Mechanical reinforced fiber needle felt/silica aerogel composite with its flammability

Fiber needle felt–silica aerogel composite was successfully prepared by via sol–gel process based on water glass. The thermal conductivity show V-type variation tendency with the increase of water to Si. Thermogravimetric analysis-differential scanning calorimetry analysis revealed that the thermal stability was up to approximately 390.58?°C. It has been found that the fire hazard of the composites decreased with the increased ratio of water to Si according to the cone calorimeter test, which can be characterized by peak heat release rate, fire performance index, and fire growth rate index. The fiber needle felt/aerogels present greatly improved compressive and flexural strength (elastic modulus: 0.1–0.97?MPa; flexural modulus: 0.33–0.66?MPa) while keeping inherent properties of pure silica aerogel: low bulk density (0.166?g/cm³), low thermal conductivity of 0.0236?W/m·K, and high specific surface area (1091.62?m²/g). As a result, the as-prepared composite shows a great potential to be applied in the thermal insulation field.

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Biodiesel fuel production by the transesterification reaction of soybean oil using immobilized lipase

The enzymatic alcoholysis of soybean oil with methanol and ethanol was investigated using a commercial, immobilized lipase (Lipozyme RMIM). The effect of alcohol (methanol or ethanol), enzyme concentration, molar ratio of alcohol to soybean oil, solvent, and temperature on biodiesel production was determined. The best conditions were obtained in a solvent-free system with ethanol/oil molar ratio of 3.0, temperature of 50 degrees C, and enzyme concentration of 7.0% (w/w). Three-step batch ethanolysis was most effective for the production of biodiesel. Ethyl esters yield was about 60% after 4 h of reaction.     

Synthesis of nanoporous silica aerogel by ambient pressure drying

A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol, which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 °C under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to the silica sol and aged in a 70%EtOH/30%TEOS solution.     

Enhancement in thermal stability and resistance to denaturants of lipase encapsulated in mesoporous silica with alkyltrimethylammonium (CTAB)

We assembled a highly durable conjugate with both a high-density accumulation and a regular array of lipase, by encapsulating it in mesoporous silica (FSM) with alkyltrimethylammonium (CTAB) chains on the surface. The activity for hydrolyzing esters of the lipase immobilized in mesoporous silica was linearly related to the concentration of lipase, whereas that of non-immobilized lipase showed saturation due to self-aggregation at a high concentration. The lipase conjugate also had increased resistance to heating when stayed in the silica coupling with CTAB. In addition, encapsulating the enzyme with FSM coupled CTAB caused the lipase to remain stable even in the presence of urea and trypsin, suggesting that the encapsulation prevented dissociation and denaturing. This conjugate had much higher activity and much higher stability for hydrolyzing esters when compared to the native lipase. These results show that FSM provides suitable support for the immobilization and dispersion of proteins in mesopores with disintegration of the aggregates.     

Enantioselective transesterification of a tertiary alcohol by lipase A from Candida antarctica

Chiral tertiary alcohols and their esters represent important flavor compounds and are useful building blocks. Unfortunately, they are accepted by only a few lipases/esterases as substrates and enantioselectivity is usually very low. We report here a highly enantioselective transesterification of the tertiary alcohol 2-phenylbut-3-yn-2-ol using lipase A from Candida antarctica (CAL-A). Under optimized conditions, the corresponding acetate was obtained with 94%ee at 35% conversion equivalent to an enantioselectivity factor of E=65. In contrast, enantioselective hydrolysis of the racemic acetate was not feasible as this is very prone to autohydrolysis.     

Effect of sepiolite fiber on the structure and properties of the sepiolite/silica aerogel composite

Sepiolite fiber-reinforced silica aerogel composites for thermal insulators were prepared by dispersing sepiolite fiber in silica sol, aging, solvent exchanging, and drying in supercritical fluid. The surface treated sepiolite fiber and sepiolite/silica aerogel composite were characterized by scanning electron microscope; transmission electron microscope and Fourier transform infrared spectroscopy. The influence of surface treated sepiolite fiber on the mechanical and thermal properties of the aerogel composite was studied. The results indicate the hydroxyl groups on silica sol particles surface able to condense with the hydroxyls of sepiolite fibers with forming Si–O–Si between sepiolite fibers and aerogel matrix in the sol–gel process, which achieves excellent interfacial interaction in the sepiolite/silica aerogel composite, so the mechanical properties of the aerogel composite have been improved effectively without sacrificing much thermal insulating performance.     

Production of biodiesel fuel by transesterification of rapeseed oil

Fatty acid methyl esters (FAMEs) show large potential applications as diesel substitutes, also known as biodiesel fuel. Biodiesel fuel as renewable energy is an alternative that can reduce energy dependence on petroleum as well as air pollution. Several processes for the production of biodiesel fuel have been developed. Transesterification processes under alkali catalysis with short-chain alcohols give high yields of methyl esters in short reaction times. We investigated transesterification of rapeseed oil to produce the FAMEs. Experimental reaction conditions were molar ratio of oil to alcohol, concentration of catalyst, type of catalyst, reaction time, and temperature. The conversion ratio of rapeseed oil was enhanced by the alcohol:oil mixing ratio and the reaction temperature.     

Characterization of anticancer hypocrellin A encapsulated with silica nanoparticles

Hypocrellins, natural photosensitizers including hypocrellin A (HA) and hypocrellin B (HB), have been used as a traditional Chinese herbal medicine to cure various skin diseases. Hypocrellins have excellent antiviral activity, which can inhibit the growth of human immunodeficiency virus. They also exhibit significant light-induced antitumor property. In this article, thermal analysis technologies (e.g., differential scanning calorimetry and thermogravimetry) are employed to characterize whether the photosensitive hypocrellin A could be encapsulated with silica nanoparticle (SN) material or not, and evaluate the stability of inclusion complex. The results show that the inclusion complex exhibits improved performance in both stability and hydrophilicity than natural hypocrellin A. Fluorescence spectrophotometry studies have also been performed to verify the thermal analysis results. The results suggest that the thermal analysis technology could be used as an effective and rapid tool to characterize the encapsulation properties of the novel anticancer HA–SN complex.     

Nonlinear optical response of chloroaluminiumphthalocyanine encapsulated by silica core-shell particles

We report for the first time on the synthesis of core-shell particles containing chloroaluminiumphthalocyanine (ClAlPc) prepared using a sol-gel technique. These particles have the dye molecules at the core, encapsulated by silica shell. The mean size of the particle is determined from HRTEM studies and is found to be approximately 0.08 microm. The surface and bulk compositions of the core-shell particles are studied by XPS and EDAX measurements, respectively. Time-resolved fluorescent measurements indicate a decrease in fluorescence lifetime for the core-shell particles as compared to that of bare dye dissolved in ethanol. This is analyzed on the basis of available theoretical models. Third-order nonlinear optical effects are investigated by the Z-scan technique using 8 ns pulses at a wavelength of 532 nm from a frequency-doubled Nd:YAG laser. The analysis indicates that both singlet and triplet excited-state absorption contribute to nonlinear absorption.     

Design,synthesis and activity study of tyrosinase encapsulated silica aerogel (TESA) biosensor for phenol removal in aqueous solution

Tyrosinase encapsulated silica aerogel (TESA) was synthesized via an alcohol-free colloidal sol–gel route at room temperature and at neutral pH. Characterization on TESA indicated that 98% of enzyme was effectively loaded and located inside the aerogel network. TESA without solvent extraction showed higher tyrosinase activity than TESA extracted by amyl acetate/acetone (v/v:1/1). Stability of tyrosinase in TESA was enhanced towards extreme temperature, acidic and basic conditions. Optimization study indicates that 500 U enzyme/g silica aerogel; aged for 2 days, showed superior performance in the oxidation of catechol. The activity of TESA was remarkably enhanced; which was active at a wider temperature (up to 80 °C) and pH range (4–9). In contrast, free tyrosinase was totally inactive at these pH values and temperature >55 °C. TESA successfully removed about 90% of phenol in aqueous solution after 3 h of contact time with excellent reusability.     

Non-covalent interactions of a drug molecule encapsulated in a hybrid silica gel

The drug molecule Propranolol has been encapsulated by a sol-gel process in an organic-inorganic hybrid matrix by in-situ self-assembly; the 2D HETCOR solid state NMR spectroscopy provides direct proof of the intimate spatial relationship between the host matrix and guest drug molecules.     

Structure and dynamics of lysozyme encapsulated in a silica sol-gel matrix

Proteins entrapped in sol-gel matrices have been extensively studied during the last 15 years, showing that most of them can be encapsulated with retention of their native structure and functionality and with enhanced stability. However, relatively little is known about the structural and dynamical details of the biomolecule-matrix interactions. To achieve this goal, the model protein hen egg white lysozyme (HEWL) has been entrapped in sol-gel matrices prepared from tetraethyl orthosilicate through an alcohol-free sol-gel route, and the photophysical properties of its fluorescent tryptophans have been determined using both steady-state and time-resolved fluorescence techniques. By combining fluorescence spectra, quenching experiments, lifetimes, and time-resolved fluorescence anisotropy measurements, we have obtained information on the structure, dynamics, and solvation properties of the entrapped protein. Our results show that the environment of HEWL within the silica pore as well as its internal dynamics is similar to that in aqueous solution, except that the protein showed no or, depending on conditions, very much slower global motion but retained its internal angularly restricted (hindered) segmental rotation upon entrapment. The experiments carried out at different experimental conditions indicate that, below the isoelectric point of the protein, a strong electrostatic interaction is established between the protein molecule and the negatively charged sol-gel walls, which is ultimately responsible for the total arrest of the overall rotation of the protein, but without significant effect upon its segmental rotational relaxation. The electrostatic nature of the interaction is clearly established since either reducing the positive charge of the protein (by increasing the pH toward its isoelectric point) or increasing the ionic strength of the solution (shielding against the attractive interaction) leads to a situation in which the protein freely rotates within the matrix pore, albeit an order of magnitude more slowly than that in free solution under similar macroscopic solution conditions, and still retains its segmental rotational properties.     

Remarkable improvement of failure strain of preferentially aligned short pineapple leaf fiber reinforced nitrile rubber composites with silica hybridization

Preferentially aligned short fiber reinforced nitrile rubber (NBR) composites with very high moduli at low elongation and high elongation at break were developed by using short and fine pineapple leaf fiber (PALF) and silica as the hybrid (two component) reinforcement. The amount of PALF was fixed at 10 parts (by weight) per hundred of rubber (phr) while that of silica was varied from 0 to 30 phr. Uniaxial NBR composites were prepared and tested for their mechanical properties in the directions both parallel and perpendicular to the fiber axis. Comparison was made against silica-NBR composites of the same total filler loadings. All composites with PALF display very distinct stress-strain curves. The stress rises sharply when the composite is stretched, while that of silica filled composites with the same loading rises gradually. The addition of silica initially lowers the early part of the stress-strain curve but prolongs breaking to greater strains. Further addition of silica raises the early part of the stress-strain curve back to and above that of the lower silica contents. It also significantly increases the elongation at break. Observation of other properties is also reported. Considering all the properties evaluated, reinforcement of NBR with PALF-silica hybrid shows great promise for engineering applications.     

Inhibition of stigmasterol oxidation by antioxidants in purified sunflower oil

A study was conducted to analyze the effect of the antioxidants butylated hydroxytoluene, alpha-tocopherol, ethanolic extracts of rosemary, and green tea on stigmasterol resistance against degradation and formation of its oxidation products in purified triacylglycerols (TAG) from sunflower oil. The content of stigmasterol and its oxidation products 7alpha- and 7beta-hydroxy, alpha- and beta-epoxy, triol, and 7-ketostigmasterol were determined during incubation at 60 degrees C for 3, 6, and 9 days. In addition, peroxide value and fatty acid composition were also determined in the samples. Correlation between the levels of the accumulated stigmasterol oxides and peroxide value of the TAG with antioxidants during incubation was significant only for rosemary extract (R = 0.6799, p < 0.05). The lack of correlation precludes the use of peroxide values to determine the level of sterol oxidation products in the used model system. Correlation between stigmasterol content and the level of stigmasterol oxides was significant for all samples (R = 0.8874, p < 0.05). The total increase of the stigmasterol oxidation products was the lowest in samples with alpha-tocopherol, but the content of stigmasterol-triol increased the most in this sample. In all the analyzed samples, alpha-epoxy-stigmasterol was formed in the highest amounts among the analyzed stigmasterol oxidation products.     

A superhydrophobic silica aerogel with high surface area for needle trap microextraction of chlorobenzenes

Microchimica Acta - The authors have synthesized a superhydrophobic silica aerogel by using a sol-gel technique. The material is shown to be an efficient sorbent for needle trap microextraction of...     

Immobilization of lipase onto cellulose ultrafine fiber membrane for oil hydrolysis in high performance bioreactor

Practical application of biphasic enzyme-immobilized membrane bioreactors (EMBR) requires efficient loading of the enzyme with retention of enzymatic activity. Here, we report a method to fabricate an ultrafine fiber membrane conjugated to lipase with high levels of enzyme loading and activity retention. A cellulose acetate (CA) non-woven ultrafine fiber membrane was prepared with 200 nm nominal fiber diameter by electrospinning, followed by alkaline hydrolysis to obtain regenerated cellulose (RC). The RC ultrafine fiber membrane was oxidized by exposure to NaIO₄, simultaneously generating aldehyde groups to couple with pentaethylenehexamine (PEHA) as a spacer for lipase immobilization. A biphasic EMBR was assembled with the PEHA-modified and lipase-immobilized membranes. The effect of operation variables, namely aqueous-phase system, reaction pH, accelerant (sodium taurocholate) content, reaction temperature, and membrane usage on the performance of this bioreactor was investigated with the hydrolysis of olive oil. A bioreactor activity as high as 9.83 × 10⁴ U/m² was obtained under optimum operational conditions.     

Structural characterization study of FeCo alloy nanoparticles in a highly porous aerogel silica matrix

A series of FeCo-SiO(2) nanocomposite aerogels having different FeCo loadings of 3, 5, and 8 wt % were prepared using a novel urea-assisted sol-gel route. The size of the nanoparticles, which was estimated using Scherrer analysis of the main peak of the x-ray diffraction pattern, varies from 3 to 8 nm. X-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) techniques at both Fe and Co K edges were used to investigate the structure of the FeCo nanoparticles. EXAFS and XANES show that FeCo nanoparticles have the typical bcc structure. Evidence of oxidation was observed in low FeCo content aerogels. Spatially resolved electron energy loss spectroscopy analysis suggests the formation of a passivation layer of predominantly iron oxide.     

Partial hydrogenation of sunflower oil: Influence of the process conditions on the physicochemical properties of the products

The influence of the process conditions on the fatty acid composition and solid fat content of the products was examined for partial hydrogenation of sunflower oil in a static reactor using 1.0 wt% Pd/C powder catalyst. The solid fat content curves of the oil hydrogenation products were analyzed in relation to the process conditions.