Design of stimuli-responsive transition metal dichalcogenides

Stimuli-responsive systems are an emerging class of materials in fields as diverse as electronics, optoelectronics, cancer detection, drug delivery, or sensing. Especially focusing on nanomaterials, 2D transition metal dichalcogenides have recently attracted the scientific community's attention due to their remarkable intrinsic stimuli-responsive behaviour upon external stimuli such as pH, light, voltage, or certain pathogens. This significant response can be further enhanced by forming mixed-dimensional heterostructures and by molecular functionalization, capitalizing on chemistry to manipulate and boost their intrinsic stimuli-responsive properties. Furthermore, thanks to the endless possibilities of chemistry, a new class of smart materials based on the combination of stimuli-responsive molecular systems with transition metal dichalcogenides has recently been synthesized. In these materials, the physical properties of the 2D layers are reversibly modified by the switchable molecules, not only enhancing their stimuli-responsive behaviour but also providing memory to the hybrid. Therefore, this review explores the recent breakthroughs in the chemical design of smart transition metal dichalcogenides with built-in responsiveness.

Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications

One-dimensional (1D) electrospun nanomaterials have attracted significant attention due to their unique structures and outstanding chemical and physical properties such as large specific surface area, distinct electronic and mass transport, and mechanical flexibility. Over the past years, the integration of metal sulfides with electrospun nanomaterials has emerged as an exciting research topic owing to the synergistic effects between the two components, leading to novel and interesting properties in energy, optics and catalysis research fields for example. In this review, we focus on the recent development of the preparation of electrospun nanomaterials integrated with functional metal sulfides with distinct nanostructures. These functional materials have been prepared via two efficient strategies, namely direct electrospinning and post-synthesis modification of electrospun nanomaterials. In this review, we systematically present the chemical and physical properties of the electrospun nanomaterials integrated with metal sulfides and their application in electronic and optoelectronic devices, sensing, catalysis, energy conversion and storage, thermal shielding, adsorption and separation, and biomedical technology. Additionally, challenges and further research opportunities in the preparation and application of these novel functional materials are also discussed.

Synthesis and characterization of a novel magnetic calcium-rich nanocomposite and its remediation behaviour for As(III) and Pb(II) co-contamination in aqueous systems

Herein, a novel magnetic calcium-rich biochar (MCRB), prepared by loading Fe₃O₄ nanoparticles (Fe₃O₄ NPs) on crab shell-derived biochar, was studied for remediation of arsenic and lead co-contamination. Characteristics of the MCRB demonstrated that Fe₃O₄ NPs adhered on the biochar matrix uniformly. Batch experiments on the effects of pH, contact time and initial concentrations revealed that for both metals, removal by the MCRB was pH-dependent with an optimal pH of 6, and that the MCRB had a strong ability for removing arsenic and lead with maximum removal capacities of 15.8 and 62.4 mg g^-1, respectively. The mechanisms of the simultaneous removal of arsenic and lead involved both competitive and synergistic effects. The As(III) addition enhanced Pb(II) removal by 5.4-18.8%, while the presence of Pb(II) suppressed As(III) removal by 5.8-17.8%. Competitive complexation of the two metals with biochar was responsible for the suppression, while the enhancement was due mainly to the formation of the Pb(II)-As(III)-FeO ternary surface complex with As(III) as the bridging molecule. These new insights can further our understanding of the application of MCRB as a potential material for use in the treatment of arsenic and lead co-contamination.

Enhanced and selective photocatalytic reduction of CO2 by H2O over strategically doped Fe and Cr into porous boron carbon nitride

Strategic doping of metals and non-metals into a photocatalyst can help in tuning the band gap and alignment of band structure.

Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag₂S, MoS₂, and reduced graphene oxide (RGO) flakes via a one-pot synthesis. The RGO support assists the growth of two-dimensional MoS₂ nanosheets partially covered by silver sulfides as revealed by high-resolution transmission electron microscopy. Compared with the bare MoS₂ and MoS₂/RGO, the Ag₂S/MoS₂ anchored on the RGO surface (the ternary system Ag₂S/MoS₂/RGO) demonstrated a high catalytic activity toward hydrogen evolution reaction (HER). Its superior electrochemical activity toward HER is evidenced by the positively shifted (-190 mV vs reversible hydrogen electrode (RHE)) overpotential at a current density of -10 mA/cm² and a small Tafel slope (56 mV/dec) compared with a bare and binary system. The Ag₂S/MoS₂/RGO ternary catalyst at an overpotential of -200 mV demonstrated a turnover frequency equal to 0.38 s^-1. Electrochemical impedance spectroscopy was applied to understand the charge-transfer resistance; the ternary sample shows a very small charge-transfer resistance (98 Ω) at -155 mV vs RHE. Such a large improvement can be attributed to the synergistic effect resulting from the enhanced active site density of both sulfides and to the improved electrical conductivity at the interfaces between MoS₂ and Ag₂S. This ternary catalyst opens up further optimization strategies to design a stable and cheap catalyst for hydrogen evolution reaction, which holds great promise for the development of a clean energy landscape.

Evaluation of dual layered photoanode for enhancement of visible-light-driven applications

Ternary structures consisting of hollow g-C₃N₄ nanofibers/MoS₂/sulfur, nitrogen-doped graphene and bulk g-C₃N₄ (TCN) were designed as a dual layered film and fabricated using a spin-coating method. The first ternary structures were spin-coated on fluorine-doped tin oxide (FTO) glass, followed by spin-coating of g-C₃N₄ film to form dual layers. We characterized the microstructural morphologies, chemical composition/bonding and optical properties of the dual layered film and observed significantly reduced recombination rates of photo-induced electron–hole pairs due to effective separation of the charge carriers. We tested methylene blue (MB) photodegradation and observed remarkable MB degradation by the dual layered film over 5 hours, with a kinetic rate constant of 1.24 × 10⁻³ min⁻¹, which is about four times faster than that of bare TCN film. Furthermore, we estimated the H₂ evolution of the dual layered film to be 44.9 μmol over 5 hours, and carried out stable recycling over 45 hours under visible irradiation. Due to the lower electrochemical impedance spectroscopy (EIS) resistance value of the dual layered film (∼50 ohm cm²) compared to the TCN film, the ternary structures and bulk g-C₃N₄ film were well-connected as a heterojunction, reducing the resistance at the interface between the film and the electrolyte. These results indicate that the effective separation of the photo-induced electron–hole pairs using the dual layered film dramatically improved its photo-response ability under visible light irradiation.

Ternary structures consisting of hollow g-C₃N₄ nanofibers/MoS₂/sulfur, nitrogen-doped graphene and bulk g-C₃N₄ (TCN) were designed as a dual layered film and fabricated using a spin-coating method.

Advanced electrospun nanomaterials for highly efficient electrocatalysis

We highlight the recent developments of electrospun nanomaterials with controlled morphology, composition and architecture for highly efficient electrocatalysis.