Cutting a path from the Atlantic to the Pacific, the Panama Canal set a new course for the development of Central America—but at considerable cost to Panamanians. Sleuth and scholar Marixa Lasso ...recounts how the canal’s American builders displaced 40,000 residents and erased entire towns in the guise of bringing modernity to the tropics.
Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent ...large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates. But metal-oxide formation by the sol-gel route requires an annealing step at relatively high temperature, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol-gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm(2) V(-1) s(-1) (with an Al(2)O(3) gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.
Nanostructures for enzyme stabilization Kim, Jungbae; Grate, Jay W.; Wang, Ping
Chemical engineering science,
02/2006, Letnik:
61, Številka:
3
Journal Article
Recenzirano
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.
Despite intensive research on photochemical activation of sol–gel metal oxide materials, the relatively long processing time and lack of deep understanding of the underlying chemical courses have ...limited their broader impact on diverse materials and applications such as thin‐film electronics, photovoltaics, and catalysts. Here, in‐depth studies on the rapid photochemical activation of diverse sol–gel oxide films using various spectroscopic and electrical investigations for the underlying physicochemical mechanism are reported. Based on the exhaustive chemical and physical analysis, it is noted that deep ultraviolet‐promoted rapid film formation such as densification, polycondensation, and impurity decomposition is possible within 5 min via in situ radical‐mediated reactions. Finally, the rapid fabrication of all‐solution metal oxide thin‐film‐transistor circuitry, which exhibits stable and reliable electrical performance with a mobility of >12 cm2 V−1 s−1 and an oscillation frequency of >650 kHz in 7‐stage ring oscillator even after bending at a radius of <1 mm is demonstrated.
The general physicochemical mechanisms underlying photoactivated sol–gel reactions are described, with comprehensive chemical and structural analysis inducing rapid (<5 min) fabrication of various metal oxide films at low temperatures (<150 °C), and all‐solution processed high‐performance electronic devices and circuitry on ultrathin polymeric substrates are demonstrated. This will open new possibilities to prepare future electronic materials in a fast, scalable, and economic manner.
Silica/polyacrylonitrile (SiO2/PAN) hybrid nanofiber membranes were fabricated by using sol-gel and electrospinning techniques and their electrochemical performance was evaluated for use as ...separators in lithium-ion batteries. The aim of this study was to design high-performance separator membranes with enhanced electrochemical performance and good thermal stability compared to microporous polyolefin membranes. In this study, SiO2 nanoparticle content up to 27 wt% was achieved in the membranes by using sol-gel technique. It was found that SiO2/PAN hybrid nanofiber membranes had superior electrochemical performance with good thermal stability due to their high SiO2 content and large porosity. Compared with commercial microporous polyolefin membranes, SiO2/PAN hybrid nanofiber membranes had larger liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO2/PAN hybrid nanofiber membranes with different SiO2 contents (0, 16, 19 and 27 wt%) were also assembled into lithium/lithium iron phosphate cells, and high cell capacities and good cycling performance were demonstrated at room temperature. In addition, cells using SiO2/PAN hybrid nanofiber membranes with high SiO2 contents showed superior C-rate performance compared to those with low SiO2 contents and commercial microporous polyolefin membrane.
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•SiO2/PAN membranes were prepared using sol-gel and electrospinning techniques.•SiO2 nanoparticle content up to 27 wt% was achieved by using sol-gel technique.•High cell capacities and good cycling performance were demonstrated.•Superior C-rate performance was obtained for cells with SiO2/PAN membranes.
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.
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.
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 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.
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