Sol-gel Media Research Articles

In Situ Imaging of Faujasite Surface Growth Reveals Unique Pathways of Zeolite Crystallization.

Zeolite crystallization occurs by complex processes involving a variety of possible mechanisms. The sol gel media used to prepare zeolites leads to heterogeneous mixtures of solution and solid states with diverse solute species. At later stages of zeolite synthesis when growth occurs predominantly from solution, classical two-dimensional nucleation and spreading of layers on crystal surfaces via the addition of soluble species is the dominant pathway. At earlier stages, these processes occur in parallel with nonclassical pathways involving crystallization by particle attachment (CPA). The relative roles of solution- and solid-state species in zeolite crystallization have been a subject of debate. Here, we investigate the growth mechanism of a commercially relevant zeolite, faujasite (FAU). In situ atomic force microscopy (AFM) measurements reveal that supernatant solutions extracted from a conventional FAU synthesis at various times do not result in growth, indicating that FAU growth predominantly occurs from the solid state through a disorder-to-order transition of amorphous precursors. Elemental analysis shows that supernatant solutions are significantly more siliceous than both the original growth mixture and the FAU zeolite product; however, in situ AFM studies using a dilute clear solution with a lower Si/Al ratio revealed three-dimensional growth of surfaces that is distinct from layer-by-layer and CPA pathways. This unique mechanism of growth differs from those observed in studies of other zeolites. Given that relatively few zeolite frameworks have been the subject of mechanistic investigation by in situ techniques, these observations of FAU crystallization raise the question whether its growth pathway is characteristic of other zeolite structures.

Nano sulfated zirconia over silica for highly effective nano sulfated zirconia

Sulfated zirconia over silica core (NSZS) was synthesised using an ultrasonic-irradiated sol-gel media in which zirconia nanoparticles were distributed on a silica core created by applying ultrasonic irradiation to the sol-gel medium. In order to produce a highly effective catalyst, it is important to have a high surface-to-volume ratio, which the synthesised core-shell catalytic system fully meets. An ultrasonic titanium horn in a sonochemical glass reactor was used for the synthesis. The generated catalyst's crystalline size was 8 nm using this procedure. XRD, N2 Physiosorption, TG-DTA, FTIR, and SEM were used to analyse the produced catalysts. Isobutane alkylation with butene-1 catalysed at 98 percent efficiency by the catalyst after 26 hours of speed of a person's response. A 94 percent activity level was achieved after four and two rounds of regeneration, respectively. Nanoparticles that are not agglomerated may be formed by ultrasonic irradiation, as shown by the NSZS's properties.

Dehydroabietylamine-decorated imino-phenols: supramolecular gelation and gel phase selective detection of Fe3+, Cu2+ and Hg2+ ions under different experimental conditions

Dehydroabietylamine-linked Schiff bases 1–3 have been synthesized, characterized and employed in metal ion sensing in a sol–gel medium. The compounds have a propensity for gel formation from aqueous organic solvents.

Effects of synthesis conditions and release medium pH on release properties of acyclovir – mercaptopropyl modified silica composite

Objective The purpose of the present study was to evaluate the prospect of use of mercaptopropyl modified silica as a platform for development of new oral formulation of antiviral drug acyclovir (ACV) which is able to control release of the drug irrespective of release medium pH. Methods The composites of ACV with mercaptopropyl modified silica were synthesized using sol-gel technology under different conditions (synthesis pH, drug loading). The composites were characterized using scanning electron microscopy, dynamic light scattering and differential scanning calorimetry methods. The effects of the synthesis conditions on physicochemical properties of the prepared composites and their release properties were studied. Results The sol-gel synthesis conditions and release medium pH influence significantly release properties of the composites. The influence was explained by contributions of different factors, such as the drug-silica interactions in the composites, structure of the silica matrix and its stability in release media, hydrophobic nature of ACV, its pH-dependent solubility. It was found that all the synthesized composites followed the zero-order kinetics which is controlled by anomalous diffusion. Conclusion The studies showed that the composites exhibited controlled release of ACV up to 80 h. However, the release properties of the drug depend significantly on pH of release medium, i.e. the release properties (the release rate, the amount of released ACV) will change during transition of the composites through various segments of GIT. Therefore, the synthesized composites are not a promising basis for development of new oral dosage form of ACV

A naphthalimide-linked new pyridylazo phenol derivative for selective sensing of cyanide ions (CN-) in sol-gel medium.

Napthalimide-linked pyridylazo derivatives 1 and 2 have been designed and synthesized. Compound 1 acts as a gelator in DMF-H2O (1 : 1, v/v). The brown gel is photostable and shows good viscoelastic properties. The value of G' is almost 10 times higher than that of G'' over the entire range of frequencies at a constant strain of 1%. The SEM image shows the presence of densely stacked flakes. In comparison, compound 2, devoid of free phenolic -OH, does not show gelation properties under identical conditions. However, the brown gel of 1 shows selective sensing of CN- ions over a series of anions involving phase change through the deprotonation mechanism. While the brown gel of 1 is selectively ruptured in the presence of CN- to the sol, compound 1 in solution shows measurable UV-vis and emission changes in the presence of CN- over the other anions and validates the visual sensing of CN-. In the test-kit application, the yellow paper strip turned into pinkish-red upon contact with CN-.

Aqueous sol–gel processing of precursors and synthesis of aluminum oxynitride powder therefrom

For the first time, aluminum oxynitride (ALON) powders were synthesized using the precursors processed through aqueous sol–gel procedures. Appropriate quantities of aluminum nitride (AlN) powder and aqueous boehmite sol were mixed to obtain molecular stoichiometry of AlON. However, during the course of process, AlN powders reacted with the aqueous boehmite sol and disintegrated into its hydrated compounds. Such reactions altered the molecular stoichiometry between boehmite and AlN which was initially formulated for the eventual formation of AlON. Extensive investigations were carried out to analyse the behavior of AlN during the sol–gel processing. Hydrolysis of AlN in the aqueous sol–gel medium was circumvented by subjecting AlN to a surface modification process. The homogeneously dispersed boehmite sol and AlN mixture was further gelled, dried, and heat treated at temperatures between 1600 and 1850 °C for the formation of AlON powder. AlON phase formation was confirmed through XRD investigations, and its physical and microstructural properties were also evaluated through FESEM and TEM analyses. AlON powder with an average particle size of 490 nm was successfully synthesized in this study. This process is suitable for producing AlON powder in bulk quantities, and it can be used readily for further processes such as shaping and sintering to produce various optical products based on AlON.

Cholesterol linked benzothiazole: a versatile gelator for detection of picric acid and metal ions such as Ag+, Hg2+, Fe3+ and Al3+ under different conditions

The interaction of compound 1 with nitrophenols and metal ions has been studied in sol–gel medium. The nitrobenzene gel selectively recognizes picric acid, Ag+ and Hg2+ ions. In CH3CN, compound 1 further shows affinity towards Fe3+, Al3+ and Hg2+.

Optimization of sol-gel medium for entrapment of acetylcholinesterase enzyme in biosensor for pesticide detection

Pesticides are chemical substances used to kill and control pests or diseases that can damage crops. The use of pesticides should be done precisely because the accumulation of chemicals contained in pesticides can cause various health effects. Therefore, detection of pesticide residues on plants is important to reduce the risk of poisoning due to pesticide residues. Some of the conventional methods that have been done to detect pesticide residues have weaknesses among expensive tools, takes a long time, and are generally performed by trained laboratory technicians. Biosensors are analytical devices that can measure the quantitative or semi-quantitative targets of analyte by utilizing a bioreceptor such as enzyme. Several studies have shown that enzyme-based acetylcholinesterase-based biosensors can be used to detect pesticide residues in vegetable samples. The objective of this research was to get a proper silica based sol-gel formulation with molar ratio of H2O:TEOS and NaOH concentration as immobilization medium of acetylcholinesterase enzyme for biosensor application. Response Surface Methodology (RSM) was used in order to determine the interaction between the parameters studied and resulting responses which were amount and activity of acetylcholinesterase enzyme. Based on the research, the best result for immobilized enzyme activity was shown by molar ratio (H2O: TEOS) 1: 8 and 4 mM NaOH treatment.

Pyrrole-based tetra-amide for hydrogen pyrophosphate (HP2O73−) and F− ions in sol-gel medium

A simple pyrrole-based tetra-amide 1 shows selective fluorescence sensing of HP2O73− over a series of other anions in CH3CN by exhibiting excimer emission at ~450 nm. In DMSO:CHCl3 (1:5 v/v), compound 1 forms gel that undergoes disintegration to sol in the presence of basic anions such as F−, AcO− and H2PO4−. However, the gel state of 1 under a particular condition is observed to be selective to F− over AcO− and H2PO4− anions. The recognition properties of the receptor have been studied by fluorescence, UV–vis and 1H NMR spectroscopic methods.

Solution Combustion Synthesis of Nanoscale Materials.

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol-gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual properties are outlined. To demonstrate the versatility of the approach, several application categories of SCS produced materials, such as for energy conversion and storage, optical devices, catalysts, and various important nanoceramics (e.g., bio-, electro-, magnetic), are discussed.

Isomeric chiral pyrrole diamides and their efficacy in enantioselective sensing of tartrate in sol–gel medium

Pyridinium motif-based chiral pyrrole diamide clefts 1 and 2 have been designed and synthesized for chiral recognition of hydroxycarboxylates in sol–gel medium. Of the two isomeric chiral receptors, receptor 1 shows selective sensing of d-tetrabutylammonium tartrate over its mirror image isomer in CH3CN. The isomeric receptor 2 did not show any enantioselectivity in the recognition. Moreover, the receptor 1 validates prompt visual sensing of d-tartrate through gelation. The recognition properties of the receptors have been studied by fluorescence, UV–vis, 1H NMR and CD spectroscopic methods.

L-Glutamic acid functionalized silver nanoparticles and its nonlinear optical applications

l-Glutamic acid functionalized silver (Glu-Ag) nanoparticles (NPs) were synthesized in the aqueous medium and in a sol–gel matrix. Both samples showed different UV/Vis, zeta potential, TEM and SEM profiles. Surface enhanced raman spectra of the colloidal NPs reveal that the amino moiety of Glu is bound on the Ag surface with the charged carboxylate group pointing outwards. In contrast, in the sol–gel media, the attachment of Glu to the Ag NP surface was through the carboxylate group. Intensity-dependent nonlinear optical absorption measured using the open aperture Z-scan technique revealed that the aqueous solution of Glu-Ag is an efficient optical limiter.

Effect of micellar and sol–gel media on the spectral and kinetic properties of tetracycline and its complexes with Mg2+

The spectroscopic and photophysical properties of the broad-spectrum antibiotic tetracycline (TC) and its Mg(2+) complexes were studied in organized media attained by means of three iso-structural quaternary ammonium surfactants able to self-assemble in water at low c.m.c. values, thus giving spherical micelles and sol-gel media upon increasing the concentration. Specific protonated forms of TC and its complexes were introduced in these micro-heterogeneous environments and then investigated through steady-state (both in absorption and emission) and pulsed (up to femtosecond resolution) spectroscopic techniques. Free TC showed minor spectral and kinetic variations while complexes remained unchanged in the presence of spherical micelles, meaning that TC is likely to be placed at the interface between the micelle and the bulk aqueous solution, without altering its bioactivity. Ultrafast transient absorption spectroscopy proved to be a powerful tool to gain deep insight into the distribution of the investigated species between the heterogeneous structure of sol-gel media. In fact, according to the polarity and net charge of free TC and its complexes, these species can be mostly found in the hydrophobic (intertwined worm-like micelles) or in the hydrophilic domains (basically aqueous pools) that the sol-gel is made up of. In the first case, the properties are dramatically altered (highly enhanced fluorescence and lengthened lifetime of the first singlet excited state up to the nanosecond time scale), leading to the improved traceability of the drug.

Synthesis and characterization of nano Ag/Pt and methyl violet co-doped sol–gel porous material

Nano Ag/Pt and methyl violet (MV) co-doped sol–gel substrates have been prepared and characterized by spectral and microscopic techniques. MV was encapsulated in the sol–gel medium along with the bimetal nanoparticles and the resultant materials were compared. MV adsorbed on the surface of nanometal particles and encapsulated into the substrate of both is proposed as a scheme. Photodegradation of four different dyes (MV, methyl green, malachite green and Congo red) as probes, by prepared only bimetal doped substrate is examined and discussed to understand the mechanism.

Materials chemistry for catalysis: Coating of catalytic oxides on metallic foams

Catalytic structured reactors are designed to improve both heat and mass transfers during reactions in the presence of catalytic layers. The know-how acquired in the coating of stainless steel walls by catalytic layers of VO x /TiO 2, active in the abatement of volatile organic compounds and in the production of chemical intermediates, was extended to metallic foams. The preferred and original way was to first make a deposit of a silica-like primer by cold plasma assisted polymerization of tetramethyldisiloxane in the presence of oxygen. After mineralisation, this layer was supposed to act as a barrier against poisoning by elements of the metallic substrate, as well as a stabilizer of the catalyst layers. The cells of the foam were homogeneously covered by a 5 μm-thick polysiloxane film ending in ca. 1 μm thick silica after calcination. After studying the textural properties and zeta potential of aqueous suspensions of TiO 2 particles, the silica-coated foams were dipped in a 37 wt.% aqueous suspension of TiO 2-anatase. The final VO x /TiO 2/SiO 2/foams were obtained by grafting polyvanadate specie in sol–gel medium. At every step of coating, the multilayer materials were studied mainly by X-ray Photoelectron Spectroscopy and Electron Probe Micro-Analysis. Moreover the mechanical and chemical stability of the successive coatings was checked.

Biosilicification Templated by Amphiphilic Block Copolypeptide Assemblies

An amphiphilic poly(L-lysine·HBr)-block-poly(L-leucine) (KL) diblock copolypeptide and its supramolecular assembly are used as a template to direct silica formation, which proceeds by a cooperative process involving biomimetic mineralization and copolypeptide reassembly under ambient conditions. Various silica structures can be obtained by using different counterions, changing the chain length of the KL diblocks, and applying a sol-gel mineralization method. We find that the chain length of the KL diblock is an important factor in terms of controlling biosilica morphologies. We also find that the nature of the counterions strongly affects the resulting silica structures. For the same KL diblock, variation of anions from phosphate to sulfate and to carbonate can produce hexagonal silica platelets, silica rods, and fused silica platelets, respectively. In contrast, application of a sol-gel method can replicate the copolypeptide fibril network morphology in water, while employment of ultrasonication to the sol-gel medium transforms the silica fibrils to rigid silica rods. The resulting silica morphology has been systematically characterized using SEM and TEM, and the polypeptide conformation is explored using FT-IR and CD spectroscopy.

Experimental and theoretical spectral properties of ethyl 2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetate doped sol-gel materials: new materials with potential optical application

Silica xerogels and monoliths, containing ethyl 2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetate (K4) or Sm 3+ ions and K4 are prepared by sol-gel technique. NMR investigations, UV/Vis, IR- and luminescence spectral properties of K4 in solution and in monoliths are presented. The IR-spectroscopic properties of the prepared sol-gel materials are examined by applying the reduced- difference procedure to non-polarized IR-spectra. The results show that the sol-gel medium did not interact with K4 as well as in the presence of Sm 3+ ions the K4 form a (Sm(L)2(H2O)4) · (NO3)3 complex in the matrix.

Optimization of radical photopolymerization in hybrid sol-gel glasses: advantages of bicomponent photoactive systems

AbstractUse of organosilanes as hybrid systems is of increasing importance for their promising applications in the optical field. Considerable attention has been paid to the study of the inorganic network. However, poor information concerning the organic part involved in the solgel process is available. This is yet a fundamental requirement for optical applications where homogeneity at molecular scale is essential. Taking into account the specificity of the sol-gel medium, characteristics of the organic part have to be adapted with the view of optimizing the properties of the final material. Hybrid material used in this study consisted of organosilane precursor with methacrylate functions, titanium isoproxide, methacrylic acid and photoinitiator. The polycondensation of the inorganic component was achieved sequentially and simultaneously with the photopolymerization of the organic one to provide a mutually interpenetrating network. Polymerization in the UV range presents the advantages of fast-curing at temperature compatible with fragile substrates and spatio-temporal selectivity of the reaction. Characteristics of the photopolymerization process taking place in hybrid sol-gel materials were investigated by UV and Real Time FTIR spectroscopy. Besides the study of the organic network, NMR investigations led information relative to the inorganic network formation during the sol maturation. The whole results provide insights into the optimization of the photochemical step. Indeed, it was demonstrated that titanium components added as passive components to increase the refractive index of the layer, can induce polymerization under a medium pressure mercury arc lamp irradiation. In addition, mix photoactive systems involving an organic photoinitiator and titanium components were investigated and led to a better efficiency for the photoinitiation. Final materials with higher conversion ratio of the methacrylate function and requiring shorter irradiation times were achieved.

Size selected silicon particles in sol-gel glass by centrifugal processing

Centrifugal processing was used to induce size selectivity in Si particles suspended in a silica sol-gel precursor solution. A model was developed to describe Stokes settling of the silicon particles in the sol-gel medium whose viscosity increases exponentially with time eventually leading to hardening to a solid glassy material. An empirical modification to the theoretical model accounts for settling of particle agglomerates. Experimental results for polydisperse silicon particulates centrifuged in a sol-gel of tetraethyl orthosilicate catalyzed by phosphoric acid are reported; the particle size and spatial distribution in the gelled matrix are explained by the model. The utility of centrifugal processing to produce functionally graded materials and semiconductor nanostructures is discussed.

Spectroscopic determination of cholinesterase activity and inhibition in sol-gel media

Spectroscopic determination of cholinesterase activity and inhibition in sol-gel media