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Studying the localized electrocatalytic activity of heterogeneous electrocatalysts is crucial for understanding electrocatalytic reactions and further improving their performance. However, correlating the electrocatalytic activity with the microscopic structure of two-dimensional (2D) electrocatalysts remains a great challenge due to the lack of in situ imaging techniques and methods of tuning structures with atomic precision. Here, we present a general method of probing the layer-dependent electrocatalytic activity of 2D materials in situ using a plasmonic imaging technique. Unlike the existing methods, this approach was used to visualize the surface charge density and electrocatalytic activity of single 2D MoS2 nanosheets, enabling the correlation of layer-dependent electrocatalytic activity with the surface charge density of single MoS2 nanosheets. This work provides insights into the electrocatalytic mechanisms of 2D transition metal dichalcogenides, and our approach can serve as a promising platform for investigating electrocatalytic reactions at the heterogeneous interface, thus guiding the rational design of high-performance electrocatalysts.

We have performed sound velocity and unit cell volume measurements of three synthetic, ultrafine micro/nanocrystalline grossular samples up to 50 GPa using Brillouin spectroscopy and synchrotron X-ray diffraction. The samples are characterized by average grain sizes of 90 nm, 93 nm and 179 nm (hereinafter referred to as samples Gr90, Gr93, and Gr179, respectively). The experimentally determined sound velocities and elastic properties of Gr179 sample are comparable with previous measurements, but slightly higher than those of Gr90 and Gr93 under ambient conditions. However, the differences diminish with increasing pressure, and the velocity crossover eventually takes place at approximately 20–30 GPa. The X-ray diffraction peaks of the ultrafine micro/nanocrystalline grossular samples significantly broaden between 15–40 GPa, especially for Gr179. The velocity or elasticity crossover observed at pressures over 30 GPa might be explained by different grain size reduction and/or inhomogeneous strain within the individual grains for the three grossular samples, which is supported by both the pressure-induced peak broadening observed in the X-ray diffraction experiments and transmission electron microscopy observations. The elastic behavior of ultrafine micro/nanocrystalline silicates, in this case, grossular, is both grain size and pressure dependent.

Biological synthesis of quantum dots (QDs) as an environmental-friendly and facile preparation method has attracted increasing interests. However, it is difficult to distinguish the roles of bio-thiols in QDs synthesis process because of the complex nature in organisms. In this work, the CdSe QDs synthesis conditions in organisms were reconstructed by using a simplified in vitro approach to uncover the roles of two small bio-thiols in the QDs formation. CdSe QDs were synthesized with glutathione (GSH) and L-cysteine (Cys) respectively. Compared with Cys at the same molar concentration, the CdSe QDs synthesized by GSH had a larger and broader particle size distribution with improved optical properties and crystal structure. Furthermore, quantum chemical calculations indicate that the stronger Cd2+ binding capacity of GSH contributed a lot to the CdSe QDs formation despite of the greater capability Cys for selenite reduction. This work clearly demonstrates the different roles of small thiols in the Cd2+ stabilization in the environment and biomimetic QDs synthesis process.

LiNi1/3Co1/3Mn1/3O2 nanocrystallites were synthesized by a one-step hydrothermal method, and uniform second particles were formed by a subsequent calcination process. X-ray diffraction results indicate that the as-synthesized material can be indexed by α-NaFeO2 layered structure with R-3 m space group. The results of Rietveld refinements show the I 003/I 104 value of the material is 2.032, and the nanostructured material presents low cation mixing, small cell volume, and a consequent suppression of lattice strain. The rate performances of the as-synthesized material can be further improved by coating Al2O3. The discharging capacity of Al2O3-coated material reaches 154.4 mAh g−1, and the capacity retention maintains 80.3 % after 50 cycles at 5 C in the voltage range of 2.5 to 4.5 V, while those of the bare one is only 139.0 mAh g−1 and 71.6 %, respectively. The transmission electron microcopy observation shows no zigzag layer exists on the surface of particle after cycles for Al2O3-coated LiNi1/3Co1/3Mn1/3O2. Compared to bare LiNi1/3Co1/3Mn1/3O2, the de-intercalation potential difference before and after cycles of Al2O3-coated one is smaller. This indicates that Al2O3 coating can reduce the electrochemistry polarization in the electrode bulk.

Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

The concentration of nitrate in aquatic systems is rising with the development of modern industry and agriculture, causing a cascade of environmental problems. Here we describe a previously unreported nitrate formation process. Both indoor and outdoor experiments are conducted to demonstrate that nitrate may be formed from abundant atmospheric nitrogen and oxygen on nano-sized titanium dioxide surfaces under UV or sunlight irradiation. We suggest that nitric oxide is an intermediate product in this process, and elucidate its formation mechanisms using first-principles density functional theory calculations. Given the expanding use of titanium dioxide worldwide, such a titanium dioxide-mediated photocatalysis process may reveal a potentially underestimated source of nitrate in the environment, which on one hand may lead to an increasing environmental pollution concern, and on the other hand may provide an alternative, gentle and cost-effective method for nitrate production.

Electrochemically active bacteria (EAB) are ubiquitous in environment and have important application in the fields of biogeochemistry, environment, microbiology and bioenergy. However, rapid and sensitive methods for EAB identification and evaluation of their extracellular electron transfer ability are still lacking. Herein we report a novel photometric method for visual detection of EAB by using an electrochromic material, WO(3) nanoclusters, as the probe. This method allowed a rapid identification of EAB within 5 min and a quantitative evaluation of their extracellular electron transfer abilities. In addition, it was also successfully applied for isolation of EAB from environmental samples. Attributed to its rapidness, high reliability, easy operation and low cost, this method has high potential for practical implementation of EAB detection and investigations.

Metal sulfide semiconductors, such as molybdenum disulfide (MoS2) and bismuth trisulphide (Bi2S3), are of considerable interest for their excellent applications in photocatalysis and in many other fields. However, the controllable synthesis of MoS2/Bi2S3 hybrid nanostructures remains a challenge. In this study, we report a unique sacrificial templating strategy for preparing layer-controlled MoS2 on three-dimensional (3D) Bi2S3 micro-flowers. For this approach, Bi2S3 was utilized as a sacrificial template to regulate the ion exchange, and the dosage of molybdenum was adjusted to tune the dynamic formation, thus converting the MoS2 nanosheets on the Bi2S3 micro-flowers from monolayer to multilayer. Such a 3D flower-like hybrid nanostructure enables MoS2/Bi2S3 to exhibit adsorption-promoted photocatalysis under visible light irradiation, especially for the excellent photodegradation of low-concentration organic pollutants, for example, azo dye and atrazine. The observed superiority of the 3D MoS2/Bi2S3 was mainly attributed to the increased mass transfer, robust light-harvesting capacity, improved charge separation, lower oxygen-activation barrier and enhanced active oxygen yield. Our findings are of interest for the development of novel S-based photocatalysts and provide a new opportunity to efficiently remove low-concentration refractory pollutants. Researchers have combined inorganic ‘microflowers’ and metallic nanosheets to help remove persistent organic pollutants with sunlight. Bismuth trisulphide (Bi2S3) is a promising environmental photocatalyst because of its low toxicity and direct bandgap, but suffers from lower-than-expected chemical activity due to charge recombination. To better separate photogenerated charges, Han-Qing Yu and co-workers from the University of Science and Technology of China developed a one-pot, hydrothermal synthesis that transforms bismuth precursors into three-dimensional (3D) microstructures with petal-like shapes. The Bi2S3 microflowers then act as a template, growing multilayers of MoS2 onto the hybrid framework. The large, charge-stabilizing surface area of 3D MoS2/Bi2S3 had promising photocatalytic activity. For example, concentrations of atrazine — a common weed-killer difficult to remove from water runoff streams — were 89% lower after 4 hours of exposure to light and 3D MoS2/Bi2S3. A sacrificial strategy is developed for preparing layer-controlled MoS2 on three-dimensional Bi2S3 micro-flowers using a facile method. The nanostructured hybrid enables adsorption-promoted photocatalysis under visible light irradiation for excellent degradation of low-concentration organic pollutants, because of the increased mass transfer, robust light-harvesting capacity, improved charge separation, reduced oxygen-activation barrier and enhanced active oxygen yield.