Modified Sol Gel Method Research Articles

Investigation of the structural, optical and magnetic properties of nickel ferrite nanoparticles synthesized through modified sol–gel method

Nickel ferrite nanoparticles were successfully synthesized by through modify sol–gel method with the aid of nickel (II) nitrate, iron (III) nitrate, and lactose without adding external surfactant. Moreover, lactose plays role as capping agent, reducing agent, and natural template in the synthesis of NiFe2O4 nanoparticles. The as-synthesized NiFe2O4 nanoparticles were characterized by means of several techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and UV–Vis diffuse reflectance spectroscopy. The magnetic properties of as-prepared NiFe2O4 nanoparticles were also investigated with vibrating sample magnetometer. To evaluate the photocatalyst properties of nanocrystalline NiFe2O4, the photocatalytic degradation of methyl orange under ultraviolet light irradiation was carried out.

Colossal dielectric permittivity and electrical properties of the grain boundary of Ca1−3x/2YbxCu3−yMgyTi4O12 (x=0.05, y=0.05 and 0.30)

Dielectric properties of Ca1−3x/2YbxCu3−yMgyTi4O12 (x=0.05, y=0.05 and 0.30) prepared using a modified sol–gel method and sintered at 1070°C for 4h were investigated. The mean grain sizes of the CaCu3Ti4O12 and co-doped Ca0.925Yb0.05Cu3−yMgyTi4O12 (y=0.05 and 0.30) ceramics were ≈15.86, ≈3.37, and ≈2.32μm, respectively. Interestingly, the dielectric properties can be effectively improved by co-doping with Yb3+ and Mg2+ ions to simultaneously control the microstructure and properties of grain boundaries, respectively. These properties were improved over those of single-doped and un-doped CaCu3Ti4O12 ceramics. A highly frequency−independent colossal dielectric permittivity (≈104) in the range of 102–106Hz with very low loss tangent values of 0.018–0.028 at 1kHz were successfully achieved in the co-doped Ca0.925Yb0.05Cu3−yMgyTi4O12 ceramics. Furthermore, the temperature stability of the colossal dielectric response of Ca1−3x/2YbxCu3−yMgyTi4O12 was also improved to values of less than ±15% in the temperature range from −70 to 100°C.

Fabrication of Nb-doped lead zirconate titanate thick films synthesized by sol–gel dip coating method

Modifying the lead zirconate titanate thick films by Nb5+ can thoroughly optimize the properties of the thick films in micro-electromechanical systems, sensors, and microactuators. In this article, the Nb5+ is doped in sol–gel synthesized thick films of PZT with the thickness of more than 27 µm. In order to produce the thick films, a new modified sol–gel method based on the niobium chloride precursor is applied. The lattice constants, lattice distortion, and the preferred-orientation of the films are measured by means of X-ray diffraction. The surface morphology and grain size of the films are examined by field emission scanning electron microscopy. The results demonstrated the formation of pure perovskite phase with the tetragonal lattice parameters of ct = 4.114 A and at = 4.039 A and the average grain size of 28 nm in the sample with 2 at.% Nb. Moreover, the hysteresis loops and dielectric constants of the films are compared by electrical measurements. The results illustrated 1.23-fold increase in remanent (from 5.7 µC cm−2 for undoped sample to 12.7 µC cm−2 for 2 at.% Nb) and 6.65-fold increase in dielectric constant (from 275 for undoped sample to 2080 for 3 at.% Nb).

Cu2O/TiO2 heterostructures on a DVD as easy&cheap photoelectrochemical sensors

Cu2O nanoparticles have been grown by pulse-electrochemical deposition on a Digital Versatile Disk (DVD) which acts as a nanostructured electrode. Prior to Cu2O deposition, the silver-coated rectangular-shaped grooves of the disassembled DVD were coated with a TiO2 thin film by a modified sol–gel method, where oxalic acid is used in place of the usual mineral acids to peptize the precipitated hydrous titania formed from the hydrolysis of titanium iso-propoxide. This procedure leaves no inorganic residues after UV-curing, resulting in a high quality film, mainly composed of TiO2-anatase. As demonstrated by Atomic Force Microscopy (AFM) measurements, the DVD grooves are filled by a 120–130nm thick TiO2 film, while the thickness of the TiO2 deposit on the crests is only ca. 50nm. This inhomogeneous thickness leads to an inhomogeneous electric field when the DVD is used as an electrode for depositing Cu2O nanoparticles, which eventually leads to the growth of Cu2O nanoparticles only on the DVD crests. A highly regular and reproducible Cu2O/TiO2 stripe-like heterostructure is obtained where both semiconducting oxides are aside. This system has been characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray photoemission spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, Raman spectroscopy and photocurrent measurements. A possible use of this easy&cheap electrode as a visible light responsive sensor to water soluble organics in basic solution is suggested.

Evidence for enhanced optical properties through plasmon resonance energy transfer in silver silica nanocomposites

Silver nanoparticles were dispersed in the pores of monolithic mesoporous silica prepared by a modified sol–gel method. Structural and microstructural analyses were carried out by Fourier transform infrared spectroscopy and transmission electron microscopy. X-ray photoelectron spectroscopy was employed to determine the chemical states of silver in the silica matrix. Optical absorption studies show the evolution absorption band around 300 nm for silver (Ag) in a silica matrix and it was found to be redshifted to 422 nm on annealing. Photoluminescence studies indicate the presence of various luminescent emitting centers corresponding to silver ions and silver dimers in the SiO2 matrix. The enhancement of absorption and photoluminescence properties is attributed to plasmon resonance energy transfer from Ag nanoparticles to luminescent species in the matrix.

Correlation between lattice strain and magnetic behavior in non-magnetic Ca substituted nano-crystalline cobalt ferrite

Magnetic nanoparticles of calcium (Ca)-substituted cobalt ferrite i.e. Co1−xCaxFe2O4 (x=0.00, 0.01, 0.015, 0.02, 0.05, 0.1, and 0.15) have been synthesized by the citric acid modified sol–gel method. X-ray powder diffraction (XRD)patterns confirm the formation of spinel phase. The particle size decreases with the Ca concentration. The Rietveld refinement of XRD patterns using the space group – Fd3̅m shows monotonically increasing of lattice parameter with the increasing concentration of Ca. The FT-IR spectrum recorded in the range of 325–1000cm−1 and Raman spectrum obtained in the range of 88–800cm−1 shows the formation of spinel phase belonging to Fd3̅m space group supporting structural analysis from XRD patterns. Magnetocrystalline anisotropy has been obtained using “Law of Approach (LA) to Saturation magnetization”. Saturation magnetization and remnant magnetization is maximum for 1% Ca substitution which could be due to strain mediated magnetism. However these magnetic properties decrease with the Ca substitution for the percentage above 1%. It could be due to decrease of magnetic exchange interaction in the sample. A correlation between magnetic behavior and lattice strain has been established in non-magnetic Ca substituted nano-crystalline cobalt ferrite. In order to investigate the ferromagnetic nature of the sample, Arrott plot analysis has been carried out. Difference in saturation magnetization obtained from LA to saturation and Arrott plot analysis gives the qualitative information about the influence of lattice strain on saturation magnetization.

Synthesis, surface characterization and electrokinetic properties of colloidal silica nanoparticles with magnetic core

In order to obtain functionalized silica colloids with magnetic properties, the three-step reaction, was carried out. The aqueous suspension of iron oxide nanoparticles as magnetic core (maghemite—γ-Fe2O3) was synthesized according to the Massart’s method (Massart in IEEE Trans Magn 17:1247–1248, 1981). A silica shell was obtained onto maghemite employing a modified sol–gel method by Salgueirino (Salgueirino-Maceira et al. in Adv Mater 19:4131–4144, 2006). As-synthesized magnetic silica core/shell nanocomposites were further functionalized by the post-grafting approach, using (3-Aminopropyl)-trimethoxysilane (APTMS) (Pham et al. in Langmuir 18:4915–4920, 2002). The obtained materials were characterized by nitrogen adsorption/desorption measurements, X-ray powder diffractometry (XRD), transmission electron microscopy (TEM). Particle sizes were measured by diffraction laser (DL). In order to establish colloidal stability of the system, zeta potential were measured. The syntheses routes led to obtain both, good purity of maghemite particles (more than 90 %) and their good coverage by outer silica shell. Thanks to their nanometer size and surface properties (especially, presence of amino groups which can ensure the electrostatic interaction between surface of adsorbent and adsorbate molecules), as-prepared nanocomposites can be considered as promising adsorbents. It can be found in the literature, that such systems are used in medicine as targeted drug delivery systems (Chen et al. in J Magn Magn Mater 322:2439–2445, 2010; Bele et al. in J Chromatogr B 867:160–164, 2008) or in environment protection as magnetically removable adsorbents (Giakisikli and Anthemidis in Anal Chim Acta 789:1–16, 2013; Tural et al. in J Phys Chem Solids 72:968–973, 2011).

Effective role of trifluoroacetic acid (TFA) to enhance the photocatalytic activity of F-doped TiO2 prepared by modified sol–gel method

Highly photoactive mesoporous F-doped TiO2 with improved physico-chemical characteristics is achieved using modified sol–gel method. The usage of trifluoroacetic as fluorine precursor significantly modifies the morphology, size, pore shape, crystal phase, crystal structure, surface chemical state and to a lesser extent, {101} and {001} facets. The accessibility of fluoride ions on TiOTi polymer chains during crystal growth during the sol–gel process remarkably influences the properties of catalyst. To the best of our knowledge, preparation of F-doped TiO2 using modified sol–gel and trifluoroacetic acid are limited, and still not enough. Thus this work provides additional insight by using an approach which is less hazardous, less costly and practical for large scale agile development in the photocatalysis industry.

Nanostructured Anatase Titania Spheres as Light Scattering Layer in Dye-sensitized Solar Cells

Incorporation of scattering layer on the nanocrystalline titania coating is an effective way to increase the efficiency of Dye sensitized solar cell. In this work, nanostructured titania spheres of ∼400nm size were synthesized through modified sol gel method using ethylene glycol as coordinating ligand. The anatase titania spheres were characterized using XRD, SEM and TEM. The performance of the synthesized nanostructured spherical anatase titania were studied by coating additional layers of scattering layer over the conventional photo anode. The photovoltaic performances of the dye sensitized solar cells were measured under AM1.5G solar spectrum with light intensity of 100 mW/cm2. DSSC with scattering layer achieved photovoltaic parameters such as, Voc of 0.690V, Jsc of 10.44mA/cm2, fill factor of 0.68 and solar to electric power conversion efficiency of 4.92%.

Effect of Mo-Doped Mesoporous Al-SSP Catalysts for the Catalytic Dehydration of Ethanol to Ethylene

The catalytic dehydration of ethanol to ethylene over the mesoporous Al-SSP and Mo-doped Al-SSP catalysts was investigated. The Al-SSP catalyst was first synthesized by the modified sol-gel method and then doped with Mo by impregnation to obtain 1% Mo/Al-SSP and 5% Mo/Al-SSP catalysts (1 and 5 wt% of Mo). The final catalysts were characterized using various techniques such as XRD, N2physisorption, SEM/EDX, TEM, and NH3-TPD. The catalytic activity for all catalysts in gas-phase ethanol dehydration reaction was determined at temperature range of 200°C to 400°C. It was found that the most crucial factor influencing the catalytic activities appears to be the acidity. The acid property of catalysts depended on the amount of Mo loading. Increased Mo loading in Al-SSP resulted in increased weak acid sites, which enhanced the catalytic activity. Besides acidity, the high concentration of Al at surface of catalyst is also essential to obtain high activity. Based on the results, the most suitable catalyst in this study is 1% Mo/Al-SSP catalyst, which can produce ethylene yield of ca. 90% at 300°C with slight amounts of diethyl ether (DEE) and acetaldehyde.

Double Walled Carbon Nanotube/TiO2 Nanocomposites for Photocatalytic Dye Degradation

Double walled carbon nanotube (DWCNT)/N,Pd codoped TiO2 nanocomposites were prepared by a modified sol-gel method and characterised using FTIR, Raman spectroscopy, TGA, DRUV-Vis, XRD, SEM, and TEM analyses. TEM images showed unique pearl-bead-necklace structured morphologies at higher DWCNT ratios. The nanocomposite materials showed characteristic anatase TiO2 Raman bands in addition to the carbon nanotube D and G bands. Red shifts in the UV-Vis absorption edge were observed at low DWCNT percentages. The photocatalytic activity of DWCNT/N,Pd TiO2 nanocomposite was evaluated by the photocatalytic degradation of eosin yellow under simulated solar light irradiation and the 2% DWCNT/N,Pd TiO2 nanocomposite showed the highest photoactivity while the 20% DWCNT/N,Pd TiO2 hybrid was the least efficient. The photocatalytic enhancement was attributed to the synergistic effects of the supporting and electron channeling role of the DWCNTs as well as the electron trapping effects of the platinum group metal. These phenomena favour the separation of the photogenerated electron-hole pairs, reducing their recombination rate, which consequently lead to significantly enhanced photoactivity.

Band gap and Schottky barrier engineered photocatalyst with promising solar light activity for water remediation

A novel nanophotocatalyst of Mo- and S-doped TiO2(Mo,S-codoped TiO2) was synthesizedviaa modified sol–gel method in conjunction with photochemical reduction. The nanophotocatalyst showed great potential for environmental applications.

Role of ionic and nonionic surfactant on the phase formation and morphology of Ba(Ce,Zr)O3 solid solution

Ceramic powder of BaCe0.54Zr0.36Y0.1O2.95 (BCZY) was successfully synthesized via a modified sol–gel method using metal nitrate salts as precursors. The synthesis was accomplished by using three different types of surfactants which are cationic (benzalkonium chloride), anionic (sodium dodecyl sulfate) and a nonionic surfactant (polyoxyethylene (10) oleyl ether). Citric acid and ethylene glycol were used as a chelating and a polymerization agent, respectively. The crystal form and morphology of the powders were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometer and scanning electron microscope (SEM). FTIR spectra showed the traces of carbonate residues in all samples due to the presence of hydrocarbon group in the surfactant structure even after calcination process at T = 1100 °C. Samples prepared using cationic and anionic surfactant consists of the multi-phases compounds which are dominated by BaCO3, BaCeO3, CeO2 and BaZrO3. On the other hand, the samples prepared by using nonionic surfactants produce a single phase of BCZY perovskite-type oxide. SEM images revealed that the sample prepared without surfactant exhibits severe agglomeration. Morphology of the particles for the BCZY prepared by applying the cationic and anionic surfactant was, respectively, cubical and spherical in shape. As for nonionic surfactant, the particle obtained was spherical and uniform in shape. The optimum result was obtained by adding a nonionic surfactant, Brij97, which indicates high crystallinity of the BCZY powder at a temperature of 950 °C and the particle size ranging from 20 to 80 nm. It can be concluded that surfactant affects the phase formation of BCZY ceramic powder as well as its morphology.

Size and temperature dependence of optical properties of Eu3+:Sr2CeO4 nanocrystals for their application in luminescence thermometry

The synthesis of Eu3+:Sr2CeO4 nanocrystals prepared by a modified sol–gel method is reported. The nanocrystalline powders were annealed at different temperatures to control the average grain size of nanocrystals. The absorption, emission and excitation spectra of Eu3+:Sr2CeO4 nanocrystals were investigated in a temperature range of 10–300K. In particular the influence of temperature and average nanocrystal size on the optical properties of Eu3+:Sr2CeO4 was investigated. It was found that with increasing grain size the luminescence lifetimes significantly decreased. The shortening of lifetimes was extremely strong at elevated temperature. Due to the strong temperature dependence of the f–f and charge transfer (CT) luminescence intensity ratio the Eu3+:Sr2CeO4 nanocrystals can be used in the long contact temperature sensing.

Synthesis and characterization of novel samarium-doped CuAl2O4 and its photocatalytic performance through the modified sol–gel method

A novel samarium-doped cubic phase of copper aluminate nanoparticles (Sm/CuAl2O4) were successfully synthesized by modify sol–gel method with the aid of copper(II) nitrate trihydrate, aluminum nitrate nonahydrate, samarium nitrate hexahydrate, and sucrose without adding external surfactant, capping agent or template. Besides, the effect of the dosage of sucrose on the particle size of final product was investigated. Sucrose plays role as capping agent, reducing agent, and chelating agent in the synthesis CuAl2O4 nanoparticles. The photocatalytic activities of CuAl2O4 catalysts were studied for the mineralization of methyl orange under visible light. Furthermore, samarium was doped to obtain improvement in photocatalytic activity of CuAl2O4. The copper aluminate nanoparticles were characterized by using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and EDX.

Synthesis and characterization of hierarchical porous SnO2 for enhancing ethanol sensing properties

Hierarchical porous SnO2 (HP-SnO2) nanoparticles (NPs) were synthesized via a modified sol-gel method by employing polystyrene (PS) microspheres as a template and SnCl2 as a tin source. The samples presented a three-dimensional random arrangement of macropores with average pore diameter of about 210nm, of which the pores walls were composed of NPs with the size of about 11nm. The N2-sorption analysis showed that the presence of the hierarchical mesoporous structure in the samples. The gas-sensing measurements showed that the response of HP-SnO2 based sensor reached the maximum value at the operating temperature of 240°C, which was 60°C lower than that of SnO2 based sensor. Moreover, the HP-SnO2 exhibited a significant improvement for the response and a short response-recovery time to ethanol vapor. The results indicated that HP-SnO2 NPs were of great potential for application in ethanol sensors.

Au-loaded TiO2 and Ag-loaded TiO2 synthesized by modified sol–gel/impregnation method as photocatalysts

In this work, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were synthesized by modified sol–gel method together with impregnation method. The samples were characterized by their physicochemical properties using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy in order to obtain the correlation between structure and photocatalytic properties. XRD results indicated unloaded TiO2, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were all in the anatase phase with average crystallite size in the range of 10–13 nm. In addition, XPS analysis confirmed the presence of Au and Ag elements in Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles, respectively. The photocatalytic activities of TiO2, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were evaluated through the mineralization of formic acid under UV-light illumination. The results showed that Au-loading and Ag-loading could effectively improve the photocatalytic activities of TiO2. Furthermore, Au-loaded TiO2 exhibited a higher photocatalytic activity than Ag-loaded TiO2.

Fabrication of densely packed LiNi0.5Mn1.5O4 cathode material with excellent long-term cycleability for high-voltage lithium ion batteries

Densely packed submicron polyhedral LiNi0.5Mn1.5O4 material with disordered Fd3¯m structure was synthesized via a modified sol–gel method. The as-synthesized material has a high tap density of 2.15 g cm−3, guaranteeing a high volumetric energy density for high power batteries. Electrochemical properties were investigated in both a LiNi0.5Mn1.5O4/Li half-cell and a LiNi0.5Mn1.5O4/graphite full-cell. The LiNi0.5Mn1.5O4/Li half-cell exhibits a superior cycle stability and rate capability. Here the LiNi0.5Mn1.5O4 material can deliver capacity retentions of 86% at 25 °C and 75% at 55 °C within 1000 cycles for a charge–discharge rate of 1 C. At a much higher rate of 10 C, a discharge capacity of 95 mAh g−1 can be still obtained. The LiNi0.5Mn1.5O4/graphite full-cell delivers a stable discharge capacity of 130.2 mAh g−1 at 0.2 C, corresponding to a discharge energy density as high as 576.2 Wh kg−1. After 100 cycles, the full cell can maintain a working voltage of 4.55 V and capacity retention of 84.6%. The excellent cycle stability is attributed to the dense structure, large particle size, low specific surface area and less exposed (110) facets, which dramatically reduce irreversible surface chemical reactions and manganese dissolution.

“Defect-free” interlayer with a smooth surface and controlled pore-mouth size for thin and thermally stable Pd composite membranes

Thin and thermally stable Pd membrane can be successfully coated on “defect-free” alumina sol/γ-Al2O3 interlayer with a controlled pore-mouth size of ca. 0.08 μm obtained by modified sol–gel method on macroporous α-Al2O3 support. The “modified” bubble-point method and home-developed “modified” liquid-liquid displacement method were used to check the size and amount of defects (>3 μm), and characterize pore-mouth size distribution of interlayers, respectively. The modified sol–gel method shows superiority in smoothening out defects and bumps compared to conventional suspended particles sintering method as the incorporation of alumina sol–gel particles can significantly improve the adhesion and dispersal uniformity of γ-Al2O3 particles. The synthesized Pd composite membranes of 4.5 μm thickness exhibit high hydrogen permeance and selectivity compared to similar studies. In addition, the good membrane stability was verified by the long-term operation under hydrogen permeation conditions. This can be mainly ascribed to the formation of defect-free and smooth interlayer which effectively suppress the shear stress between Pd layer and intermediate layer when enduring thermal cycles and hydrogen adsorption and desorption cycles.

La0.6Sr0.4CoO3−δ –Ce0.8Gd0.2O2−δ nanocomposites prepared by a sol–gel process for intermediate temperature solid oxide fuel cell cathode applications

La0.6Sr0.4CoO3−δ (LSC)–Ce0.8Gd0.2O2−δ (GDC) nanocomposite materials were prepared by a modified sol–gel method to improve solid oxide fuel cell cathode performance in intermediate temperature. Metal acetates precursors and citric acid combined with ethylene glycol as complex agents were used in the sol–gel process. Nano foam-like GDC powders were introduced into the sol–gel process to get the nanocomposites with the GDC content in the range of 10–50 wt%. In addition, pure LSC nano powders were also synthesized for comparison. The crystalline phases, morphologies, and elemental distributions of the pure LSC and LSC–GDC composite powders were characterized, and their electrode performances were investigated with electrochemical impedance spectroscopy. The results showed the GDC particles were largely covered by LSC, and the optimal GDC content was 30 wt% for the LSC–GDC electrode performance in this study.