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The development of visible light-responsive semiconductor photocatalysts has inspired extensive interest, but the number is very limited for the quantum dot (QD)-based ones. Herein, an emerging mono-elemental material, violet phosphorus (VP) QDs, was synthesized via liquid-phase exfoliation, whose lateral size and thickness could be tuned by varying the centrifugation speed. The VPQDs show a bandgap of 2.06 eV with potentials of conduction and valence bands straddled for the water reduction and oxidation, and the longitudinal destruction of VP exposes abundant surface active sites. More importantly, the VPQDs exhibit rapid photogenerated charge mobility and improved charge separation efficiency after loading with a Rh cocatalyst. Consequently, we give the first demonstration that the VPQDs as a novel 600 nm-class photocatalyst are active for H2 evolution under visible light irradiation, showing activities of approximately 18 and 80 times greater than that of bulk VP and black phosphorus QDs, and delivering an apparent quantum yield of 2.86% at 475 nm. To our knowledge, the photocatalytic H2 evolution rate of 3325.1 μmol h−1 g−1 observed on the VPQDs in this work should be the highest among all the mono-elemental-based photocatalysts. [ABSTRACT FROM AUTHOR]

Cr2Se3 crystallizes in a NiAs-type structure and is antiferromagnetic with a Néel temperature of TN = 43 K (M. Yuzuri, 1973). Here seven samples with nominal composition Cr2+xSe3 (x = −0.04, −0.02, 0, 0.04, 0.06, 0.08 and 0.12) were prepared by solid state reaction and spark plasma sintering (SPS). The phase composition was characterised by X-ray diffraction (XRD). The electrical conductivity, Seebeck coefficient, thermal conductivity, and Hall effect measurements of all compounds were performed. Both Seebeck coefficients and Hall coefficients show that Cr2+xSe3 are p-type materials when x = −0.04, −0.02, 0 and 0.04, and switch to n-type when x = 0.06, 0.08 and 0.12. An effective magnetic moment μeff = 3.85 μB per Cr ion in Cr2Se3 is obtained by the Curie–Weiss law. We also calculate and compare the band gap values of Cr2+xSe3 by various methods, such as the Arrhenius formula, the Goldsmid–Sharp equation and the optical spectrum. Moderate zT values are obtained for p-type Cr2.04Se3 and n-type Cr2.08Se3 at a relatively low temperature above room temperature. These results indicate the availability of p- and n-type legs in binary transition metal chalcogenides and reveal their potential for wide scale thermoelectric applications. [ABSTRACT FROM AUTHOR]

Engineering of thermoelectric materials through hybridization with nanoparticles has been proved effective to boost their thermoelectric efficiency by providing the means to decouple thermal and electrical transport phenomena. Here, we report the synthesis of p-type Bi0.5Sb1.5Te3/X wt% Sb2O3 (X = 0, 1, 2, 4, 6) nanocomposites, in which the Sb2O3 nanoparticles are dispersed mainly at the grain boundaries of the Bi0.5Sb1.5Te3 matrix. It is shown that incorporation of up to 4 wt% Sb2O3 into the matrix results in simultaneous enhancement of the Seebeck coefficient (by filtering of low energy charge carriers) and decline of thermal conductivity (mainly by charge carrier scattering at the interfaces), both of which contribute to improving the thermoelectric figure of merit to a maximum of 1.51 at 350 K. Moreover, the nanocomposites with 2, 4, and 6 wt% Sb2O3 demonstrate ZT ＞ 1.0 up to 450 K, making them commercially appealing for thermoelectric applications in a wide temperature range. Furthermore, it is shown that Bi0.5Sb1.5Te3/4 wt% Sb2O3 samples exhibit excellent thermal and chemical stability in ambient atmosphere and 300–475 K temperature range over a 24 month period. [ABSTRACT FROM AUTHOR]

Thin-layer MoS 2 has attracted much interest because of its potential in diverse technologies, including electronics, optoelectronics and catalysis these few years. In particular, finding a simple and effective solution for large-scale growth of thin-layer semiconductor nanosheets is a prerequisite for achieving their excellent performance. In this paper, we investigated four different substrates under identical conditions for MoS 2 film growth and observed a strong correlation between substrate surface conditions and MoS 2 growth. To enhance substrate performance, a low-concentration NaCl water solution (25 mg mL -1 ) was employed for pre-treating the substrate surface, thereby modifying its initial state. In the chemical vapor deposition (CVD) growth environment, the introduced halide ions served as surface dangling bonds. The pre-treated led to a remarkable 90% increase in the growth rate of MoS 2 on the substrate surface, facilitating the production of large monolayer MoS 2 sheets (∼200 μm). This growth mechanism further enabled the manufacturing of ultra-large single crystals (∼1 mm). Consequently, our research presents a straightforward and cost-effective approach for the large-scale production of nanosheets. Field-effect transistors (FETs) based on the pre-treated monolayer MoS 2 exhibited high mobility (12 cm 2 V -1 s -1 ) and a large on/off ratio (10 4 ). Therefore, our research provides a simple and low-cost approach for large-scale production of nanosheets for use in high-quality electronics over large areas., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Two-dimensional (2D) Nb-based oxynitrides are promising visible-light-responsive photocatalysts for the water splitting reaction, but their photocatalytic activity is degraded by the formation of reduced Nb 5+ species and O 2- vacancies. To understand the influence of nitridation on the formation of crystal defects, this study synthesized a series of Nb-based oxynitrides through the nitridation of LaKNaNb 1- x Ta x O 5 ( x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). During nitridation, K and Na species volatilized, which helped transform the exterior of LaKNaNb 1- x Ta x O 5 into a lattice-matched oxynitride shell. Ta inhibited defect formation, yielding Nb-based oxynitrides with a tunable bandgap between 1.77 and 2.12 eV, straddling the H 2 and O 2 evolution potentials. After loading with Rh and CoO x cocatalysts, these oxynitrides exhibited good photocatalytic activity for H 2 and O 2 evolution in visible light (650-750 nm). The nitrided LaKNaTaO 5 and LaKNaNb 0.8 Ta 0.2 O 5 delivered the maximum H 2 (19.37 μmol h -1 ) and O 2 (22.81 μmol h -1 ) evolution rates, respectively. This work provides a strategy for preparing oxynitrides with low defect densities and demonstrates the promising performance of Nb-based oxynitrides for water splitting., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Reducing the thermal conductivity ( κ ) of mesoporous N-doped titania (TiO 2 ) is crucial for the development of TiO 2 -based materials that exhibit excellent electronic, photochemical, and thermoelectric properties. Mesopores can contribute to the reduction of κ via phonon scattering, and the scattering effect due to the randomness of crystal interfaces should be significantly reduced to clarify the role of mesopores in reducing thermal conductivity. Highly ordered mesoporous N-doped TiO 2 comprising large crystallites was prepared with silica colloidal crystals as a template into which a Ti source was introduced, followed by calcination with urea. N-doped samples comprising large crystallites exhibiting random mesopores were also prepared and used for the investigation of the effects of the shape and arrangement of the mesopore on phonon scattering. The mesostructures of the two separately prepared N-doped TiO 2 samples were retained after sintering at 873 K and 80 MPa to fabricate pellets. Furthermore, the effective suppression of the long mean-free-path phonon conduction by the thin pore walls at a nanometer scale thickness significantly reduced the thermal conductivities of both samples. The presence of ordered mesopores further contributed to the reduction of κ , which was probably due to the enhanced contribution of the backscattering of phonons caused by ordered pore wall surfaces., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)