Thermoelectric material has the unique ability to directly convert waste heat into electricity, and theoretical guidance is an efficient method for exploring high-performance nanostructured thermoelectric materials. By using first-principles method, we systematically present the ballistic thermoelectric properties of four representative series of transition metal dichalcogenides (WSe2, MoSe2, WS2, and MoS2), each including monolayer, zigzag (10, 0), and armchair (6, 6) nanotubes. Consistent regularity can be seen for each considered series. From monolayer to small nanotubes, degeneration of thermoelectric figure of merit is observed, which indicates that transition metal dichalcogenide monolayers exhibit better thermoelectric performance than the small nanotubes. In addition, it is interesting to find out the divergence pattern with regard to the phononic thermal conductance, which points out that the room-temperature phononic thermal conductance of monolayers is bigger than that of zigzag (10, 0) nanotube but lower than that of armchair (6, 6) nanotube.

Nowadays, new emerging two-dimensional (2D) materials have become a hot topic in the field of theoretical physics, material science, and nanotechnology engineering due to their high surface area, planar structure, and quantum confinement effect. Within a two-dimensional framework, we systematically concentrate on the buckled and puckered systems consisting of the VA group elements (denoted as arsenene, antimonene, and bismuthene). Among these studied systems, the buckled antimonene harbors a thermoelectric figure of merit (ZT) of 2.15 at room temperature. This is probably the highest value that has ever been reported in pristine 2D materials. By simple biaxial strain engineering, the ZT can even get enhanced to 2.9 under 3% tensile strain. The enhancement mainly results from both tuning the electronic structures and reducing the thermal conductance. This work predicts a new promising candidate in thermoelectric devices, based on the fact that buckled antimonene has been lately fabricated and proved to be stable at ambient conditions.

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In recent years, Cu foam has attracted intensive attention owing to its remarkable performance for oil/water separation. Most research mainly focused on Cu foam with surfactant decoration, which results in superhydrophobic or even stimuliresponsed membranes. Fabricating Cu foam with intrinsic superhydrophilicity via simple operations still remains as a challenge. Herein, we synthesized superhydrophilic and under-water superoleophobic Cu foam that consists of oxychloridized hierarchical nanoparticles with metal Cu core and polar Cu2O/CuO1-x/2Clx shell via the combination of anodization, HCl etching and calcination. This material shows ultrahigh water permeability (5 μl water-droplet permeating within 9 ms). And the oil/water separation efficiency of superhydrophilic Cu foam (SCuF) is above 99% with the oil content in separated water lower than 3 ppm. Moreover, the oil/water separation performance of SCuF for repeated use and anticorrosion are also excellent. To the best of our knowledge, it is the first attempt to synthesize intrinsic superhydrophilic Cu foam for effective oil/water separation. Due to the greatly enhanced specific surface area and active sites, it has potential applications in catalysis, hydrogen evolution process, electrode materials and many other environmental protection and energy fields.

An in situ Raman study of the mechanism of HER catalytic performance enhanced by high-index facets on Ti@TiO2 nanosheets.