Silicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively ...used protective material, crystalline TiO2 could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO2 would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (Ovac) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of Ovac distribution, Ovac along GBs and Ovac inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p‐Si/TiO2/Pt heterojunction photocathode with controllable Ovac distribution in TiO2 shows a +400 mV onset potential shift and yields an applied bias photon‐to‐current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction.
This communication describes the carrier transport mechanism employing conductive atomic force microscopy (c‐AFM) by controlling the oxygen vacancies (Ovac) distribution for grain boundaries (GBs) in crystalline TiO2. Compared to Ovac distributed along the GBs, the Ovac inside the grains could narrow the depletion layer in grain‐GB‐grain junction to facilitate electron tunneling across GBs, improving the electron collection at the photoelectrode surface.
Production of ammonia is currently realized by the Haber-Bosch process, while electrochemical N
fixation under ambient conditions is recognized as a promising green substitution in the near future. A ...lack of efficient electrocatalysts remains the primary hurdle for the initiation of potential electrocatalytic synthesis of ammonia. For cheaper metals, such as copper, limited progress has been made to date. In this work, we boost the N
reduction reaction catalytic activity of Cu nanoparticles, which originally exhibited negligible N
reduction reaction activity, via a local electron depletion effect. The electron-deficient Cu nanoparticles are brought in a Schottky rectifying contact with a polyimide support which retards the hydrogen evolution reaction process in basic electrolytes and facilitates the electrochemical N
reduction reaction process under ambient aqueous conditions. This strategy of inducing electron deficiency provides new insight into the rational design of inexpensive N
reduction reaction catalysts with high selectivity and activity.
Unfrozen water content significantly affects the thermal‐hydro‐mechanical characteristics of frozen soil. Currently, theoretical explanations for the presence of unfrozen water include capillary ...action, surface effects, adsorption forces, and the electrical double layer. However, the relationships between unfrozen water and these actions are not well explained, except for capillary forces. In addition, although frost heave experiments indicate that the electrical double‐layer solution on a clay particle contains the main portion of unfrozen water, the electrical double‐layer theory which produces a cation solution has not previously been used to calculate unfrozen water content. In this paper, it is assumed that the residual unfrozen water at very low temperatures (below −18°C) is held within the adsorption‐layer solution and that the remaining unfrozen water within the influence of surface effects is the cationic solution in the diffuse layer. Based on these assumptions, a theoretical model of unfrozen water is established with independent variables of temperature, specific surface area, and electrical double‐layer parameters. While the input parameters of the theoretical model are numerous and difficult to obtain, the theoretical model is simplified as a parametric model. Results of the parametric model are strongly consistent with experimental data within a certain temperature range, supporting the hypothetical conditions. The similarity in the underlying mathematical structure of the derived theoretical and parametric models to current semi‐empirical models further suggests that the surface effects of clay are the main causes of unfrozen water in frozen soil.
Key Points
The presence of unfrozen water is explained by surface effects, adsorption forces, and the nature of the electrical double‐layer solution
The surface effects are defined as the combined actions of molecules and negative charges on the clay surface
The residual unfrozen water is a stable adsorption‐layer solution
Cobalt‐copper (CoCu) catalysts have industrial potential in CO/CO2 hydrogenation reactions, and CoCu alloy has been elucidated as a major active phase during reactions. However, due to elemental ...surface segregation and dealloying phenomena, the actual surface morphology of CoCu alloy is still unclear. Combining theory and experiment, the dual effect of surface segregation and varied CO coverage over the CoCu(111) surface on the reactivity in CO2 hydrogenation reactions is explored. The relationship between C−O bond scission and further hydrogenation of intermediate *CH2O was discovered to be a key step to promote ethanol production. The theoretical investigation suggests that moderate Co segregation provides a suitable surface Co ensemble with lateral interactions of co‐adsorbed *CO, leading to promoted selectivity to ethanol, in agreement with theory‐inspired experiments.
A method is described for theory‐based catalyst optimization of CoCu alloys in CO2 hydrogenation. Moderate Co surface segregation, boosted ethanol production, and suppressed methane generation suggest that theory‐guided catalyst optimization could be beneficial in similar alloy systems.
The sites of plant flavonoid biosynthesis, storage and final function often differ at the subcellular, cell, and even tissue and organ levels. Efficient transport systems for flavonoids across ...endomembranes and the plasma membrane are therefore required. However, a clear picture of the dynamic trafficking of flavonoids is only now beginning to emerge and appears to have many players. Here, we review current hypotheses for flavonoid transport, discuss whether these are mutually exclusive, highlight the importance of flavonoid efflux from vacuoles to the cytosol and consider future efforts to catch flavonoids ‘in the act’ of moving within and between cells. An improved understanding of transport mechanisms will facilitate the successful metabolic engineering of flavonoids for plant protection and human health.
Antibiotics are widely used in humans and animals, but there is a big concern about their negative impacts on ecosystem and human health after use. So far there is a lack of information on emission ...inventory and environmental fate of antibiotics in China. We studied national consumption, emissions, and multimedia fate of 36 frequently detected antibiotics in China by market survey, data analysis, and level III fugacity modeling tools. Based on our survey, the total usage for the 36 chemicals was 92700 tons in 2013, an estimated 54000 tons of the antibiotics was excreted by human and animals, and eventually 53800 tons of them entered into the receiving environment following various wastewater treatments. The fugacity model successfully predicted environmental concentrations (PECs) in all 58 river basins of China, which are comparable to the reported measured environmental concentrations (MECs) available in some basins. The bacterial resistance rates in the hospitals and aquatic environments were found to be related to the PECs and antibiotic usages, especially for those antibiotics used in the most recent period. This is the first comprehensive study which demonstrates an alarming usage and emission of various antibiotics in China.
Understanding the structure–activity relationship of surface lattice oxygen is critical but challenging to design efficient redox catalysts. This paper describes data‐driven redox activity ...descriptors on doped vanadium oxides combining density functional theory and interpretable machine learning. We corroborate that the p‐band center is the most crucial feature for the activity. Besides, some features from the coordination environment, including unoccupied d‐band center, s‐ and d‐band fillings, also play important roles in tuning the oxygen activity. Further analysis reveals that data‐driven descriptors could decode more information about electron transfer during the redox process. Based on the descriptors, we report that atomic Re‐ and W‐doping could inhibit over‐oxidation in the chemical looping oxidative dehydrogenation of propane, which is verified by subsequent experiments and calculations. This work sheds light on the structure–activity relationship of lattice oxygen for the rational design of redox catalysts.
Data‐driven interpretable descriptors were constructed to predict the redox activity of surface lattice oxygen on doped vanadium oxides by combining density functional theory (DFT) and machine learning (ML). Based on descriptors, physical insights into the structure–activity relationships were obtained and further guided the experimental verification of efficient redox catalysts for chemical looping oxidative dehydrogenation (CL‐ODH) of propane.
Direct conversion of methane to methanol using oxygen is experiencing renewed interest owing to the availability of new natural gas resources. Copper-exchanged zeolites such as mordenite and ZSM-5 ...have shown encouraging results, and di- and tri-copper species have been suggested as active sites. Recently, small eight-membered ring (8MR) zeolites including SSZ-13, -16, and -39 have been shown to be active for methane oxidation, but the active sites and reaction mechanisms in these 8MR zeolites are not known. In this work, we use density functional theory (DFT) calculations to systematically evaluate monocopper species as active sites for the partial methane oxidation reaction in Cu-exchanged SSZ-13. On the basis of kinetic and thermodynamic arguments, we suggest that CuIIOH+ species in the 8MR are responsible for the experimentally observed activity. Our results successfully explain the available spectroscopic data and experimental observations including (i) the necessity of water for methanol extraction and (ii) the effect of Si/Al ratio on the catalyst activity. Monocopper species have not yet been suggested as an active site for the partial methane oxidation reaction, and our results suggest that CuIIOH+ active site may provide complementary routes for methane activation in zeolites in addition to the known Cu–O–Cu2+ and Cu3O3 motifs.
Tens of thousands of metal–organic frameworks (MOFs) have been developed in the past two decades, and only ≈100 of them have been demonstrated as porous and hydrophobic. These hydrophobic MOFs ...feature not only a rich structural variety, highly crystalline frameworks, and uniform micropores, but also a low affinity toward water and superior hydrolytic stability, which make them promising adsorbents for diverse applications, including humid CO2 capture, alcohol/water separation, pollutant removal from air or water, substrate‐selective catalysis, energy storage, anticorrosion, and self‐cleaning. Herein, the recent research advancements in hydrophobic MOFs are presented. The existing techniques for qualitatively or quantitatively assessing the hydrophobicity of MOFs are first introduced. The reported experimental methods for the preparation of hydrophobic MOFs are then categorized. The concept that hydrophobic MOFs normally synthesized from predesigned organic ligands can also be prepared by the postsynthetic modification of the internal pore surface and/or external crystal surface of hydrophilic or less hydrophobic MOFs is highlighted. Finally, an overview of the recent studies on hydrophobic MOFs for various applications is provided and suggests the high versatility of this unique class of materials for practical use as either adsorbents or nanomaterials.
The structural design, preparation strategies, characterization methods, and potential applications of hydrophobic metal–organic frameworks (MOFs), a class of unique materials with both microporosity and hydrophobicity, are overviewed herein. It is highlighted that hydrophobic MOFs can be prepared by some facile procedures, and this type of materials can act as either advanced adsorbents or nanomaterials.
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