Activating a Semiconductor-Liquid Junction via Laser-Derived Dual Interfacial Layers for Boosted Photoelectrochemical Water Splitting.

The semiconductor-liquid junction (SCLJ), the dominant place in photoelectrochemical (PEC) catalysis, determines the interfacial activity and stability of photoelectrodes, whcih directly affects the viability of PEC hydrogen generation. Though efforts dedicated in past decades, a challenge remains regarding creating a synchronously active and stable SCLJ, owing to the technical hurdles of simultaneously overlaying the two advantages. The present work demonstrates that creating an SCLJ with a unique configuration of the dual interfacial layers can yield BiVO4 photoanodes with synchronously boosted photoelectrochemical activity and operational stability, with values located at the top in the records of such photoelectrodes. The bespoke dual interfacial layers, accessed via grafting laser-generated carbon dots with phenolic hydroxyl groups (LGCDs-PHGs), are experimentally verified effective, not only in generating the uniform layer of LGCDs with covalent anchoring for inhibited photocorrosion, but also in activating, respectively, the charge separation and transfer in each layer for boosted charge-carrier kinetics, resulting in FeNiOOH-LGCDs-PHGs-MBVO photoanodes with a dual configuration with the photocurrent density of 6.08 mA cm-2 @ 1.23 VRHE , and operational stability up to 120 h @ 1.23 VRHE . Further work exploring LGCDs-PHGs from catecholic molecules warrants the proposed strategy as being a universal alternative for addressing the interfacial charge-carrier kinetics and operational stability of semiconductor photoelectrodes.

Low concentration of Tween-20 enhanced the adhesion and biofilm formation of Acidianus manzaensis YN-25 on chalcopyrite surface.

Although Tween-20 was used as an important catalyst to increase chalcopyrite bioleaching rate by acidophiles, the effect of Tween-20 on initial adhesion and biofilm development of acidophiles on chalcopyrite has not been explored until now. Herein, the role of Tween-20 in early attachment behaviors and biofilm development by Acidianus manzaensis strain YN-25 were investigated by adhesion experiments, adhesion force measurement, visualization of biofilm assays and a series of analyses including extended Derjaguin Landau Verwey Overbeek (DLVO) theory, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The bacterial adhesion experiments showed that 2 mg/L of Tween-20 increased the adhesion percentage (by 8%) of A. manzaensis YN-25. Tween-20 could promote the early adhesion of A. manzaensis YN-25 by changing the Lewis acid-base interaction and electrostatic force to increase total interaction energy and adhesion force. Besides, the functional groups on the surface of cells (carboxyl, hydroxyl and amino functional groups) contributed to the adhesion of A. manzaensis YN-25 on chalcopyrite. Furthermore, the promotion of biofilm formation by Tween-20 was mainly attributed to the reduction of S0 passivation layer formation and complexing more Fe3+ on chalcopyrite surface, contributing to the erosion of chalcopyrite and creating more corrosion pits. Live/dead staining showed low live/dead ratio (ranged from 0.35 to 1.32) during the biofilm development process. This report offers a better understanding of the effects of Tween-20 on attachment and biofilm development of acidophilic microorganisms and would lay a theoretical foundation for the better application of catalyst in bioleaching.

Ag+ significantly promoted the biofilm formation of thermoacidophilic archaeon Acidianus manzaensis YN-25 on chalcopyrite surface.

Silver ion (Ag+) is an important catalyst to improve chalcopyrite bio-dissolution, but its effects on initial adhesion behaviors and biofilm formation of acidophiles onto metal sulfide were still unknown. In this study, initial attachment behavior and adhesion force in the presence of Ag+ (0, 1, 2, 5, 10 and 20 mg/L) were comparatively analyzed for Acidianus manzaensis YN-25. Biofilm was observed by fluorescent images in the presence of 0, 1 and 2 mg/L Ag+. X-ray photoelectron spectroscopy (XPS) corroborated the catalytic mechanisms of Ag+ to biofilm formation. Results showed that Ag+ could significantly promote the attachment of cells on chalcopyrite, and the optimum concentration of Ag+ was 2 mg/L with the biggest percentage of attached cells (74%), followed by 5 mg/L (71%), whereas that for the control (0 mg/L) was only 61%. Ag+ significantly increased the interaction force between A. manzaensis YN-25 and chalcopyrite. Compared with the control, larger coverage of biofilm (up to 40% versus 32%) and more corrosion pits were observed on chalcopyrite in the presence of 2 mg/L Ag+. Moreover, Ag+ catalyzed chalcopyrite corrosion and accelerated biofilm formation by producing a loose porous Ag2S layer and Ag0 to decrease the resistivity. The live/dead ratio was small with a range of 0.31-1.38, suggesting that dead cells were a great slice during the whole life-cycle of biofilm on chalcopyrite. This report offers a profound insight into the promotion mechanism of Ag+ on adhesion behaviors and biofilm formation by thermoacidophilic archaeon under extremely acidic conditions.

Deep Molecular Orbital Driven High-Temperature Hydrogen Tautomerization Switching.

Hydrogen tautomerization molecular switches, a promising class of molecular components for the construction of complex nanocircuits, have been extensively studied using low-temperature scanning tunneling microscopy. However, these molecules are generally only reliably controllable in cryogenic environments, obstructing their utility in real devices. Here, we use dispersion-inclusive density functional theory and systematically investigate the adsorption and tautomerization behaviors of porphycene on six transition-metal surfaces. Among these surfaces, we found that hydrogen tautomerization on the Pt(110) surface corresponds to the largest switching barrier, allowing a controllable transition at high temperature. The switching behavior is closely related to the exceptional degree of charge transfer in the HOMO-2 orbital, illustrating the important role of deep orbital-surface interactions in porphycene molecular switching. Our work provides an in-depth understanding of the porphycene tautomerization mechanism and highlights new research avenues toward the practical application of molecular switches.

Vertical distribution of microbial communities in chromium-contaminated soil and isolation of Cr(â ¥)-Reducing strains.

Soil ecosystems surrounding chromium slag undergo continuous harsh physicochemical conditions due to multiple heavy metals contamination. Previous studies of soil microbial communities mainly focused on surface soil layer, while little was known about the depth-related distributions of the microbial communities in chromium (Cr)-contaminated soil. In this study, a comprehensive analysis of depth-related distributions of microbial communities in Cr-contaminated soil was carried out by Illumina sequencing of 16s rRNA genes. The results revealed that bacterial diversities at 0 cm depth layer were significantly higher than those below 20 cm depths. And there was a remarkable difference in bacterial compositions along with the sampling depths especially for the dominant phyla of Proteobacteria, Actinobacteria, Chloroflexi and Fimicutes (p < 0.05). While the archaea accounted for a relatively low proportion of the microbes and showed stability in the compositions with the predominant phyla of Thaumarchaeota and Euryarchaeota. The linear discriminate analysis (LDA) and effect size (LEfSe) analysis showed that there were thirty-seven kinds of biomarker microbes existing in the five soil layers with LDA threshold of 4.0, and each layer showed distinct microbial divisions, indicating that microbes with different biological functions might survive along with the sampling depths. The environmental variables including total chromium (Cr), Cr(Ⅵ), Mn, Ni, and Zn had considerable influences on microbial community composition in the contaminated soil. A total of 25 Cr(Ⅵ)-reducing strains were further isolated and identified, which were phylogenetically affiliated to Proteobacteria, Actinobacteria and Firmicutes. Among the isolated Cr(Ⅵ)-reducing strains, Bacillus stratosphericus was the first time to be reported with Cr(Ⅵ) reducing capacity.

Switchable Schottky Contacts: Simultaneously Enhanced Output Current and Reduced Leakage Current.

Metal-semiconductor contacts are key components of nanoelectronics and atomic-scale integrated circuits. In these components Schottky diodes provide a low forward voltage and a very fast switching rate but suffer the drawback of a high reverse leakage current. Improvement of the reverse bias characteristics without degrading performance of the diode at positive voltages is deemed physically impossible for conventional silicon-based Schottky diodes. However, in this work we propose that this design challenge can be overcome in the organic-based diodes by utilizing reversible transitions between distinct adsorption states of organic molecules on metal surfaces. Motivated by previous experimental observations of controllable adsorption conformations of anthradithiophene on Cu(111), herein we use density functional theory simulations to demonstrate the distinct Schottky barrier heights of the two adsorption states. The higher Schottky barrier of the reverse bias induced by a chemisorbed state results in low leakage current, while the lower barrier of the forward bias induced by a physisorbed state yields a larger output current. The rectifying behaviors are further supported by nonequilibrium Green's function transport calculations.

Tuning the work function of stepped metal surfaces by adsorption of organic molecules.

Understanding the binding mechanisms for aromatic molecules on transition-metal surfaces, especially with defects such as vacancies, steps and kinks, is a major challenge in designing functional interfaces for organic devices. One important parameter in the performance of organic/inorganic devices is the barrier of charge carrier injection. In the case of a metallic electrode, tuning the electronic interface potential or the work function for electronic level alignment is crucial. Here, we use density-functional theory (DFT) calculations with van der Waals (vdW) interactions treated with both screened pairwise (vdWsurf) and many-body dispersion (MBD) methods, to systematically study the interactions of benzene with a variety of stepped surfaces. Our calculations confirm the physisorptive character of Ag(2 1 1), Ag(5 3 3), Ag(3 2 2), Ag(7 5 5) and Ag(5 4 4) surfaces upon the adsorption of benzene. The MBD effects reduce the adsorption energies by about 0.15 eV per molecule compared to the results from the DFT + vdWsurf method. In addition, we find that the higher the step density, the larger the reduction of the work function upon the adsorption of benzene. We also study the effect of vdW interactions on the electronic structure using a fully self-consistent implementation of the vdWsurf method in the Kohn-Sham DFT framework. We find that the self-consistent vdWsurf effects increase the work function due to the lowered Fermi level and the increased vacuum level. As a result, the benzene/Ag(2 1 1) system has the lowest work function (3.67 eV) among the five adsorption systems, significantly smaller than the work function of the clean Ag(1 1 1) surface (4.74 eV). Our results provide important insights into the stability and electronic properties of molecules adsorbed on stepped metal surfaces, which could help in designing more appropriate interfaces with low work functions for electron transfer.