Non-hydrolytic Sol Gel Synthesis Research Articles

Non-hydrolytic sol-gel synthesis of BaTiO3 nano-powder: Effect of calcination temperature and modified titanium source on particles

In this study, BaTiO3 nanopowders were prepared by non-hydrolytic sol-gel (NHSG) method using barium acetate and tetrabutyl titanate (TBT) as precursors and acetylacetone (Hacac) as additive. The effects of acetylacetone modification and calcination temperature on nanoparticle size and crystalline phase were evaluated. The products were analysed by SEM, TEM, DSC/TG, FTIR, XRD, Raman. FTIR analysis showed the formation of Ba-O-Ti bond at the sol stage of the NHSG method. DSC/TG and XRD analyses showed that BaTiO3 was produced at 500 ℃. According to SEM/TEM, the particle size of the powder becomes larger as the temperature increases, meanwhile the addition of acetylacetone can make the final product particle size decrease. Raman analysis showed that BaTiO3 has the presence of tetragonal phase, so the crystalline phases of the product and impurities were analysed by XRD refinement, and the results showed that the relative content of tetragonal phase of BaTiO3 was linearly correlated with the calcination temperature.

Non-hydrolytic sol-gel synthesis of zirconium phosphonates with controlled mesoporosity

We disclose the preparation of high-surface-area mesoporous zirconium phosphonates by the non-hydrolytic sol-gel reactions (NHSG) of Zr(NEt2)4 with trimethylsilylated phosphonates RP(O)(OSiMe3)2 (R = Me, tBu, Ph, OSiMe3), and bis-phosphonates (Me3SiO)2(O)P–X–P(O)(OSiMe3)2 (X = CH2, C6H4, CH2(C6H4)CH2, and CH2(C6H4)2CH2) in dry toluene under ambient pressure. Zirconium phosphonate xerogels are prepared by condensation reaction with the elimination of silylamine Me3SiNEt2. This irreversible reaction provides the amorphous xerogels and drives the formation of the porous structure. The influence of organic moieties bonded to phosphorus atoms on porosity was examined in this study. The final surface area of dried xerogels reached 720 m2 g−1 without any extra templating agent. Xerogels were characterized by 13C, 29Si, and 31P solid-state NMR to define atomic homogeneity and evidence the presence of organic phosphonate substituents and residual amido and trimethylsilyl groups. The amount of residual reactive groups was determined by gravimetric measurements and the thermal analysis (TG-DSC) method. These groups may be applied in post-synthetic surface modification, such as controlling the hydrophobic/hydrophilic properties.The catalytic properties of NHSG-prepared xerogels were tested on a model reaction of aminolysis of styrene oxide in a batch mode employing relatively bulky molecules. Products were identified and quantified by the 1H NMR spectroscopy. Catalyst performance parameters, such as selectivity, conversion, turnover frequency, and others, were exceeded compared to benchmark microporous layered zirconium phosphonate catalysts.

Non-hydrolytic sol-gel synthesis of Al2W3O12 nanopowders

Non-hydrolytic sol-gel synthesis of Al2W3O12 nanopowders

Effects of process parameters on nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3 powders

Effects of process parameters on nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3 were systematically investigated. It is discovered that the optimized concentration is 0.8 mol/L. Fine concentration has no obvious effect on low-temperature synthesis of Ba0.6Sr0.4TiO3, but coarse concentration greatly affects the synthesis rate of Ba0.6Sr0.4TiO3. The impurity phase BaCO3 caused by the volatilization of titanium source (Ti(OC4H9)4) can be effectively eliminated by adjusting Ba–Sr–Ti mole ratio to 0.6:0.4:1.2. The pure phase of Ba0.6Sr0.4TiO3 can be synthesized at low temperature of 600 °C with the optimized process parameters due to the formation of Ba–O–Ti and Sr–O–Ti bonds in the xerogel. The particle size of Ba0.6Sr0.4TiO3 powder is 17–43 nm with the monocrystalline structure.

Effects of raw materials on nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3

The effects of raw materials on the nonhydrolytic sol-gel synthesis of Ba0.6Sr0.4TiO3 were systematically studied in this work. The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM). Ba(CH3COO)2, Sr(CH3COO)2, BaCO3 and SrCO3 can undergo deesterification substitution reaction with Ti(OC4H9)4 to synthesize Ba0.6Sr0.4TiO3 phase. Sample taking Ba(CH3COO)2 and Sr(CH3COO)2 as barium and strontium source has better Ba0.6Sr0.4TiO3 synthesis results than that of samples using BaCO3 or SrCO3. Ba0.6Sr0.4TiO3 phase can not be synthesized at low temperature taking BaCl2, SrCl2 and TiOSO4 as barium, strontium or titanium source due to their strong ionic bonding. TiCl4 undergoes an alcoholysis reaction with (oxygen donor) alcohol to form a multimolecular association structure and solvated complex chlorotitanium alkoxide, which reduces the possibility of a deesterification polycondensation reaction. The Ba0.6Sr0.4TiO3 phase cannot be synthesized at low temperatures when CH3CH2OH or C3H7OH is used as the solvent. The synthesis of Ba0.6Sr0.4TiO3 is insufficient because of the coordination ability and solvation effect when CH3COOH is used as the solvent. The synthesis of Ba0.6Sr0.4TiO3 is the best when Ba(CH3COO)2, Sr(CH3COO)2, Ti(OC4H9)4 and glycerol (C3H8O3) are used as the barium source, strontium source, titanium source and solvent, respectively. Pure Ba0.6Sr0.4TiO3 phase with a particle size of 17–43 nm and high dispersion is synthesized when the molar ratio of barium-strontium-titanium is 0.6:0.4:1.2.

Effect of iron source on nonhydrolytic sol-gel synthesis of Fe2TiO5

Fe2TiO5 was synthesized via nonhydrolytic sol-gel method at 600?C. The effects of iron sources on the synthesis of Fe2TiO5 were investigated. It was demonstrated that Fe-O-Ti bonds will not be formed in the xerogels prepared by taking FeCl3 as iron source because it is strong Lewis acid and induces homocondensation. Fe-O-Ti bonds were formed in the xerogels prepared by using Fe(OC2H5)3 and FeOH(CH3COO)2 as iron sources. However, the hydroxyl group in FeOH(CH3COO)2 easily leads to homocondensation and particles agglomeration. Thus, Fe(OC2H5)3 is optimal iron source with both excellent synthesis and particle dispersion effects.

Non-hydrolytic sol-gel synthesis of mesoporous iron-aluminum oxide and their properties in the oxidation of hydrocarbons by hydrogen peroxide

Iron-containing alumina materials were prepared by the non-hydrolytic sol-gel method in the presence of surfactants and their use as catalysts in the oxidation of hydrocarbons was studied. The solids were mesoporous, with large specific surface areas, > 250 m 2 /g for the solids treated at 500 °C, depending on the surfactant used (cetyltrimethylammonium bromide, sodium dodecyl sulfate or hexadecylamine), and the calcination treatment applied (500 or 1000 °C). Iron was well distributed on the alumina surface, as confirmed by the EPR signals at 4.3 and 2.0 G and SEM imaging. The catalytic activity in the oxidation of cyclooctene, cyclohexane, and n -hexane was evaluated. After reaction for 48 h, the solid prepared with cetyltrimethylammonium bromide and calcined at 1000 °C showed a 25% conversion of cyclohexane with 51% selectivity to cyclohexanone. These were promising results, considering the mild reaction conditions, using a non-polluting oxidant at room temperature or 50–55 °C. • Iron-containing alumina catalysts were prepared by a non-hydrolytic sol-gel method. • Surfactants played a fundamental role in pore structuring in situ. • Iron-aluminas were effective oxidation catalysts, using H 2 O 2 as oxidant. • Cyclooctene, cyclohexane, and n-hexane were successfully oxidized. • Oxidation was effective under mild, environmentally friendly conditions.

Sol-gel synthesis pathway and electrochemical performance of ionogels: A deeper look into the importance of alkoxysilane precursor

There is a great interest in the application of ionogels as electrolyte for energy storage devices due to their enhanced safety compared to conventional electrolytes. This work aims to shed light on an often-overlooked aspect of ionogel synthesis which is the impact of the precursors on the sol-gel reaction kinetics and the electrochemical properties of the resultant ionogels. Using time-resolved Raman spectroscopy the non-hydrolytic sol-gel synthesis of ionogels from four different alkoxysilane precursors were monitored. Their electrochemical performance as electrolyte for electric double-layer capacitors were characterised using cyclic voltammetry and electrochemical impedance spectroscopy. Our findings suggest that presence of ionic liquid does not impact the sol-gel process kinetics of all four formulations in the same manner. In addition, ionogel formulations with the longest gelation time demonstrated poor electrochemical properties caused by the further ingress of silica into the activated carbon electrodes. This was confirmed with EDX analysis.

Non-hydrolytic sol–gel synthesis of polypropylene/TiO2 composites by reactive extrusion

An original way to synthesise polypropylene/titanium dioxide (PP/TiO2) composites combining non-hydrolytic sol–gel chemistry and reactive extrusion was reported. The non-hydrolytic sol–gel reaction between titanium alkoxide as a titanium dioxide precursor and an acid anhydride as an oxygen donor at 240 °C was first evaluated and optimised in an alkane liquid medium. TiO2 was present essentially in crystalline anatase form when synthesised in squalane with a domain size around 10 nm. Based on these encouraging results, the synthesis was adapted to reactive extrusion that means at high temperature in molten viscous polypropylene and for short reaction times (few minutes maximum). The proof of concept was evidenced through the formation of amorphous TiO2-based inorganic domains of size around 1 µm within the polymer matrix from the reaction between titanium isopropoxide and acetic anhydride. A condensation degree of 79% was obtained. To optimise the polymer/filler interface, titanium dioxide precursors and oxygen donors with different alkyl chain lengths were evaluated. Hexanoic anhydride as substituent of acetic anhydride and titanium tetrakis 2-ethylhexyloxide as substituent of titanium isopropoxide were used. The oxygen donor contribution appeared to be dominant for the particle dispersion state. The polypropylene (PP)/TiO2 composite synthesised from the reaction between titanium isopropoxide and hexanoic anhydride showed the narrowest TiO2 particle diameter distribution with a mean particle size around 700 nm.

One-step non-hydrolytic sol-gel synthesis of mesoporous SiO2-Al2O3-NiO catalysts for ethylene oligomerization

Mesoporous SiO2-Al2O3-NiO mixed oxide catalysts with different Si/Al ratio and a Ni content of ≈5.5 wt% have been prepared by a simple, one-step non-hydrolytic sol-gel route and evaluated in the oligomerization of ethylene. The catalysts were characterized by TEM-EDX, N2-physisorption, NH3-TPD, powder XRD, 29Si and 27Al MAS-NMR, XPS, and H2-TPR. The Si/Al ratio was found to influence both the texture and the acidity of the materials. According to XRD, part of the Ni formed NiO crystallites, but according to XPS, no bulky NiO was detected at the surface of the catalysts. XPS spectra and TPR experiments are consistent with the formation of dispersed Ni2+ species strongly interacting with the surface. The samples with high Al content displayed excellent performances with very high specific activity up to 270 mmol ethylene converted per g of catalyst per hour at 150 °C, and a percentage of butenes in the products of ≈70%. These catalysts compare well with model catalysts prepared by time-consuming multistep procedures from expensive ordered mesoporous silica supports.

Synthesis of high surface area aluminophosphate and -phosphonate xerogels by non-hydrolytic sol-gel reactions

We disclose the preparation of high-surface-area mesoporous aluminophosphates and aluminophosphonates by the non-hydrolytic sol-gel reactions (NHSG) of Al(NMe 2 ) 3 with trimethylsilylated phosphate OP(OSiMe 3 ) 3 , phosphonates RP(O)(OSiMe 3 ) 2 (R = Me, t Bu, Ph), and bis-phosphonates (Me 3 SiO) 2 (O)P–X–P(O)(OSiMe 3 ) 2 (X = C 6 H 4 , (C 6 H 4 ) 2 ) in dry toluene. The reactions proceed by silylamine elimination of Me 3 SiNMe 2 to provide organic-inorganic hybrid xerogels with properties influenced by organic substituents and the Al:P ratio of the precursors. Dried xerogels exhibit large surface areas (up to 1000 m 2 g −1 ) and matrices based on condensed Al–O–P networks. They stay stable under relatively harsh thermal conditions. 27 Al, 13 C, and 29 Si solid-state NMR spectroscopy was employed to characterize the aluminum coordination and the residual amido and trimethylsilyl groups. The catalytic performance of NHSG prepared material was examined in gas-phase dehydration of ethanol to ethylene exhibiting conversion and selectivity comparable to weak solid acid benchmark catalysts. The number of unreacted surface groups was determined by gravimetric measurements and by thermal analysis (TG-DSC). These residual groups have the potential to be used in post-synthetic grafting of catalytically active metal centers. • Aluminophosphates and aluminophosphonates are prepared by non-hydrolytic sol-gel synthesis. • Mesoporous xerogels with large surface areas (1030 m 2 g -1 ). • Gas-phase dehydration of ethanol to ethylene with good conversion and selectivity.

Gas phase dehydration of glycerol to acrolein over WO3-based catalysts prepared by non-hydrolytic sol-gel synthesis.

Solid acid catalysts based on WO3–SiO2 and WO3–ZrO2–SiO2 were prepared by one-pot non-hydrolytic sol–gel method and tested in the gas phase glycerol dehydration to acrolein. Their structural and textural characteristics were determined by X-ray diffraction (XRD), N2 adsorption, X-ray energy dispersive spectroscopy (XEDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Their acid characteristics were studied by both temperature programmed desorption of ammonia (NH3-TPD) and FTIR of adsorbed pyridine. Under our operating conditions, all the catalysts were active and selective in the transformation of glycerol to acrolein, which was always the main reaction product. The high selectivity to acrolein is achieved on catalysts presenting a higher proportion of Brønsted acid sites. In addition, the role of oxygen in the feed on catalytic performance of these catalysts is also discussed.

Structural characterization and functional correlation of Fe3O4 nanocrystals obtained using 2-ethyl-1,3-hexanediol as innovative reactive solvent in non-hydrolytic sol-gel synthesis

An original non-hydrolytic sol-gel approach, using 2-ethyl-1,3-hexanediol as reactive solvent, was proposed to synthetize nanostructured magnetite. Iron-oxide nanoparticles were prepared and studied as a function of the precursor-to-solvent ratio. The crystallization degree of nanoparticles was followed by the combined Rietveld and Reference Intensity Ratio method. This procedure has allowed the determination of both amorphous and crystalline content of nanomagnetite, using hematite as suitable internal standard. The results of Rietveld method show that the crystalline content decreases as the precursor-to-solvent is increased, ranging from 67 to 60 wt%. Information on the crystallite size-strain distribution and microstructural evolution of nanocrystals was supplied by line profile analysis of the powder diffraction patterns, employing the Whole Powder Pattern Modeling analysis: the obtained log-normal distribution curves become increasingly narrow and symmetrical, while nanoparticle microstrain increases as the precursor concentration is increased. The dimensional analysis of the Transmission Electron Microscopy images has allowed to obtain the nanoparticle grain-size distribution. Nanoparticle dimensions decreases from 15 to 9 nm increasing the precursor concentration. The comparison between the results of X-ray diffraction and microscopic characterization techniques highlighted the effect of several factors, such as size, shape and microstructure of magnetite nanoparticles, on their functional magnetic response. Magnetic characterizations show that magnetite nanoparticles are not in the superparamagnetic phase even at room temperature, independent of the precursor concentration. On the other hand, the room-temperature saturation magnetization, ranging from 73 to 60 emu/g, is a function of the nanoparticle average size, decreasing as the precursor concentration increases.

Hybrid microporous and mesoporous organosilicate covalent polymers with high porosity

A novel non-hydrolytic sol-gel synthesis of hybrid organosilicates is reported allowing control of micro/mesoporous character of the xerogels by variation of the silicon precursor. The polycondensation reaction of silicon(IV) acetate, Si(OAc)4, with 1,3,5-trihydroxybenzene (THB) in dry dioxane at 100 °C produces acetic acid and highly porous amorphous aromatic organosilicate xerogels. Their apparent BET surface areas are as high as 990 m2 g−1 and the total pore volume is 0.843 cm3 g−1. These materials are mostly microporous with a low abundance of mesopores and an average pore size of 3.5 nm. The reaction of HSi(OAc)3 with THB produced a novel mesoporous material with properties superior to xerogels obtained from Si(OAc)4. The BET surface area of 933 m2 g−1 is retained upon heating and average pore size reached 6.0 nm. The total pore volume of 1.36 cm3 g−1 is the highest value achieved in porous aromatic organosilicates so far and is comparable to values typical for 3D covalent organic networks (COFs). The materials are stable up to 400–500 °C but they are sensitive to hydrolysis in moist air. The reactions of other silicon precursors (MeSi(OAc)3 and tBuSi(OAc)3) and larger polyphenol connectors, 1,3,5-tris(4′-hydroxyphenyl)benzene (THPB), 2,4,6-tris(4′-hydroxyphenyl)-1,3,5-triazine (THPTA), and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), produced materials with less satisfactory properties.

Non-hydrolytic sol–gel synthesis and reactive suspension method: an innovative approach to obtain magnetite–epoxy nanocomposite materials

Innovative magnetite–epoxy nanocomposites were prepared starting from magnetite nanoparticles suspended in alcoholic or amino reactive solvents, synthesized by non-hydrolytic sol–gel process from iron (III) acetylacetonate. The obtained suspensions, also synthesized using microwave heating, were mixed with an epoxy monomer (bisphenol A diglycidyl ether, DGEBA), and the formulations were subsequently cured. The thermally activated ring-opening polymerization produced a three-dimensional network in which the suspending medium was covalently linked to the epoxy network according to the chain or step polymerization mechanisms during the cross-linking reaction. This synthetic strategy allowed to obtain nanocomposites in which the nanoparticles play an active role in the polymeric structure, affecting the structural (mechanical and thermal) and functional (magnetic) properties of the final system. The presence of magnetite nanoparticles in the composite resulted in distinct reinforcing effects, acting as rigid filler and/or as cross-linking point, depending on the different chemical environment at the nanoparticle–polymer interphase.

Mesoporous titanosilicates by templated non-hydrolytic sol–gel reactions

A novel templated non-hydrolytic sol–gel synthesis of titanosilicate xerogels is reported. Acetamide elimination from silicon acetate and titanium diethylamide allows obtaining titanosilicates with a high content of Si–O–Ti bonds but low surface areas. These xerogels lose porosity on calcination. However, with addition of Pluronic P123 as a structure-directing agent, we synthesized mesoporous titanosilicate materials with large surface areas (up to 615 m2 g−1) and well dispersed tetrahedral Ti that are stable at temperatures up to 500 °C. These potential catalysts were characterized by variety of physico-chemical methods (IR, GC–MS, XRD, 29Si and 13C CPMAS NMR, DRUV-Vis, and N2 porosimetry) and tested in cyclohexene epoxidation with cumyl hydroperoxide in toluene. They display catalytic activity with the 100 % selectivity to cyclohexene oxide and high catalytic yields up to 96 % which is comparable to previously reported titanosilicate catalysts.

Quantitative phase analysis and microstructure characterization of magnetite nanocrystals obtained by microwave assisted non-hydrolytic sol–gel synthesis

An innovative preparation procedure, based on microwave assisted non-hydrolytic sol–gel synthesis, to obtain spherical magnetite nanoparticles was reported together with a detailed quantitative phase analysis and microstructure characterization of the synthetic products. The nanoparticle growth was analyzed as a function of the synthesis time and was described in terms of crystallization degree employing the Rietveld method on the magnetic nanostructured system for the determination of the amorphous content using hematite as internal standard. Product crystallinity increases as the microwave thermal treatment is increased and reaches very high percentages for synthesis times longer than 1h. Microstructural evolution of nanocrystals was followed by the integral breadth methods to obtain information on the crystallite size-strain distribution. The results of diffraction line profile analysis were compared with nanoparticle grain distribution estimated by dimensional analysis of the transmission electron microscopy (TEM) images. A variation both in the average grain size and in the distribution of the coherently diffraction domains is evidenced, allowing to suppose a relationship between the two quantities. The traditional integral breadth methods have proven to be valid for a rapid assessment of the diffraction line broadening effects in the above-mentioned nanostructured systems and the basic assumption for the correct use of these methods are discussed as well.

Ferroelastic domain organization and precursor control of size in solution-grown hafnium dioxide nanorods.

We demonstrate that the degree of branching of the alkyl (R) chain in a Hf(OR)4 precursor allows for control over the length of HfO2 nanocrystals grown by homocondensation of the metal alkoxide with a metal halide. An extended nonhydrolytic sol-gel synthesis has been developed that enables the growth of high aspect ratio monoclinic HfO2 nanorods that grow along the [100] direction. The solution-grown elongated HfO2 nanorods show remarkable organization of twin domains separated by (100) coherent twin boundaries along the length of the nanowires in a morphology reminiscent of shape memory alloys. The sequence of finely structured twin domains each spanning only a few lattice planes originates from the Martensitic transformation of the nanorods from a tetragonal to a monoclinic structure upon cooling. Such ferroelastic domain organization is uncharacteristic of metal oxides and has not thus far been observed in bulk HfO2. The morphologies observed here suggest that, upon scaling to nanometer-sized dimensions, HfO2 might exhibit mechanical properties entirely distinctive from the bulk.

Non-hydrolytic sol–gel synthesis of tantalum sulfides

Non-hydrolytic sol–gel synthesis provides a low temperature solution based approach to solid-state materials. In this work, reactions of TaX5 (X = F, Cl, Br, I) with the thio-ethers di-tert-butylsulfide and hexamethyldisilathiane were carried out in chloroform or acetonitrile. The influence of synthetic parameters such as temperature, reaction time, starting sulfur to tantalum ratio, and solvent volume were explored, and optimized conditions for the preparation of phase pure crystalline TaS2 were established. Amorphous powders were recovered for most of the samples, but crystalline 1T- and 3R-TaS2 modifications could be selectively prepared by heat treatments of the as-recovered precursors at 700 and 800 °C, respectively. The crystallite sizes could be adjusted by tuning the starting sulfur to tantalum ratios, and by choice of solvent. For specific conditions, nanocrystalline 1T-TaS2 was directly recovered from solution. To our knowledge, this is the first time that crystalline TaS2 was directly obtained from low temperature solution based routes.

A non-hydrolytic sol–gel synthesis of reduced graphene oxide/TiO2 microsphere photocatalysts

Reduced graphene oxide/TiO2 microspheres were produced by a non-hydrolytic sol–gel reaction of tetrabutyl orthotitanate and acetone followed by hydrothermal treatment. In the hydrothermal treatment, ammonia was used as a medium solution, and reaction temperature was varied from 120 to 180°C to investigate the effect on crystal phase and morphology of the prepared samples. Prior to the hydrothermal treatment, graphene oxide was introduced into the medium solution as an impurity material. Graphene oxide was characterized using AFM to confirm the formation of single-layer graphene sheet and its image. Prepared catalysts were characterized by XRD, SEM, N2 adsorption (BET), Raman spectroscopy, FTIR and UV–visible diffuse reflectance spectra. Ammonia as a medium in hydrothermal reaction promoted the formation of nanoflakes and nanorods on the microspheres. Hydrothermal reaction temperature was found to have a significant effect on the morphology and crystal phase of the catalyst. Lower hydrothermal treatment temperature produced amorphous samples with higher surface area that increased methylene blue adsorption capacity significantly. Higher hydrothermal treatment temperature, on the other hand, produced anatase crystal phase TiO2 with lower surface area. Prepared samples at higher treatment temperature showed comparable photocatalytic activity to commercial P25 TiO2 on the photocatalytic degradation of methylene blue under UV–visible light irradiation. The photocatalytic activity of prepared RGO/TiO2 microspheres photocatalysts were further tested using orange II. The preparation method proposed in this study could produce reduced graphene oxide/TiO2 photocatalyst that is promising for use in organic pollutants treatment in water in terms of high photocatalytic activity and easy recovery owing to microsized photocatalyst.