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Abstract Pervious concrete is designed to be porous to allow permeation of water and air for combating the environmental and drainage problems arising from urbanization. However, despite extensive research, it is still not clear how best to design pervious concrete mixes to achieve good concurrent permeability-strength performance. In a previous study, the authors found that there is a necessity to distinguish between interconnected porosity and open porosity, and between unsubmerged permeability and submerged permeability. In this study, based on the thinking that fine aggregate may be added to reduce the paste volume provided the fine aggregate is fine enough to form a coherent mass with the paste, further research was conducted to develop the mortar type pervious concrete with reduced paste volume and investigate the roles of the mortar volume in porosity, permeability and strength. A new series of concrete mixes with varying mortar volume were tested and the results revealed that the interconnected porosity is the major factor determining the permeability while the open porosity and water/cement ratio are the major factors determining the strength. More importantly, the mortar volume plays a key role in each performance attribute.

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Integration of non-noble transition metal oxides with graphene is known to construct high-activity electrocatalysts for oxygen evolution reduction (OER). In order to avoid the complexity of traditional synthesis process, a facile electrochemical method is elaborately designed to engineer efficient WO3-x/graphene (photo-)electrocatalyst for OER by a two-electrode electrolysis system, where graphite cathode is exfoliated into graphene and tungsten wire anode evolves into VO-rich WO3-x profiting from formed reductive electrolyte solution. Among as-prepared samples, WO3-x/G-2 shows the best electrocatalytic performance for OER with an overpotential of 320 mV (without iR compensation) at 10 mA/cm2, superior to commercial RuO2 (341 mV). With introduction of light illumination, the activity of WO3-x/G-2 is greatly enhanced and its overpotential decreases to 290 mV, benefiting from additional reaction path produced by photocurrent effect and extra active sites generated by photogenerated carriers (h+). Characterization results indicate that both VO-rich WO3-x and graphene contribute to the efficient OER performance. The activity of WO3-x for OER is decided by the synergistic effect between VO concentration and particle size. The graphene could not only disperse WO3-x nanoparticles, but also improve the holistic conductivity and promote electron transmission. This work supports a novel method for engineering WO3-x/graphene composite for highly efficient (photo-)electrocatalytic performance for OER. [ABSTRACT FROM AUTHOR]

A Lewis structure corresponding to the most stable electron-localized state is often used as a reference for the measure of electron delocalization effect in the valence bond (VB) theory. As the simplest variant of ab initio VB theory, the generalized block-localized wavefunction (BLW) method defines the wavefunction for an electron-localized state with block-localized orbitals without the orthogonalization constraint on different blocks. The validity of the method can be critically examined with experimental evidences. Here the BLW method has been applied to the investigation of the roles of both the π conjugation and σ hyperconjugation effects in the conformational preference of formic acid for the trans (Z) conformer over the cis (E) conformer. On one hand, our computations showed that the deactivation of the π conjugation or σ hyperconjugation has little impact on the Z-E energy gap, thus neither is decisive and instead the local dipole-dipole electrostatic interaction between the carbonyl and hydroxyl groups is the key factor determining the Z-E energy gap. On the other hand, the present study supported the conventional view that π conjugation is largely responsible for the C-O rotation barrier in formic acid, though the existence of hyperconjugative interactions in the perpendicular structure lowers the barrier considerably. [ABSTRACT FROM AUTHOR]