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Wearable technologies are attracting increasing attention in the materials science field, prompting a quest for active components with beneficial functional attributes whilst ensuring human and environmental safety. Hydrogels are highly biocompatible platforms with interesting mechanical properties, which can be exploited for the construction of strain sensors. In order to improve the directionality of their strain response and combine it with electrical properties to fabricate piezoresistive devices, it is possible to incorporate various types of nanofillers within the polymeric network of the hydrogels. 2D materials are ideal nanofillers thanks to their intrinsic two‐dimensional anisotropy and unique electronic properties. Herein, the covalent functionalization of 2D 1T‐MoS2 is exploited to build robust hybrid cross‐linked networks with a polyethylene glycol diacrylate gel (PEGDA). The conductivity of this nanocomposite is also further improved by inducing the interfacial polymerization of aniline. The resulting free‐standing samples demonstrate a linear and highly reversible piezoresistive response in a pressure range compatible with that of peripheral blood, while also featuring good compatibility with human skin cells, thereby making them interesting options for incorporation into wearable strain sensors. [ABSTRACT FROM AUTHOR]

MoS2 and WS2 have gathered significant attention due to their tunable properties and wide range of applications. Liquid‐phase exfoliation (LPE) is a facile method to prepare 2D MoS2 and WS2. Currently, the principally employed solvents for LPE of MoS2 and WS2 are expensive and toxic, and have high boiling points. These drawbacks encourage to find more sustainable alternatives to the liquid medium used for the preparation of 2D material inks. Water is the best option, but surfactants are necessary for LPE in water, since MoS2 and WS2 are hydrophobic. Organic molecules with amphoteric character such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium hexadecyl sulfonate (SHS) are selected as suitable candidates for the role. However, the study of these surfactants used in LPE is barely systematically reported. In this work, a detailed investigation is presented on their impact on the LPE of MoS2 and WS2, which are representatives of transition‐metal dichalcogenides. By characterizing and qualifying the products from average number of layers, it is found that all the surfactants work efficiently to exfoliate MoS2 and WS2 into few layers, and SHS stabilizes the 2D layers better than the other two. However, in terms of yield and relative surfactant concentration, a real trade‐off is not identified between maximized quantity of exfoliated materials and minimized surfactant concentration, which prompts to select the colloidal ink based on the specific further needs for processing. [ABSTRACT FROM AUTHOR]

The photoelectrocatalytic (PEC) hydrogen evolution reaction (HER) holds immense promise as a clean and sustainable method for hydrogen production. However, finding a suitable catalyst which is efficient, stable and scalable still remains an open challenge. BiOBr is a 2D layered material studied as photoelectrocatalyst because of its suitable band gap for light absorption and potential for up‐scalable production. However, its application in HER is not commonly reported, because of instability in a cathodic PEC environment, driven by a strong tendency to reduction to metallic bismuth. To solve this problem, 2D MoS2 is used to induce the formation of a van der Waals (vdW) layered heterojunction (HJ) to stabilize the lattice of BiOBr during HER. By performing PEC HER with the HJs containing different ratios of MoS2, it is found that the HJ with 1 % MoS2 can increase the stability of BiOBr, while the one with 50 % MoS2 can even accelerate the reduction of BiOBr to metallic bismuth. DFT calculations reveal that the interface between BiOBr and MoS2 in the HJ with 1 % MoS2 tends to push active electrons on the sulfur atoms, thus favoring HER. On the other hand, in the 50 % HJ, active electrons are prone to react with BiOBr to induce reduction. In situ wide‐angle X‐ray diffraction (WAXD) on the MoS2/BiOBr HJs with 1 % and 50 % of MoS2 allows to track the phase change and the phase transfer speed of BiOBr during PEC HER. Interestingly, when the HJ is illuminated with UV light, a lower amount of BiOBr is reduced to Bi under negative potential, due to the presence of photogenerated holes reacting with the extra electrons derived from the negative bias and preventing the BiOBr photon absorber to be further reduced. [ABSTRACT FROM AUTHOR]

Bi2S3 has gained considerable attention as a semiconductor for its versatile functional properties, finding application across various fields, and liquid phase exfoliation (LPE) serves as a straightforward method to produce it in nano-form. Till now, the commonly used solvent for LPE has been N-Methyl-2-pyrrolidone, which is expensive, toxic and has a high boiling point. These limitations drive the search for more sustainable alternatives, with water being a promising option. Nonetheless, surfactants are necessary for LPE in water due to the hydrophobic nature of Bi2S3, and organic molecules with amphoteric characteristics are identified as suitable surfactants. However, systematic studies on the use of ionic surfactants in the LPE of Bi2S3 have remained scarce until now. In this work, we used sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS) and sodium hexadecyl sulfonate (SHS) as representative species and we present a comprehensive investigation into their effects on the LPE of Bi2S3. Through characterizations of the resulting products, we find that all surfactants effectively exfoliate Bi2S3 into few-layer species. Notably, SDBS demonstrates superior stabilization of the 2D layers compared to the other surfactants, while SHS becomes the most promising surfactant for obtaining products with high yield. Moreover, the resulting nano-inks are used for fabricating films using spray-coating, reaching a fine tuning of band gap by controlling the number of cycles, and paving the way for the utilization of 2D Bi2S3 in optoelectronic devices. [ABSTRACT FROM AUTHOR]

During water electrolysis, adding an electrocatalyst for the hydrogen evolution reaction (HER) is necessary to reduce the activation barrier and thus enhance the reaction rate. Metal chalcogenide-based 2D nanomaterials have been studied as an alternative to noble metal electrocatalysts because of their interesting electrocatalytic properties and low costs of production. However, the difficulty in improving the catalytic efficiency and industrializing the synthetic methods have become a problem in the potential application of these species in electrocatalysis. Liquid-phase exfoliation (LPE) is a low-cost and scalable technique for lab- and industrial-scale synthesis of 2D-material colloidal inks. In this work, we present, to the best of our knowledge, for the first time a systematic study on the surfactant-assisted LPE of bulk Bi2S3 crystalline powder to produce nanosheets (NSs). Different dispersing agents and LPE conditions have been tested in order to obtain colloidal low-dimensional Bi2S3 NSs in H2O at optimized concentrations. Eventually, colloidally stable layered nano-sized Bi2S3 suspensions can be produced with yields of up to ~12.5%. The thus obtained low-dimensional Bi2S3 is proven to be more active for HER than the bulk starting material, showing an overpotential of only 235 mV and an optimized Tafel slope of 125 mV/dec. Our results provide a facile top-down method to produce nano-sized Bi2S3 through a green approach and demonstrate that this material can have a good potential as electrocatalyst for HER. [ABSTRACT FROM AUTHOR]

The article titled "Cover Feature: Stabilizing Layered BiOBr Photoelectrocatalyst by Van Der Waals Heterojunction Strategy" discusses the use of 2D MoS2/BiOBr van der Waals heterojunctions for photoelectrocatalytic hydrogen production. The article highlights the role of a MoS2/BiOBr heterojunction as a photocathode, where photogenerated electrons from BiOBr can flow in two directions. One direction drives the hydrogen evolution reaction on the MoS2 surface, while the other direction accumulates on BiOBr and reduces it to metallic Bi. The article emphasizes that a small ratio of MoS2 in the heterojunction can prevent electron transfer to MoS2, thus maintaining the accumulation of electrons on BiOBr and preventing deactivation. The full research article provides more detailed information on this topic. [Extracted from the article]

The wide interest in developing green energy technologies stimulates the scientific community to seek, for devices, new substitute material platforms with a low environmental impact, ease of production and processing and long-term stability. The synthesis of metal oxide (MO) semiconductors fulfils these requirements and efforts are addressed towards optimizing their functional properties through the improvement of charge mobility or energy level alignment. Two MOs have rising perspectives for application in light harvesting devices, mainly for the role of charge selective layers but also as light absorbers, namely MoO3 (an electron blocking layer) and Co3O4 (a small band gap semiconductor). The need to achieve better charge transport has prompted us to explore strategies for the doping of MoO3 and Co3O4 with vanadium (V) ions that, when combined with oxygen in V2O5, produce a high work function MO. We report on subcritical hydrothermal synthesis of V-doped mesostructures of MoO3 and of Co3O4, in which a tight control of the doping is exerted by tuning the relative amounts of reactants. We accomplished a full analytical characterization of these V-doped MOs that unambiguously demonstrates the incorporation of the vanadium ions in the host material, as well as the effects on the optical properties and work function. We foresee a promising future use of these materials as charge selective materials in energy devices based on multilayer structures. [ABSTRACT FROM AUTHOR]

BiOI is a promising material for use in photoelectrocatalytic water oxidation, renowned for its chemical inertness and safety in aqueous media. For device integration, BiOI must be fabricated into films. Considering future industrial applications, automated production is essential. However, current BiOI film production methods lack automation and efficiency. To address this, a continuous automated process is introduced in this study, named AutoDrop, for producing BiOI films. Autodrop results to be a fast and facile method for producing BiOI photoelectrodes. Nanostructured thin films of this layered material are prepared using a syringe pump to dispense the precursor solution onto a continuously spinning substrate. These films are integrated into a multilayered photoelectrode, featuring mesoporous TiO 2 as an electron-transporting layer on top of FTO glass. In testing the photoelectrochemical performance of the BiOI/TiO 2 photoelectrodes, the highest photocurrent (44 μA cm -2 ) is found for a heterojunction with a BiOI thickness of 320 nm. Additionally, a further protective TiO 2 ultrathin layer in contact with BiOI, grown by atomic layer deposition, enhances the durability and efficiency of the photoanode, resulting in a more than two-fold improvement in photocurrent after 2 hours of continuous operation. This study advances the automation in the sustainable production of photoelectrode films and provides inspiration for further developments in the field., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

As a semiconductor used for the photocatalytic hydrogen evolution reaction (HER), BiOBr has received intensive attention in recent years. However, the high recombination of photoexcited charge carriers results in poor photocatalytic efficiency. The combination with other photoactive semiconductors might represent a valuable approach to deal with the intrinsic limitations of the material. Given that BiOBr has a 2D structure, we propose a simple liquid-phase exfoliation method to peel BiOBr microspheres into few-layer nanosheets. By tuning the weight ratio between the precursors, we prepare a series of 2D MoS 2 /BiOBr van der Waals (vdW) heterojunctions and study their behaviour as (photo)electrocatalysts for the HER, finding dramatic differences as a function of weight composition. Moreover, we found that pristine 2D BiOBr and the heterojunctions, with the exception of the 1% MoS 2 /BiOBr composition, undergo photocorrosion, with BiOBr being reduced to metallic Bi. These findings provide useful guidelines to design novel 2D material-based (photo)electrocatalysts for the production of sustainable fuels.

2D materials are interesting flat nanoplatforms for the implementation of different electrochemical processes, due to the high surface area and tunable electronic properties. 2D transition metal dichalcogenides (TMDs) can be produced through convenient top-down liquid-phase exfoliation (LPE) methods and present capacitive behaviour that can be exploited for energy storage applications. However, in their thermodynamically stable 2H crystalline phase, they present poor electrical conductivity, being this phase a purely semiconducting one. Combination with conducting polymers like polyaniline (PANI), into nanohybrids, can provide better properties for the scope. In this work, we report on the preparation of 2D WS 2 @PANI hybrid materials in which we exploit the LPE TMD nanoflakes as scaffolds, onto which induce the in-situ aniline polymerization and thus achieve porous architectures, with the help of surfactants and sodium chloride acting as templating agents. We characterize these species for their capacitive behaviour in neutral pH, achieving maximum specific capacitance of 160 F/g at a current density of 1 A/g, demonstrating the attractiveness of similar nanohybrids for future use in low-cost, easy-to-make supercapacitor devices., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Crisci, Boll, Merola, Pflug, Liu, Gallego, Lamberti and Gatti.)