Aqueous Particulate Sol Gel Research Articles

A facile particulate sol–gel route to synthesize nanostructured CoTiO3 thin films and powders and their characteristics

Nanostructured CoTiO3 thin films and powders were prepared by a straightforward aqueous particulate sol–gel route. Titanium(IV) isopropoxide and cobalt chloride were used as titanium and cobalt precursors, respectively. Also, hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. The effect of Co:Ti molar ratio and annealing temperature were studied on the crystallization behavior and chemical properties of the products. X-ray diffraction and Fourier transform infrared spectroscopy revealed that the powders crystallized at the low annealing temperature of 300 °C for 1 h, containing anatase-TiO2, rutile-TiO2, CoTiO3 and Co3O4 phases, depending on annealing temperature and Co:Ti molar ratio. Furthermore, TiO2 transformation from anatase to rutile phase occurred at 500 °C. The activation energy of crystallite growth was calculated in the range of 3.1–8.5 kJ/mol. Simultaneous differential thermal analysis showed that the final annealing temperature to obtain organic-free cobalt titanate powders could be determined at 560 °C. Field emission scanning electron microscope analysis revealed that the deposited thin films had crystallite and nanostructured morphology with the average grain size in the range 22–32 nm at 500 °C. Atomic force microscopy illustrated 2D and 3D topographies of thin films annealed at 500 °C for 1 h showed that the deposited films had homogeneous, rough structure with nanosized grains.

Semiconductor TiO2–Al2O3 thin film gas sensors derived from aqueous particulate sol–gel process

Nanostructured TiO2–Al2O3 films and powders were prepared by a straightforward aqueous particulate sol–gel route. Titanium (IV) isopropoxide and aluminum chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the porosity. The effect of Al:Ti molar ratio was studied on the crystallization behavior of the products. X-ray diffraction (XRD) revealed that the powders crystallized at 800°C, containing anatase-TiO2, rutile-TiO2 and cubic-Al2O3 phases. Furthermore, it was found that Al2O3 retarded the anatase to rutile transformation. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO2–Al2O3 binary mixed oxide, being 3nm at 600°C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20–70nm at 800°C depending on Al:Ti molar ratio. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at operating temperature of 400°C.

Sensor Performance of Nanostructured TiO2–Cr2O3 Thin Films Derived by a Particulate Sol–Gel Route with Various Cr:Ti Molar Ratios

Nanocrystalline and nanostructured TiO2–Cr2O3 thin films and powders were prepared by a facile and straightforward aqueous particulate sol–gel route at low temperature of 400°C. The prepared sols showed a narrow particle size distribution with hydrodynamic diameter in the range of 17.7 nm to 19.0 nm. Moreover, the sols were stable over 4 months, with constant zeta potential measured during this period. The effect of the Cr:Ti molar ratio on the crystallization behavior of the products was studied. X-ray diffraction (XRD) analysis revealed that the powders crystallized at low temperature of 400°C, containing anatase-TiO2, rutile-TiO2, and Cr2O3 phases, depending on the annealing temperature and Cr:Ti molar ratio. Furthermore, it was found that Cr2O3 retarded the anatase to rutile transformation up to 800°C. The activation energy of crystallite growth was calculated to be in the range of 1.3 kJ/mol to 2.9 kJ/mol. Transmission electron microscopy (TEM) imaging showed that one of the smallest crystallite sizes was obtained for TiO2–Cr2O3 binary mixed oxide, being 5 nm at 500°C. Field-emission scanning electron microscopy (FESEM) analysis revealed that the deposited thin films had nanostructured morphology with average grain size in the range of 20 nm to 40 nm at 500°C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of NO2 gas at low operating temperature of 200°C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, calibration curves revealed that TiO2–Cr2O3 sensors followed the power law \({S = A[\mathrm{gas}]^{B}}\) (where S is the sensor response, the coefficients A and B are constants, and [gas] is the gas concentration) for two types of gas, exhibiting excellent capability for detection of low gas concentrations.

Sensor Performance of Nanostructured TiO2–SnO2 Films Prepared by an Aqueous Sol–Gel Process

Nanostructured TiO2–SnO2 thin films and powders were prepared by a facile aqueous particulate sol–gel route. The prepared sols showed a narrow particle size distribution with hydrodynamic diameter in the range 17.2–19.3 nm. Moreover, the sols were stable over 5 months, since the constant zeta potential was measured during this period. The effect of Sn:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction analysis revealed that the powders were crystallised at the low temperature of 400 °C containing anatase-TiO2, rutile-TiO2 and cassiterite-SnO2 phases, depending on annealing temperature and Sn:Ti molar ratio. Furthermore, it was found that SnO2 retarded the anatase to rutile transformation up to 800 °C. The activation energy of crystallite growth was calculated in the range 0.96–6.87 kJ/mol. Transmission electron microscope image showed that one of the smallest crystallite sizes was obtained for TiO2–SnO2 binary mixed oxide, being 3 nm at 600 °C. Field emission scanning electron microscope analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20–40 nm at 600 °C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption.

Influence of annealing temperature on the structural and anti-corrosion characteristics of sol–gel derived, spin-coated thin films

Recently, an aqueous particulate sol–gel process using metallic chloride precursors was introduced to synthesize zirconium titanate. In this paper, the effect of annealing temperature on the structural and corrosion protection characteristics of spin-coated thin films obtained from this sol–gel system was investigated. Based on scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic reflectometry studies, it was found that the flatness and thickness of the thin films were decreased by increasing the annealing temperature. Also, the corrosion protection of stainless steel AISI 316L provided by the prepared coatings, as analyzed by electrochemical potentiodynamic polarization experiments in a simulated body fluid, was improved in this order: 500°C-annealed sample<900°C-annealed sample<700°C-annealed sample, attributed to a compromise between the defect density and the adhesion of the films to the substrate.

Low temperature nanocrystalline TiO2–Fe2O3 mixed oxide by a particulate sol–gel route: Physical and sensing characteristics

Nanocrystalline TiO2–Fe2O3 thin films and powders were prepared by a straightforward aqueous particulate sol–gel route at the low temperature of 300°C. Titanium(IV) isopropoxide and iron(III) chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powder crystallised at the low temperature of 300°C, containing anatase-TiO2 and hematite-Fe2O3 phases. Furthermore, it was found that Fe2O3 retarded the anatase-to-rutile transformation up to 500°C. The activation energies for crystallite growth of TiO2 and Fe2O3 components in the binary system were calculated 10.62 and 0.67kJ/mol, respectively. Moreover, one of the smallest crystallite sizes was obtained for TiO2–Fe2O3 binary mixed oxide, being 6nm at 300°C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanostructured morphology. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas (i.e., 25ppm) at low operating temperature of 150°C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, TiO2–Fe2O3 sensors follow the power law for the detection of CO gas.

Zirconium titanate thin film prepared by an aqueous particulate sol–gel spin coating process using carboxymethyl cellulose as dispersant

This paper deals with the preparation of ZrTiO4 thin film by a novel aqueous particulate sol–gel deposition method using carboxymethyl cellulose as dispersant. The structural characterization was performed by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. According to the results, the amorphous xerogel crystallizes to polycrystalline ZrTiO4 nanoparticles due to structural ordering conducted by calcination at 700°C. A well-covering, crack-free, and homogeneous ZrTiO4 thin film was processed, which is attributable to the efficient role of the dispersing agent in the aqueous sol. It was also found that the outermost layer of the coating surface consists of nanoparticles with 20nm in size.

Multilayer zirconium titanate thin films prepared by a sol–gel deposition method

Zirconium titanate multilayer thin films were prepared by an aqueous particulate sol–gel process followed by spin coating. The obtained structures were studied by transmission electron microscope, scanning electron microscope, atomic force microscope, and spectroscopic reflection analyses. According to the results, sound thin films up to three layers were developed, accompanied by an increase in thickness and roughness by increasing the number of the layers. It was also found that the coatings consist of globular nanoparticles with an average diameter of 50nm. Considering the contribution of roughness to biological responses, the optimization of the surface characteristics to meet an optimal performance seems to be a challenging issue, which demands future studies.

Tailoring of morphology and crystal structure of nanomaterials in MgO–TiO2 system by controlling Mg:Ti molar ratio

The morphological manipulation and structural characterisation of TiO2–MgO binary system by an aqueous particulate sol–gel route were reported. Different crystal structures including pure MgTiO3, mixtures of MgTiO3 and TiO2 and mixtures of MgTiO3 and Mg2TiO4 were tailored by controlling Mg:Ti molar ratio and annealing temperatures as the processing parameters. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that all compounds crystallised at the low temperature of 500 °C. Furthermore, it was found that the average crystallite size of the compounds depends upon the Mg:Ti molar ratio as well as the annealing temperature, being in the range 3–5 nm at 500 °C and around 6 nm at 700 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanocrystalline structure with the average grain size of 25–30 nm at 500 °C depending upon the Mg:Ti molar ratio. Moreover, atomic force microscope (AFM) images presented that the thin films had a hill-valley like morphology made up of small grains.

Dye-sensitized solar cells based on a single layer deposition of TiO2 from a new formulation paste and their photovoltaic performance

A new strategy for enhancing the efficiency and reducing the production cost of TiO2 solar cells by design of a new formulated TiO2 paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO2 compound. Different TiO2 pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol–gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO2 paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO2 photoanode electrodes for solar cell application. Photovoltaic measurements showed that TiO2 solar cell with pure anatase crystal structure had higher power conversion efficiency (PCE) than that made of pure rutile-TiO2. However, the PCE of solar cells depends on the anatase to rutile weight ratio, reaching a maximum at a specific value due to the synergic effect between anatase and rutile TiO2 nanoparticles. Moreover, it was found that the PCE of solar cells made of crystalline TiO2 powders was much higher, increasing in the range 32–84% depending on anatase to rutile weight ratio, than that of prepared by amorphous powders. TiO2 solar cell with the morphology of mixtures of nanoparticles and microparticles had higher PCE than the solar cell with the same phase composition containing TiO2 nanoparticles due to the role of TiO2 microparticles as light scattering particles. The presented strategy would open up new insight into fabrication and structural design of low-cost TiO2 solar cells with high power conversion efficiency.

Synthesis of Nanostructured and Nanoporous TiO2-AgO Mixed Oxide Derived from a Particulate Sol-Gel Route: Physical and Sensing Characteristics

Nanocrystalline TiO2-AgO thin films and powders were prepared by an aqueous particulate sol-gel route at the low temperature of 573 K (300 °C). Titanium tetraisopropoxide and silver nitrate were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the phase composition of the mixed oxide depends upon the annealing temperature, being a mixture of TiO2 and AgO in the range 573 K to 773 K (300 °C to 500 °C) and a mixture of TiO2, AgO, and Ag2O at 973 K (700 °C). Furthermore, one of the smallest crystallite sizes was obtained for TiO2-AgO mixed oxide, being 4 nm at 773 K (500 °C). Field emission–scanning electron microscopic (FE-SEM) and atomic force microscopic (AFM) images revealed that the deposited thin films had nanostructured and nanoporous morphology with columnar topography. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response toward low concentrations of CO gas (i.e., 25 ppm) at low operating temperature of 473 K (200 °C), resulting in an increase of the thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, TiO2-AgO sensors follow the power law for the detection of CO gas.

Synthesis and characterisation of nanosized TiO 2–ZrO 2 binary system prepared by an aqueous sol–gel process: Physical and sensing properties

Nanostructured TiO 2–ZrO 2 thin films and powders were prepared by a straightforward aqueous particulate sol–gel route. Titanium (IV) isopropoxide and zirconium (IV) acetate hydrate were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that the powder were crystallised at the low temperature of 500 °C, containing anatase-TiO 2 and tetragonal-ZrO 2 phases. Furthermore, it was found that ZrO 2 retarded the anatase-to-rutile transformation up to 900 °C. The activation energies for crystallite growth of TiO 2 and ZrO 2 components in the binary system were calculated 10.16 and 3.12 kJ/mol, respectively. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO 2–ZrO 2 binary mixed oxide, being 5 nm at 500 °C. Field emission scanning electron microscope (FESEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size of 20 nm at 500 °C and 36 nm at 900 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO and NO 2 gases at low operating temperature of 150 °C, resulted in an increase of thermal stability of sensing films as well as a decrease in the power consumption. Furthermore, calibration curves revealed that TiO 2–ZrO 2 sensor follows the power law, S = A[ gas] B (where S is sensor response, coefficients A and B are constants and [ gas] is gas concentration) for the two types of gases, and it has excellent capability for the detection of low gas concentrations.

Nanostructured TiO 2–CeO 2 mixed oxides by an aqueous sol–gel process: Effect of Ce:Ti molar ratio on physical and sensing properties

Nanostructured TiO 2–CeO 2 thin films and powders were prepared by a straightforward aqueous particulate sol–gel route. Titanium (IV) isopropoxide and cerium chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. The effect of Ce:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders crystallised at the low temperature of 500 °C, containing anatase–TiO 2, rutile–TiO 2 and cubic-CeO 2 phases, as well as Ti 8O 15, Ti 3O 5 and Ce 11O 20 depending on annealing temperature and Ce:Ti molar ratio. Furthermore, it was found that CeO 2 retarded the anatase to rutile transformation up to 700 °C. The activation energy of crystallite growth was calculated in the range 1.92–8.79 kJ/mol. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO 2–CeO 2 binary mixed oxide, being 3 nm at 500 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 17–28 nm at 500 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, calibration curves revealed that TiO 2–CeO 2 sensors follow the power law, S = A[gas] B (where S is sensor response, coefficients A and B are constants and [gas] is the gas concentration) for the two types of gases, and they have excellent capability for the detection of low gas concentrations.

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li4Ti5O12 and Li2TiO3) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m2/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.

Low temperature nanostructured zinc titanate by an aqueous particulate sol–gel route: Optimisation of heat treatment condition based on Zn:Ti molar ratio

Nanocrystalline zinc titanate (ZnTiO 3) thin films and powders with purity of 94% were produced at the low sintering temperature of 500 °C and the short sintering time of 1 h by a straightforward aqueous particulate sol–gel route. The effect of Zn:Ti molar ratio was studied on the crystallisation behaviour of zinc titanates. The prepared sols showed a narrow particle size distribution in the range 17–19 nm. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders contained mixtures of the rhombohedral-ZnTiO 3, cubic-ZnO, cubic-Zn 2TiO 4 phases, as well as the anatase-TiO 2 and the rutile-TiO 2 depending on the sintering temperature and Zn:Ti molar ratio. Moreover, it was found that Zn:Ti molar ratio and sintering temperature influence the preferable orientation growth of the zinc titanate, being on (2 1 1) planes for molar ratios of Zn:Ti = 25:75 and 50:50 and on ( 1 1 ¯ 0 ) planes for molar ratio of Zn:Ti = 75:25 at sintering temperature of 600 °C. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was around 2 nm and a gradual increase occurred up to 8 nm by heat treatment at 1000 °C. The activation energy for crystal growth of nanocrystalline ZnTiO 3 calculated in the range 07.86–14.79 kJ/mol. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 19–23 nm at 600 °C and 34–39 nm at 800 °C depending upon the Zn:Ti molar ratio.