High performance of 3D silicon nanowires array@CrN for electrochemical capacitors.

Silicon nanowire (SiNW) arrays were coated with chromium nitride (CrN) for use as supercapacitor electrodes. The CrN layer of different thicknesses was deposited onto SiNWs using bipolar magnetron sputtering method. The areal capacitance of the SiNWs-CrN, as measured in 0.5 M H2SO4 electrolyte, was as high as 180 mF cm-2 at a scan rate of 5 mV s-1 (equivalent to 31.8 mF cm-2 at 1.6 mA cm-2) with an excellent electrochemical retention of 92% over 15 000 cycles. This work paves the way toward using CrN modified 3D SiNWs arrays for micro-supercapacitor application.

Green chemistry approach for the synthesis of ZnO-carbon dots nanocomposites with good photocatalytic properties under visible light.

We report on a simple and one-pot synthetic method to produce ZnO/carbon quantum dots (ZnO/CQDs) nanocomposites. The morphological features and chemical composition of the nanocomposites were characterized using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analyses (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties of the nanocomposites were examined using UV-visible (UV-vis) spectrophotometry. The photocatalytic activity of the ZnO/CQDs was evaluated for the degradation of a model organic pollutant, rhodamine B, under visible light irradiation at room temperature. The highly efficient photodegradation capability of the nanocomposite was demonstrated by comparison with ZnO particles, prepared using identical experimental conditions. Overall, the present approach adheres to green chemistry principles and the nanocomposite holds promise for the development of remarkably efficient catalytic systems.

Reduction of Cr(VI) to Cr(III) using silicon nanowire arrays under visible light irradiation.

We report an efficient visible light-induced reduction of hexavalent chromium Cr(VI) to trivalent Cr(III) by direct illumination of an aqueous solution of potassium dichromate (K2Cr2O7) in the presence of hydrogenated silicon nanowires (H-SiNWs) or silicon nanowires decorated with copper nanoparticles (Cu NPs-SiNWs) as photocatalyst. The SiNW arrays investigated in this study were prepared by chemical etching of crystalline silicon in HF/AgNO3 aqueous solution. The Cu NPs were deposited on SiNW arrays via electroless deposition technique. Visible light irradiation of an aqueous solution of K2Cr2O7 (10(-4)M) in presence of H-SiNWs showed that these substrates were not efficient for Cr(VI) reduction. The reduction efficiency achieved was less than 10% after 120 min irradiation at λ>420 nm. Addition of organic acids such as citric or adipic acid in the solution accelerated Cr(VI) reduction in a concentration-dependent manner. Interestingly, Cu NPs-SiNWs was found to be a very efficient interface for the reduction of Cr(VI) to Cr(III) in absence of organic acids. Almost a full reduction of Cr(VI) was achieved by direct visible light irradiation for 140 min using this photocatalyst.

The antimicrobial effect of silicon nanowires decorated with silver and copper nanoparticles.

The paper reports on the preparation and antibacterial activity of silicon nanowire (SiNW) substrates coated with Ag or Cu nanoparticles (NPs) against Escherichia coli (E. coli) bacteria. The substrates are easily prepared using the metal-assisted chemical etching of crystalline silicon in hydrofluoric acid/silver nitrate (HF/AgNO3) aqueous solution. Decoration of the SiNWs with metal NPs is achieved by simple immersion in HF aqueous solutions containing silver or copper salts. The SiNWs coated with Ag NPs are biocompatible with human lung adenocarcinoma epithelial cell line A549 while possessing strong antibacterial properties to E. coli. In contrast, the SiNWs decorated with Cu NPs showed higher cytotoxicity and slightly lower antibacterial activity. Moreover, it was also observed that leakage of sugars and proteins from the cell wall of E. coli in interaction with SiNWs decorated with Ag NPs is higher compared to SiNWs modified with Cu NPs.

Investigation of silicon-based nanostructure morphology and chemical termination on laser desorption ionization mass spectrometry performance.

We have evaluated the laser desorption ionization mass spectrometry (LDI-MS) performance of six nanostructured silicon surfaces of different morphologies and chemical functionalizations. The substrates have been synthesized either by metal-assisted etching method or by vapor-liquid-solid (VLS) growth technique. In addition to the commercial nanostructured silicon-based surface (NALDI) target plates, serving as reference, the homemade surfaces have been evaluated in mass spectrometry experiments conducted with peptide solutions mimicking tryptic digests. LDI surfaces synthesized by metal-assisted etching method were the most efficient in terms of signal intensities and number of detected peptides. The surface providing the best LDI-MS performance was composed of two nanostructured layers. Interestingly, we also observed a significant influence of the type of organic coating (hydrocarbon vs fluorocarbon) on peptide ionization discrimination.

Silicon nanowire arrays-induced graphene oxide reduction under UV irradiation.

This paper reports on efficient UV irradiation-induced reduction of exfoliated graphene oxide. Direct illumination of an aqueous solution of graphene oxide at λ = 312 nm for 6 h resulted in the formation of graphene nanosheets dispersible in water. X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, atomic force microscopy (AFM) and electrochemical measurements (cyclic voltammetry and electrochemical impedance spectroscopy) suggest a restoration of the sp(2) carbon network. The results were compared with graphene nanosheets prepared by photochemical irradiation of a GO aqueous solution in the presence of hydrogenated silicon nanowire (SiNW) arrays or silicon nanowire arrays decorated with silver (SiNW/Ag NPs) or copper nanoparticles (SiNW/Cu NPs). Graphene nanosheets obtained by illumination of the GO aqueous solution at 312 nm for 6 h in the presence of SiNW/Cu NPs exhibited superior electrochemical charge transfer characteristics. This is mainly due to the higher amount of sp(2)-hybridized carbon in these graphene sheets found by XPS analysis. The high level of extended conjugated carbon network was also evident by the water insoluble nature of the resulting graphene nanosheets, which precipitated upon photochemical reduction.

Photocatalytic activity of silicon nanowires under UV and visible light irradiation.

The communication reports on the high performance of hydrogen-terminated silicon nanowires and silicon nanowires coated with metal (Ag, Cu) nanostructures for the photodegradation of rhodamine B under UV and visible light irradiation.