Shifei Kang

Facile One-Step Synthesis of Hybrid Graphitic Carbon Nitride and Carbon Composites as High-Performance Catalysts for CO2 Photocatalytic Conversion

Utilizing and reducing carbon dioxide is a key target in the fight against global warming. The photocatalytic performance of bulk graphitic carbon nitride (g-C3N4) is usually limited by its low surface area and rapid charge carrier recombination. To develop g-C3N4 more suitable for photocatalysis, researchers have to enlarge its surface area and accelerate the charge carrier separation. In this work, novel hybrid graphitic carbon nitride and carbon (H-g-C3N4/C) composites with various carbon contents have been developed for the first time by a facile one-step pyrolysis method using melamine and natural soybean oil as precursors. The effect of carbon content on the structure of H-g-C3N4/C composites and the catalytic activity for the photoreduction of CO2 with H2O were investigated. The results indicated that the introduction of carbon component can effectively improve the textural properties and electronic conductivity of the composites, which exhibited imporved photocatalytic activity for the reduction of CO2 with H2O in comparison with bulk g-C3N4. The highest CO and CH4 yield of 22.60 μmol/g-cat. and 12.5 μmol/g-cat., respectively, were acquired on the H-g-C3N4/C-6 catalyst with the carbon content of 3.77 wt % under 9 h simulated solar irradiation, which were more than twice as high as that of bulk g-C3N4. The remarkably increased photocatalytic performance arises from the synergistic effect of hybrid carbon and g-C3N4.

A High-Performance, Low-Tortuosity Wood-Carbon Monolith Reactor

A highly efficient 3D wood-derived carbon monolith reactor with a low tortuosity is demonstrated for high-temperature reaction applications, using catalytic steam reforming of biomass tar as the model system. Outstanding catalytic activity is achieved as the reactant gases flow through this 3D natural wood-derived catalyst, where over 99% toluene conversion and good stability at 700 °C are observed.

Efficient Photocatalytic Bilirubin Removal over the Biocompatible Core/Shell P25/g-C 3 N 4 Heterojunctions with Metal-free Exposed Surfaces under Moderate Green Light Irradiation

Highly-monodispersed g-C3N4/TiO2 hybrids with a core/shell structure were synthesized from a simple room temperature impregnation method, in which g-C3N4 was coated through self-assembly on the commercially available Degussa P25 TiO2 nanoparticles. Structural and surface characterizations showed that the presence of g-C3N4 notably affected the light absorption characteristics of TiO2. The g-C3N4/TiO2 heterojunctions with metal-free exposed surfaces were directly used as biocompatible photocatalysts for simulated jaundice phototherapy under low-power green-light irradiation. The photocatalytic activity and stability of g-C3N4/TiO2 were enhanced relative to pure P25 or g-C3N4, which could be ascribed to the effective Z-scheme separation of photo-induced charge carriers in g-C3N4/TiO2 heterojunction. The photoactivity was maximized in the 4 wt.% g-C3N4-coated P25, as the bilirubin removal rate under green light irradiation was more than 5-fold higher than that under the clinically-used blue light without any photocatalyst. This study approves the future applications of the photocatalyst-assisted bilirubin removal in jaundice treatment under moderate green light which is more tolerable by humans.

Surfactant-assisted Nanocasting Route for Synthesis of Highly Ordered Mesoporous Graphitic Carbon and Its Application in CO2 Adsorption

Highly ordered mesoporous graphitic carbon was synthesized from a simple surfactant-assisted nanocasting route, in which ordered mesoporous silica SBA-15 maintaining its triblock copolymer surfactant was used as a hard template and natural soybean oil (SBO) as a carbon precursor. The hydrophobic domain of the surfactant assisted SBO in infiltration into the template’s mesoporous channels. After the silica template was carbonized and removed, a higher yield of highly-ordered graphitic mesoporous carbon with rod-like morphology was obtained. Because of the improved structural ordering, the mesoporous carbon after amine modification could adsorb more CO2 compared with the amine-functionalized carbon prepared without the assistance of surfactant.

Nanocasting synthesis of chromium doped mesoporous CeO 2 with enhanced visible-light photocatalytic CO 2 reduction performance

Chromium doped mesoporous CeO2 catalysts were synthesized via a simple nanocasting route by using silica SBA-15 as the template and metal nitrates as precursors. The effect of Cr doping concentration (5%, 10%, 15% and 20% of the initial Cr/(Cr+Ce) molar percentage) on the structures of these catalysts and their photocatalytic performances in reduction of CO2 with H2O were investigated. The results indicated that the introduction of Cr species could effectively extend the spectral response range from UV to visible light region (400-700nm) and improve the electronic conductivity for the mesoporous CeO2 catalysts which exhibited an enhanced photocatalytic activity in the reduction of CO2 with H2O when compared with the non-doped counterpart. The highest CO and CH4 yield of 16.2μmol/g-cat. and 10.1μmol/g-cat., respectively, were acquired on the optimal chromium doped CeO2 catalyst with the initial Cr(Cr+Ce) molar percentage of 15% under 8h visible-light irradiation, which were more than twice as high as that of bare CeO2. The remarkably increased photocatalytic performance should be attributed to the advantageous structural and compositional features of the chromium doped mesoporous CeO2.

Scalable and clean exfoliation of graphitic carbon nitride in NaClO solution: enriched surface active sites for enhanced photocatalytic H2 evolution

Graphitic carbon nitride (g-C3N4) has attracted wide attention as a promising visible-light-driven metal-free semiconductor photocatalyst. The transportation and transformation of photogenerated carriers during the photocatalytic process of g-C3N4 are restricted by the insufficient surface active sites and low charge separation efficiency. As a top-down strategy, the exfoliation of layer-stacked bulk g-C3N4 into nanosheets is widely recognized as an applicable route, yet still challenging in terms of scalable and clean synthesis. Herein, this challenge was tackled via a simple hydrothermal method in NaClO solution, in which the synergetic effect of alkaline metal ion intercalation and the oxidative exfoliation of bulk g-C3N4 was involved. Highly active g-C3N4 nanosheets were easily made in the laboratory in tens of grams and this simple process could readily be extended to the scale of kilograms. The hydrothermal treatment created vertical channels for directional electron transfer and obtained ultrathin holey g-C3N4 nanosheets with remarkable hierarchical porosity and good hydrophilicity. The holey g-C3N4 nanosheets exhibit a high specific surface area (170.7 m2 g−1), a narrow band gap (2.55 eV), a large number of exposed edges, and superior electron transport ability. These holey g-C3N4 nanosheets have an average H2 evolution rate 9 times that of bulk g-C3N4. This green, facile and scalable method to synthesize few-layer g-C3N4 nanosheets affords a new strategy to design and fabricate other functional 2D materials.

Constructing Highly Uniform Onion-Ring-like Graphitic Carbon Nitride for Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution

The introduction of microstructure to the metal-free graphitic carbon nitride (g-C3N4) photocatalyst holds promise in enhancing its catalytic performance. However, producing such microstructured g-C3N4 remains technically challenging due to a complicated synthetic process and high cost. In this study, we develop a facile and in-air chemical vapor deposition (CVD) method that produces onion-ring-like g-C3N4 microstructures in a simple, reliable, and economical manner. This method involves the use of randomly packed 350 nm SiO2 microspheres as a hard template and melamine as a CVD precursor for the deposition of a thin layer of g-C3N4 in the narrow space between the SiO2 microspheres. After dissolution of the microsphere template, the resultant g-C3N4 exhibits uniquely uniform onion-ring-like microstructures. Unlike previously reported g-C3N4 powder morphologies that show various degrees of agglomeration and irregularity, the onion-ring-like g-C3N4 is highly dispersed and uniform. The calculated band gap for onion-ring-like g-C3N4 is 2.58 eV, which is significantly narrower than that of bulk g-C3N4 at 2.70 eV. Experimental characterization and testing suggest that, in comparison with bulk g-C3N4, onion-ring-like g-C3N4 facilitates charge separation, extends the lifetime of photoinduced carriers, exhibits 5-fold higher photocatalytic hydrogen evolution, and shows great potential for photocatalytic applications.

CuO/Cu2O nanowire arrays grafted by reduced graphene oxide: synthesis, characterization, and application in photocatalytic reduction of CO2

CuO/Cu2O nanowire arrays (NWAs) were prepared on a Cu foil substrate through a simple thermal process. The NWAs were then grafted with reduced graphene oxide (rGO) nanosheets via self-assembly. The combination of various characterization techniques including SEM, TEM, XRD, and XPS revealed the unique integration between CuO/Cu2O NWAs and umbrella-like rGO nanosheets. The CuO/Cu2O NWAs@rGO sample was found to be more active than bare CuO/Cu2O NWAs for the photocatalytic reduction of CO2 under simulated solar light. The improved photocatalytic activity was attributed to the slow recombination of charge carriers and the efficient transfer of photo-generated electrons through rGO nanosheets.

Synthesis and properties of magnetic carbon nanocages particles for dye removal

Magnetic carbon nanocages (MCNCs) with multiform pore structure have been synthesized by a simple low temperature carbonization process. Biorenewable lignin was used as a cheap and carbon-rich precursor for the first time. The products were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, energy dispersive X-ray spectroscopy (EDS), vibrating samplemagnetometer (VSM), transmission electronmicroscopy (TEM), and Raman spectrum. XRDpattern and Raman spectrum showed that the product has a high degree of graphitization crystallinity. TEM micrograph indicated that the synthesized MCNCs have the hierarchical pore and cage structure. Due to these characteristics, the obtained magnetic carbon nanocages can be used as efficient and recycled adsorbents in the removal of dye staff from textile wastewater.

Facile synthesis of highly active fluorinated ultrathin graphitic carbon nitride for photocatalytic H2 evolution using a novel NaF etching strategy

Although graphitic carbon nitride (GCN) has been intensively studied in photocatalytic research, its performance is still hindered by its inherently low photo-absorption and inefficient charge separation. Herein, we report a simple NaF solution treating method to produce fluorinated and alkaline metal intercalated ultrathin GCN with abundant in-plane pores and exposed active edges, and therefore an enhanced number of actives sites. Compared to bulk GCN, NaF treated GCN has a larger specific surface area of 81.2 m2 g−1 and a relatively narrow band gap of 2.60 eV, which enables a 6-fold higher photocatalytic rate of hydrogen evolution.