Non-hydrolytic Sol Gel Research Articles

Low-temperature preparation of novel stabilized aluminum titanate ceramic fibers via nonhydrolytic sol-gel method through linear self-assembly of precursors

Stabilized aluminum titanate fibers were prepared via nonhydrolytic sol-gel (NHSG) method through linear self-assembly of precursors. The results show that NHSG method generates the heterogeneous condensation with the formation of Al–O–Ti, Mg–O–Ti, Fe–O–Ti, Mg–O–Al, Fe–O–Ti bonds, which ensures that magnesium ions and iron ions can enter aluminium titanate lattice and stabilize it at 750 °C. Bimolecular associated structure of chlorotitanium ethoxide titanium precursor promotes the self-linear-assemble of all precursors, which enables the excellent spinnability of sol. Stabilized aluminum titanate fibers have excellent corrosion resistance. The thermal expansion coefficient of stabilized aluminum titanate ceramic is −0.142 × 10−6°C−1.

Sol-gel synthesized plasmonic nanoparticles and their integration into dye sensitized solar cells

In the present study, we synthesized silver nanoparticles in titanosilicate matrix through low cost non-hydrolytic sol-gel method using titanium isopropoxide (TIP), tetraethylorthosilicate (TEOS, (Si(OC 2 H 5 ) 4 ) and ethanol (C 2 H 5 OH) as solvents. These were investigated for the plasmonic effect of nanoparticles in dye sensitized solar cells (DSSC). The fabricated dye-sensitized solar cells with Ag: SiO 2 -TiO 2 films coated in fluorine doped tin oxide (FTO) glass plate with dye of amaranthus red shows an improved output voltage. The samples were optically and structurally well studied by absorption spectroscopy, Fourier transform infrared spectroscopy(FTIR), X-Ray diffraction (XRD) and transmission electron microscopy(TEM). The XRD studies confirmed the crystalline nature of TiO 2 and Ag. • Synthesis and structural characterization of plasmonic nanoparticles obtained through non hydrolytic sol-gel method. • Integration of plasmonic nanoparticles into DSSC solar cells. • Fine tuning the efficiency of DSSC using an optimum amount of Organic dye and Plasmonic nano particles

Preparation of Nano-TiO2/Diatomite Composites by Non-hydrolytic Sol–Gel Process and its Application in Photocatalytic Degradation of Crystal Violet

The dispersion of anatase TiO2 on diatomic material was a prospective route to avoid agglomerates of these particles. In this work, the TiO2/diatomite composites were prepared using a solvothermal process and a non-hydrolytic sol-gel method at low temperature on the raw (TDB) and the purified (TDS) diatomite. The synthesized samples were characterized utilizing various techniques. These given that TiO2 anatase was impregnated well on the surface of diatomite, and the immobilization of these particles tends to increase the thermal stability of the composite as compared to the raw diatomite. In addition, the photodegradation of crystal violet (CV) in solution was in the direction of TDB > TDS > TiO2. The 99.996% of CV can be degraded in 210 min of irradiation time at pH 10. These results revealed that the immobilization of titanium on diatomite improves the photocatalytic degradation by reducing the crystallite size of anatase TiO2.

Synthesis and characterization of environmentally friendly BiVO4 yellow pigment by non-hydrolytic sol-gel route

Monoclinic bismuth vanadate (m-BiVO4) yellow pigments were synthesized by non-hydrolytic sol-gel (NHSG) route without any surfactants. The presence of Bi–O–V band in the sol and xerogel, indicates that the excellent atomic scale homogeneity could be reached. It is beneficial to achieve high purity m-BiVO4 phase and submicron scale particles (738 nm) with homogenous distribution at low temperature (400 °C), resulting in a brilliant yellow hue (b* = 71.18, hab = 89.73). These pigments have better chromatic performance than previously reported and commercially available BiVO4 yellow pigments. Meanwhile, the cytotoxicity of the pigment was tested in Mus musculus skin melanoma cells, and showed nontoxic for human cells, indicating its potential application in the high quality paints for automotive and architectural finishes.

Nonhydrolytic sol–gel synthesized oligosiloxane resin reinforced thiol-ene photocured coatings for the immobilization of acetylcholinesterase

Acetylcholinesterase (AChE), which is responsible for the hydrolysis of neurotransmitter acetylcholine, is a critical enzyme for the nervous system and also a biomarker for organophosphorous pesticide detection. The immobilization of AChE is an active area of research and recently the use of sol–gel-derived materials for enzyme immobilization has gained a lot of attraction. In this work, AChE was covalently immobilized onto a photocured substrate which was reinforced with an oligosiloxane resin. The oligosiloxane resin was designed to have both vinyl and epoxide groups and prepared via nonhydrolytic sol–gel technique. The strategy employed in this study offered a platform that has good mechanical and thermal properties and also suitable for modification. Thus, AChE was also immobilized onto these substrates after amine modification of the epoxy groups and followed by glutaraldehyde activation. Over 80% enzyme immobilization yield was achieved. At certain pH values (5.5 and 8.5) and under relatively higher temperatures (above 40 °C) the immobilized enzymes were found to have higher catalytic activity than the free enzyme. Furthermore, by immobilization the reuse and the storage stability of the enzyme was improved and the stability of the immobilized enzyme against the inhibitory effects of certain metal cations was enhanced.

Non-hydrolytic sol-gel route to synthesize TiO2 nanoparticles under ambient condition for highly efficient and stable perovskite solar cells

For developing low-temperature processed electron-transporting layer in perovskite solar cells, titanium oxide (TiO2) nanoparticle was synthesized through the non-hydrolytic sol-gel route. TiO2 nanoparticles showed uniform film coverage, high transparency in the visible region with wide optical bandgap, and high electrical conductivity after systematically optimizing the synthetic reaction time, the thermal annealing temperature, and the concentration of Nb doping. When TiO2 nanoparticle was introduced as an electron-transporting layer through low-temperature deposition process, the perovskite solar cells fabricated in ambient conditions showed high efficiencies of 18.97% and 13.51% on the rigid glass and the flexible plastic substrate, respectively. An impressively high open circuit voltage of 1.17 V and short circuit current density of 22.21 mA cm−2 were achieved due to the well aligned work function and better electrical conductivity of Nb-doped LT-TiO2 layer. Importantly, solar cells fabricated with TiO2 nanoparticle showed high thermal stability, negligible hysteresis, and reduced charge recombination loss at electron-transporting layer/perovskite interfaces. This study shows that TiO2 nanoparticle can be obtained through the low cost and facile synthesis and has high potential as an electron-transporting layer for low-temperature processable perovskite solar cells.

Highly Tough, Li‐Metal Compatible Organic–Inorganic Double‐Network Solvate Ionogel

AbstractIonogels are considered promising electrolytes for safe lithium‐ion batteries (LIBs) because of their low flammability, good thermal stability, and wide electrochemical stability window. Conventional ionic liquid‐based ionogels, however, face two main challenges; poor mechanical property and low Li‐ion transfer number. In this work, a novel solvate ionogel electrolyte (SIGE) based on an organic–inorganic double network (DN) is designed and fabricated through nonhydrolytic sol–gel reaction and in situ polymerization processes. The unprecedented SIGE possesses high toughness (bearing the deformation under the pressure of 80 MPa without damage), high Li‐ion transfer number of 0.43, and excellent Li‐metal compatibility. As expected, the LiFePO4/Li cell using the newly developed SIGE delivers a high capacity retention of 95.2% over 500 cycles, and the average Coulombic efficiency is as high as 99.8%. Moreover, the Ni‐rich LiNi0.8Co0.1Mn0.1O2(NCM811)/Li cell based on the modified SIGE achieves a high Coulombic efficiency of 99.4%, which outperforms previous solid/quasi‐solid‐state NCM811‐based LIBs. Interestingly, the SIGE‐based pouch cells are workable under extreme conditions (e.g., severely deforming or clipping into segments). In terms of those unusual features, the as‐obtained SIGE holds great promise for next‐generation flexible and safe energy‐storage devices.

Synthesis of aluminophosphate xerogels by non-hydrolytic sol–gel condensation of EtAlCl2 with trialkylphosphates

We have investigated the preparation of high-surface-area mesoporous aluminophosphates by non-hydrolytic sol–gel method based on reactions of EtAlCl2 with trialkylesters of phosphoric acid (OP(OR)3, R = Me, Et, iPr, nBu, in dry organic solvents. The condensations proceed by alkylchloride elimination. Various reaction and calcination conditions were examined. Porosity is obtained after calcination by removal of organic residual groups. This thermal processing at 300 °C of as-synthesized precursor gels leads to amorphous aluminophosphate xerogels with surface areas of 400–500 m2 g–1 provided by small mesopores (2–8 nm). Changes in the coordination environment of aluminium from six- to four-coordinate are evidenced by shift of 27Al MAS NMR resonances.

NO2 sensing properties of WO3 porous films with honeycomb structure

WO3 porous films (WPFs) were synthesized by a non-hydrolytic sol-gel (NHSG) method using WCl6, C2H5OH, and C3H7NO as the precursors. The polyethylene glycol (PEG) was employed as a porogen to prepare the porous structure. The microstructures of WPFs were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption-desorption isotherms were used to characterize the specific surface areas of the samples. The results indicated that the honeycomb-like WPFs were assembled by numerous WO3 nanoparticles with the diameter of 20–60 nm. Gas sensing measurements showed that the peak sensor response to NO2 was obtained at the operating temperature of 100 °C. The sensor based on WPFs showed excellent reversibility and fast response to NO2 at various operating temperatures and NO2 concentrations. The sensor also exhibited a significant NO2 selectivity compared with NH3, SO2, CH3OH, and C2H5OH, demonstrating a promising application in detecting NO2. The porous structure formation process of the WPFs was analyzed and gas sensing mechanism based on electron depletion theory as well as first principle calculations were discussed.

Acetic Anhydride as an Oxygen Donor in the Non-Hydrolytic Sol-Gel Synthesis of Mesoporous TiO2 with High Electrochemical Lithium Storage Performances.

An original, halide-free non-hydrolytic sol-gel route to mesoporous anatase TiO2 with hierarchical porosity and high specific surface area is reported. This route is based on the reaction at 200 °C of titanium(IV) isopropoxide with acetic anhydride, in the absence of a catalyst or solvent. NMR spectroscopic studies indicate that this method provides an efficient, truly non-hydrolytic and aprotic route to TiO2 . Formation of the oxide involves successive acetoxylation and condensation reactions, both with ester elimination. The resulting TiO2 materials were nanocrystalline, even before calcination. Small (about 10 nm) anatase nanocrystals spontaneously aggregated to form mesoporous micron-sized particles with high specific surface area (240 m2 g-1 before calcination). Evaluation of the lithium storage performances shows a high reversible specific capacity, particularly for the non-calcined sample with the highest specific surface area favouring pseudo-capacitive storage: 253 mAh g-1 at 0.1 C and 218 mAh g-1 at 1 C (C=336 mA g-1 ). This sample also shows good cyclability (92 % retention after 200 cycles at 336 mA g-1 ) with a high coulombic efficiency (99.8 %). Synthesis in the presence of a solvent (toluene or squalane) offers the possibility to tune the morphology and texture of the TiO2 nanomaterials.

LaMgAl11O19 synthesis using non-hydrolytic sol-gel methods

Polycrystalline LaMgAl11O19 (LMA) was prepared by four different non-hydrolytic sol-gel methods. From stable solutions, four powder precursors containing an amorphous and nanocrystalline phase with specific reactivity were obtained. The particle size, morphology, thermal behaviour, and phase composition of the powder precursors were studied using DLS, TEM, DSC/TG and XRD. Bulk ceramic samples containing LMA were prepared at 1200 °C for 16 h and examined in terms of phase purity and microstructure using XRD, SEM, and TEM. Raman spectroscopy of pure LMA was used to study the structure in detail. A mechanism of LMA formation and a relation between powder precursor properties and final phase composition is proposed. These findings may be useful for designing modern technologies for fabrication of LMA for optical or protective coating applications.

Two-Dimensional Atomically Thin Tin-Based Fluorescent Oxide Synthesized at Ambient Temperature and Its Biomedical Applications

Synthesis of atomically thin tin oxide nanosheets using a nonhydrolytic sol–gel method at ambient temperature is reported in the present work. After 10 min of probe sonication and 7 days of incubation at ambient temperature, ultrathin tin oxide nanosheets (SnONS) from 2 nm to 5 μm were formed due to interaction between tin chloride and acetone. The most upsurging property of SnONS was the inherent yellow fluorescence (λex= 420 and λem= 540 nm) phenomenon rarely reported with respect to tin-based nanosheets. The relative quantum yield of SnONS was ∼16%. The origin of fluorescence in SnONS is speculated to originate from multiple transitions in oxygen states of Sn, as confirmed by X-ray photoelectron spectroscopy. For biological applications, SnONS was phase transferred from acetone to water without compromising the fluorescent properties of SnONS. Image cytometry (Nucleo-Counter NC-3000) and laser confocal microscopy were used for comprehending the cellular biocompatibility and internalization of nanoparti...

Synthesis of High-Refractive-Index Epoxy-Modified Vinyl Methyl Phenyl Silicone Resins for Encapsulation of LEDs

A series of high-refractive-index epoxy-modified vinyl methyl phenyl silicone resins with different content of vinyl groups have been synthesized by a combination of hydrolytic and nonhydrolytic sol–gel processes to improve their adhesion. The products were characterized by Fourier-transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The results showed that epoxy and vinyl groups were successfully introduced into the products while the content of hydroxyl groups was low. Then, epoxy-modified silicone materials were manufactured by addition reaction between the epoxy-modified vinyl methyl phenyl silicone resins and hydrogen-containing phenyl silicone resin. The epoxy-modified silicone materials were characterized by thermal aging (250°C for 2 h) experiments, light transmittance measurements, thermogravimetric analysis, red dye penetration tests, reflow soldering (270°C for 10 cycles), and lumen depreciation (50 mA for 165 h) tests. The results showed that the epoxy-modified silicone materials exhibited high transmittance (> 90%) and good thermal stability. The epoxy-modified silicone materials showed better resistance to high temperature and ultraviolet (UV) radiation than commercial epoxy resin (6103). The introduced epoxy groups greatly improved the adhesion of the silicone resin. The epoxy-modified silicone material prepared using epoxy-modified vinyl methyl phenyl silicone resin with higher content of vinyl groups showed better mechanical performance (50 Shore D). The epoxy-modified silicone material EVMPS-3′ is expected to be applicable in packaging of high-power light-emitting diodes (LEDs).

One-step nonhydrolytic sol-gel synthesis of mesoporous TiO2 phosphonate hybrid materials.

Mesoporous TiO2–octylphosphonate hybrid materials were prepared in one step by a nonhydrolytic sol–gel method involving the reaction of Ti(OiPr)4, acetophenone (2 equiv) and diethyl octylphosphonate (from 0 to 0.2 equiv) at 200 °C for 12 hours, in toluene. The different samples were characterized by 31P magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and nitrogen physisorption. For P/Ti ratios up to 0.1, the hybrid materials can be described as aggregated, roughly spherical, crystalline anatase nanoparticles grafted by octylphosphonate groups via Ti–O–P bonds. The crystallite size decreases with the P/Ti ratio, leading to an increase of the specific surface area and a decrease of the pore size of the hybrid samples. For a P/Ti ratio of 0.2, the volume fraction of organic octyl groups exceeds 50%. The hybrid material becomes nonporous and can be described as amorphous TiO2 clusters modified by octylphosphonate units, where the octyl chains form an organic continuous matrix.

Low temperature synthesis of nanocrystalline V2O5 using the non-hydrolytic sol–gel method

Vanadium oxide was synthesized using the non-hydrolytic sol-gel method. Reactions with two different vanadium precursors, VCl3 and VOCl3, were investigated at room temperature. All raw and heat-treated samples were characterized by powder x-ray diffraction, energy-dispersive x-ray spectroscopy coupled with scanning electron microscopy, and thermal analysis. For the VCl3 precursor, crystalline V2O5 was formed following heat treatments between 200 and 250 °C. Broad diffraction features, indicative of nanocrystalline material, were observed in dried samples for VOCl3, while heat treatment to 250 °C produced well-crystallized V2O5. Interesting porous morphologies with large crystallographic coherence lengths were observed for the heat-treated samples.

Stimuli-responsive amphoteric ion exchange polymers bearing carboxylic and amine groups grafted to a cross-linkable silica network

Stimuli-responsive hybrid organic-inorganic amphoteric ion exchange polymers were synthesized via a non-hydrolytic sol–gel process with carboxylic acid and amine groups in silica side chains. Structural characterization of samples with a ratio carboxylic acid/amine 1:2 (PSU-SiCA(1:2)) and 2:2 (PSU-SiCA(2:2)) showed a degree of functionalization of 0.5 in both cases. The ion exchange capacity, analysed by acid-base titration, elemental analysis and thermogravimetric analysis, was 1.8 meq/g for PSU-SiCA(1:2) and 1.2 meq/g for PSU-SiCA(2:2). pH-Dependent properties for acidic, basic and zwitterionic forms were studied including hydration isotherms, ionic conductivity and selective deposition on acidic and basic substrates. The water uptake and ionic conductivity of the acidic and basic forms were highest for PSU-SiCA(1:2), due to the higher IEC. The zwitterionic forms, which contain a minimum of mobile ions, showed the lowest water uptake and ionic conductivity. The acidic form deposited on basic Al2O3 substrates and the basic form on acidic SiO2, whereas the zwitterionic polymer was deposited on neither. The stimulus-dependent ionic conductivity and hydration and the selective deposition depending on interfacial charges are striking properties, which make these hybrid bio-friendly ionomers compelling for applications.

Influence of Synthesis Conditions on Microstructure and NO₂ Sensing Properties of WO₃ Porous Films Synthesized by Non-Hydrolytic Sol⁻Gel Method.

Nanostructured tungsten trioxide porous films were prepared by a non-hydrolytic sol–gel method following the inorganic route in which ethanol and PEG were used as the oxygen-donor and structure-directing reagent, respectively. The effects of aging time of the precursor solution, PEG content, and calcination temperature on the structure, morphology, and NO2 sensing properties of WO3 films were systematically investigated by using the techniques of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and gas sensing measurements. The results demonstrated that a series of WO3 films with different microstructures could be obtained by manipulating the synthesis parameters. Furthermore, a suitable synthesis condition of WO3 films for NO2 sensing application was determined.

A full palette: Crystal chemistry, polymorphism, synthetic strategies, and functional applications of lanthanide oxyhalides

Ionic compounds wherein lanthanide cations are arrayed alongside anions adopt a wide range of crystal structures as a result of the variation of ionic radii and electronic configurations across the lanthanide series. Owing to the constricted nature of 4f orbitals, local coordination environments and structural preferences in such compounds are primarily dictated by electrostatic interactions and steric considerations with the primary driving force being the minimization of the crystal lattice energy. In this review, we examine a broad class of dianionic rare-earth compounds, lanthanide oxyhalides that present a multidimensional design space for tuning of functional properties by dint of the possibilities for extensive alloying on cationic and anionic sublattices; the considerable span of ionic radii and hardness across the lanthanide series and down the halide group, respectively; a large tolerance window for point defects such as oxide and halide vacancies; as well as multiple accessible polymorphs. In addition to their structural versatility, control over functional properties is accessible based on alteration of microstructure and surface chemistry. Synthetic strategies for accessing atomistic, nanoscale, and mesoscale control are discussed using illustrative examples placing particular emphasis on non-hydrolytic sol—gel processes that provide access to well-defined solid-solution nanocrystals. The reactivity and post-synthetic modification of these compounds is further delineated. Methods for defining color centers within these compounds, cooperativity of the optical response of the color centers with the host lattice (determined by overlap integrals specific to each structure type and the polarization and ligand field effects of different halide ions) and adjacent color centers (reliant on energy transfer schema), and their practical application in phosphors are further detailed. Mechanisms facilitating down- and up-conversion of energy absorbed from incident electromagnetic radiation or high-energy particles are delineated with particular emphasis on X-ray and electron-beam excitation. The accessible energy conversion mechanisms, efficacious radiative recombination channels, and opportunities for systematically tuning color through compositional modulation have led to the emergence of these materials as potential candidates for phosphors. These materials have potential applications in solid-state lighting, radiation detection, and as the active elements of imaging devices. The tolerance towards large concentrations of anion vacancies and the facile diffusivity of anions in these compounds further underpins the function of lanthanide oxyhalides as ion conductors, gas sensors, and heterogeneous catalysts. Increasing interest has focused on utilization of well-defined color centers for quantum information science and multiplexed sensing in biological systems. Such applications require additional control of the positioning of dopant atoms and understanding of their interactions with the host lattice and other dopant atoms.

Tuning Texture and Morphology of Mesoporous TiO₂ by Non-Hydrolytic Sol-Gel Syntheses.

The development of powerful synthetic methodologies is paramount in the design of advanced nanostructured materials. Owing to its remarkable properties and low cost, nanostructured TiO2 is widely investigated for applications such as photocatalysis, energy conversion or energy storage. In this article we report the synthesis of mesoporous TiO2 by three different non-hydrolytic sol-gel routes, and we investigate the influence of the synthetic route and of the presence and nature of the solvent on the structure, texture and morphology of the materials. The first route is the well-known ether route, based on the reaction of TiCl4 with iPr2O. The second and third routes, which have not been previously described for the synthesis of mesoporous TiO2, involve the reaction of Ti(OiPr)4 with stoichiometric amounts of acetophenone and benzoic anhydride, respectively. All materials are characterized by XRD, N2 physisorption and SEM. By playing with the non-hydrolytic route used and the reaction conditions (presence of a solvent, nature of the solvent, calcination), it is possible to tune the morphology and texture of the TiO2. Depending on the reaction conditions, a large variety of mesoporous TiO2 nanostructures could be obtained, resulting from the spontaneous aggregation of TiO2 nanoparticles, either rounded nanoparticles, platelets or nanorods. These nanoparticle networks exhibited a specific surface area up to 250 m2 g−1 before calcination, or up to 110 m2 g−1 after calcination.

Clean Block Copolymer Microparticles from Supercritical CO2: Universal Templates for the Facile and Scalable Fabrication of Hierarchical Mesostructured Metal Oxides.

Metal oxide microparticles with well-defined internal mesostructures are promising materials for a variety of different applications, but practical routes to such materials that allow the constituent structural length scales to be precisely tuned have thus far been difficult to realize. Herein, we describe a novel platform methodology that utilizes self-assembled block copolymer (BCP) microparticles synthesized by dispersion polymerization in supercritical CO2 (scCO2) as universal structure directing agents for both hydrolytic and nonhydrolytic sol-gel routes to metal oxides. Spherically structured poly(methyl methacrylate- block-4-vinylpyridine) (PMMA- b-P4VP) BCP microparticles are translated into a series of the corresponding organic/inorganic composites and pure inorganic derivatives with a high degree of fidelity for the metal oxides TiO2 and LiFePO4. The final products are comprised of particles close to 1 μm in size with a highly ordered internal morphology of interconnected spheres between 20-40 nm in size. Furthermore, our approach is readily scalable, enabling grams of pure or carbon-coated TiO2 and LiFePO4, respectively, to be fabricated in a facile two step route involving ambient temperature mixing and drying stages. Given that both length scales within these BCP microparticles can be controlled independently by minor variations in the reagent quantities used, the present general strategy could represent a milestone in the design and synthesis of hierarchical metal oxides with completely tunable dimensions.