Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation. Currently, their stability in water is a vital and urgent research question. In this paper a novel approach to stabilize a bismuth halide perovskite [(CH₃)₂NH₂]₃[BiI₆] (DA₃BiI₆) in water using dimethylammonium iodide (DAI) without the assistance of acids or coatings is reported. The DA₃BiI₆ powder exhibits good stability in DAI solutions for at least two weeks. The concentration of DAI is found as a critical parameter, where the I⁻ ions play the key role in the stabilization. The stability of DA₃BiI₆ in water is realized via a surface dissolution-recrystallization process. Stabilized DA₃BiI₆ demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I⁻ ions and with PtCl₄ as a co-catalyst (Pt-DA₃BiI₆), photocatalytic H₂ evolution with a rate of 5.7 μmol·h⁻¹ from HI in DAI solution, obtaining an apparent quantum efficiency of 0.83% at 535 nm. This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.

In the next generation wireless communication systems operating at near terahertz frequencies, dielectric substrates with the lowest possible permittivity and loss factor are becoming essential. In this work, highly porous (98.9% ± 0.1%) and lightweight silica foams (0.025 ± 0.005 g/cm³), that have extremely low relative permittivity (ε_r = 1.018 ± 0.003 at 300 GHz) and corresponding loss factor (tan δ < 3 × 10^-4 at 300 GHz) are synthetized by a template-assisted sol-gel method. After dip-coating the slabs of foams with a thin film of cellulose nanofibers, sufficiently smooth surfaces are obtained, on which it is convenient to deposit electrically conductive planar thin films of metals important for applications in electronics and telecommunication devices. Here, micropatterns of Ag thin films are sputtered on the substrates through a shadow mask to demonstrate double split-ring resonator metamaterial structures as radio frequency filters operating in the sub-THz band.

Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS₂ nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm^-1) as well as high selectivity towards H₂S relative to CO, NH₃, H₂, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm^-1, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS₂ alone are not sufficient to explain the observed high sensitivity towards H₂S. A major role in this behavior is also played by O doping in the S sites of the WS₂ lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.