Atomic layer deposition of tungsten sulfide using a new metal-organic precursor and H2S: thin film catalyst for water splitting.

Transition metal dichalcogenides (TMDs) are extensively researched in the past few years due to their two-dimensional layered structure similar to graphite. This group of materials offers tunable optoelectronic properties depending on the number of layers and therefore have a wide range of applications. Tungsten disulfide (WS2) is one of such TMDs that has been studied relatively less compared to MoS2. Herein, WS x thin films are grown on several types of substrates by atomic layer deposition (ALD) using a new metal-organic precursor [tris(hexyne) tungsten monocarbonyl, W(CO)(CH3CH2C≡CCH2CH3)3] and H2S molecules at a relatively low temperature of 300 °C. The typical self-limiting film growth by varying both, precursor and reactant, is obtained with a relatively high growth per cycle value of ∼0.13 nm. Perfect growth linearity with negligible incubation period is also evident in this ALD process. While the as-grown films are amorphous with considerable S-deficiency, they can be crystallized as h-WS2 film by post-annealing in the H2S atmosphere above 700 °C as observed from x-ray diffractometry analysis. Several other analyses like Raman and x-ray photoelectron spectroscopy, transmission electron microscopy, UV-vis. spectroscopy are performed to find out the physical, optical, and microstructural properties of as-grown and annealed films. The post-annealing in H2S helps to promote the S content in the film significantly as confirmed by the Rutherford backscattering spectrometry. Extremely thin (∼4.5 nm), as-grown WS x films with excellent conformality (∼100% step coverage) are achieved on the dual trench substrate (minimum width: 15 nm, aspect ratio: 6.3). Finally, the thin films of WS x (as-grown and 600/700 °C annealed) on W/Si and carbon cloth substrate are investigated for electrochemical hydrogen evolution reaction (HER). The as-grown WS x shows poor performance towards HER and is attributed to the S-deficiency, amorphous character, and oxygen contamination of the WS x film. Annealing the WS x film at 700 °C results in the formation of a crystalline layered WS2 phase, which significantly improves the HER performance of the electrode. The study reveals the importance of sulfur content and crystallinity on the HER performance of W-based sulfides.

Anti-inflammatory effect of bee venom in phthalic anhydride-induced atopic dermatitis animal model.

Globally, many people have been affected with atopic dermatitis (AD), a chronic inflammatory skin disease. AD is associated with multiple factors such as genetic, inflammatory, and immune factors. Bee venom (BV) is now widely used for the treatment of several inflammatory diseases. However, its effect on 5% phthalic anhydride (PA)-induced AD has not been reported yet. We investigated the anti-inflammatory and anti-AD effects of BV in a PA-induced animal model of AD. Balb/c mice were treated with topical application of 5% PA to the dorsal skin and ears for induction of AD. After 24 h, BV was applied on the back and ear skin of the mice three times a week for 4 weeks. BV treatment significantly reduced the PA-induced AD clinical score, back and ear epidermal thickness, as well as IgE level and infiltration of immune cells in the skin tissues compared to those of control mice. The levels of inflammatory cytokines in the serum were significantly decreased in BV-treated group compared to PA-treated group. In addition, BV inhibited the expression of iNOS and COX-2 as well as the activation of mitogen-activated protein kinase (MAPK) and NF-Ò¡B induced by PA in the skin tissues. We also found that BV abrogated the lipopolysaccharide or TNF-α/IFN-γ-induced NO production, expression of iNOS and COX-2, as well as MAPK and NF-Ò¡B signaling pathway in RAW 264.7 and HaCaT cells. These results suggest that BV may be a potential therapeutic macromolecule for the treatment of AD.

Hydrogen Evolution Reaction by Atomic Layer-Deposited MoNx on Porous Carbon Substrates: The Effects of Porosity and Annealing on Catalyst Activity and Stability.

Molybdenum-based compounds are considered as a potential replacement for expensive precious-metal electrocatalysts for the hydrogen evolution reaction (HER) in acid electrolytes. However, coating of thin films of molybdenum nitride or carbide on a large-area self-standing substrate with high precision is still challenging. Here, MoNx is uniformly coated on carbon cloth (CC) and nitrogen-doped carbon (NC)-modified CC (NCCC) substrates by atomic layer deposition (ALD). The as-deposited film has a nanocrystalline character close to amorphous and a composition of approximately Mo2 N with significant oxygen contamination, mainly at the surface. Among the as-prepared ALD-MoNx electrodes, the MoNx /NCCC has the highest HER activity (overpotential η≈236 mV to achieve 10 mA cm-2 ) owing to the high surface area and porosity of the NCCC substrate. However, the durability of the electrode is poor, owing to the poor adhesion of NC powder on CC. Annealing MoNx /NCCC in H2 atmosphere at 400 °C improves both the activity and durability of the electrode without significant change in the phase or porosity. Annealing at an elevated temperature of 600 °C results in formation of a Mo2 C phase that further enhances the activity (η≈196 mV to achieve 10 mA cm-2 ), although there is a huge reduction in the porosity of the electrode as a consequence of the annealing. The structure of the electrode is also systematically investigated by electrochemical impedance spectroscopy (EIS). A deviation in the conventional Warburg impedance is observed in EIS of the NCCC-based electrode and is ascribed to the change in the H+ ion diffusion characteristics, owing to the geometry of the pores. The change in porous nature with annealing and the loss in porosity are reflected in the EIS of H+ ion diffusion observed at high-frequency. The current work establishes a better understanding of the importance of various parameters for a highly active HER electrode and will help the development of a commercial electrode for HER using the ALD technique.