NO2 gas sensor based on graphene decorated with Ge quantum dots.

We report a NO2 gas sensor based on germanium quantum dots (GeQDs)/graphene hybrids. Graphene was directly grown on germanium through chemical vapor deposition and the GeQDs were synthesized via molecular beam epitaxy. The samples were characterized by atomic force microscope, Raman spectra, scanning electron microscope, x-ray photoelectron spectroscope and transmission electron microscope with energy dispersive x-ray. By introducing GeQDs on graphene, the gas sensor sensitivity to NO2 was improved substantially. With the optimization of the growth time of GeQDs (600 s), the response sensitivity to 10 ppm NO2 can be as high as 3.88, which is 20 times higher than that of the graphene sensor without GeQDs decoration. In addition, the 600 s GeQDs/graphene hybrid sensor exhibits fast response and recovery rates as well as excellent stability. Our work may provide a new route to produce low-power consumption, portable, and room temperature gas sensor which is amenable to mass production.

Highly Enhanced Visible-Light-Driven Photoelectrochemical Performance of ZnO-Modified In2S3 Nanosheet Arrays by Atomic Layer Deposition.

Photoanodes based on In2S3/ZnO heterojunction nanosheet arrays (NSAs) have been fabricated by atomic layer deposition of ZnO over In2S3 NSAs, which were in situ grown on fluorine-doped tin oxide glasses via a facile solvothermal process. The as-prepared photoanodes show dramatically enhanced performance for photoelectrochemical (PEC) water splitting, compared to single semiconductor counterparts. The optical and PEC properties of In2S3/ZnO NSAs have been optimized by modulating the thickness of the ZnO overlayer. After pairing with ZnO, the NSAs exhibit a broadened absorption range and an increased light absorptance over a wide wavelength region of 250-850 nm. The optimized sample of In2S3/ZnO-50 NSAs shows a photocurrent density of 1.642 mA cm-2 (1.5 V vs. RHE) and an incident photon-to-current efficiency of 27.64% at 380 nm (1.23 V vs. RHE), which are 70 and 116 times higher than those of the pristine In2S3 NSAs, respectively. A detailed energy band edge analysis reveals the type-II band alignment of the In2S3/ZnO heterojunction, which enables efficient separation and collection of photogenerated carriers, especially with the assistance of positive bias potential, and then results in the significantly increased PEC activity.

Controlled growth of vertically aligned ultrathin In2S3 nanosheet arrays for photoelectrochemical water splitting.

This paper reports a facile solvothermal method for the in situ growth of vertically aligned In2S3 nanosheet arrays (NSAs) on fluorine-doped tin oxide substrates. The as-synthesized two-dimensional graphene-like In2S3 nanosheets show an ultrathin thickness down to 3.7 nm consisting of the duodenary interplanar spacing of the (222) plane and a tunable bandgap varying from 2.32 to 2.58 eV. The film thickness and nanosheet density of the In2S3 NSAs can be adjusted by varying the reaction time and precursor concentration. The In2S3 NSAs with a higher film thickness exhibit relatively higher photocurrent due to their stronger light absorption as well as larger surface area for sufficient charge separation and redox reaction. The photoelectrochemical performance of the In2S3 photoanodes can be greatly enhanced by constructing an effective heterojunction with ZnO to promote the photocarrier separation. The In2S3/ZnO NSAs have demonstrated an optimal photocurrent density of 349.1 µA cm-2 at 1.2 V vs. RHE and a maximum incident photon to current efficiency of 10.26% at 380 nm, which are 13.5 and 38 times higher than those of the pristine In2S3 counterparts, respectively.