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Two-dimensional (2D) nanosheet heterostructures have recently shown superior room-temperature (RT) sensitivity in detecting trace ammonia (NH3) recently. However, the low response and sluggish response kinetic process toward NH3 are still challenging issues. Here, we propose a strategy of substitutional and interstitial doping of selenium (Se) into the 2D SnS/SnS2 nanosheet heterostructures, effectively improving the NH3-sensitive capability at RT. The facile one-step hydrothermal method was adopted to synthesize the SeS–SnS/SnS2 (substitutional) and Sei–SnS/SnS2 (interstitial) nanocomposites. Also, the successful substitutional or interstitial doping of Se into both layers of SnS and SnS2 of the SnS/SnS2 heterostructure was verified by the detailed XRD characterization. After exposure to 10 ppm of NH3, the SeS–SnS/SnS2 sensors show a response of 11.46. Comparatively, the sensor based on Sei–SnS/SnS2 achieves a higher response (16.46), which is 13 times beyond the undoped SnS/SnS2 to 10 ppm of NH3 with the response time (tres) only of 3 s. The superior NH3-sensing characteristics of Se codoped nanosheet heterostructures are further investigated by combining band alignment and first-principles calculations. It clarifies that the lattice symmetry breaking due to Se doping provides more active sites for NH3 adsorption. In addition, the Se-doping increases the width of the space charge layer at the heterogeneous interface, leading more oxygen species to promote the adsorption and reaction with more NH3 molecules on the surface. This result lights a way for future research on gas detection through synergistic doping heterostructure materials. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) are recently gaining scientific attention in the gas sensor field. However, the general layer-stacking of two-dimensional (2D) materials significantly limits the performance of LDHs-based gas sensors due to the resulting reduction of gas-active sites. To address the issue, we designed and successfully constructed a nanocomposite of ZIF-8/LDHs/Ti3C2Tx via a sequential induced growth of LDHs and ZIF-8 on the 2D Ti3C2Tx nanosheets. The achieved ZIF-8/LDHs/Ti3C2Tx nanocomposite exhibits the uniform coverage of hexagonal ZIF-8 particles on LDHs/Ti3C2Tx. In the nanocomposite, the ZIF-8 particles grown with Zn atoms in LDHs as the core sites form a tight ternary heterostructure with LDHs and Ti3C2Tx, and a two-dimensional electron gas (2DEG) region with high conductivity is generated during an isopropanol (IPA)-sensing process. Benefiting from the modification of ZIF-8 and the generation of 2DEG, the gas adsorption sites and effective conductive pathway are prominently increased, which is crucial for the improvement of gas-sensing performance. Resultantly, the as-fabricated ZIF-8/LDHs/Ti3C2Tx sensor can detect rarefied IPA at the sub-ppm level with a theoretical limit of detection of 9 ppb; it shows a response value of 61.82 toward 50 ppm IPA at room temperature (RT), which is about 27 times boost in contrast to LDHs/Ti3C2Tx. Notably, the ZIF-8/LDHs/Ti3C2Tx sensor still shows a significant response (5.12) toward 2.5 ppm IPA under high relative humidity (85 %RH) at RT. The gas-sensing mechanism was clarified from the heterostructure effect, adsorption energy calculation, and morphology promotion. Above all, this research provides a route to explore the application potential of LDHs-based nanocomposites in both atmospheric and breath IPA detection. [ABSTRACT FROM AUTHOR]

Group‐IV monochalcogenides with unique 2D puckered honeycomb structure (MX, M = Ge, Sn/X = S, Se) have a great prospect in the gas‐sensor field. Herein, an exploratory study on 2D SnS is synthesized through a solvothermal method, is performed for promising methanol sensor. To break through the inhibition of the general agglomeration and poor conductivity of solvothermal synthesized SnS on gas‐sensing performance, a hybrid of SnS@rGO is designed and constructed based on poly(diallyl dimethyl ammonium chloride) (PDDA)‐assisted electrostatic self‐assembly. With directed growth of SnS on the PDDA‐modulated graphene oxide (GO), an expected architecture characterized by well‐dispersed loosely arranged SnS nanosheets attaching on the highly conductive rGO is achieved. The unique hybrid architecture and the conductivity modulation of rGO promotes sensing responses and dynamic characteristic of SnS‐based sensor toward methanol detection. The achieved SnS@rGO hybrid with less stacking architecture of SnS displays a ≈3.3‐fold enhancement in gas response to 15 ppm methanol in comparison to the flower‐like stacked SnS. The formation mechanism of SnS@rGO hybrid based on the oriented growth of SnS by PDDA‐modulated GO is clarified schematically and the response enhancement of the hybrid is demonstrated in terms of the unique architecture and the conductivity modulation. [ABSTRACT FROM AUTHOR]

Uniform core‐shell hetero‐array of polypyrrole‐wrapped silicon nanowires (LNWs/PPy C‐S nanowires) with enhanced gas‐sensing response at room temperature was prepared via a two‐step process. The aligned silicon nanowires were first formed by metal‐assisted chemical etching (MACE). To achieve a loose silicon nanowires (LNWs) array facilitating the uniform deposition of PPy shell on whole wire surface, a repeated MACE treatment was further developed based on reoxidation of the MACE‐produced Ag dendrites. The PPy‐shell with adjustable thickness was then formed uniformly on the LNWs via vapor chemical polymerization (VCP) of pyrrole monomer (Py). The gas sensor based on the well‐defined LNWs/PPy C‐S heteronanowires array exhibits about 8.2 times response enhancement to 5 ppm NO2 gas compared with the pristine one at room temperature. Very low detection resolution of 50 ppb NO2 is observed when PPy shell has thickness of about 10 nm. The organic/inorganic C‐S composite of LNWs/PPy nanowires shows a different characteristic of shell thickness effect on sensing response from the general semiconductor oxides‐based C‐S sensor; much thinner PPy shell is extremely preferred for higher sensing response. A sensing mechanism model was proposed to demonstrate the featured effect of organic shell thickness on sensing behavior of LNWs/PPy C‐S heteronanowires. POLYM. COMPOS., 40:3275–3284, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Development of novel Gd-based contrast agents for targeted magnetic resonance imaging (MRI) of liver cancer remains a great challenge. Herein we reported a novel Gd-based MRI contrast agent with improved relaxivity for specifically diagnosing liver cancer. This GSH-responsive macromolecular contrast agent (mCA), POLDGd, was prepared by RAFT polymerization, and its lactic acid moiety could precisely target the ASGP-R surface protein on liver cancer cells, whereas PODGd without the lactic acid moiety was prepared as a control. POLDGd had a high molecular weight of 45 kDa and a particle size of 103 nm. Its longitudinal relaxivity (11.39 mM -1 s -1 ) measured via a 3.0 T MR scanner was three times that of the clinically used contrast agent DTPA-Gd. In comparison with the PODGd-treated group, the signal enhancement at the tumor site was significantly prolonged, with a maximum enhancement peak of about 190% after intravenous injection of POLDGd into tumor-bearing mice. A high accumulation level of POLDGd in the liver tumors observed via MRI was also confirmed by fluorescence imaging. POLDGd showed minimal side effects, which may be ascribed to its metabolism through the kidneys. Therefore, POLDGd may be used as a highly effective biosafe nanoscale contrast agent for targeted MRI of liver cancer.