Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Metal-based electrocatalysts with different sizes (single atoms, nanoclusters, and nanoparticles) show different catalytic behaviors for various electrocatalytic reactions. Regulating the coordination environment of active sites with precision to rationally design an efficient electrocatalyst is of great significance for boosting electrocatalytic reactions. This review summarizes the recent process of heterogeneous supported single atoms, nanoclusters, and nanoparticles catalysts in electrocatalytic reactions, respectively, and figures out the construct strategies and design concepts based on their strengths and weaknesses. Specifically, four key factors for enhancing electrocatalytic performance, including electronic structure, coordination environment, support property, and interfacial interactions are proposed to provide an overall comprehension to readers in this field. Finally, some insights into the current challenges and future opportunities of the heterogeneous supported electrocatalysts are provided.

Design concept for electrocatalysts

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently emerged as a new class of atomically thin semiconductors for diverse electronic, optoelectronic, and valleytronic applications. To explore the full potential of these 2D semiconductors requires a precise control of their band gap and electronic properties, which represents a significant challenge in 2D material systems. Here we demonstrate a systematic control of the electronic properties of 2D-TMDs by creating mixed alloys of the intrinsically p-type WSe2 and intrinsically n-type WS2 with variable alloy compositions. We show that a series of WS2xSe2-2x alloy nanosheets can be synthesized with fully tunable chemical compositions and optical properties. Electrical transport studies using back-gated field effect transistors demonstrate that charge carrier types and threshold voltages of the alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. A highly p-type behavior is observed in selenium-rich alloy, which gradually shifts to lightly p-type, and then switches to lightly n-type characteristics with the increasing sulfur atomic ratio, and eventually evolves into highly n-doped semiconductors in sulfur-rich alloys. The synthesis of WS2xSe2-2x nanosheets with tunable optical and electronic properties represents a critical step toward rational design of 2D electronics with tailored spectral responses and device characteristics. © 2015 American Chemical Society.

Synthesis of WS2xSe2-2x alloy nanosheets with composition-tunable electronic properties

Molybdenum disulfide (MoS2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS2 nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS2 always outperforms the corresponding 2H phase MoS2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS2 or other layered materials with enhanced HER performance.

(Invited) Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Single-atom site catalysts (SACs) have received considerable attention for electrocatalytic applications, owing to their maximum atom-utilization efficiency, well-identified active centers, and tunable supports. Carbon-supported SACs have been widely applied in electrocatalysis, and their progress has been intensively reviewed. Non-carbon-supported SACs have drawn ever-increasing attention recently, and are emerging as an indispensable class of SACs. This review comprehensively summarizes the recent exciting progress on the non-carbon-supported SACs and their applications in electrocatalytic reactions. Eight types of non-carbon-supported SACs are firstly categorized to show their diversity. Subsequently, the anchoring and stabilization mechanisms for each type of non-carbon-supported SACs are systematically unraveled. Furthermore, the advanced characterization techniques for identifying and monitoring the atomic structure of SACs are highlighted. Thereafter, the advances of non-carbon-supported SACs for electrochemical energy conversion are discussed, which emphasizes their applications in the hydrogen evolution reaction, the oxygen evolution reaction, the oxygen reduction reaction, the N2 reduction reaction, and the CO2 reduction reaction. Finally, perspective insights into the current challenges and the future prospects for non-carbon-supported SACs are provided.

Non-carbon-supported single-atom site catalysts for electrocatalysis

Bimetallic chalcogenides for electrocatalytic CO2 reduction

A type-II van der Waals heterojunction photocatalyst is not only an ideal material for hydrogen production by water splitting, but also an important way to improve efficiency and produce low-cost clean energy. In this work, we unexpectedly found that monolayers of AlN and C2N, g-C3N4, and C6N8 all formed type-II heterojunctions according to density functional theory, and we report a comparison of their photocatalytic performance. Among them, the AlN/C2N heterojunction has an appropriate band gap value of 1.61 eV for visible light water splitting. It has higher carrier mobility than the AlN/g-C3N4 heterojunction (electron 253.1 cm2 V-1 s-1 > 31.6 cm2 V-1 s-1 and hole 11043.4 cm2 V-1 s-1 > 524.7 cm2 V-1 s-1), and an absorption peak similar those of monolayer C2N in visible light (8 × 104 cm-1) and monolayer AlN in ultraviolet light (11 × 104 cm-1). The Bader charge shows that the charge transfer number of the AlN/g-C3N4 heterojunction is higher than that of the AlN/C2N heterojunction, and its Gibbs free energy (-0.22 eV) is smaller than that of single-layer g-C3N4 (-0.30 eV). The AlN/C6N8 heterojunction also has a perfect band gap of 2.16 eV and an absorption peak of over 10 × 104 cm-1 in the UV region. Since a type-II heterojunction can effectively promote the separation of photogenerated electron-hole pairs and prevent their rapid recombination, the above heterojunctions are promising candidates for new photocatalysts.

Two-dimensional AlN/g-CNs van der Waals type-II heterojunction for water splitting.

The invention relates to a PC/ABS doped composite super-tough chemical-resistant material The material comprises the following components in parts by weight: 50-80 parts of PC resin; 10-30 parts of ABS resin; 1-10 parts of an inorganic nanoparticle; 20-30 parts of an elastic silicone acrylate emulsion; 05-5 parts of a peralkyl acrylate copolymer emulsion; 5-10 parts of a polydimethylsiloxane-styrene-methyl methacrylate graft copolymer; 01-1 part of an antioxidant; 01-1 part of a lubricant; 5-10 parts of a toughener; and 01-1 part of a heat stabilizer The PC/ABS doped composite material has excellent mechanical properties, high-temperature resistance, low-temperature resistance, and chemical resistance

PC/ABS doped composite super-tough chemical-resistant material

Abstract. Bulk-layered materials were constructed into nanowall arrays, and their optical absorption properties were investigated by the finite-difference time-domain technique. The results showed that the nanowall array exhibits excellent absorption properties in both ultraviolet and visible bands. For WS2, MoS2, WSe2, MoSe2, and MoTe2, when the excitation wavelength increases to a certain value, the absorption begins to obviously decrease, and the corresponding excitation wavelength shows a redshift trend. However, the absorptivity of graphene nanowall arrays remains above 0.9 in the 350- to 1200-nm band. In addition, with similar structural parameters, the absorption properties of nanowall arrays are better than those of nanorod arrays. The change in the structural parameter and morphology can lead to an increase in the pore number, specific surface area, and multistage reflection and achieve optical absorption enhancement. Graphene nanowall arrays show excellent absorption properties by our experimental measurement.

Design of graphene-like nanowall arrays and their optical absorption properties

A series of Cu-ZSM-5 molecular sieve adsorbents were prepared by the impregnation method. The experimental results revealed that the mercury removal efficiency of the 2.5 wt% CuCl2-ZSM-5 can reach up to 99%. Furthermore, both the crystal type and pore size distribution of the ZSM-5 molecular sieve remain the same after the process of copper-based active materials impregnated modification, and its specific surface area decreases as the load increases. Importantly, the surface of ZSM-5 modified by CuCl2 equips many more Cu-O functional groups, which are beneficial to the catalytic oxidation of mercury and can even oxidize Hg0 to Hg2+. The adsorption process strictly follows the Mars–Maessen reaction mechanism.

https://www.mdpi.com/2079-6412/12/6/772/pdf?version=1654489509

Jian Zeng

Papers

Bimetallic chalcogenides for electrocatalytic CO2 reduction

Two-dimensional AlN/g-CNs van der Waals type-II heterojunction for water splitting.

PC/ABS doped composite super-tough chemical-resistant material

Design of graphene-like nanowall arrays and their optical absorption properties

Removal of Elemental Mercury from Simulated Flue Gas by a Copper-Based ZSM-5 Molecular Sieve