Recent breakthroughs in nanotechnology have made various nanostructured materials more affordable for a broader range of applications. Although we are still at the beginning of exploring the use of ...these materials for biocatalysis, various nanostructures have been examined as hosts for enzyme immobilization via approaches including enzyme adsorption, covalent attachment, enzyme encapsulation, and sophisticated combinations of methods. This review discusses the stabilization mechanisms behind these diverse approaches; such as confinement, pore size and volume, charge interaction, hydrophobic interaction, and multipoint attachment. In particular, we will review recently reported approaches to improve the enzyme stability in various nanostructures such as nanoparticles, nanofibers, mesoporous materials, and single enzyme nanoparticles (SENs). In the form of SENs, each enzyme molecule is surrounded with a nanometer scale network, resulting in stabilization of enzyme activity without any serious limitation for the substrate transfer from solution to the active site. SENs can be further immobilized into mesoporous silica with a large surface area, providing a hierarchical approach for stable, immobilized enzyme systems for various applications, such as bioconversion, bioremediation, and biosensors.
The Fe2O3/CuFe2O4/chitosan nanocomposites have been successfully synthesized via a new sol–gel auto-combustion route. To prepare the nanocomposites, copper ferrite (CuFe2O4) and iron (II) oxide ...(Fe2O3) nanostructures were first prepared utilizing onion as a green reductant for the first time, and characterized by SEM, TEM, XRD, IR and VSM. Then chitosan was added into the nanostructures dispersed in water. Chitosan was used to functionalize and modify the nanostructures and also to improve surface properties. The nanocomposites were also characterized by several techniques including SEM, TEM, XRD, IR and VSM. The effects of amount of onion and chitosan on the morphology and particle size of nanocomposites were evaluated.
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•Fe2O3/CuFe2O4/chitosan nanocomposites were synthesized for the first time.•A simple, low-cost and friendly route was used to synthesize the nanocomposites.•Effects of amount of onion and chitosan were investigated.
Recently, organic–inorganic hybrid materials have attracted tremendous attention thanks to their outstanding properties, their efficiency, versatility and their promising applications in a broad ...range of areas at the interface of chemistry and biology. This article deals with a new family of surface‐reactive organic–inorganic hybrid materials built from chitosan microspheres. The gelation of chitosan (a renewable amino carbohydrate obtained by deacetylation of chitin) by pH inversion affords highly dispersed fibrillar networks shaped as self‐standing microspheres. Nanocasting of sol–gel processable monomeric alkoxides inside these natural hydrocolloids and their subsequent CO2 supercritical drying provide high‐surface‐area organic–inorganic hybrid materials. Examples including chitosan–SiO2, chitosan–TiO2, chitosan–redox‐clusters and chitosan–clay‐aerogel microspheres are described and discussed on the basis of their textural and structural properties, thermal and chemical stability and their performance in catalysis and adsorption.
Gelling together: Gelation of a chitosan biopolymers by pH inversion affords highly dispersed self‐standing microspheres (see figure). Nanocasting and nanoreplication by sol–gel chemistry and/or intercalation by ion exchange provide a new family of surface‐reactive organic–inorganic hybrid materials.
The reversible micellization and sol–gel transition of block copolymer solutions in an ionic liquid (IL) triggered by a photostimulus is described. The ABA triblock copolymer employed, denoted ...P(AzoMA‐r‐NIPAm)‐b‐PEO‐b‐P(AzoMA‐r‐NIPAm)), has a B block composed of an IL‐soluble poly(ethylene oxide) (PEO). The A block consists of a random copolymer including thermosensitive N‐isopropylacrylamide (NIPAm) units and a methacrylate with an azobenzene chromophore in the side chain (AzoMA). A phototriggered reversible unimer‐to‐micelle transition of a dilute ABA triblock copolymer (1 wt %) was observed in an IL, 1‐butyl‐3‐methylimidazolium hexafluorophosphate (C4mimPF6), at an intermediate “bistable” temperature (50 °C). The system underwent a reversible sol–gel transition cycle at the bistable temperature (53 °C), with reversible association/fragmentation of the polymer network resulting from the phototriggered self‐assembly of the ABA triblock copolymer (20 wt %) in C4mimPF6.
Make or break: The reversible micellization and gel‐to‐sol transition of an ionic liquid/ABA block copolymer solution triggered by a photostimulus is described. Photorheology is employed to monitor the light‐induced viscoelastic property changes of the functional liquid resulting from hierarchical changes in the microscopic substructure of the macromolecular building blocks.
Hybrid silica membranes are of great interest for molecular separation owing to their outstanding hydrothermal stability. Despite good separation properties in liquid applications, the selectivity ...for gas separations has yet been too low. Here, we report membranes from 1,2-bis(triethoxysilyl)ethane (BTESE) with H2/N2 permselectivity between 50 and over 400. The membranes are fabricated from a dip-sol with a H+:Si ratio of 0.01 that is applied onto a support system with a controlled low water content (pre-treated at RH<0.5%). For support systems pre-treated at 90% RH, H2/N2 permselectivities≤10 are obtained, indicating larger pores. The pore formation process is studied in situ by Small-Angle X-ray Scattering in a dedicated setup. The formation of larger pores can be understood by a higher condensation rate and longer drying times when more water is present. This results in a stronger network that better withstands the compressive forces during drying. By limiting both the water and acid contents in the dipped sol, a dense pore structure is obtained that gives the highest H2/N2 and CO2/CH4 permselectivities found to date for hybrid silica membranes. Further variation of the water and acid concentration will allow for additional tuning of the separation properties for both gas and liquid separation.
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•Tunable pore structure in hybrid silica membranes by adapting acid and water content.•Pore formation process during drying followed in situ with SAXS.•Isotropic and selective organosilica membranes prepared in single dipping step.•Water from moist support system acts as reactant, giving larger pores.•Highest permselectivity of hybrid silica membranes to date: H2/N2>400; CO2/CH4>100.
A novel sol–gel method was adopted to prepare polyethylene glycol/silicon dioxide shape-stabilized phase change materials (PEG/SiO2 ss-PCMs) with various PEG mass fractions. The gelatinization was ...carried out by adjusting temperature instead of adding coagulant. In PEG/SiO2 composites, PEG acted as the phase change material and silica gel served as the supporting material to keep the stable shape of the composites during the phase transition. Various characterization techniques were employed to investigate the structures and properties of the composites. Results showed that the composites exhibited the stable core–shell structures by impregnating PEG into multi-mesoporous silica gel; they could remain in the solid form even if the temperature exceeded the melting point of PEG. It was physical adsorption between PEG and silica gel, and the crystal structure of PEG component was unaffected, so that PEG in the composites retained an excellent phase change performance. The enthalpies of the composites varied from 63.4J/g to 128.4J/g (PEG mass fractions: 50–80%), which was proportional to PEG content. The thermal conductivities were increased to 0.558Wm−1K−1 by addition of graphite in mass fraction of 2.7%. Moreover, the composites presented excellent thermal stabilities and possessed a broad applicable temperature range, and they were suitable for thermal energy storage applications in building envelopes.
•The novel shape-stabilized phase change materials (ss-PCMs) are designed for building envelops.•Stable core–shell structures of ss-PCMs are formed by impregnating PEG into mesoporous silica gel.•The enthalpies of ss-PCMs vary from 63.4J/g to 128.4J/g.•Thermal conductivity of ss-PCM with 2.7% graphite is 0.558Wm−1K−1.•ss-PCMs have high thermal stabilities and good compatibilities.
A novel heterostructured Si@C@Ge anode is developed via a two‐step sol–gel method. A facile and straightforward Ge decoration significantly boosts the Li‐storage performance of core–shell Si@C ...nanoparticles on both mechanics and kinetics. The Si@C@Ge anode shows unprecedented electrochemical performance in terms of accessible capacity, cycling stability, and rate capability when compared to those of a core–shell Si@C anode. Based on the experimental results and analysis of the mechanism, it is evident that high‐conductivity Ge nanograins on the surface facilitates the Li diffusivity and electron transport and guarantees high ion accessibility. Moreover, it is the Ge nanograins that serve as buffering cushion to tolerate the mechanic strain distribution on the electrode during lithiation/delithiation processes.
A facile Ge decoration on Si@C core–shell nanoparticles is developed via a sol–gel method. With this optimal design, Si@C@Ge core–satellite nanoparticles are expected to exhibit significant enhancement in structural stability and electrochemical kinetics, delivering an unprecedented capacity of 1854 mA h g−1 over 150 cycles and an excellent rate capability of 541 mAh g−1 at 10 A g−1.
We have developed a novel flexible pH sensor based on a polymeric substrate by low-cost sol–gel fabrication process of iridium oxide (IrO
x
) sensing film. A pair of miniature IrO
x
/AgCl electrodes ...on a flexible substrate generated electrical potentials in solutions by electrochemical mechanisms responding to their pH levels. Our flexible IrO
x
pH sensors exhibited promising sensing performance with a near-Nernstian response in sensitivity repeatedly and reversibly between −51.1
mV/pH and −51.7
mV/pH in the pH range between 1.5 and 12 at 25
°C. The fabrication processes including sol–gel deposition, thermal oxidation, and AgCl electro-plating on polymeric substrates were reported. The performance and characterization of the flexible pH sensors in sensitivity, response time, stability, reversibility, repeatability and selectivity were also discussed. Our IrO
x
pH electrodes on a deformable substrate demonstrated their sensing capability while they were conformed to a curved surface inside a limited space with distinct responding potentials at various pH levels similar to the traditional glass-rod pH electrodes.
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Waterproof and flame-retardant fabrics are widely utilized in many fields, such as automotive interiors, indoor decorations, outdoor clothing and tents. Herein, a facile one-pot ...sol-gel approach was developed to construct superhydrophobic and flame-retardant (SFR) coatings on cotton fabrics. The cotton fabric was activated by O2 plasma and then immersed into the ethanol suspension containing tetraethoxysilane (TEOS), hydroxyl-terminated polydimethylsiloxane (HPDMS) and ammonium polyphosphate (APP). The hydrogen bonding interaction between APP and cellulose motivated the APP to attach to the cotton fibers during the initial stirring process. After the addition of ammonia, the in situ sol-gel reaction of TEOS and HPDMS was initiated to generate polydimethylsiloxane-silica hybrid (PDMS-silica). The micro-nano structured composite coating on cotton fabric was successfully fabricated by the PDMS-silica and APP. The SFR cotton fabric showed outstanding durability and self-cleaning ability with a water contact angle (WCA) above 160°. When exposed to fire, the SFR cotton fabric quickly charred to extinguish the fire by generating a dense intumescent char layer under the physical barrier effect of PDMS-silica and the intumescent flame-retardant effect of APP. This one-pot approach for fabricating SFR cotton fabric is simple, cost-effective and timesaving, demonstrating significant advantages in practical production.
Silica sol–gel coatings were deposited on AZ31B and AZ91D magnesium substrates with the aim of controlling the degradation rate, corrosion attack and further dissolution of magnesium alloys for ...temporal implants. Two different silica sols were prepared with and without colloidal silica particles (MTL and TG sols) and deposited by dip-coating on both alloys. The coatings were characterised in SBF using three different in vitro tests; hydrogen evolution, pH variation and potentiodynamic polarization curves. The results show that the corrosion behaviour depends on the alloy and on the coating composition. Coatings on AZ91D-MTL were able to block the degradation of the alloy during 8 days of immersion in SBF, whereas coatings AZ91D-TG only maintain their stability during 3 days. Mg(OH)
2
and hydroxyapatite (HAp) were identified as the compounds precipitated on AZ31B samples, not appearing on AZ91D samples. The electrochemical tests confirm the promising corrosion results obtained for coated AZ91D samples.
Suitable silica sol–gel coatings were deposited on Mg alloys showing a great potential to control the degradation rate, corrosion attack and further dissolution of the magnesium alloys.
Highlights
Silica sol–gel coatings are able to block the degradation and corrosion attack of Mg alloys.
Different corrosion processes were identified that depend on the alloy and composition of the coatings.
Mg(OH)
2
and HAp precipitate onto the alloys, promoting the osteointegration.
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