Mild Sol-gel Process Research Articles

Bioinspired silicification of chloroplast for extended light-harvesting ability

We report a hybrid bioactive system inspired by the biosilicification of diatoms. Monodisperse chloroplast/silica hybrid microspheres with core–shell structure were designed and prepared. Natural fresh chloroplasts, the photosynthetic plant organelle, were surfacely covered with silica shell by mild sol–gel process. The charge of chloroplast surface attracts negatively charged silica particles in the sol generated from subsequent hydrolysis and condensation of the tetraethyl orthosilicate (TEOS), which benefits single-chloroplast encapsulation. SEM images confirm the closed topologies, sizes, and dispersions of hybrid microspheres comparable to those of parent chloroplasts. The elemental analysis using EDX, the particle size distribution analyses using DLS, the thermochemical analyses using TGA measurements and structural characterization using XRD provide evidence for the formation of silica coating. Monitoring declines in the visible light absorption production yields information regarding the declines in the light-harvesting ability of chlorophyll, which confirmed that the silica shell in the present work extends the photochemical vitality of chloroplasts. Results from oxygen production measurements also demonstrate the existence of silica shell confers real protection on the bioactivity of chloroplasts. We envisage that the stand-alone chloroplast encapsulation enables preparation of living-cell-templated microspheres exhibiting capacity for photosynthetic bioreactors, sensors, green coatings, catalysts, more generally opening a window for construction of stable, environment friendly, functional hybrid materials.

Facile synthesis of Cu2+-modified mesoporous silica-coated magnetic graphene composite for enrichment of microcystin-LR followed by mass spectrometry analysis

MCs is a group of potent hepatotoxic peptides produced by cyanobacterial in eutrophic water, among which microcystin-LR is the most abundant and toxic. Long-time accumulation of even trace dosage from drinking water would cause significantly hepatic injury to animal and humans. Here we reported a novel Cu2+-modified mesoporous silica coated magnetic graphene composite (magG@mSiO2@-Cu2+) through mild sol-gel process and surface modification. Next, the composites were successfully applied for enrichment and separation of microcystin-LR followed by MALDI-TOF MS analysis based on the virtues of excellent hydrophilicity, high surface area (261cm2g−1), sensitively magnetic separation property, accessible porosity (3.10nm) and large amount of modified Cu2+ ions. Even performed in a lower concentration (0.5μg/L), at which microcystin-LR could not be detected directly, after treatment with the composites the S/N ratio could appear to be 82.93. Furthermore, the novel composites also exhibited high enrichment efficiency in real water sample. It provided a sensitive and efficient technique for enrichment and detection of microcystin-LR and developed a potent method for separation of pollutant in contaminated water.

Effects of supercritical carbon dioxide treatment conditions on the gas separation properties of polydimethylsiloxane hybrid membrane materials for air purification

A siloxane/polydimethylsiloxane (PDMS) hybrid membrane containing fluorinated side chains was prepared by a convenient and mild sol–gel process and a crosslinking reaction. The effects of the supercritical carbon dioxide (scCO2) conditions (i.e., treatment temperature, treatment time, and treatment pressure) on the permeation properties of fluorinated PDMS containing hybrid membrane were investigated. The chemical structure, microstructure, and physical performance of the membranes treated before and after were also discussed. The chemical structure of the PDMS membranes did not change with the scCO2 treatment conditions. The membranes still retained better membrane-forming abilities, higher permeability, and selectivity than normal PDMS membranes. Compared to those of the membrane with membrane formation after scCO2 treatment, the oxygen permeability coefficient and oxygen/nitrogen separation factor of the membrane with scCO2 treatment before membrane formation were higher and were up to 7.11 × 10−8 cm3 (STP) cm/(cm2 s cmHg) and 3.27, respectively. The permeation properties of the hybrid membrane were obviously higher than those of Robeson's upper bound. The high air-purification performance of the hybrid membrane may have been due to the introduction of fluorine atoms into PDMS membrane, and the increase in free volume resulted from the plasticizing function of the scCO2 treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation and characterization of chitosan/β-GP membranes for guided bone regeneration

Bioabsorbable chitosan/β-glycerol phosphate (CS/β-GP) composite membranes were fabricated through a relatively PH neutral and mild sol-gel process for guided bone regeneration (GBR). Their structural properties, morphology, and tensile strength were investigated. FTIR and XRD analyses indicated that there were chemical bonds between the CS andβ-GP. SEM analysis revealed that the CS/β-GP composite membranes had a porous structure both at the surface and in sublayers. Even though the incorporation ofβ-GP in the CS matrix decreased the initial tensile strength of the membrane, the CS/β-GP membranes were still fit for GBR application with their tensile strength of roughly 1 MPa. The concentration ofβ-GP was proportional to the pore size and thickness but was inversely proportional to the tensile strength of the CS/β-GP membrane. The present findings indicate that, based on its characteristics, the CS/β-GP composite membrane is a potential bioresorbable membrane for use in guided bone regeneration.

Gas separation properties of siloxane/polydimethylsiloxane hybrid membrane containing fluorine

A cross-linking agent containing silicon–hydrogen bond and trimethoxylsilicon groups was synthesized by silicon–hydrogen addition reaction. Based on a convenient and mild sol–gel process as well as cross-linking reaction, a siloxane/polydimethylsiloxane (PDMS) hybrid membrane containing fluorinated side-chains was also prepared by using 13-fluorinated triethoxysilane and PDMS containing vinyl group as matrix materials. The chemical structure, microstructure and mechanical property of the hybrid membrane were characterized. The effects of gas pressure difference, temperature and fluorine content on permselectivity of the hybrid membrane were investigated. The results showed that the membrane had better membrane-forming and high permeability as well as selectivity than normal PDMS membranes. The oxygen permeability coefficient was 602 Barrer and oxygen/nitrogen separation factor was up to 3.47. The permeation properties of the hybrid membrane fluorinated are higher obviously than those of Robeson's upper bound and of unfluorinated PDMS membrane. Both a high permeability and a high selectivity of the hybrid membrane may be attributed to the introduction of fluorine atom into PDMS membrane, cross-linking network of molecule structure and mild sol–gel process.

Quantum-sized ZnO nanoparticles: Synthesis, characterization and sensing properties for NO2

Quantum-sized ZnO nanoparticles have been synthesized at room temperature by a mild sol–gel process using tetraethylorthosilicate (TEOS) as the capping agent to control the particle growth of ZnO. The crystal structure, particle size and optical properties have been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra and Raman spectra, respectively. The results show that the ZnO nanoparticles exhibit hexagonal wurtzite structure and the average crystallite size is 5.7 nm which is a little less than TEM results. It has been testified by room-temperature PL spectra that the TEOS capped the surface of ZnO nanoparticles and obviously reduced grain size, as an emission at 520 nm almost disappeared and a new peak with an anomalous blue shift as great as 9 nm, appeared for the TEOS capped ZnO. The sensing tests indicate that the ZnO based sensors not only show a high response to NO2 but also exhibit high selectivity over CO and CH4 at a low operating temperature of 290 °C. The response increases with NO2 concentration and decreases with calcination temperature, and is in agreement with Raman and XRD results.

Analysis of phenolic compounds catalyzed by immobilized horseradish peroxidase in silica glass

Horseradish peroxidases are entrapped into tetramethyl orthosilicate derived silicates by a mild sol–gel process. Compared with free enzymes in solution, silica immobilized Horseradish peroxidases are more robust, stable in a long-term and ease of recycle. Therefore, a phenolic compounds analysis method is established on the immobilized enzyme catalyzed oxidation reaction to produce intensely colored products for spectrophotometric analysis. The absorbance of colored product and analyte concentrations is linearly related. The similar methods also employ on analyzing 2-chlorophenol, 3-chlorophenol and 2,4-dichlorophenol. Furthermore, this method permits to reuse immobilized HRP to examine phenolic compounds. The thin silica film is used as an immobilization carrier. It has shorter pathlength for diffusion of analytes, which will lead to faster response times. Decomposition of quinone-imine colored product also has an effect on accuracy and precision of measurement. Decomposition rate constant is 5.549 × 10−4 min−1. The interference substances have no obvious effect on the analytic results, except for formaldehyde and Pb2+. The proposed method can examine a real sample in waste water.

Organic-inorganic hybrid silica as supporting matrices for selective recognition of bovine hemoglobin via covalent immobilization

The synthesis of poly-aminophenylboronic acid (APBA) imprinted hybrid silica-based polymers for selective recognition of bovine hemoglobin (BHb) was described, where the mesoporous hybrid silica supporting matrices were prepared by a mild sol-gel process with tetraethoxysilane and 3-aminopropyltriethoxysilane as two precursors. Covalent immobilization of BHb was adopted in order to create homogeneous recognition sites. After removal of the template, the resulting imprinted polymers showed high binding affinity toward BHb and the imprinting factor (alpha) reached 2.12. The specificity of the BHb recognition was evaluated with competitive experiments, indicating the imprinted polymers have a higher selectivity for the template BHb. The easy preparation protocol and good protein recognition properties made the approach an attractive solution to depletion of high-abundance protein from bovine blood.

Preparation and evaluation of a macroporous molecularly imprinted hybrid silica monolithic column for recognition of proteins by high performance liquid chromatography

A novel type of macroporous molecularly imprinted hybrid silica monolithic column was first developed for recognition of proteins. The macroporous silica-based monolithic skeleton was synthesized in a 4.6 mm i.d. stainless steel column by a mild sol–gel process with methyltrimethoxysilane (MTMS) as a sole precursor, and then vinyl groups were introduced onto the surface of the silica skeleton by chemical modification of γ-methacryloxypropyltrimethoxysilane (γ-MAPS). Subsequently, the molecularly imprinted polymer (MIP) coating was copolymerized and anchored onto the surface of the silica monolith. Bovine serum albumin (BSA) and lysozyme (Lyz), which differ greatly in molecular size, isoelectric point, and charge, were representatively selected for imprinted templates to evaluate recognition property of the hybrid silica-based MIP monolith. Some important factors, such as template–monomer molar ratio, total monomer concentration and crosslinking density, were systematically investigated. Under the optimum conditions, the obtained hybrid silica-based MIP monolith showed higher binding affinity for template than its corresponding non-imprinted (NIP) monolith. The imprinted factor (IF) for BSA and Lyz reached 9.07 and 6.52, respectively. Moreover, the hybrid silica-based MIP monolith displayed favorable binding characteristics for template over competitive protein. Compared with the imprinted silica beads for stationary phase and in situ organic polymer-based hydrogel MIP monolith, the hybrid silica MIP monolith exhibited higher recognition, stability and lifetime.

Synthesis of MS/TiO2 (M = Pb, Zn, Cd) nanocomposites through a mild sol–gel process

In a sol–gel process, metal acetates reacted with thioacetamide to form the corresponding metal sulfides homogeneously dispersed in a colloid. The as-prepared dry gels were decomposed by heat treatment at 120 °C to form MS/TiO2 (M = Pb, Zn, Cd) nanocomposites. The products were analyzed by infrared spectroscopy, X-ray powder diffraction, transmission electron microscopy, elemental analysis, UV-Vis absorption, and photoluminescence. The final nanocomposites consisted of amorphous titanium dioxide nanoparticles and nanocrystalline metal sulfides. Nanocrystalline PbS in the gel had fine optical properties and showed obvious quantum confinement effects.