Low Temperature Sol-gel Route Research Articles

Hierarchically grown nanostructure for suppressing leaching in fiber optic chemical sensing

Owing to fiber-optic pH sensing, phenolphthalein immobilized SiO2 nanoparticles (P-SNPs) and phenolphthalein immobilized SiO2–TiO2 nanoparticles (P-STNPs) are synthesized by low-temperature sol-gel route. The P-SNPs revealed hierarchical structure, surface roughness (Ra) 7 nm, surface area ∼442 m2/g, n (refractive index) 1.37 at 550 nm which is significant for pH sensing. The P-STNPs exhibited granular structure, low Ra 3 nm, surface area ∼219 m2/g, n around 1.52 at 550 nm. Both matrices are thermally stable around 250 °C. The P-SNPs and P-STNPs sensitivity is calculated ∼22 counts/pH and 19 counts/pH with the determination coefficient (R2) ∼ 0.99. The pka value of P-SNPs is measured ∼9.5 and time response 0.11s within pH 12 without leaching which is higher than P-STNPs (9.1) and 3.9 s with leaching. Experimental findings suggested P-SNPs have the potential for practical usage in intense basic media.

Mild Sol–Gel Conditions and High Dielectric Contrast: A Facile Processing toward Large-Scale Hybrid Photonic Crystals for Sensing and Photocatalysis

Solution processing of highly performing photonic crystals has been a towering ambition for making them technologically relevant in applications requiring mass and large-area production. It would indeed represent a paradigm changer for the fabrication of sensors and for light management nanostructures meant for photonics and advanced photocatalytic systems. On the other hand, solution-processed structures often suffer from low dielectric contrast and poor optical quality or require complex deposition procedures due to the intrinsic properties of components treatable from solution. This work reports on a low-temperature sol–gel route between the alkoxides of Si and Ti and poly(acrylic acid), leading to stable polymer–inorganic hybrid materials with tunable refractive index and, in the case of titania hybrid, photoactive properties. Alternating thin films of the two hybrids allows planar photonic crystals with high optical quality and dielectric contrast as large as 0.64. Moreover, low-temperature treatments also allow coupling the titania hybrids with several temperature-sensitive materials including dielectric and semiconducting polymers to fabricate photonic structures. These findings open new perspectives in several fields; preliminary results demonstrate that the hybrid structures are suitable for sensing and the enhancement of the catalytic activity of photoactive media and light emission control.

Novel sol–gel method for low temperature synthesis of nanostructured Mn3O4: Structure, cation valence states, optical and electrical properties

Novel low temperature sol–gel route for the synthesis nanostructured Hausmannite, Mn3O4with very small crystallite size (9 ± 1 nm) and phase purity is reported. Reaction temperature of 0–5 °C and drying temperature of 40 °C is the lowest reported so far. Average particle size (8 ± 1 nm) measured from Transmission Electron Microscopy is in good agreement with the crystallite size indicating monodispersed nature. Raman analysis indicates the presence of +4 valence states for Mn over and above +2 and +3 and the presence of an Mn2O3 like surface layer. XPS analysis confirms the phase purity as well as the presence of Mn4+ions. Presence of +4 valence state for Mn is attributed to the presence of cation vacancies that lead to disproportionate reactions. UV–visible absorption spectra is quite broad with charge transitions associated with Mn2+, Mn3+ and Mn4+ states and d-d crystal field transitions. DC electrical conductivity is about two orders of magnitude higher than that of single crystalline Mn3O4 and the conduction mechanism is defect dependent.

Electrocatalytic properties of La1-xCuxCoO3 (0 ≤ x ≤ 0.8) film electrodes for oxygen evolution in alkaline medium: Part II. A comparative study

The present study concerns with the preparation of perovskite-type oxide film electrodes of La, Cu and Co having composition La 1-x Cu x CoO 3 (0 ≤ X ≤ 0.8) on Ni conducting support by using low temperature sol-gel route at pH 4.00 and studied their electrocatalytic properties towards oxygen evolution reaction (OER) in alkaline medium. X-ray diffraction study of the material indicated the formation of almost pure perovskite phase with hexagonal crystal geometry. The electrocatalytic activity of the material was determined in three electrode single compartment glass cell. Techniques used were cyclic voltammetry (CV), roughness factor and anodic polarization studies (Tafel plot). Each cyclic voltammogram exhibited an anodic and corresponding cathodic peak prior to the oxygen evolution reaction. The observed anodic and cathodic peak potential values were 553±31 and 312±27 mV, respectively. The study of anodic polarization curve indicates that the oxide with 0.6 mol Cu-substitution (j a = 182.4 mA cm -2 at 750 mV) showed highest electrocatalytic activity with lowest Tafel slope value (b = 65 mV decade -1 ) towards OER. Thermodynamic properties of the material have also been investigated by recording the anodic polarization curve at different temperature. The value of electrochemical activation energy was found to be lowest with most active 0.6 Cu-substituted oxide material. Electrocatalytic activities of the oxide electrodes, so obtained, were compared with the similar oxide prepared at 3.75 pH.

Structural and 3rd order nonlinear optical properties of organic dyes immobilized silica nano-composite

Low-temperature sol-gel route is used to synthesized the silica and three different organic dyes i.e., phenol red (PR), creosol red (CR) and bromophenol blue (BPB) individually encapsulated within silica nano-composite matrix. FTIR analysis shows heterogeneous bonding between silica and dye species. The PR encapsulated silica (PR-Si) nano-composite matrix exhibited average surface roughness (Ra) ~ 1.6 nm than other matrices, which is advantageous for non-linear behaviour. FESEM/EDX analysis confirmed the crack-free, porous structures of successfully dyes encapsulated silica nano-composite matrix. The closed z-scan characterization of PR-Si, CR-Si, and BPB-Si shows self-defocusing phenomena with the negative nonlinear refractive index. From the open z-scan measurement, the strength of nonlinear absorption (NLA) is observed in the order of PR-Si > CR-Si > BPB-Si nano-composite matrix. Smooth surface and low surface roughness of the PR-Si causes strong nonlinear character during the interaction with the excitation beam. The prominent NLO response of the PR-Si nano-composite matrix has provided a new avenue in the development of NLO devices especially all-optical control as well as optical switching.

Third-order nonlinearity and optical limiting properties of sol–gel-based bromophenol blue dye immobilized in silica–titania nanohybrid

Silica–titania (ST) nanohybrid and bromophenol blue (BPB) immobilized ST nanohybrid matrix are synthesized by low-temperature sol–gel route. The influence of BPB on the structural, morphological, and nonlinear optical properties of silica–titania nanohybrid was investigated by fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), atomic force microscopy (AFM), and z-scan technique. FTIR analysis confirms the chemical bonding between hydrophobic BPB dye species and hydrophilic type ST nanohybrid matrix. TEM and AFM analysis shows that the synthesized immobilized nanohybrid has inter-dispersed structure with average particle size of 0.8 ± 0.3 nm, smooth morphology, and low average surface roughness ~4.57 nm. The immobilization of BPB greatly improves the nonlinear refraction response and the nonlinear refractive index increases from 4.8 × 10–9 cm2/W to 451.9 × 10–9 cm2/W. Reverse saturable absorption is observed in both BPB and BPB/ST nanohybrid. However, the magnitude of nonlinear absorption coefficient in BPB/ST is lower than the BPB dye due to the occurrence of saturable absorption of the ST matrix. The optical limiting (OL) behavior of the BPB/ST nanohybrid reveals the low OL threshold at 0.33 kW/cm2. The synthesized BPB/ST nanohybrid has potential as an optical limiters for safety of photonic and optoelectronic devices under low-powered CW laser.

Formation and optical properties of pure nano-sized anatase titania by low-temperature aqueous sol-gel route

Nanocrystalline anatase titania particles were synthesized by low-temperature aqueous sol-gel transformations from new types of precursors [Ti{OPri}4] (A), [{acac}2Ti{OPri}{ONC9H6}] (1), and [{acac}2Ti{ONC9H6}2] (2) {where, ONC9H6 = 8-hydroxyquinoline}. Formation of all the precursors was confirmed by elemental analysis, molecular weight measurements, FTIR, and NMR (1H and 13C). Titania samples (a), (b), and (c) were formed by aqueous sol-gel transformations of (A), (1), and (2), respectively. The resulting nano-materials were characterized using XRD, TEM, SEM, EDX, SAED, FTIR, and UV-Visible spectroscopic techniques. From the X-ray pattern, the phase purity of the synthesized powders was confirmed as anatase TiO2. Crystallite size of all the oxide samples was measured by XRD and TEM, found to be 26 nm (a), 11 nm (b), and 8 nm (c). Surface morphologies of all the samples were evaluated by SEM. Selected area diffraction (SAED) of (b) and (c) are also corroborated the XRD results. The absorption spectra of oxide samples, (a), (b), and (c) show energy band gap of 2.9 eV, 3 eV, and 3.1 eV, respectively. SAED-EDX analysis confirmed the formation of pure anatase-phase titania nanoparticles.

TiP2O7 exhibiting reversible interaction with sodium ions in aqueous electrolytes

The reversible electrochemical cycling of sodium ions in several variants of low cost, easy to produce TiP2O7 as the negative electrode material in an aqueous battery is demonstrated for the first time. TiP2O7 is synthesized using a high temperature solid-state route and a low temperature sol gel route. The materials are electrochemically characterized in an aqueous 1M Na2SO4 electrolyte with a Na0.44MnO2 counter electrode material. While little capacity for sodium ion cycling is reflected in cyclic voltammetry, all observed samples exhibited reversible cycling of sodium ions in galvanostatic cycling with potential limitation. To our knowledge, this is the first report of solid-state synthesized TiP2O7 reversibly cycling sodium ions, and the first report of TiP2O7 reversibly cycling sodium ions in aqueous electrolytes. Discharge specific capacity is found to be positively correlated with crystallite size and low specific currents.

TiP2O7 Exhibiting Reversible Insertion of Sodium Ions in an Aqueous Environment

Aqueous sodium ion batteries are attractive for large-scale energy storage due to their low cost, intrinsic safety and environmental friendliness [1,2]. A key challenge in designing aqueous batteries is creating electrode pairs that operate within the stable potential window of water, with anode material selection being particularly challenging. Furthermore, good materials for sodium ion cycling are limited [2,3]. TiP2O7 presents a promising anode material due to its lower intercalation/deintercalation potentials, allowing for more optimized use of an aqueous electrolyte’s stability window [1-3]. TiP2O7 is typically reported to exclusively cycle lithium ions, showing no capacity in sodium aqueous electrolytes in cyclic voltammetry tests [3]. One report demonstrated that a low temperature polymorph of TiP2O7 exhibits reversible cycling of sodium ions in an organic electrolyte [4]. In this work, the reversible insertion of sodium ions in TiP2O7 as the anode material in an aqueous battery is demonstrated. Several polymorphs of TiP2O7 are synthesized using a high temperature solid-state route and a low temperature sol gel route. In addition to physical characterization, the materials are electrochemically characterized in an aqueous 1M Na2SO4 electrolyte against Na0.44MnO2 cathode material. While no capacity for sodium ion cycling is reflected in cyclic voltammetry tests of these TiP2O7, all polymorphs exhibited reversible cycling of sodium ions in constant current galvanostatic cycling with potential limitation. To our knowledge, this is the first report of solid-state synthesized TiP2O7 reversibly cycling sodium ions. Specific capacity is found to be positively correlated with both crystallite size and lattice parameter. A full cell rate study with three electrode data in aqueous Na2SO4 electrolyte is presented. Acknowledgments This work is supported by Carnegie Mellon University and Aquion Energy Inc.

Low temperature nanocrystalline zinc oxide for photovoltaic applications

Nanocrystalline ZnO was synthesized by a low temperature sol-gel route. The ZnOnanocrystals were investigated by X-ray diffraction (XRD), electron paramagnetic resonance (EPR), photoluminescence (PL), and conductivity measurements. The goal was the development of nanocrystalline ZnO as a transparent conductive oxide blocking ultraviolet (uv) light and using a defect photoluminescence band for down-shifting uvlight into the visible range, where organic photoactive polymers have their absorption maximum. The resulting defects and physical properties are discussed with respect to the conductivity of ZnO nanocrystals.

Reversible Li+ Storage in a LiMnTiO4 Spinel and Its Structural Transition Mechanisms

In this work, LiMnTiO4 (a structural analogue of classic spinel LiMn2O4) with a disordered cubic spinel structure (Fd3̅m) has been synthesized by a low-temperature sol–gel route. The as-obtained LiMnTiO4 exhibits excellent cycling stability in a wide voltage range from 1.5 to 4.8 V with high discharge capacities of 290, 250, and 140 mA h g–1 at a C/40, C/19, and 1C rate, respectively. Combined long- and short-range structural characterization techniques are used to reveal the correlation between structure and electrochemical behavior. During cycling, the charge/discharge profiles of LiMnTiO4 evolve from initially two well-separated plateaus into sloping regimes. In the early stage of discharge, LiMnTiO4 undergoes phase transitions from an initial spinel phase to mixtures of predominant rock-salt (Fm3̅m) and tetragonal (I41/amd) structures along with a decrease in crystallite size from 12 nm to 3 to 4 nm. During further cycling, the spinel/rock-salt phase transition was found to be reversible with the cubic framework remaining intact. The presence of the tetragonal phase after the first discharge suggests that the Mn3+ Jahn–Teller distortion is partially involved during lithiation from Li1–yMn3+yTiO4 to Li1+xMn3–xTiO4 and the fraction of such a tetragonal phase remains at about 30–40% during subsequent cycling.

A low-temperature sol–gel route for the synthesis of bioactive calcium silicates

Sol–gel-derived bioactive calcium silicates, synthesized from calcium nitrate tetrahydrate and calcium 2-methoxyethoxide as calcium precursor respectively, were calcified under different temperatures. A series of techniques including SEM, TGA, solid 29Si NMR, nitrogen adsorption, and simulated body fluids (SBF) soaking were employed to study their textural features and in vitro bioactivity. It was confirmed that calcium 2-methoxyethoxide is a promising candidate of calcium precursor for bioactive calcium silicates stabilized under low temperatures. This has implications in fabrication of organic–inorganic hybrid composites.

Structure switch between α-Fe2O3, γ-Fe2O3 and Fe3O4 during the large scale and low temperature sol–gel synthesis of nearly monodispersed iron oxide nanoparticles

With same procedure and same starting materials, nearly monodispersed α-Fe2O3, γ-Fe2O3 and Fe3O4 nanoparticles were synthesized on an large scale of about 60g in a single reaction through a low temperature sol–gel route. The simple preparation process includes the reactions between FeCl2 and propylene oxide in ethanol solution at boiling point to form a sol and the following drying of the sol. The different iron oxide phases can be obtained just by changing of the drying conditions for the sol solution. The strategy developed in this study offers important advantages over the conventional routes for the synthesis of α-Fe2O3, γ-Fe2O3 and Fe3O4 nanoparticles, showing potential for its application in industrial production of iron oxides.

Preparation of highly stable TiO2 sols and nanocrystalline TiO2 films via a low temperature sol–gel route

Highly stable TiO2 sols were prepared by adjusting the water-to-titanium molar ratio to ~4 in the process of hydrolysis and condensation of titanium isopropoxide in ethanol with HNO3. Particularly, long-term stable TiO2 sols were prepared without adding any chemical additives. Anatase TiO2 nanocrystallites with sizes of 3–5 nm in diameter were uniformly dispersed in the stable sol. Crystallized TiO2 films were successfully deposited on Si (100) using the stable sol via a dip-coating process with low temperature curing at as low as 100 °C. The synthesized TiO2 sols and films are promising for use in flexible or dye-sensitized solar cells.

Facile and ultra large scale synthesis of nearly monodispersed CoFe2O4 nanoparticles by a low temperature sol–gel route

Nearly monodispersed cobalt ferrite nanoparticles were synthesized by a low temperature sol–gel route using propylene oxide as a gelation agent. The nanoparticles were obtained by the reaction of FeCl2 and CoCl2 in ethanol solution with propylene oxide to form the sol, followed by the boiling of the sol solution. The unique chemistry of this procedure allows the formation of highly homogeneous gel intermediate, resulting in the great reducing of crystallization temperature of ferrites to less than 100 °C without postannealing step. This guarantees the preparation of well defined and non-aggregated ferrite nanoparticles on an ultra-large scale of about 75 g in a single reaction. This large scale synthesis strategy offers important advantages over other conventional routes for the preparation of CoFe2O4 nanoparticles, showing the promising application of this route in the industrial production.

Synthesis on an ultra large scale of nearly monodispersed γ-Fe2O3 nanoparticles with La(III) doping through a sol–gel route assisted by propylene oxide

Nearly monodispersed La3+ doped γ-Fe2O3 nanoparticles were synthesized on an ultra-large scale of about 60 g in a single reaction by a low temperature sol–gel route. The nanoparticles were obtained by the reaction of FeCl2 and La(NO3)3 in ethanol solution with propylene oxide to form the sol, followed by the boiling of the sol solution. The La3+ doping promotes the phase transformation temperature of γ-Fe2O3 nanoparticles from 350 to 650 °C by the La3+ doping induced enhancement of phase transformation activation energy. This large scale synthesis strategy offers important advantages over other conventional routes for the preparation of undoped and doped γ-Fe2O3 nanoparticles. These guarantee the promising application of this route in the industrial production.

High Power Capability, Impurity-Free and Nano-sized LiNi0.5Mn1.5O4 Cathode Material in Li ion Battery Synthesized by Low-Temperature Sol-Gel Route.

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Synthesis and photoluminescence of well-dispersible anatase TiO 2 nanoparticles

High-purity anatase TiO 2 nanoparticles were prepared using a low-temperature sol–gel route. The as-prepared sample was characterized by X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetric analysis, UV–vis spectroscopy, and photoluminescence. It is shown that the as-prepared sample crystallized in a pure anatase phase with an average crystallite size of about 7 nm, and the surfaces were highly hydrated. These nanoparticles were stabilized as a water suspension via the cooperation of DLVO force and surface hydration force. These suspensions showed characteristic band-gap emission at 397 ± 1.5 nm , which is a little red-shifted compared with the band-gap energy of indirect electronic transition measured in the UV–vis absorption spectrum. These observations were explained by the light-induced relaxation of polar water molecules in the surface hydration layer.

Preparation and structure of nanostructured Ti–Ni–O with modified low temperature sol–gel route

A series of nanoscaled Ti–Ni–O samples doped with different TiO2 content are prepared by modified low temperature sol–gel route at 400 °C. BET data reveals that the content of dopant TiO2 influences the grain size. XRD analysis indicates that the lattice parameter of particles increased with the TiO2 content. XPS results show that the surface state of nickel and titanium ion changed. Both of the latter two results suggest that there is an interaction takes place between TiO2 and NiO.

Anatase coating on NiTi via a low-temperature sol–gel route for improving corrosion resistance

NiTi was dip-coated with TiO 2 using Ti(OC 5 H 9 ) 4 as precursor. Subsequent hydrothermal treatment of the sample at 200 °C resulted in a film composed of nanosized anatase particles. EIS and polarization studies indicated a significantly larger increase in corrosion resistance compared with the coated samples dry-heated at 500 °C.