Layered transition metal dichalcogenides are noble-metal free electrocatalysts for the hydrogen evolution reaction (HER). Instead of using the common hydrothermal synthesis, which requires high pressure and temperature, herein a relatively simple and controlled colloidal synthesis was used to produce an alloy of MoWSe with nanoflower morphology as a model system for the electrocatalysis of hydrogen evolution in both acidic and alkaline environments. The results show that MoWSe alloys exhibit better catalytic activity in both acidic and alkaline solutions with low overpotentials compared to pure MoSe and WSe. Moreover, the electrode kinetics was studied using electrochemical impedance spectroscopy (EIS) and the results indicate that the alloys exhibit improved catalytic activity with low Tafel slopes, making them appealing for HER in either environment. Additionally, when MoSe nanoflowers (NFs) are prepared by using different metal salts and chalcogenide precursors, changes in the HER catalytic activity were observed, despite the morphology and crystal structure similarities. This finding suggests that different results reported in the literature could originate from different synthetic methods of the TMD, emphasizing that a better understanding of the relationship between the synthetic route and the catalytic performance is still lacking.

Since its role in the prevention of osteoporosis in humans was proven some 30 years ago, calcium bioavailability has been the subject of numerous scientific studies. Recent technology allowing the production of a stable amorphous calcium carbonate (ACC) now enables a bioavailability analysis of this unique form of calcium. This study thus compares the solubility and fractional absorption of ACC, ACC with chitosan (ACC-C), and crystalline calcium carbonate (CCC). Solubility was evaluated by dissolving these preparations in dilute phosphoric acid. The results demonstrated that both ACC and ACC-C are more soluble than CCC. Fractional absorption was evaluated by intrinsically labeling calcium carbonate preparations with 45 Ca, orally administrated to rats using gelatin capsules. Fractional absorption was determined by evaluating the percentage of the administrated radioactive dose per milliliter that was measured in the serum, calcium absorption in the femur, and whole-body retention over a 34-hour period. Calcium serum analysis revealed that calcium absorption from ACC and ACC-C preparations was up to 40% higher than from CCC, whereas retention of ACC and ACC-C was up to 26.5% higher than CCC. Absorbed calcium in the femurs of ACC-administrated rats was 30% higher than in CCC-treated animals, whereas 15% more calcium was absorbed following ACC-C treatment than following CCC treatment. This study demonstrates the enhanced solubility and bioavailability of ACC over CCC. The use of stable ACC as a highly bioavailable dietary source for calcium is proposed based on the findings of this study. ß

MoSe2 is a 2D layered transition metal dichalcogenide that has attracted much attention because its properties may be easily altered by both morphology control and doping by substitutional transition metals. Here, the study of Ru-doped MoSe2 nanoflowers is presented, and the effect of Ru doping on their optical, electronic, and catalytic properties is presented. A significant enhancement in their catalytic properties toward the hydrogen evolution reaction (HER) is evident, showing an overpotential as low as 143 mV (at 10 mA cm–2) for samples by substituting 11.4% of the Mo with Ru. In order to gain understanding of the dopants’ interaction with the host and the nature of the atomic-scale substrate for the catalytic reaction, density functional theory (DFT) calculations are employed to trace the modulation of the density of states (DOS) near the Fermi level and to model possible dopant sites. The Ru dopants have two additional d electrons and a high DOS near the Fermi level. The optical absorption spectra were significantly affected by Ru doping, and the optical band gap of MoSe2 increased due to the Burstein–Moss effect. The increased charge carrier density enhances the conductance of the samples, but the most significant change is the reduction in the charge transfer resistance during the HER upon doping.

Thin films of layered semiconductors emerge as highly promising materials for energy harvesting and storage, optoelectronics and catalysis. Their natural propensity to grow as oriented crystals and films is one of their distinct properties under recent focal interest. Specifically, the reaction of transition metal films with chalcogen vapor can result in films of vertically aligned (VA) layers, while metal-oxides react with chalcogens in vapor phase to produce horizontally aligned crystals and films. The growth mechanisms of vertically oriented films are not yet fully understood, as well as their dependence on the initial metal film thickness and growth conditions. Moreover, the resulting electronic properties and the role of defects and disorder had not yet been studied, despite their critical influence on catalytic and device performance. In this work, we study the details of oriented growth of MoS2 with complementary theoretical and experimental approaches. We present a general theoretical model of diffusion-reaction growth that can be applied to a large variety of layered materials synthesized by solid-vapor reaction. Moreover, we inspect the relation of electronic properties to the structure of vertically aligned MoS2 and shed light on the density and character of defects in this material. Our measurements on Si-MoS2 p-n hetero-junction devices point to the existence of polarizable defects that impact applications of vertical transition-metal dichalcogenide materials.