Without using precious elements, a highly efficient and selective molecular-based photocatalytic system for CO2-to-CO conversion in fully aqueous media has been developed. Our copper­(I)-based water-soluble photosensitizer (CuPS) preserves its highly luminescent and long-lived excited state even in aqueous media. The CuPS-driven CO2 reduction catalyzed by a water-soluble cobalt porphyrin possessing four N-methylpyridinium acceptors at the meso positions (CoTMPyP) achieves the highest catalytic activity among those reported for aqueous systems: TONCO = 2680 and TOFCO max = 1600–2600 h–1 with SelCO2 = 77–90% (selectivity for CO vs H2). The observed photocatalytic enhancement is discussed in terms of the 6-electron chargeable character of CoTMPyP, permitting its rapid release of CO via reduction of CoII to CoI by intramolecular electron transfer from the reducing equivalent stored at one of the acceptors.

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To stop global warming and climate changes, substantial efforts have been made to diminish CO 2 emission. Photocatalytic and electrocatalytic CO 2 reduction into fuels has thus become a highly important topic. Our recent interest has been to develop earth-abundant and environmentally friendly photocatalytic systems consisting of a non-precious-metal molecular CO 2 reduction catalyst combined with subcomponents, especially using aqueous conditions without any organic solvents. However, CO 2 reduction in water suffers from a drawback of decreasing its reaction yield due to concomitant H 2 evolution, which can be driven by an overpotential less than that for CO 2 reduction. Herein, we demonstrate a strategy to suppress H 2 evolution using a cobalt porphyrin CO 2 reduction catalyst possessing four N-methylpyridinium acceptors. The H 2 evolution path is not favored by the active intermediate possessing a low-spin d 7 Co II center because of its mismatch in forming an effective MO association with a 1s(H + ) orbital. This is a rare example of catalysts avoiding the standard path relying on a filled (d z2 ) 2 orbital in binding CO 2 . Instead, both πand σ-type frontier MO associations are simultaneously formed by two degenerated π*(CO 2 ) orbitals using a filled (d xz ) 2 and a half-filled (d z2 ) 1 orbital. We also find that highly electron charged intermediates show switching in configuration from (d xz ) 2 (d z2 ) 1 to (d xz ) 1 (d z2 ) 2 , leading us to allow the standard σ-type interaction with CO 2 . Correlation between the multielectron charging behaviors of cobalt porphyrins and the mechanism of photo-and electrocatalytic CO 2 reduction is rationalized using our electrochemical and DFT results. This study sheds a light on strategies to rationally control the reaction rates and pathways based on the frontier MO engineering.

Hopeite coating on metals by the phosphate chemical conversion (PCC) method has received more attention for its potential biomedical use. It is difficult to get a PCC phosphate coating due to the presence of a passive oxide layer on the surface of titanium. In this research, we report on effects of ultrasonic irradiation (UI) on formation, crystal size, microstructure, and corrosion resistance of the PCC coatings on Ti. It is shown that both coatings formed with and without UI are composed of hopeite (Zn 3 (PO 4 ) 2 •4H 2 O) with similar crystal shape. FE-SEM observation demonstrates that UI can significantly decrease crystal size from 50−100 to 5−20 μm within a duration time of 30−60 min. Short period PCC treatment of 5 min shows that UI can enhance the formation of coating with the increase of nucleation rate. And the nucleation rate with UI of 250 W is significantly higher than that of 50 W. The electrochemical analysis reveals that the corrosion resistance of the coatings can also be improved by ultrasonic irradiation treatment. Human fibroblast cell culture studies indicate that the cells attach and spread well on the surface of PCC coatings, which is indicative of the fact that the coatings have excellent biocompatibility and bioactivity.

In this work, considering the effect of porosity, pore size, saturation of water and tortuosity fractal dimension, an analytical model for the capillary pressure and water relative permeability is derived in unsaturated porous rocks. Besides, the formulas of calculating the capillary pressure and water relative permeability are given by taking into account the fractal distribution of pore size and tortuosity of capillaries. It can be seen that the capillary pressure for water phase decreases with the increase of saturation in unsaturated porous rocks. It is found that the capillary pressure for water phase decreases as the tortuosity fractal dimension decreases. It is further seen that the capillary pressure for water phase increases with the decrease of porosity, and at low porosity, the capillary pressure increases sharply with the decrease of porosity. Besides, it can be observed that the water relative permeability increases with the increase of saturation in unsaturated porous rocks. This predicted the capillary pressure and water relative permeability of unsaturated porous rocks based on the proposed models which are in good agreement with the experimental data and model predictions reported in the literature. § Corresponding author. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited. 1840015-1 B. Xiao et al.The proposed model improved the understanding of the physical mechanisms of water flow through unsaturated porous rocks.

In this study, the optimization of the fractal-like architecture of porous fibrous materials related to permeability, diffusivity, and thermal conductivity was analyzed by applying the established theoretical models. It was observed that the ratio of dimensionless permeability over dimensionless effective diffusivity decreased with the decrease of porosity and tortuosity fractal dimension, respectively, which implied that lower porosity and tortuosity fractal dimension were beneficial to wind/water resistant fabric, as it reduced the ratio of dimensionless permeability over dimensionless effective diffusivity. Besides, it was found that the ratio of the dimensionless total effective thermal conductivity over dimensionless effective diffusivity increased with tortuosity fractal dimension, which implied lower tortuosity fractal dimension was beneficial to clothing insulation, as it reduced the ratio of dimensionless total effective thermal conductivity over dimensionless effective diffusivity. The optimization results indicated that fabrics with more aligned fibers were preferred for protective clothing, as the low tortuosity fractal dimension implied fibers in the fibrous materials should be more aligned.

The investigation of fluids transport through porous gas diffusion layer (GDL) is very important to improve the performance of proton exchange membrane fuel cell (PEMFC). In this paper, the fractal analytical models of capillary pressure for water phase and water and gas relative permeabilities of fibrous GDL are obtained. The determined capillary pressure and relative permeabilities based on the present models are in good agreement with the available experimental data and existing models reported in the literature. Thus the validity of the proposed models for the capillary pressure and relative permeabilities is verified. It is found that the capillary pressure increases with the increase of fiber volume fraction and tortuosity fractal dimension. On the other hand, it is seen that the capillary pressure decreases with increasing water saturation. It is seen that the water relative permeability decreases with increasing tortuosity fractal dimension. On the contrary, it is found that the gas relative permeability increases with tortuosity fractal dimension. Besides, it is observed that the porosity has little effect on the water and gas relative permeabilities.

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