Preparation and Sensitivity of SnO2 Grafted MCM-41 Sensor

Tin dioxide is one of the most widely used semiconductor gas sensor to detect reducing gases1-3. The sensing mechanism of SnO2 is usually based on the change of the resistance of the sensor in different gas environment. In air, the surface-adsorbed oxygen species on the surface of SnO2 act as surface acceptors of electrons, hence diminishing the conductivity of SnO2. However, when reducing gases such as H2, CO, or CH4 are introduced in the air stream, the resistance of the SnO2 sensor is …     

Preparation of supported mesoporous thin films concerning template removal by supercritical fluid extraction

Thin films of silicate MCM-41 and silicate MCM-48 have been prepared on porous ceramic supports by the hydrothermal method. A comparative study of template removal has been made on supported thin films and on powder. By supercritical fluid extraction (SFE) with CH(3)OH-modified CO(2), at least 78% of the template can be removed from as-synthesized materials at 85 degrees C. X-ray diffraction (XRD) observations indicate that the resulting supported thin films after SFE are structurally stable and ordered with a weak pore contraction. The advantages of SFE over calcination in template removal are presented with a series of results obtained on supported thin films and on powder by XRD and N(2) adsorption-desorption.     

Growth of La2CuO4 nanofibers under a mild condition by using single walled carbon nanotubes as templates

La₂CuO₄ nanofibers (ca. 30 nm in diameter and 3 μm in length) have been grown in situ by using single walled carbon nanotubes (SWNTs; ca. 2 nm in inner diameter; made via cracking CH₄ over the catalyst of Mg_0.8Mo_0.05Ni_0.10Co_0.05O_x at 800 °C) as templates under mild hydrothermal conditions and a temperature around 60 °C. During synthesis, the surfactant poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and H₂O₂ were added to disperse SWNTs and oxidize the reactants, respectively. The structure of La₂CuO₄ nanofibers was confirmed by powder X-ray diffraction (XRD) and their morphologies were observed with field emission scanning electron microscope (FESEM) at the hydrothermal synthesis lasting for 5, 20 and 40 h, respectively. The La₂CuO₄ crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. Twenty hours is an optimum reaction time to obtain regular crystal fibers. The La₂CuO₄ nanofibers are probably cubic rather than round and may capsulate SWNTs.     

On-line sample cleanup and enrichment chromatographic technique for the determination of ambroxol in human serum

A sensitive and efficient on-line clean up and pre-concentration method has been developed using column-switching technique and protein-coated μ-Bondapak CN silica pre-column for quantification of ambroxol (AM) in human serum. The method is performed by direct injection of serum sample onto a protein-coated μ-Bondapak CN silica pre-column, where AM is pre-concentrated and retained, while proteins and very polar constituents are washed to waste using a phosphate buffer saline (pH 7.4). The retained analyte on the pre-column is directed onto a C(18) analytical column for separation, with a mobile phase consisting of a mixture of methanol and distilled deionized water (containing 1% triethylamine adjusted to pH 3.5 with ortho-phosphoric acid) in the ratio of 50:50 (v/v). Detection is performed at 254 nm. The calibration curve is linear over the concentration range of 12-120 ng/mL (r(2) = 0.9995). The recovery, selectivity, linearity, precision, and accuracy of the method are convenient for pharmacokinetic studies or routine assays.     

Halogen-Incorporated Sn Catalysts for Selective Electrochemical CO2 Reduction to Formate

Electrochemically reducing CO₂ to valuable fuels or feedstocks is recognized as a promising strategy to simultaneously tackle the crises of fossil fuel shortage and carbon emission. Sn-based catalysts have been widely studied for electrochemical CO₂ reduction reaction (CO₂RR) to make formic acid/formate, which unfortunately still suffer from low activity, selectivity and stability. In this work, halogen (F, Cl, Br or I) was introduced into the Sn catalyst by a facile hydrolysis method. The presence of halogen was confirmed by a collection of ex situ and in situ characterizations, which rendered a more positive valence state of Sn in halogen-incorporated Sn catalyst as compared to unmodified Sn under cathodic potentials in CO₂RR and therefore tuned the adsorption strength of the key intermediate (*OCHO) toward formate formation. As a result, the halogen-incorporated Sn catalyst exhibited greatly enhanced catalytic performance in electrochemical CO₂RR to produce formate.     

CO2 adsorption over Si-MCM-41 materials having basic sites created by postmodification with La2O3

Moderate basic sites could be created onto mesoporous Si-MCM-41 materials by postsynthesis modification with highly dispersed La2O3. The La2O3-modified MCM-41 materials (designated here as LaM) have been characterized by Fourier transform infrared spectroscopy, temperature-programmed desorption, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and N2 adsorption/desorption and have been tested as model adsorbents for CO2 adsorption. XRD and N2 adsorption results showed that all LaM materials still maintained their uniform hexagonal mesoporous structure even after postsynthesis modification with La2O3 loading up to 20 wt %. Although the surface area, pore size, and pore volume of LaM materials decreased with increasing La2O3 loading, their capacity for CO2 storage could be significantly improved when La2O3 loading was increased from 0 to 10 wt %. Unidentate and bidentate carbonates have been identified by in situ FTIR as the two types of CO2 species adsorbed on LaM surface. The LaM material also possesses good thermal stability, allowing the model adsorbent to be regenerated at high temperature and recyclable.     

pH-Controllable drug release using hydrogel encapsulated mesoporous silica

Amine-functionalized mesoporous SBA-15 silica loaded with bovine serum albumin (BSA) has been successfully encapsulated with a thin layer coating of poly(acrylic acid) PAA, with the entrapped BSA being released from the PAA-encapsulated SBA-15 at the higher pH value of 7.4 rather than at the lower pH value of 1.2. This novel drug delivery system has a potential application in the release of protein drug to the site of higher pH value, such as small intestine or colon.     

Aminated MCM-41-tethered Wilkinson''s complex: active immobilized catalyst precursor for cyclohexene hydroformylation

CuO/Ce_0.7Sn_0.3O₂ catalysts were prepared for the catalytic oxidation of CO. The catalysts were characterized by means of CO-TPD, XRD and TPR. A synergistic interaction between CuO and Ce_0.7Sn_0.3O₂ is responsible for the high activity of carbon monoxide at low temperature.This revised version was published online in December 2005 with corrections to the Cover Date.     

金属有机化学气相沉积法制备SnO2/MCM-41半导体传感器及其性能研究

采用金属有机化学气相沉积(MOCVD)法制备了SnO2/MCM-41半导体传感器, 考察了沉积时间和沉积温度对SnO2/MCM-41半导体传感器的SnO2沉积量、比表面积和孔径的影响; 研究发现, 随着SnO2沉积量的增加, 孔径有规律地下降, 说明SnO2较均匀地沉积在介孔分子筛MCM-41的孔道之中. SnO2/MCM-41半导体传感器对CO和H2具有较高的传感性能, 其传感性能的大小与CO和H2的浓度成正比.     

Synthesis, characterization and sensing application of novel semiconductor oxides

Mesoporous SnO(2) with high surface areas were synthesized using a cationic surfactant (N-cetyl-N,N,N-trimethylammonium bromide) as a synthetic template. Acidity of the starting synthesis slurry was used as one of the controlling parameters for the synthesis. After the SnO(2) was synthesized at pH 7.15, it was calcined at 723 K for 10 h in air. It had a BET surface area of 156.8 m(2) g(-1) with a pore diameter of 38.4 A. Infrared spectroscopy (FTIR) and thermal analysis techniques (thermogravimetry and differential thermal analysis) showed that the surfactant was incorporated in the mesopores of SnO(2) and calcination in air at 673-723 K was needed to remove the surfactant completely from the mesopores. The effects of SnO(2) surface area on its gas sensing properties were also investigated. It was observed that SnO(2) with higher surface areas had much higher sensitivities to hydrogen at 573 K.