Two-dimensional (2D) nanostructures are highly attractive for fabricating nanodevices due to their high surface-to-volume ratio and good compatibility with device design. In recent years 2D nanostructures of various materials including metal oxides, graphene, metal dichalcogenides, phosphorene, BN and MXenes, have demonstrated significant potential for gas sensors. This review aims to provide the most recent advancements in utilization of various 2D nanomaterials for gas sensing. The common methods for the preparation of 2D nanostructures are briefly summarized first. The focus is then placed on the sensing performances provided by devices integrating 2D nanostructures. Strategies for optimizing the sensing features are also discussed. By combining both the experimental results and the theoretical studies available, structure-properties correlations are discussed. The conclusion gives some perspectives on the open challenges and future prospects for engineering advanced 2D nanostructures for high-performance gas sensors devices.

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Non-Markovian evolution of an open quantum system can be induced by the memory effects of a reservoir. Although a reservoir with stronger memory effects may seem like it should cause stronger non-Markovian effects on the system of interest, this seemingly intuitive thinking may not always be correct. We illustrate this by investigating a qubit (a two-level atom) that is coupled to a hierarchical environment, which contains a single-mode cavity and a reservoir consisting of infinite numbers of modes. We show how the non-Markovian character of the system is influenced by the coupling strength between the qubit and cavity and the correlation time of the reservoir. In particular, we found a new phenomenon whereby the qubit Markovian and non-Markovian transition exhibits a anomalous pattern in a parameter space depicted by the coupling strength and the correlation time of the reservoir.

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A novel method was used to prepare starch-grafted graphene nanosheets (GN-starch), in which graphene oxide was reduced with hydrazine hydrate in the presence of starch. The obtained GN-starch was characterized by electron microscopy, FTIR analysis, Raman spectra, thermogravimetric analysis, and UV–visible spectra, which confirmed that starch was effectively functionalized on the surface of graphene. Also, GN-starch exhibited high solubility and stability in water. The composites were also fabricated by using GN-starch as the filler in a plasticized-starch (PS) matrix. Because of the strong interaction between starch in GN-starch and the PS matrix, GN-starch can be well dispersed in the PS matrix and improve tensile strength to 25.4 MPa at a GN-starch content of 1.774 wt % and a moisture barrier even at a very low loading (0.248 wt %) of GN-starch fillers. PS/GN-starch composites could protect against UV light, and the conductivity of the composite could reach 9.7 × 10–4 S/cm at a GN-starch content of 1.774 wt %.

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