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Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for the reduction of CO2 into fuels. However, the reduction mechanism of CO2 using g-C3N4 is not clear in the literature. In the present study, the fixation of CO2 and the formation of carbamate on the nitrogen atom at the edge of g-C3N4 were investigated using first-principles density functional theory. The calculated results shows that two adjacent bare nitrogen atoms at the edge of g-C3N4 could be the activation sites for the proton and CO2 molecule respectively, which are crucial to the formation of carbamate. The calculated energy barrier of carbamate formation is 0.95 eV for a preferential pathway. From studies on these micro processes, we propose a mechanism with proton assistance for the g-C3N4-catalyzed photoreduction of CO2 to CO. [ABSTRACT FROM AUTHOR]

Motivated by the photocatalytic reactions of small molecules on g-C 3 N 4 by these insights, we sought to explore the adsorption of H 2 O and CO 2 molecules on the graphene side and H 2 O, H 2 , O 2 , CO, NO, and CO 2 molecules on the g-C 3 N 4 side of hybrid g-C 3 N 4 /graphene nanocomposite using first-principles calculations. The atomic structure and electronic properties of hybrid g-C 3 N 4 /graphene nanocomposite is explored. The adsorption of small molecules on graphene/g-C 3 N 4 nanocomposite is thoroughly investigated. The computational studies revels that all small molecules on graphene/g-C 3 N 4 nanocomposite are the physisorption. The adsorption characteristics of H 2 O and CO 2 molecules on the graphene side are similar to that on graphene. The adsorption of H 2 O, H 2 , O 2 , CO, NO, and CO 2 molecules on the g-C 3 N 4 side always leads to a buckle structure of graphene/g-C 3 N 4 nanocomposite. Graphene as a substrate can significantly relax the buckle degree of g-C 3 N 4 in g-C 3 N 4 /graphene nanocomposite. [ABSTRACT FROM AUTHOR]

Interfacial issues, such as the interfacial structure and the interdiffusion of atoms at the interface, are fundamental to the understanding of the ignition and reaction mechanisms of nanothermites. This study employs first-principle density functional theory to model Al/MoO3 by placing an Al adatom onto a unit cell of a MoO3(010) slab, and to probe the initiation of interfacial interactions of Al/MoO3 nanothermite by tracking the adsorption and subsurface-penetration of the Al adatom. The calculations show that the Al adatom can spontaneously go through the topmost atomic plane (TAP) of MoO3(010) and reach the 4-fold hollow adsorption-site located below the TAP, with this subsurface adsorption configuration being the most preferred one among all plausible adsorption configurations. Two other plausible configurations place the Al adatom at two bridge sites located above the TAP of MoO3(010) but the Al adatom can easily penetrate below this TAP to a relatively more stable adsorption configuration, with a small energy barrier of merely 0.2 eV. The evidence of subsurface penetration of Al implies that Al/MoO3 likely has an interface with intermixing of Al, Mo and O atoms. These results provide new insights on the interfacial interactions of Al/MoO3 and the ignition/combustion mechanisms of Al/MoO3 nanothermites. [ABSTRACT FROM AUTHOR]

Effects of impeller blade number on gas dispersion and mass transfer rate were thoroughly investigated for mechanically agitated vessels equipped with 2-, 4-, 6- and 8-straight blades disk turbine impellers. The results show that under the same rotational speed, the impeller with more blades always can disperse gas more effectively, which induces a higher value of La>. However, with the same total power consumption, the 4-blade impeller can obtain a higher < KLa> value than the 6- and 8-blade impellers under a lower gassing rate condition (Qg< 0.5 wm), but if Qg exceeds 0.5 wm, the 6-blade impeller will perform better than the 4- and 8-blade impellers. To examine the results obtained from the single impeller systems, the same approach is applied to measure < KLa> values for the triple stage 6-blade impeller system (3x6) and quadruple stage 4-blade impeller system (4×4). From the experimental results, it can be found that the 4×4 system gives higher < KLa> value than the 3x6 system under gas completely dispersed conditions. By correlating < KLa> with n b , N and Vs, the following correlation can be given as: or These two correlations can also be used to evaluate the mass transfer coefficient of each impeller region for the multiple impeller systems and the deviation is always less than 10%. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4 ) is a promising photocatalyst for the reduction of CO 2 into fuels. However, the reduction mechanism of CO 2 using g-C 3 N 4 is not clear in the literature. In the present study, the fixation of CO 2 and the formation of carbamate on the nitrogen atom at the edge of g-C 3 N 4 were investigated using first-principles density functional theory. The calculated results shows that two adjacent bare nitrogen atoms at the edge of g-C 3 N 4 could be the activation sites for the proton and CO 2 molecule respectively, which are crucial to the formation of carbamate. The calculated energy barrier of carbamate formation is 0.95 eV for a preferential pathway. From studies on these micro processes, we propose a mechanism with proton assistance for the g-C 3 N 4 -catalyzed photoreduction of CO 2 to CO.

The optical properties and condensation degree (structure) of polymeric g-C 3 N 4 depend strongly on the process temperature. For polymeric g-C 3 N 4 , its structure and condensation degree depend on the structure of molecular strand(s). Here, the formation and electronic structure properties of the g-C 3 N 4 nanoribbon are investigated by studying the polymerization and crystallinity of molecular strand(s) employing first-principle density functional theory. The calculations show that the width of the molecular strand has a significant effect on the electronic structure of polymerized and crystallized g-C 3 N 4 nanoribbons, a conclusion which would be indirect evidence that the electronic structure depends on the structure of g-C 3 N 4 . The edge shape also has a distinct effect on the electronic structure of the crystallized g-C 3 N 4 nanoribbon. Furthermore, the conductive band minimum and valence band maximum of the polymeric g-C 3 N 4 nanoribbon show a strong localization, which is in good agreement with the quasi-monomer characters. In addition, molecular strands prefer to grow along the planar direction on graphene. These results provide new insight on the properties of the g-C 3 N 4 nanoribbon and the relationship between the structure and properties of g-C 3 N 4 .

Internal floating roof tank has the advantages of external floating roof tank and fixed roof tank and has its own evaporation loss properties. The influences of volatile organic compounds (VOCs) distribution gradient, molecular diffusion, thermal diffusion and forced convection on the evaporation loss of oil were studied in the space of the homemade platform of an internal floating roof tank. The results showed that thermal diffusion with temperature change was the main cause for the static loss in the internal floating roof tank. On this basis, there were some measures for reduction of the evaporation loss and formulas to calculate the evaporation loss of the internal floating roof tank in this research.