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Hydrogen is an active substitute for current commercial fuels as a green energy source. However, the progress toward hydrogen economy is stalled due to a lack of efficient and economical storage systems usually restrained by the material used. Some specific issues still need to improve in recent practical hydrogen storage methods: low surface area, limited capacity to attract gas adsorbate, high-temperature medium for hydrogen desorption, and extreme reactivity towards Oxygen and air. The paper presents a study on the surface modification of silicon nanostructures (SiNSs) synthesized by chemical etching, followed by structure optimization to enhance the hydrogen storage capacity. The standard anodization method prepares porous silicon (PS) while metal-assisted chemical etching fabricates Si and Porous Si nanowires (PSiNWs) on Si and PS substrates. Morphological features like surface area and porous nature were evaluated using SEM, AFM, and BET to interpret the gas-surface interaction. The modified surface area and average roughness of SiNSs increase maximum to 437 m2 g−1 and 501 nm, respectively. The PS shows the highest gas-surface interaction (up to 86.6%) and surface energy due to uniform pore distributions and high surface area. The NMR and FTIR investigate the hydrogen termination on the surface, whereas TG-DSC indicates the desorption of surface hydrides at ∼290 °C. A rank matrix is constructed considering various adsorption-desorption and fabrication parameters to select optimized SiNS, whereas PS is selected as a suitable candidate for hydrogen storage. • Electrochemical anodization and metal-assisted chemical etching fabricate porous silicon and porous Si nanowires. • The gas physisorption improves in nanopores due to the overlap of attractive fields from adjacent pore walls. • High resistivity substrate Si nanostructures exhibit uniform and homogeneous pore size distribution. • Continuous water rinsing on the hydrogenated surface of Si nanostructures causes hydrogen desorption from the surface. • Porous silicon stands prominently and has a high potential for hydrogen storage based on the rank matrix. [ABSTRACT FROM AUTHOR]

Abstract Porous silicon nanowires (PSiNWs) surfaces were grafted with organic functional groups. The obtained hybrid structure was tested as probe electrode for the electrochemical detection of mercury (Hg(II)) in solution. An electrochemical study of the Glycyl-Glycyl-Glycine-modified PSiNWs electrode is achieved in the presence of mercury ions. The recorded cyclic voltammograms show a quasi-irreversible process corresponding to the Hg(II)/Hg couple. These results demonstrate the potential role of peptides grafted on porous silicon nanowire in developing strategies for simple and fast detection of metal ions in solution. [ABSTRACT FROM AUTHOR]

Graphical abstract The marriage of porous silicon nanowires and OTS provides a barrier to water molecules in gas detection process. Highlights • The interferences of different humidity in gas detection progress were studied for SiNWs-based gas sensors. • OTS was utilized to modify partially insensitive porous SiNWs surface with the Si-O bond for improving humidity resistance. • The ultra-low concentration NO 2 detection and excellent reversibility of the OTS/SiNWs sensor was observed in high humidity. • Possible mechanism for enhanced performance of OTS/SiNWs was analyzed. Abstract Porous silicon nanowires (SiNWs) is considered as one of promising candidates for high-performance NO 2 sensor application in human health and quality life owing to its fast response and stable operation at room temperature. However, the development of SiNWs-based gas sensors for stable detection of ppb-level NO 2 in practical high-humidity environments remains a challenge. In this study, octadecyltrichlorosilane (OTS) was utilized to modify partially insensitive SiNWs surface with the Si-O bond, yielding an immunity to high humidity in gas detection process. The modified OTS provides an umbrella-like barrier blocking water molecules attraction on the nanowire surface which disinhibits the main adsorption sites and sensing channels of the sensor. The OTS-modified porous SiNWs (OTS/SiNWs) sensor exhibited a practical capability to detect 5 ppb NO 2 at humidity of 25%–55% RH and a response of 1.8% to 50 ppb NO 2 at 75% RH at room temperature. Moreover, the fast response/recovery characteristics and good reversibility of the OTS/SiNWs sensor was observed even under high humidity conditions. In addition, the OTS/SiNWs sensor displayed excellent stability to humidity variations. The enhanced gas sensing performance is attributed to a marriage of porous structure of SiNWs and OTS. The simple modification for SiNWs-based gas sensor will broaden new avenues, not only in chemical trace detection, but also in high humidity health monitoring. [ABSTRACT FROM AUTHOR]

As a most promising anode candidate, silicon has the shortcomings of low electron conductivity and high volume expansion of 300%, hindering its applications in lithium ion batteries (LIBs). In this study, one-dimension porous silicon nanowires (pSi-NWs) were prepared through a simple metal-assisted chemical etching process by using metallurgical silicon as raw material. To consolidate the structural integrity of pSi-NWs, a crossed carbon skeleton (c-Cs) was introduced into pSi-NWs via in-situ polymerization and carbonization process. The resultant pSi-NWs@c-Cs composite delivered the high capacity of 1253 mAh g −1 with good cycling stability as well as the notable rate capability (476 mAh g −1 at 4 A g −1 ), much superior to those of pSi-NWs and pSi-NWs@reduced graphene oxide composite. The enhanced electrochemical performance of pSi-NWs@c-Cs composite is attributed to the crossed carbon skeleton in constructing the advanced Si/C interface to more effectively improve the electron conductivity of pSi-NWs and acting as the protective shell to keep the structure integrity of pSi-NWs. As the additive of commercial graphite anode, 28% of capacity augment (460 mAh g −1 at 0.2 A g −1 ) was realized by adding 20 wt% of pSi-NWs@c-Cs composite into graphite, demonstrating its promising applications in LIBs. [ABSTRACT FROM AUTHOR]

In this paper, we report, for the first time, an investigative study involving the engineering of lightly doped porous silicon nanowire arrays (pSiNWs) by exposing solid silicon nanowire arrays (SiNWs) to an acid vapor emanating from HF/HNO 3 hot solution. SEM and TEM images exhibit vertically distributed SiNW arrays on the whole silicon (Si) surface with relatively smooth surface sidewalls. By submitting the SiNW arrays to Acid Vapor Etching (AVE), they become porous with a substantial decrease in their densities and lengths. Increasing etching duration leads to a higher porosity without affecting the wire diameter which remains almost constant nearly 100 nm. Exceeding a critical etching duration, a porous structure is observed superseding the SiNW structure. The morphological characterizations have been correlated to the optical properties. We note a blue shift of the strong visible photoluminescence (PL) bands after AVE treatment due to the decrease of the silicon quantum dots diameter (Si-QDs). UV–Visible measurement shows a decrease of the total reflectivity by 5% after AVE treatment. [ABSTRACT FROM AUTHOR]

Highlights: [•] The metal-assisted chemical etching of c-Si leads to the formation of porous SiNWs. [•] The SiNWs formation is a result of a series of redox reactions in AgNO3/HF solution. [•] The formed silver particles regulated the sizes of SiNWs and their orientations. [•] The size, the porosity, and the reflectivity of the SiNWs depend on etching time. [•] The QSSPC measurement reveals a detorioration of the minority carrier lifetime. [ABSTRACT FROM AUTHOR]

Highlights: [•] Measured reflectance of porous silicon nanowires films inferior to 0.1%. [•] Modeling using the transfer matrix formalism. [•] Absorbance of porous silicon nanowires superior to that obtained with silicon nanowires. [•] Ultimate efficiency equal to 25% for normal incidence angle. [Copyright &y& Elsevier]

Porous silicon nanowires (PSi NWs) are a promising material for applications in sensorics, photovoltaics, and biomedicine. However, the structural and optical properties of PSi NWs are extremely sensitive to the concentrations of chemical solutions used in their manufacture. In this study, PSi NWs were fabricated by a two step metal-assisted chemical etching method from highly doped crystalline silicon wafers with a resistivity of <0.005 Ω cm. It was shown that the structural and optical properties of the obtained samples depend on the concentration of hydrogen peroxide (H 2 O 2), which in our experiments varied from 5 to 30%. As a result of etching, a layer of NWs with a diameter of 50–200 nm is obtained from above, and a thin layer of porous silicon is obtained from below. The ratio of the thicknesses of these two layers can be tuned by choosing the required concentration of H 2 O 2. The porosity of the samples, calculated in the approximation of the effective Bruggeman medium from the IR reflection spectra, was 40–50%. Electron microscopy demonstrated the presence of a large amount of silicon nanocrystals in the volume of PSi NWs, which exhibited efficient visible photoluminescence due to quantum confinement effect. It was shown that the size of the nanocrystals can be also tunable on the used concentration of H 2 O 2. [ABSTRACT FROM AUTHOR]