounced in the presence of N(2) or H(2)O, showing that chemical activation of discarded yeast with potassium hydroxide could afford high-performance microporous carbon materials for the capture of CO(2).

Carbon Nanosheets: Synthesis and Application

Carbon nanosheets (CNSs) with tunable sizes, morphologies, and pore structures have been synthesized through several chemical routes. Graphitized CNSs have been synthesized through exfoliation, chemical vapor deposition, or high-temperature carbonization. Porous CNSs have been synthesized by using various methods, including pyrolysis, self-assembly, or a solvothermal method in connection with carbonization. These CNSs have successfully been used as detectors for metal ions, as cathodes for field electron emissions, as electrodes for supercapacitors and fuel cells, and as supports for photocatalytic and catalytic oxygen reduction. Therefore, the synthesis and application of CNSs are receiving increasing levels of interest, particularly as application benefits, in the context of future energy/chemical industry, are becoming recognized. This review provides a summary of the most recent and important progress in the production of CNSs and highlights their application in environmental and energy-related fields.

Preparation of mesoporous carbon from commercial activated carbon with steam activation in the presence of cerium oxide

Mesoporous carbon was prepared from the commercial activated carbon by steam activation with cerium oxide as catalyst. Steam activation with a catalyst loading of 0.5-2.0 wt% at 680-870 degrees C was examined. The surface area and pore size were evaluated by nitrogen adsorption at 77 K, and the structure of cerium oxide was characterized by XRD, XPS, and TEM. The results showed that the catalyst promoted the development of a mesopore at lower temperature (680-740 degrees C), and the mesopore was concentrated around 4-10 nm. The noncatalytic activation was advantageous in mesopore development and the catalyst would restrict the formation of mesopores at high temperature (800-870 degrees C). Higher loading of cerium oxide and higher activation temperature caused the aggregation of cerium oxide and then resulted in scattered pore size distribution.

Nitrogen- and oxygen-enriched 3D hierarchical porous carbon fibers: synthesis and superior supercapacity

A nitrogen- and oxygen-enriched hierarchical porous carbon fiber was fabricated by phase-separable wet-spinning and the subsequent chemical activation of polyacrylonitrile (PAN) precursors. The wet-spinning could readily offer an interpenetrating 3D meso-/macro-porous network owing to the phase-separation of PAN in the coagulation bath (DMSO/H2O), caused by the different solubility of PAN in DMSO and H2O, and the different content of PAN in the fiber and the coagulation bath. The latter chemical activation introduced abundant small-sized nanopores within the meso-/macro-porous network skeleton. The obtained hierarchical porous carbon fiber exhibited a high specific surface area of 2176.6 m2 g−1 and a large pore volume of 1.272 cm3 g−1, and was highly doped with heteroatoms of nitrogen and oxygen. When it was used as a supercapacitor electrode, high performance of reversible specific capacitances of 329 F g−1 at 0.1 A g−1 and 223 F g−1 at 20 A g−1 as well as the capacitance retention of 97.6% after 2000 cycles were achieved in a two-electrode cell.

Reaction Kinetics of Transesterification between Vegetable Oil and Methanol under Supercritical Conditions

Abstract The dynamic transesterification reaction of peanut oil in supercritical methanol media was investigated. The reaction temperature and pressure were in the range of 250°C–310°C and 10.0 MPa–16.0 Mpa, respectively. The molar ratio of peanut oil to methanol was 1:30. It was found that the yield of methyl esters was higher than 90% under the supercritical methanol. The apparent reaction order and activation energy of transesterification was 1.5 and 7.472 kJ/mol, respectively. In this method, the reaction time was shorter and the processing was simpler than that of the common acid catalysis transesterification.