Novel N-doped (BiO)(2)CO(3) hierarchical microspheres (N-BOC) were fabricated by a facile one-pot template free method on the basis of hydrothermal treatment of bismuth citrate and urea in water for the first time. The N-BOC sample was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, N(2) adsorption-desorption isotherms, and Fourier transform-infrared spectroscopy. The N-BOC was constructed by the self-assembly of single-crystalline nanosheets. The aggregation of nanosheets led to the formation of hierarchical framework with mesopores, which is favorable for efficient transport of reaction molecules and harvesting of photoenergy. Due to the in situ doped nitrogen substituting for oxygen in the lattice of (BiO)(2)CO(3), the band gap of N-BOC was reduced from 3.4 to 2.5 eV, making N-BOC visible light active. The N-BOC exhibited not only excellent visible light photocatalytic activity, but also high photochemical stability and durability during repeated and long-term photocatalytic removal of NO in air due to the special hierarchical structure. This work demonstrates that the facile fabrication method for N-BOC combined with the associated outstanding visible light photocatalytic performance could provide new insights into the morphology-controlled fabrication of nanostructured photocatalytic materials for environmental pollution control.
Alpha calcium sulfate hemihydrate (α-HH) is an important class of cementitious material and exhibits considerable morphology-dependent properties. In the reverse microemulsions of water/n-hexanol/cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfonate (SDS), the morphology and aspect ratio of α-HH are successfully controlled by adjusting the mass ratio of CTAB/H(2)O and the concentration of SDS. As the ratio of CTAB/H(2)O is increased from 1.3 to 4.5, the crystal length decreases from 120 to 150 μm to 0.5-1.2 μm with the corresponding aspect ratio reduced sharply from 180 to 250 to 2-7. With increasing SDS concentration, the crystal morphology gradually changes from submicrometer-sized long column to rod, hexagonal plate, and even nanogranule. The preferential adsorption of CTAB on the side facets and SDS on the top facets contributes to the morphology control. This work presents a simple, versatile, highly efficient approach to controlling the morphology of α-HH on a large scale and will offer more opportunities for α-HH multiple applications.
Graphitic carbon nitride (g-C 3 N 4 ) is an intriguing metal-free photocatalyst for pollution control. This research represents an efficient visible light photocatalytic removal of gaseous NO at 600 ppb level with porous g-C 3 N 4 nanostructures synthesized by pyrolysis of thiourea. TG-DSC was employed to simulate the pyrolysis of thiourea, and the mechanistic formation process of g-C 3 N 4 was revealed. The crystallinity, morphology, surface area, pore structures, band structure, and photocatalytic activity of g-C 3 N 4 can be engineered by variation of pyrolysis temperature and time. A layer-by-layer coupled with layer-splitting process was proposed for the gradual reduction of layer thickness and size of g-C 3 N 4 obtained at elevated temperature and prolonged time. The visible light photocatalytic activity of g-C 3 N 4 nanosheets toward NO purification was significantly enhanced due to the enhanced crystallinity, nanosheet structure, large surface areas and pore volume and enlarged band gap as the pyrolysis temperature was increased and the pyrolysis time was prolonged. The optimized g-C 3 N 4 nanosheets (CN-600 °C and CN-240 min) exhibited higher photocatalytic activity of 32.7% and 32.3% than C-doped TiO 2 (21.8%) and BiOI (14.9%), which are also highly stable and can be used repeatedly without obvious deactivation under repeated irradiation, demonstrating their great potential for practical applications.
In this article, the underlying eff ect of phosphoric acid etching and additional water vapor on chlorine desorption behavior over a model catalyst La3Mn2O7 was explored. Acid treatment led to the formation of LaPO4 and enhanced the mobility of lattice oxygen of La3Mn2O7 evidenced by a range of characterization (i.e., X-ray diff raction, temperature-programmed analyses, NH3−IR, etc.). The former introduced thermally stable Bronsted acidic sites that enhanced dichloromethane (DCM) hydrolysis while the latter facilitated desorption of accumulated chlorine at elevated temperatures. The acid-modified catalyst displayed a superior catalytic activity in DCM oxidation compared to the untreated sample, which was ascribed to the abundance of proton donors and Mn(IV) species. The addition of water vapor to the reaction favored the formation and desorption of HCl and avoided surface chlorination at low temperatures. This resulted in a further reduction in reaction temperature under humid conditions (T90 of 380 °C for the modified catalyst). These results provide an in-depth interpretation of chlorine desorption behavior for DCM oxidation, which should aid the future design of industrial catalysts for the durable catalytic combustion of chlorinated organics.
Xiaole 2019. Efficient elimination of chlorinated organics on a phosphoric acid modified CeO2 catalyst: a hydrolytic destruction route. Environmental Science and Technology 53 (21) , pp.
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