This review provides a comprehensive summary of the intercalation and exfoliation processes in TMDs, as well as their properties and applications.

Two-dimensional (2D) materials, as adsorbents, have garnered great attention in removing heavy metal ions (HMIs) from drinking water due to their extensive exposed adsorption sites. Nevertheless, there remains a paucity of experimental research to remarkably unlock their adsorption capabilities and fully elucidate their adsorption mechanisms. In this work, exceptional lead ion (Pb²⁺) (a common HMI) removal capacity (up to 758 mg g⁻¹) is achieved using our synthesized metallic 1T/1T′ phase 2D transition metal dichalcogenide (TMD, including MoS₂, WS₂, TaS₂, and TiS₂) nanosheets, which hold tremendous activated S chemisorption sites. The residual Pb²⁺ concentration can be reduced from 2 mg L⁻¹ to 2 μg L⁻¹ within 0.5 min, meeting the drinking water standards following World Health Organization guideline (Pb²⁺ concentrations <10 μg L⁻¹). Atomic-scale characterizations and calculations based on density functional theory unveil that Pb²⁺ bond to the top positions of transition metal atoms in a single-atom form through the formation of S-Pb bonds. Point-of-use (POU) devices fabricated by our reported metallic phase MoS₂ nanosheets exhibit treatment capacity of 55 L-water g⁻¹-adsorbent for feed Pb²⁺ concentration of 1 mg L⁻¹, which is 1-3 orders of magnitude higher than other 2D materials and commercial activated carbon.

Efficient electrocatalysts are needed for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), while the influence of electron transfer from the adjacent layer of multilayered electrocatalysts on their catalytic performance is usually neglected. Here, we used the single cobalt atom trapped graphyne catalyst (Co@GY) to study the feasibility of modulating its water-splitting catalytic activity through interfacial electron transfer. A series of Co@GY/transition-metal doped graphyne double-layered structures (Co@GY/GY and Co@GY/TM@GY, TM = Mn, Fe, Co, Ni, Cu) are systematically evaluated for water splitting via theoretical computations. The electronic structure analyses of different stacking cases revealed that the atomic metals on the adjacent TM@GY layer remarkably tune the electronic structures of the Co atom in the Co@GY layer. A strong linear correlation between ΔG_H* and the d band center of the Co atom was found, suggesting that the HER activity on the Co atom can be tailored by adjusting the TM on the adjacent TM@GY layer with different d-electron occupations. The volcano-type trend of OER catalytic performance is obtained to show the best Co@GY/Ni@GY catalyst for the OER with an over-potential of 0.38 V, indicating that higher catalytic performance arises from moderate interfacial electron transfer. These results arouse a re-thinking of the intrinsic activity origins of single-atom catalysts (SACs) and offer a new strategy for the structure designing of SACs.

Reduced graphene oxide (rGO) and Au nanodot (AuND, ∼1.5 nm) modified rGO, referred to as AuNDs-rGO, synthesized by a simple photochemical reduction method, are used for electrochemical biosensors. Our experimental results showed that the glucose oxidase (GO_X)/rGO/Nafion/glassy carbon electrode (GCE) exhibits a linear range from 0.03 to 6.28 mM and a detection limit of 0.03 mM at a signal-to-noise (S/N) ratio of 3 for the amperometric sensing of glucose, while the GO_X/AuNDs-rGO/Nafion/GCE shows a wider linear range from 0.02 to 8.82 mM and a lower detection limit of 0.02 mM. This difference may arise from the high catalytic activity of the AuNDs. Our studies demonstrate that the composites of rGO/Nafion and AuNDs-rGO/Nafion might offer a new class of electrode materials, and provide a promising platform for biosensing applications.