Liquid-phase exfoliation is the most suitable platform for large-scale production of two-dimensional materials. One of the main open challenges is related to the quest of green and bioderived solvents to replace state-of-the-art dispersion media, which suffer several toxicity issues. Here, we demonstrate the suitability of methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv Polarclean) for sonication-assisted liquid-phase exfoliation of layered materials for the case-study examples of WS₂, MoS₂, and graphene. We performed a direct comparison, in the same processing conditions, with liquid-phase exfoliation using N-methyl-2-pyrrolidone (NMP) solvent. The amount of few-layer flakes (with thickness <5 nm) obtained with Polarclean is increased by ∼350% with respect to the case of liquid-phase exfoliation using NMP, maintaining comparable values of the average lateral size, which even reaches ∼10 μm for the case of graphene produced by exfoliation in Polarclean, and of the yield (∼40%). Correspondingly, the density of defects is reduced by 1 order of magnitude by Polarclean-assisted exfoliation, as evidenced by the I(D)/I(G) ratio in Raman spectra of graphene as low as 0.07 ± 0.01. Considering the various advantages of Polarclean over state-of-the-art solvents, including the absence of toxicity and its biodegradability, the validation of superior performances of Polarclean in liquid-phase exfoliation paves the way for sustainable large-scale production of nanosheets of layered materials and for extending their use in application fields to date inhibited by toxicity of solvents (e.g., agri-food industry and desalination), with a subsequent superb impact on the commercial potential of their technological applications.

The NO₂ response in the range of 200 ppb to 1 ppm of a chemoresistive WS₂-decorated rGO sensor has been investigated at operating temperatures of 25 °C and 50 °C in dry and humid air (40% RH) under dark and Purple Blue (PB) light conditions (λ = 430 nm). Few-layers WS₂, exfoliated by ball milling and sonication technique, with average dimensions of 200 nm, have been mixed with rGO flakes (average dimension 700 nm) to yield WS₂-decorated rGO, deposited on Si₃N₄ substrates, provided with platinum (30 μm gap distance) finger-type electrodes. TEM analysis showed the formation of homogeneous and well-dispersed WS₂ flakes distributed over a thin, continuous and uniform underlying layer of interconnected rGO flakes. XPS and STEM revealed a partial oxidation of WS₂ flakes leading to the formation of 18% amorphous WO₃ over the WS₂ flakes. PB-light irradiation and mild heating of the sensor at 50 °C substantially enhanced the baseline recovery yielding improved adsorption/desorption rates, with detection limit of 400 ppb NO₂ and reproducible gas responses. Cross sensitivity tests with humid air interfering vapor highlighted a negligible influence of water vapor on the NO₂ response. A charge carrier mechanism between WS₂ and rGO is proposed and discussed to explain the overall NO₂ and H₂O response of the WS₂–rGO hybrids.

WS₂ exfoliated by a combined ball milling and sonication technique to produce few-layer WS₂ is characterized and assembled as chemo-resistive NO₂, H₂ and humidity sensors. Microstructural analyses reveal flakes with average dimensions of 110 nm, “aspect ratio” of lateral dimension to the thickness of 27. Due to spontaneous oxidation of exfoliated WS₂ to amorphous WO₃, films have been pre-annealed at 180 °C to stabilize WO₃ content at ≈58%, as determined by X-ray Photoelectron Spectroscopy (XPS), Raman and grazing incidence X-ray Diffraction (XRD) techniques. Microstructural analysis repeated after one-year conditioning highlighted that amorphous WO₃ concentration is stable, attesting the validity of the pre-annealing procedure. WS₂ films were NO₂, H₂ and humidity tested at 150 °C operating Temperature (OT), exhibiting experimental detection limits of 200 ppb and 5 ppm to NO₂ and H₂ in dry air, respectively. Long-term stability of the electrical response recorded over one year of sustained conditions at 150 °C OT and different gases demonstrated good reproducibility of the electrical signal. The role played by WO₃ and WS₂ upon gas response has been addressed and a likely reaction gas-mechanism presented. Controlling the microstructure and surface oxidation of exfoliated Transition Metal Dichalcogenides (TMDs) represents a stepping-stone to assess the reproducibility and long-term response of TMDs monolayers in gas sensing applications.

Heterostructures formed by anatase nanotitania and bidimensional semiconducting materials are expected to become the next-generation photocatalytic materials with an extended operating range and higher performances. The capability of fabricating optically transparent photocatalytic thin films is also a highly demanded technological issue, and increasing the performances of such devices would significantly impact several applications, from self-cleaning surfaces to photovoltaic systems. To improve the performances of such devices, WS₂/TiO₂ heterostructures obtained by incorporating two-dimensional transition metal dichalcogenides layers into titania mesoporous ordered thin films have been fabricated. The self-assembly process has been carefully controlled to avoid disruption of the order during film fabrication. WS₂ nanosheets of different sizes have been exfoliated by sonication and incorporated in the mesoporous films via one-pot processing. The WS₂ nanosheets result as well-dispersed within the titania anatase mesoporous film that retains a mesoporous ordered structure. An enhanced photocatalytic response due to an interparticle electron transfer effect has been observed. The structural characterization of the heterostructure has revealed a tight interplay between the matrix and nanosheets rather than a simple additive co-catalyst effect.

The design of functional coatings for touchscreens and haptic interfaces is of paramount importance for smartphones, tablets, and computers. Among the functional properties, the ability to suppress or eliminate fingerprints from specific surfaces is one of the most critical. We produced photoactivated anti-fingerprint coatings by embedding 2D-SnSe₂ nanoflakes in ordered mesoporous titania thin films. The SnSe₂ nanostructures were produced by solvent-assisted sonication employing 1-Methyl-2-pyrrolidinone. The combination of SnSe₂ and nanocrystalline anatase titania enables the formation of photoactivated heterostructures with an enhanced ability to remove fingerprints from their surface. These results were achieved through careful design of the heterostructure and controlled processing of the films by liquid phase deposition. The self-assembly process is unaffected by the addition of SnSe₂, and the titania mesoporous films keep their three-dimensional pore organization. The coating layers show high optical transparency and a homogeneous distribution of SnSe₂ within the matrix. An evaluation of photocatalytic activity was performed by observing the degradation of stearic acid and Rhodamine B layers deposited on the photoactive films as a function of radiation exposure time. FTIR and UV-Vis spectroscopies were used for the photodegradation tests. Additionally, infrared imaging was employed to assess the anti-fingerprinting property. The photodegradation process, following pseudo-first-order kinetics, shows a tremendous improvement over bare mesoporous titania films. Furthermore, exposure of the films to sunlight and UV light completely removes the fingerprints, opening the route to several self-cleaning applications.

In this work, we present a low-voltage (/spl plusmn/0.75 V) low-power (0.7 mW) current mode-based integrated interface for resistive gas sensors. The proposed interface, which includes a grounded resistive sensor, shows the capability of compensation of non-idealities of passive and active components, in particular the voltage offset. The sensitivity value has been set to about 16 mV/K/spl Omega/, while theoretical resolution is about 135 /spl Omega/, to which corresponds a gas resolution lower than 1.5 ppm.