Low Temperature Sol Gel Synthesis Research Articles

Transition Metal-Doped Layered Iron Vanadate (FeV3-xMxO9.2.6H2O, M = Co, Mn, Ni, and Zn) for Enhanced Energy Storage Properties.

With its distinctive multiple electrochemical reaction, iron vanadate (FeV3O9.2.6H2O) is considered as a promising electrode material for energy storage. However, it has a relatively low practical specific capacitance. Therefore, using the low temperature sol-gel synthesis process, transition metal doping was used to enhance the electrochemical performance of layered structured FeV3O9.2.6H2O (FVO). According to this study, FVO doped with transition metals with larger interlayer spacing exhibited superior electrochemical performance than undoped FVO. The Mn-doped FVO electrode showed the highest specific capacitance and retention of 143 Fg-1 and 87%, respectively, while the undoped FVO showed 78 Fg-1 and 54%.

Low temperature sol-gel synthesis of copper zinc ferrite for hydrogen catalytic hydrolysis of sodium borohydride

The spinal ferrites are regarded as promising for renewable energy application like hydrogen production from sodium borohydride (NaBH4) since they have superior catalytic activity. The current work considers the preparation of Cu1-xZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles via the low temperature sol-gel method. The cubic crystal structure of nanoparticles was identified by XRD spectra analysis. The average crystal size was provided concerning the full width at half maximum to be 10.0 nm according to Scherer formula. FTIR spectra of synthesized ferrite nanoparticles showed the vibrational bands of Cu1-xZnxFe2O4. The images showed a cross-linked porous surface morphology. The TEM images of the CuFe2O4 and Cu0.6Zn0.4Fe2O4 samples showed spherical nanoparticles with an average size of 10 nm. The surface area BET at 0.0, 0.2, 0.4, 0.6 and 0.8 content of zinc were 95, 66, 46, 49 and 41 m2/g. The values of direct band gaps for nanocrystalline Cu1-xZnxFe2O3 were 52.25, 2.0, 2.16, 1.9 and 2.11 eV at x = 0.0, 0.2, 0.4, 0.6, and 0.8. The hydrogen catalytic effect of Cu1-xZnxFe2O4 nanoparticles is accelerated, especially the sample CuFe2O4. The nanoparticles show high generation rates but the sample CuFe2O4 is the highest catalytic material (1810 mL/gmin).

Sol-Gel Synthesis of Translucent and Persistent Luminescent SiO2@ SrAl2O4 Eu, Dy, B Materials.

This publication offers an economically promising method of persistent luminescent silicate glass synthesis that does not involve high temperatures or ready-made (separately synthesized) PeL particles. In this study, we demonstrate the formation of SrAl2O4 doped with Eu, Dy, and B in a SiO2 glass structure using the one-pot low-temperature sol-gel synthesis method. By varying the synthesis conditions, we can use water-soluble precursors (e.g., nitrates) and a dilute aqueous solution of rare-earth (RE) nitrates as starting materials for SrAl2O4 synthesis, which can be formed during the sol-gel process at relatively low sintering temperatures (600 °C). As a result, translucent, persistently luminescent glass is obtained. The glass shows the typical Eu2+ luminescence and the characteristic afterglow. The afterglow duration is about 20 s. It is concluded that the slow drying procedure (2 weeks) is optimal for these samples to sufficiently get rid of the excess water (mainlyOH groups) and solvent molecules that can influence the strontium aluminate luminescence properties and have a pernicious effect on the afterglow. It can also be concluded that boron is playing a crucial role in the formation of trapping centers needed for PeL processes in the PeL silicate glass.

The Low-Temperature Sol-Gel Synthesis of Metal-Oxide Films on Polymer Substrates and the Determination of Their Optical and Dielectric Properties.

Photoactive, optically transparent heterostructures from silver nanowires and titanium dioxide were obtained by the sol-gel method on the surface of a polyethylene terephthalate film. The characteristics of optical transmission on the wavelength and those of dielectric permittivity, conductivity and dissipation on frequency in the range of 25-1,000,000 Hz were investigated.

Low-temperature sol–gel synthesis of magnetite superparamagnetic nanoparticles: Influence of heat treatment and citrate–nitrate equivalence ratio

Spinel ferrite nanoparticles are a remarkably versatile group of metal oxides with unique magnetic and electronic properties, making them promising candidates for certain electronic, biomedical, and environmental applications. Magnetite nanoparticles are obtained using complex synthesis methodologies that require inert atmospheres, additives to induce pH changes, expensive or toxic reagents, or complex equipment. In this work, a new approach to obtain superparamagnetic magnetite nanoparticles using citrate–nitrate sol–gel synthesis followed by heat treatment is presented. Iron nitrate and citric acid were added in different equivalence ratios (χ) (citrate/nitrate = 0.30, 0.85, and 1.40). The thermal behaviour of the xerogels was evaluated using thermal analysis techniques, and the results indicated that decreasing the equivalence ratio decreased the temperature required for magnetite formation, and the different release rates of reducing gases influenced the properties of the final material formed. The heat-treatment temperatures for the synthesis with the optimal χ were 130, 150, and 170 °C for 2, 4, and 8 h. Each condition was characterised in terms of the structure and magnetic properties of the product. The results showed that the prepared iron oxide nanoparticles were in the magnetite phase (Fe3O4) and possessed a crystallite size of 4.5–6.0 nm and average particle size of <10 nm. The magnetite nanoparticles displayed superparamagnetic behaviour, with a saturation magnetisation of up to 26.24 emu/g and remanent magnetisation of almost zero. Therefore, these superparamagnetic magnetite nanoparticles have excellent potential for biomedical and environmental applications.

Effects of Bi doping on structural and magnetic properties of cobalt ferrite perovskite oxide LaCo0.5Fe0.5O3

Literature reports on magnetic transition of LaFe0.5Co0.5O3 are highly ambiguous. The present study is an endeavour to address that particular issue of this ferrite perovskite. Here we report the low temperature sol-gel synthesis of pure and Bi-doped La1-xBixFe0.5Co0.5O3 (x = 0, 0.1 & 0.2) perovskites. All the samples were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray (EDX) analysis and magnetization studies. LaFe0.5Co0.5O3 crystallizes in a single phase rhombohedral (R-3c) structure. Substitution of Bi at the A-site results in structural transition. La0.9Bi0.1Fe0.5Co0.5O3 exhibits mixed rhombohedra (R-3c) and orthorhombic (Pbnm) phases, whereas La0.8Bi0.2Fe0.5Co0.5O3 is single phase orthorhombic (Pbnm). Favourable grain growth and good crystallinity observed in Bi doped samples are possibly due to the low melting temperature of Bi containing La1-xBixFe0.5Co0.5O3. EDX analysis confirms the chemical homogeneity of the samples. XPS studies and bond valence sum calculations confirm the nominal cationic oxidation states of the ions. Magnetization measurements reveal the weak ferromagnetic nature of La1-xBixFe0.5Co0.5O3 (x = 0, 0.1 & 0.2) which is associated to the canted antiferromagnetic structure. The magnetically active subsystem of Fe3+ ions are responsible for weak ferromagnetism which is explained by the antisymmetric Dzyaloshinskii–Moriya interaction, whereas the Co3+ ions remain predominantly in the low spin state. The increase in magnetic transition and the lower magnetic moment with an increase in Bi content can be related to the weakening of Dzyaloshinskii–Moriya interaction due to structural modification and local lattice distortion associated to the stereochemically active 6s2 lone pair electrons of the Bi3+ ions. Our results confirm the high structure sensitivity of magnetic properties of cobalt ferrite perovskite.

Mesoporous rutile TiO2: Synthesis, characterization and photocatalytic performance studies

Pure rutile phase of TiO2(R-TiO2) nanocrystals were synthesized through a low temperature sol-gel synthesis route by tuning the chemical process. This modified process directly resulted in nano spindle structures of rutile TiO2 at the instant of solvent evaporation and which further found exhibiting stabilized growth upon an increase in calcination temperatures as evidenced by XRD and HR-TEM studies. BET surface area measurement revealed the presence of mesoporosity with a highest surface area of 127.25 m2/g for the 300 °C calcinated sample. Photo-luminescence studies revealed the presence of intra-band levels at 2.90 eV and 2.68 eV. XPS studies on the highly porous R-TiO2 reveals the presence of Ti3+ ions, which may arise from the missing of oxygen or self-doping. Highly porous 300ᵒC R-TiO2 exhibited in the flat-band potential of -0.39 V as the normalized value for NHE electrode and resulted in the photocatalytic reduction hierarchy of MB > RhB > MO.

Crystalline hydroxyapatite/graphene oxide complex by low-temperature sol-gel synthesis and its characterization

This study presents a method for synthesizing hydroxyapatite (HA) with high crystallinity at low temperatures using a small amount of graphene oxide (GO), and the characters of produced GO/crystalline HA complex was investigated. The morphology and components of the synthesized HA (i.e., HA/GO) were analyzed through scanning electron microscopy, X-ray diffraction and transmission electron microscopy; additionally, the yield of the HA/GO was assessed. The HA/GO results were analyzed by comparing them with those obtained using HA synthesized without GO as a control group. A yield of ~4 mg of HA/GO was attained by the use of 100 μg of GO, demonstrating 20% improvement over the control group. The crystal phase analysis confirmed that crystalline HA of fine quality with nano-size was simply synthesized without intermediate phases using adding a small amount of GO, and the synthesized HA without GO is consist of intermediate phases (brushite and octacalcium phosphate) and hydroxyapatite. Biological characteristics of HA/GO were assessed through the behavioral analysis of mesenchymal stem cell attachment, proliferation, differentiation, and its protein adhesion capacity. HA/GO exhibited excellent biocompatibility and osteogenic differentiation behavior together with better protein adhesion ability than HA. These results demonstrate potential of HA/GO for application in bone tissue engineering. Thus, HA/GO can be developed as a biomimic biocomposite by combining it with bioactive molecules such as growth factors.

Gum ghatti-alginate hybrid bead derived titania spheres for deep removal of toxic dye Remazol Brilliant Violet from aqueous solutions

Mesoporous titania spheres was achieved using titanium (IV) isopropoxide as precursor and alginate-gum ghatti composite beads as structure directing agent via the low-temperature sol-gel synthesis method.These polysaccharides are multi-functional in nature & exhibiting secondary interactions in solution to accept new rheological and textural properties. The mixed beads of adequate mechanical strength could be obtained by keeping the ratio>1:1 for alginate to gum ghatti. The synthesized spheres were extensively characterized using FTIR, BET, SEM, TEM, and XRD. TEM study revealed that hollow titania spheres (HSAG3) are formed through the aggregationof TiO2 nanoparticles. Adsorption activity of titania spheres was investigated by employing Remazol Brilliant Violet (RBV) dye as the model reactive azo dye compounds. The dye adsorption mechanism was investigated indepthly using various kinetics models. Adsorption data found to be well expressed through pseudo second-order kinetics model. Further, data was also interpreted through Boyd model and the obtained diffusion constant value found to be in the order of 10−17 cm2/m, suggesting pore diffusion mechanism plays significant role in governing overall rate of the sorption process. The adsorption equilibrium data better conformed with the Langmuir isotherm which indicates surface homogeneity of the spheres for dye adsorption. Recycling study prompted that the adsorbent can be employed successively for 5 consecutive times without observing any significant loss in adsorption capacity. Overall the study revealed that the titania spheres can be serve as a promising adsorbent specifically for the removal of Remazol Brilliant Violet dye and other reactive anionic azo dyes in general.

Reinspection of formation of BiFe1-xMnxO3 solid solutions via low temperature sol-gel synthesis route

In this study, BiFe1-xMnxO3 (BiFeMnO; x from 0 to 0.5) solid solutions were prepared by low temperature sol-gel processing. It was demonstrated that structural, magnetic and morphological properties of BiFeMnO samples are dependent on the chemical composition of the synthesized BiFe1-xMnxO3 solid solutions. The thermal behaviour of the Bi–Fe–Mn–O precursor gels was investigated by thermogravimetric and differential scanning calorimetry (TG-DSC) measurements. From X-ray diffraction (XRD) analysis it was observed that monophasic BiFe1-xMnxO3 samples have formed up to 25 mol% of substitution. The Rietveld analysis showed that the structure of BiFeMnO specimens can be indexed by rhombohedral or orthorhombic unit cell depending on Mn3+ content. Scanning electron microscopy (SEM) was used to investigate samples morphology and revealed, that smaller particles form when Mn3+ is present inside the structure. Moreover, magnetic properties of solid solutions were also investigated, and antiferromagnetism and weak ferromagnetism were observed for the samples.

Titania-loaded cellulose-based functional hybrid nanomaterial for photocatalytic degradation of toxic aromatic dye in water

The dispersion of Titania on cellulose nanowhiskers was achieved using titanium tetra-isopropoxide as the precursor and sulphuric acid as a peptizing agent via the low-temperature sol-gel synthesis method. The photocatalytic activity of the resultant hybrid catalyst was studied through photocatalytic removal of toxic aromatic cationic thiazine dye (methylene blue). Diverse instrumental methods used for full characterizations of pristine and prepared materials allowed correlating the type of the chemical moiety incorporated to the formation of Titania-loaded cellulose-based functional nanomaterial as well as its stability and catalytic performance. Results indicated successful synthesis of multiscale Titania (19 nm ∼1 μm) and perpetual distribution over cellulose nanowhiskers. The latter showed high photocatalytic behavior towards the degradation of methylene blue (conc. 50 ppm) dye. The degradation reached 98.5 % in 40 min at a reaction rate of 0.188 min-1 as observed and measured through UV–vis spectrophotometer. Chemical oxygen demand (COD) analysis reveals substantial mineralization of the pollutants by reducing toxicity up to 68.64 % with complete recovery of the catalyst validated by total dissolved solids (TDS) analysis of treated water. Considering the above results, a mechanism has postulated. Kinetic study showed that the degradation reaction obeys pseudo-first-order reaction kinetics with appreciable recyclability after five (05) repeated uses. The results herein open new prospects for cellulose-based functional nanomaterial for various environmental applications.

Low-Temperature Sol–Gel Synthesis and Photoactivity of Nanocrystalline TiO2 with the Anatase/Brookite Structure and an Amorphous Component

Nanodispersed TiO2 consisting of anatase and brookite phases in a ratio of 3 : 1 is obtained by the sol–gel method from titanium(IV) butoxide at a temperature below 100°C. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy are used to show that the size of anatase particles is about 6 nm, and brookite particles consist of a crystal core, 4 nm in diameter, surrounded by an amorphous shell. Compared with the commercial Degussa P25 photocatalyst, which consists of the anatase and rutile phases in the same 3 : 1 ratio, the resulting TiO2 exhibits an increased photoactivity in hydroquinone oxidation. Quantum chemical modeling of anatase and brookite surfaces as well as their interface does not reveal the specific features of their electronic structure. This fact is indicative of the amorphous phase as an active participant in the transfer of charge carriers in the photocatalytic process.

Interface reaction activity of recyclable and regenerable Cu-Mn spinel-type sorbent for Hg0 capture from flue gas

To capture elemental mercury from flue gas, a series of novel Cu-Mn spinel-type sorbents were synthesized using the proposed low-temperature sol-gel auto-combustion synthesis method. CuMn2O4 sorbent exhibited excellent mercury removal performance in a wide temperature window of 50–350 °C, which is closely related to the mobile-electron environment caused by the Jahn-Teller distortion. The adsorbed mercury species exist in the forms of Cu-Hg amalgam and HgO on the sorbent surface. The chemisorption mechanism is responsible for Hg0 adsorption on CuMn2O4 surface. Mercury removal by CuMn2O4 sorbent is controlled by mass transfer process when the superficial velocity of flue gas is less than 16.9 cm/s. The surface reaction kinetics dominates mercury removal process when the superficial velocity is larger than 16.9 cm/s. The results of repeated adsorption-regeneration experiments indicate that CuMn2O4 sorbent exhibits excellent regenerability and recyclability for mercury removal from flue gas. During the regeneration process, the gas-phase O2 in air can decompose over sorbent surface to regenerate the consumed chemisorbed oxygen and replenish the oxygen vacancy. Mercury desorption from spent sorbents is a first-order desorption reaction process. The pre-exponential factor and activation energy for Hg0 desorption from used sorbent surface are 1.06 × 104 s−1 and 61.43 kJ/mol, respectively.

Unraveling the Charge State of Oxygen Vacancies in ZrO2–x on the Basis of Synergistic Computational and Experimental Evidence

The functional properties of metal oxide semiconductors depend on intrinsic and extrinsic defects. The population of intrinsic defects is strongly affected by the synthesis method and subsequent treatments of the material, while extrinsic defects can originate from suitable doping. Stoichiometric ZrO2 is a nonreducible oxide with a large band gap. Therefore, controlling and modulating its defect profile to induce energy states in the band gap is the sole possibility to make it a photocatalyst responsive to visible light. We report a method, based on low temperature sol–gel synthesis coupled with treatments performed in mild conditions, to obtain undoped visible light-responsive ZrO2–x. The electronic structure of these materials is interpreted in relation to their oxygen vacancy defect population. On the basis of a wide set of experimental measurements (X-ray photoelectron, steady-state and time-resolved photoluminescence, electron paramagnetic resonance, and UV–visible diffuse reflectance spectroscopy) a...

SOLUTION METHOD FOR PRODUCTION OF OPTICALLY ACTIVE MULTILAYER TITANIUM DIOXIDE -NANOSILVER COATINGS ONTO POLYETHER SUBSTRATE

Photochromic multilayer TiO2/Ag/TiO2 coating was prepared on plastic PET substrate using a solution method. The titanium dioxide sol was successfully produced using the titanium tetraisopropoxide as precursor and the nitric acid as peptizing agent via the low-temperature sol-gel synthesis in aqueous medium. Titanium dioxide films were prepared by a sol-gel dip coating method from a colloid solution of nanocrystalline TiO2 sol. Thus, nanocrystalline titanium dioxide sol and an aqueous solution of silver complex [Ag(NH3)2]NO3 followed by a photolysis for the reduction of silver ions to Ag nanoparticles with a plasmon resonance have been alternately deposited layer-by-layer. In result, heterostructures possessing photochromic properties were formed. The TiO2/Ag/TiO2 coating was investigated by UV-Vis spectroscopy, X-ray diffraction and atomic force microscope (AFM) with different resolutions. The TiO2 crystal phase formed during temperature dehydration possesses high photoactivity as the generated nanoparticles size of about 10 nm is an optimum for the most effective absorption of a light quantum and the generation of electron–hole pairs on the surface. It was found the use of silver nanoparticles also promotes an increase in the photoactivity of a film owing to larger water adsorption on the surface of a composite due to the nanoparticle surface effect, which is promoted by a high concentration of the photogenerated holes whose presence is confirmed by composite conductivity type. Thus, the photochromic multilayer TiO2/Ag/TiO2 coating described in this work are expected to find important applications to the fabrication of photochromic materials, optical filters or sensors.

Heat-Treatment-Induced Evolution of the Mesostructure of Finely Divided Y3Al5O12 Produced by the Sol–Gel Method

A method was developed for the low-temperature sol–gel synthesis of one of the most popular components of functional and structural materials—nanostructured yttrium aluminum garnet Y3Al5O12—using precursors from the class of alkoxoacetylacetonates produced from the corresponding acetylacetonates. It was determined that increasing duration of heat treatment of yttrium-aluminum-containing xerogen in air to 6 h reduces the crystallization temperature of the Y3Al5O12 phase from 920–930 to 750–800°C, which was confirmed by IR spectroscopy and X-ray powder diffraction analysis. The microstructure of nanocrystalline yttrium aluminum garnet obtained at 800°С was studied; it was found that the size of crystallites is 30–40 nm, the size of particles is 30–50 nm, and the size of pores is 20–30 nm. Small-angle neutron scattering demonstrated that, in the powders synthesized at 700–800°C, there is structural ordering of the short-range type, whereas in the nanocrystalline samples heat-treated at a higher temperature (850°С), there is no such ordering.

Low-Temperature Sol-Gel Synthesis of Nitrogen-Doped Anatase/Brookite Biphasic Nanoparticles with High Surface Area and Visible-Light Performance

Nitrogen doping in combination with the brookite phase or a mixture of TiO2 polymorphs nanomaterials can enhance photocatalytic activity under visible light. Generally, nitrogen-dopedanatase/brookite mixed phases TiO2 nanoparticles obtained by hydrothermal or solvothermal method need to be at high temperature and with long time heating treatment. Furthermore, the surface areas of them are low (&lt;125 m2/g). There is hardly a report on the simple and direct preparation of N-doped anatase/brookite mixed phase TiO2 nanostructures using sol-gel method at low heating temperature. In this paper, the nitrogen-doped anatase/brookite biphasic nanoparticles with large surface area (240 m2/g) were successfully prepared using sol-gel method at low temperature (165 °C), and with short heating time (4 h) under autogenous pressure. The obtained sample without subsequent annealing at elevated temperatures showed enhanced photocatalytic efficiency for the degradation of methyl orange (MO) with 4.2-, 9.6-, and 7.5-fold visible light activities compared to P25 and the amorphous samples heated in muffle furnace with air or in tube furnace with a flow of nitrogen at 165 °C, respectively. This result was attributed to the synergistic effects of nitrogen doping, mixed crystalline phases, and high surface area.

Pseudo-solid State Batteries See the Light

Dunn and colleagues design and synthesize a thin film pseudo-solid state electrolyte for next-generation lithium batteries based on solution-processed ionogels. They first demonstrate 125 mAh/g capacity for 150 cycles with minimal capacity loss in lithium iron phosphate and lithium metal full cell devices at C/2 rate. Next, they demonstrate the ability to photo-pattern the ionogel, and thus enable versatile and scalable fabrication and processing routes, while also retaining similar excellent electrochemical performance.

Natively porous films as halide anion fluorescence optical sensors

A halogen-anion fluorescent solid-state sensor based on natively porous films doped with a quinolinium derivative is reported. The sensitive films are prepared with a low temperature sol–gel synthesis starting from bridged silsesquioxane precursors, and 6-methoxyquinolinium moieties are covalently linked to the organic–inorganic hybrid network. This sensor system is reversible and allows selective detection and measurement of halogen anion concentrations in the physiological range by a dynamic quenching effect of the sensitive fluorophore. The quenching constants are unaffected by dye inclusion in the bridged polysilsesquioxane matrix.

ChemInform Abstract: Low‐Temperature Sol—Gel Synthesis of Crystalline Materials

AbstractReview: 163 refs.