Liquid-phase exfoliation of 2D transition metal dichalcogenides (TMDs) nanosheets in water is critical for their practical applications towards advanced thin-film electronics and ionotronics. We here report a versatile strategy for liquid-phase exfoliation of clay-like water-swollen TMD multilayers into delaminated 2D TMD nanosheets (including MoS2, WS2, MoSe2, etc.) with thin thicknesses of < 2 nm (e.g., 1.4 nm of MoS2) and high nanosheet concentrations. The delaminated TMD nanosheets can form stable colloidal dispersions in water with low Zeta potentials of <–32 mV over a month, and undergo phase transformation upon annealing from metallic 1 T phase to semiconducting 2H phase. These nanosheets can be coated on various circuit substrates as thin-film ionotronics; for example, an ionotronic device with an as-delaminated MoS2 channel achieves a high transconductance of 23 µS at a low operating voltage of −0.2 V. The delaminated TMDs dispersions are capable of co-dispersing other nanomaterials including 2D MXene and graphene, and 1D carbon nanotube and cellulose nanofibrils, forming stable colloidal co-dispersions in water offering a platform to fabricate multifunctional TMD-based nanocomposite films with high electromechanical integrity. Examples of MoS2/MXene films show an electronic conductivity of 1.66 × 105 S m−1 and a tensile strength of 70 MPa, higher than pure MoS2 films of 1.08 × 104 S m−1 and 55 MPa, and MoS2/CNF films with a higher tensile strength of 178 MPa and their hydrogel films presenting a mixed electronic/ionic conductivity of 18.2/0.16 S m−1. These outcomes promise potentially scalable applications in neuromorphic ionotronics, flexible electronics, energy storage, etc.

The solid-state field-effect transistor, FET, and its theories were paramount in the discovery and studies of graphene. In the past two decades another transistor based on conducting polymers, called organic electrochemical transistor (ECT), has been developed and largely studied. The main difference between organic ECTs and FETs is the mode and extent of channel doping; while in FETs the channel only has surface doping through dipoles, the mixed ionic-electronic conductivity of the channel material in organic ECTs enables bulk electrochemical doping. As a result, organic ECTs maximize conductance modulation at the expense of speed. To date ECTs have been based on conducting polymers, but here we show that MXenes, a class of 2D materials beyond graphene, enable the realization of electrochemical transistors (ECTs). We show that the formulas for organic ECTs can be applied to these 2D ECTs and used to extract parameters like mobility. These MXene ECTs have high transconductance values but low on-off ratios. We further show that conductance switching data measured using ECT, in combination with other in situ-ex situ electrochemical measurements, is a powerful tool for correlating the change in conductance to that of the redox state, to our knowledge, this is the first report of this important correlation for MXene films. 2D ECTs can draw great inspiration and theoretical tools from the field of organic ECTs and have the potential to considerably extend the capabilities of transistors beyond those of conducting polymer ECTs, with added properties such as extreme heat resistance, tolerance for solvents, and higher conductivity for both electrons and ions than conducting polymers.

One of the main objectives in wastewater treatment and sustainable energy production is to find photocatalysts that are favorably efficient and cost-effective. Transition-metal dichalcogenides (TMDs) are promising photocatalytic materials; out of all, MoS2 is extensively studied as a cocatalyst in the TMD library due to its exceptional photocatalytic activity for the degradation of organic dyes due to its distinctive morphology, adequate optical absorption, and rich active sites. However, sulfur ions on the active edges facilitate the catalytic activity of MoS2. On the basal planes, sulfur ions are catalytically inactive. Injecting metal atoms into the MoS2 lattice is a handy approach for triggering the surface of the basal planes and enriching catalytically active sites. Effective band gap engineering, sulfur edges, and improved optical absorption of Mn-doped MoS2 nanostructures are promising for improving their charge separation and photostimulated dye degradation activity. The percentage of dye degradation of MB under visible-light irradiations was found to be 89.87 and 100% for pristine and 20% Mn-doped MoS2 in 150 and 90 min, respectively. However, the degradation of MB dye was increased when the doping concentration in MoS2 increased from 5 to 20%. The kinetic study showed that the first-order kinetic model described the photodegradation mechanism well. After four cycles, the 20% Mn-doped MoS2 catalysts maintained comparable catalytic efficacy, indicating its excellent stability. The results demonstrated that the Mn-doped MoS2 nanostructures exhibit exceptional visible-light-driven photocatalytic activity and could perform well as a catalyst for industrial wastewater treatment.

The unique properties of hydrogels enable the design of life-like soft intelligent systems. However, stimuli-responsive hydrogels still suffer from limited actuation control. Direct electronic control of electronically conductive hydrogels can solve this challenge and allow direct integration with modern electronic systems. An electrochemically controlled nanowire composite hydrogel with high in-plane conductivity that stimulates a uniaxial electrochemical osmotic expansion is demonstrated. This materials system allows precisely controlled shape-morphing at only −1 V, where capacitive charging of the hydrogel bulk leads to a large uniaxial expansion of up to 300%, caused by the ingress of ≈700 water molecules per electron–ion pair. The material retains its state when turned off, which is ideal for electrotunable membranes as the inherent coupling between the expansion and mesoporosity enables electronic control of permeability for adaptive separation, fractionation, and distribution. Used as electrochemical osmotic hydrogel actuators, they achieve an electroactive pressure of up to 0.7 MPa (1.4 MPa vs dry) and a work density of ≈150 kJ m−3 (2 MJ m−3 vs dry). This new materials system paves the way to integrate actuation, sensing, and controlled permeation into advanced soft intelligent systems.