Cavitand-functionalized porous silicon as an active surface for organophosphorus vapor detection

This paper reports on the preparation of a porous silicon-based material covalently functionalized with cavitand receptors suited for the detection of organophosphorus vapors. Two different isomeric cavitands, both containing one acid group at the upper rim, specifically designed for covalent anchoring on silicon, were grafted on H-terminated porous silicon (PSi) by thermal hydrosilylation. The covalently functionalized surfaces and their complexation properties were characterized by combining different analytical techniques, namely X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy analysis coupled with thermal desorption experiments. Complexation experiments were performed by exposing both active surfaces and a control surface consisting of PSi functionalized with a structurally similar but inactive methylene-bridged cavitand (MeCav) to dimethyl methylphosphonate (DMMP) vapors. Comparison between active and inactive surfaces demonstrated the recognition properties of the new surfaces. Finally, the nature of the involved interactions, the energetic differences between active and inactive surfaces toward DMMP complexation, and the comparison with a true nerve gas agent (sarin) were studied by DFT modeling. The results revealed the successful grafting reaction, the specific host-guest interactions of the PSi-bonded receptors, and the reversibility of the guest complexation.     

TOF-SIMS and FT-IR investigations of surface modified silicon wafers — porous silicon

Surface modification of silicon wafers by anodic etching in hydrofluoric acid results in the formation of porous silicon layers consisting of nanocrystallites covered with SiH bonds. A combination of high resolution Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and Fourier Transform Infrared Spectroscopy (FT-IR) was used to study the surface chemistry of this new material.     

Preparation of hexagonal platy particles of nanoporous silica using hydrotalcite as morphology template

Hexagonal platy composite particles with a hydrotalcite core and a nanoporous silica shell with a thickness of ca. 100 nm were synthesized by the reaction of a Mg-Al hydrotalcite with a homogeneous aqueous solution containing tetraethoxysilane, hexadecyltrimethylammonium chloride, ammonia and methanol at 3 degrees C. The calcination of the products at 500 degrees C in air led to the composite particle with a Mg/Al mixed oxide core and a nanoporous silica shell. Hexagonal platy particles of nanoporous silica with a pore diameter of 2.3 nm and BET surface area of 700 m(2) (g of silica)(-1) were obtained by removing the Mg/Al mixed oxide core.     

PEGylation of porous silicon using click chemistry

Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein-porous silicon interactions.     

利用Triton X-100合成介孔二氧化硅及其形貌研究

以非离子型表面活性剂Triton X-100为模板剂,正硅酸乙酯为硅源,合成了介孔二氧化硅分子筛.利用XRD、N2吸附—脱附、SEM、以及TG-DTA对样品进行了表征,结果表明合成的材料具有有序介孔结构、高比表面积及高孔容。同时比较了不同条件下所得产物的形貌结构,并分析了它们的形成机理。     

Synthesis of hierarchically porous bioactive glasses using natural plants as template for bone tissue regeneration

A series of highly ordered hierarchically porous silica and bio-glasses materials with macropore size of 8?C1,000???m and mesopore size of 3.1?C5.6?nm have been synthesized using six plant based materials as templates. However, the as-obtained porous structure was reported for the first time with interconnected 3D macropore up to 1,000???m. The porous silica materials were used as the host for drug loading and release, which showed a good sustained delivery function. The as-synthesized bio-glasses materials indicated the highly bioactive capability in the bone regeneration. This method can be utilized to synthesize other multi-porous bioactive glasses using different plants as templates for bone tissue repairing.     

Excellent electrochemical performance of nitrogen-enriched hierarchical porous carbon electrodes prepared using nano-CaCO3 as template

Recently, tremendous research efforts have been concentrated on developing high-performance electrode materials to meet the ever-increasing energy and power demands in supercapacitors. Herein, we presented a high-capacity supercapacitor material based on nitrogen-enriched hierarchical porous carbons (NHPCs) synthesized by the carbonization of melamine formaldehyde resins using eco-friendly and inexpensive nano-CaCO₃ as template. The effects of carbonization temperature and template content on the porous structure and electrochemical characteristics were compared and discussed in detail. The prepared NHPCs possessed large surface area up to 834 m² g^?1 and high nitrogen content up to 20.94 wt %. As electrode material for supercapacitors, NHPCs exhibited superior electrochemical performances with high specific capacitance (190 F g^?1 at 20 A g^?1), outstanding rate capability (80 %), and excellent cycling stability (over 2,000 cycles at 5 A g^?1) in 1 M sulfuric acid media. The excellent electrochemical performances are due to the synergic effects of unique hierarchical porous microstructure, abundant nitrogen and oxygen functionalities, as well as high degree of graphitization framework.     

Tuning physical surface properties of tin dioxide nanopowders using zinc oxide as template

With a view to energetic and (opto)electronic applications, tin (IV) oxide (SnO₂) nanoparticles have been successfully prepared at the nanoscale by a templating approach based on the use of zinc (II) oxide (ZnO) as template. The procedure consisted in preparing a mixture of tin precursor and template, subsequently calcined at 650 °C under air to lead to the formation of a SnO₂/ZnO composite material. Finally, the material was washed with an alkali solution to remove the template. The template/tin precursor mass ratio was varied in order to tailor the tin (IV) oxide material, especially with a view to main particle size. The resulting SnO₂ nanomaterials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption and electron microscopy. The tin (IV) oxide nanomaterial exhibited enhanced textural and physical surface properties (particle size, surface area, pore size) correlated to an increasing template/tin precursor mass ratio. For instance, from optimized experimental conditions, the specific surface area and pore volume were heightened twofold, reaching values of 49 m²/g and 0.32 cm³/g, respectively.     

Atomic and electronic structure of the surface of porous silicon layers

Atomic and electronic structure of the surface layers of porous silicon was studied by the methods of the near fine structure spectroscopy at the edge of X-ray absorption and ultrasoft X-ray emission spectroscopy. The thickness of the oxide layer and the degree of distortion of silicon-oxygen tetrahedra in this layer were estimated. The thickness of the surface oxide layer on the amorphous layer covering the nanocrystals of porous silicon that was kept during one year is several times greater than the thickness of the natural oxide in the single crystal silicon wafers. Distortion of the silicon-oxygen tetrahedron, the basic structural units of the silicon oxide, is accompanied by elongation of Si-O bonds and an increase in the Si-O-Si bond angles.     

Study of porous silicon nanostructures as hydrogen reservoirs

The amount of hydrogen present in porous silicon (PS) nanostructures is analyzed in detail. Concentration of atomic hydrogen chemically bound to the specific surface of PS is quantitatively evaluated by means of attenuated total reflection infrared (ATR-IR) spectroscopy and temperature-programmed desorption (TPD) spectroscopy. The concentration values are correlated to the PS nanoscale morphology. In particular, the influence of porosity, silicon nanocrystallite dimension, and shape on hydrogen concentration values is described. Hydrogen concentrations in fresh, aged, as well as in chemically and thermally treated PS layers are measured. Maximal hydrogen concentration of 66 mmol/g is detected in nanoporous layers with high (>95%) porosity consisting of nanocrystallites with dimensions of about 2 nm. Mass energy density that can be potentially obtained from this amount of hydrogen through a low-temperature fuel cell is estimated to be about 2176 W-h/kg and is found to be comparable with other substances containing hydrogen, such as hydride materials and methanol, which are usually used as hydrogen reservoirs.     

Characterization of pore size distribution in porous silicon by NMR cryoporosimetry and adsorption methods

The results of studying the pore size distribution of mesoporous silicon by NMR cryoporosimetry are described. These data are compared with the results obtained by adsorption methods.     

Matrix-assisted laser desorption/ionization mass spectrometry using porous silicon and silica gel as matrix

Porous silicon powder and silica gel particles have been applied as inorganic matrices for the analysis of small molecules in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOFMS). In contrast to conventional MALDI-TOFMS, the signal interference of low-molecular analytes by the matrix has been eliminated. Almost no fragmentations of the analytes were observed. Effects of various factors, such as the particle and pore size, the suspending solution, and sample preparation procedures, on the intensity of mass spectra have been investigated. The pore structure of the inorganic matrix and penetration of the analytes into the pores must be optimized for effective desorption and ionization of the analytes. Matrices (DHB and HCCA) were covalently bound to silica gel for improvement of spectrum intensity. Copyright © 2001 John Wiley & Sons, Ltd.     

Fabrication of ordered Ni nanocones using a porous anodic alumina template

Hexagonally ordered Ni nanocones have been produced using an electroless Ni deposition technique on a porous anodic alumina (PAA) template, where the pores are of a cone shape. The conical PAA film was found to exhibit hexagonal order with a period of 100 nm. The aspect ratio (cone height vs. the diameter of the base of the cone) of the conical pores on the PAA film was found to be one. The Ni nanocones and the surface morphology of the nano-conical film exhibit the same periodic structure of the template. A significant advantage of the fabrication process employed in this work is that it utilizes existing techniques.     

金属离子在多孔硅表面和吸附与电镀过程中金属在多孔硅表面的淀积

刚制备的多孔硅与金属盐溶液接触会产生金属离子在多孔硅表面和吸附现象。实验显示这一现象只发生在新鲜的多孔硅表面, 而存放一月以后的样品不具备此性质。文中把这一现象归因于新鲜的多孔硅表面电子的富集, 溶液中金属离子从多孔硅表面获得电子而附着。多孔硅表面电镀金属过程中, 一定电压下电镀电流密度在起始阶段逐渐下降, 可以用一个指数关系式较好地描述, 在本文中有一个唯象模型予以解释。     

金属离子在多孔硅表面和吸附与电镀过程中金属在多孔硅表面的淀积

刚制备的多孔硅与金属盐溶液接触会产生金属离子在多孔硅表面和吸附现象。实验显示这一现象只发生在新鲜的多孔硅表面, 而存放一月以后的样品不具备此性质。文中把这一现象归因于新鲜的多孔硅表面电子的富集, 溶液中金属离子从多孔硅表面获得电子而附着。多孔硅表面电镀金属过程中, 一定电压下电镀电流密度在起始阶段逐渐下降, 可以用一个指数关系式较好地描述, 在本文中有一个唯象模型予以解释。     

One-dimensional shape-controlled preparation of porous Cu2O nano-whiskers by using CTAB as a template

One-dimensional (1D) cuprite (Cu₂O) nano-whiskers with diameter of 15-30 nm are obtained from liquid deposition method at 25 °C by adding a surfactant, cetyl trimethyl ammonium bromide (CTAB), as a template. TEM and HRTEM show that the nano-whiskers exhibit a well-crystallized 1D structure of more than 200 nm in length, and confirms that the nano-whiskers grow mainly along the 〈111〉 direction. Moreover, there are many pores in the nano-whiskers, which is beneficial for the photocatalysis under visible light. When polyethylene glycol (PEG), glucose and sodium dodecylbenzenesulfonate (SDS) are used as templates, 1D structures cannot be obtained. According to the TEM images of the compound obtained at different stages during the growth of the Cu₂O nano-whiskers, it is found that the role of CTAB is to interact with tiny Cu(OH)₂, which can adsorb OH⁻ and become negative charged, to disperse the tiny Cu(OH)₂ solid and to induce the growth of Cu₂O along the 1D direction. Although CTAB is significant for the preparation of the 1D nanomaterials, ion character of the precursor (Cu(OH)₂·OH⁻ or Cu²⁺) is important as well since there is no nano-whiskers obtained with Cu²⁺ as the precursor. Moreover, the probable mechanism of the formation for the porous structure is discussed.     

Characterization of thermal properties of porous silicon film/silicon using photoacoustic technique

We have applied photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching. Four PS samples with close thicknesses but greatly different porosities (from 20 to 60%) were examined. From the dependences of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration (TDC), effective thermal diffusivities for the two-layered PS/Si samples were determined and found to decrease greatly from 0.095 to 0.020 cm² s^-1 as the porosity increased from 20 to 60%. This revised version was published online in August 2006 with corrections to the Cover Date.     

Delivery of nanogram payloads using magnetic porous silicon microcarriers

A transport and delivery system for nanogram quantities of molecular species that does not use microfluidic channels, pumps, or valves is described. Microparticles consisting of magnetic porous silicon are prepared, and loading and delivery of an enzymatic payload are demonstrated. The high porosity (60%) porous Si host particles are made magnetic by infusion of superparamagnetic iron oxide nanoparticles (30 nm-diameter magnetite, Fe(3)O(4)) under oxidative conditions. After magnetite incorporation, the porous microparticle is still empty enough to accommodate nanogram quantities of a molecular payload; the enzymes horseradish peroxidase or pronase E are used in the present work. The assembly can be transported to a microliter water droplet containing the enzyme substrate with the aid of an external magnetic field. The enzyme is released into the droplet upon contact. The particles can be transported through air or a hydrocarbon liquid without loss in enzymatic activity of the payload.     

IR detection of NO2 using p+ porous silicon as a high sensitivity sensor

Mesoporous silicon doped with 3.0 x 10(19) B atoms cm-3 (p(+)-type) is an insulating material which dramatically increases its electrical conductivity when exposed to traces of gaseous NO2; nitrogen dioxide chemisorption at the surface generates carriers, the population of which is readily evaluated through the intensity of IR absorption.     

High surface area of porous silicon drives desorption of intact molecules

The surface structure of porous silicon used in desorption/ionization on porous silicon (DIOS) mass analysis is known to play a primary role in the desorption/ionization (D/I) process. In this study, mass spectrometry and scanning electron microscopy (SEM) are used to examine the correlation between intact ion generation with surface ablation and surface morphology. The DIOS process is found to be highly laser energy dependent and correlates directly with the appearance of surface ions (Si(n)(+) and OSiH(+)). A threshold laser energy for DIOS is observed (10 mJ/cm(2)), which supports that DIOS is driven by surface restructuring and is not a strictly thermal process. In addition, three DIOS regimes are observed that correspond to surface restructuring and melting. These results suggest that higher surface area silicon substrates may enhance DIOS performance. A recent example that fits into this mechanism is the surface of silicon nanowires, which has a high surface energy and concomitantly requires lower laser energy for analyte desorption.