Recently amorphous MoS2 thin film has attracted great attention as an emerging material for electrochemical hydrogen evolution reaction (HER) catalyst. Here we prepare the amorphous MoS2 catalyst on Au by atomic layer deposition (ALD) using molybdenum hexacarbonyl (Mo(CO)6) and dimethyl disulfide (CH3S2CH3) as Mo and S precursors, respectively. Each active site of the amorphous MoS2 film effectively catalyzes the HER with an excellent turnover frequency of 3 H2/s at 0.215 V versus the reversible hydrogen electrode (RHE). The Tafel slope (47 mV/dec) on the amorphous film suggests the Volmer-Heyrovsky mechanism as a major pathway for the HER in which a primary discharging step (Volmer reaction) for hydrogen adsorption is followed by the rate-determining electrochemical desorption of hydrogen gas (Heyrovsky reaction). In addition, the amorphous MoS2 thin film is electrically evaluated to be rather conductive (0.22 Ω(-1) cm(-1) at room temperature) with a low activation energy of 0.027 eV. It is one of origins for the high catalytic activity of the amorphous MoS2 catalyst.

Recently MoS₂ with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS₂ due to a lack of suitable chemistry. Here we report MoS₂ growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS₂ can be directly grown on a SiO₂/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E(1)₂g and A₁g) of 2H-MoS₂ with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS₂ layers to be aligned with its basal plane parallel to the substrate.

Sandwich‐type microporous hybrid carbon nanosheets (MHCN) consisting of graphene and microporous carbon layers are fabricated using graphene oxides as shape‐directing agent and the in‐situ formed poly(benzoxazine‐co‐resol) as carbon precursor. The reaction and condensation can be readily completed within 45 min. The obtained MHCN has a high density of accessible micropores that reside in the porous carbon with controlled thickness (e.g., 17 nm), a high surface area of 1293 m2 g−1 and a narrow pore size distribution of ca. 0.8 nm. These features allow an easy access, a rapid diffusion and a high loading of charged ions, which outperform the diffusion rate in bulk carbon and are highly efficient for an increased double‐layer capacitance. Meanwhile, the uniform graphene percolating in the interconnected MHCN forms the bulk conductive networks and their electrical conductivity can be up to 120 S m−1 at the graphene percolation threshold of 2.0 wt.%. The best‐practice two‐electrode test demonstrates that the MHCN show a gravimetric capacitance of high up to 103 F g−1 and a good energy density of ca. 22.4 Wh kg−1 at a high current density of 5 A g−1. These advanced properties ensure the MHCN a great promise as an electrode material for supercapacitors.

We report the wet-chemistry synthesis of a new type of porous carbon nanosheet whose thickness can be precisely controlled over the nanometer length scale. This feature is distinct from conventional porous carbons that are composed of micron-sized or larger skeletons, and whose structure is less controlled.The synthesis uses graphene oxide (GO) as the shape-directing agent and asparagine as the bridging molecule that connects the GO and in situ grown polymers by electrostatic interaction between the molecules. The assembly of the nanosheets can produce macroscopic structures, i.e., hierarchically porous carbon monoliths which have a mechanical strength of up to 28.9 MPa, the highest reported for the analogues. The synthesis provides precise control of porous carbons over both microscopic and macroscopic structures at the same time. In all syntheses the graphene content used was in the range 0.5-2.6 wt%, which is significantly lower than that of common surfactants used in the synthesis of porous materials. This indicates the strong shape-directing function of GO. In addition, the overall thickness of the nanosheets can be tuned from 20 to 200 nm according to a fitted linear correlation between the carbon precursor/GO mass ratio and the coating thickness. The porous carbon nanosheets show impressive CO 2 adsorption capacity under equilibrium, good separation ability of CO 2 from N 2 under dynamic conditions, and easy regeneration. The highest CO 2 adsorption capacities can reach 5.67 and 3.54 CO 2 molecules per nm 3 pore volume and per nm 2 surface area at 25 C and $1 bar. Broader contextThe control of anthropogenic CO 2 emissions is a crucial matter in view of the signicant role that this gas plays in global climate change. In recent years, great efforts have been directed towards the CO 2 capture and storage. Compared with the liquid-phase absorption process, the use of porous solids, especially porous carbons, as sorbents for capturing CO 2 has shown great promise due to the low cost, high availability, large surface area, an easy-to-design pore structure, hydrophobicity and low energy requirements for regeneration. Here we present a novel route for the preparation of porous carbon nanosheets (PCNs) whose thickness can be precisely controlled over the nanometer length scale from 20 to 200 nm. Benetting from the short diffusion paths and high microporosity, the PCNs exhibit high sorption capacity, fast sorption kinetics and a good CO 2 -N 2 selectivity.

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Understanding the mechanisms that promote cooperative behaviors of bacteria in their hosts is of great significance to clinical therapies. Environmental stress is generally believed to increase competition and reduce cooperation in bacteria. Here, we show that bacterial cooperation can in fact be maintained because of environmental stress. We show that Pseudomonas aeruginosa regulates the secretion of iron-scavenging siderophores in the presence of different environmental stresses, reserving this public good for private use in protection against reactive oxygen species when under stress. We term this strategy “conditional privatization”. Using a combination of experimental evolution and theoretical modeling, we demonstrate that in the presence of environmental stress the conditional privatization strategy is resistant to invasion by non-producing cheaters. These findings show how the regulation of public goods secretion under stress affects the evolutionary stability of cooperation in a pathogenic population, which may assist in the rational development of novel therapies.

The structure of bacterial biofilms depends on environmental conditions, such as availability of nutrients, during biofilm formation. In turn, variations in biofilm structure in part reflect differences in bacterial motility during early biofilm formation. Pseudomonas aeruginosa deprived of nutrients remain dispersed on a surface, whereas cells supplemented with additional nutrients cluster and form microcolonies. At the single-cell scale, how bacteria modify their motility to favour distinct life cycle outcomes remains poorly understood. High-throughput algorithms were used to track thousands of P. aeruginosa moving using type-IV pili (TFP) on surfaces in varying nutrient conditions and hence identify four distinct motility types. A minimal stochastic model was used to reproduce the TFP-driven motility types. We report that P. aeruginosa cells differently deploy TFP to alter the distribution of motility types under different nutrient conditions. Bacteria preferentially crawl unidirectionally under nutrient-limited conditions, but preferentially stall under nutrient-supplemented conditions. Motility types correlate with subcellular localisation of FimX, a protein required for TFP assembly and implicated in environmental response. The subcellular distribution of FimX is asymmetric for unidirectional crawling, consistent with TFP assembled primarily at the leading pole, whereas for non-translational types FimX expression is symmetric or non-existent. These results are consistent with a minimal stochastic model that reproduces the motility types from the subcellular average concentration and asymmetry of FimX. These findings reveal that P. aeruginosa deploy TFP symmetrically or asymmetrically to modulate motility behaviours in different nutrient conditions and thereby form biofilms only where nutrients are sufficient, which greatly enhances their competitive capacity in diverse environments.

Amorphous molybdenum sulfide (MoSx) has been identified as an excellent catalyst for the hydrogen evolution reaction (HER). It is still a challenge to prepare amorphous MoSx as a more active and stable catalyst for the HER. Here the amorphous MoSx catalysts are prepared on carbon fiber paper (CFP) substrates at 200 °C by a simple hydrothermal method using molybdic acid and thioacetamide. Because the CFP is intrinsically hydrophobic due to its graphene-like carbon structure, two kinds of hydrophilic pretreatment methods [plasma pretreatment (PP) and electrochemical pretreatment (EP)] are investigated to convert the hydrophobic surface of the CFP to be hydrophilic prior to the hydrothermal growth of MoSx. In the HER catalysis, the MoSx catalysts grown on the pretreated CFPs reach a cathodic current density of 10 mA/cm(2) at a much lower overpotential of 231 mV on the MoSx/EP-CFP and 205 mV on the MoSx/PP-CFP, compared to a high overpotential of 290 mV on the MoSx of the nonpretreated CFP. Turnover frequency per site is also significantly improved when the MoSx are grown on the pretreated CFPs. However, the Tafel slopes of all amorphous MoSx catalysts are in the range of 46-50 mV/dec, suggesting the Volmer-Heyrovsky mechanism as a major pathway for the HER. In addition, regardless of the presence or absence of the pretreatment, the hydrothermally grown MoSx catalyst on CFP exhibits such excellent stability that the degradation of the cathodic current density is negligible after 1000 cycles in a stability test, possibly due to the relatively high growth temperature.