Hydrothermally prepared vertical multilayer WS2 nanosheets on the surface of few-layer MoS2 for the ultra-sensitive NO2 detection at room temperature.

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Expanded few-layer black phosphorus nanosheets (FL-BP NSs) were functionalized by branched polyethylenimine (PEI) using a simple noncovalent assembly to form air-stable overlayers (BP-PEI), and a CoO@BP-PEI composite was designed and synthesized using a hydrothermal method. The size of the highly dispersed CoO nanoparticles (NPs) on the FL-BP NSs can be controlled. The BP-C5 (190 °C for 5 h) sensor, with 4-6 nm CoO NPs on the FL-BP NSs, exhibited an ultrahigh sensitivity of 8.38 and a fast response of 0.67 s to 100 ppm of NO at room temperature in air, which is 4 times faster than the response of the FL-BP NS sensor, and the lower detection limit reached 10 ppb. This study points to a promising method for tuning properties of BP-based composites by forming air-stable overlayers and highly dispersed metal oxide NPs for use in high-performance gas sensors.

The 3D flower-like CoAl-layered double hydroxide (CoAl-LDH) was successfully prepared using the functional template agent of fluoride ions via a facile one-step hydrothermal route. Various techniques proved that all the samples presented 3D flower-like microstructural morphology. Representatively, the CA-2 sample, which was synthesized with the molar ratio of Co : Al of 3.65 : 1, had considerably abundant pores in its thin nanosheets. The average pore size was 2-4 nm, the specific surface area was equal to 49.45 m 2 g À1 , and the thickness of nanosheets was approximately 3.068 nm. The CA-2 sample showed an excellent response to 0.01-100 ppm NO 2 with ultrafast response/recovery time at room temperature (RT). The detection limit of the sensor even reached 10 ppb. The superior gas sensing performance could be attributed to the synergistic effects of the functional template agent of fluoride ions and specific porous 3D flower-like nanostructure. The current study showed that the 3D flower-like CoAl-LDHs might a promising material in practical detection of NO 2 at RT. Scheme 2 Schematic for the mechanism of NO 2 sensing for CoAl-LDHs. (a) SEM image of 3D flower-like CA-2 on Au electrode; (b and c) the model with response procedure of gas sensing; (d) I-V curve measured for CA-2 sensor in air and 50 ppm NO 2 exposure at RT; (e) IR spectra of CA-2 before and after NO 2 gas detection (CA-2 test NO 2 gas sensing for 2 h).21918 | RSC Adv., 2019,9,[21911][21912][21913][21914][21915][21916][21917][21918][21919][21920][21921] This journal is

MoS2@MoO2 with controllable morphology fabricated via a one-step CVD method showed enhanced NO2 sensing performance at room temperature in air.

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