Sol-gel TiO2 Research Articles

Crystallization and Optical Behaviour of Nanocomposite Sol-Gel TiO2:Ag Films

Sol-gel spin coating method was employed for depositing TiO2 and Ag-doped TiO2 films. The effects of Ag doping and the annealing temperatures (300–600 °C) were studied with respect to their structural, morphological, vibrational, and optical properties. Field Emission Scanning Electron microscopy (FESEM) investigation exhibited the grained, compact structures of TiO2-based films. Ag incorporation resulted in a rougher film surface. X-ray diffraction (XRD) results confirmed the formation of Ag nanoparticles and AgO phase, along with anatase and rutile TiO2, strongly depending on Ag concentration and technological conditions. AgO fraction diminished after high temperature annealing above 500 °C. The vibrational properties were characterized by Fourier Transform Infrared (FTIR) spectroscopy. It was found that silver presence induced changes in IR bands of TiO2 films. UV–VIS spectroscopy revealed that the embedment of Ag NPs in titania matrix resulted in higher absorbance across the visible spectral range due to local surface plasmon resonance (LSPR). Ag doping reduced the optical band gap of sol-gel TiO2 films. The optical and plasmonic modifications of TiO2:Ag thin films by the number of layers and different technological conditions (thermal and UV treatment) are discussed.

Amorphous to Crystalline Transition in Nanoimprinted Sol-Gel Titanium Oxide Metasurfaces.

Crystalline titanium dioxide (TiO2) (anatase and rutile) possesses a higher refractive index than amorphous TiO2 and near-zero absorption in the visible region, making them an ideal material for visible metasurfaces. However, fabrication limitations hinder their implementation into flat optics. In this work, a wafer-scale manufacturing platform is proposed for crystalline TiO2 metasurfaces. Sol-gel TiO2 is developed as a printable material in which its material phase can be precisely controlled to produce amorphous, anatase, or rutile, depending on the crystallization temperature. Therefore, anatase or rutile metalenses can be fabricated on a wafer scale using thermal nanoimprint lithography and sintering process. The high refractive index of the crystalline TiO2 contributes to the enhanced conversion efficiency of the fabricated metalenses. The fabricated metalenses exhibit diffraction-limited focusing and imaging capabilities, comparable to the theoretically ideal lenses.

Influence of Ag doping on structural, morphological, and optical characteristics of sol-gel spin-coated TiO2 thin films

Pure and Ag-doped Titanium dioxide (TiO2) thin films have been synthesized via the sol-gel spin coating method, and their structural, morphological, and optical properties have been investigated. X-ray diffraction analysis verifies that the polycrystalline anatase TiO2 phase is retained up to 2 % Ag doping. However, lattice expansion and grain refinement down to 25.345 nm are observed with increasing Ag content. Scanning electron microscopy (SEM) reveals the formation of large, isolated TiO2 aggregates separated by drying-induced cracks across the film surface. Optical studies show the undoped TiO2 films demonstrate excellent visible transparency (>75 % transmittance) that slightly decreases upon Ag doping, though it remains suitably high for device applications. Meanwhile, optical absorption and defect states improve with more Ag incorporation, narrowing the TiO2 bandgap from 3.83 eV (undoped) to 3.51 eV (2 % Ag-doping) due to the incorporation of Ag-induced electronic states just below the conduction band minimum. The capability to control optical and structural properties through Ag doping highlights the potential of these TiO2 films suitably tailored for photovoltaic devices or self-cleaning coatings.

TiO2 sol–gel thin films: effect of acidic and basic pH on physical characteristics

TiO2 sol–gel thin films: effect of acidic and basic pH on physical characteristics

Visible light photocatalytic response of Fe doped TiO2: Inactivation of Escherichia coli

Heterogeneous photocatalysis has been widely investigated for the removal of pollutants and pathogenic microorganisms. Various modified photocatalysts were developed for the beneficial use of solar light. E. coli inactivation by Fe doping of TiO2 (P-25) and sol–gel prepared (SynTiO2) was achieved upon solar irradiation in both isotonic (IsoT) and water matrix (WM) conditions. First order kinetic rate constants were comparatively higher for bare SynTiO2 both in IsoT (k = 0.254 min−1) and WM (k = 0.180 min−1) solutions. WM exerted an overall retardation effect for all photocatalysts except for 0.50 % Fe-TiO2 and 0.25 % Fe-SynTiO2. Release of intracellular components was followed by spectroscopic parameters as well as dissolved organic carbon (DOC) contents. E. coli cell destruction was related to the released protein, carbohydrate, and K+ ion contents. Solar photocatalytic inactivation of E. coli using novel sol–gel prepared TiO2 and Fe doped sol–gel TiO2 was successfully demonstrated as an alternative and promising method for disinfection purposes.

Synthesis, Characterization, and Photocatalytic Properties of Sol-Gel Ce-TiO2 Films

In this study, nanostructured cerium-doped TiO2 (Ce-TiO2) films with the addition of different amounts of cerium (0.00, 0.08, 0.40, 0.80, 2.40, and 4.10 wt.%) were deposited on a borosilicate glass substrate by the flow coating sol-gel process. After flow coating, the deposited films were dried at a temperature of 100 °C for 1 h, followed by calcination at a temperature of 450 °C for 2 h. For the characterization of sol-gel TiO2 films, the following analytic techniques were used: X-ray diffraction (XRD), differential thermal analysis (DTA), thermal gravimetry (TG), differential scanning calorimetry (DSC), diffuse reflectance spectroscopy (DRS), and energy dispersive X-ray spectroscopy (EDS). Sol-gel-derived Ce-TiO2 films were used for photocatalytic degradation of ciprofloxacin (CIP). The influence of the amount of Ce in TiO2 films, the duration of the photocatalytic decomposition, and the irradiation type (UV-A and simulated solar light) on the CIP degradation were monitored. Kinetics parameters (reaction kinetics constants and the half-life) of the CIP degradation, as well as photocatalytic degradation efficiency, were determined. The best photocatalytic activity was achieved by the TiO2 film doped with 0.08 wt.% Ce, under both UV-A and solar irradiation. The immobilized catalyst was successfully reused for three cycles under solar light simulator radiation, with changes in photocatalytic efficiency below 3%.

Titania-zeolite composite for tetracycline photocatalytic degradation under visible light: A comparison between doping and ion exchange

In this study, TiO2 supported over embryonic Beta zeolite (BEA) was prepared for the photocatalytic degradation of Tetracycline (TC) antibiotic under visible light. The immobilization of sol-gel TiO2 over the zeolite increased its surface area from 33 (m2/g) to 226 (m2/g) and enhanced its adsorption efficiency from 8 % to 18 %. In order to expand the photocatalytic activity of TiO2 towards the visible light region (i.e. λ > 380 nm), two different metal sensitization techniques with Iron ions from aqueous solution of FeCl3 were explored. In the ion-exchange method, the substitutional cations within the TiO2/BEA structure were exchanged with Fe3+. Whereas, in the doping technique, solgel TiO2 was doped with Fe3+ during its synthesis and before its immobilization over Zeolite. Four different samples with 20, 40, 60, and 100 % w/w of TiO2/BEA ratio were prepared. After testing the various ion-exchanged photocatalysts under blue and white lights, only Fe–60%TiO2/BEA showed better activity compared to pure TiO2 under white light at TC initial concentration, Co = 20 ppm. For the doped immobilized Titania with 60 wt% TiO2/BEA, three different doped photocatalysts were prepared with 3 %, 7 %, and 10 % per mole Fe/TiO2. All the Fe-doped TiO2/BEA photocatalysts showed better activity compared to pure TiO2 under white light. Under solar irradiations, the 3 % Fe-doped TiO2/BEA was able to degrade all TC within 120 min, while Fe–60%TiO2/BEA needed 200 min, and TiO2 needed more than 300 min. This enhanced performance was a result of both increased surface area due to immobilization over BEA as well as iron doping by Fe3+ that simultaneously increased the visible light absorption of TiO2 and minimized the charge carrier recombination effect.

Characterization and Photocatalytic and Antibacterial Properties of Ag- and TiOx-Based (x = 2, 3) Composite Nanomaterials under UV Irradiation.

Metal and metal oxide nanostructured materials have been chemically and physically characterized and tested concerning methylene blue (MB) photoremoval and UV antibacterial activity against Escherichia coli and Staphylococcus aureus. In detail, silver nanoparticles and commercial BaTiO3 nanoparticles were modified to obtain nanocomposites through sonicated sol-gel TiO2 synthesis and the photodeposition of Ag nanoparticles, respectively. The characterization results of pristine nanomaterials and synthetized photocatalysts revealed significant differences in specific surface area (SSA), the presence of impurities in commercial Ag nanoparticles, an anatase phase with brookite traces for TiO2-based nanomaterials, and a mixed cubic-tetragonal phase for BaTiO3. Silver nanoparticles exhibited superior antibacterial activity at different dosages; however, they were inactive in the photoremoval of the dye. The silver-TiOx nanocomposite demonstrated an activity in the UV photodegradation of MB and UV inhibition of bacterial growth. Specifically, TiO2/AgNP (30-50 nm) reduced growth by 487.5 and 1.1 × 103 times for Escherichia coli and Staphylococcus aureus, respectively, at a dose of 500 μg/mL under UV irradiation.

Sol-Gel Multilayered Niobium (Vanadium)-Doped TiO2 for CO Sensing and Photocatalytic Degradation of Methylene Blue.

Multilayered TiO2 films doped either with Niobium or Vanadium (1.2 at. %) were deposited by the sol-gel dip coating method on c-Si and glass substrates. The films on glass substrates were tested for CO sensing and photocatalytic degradation of methylene blue. X-ray diffraction data analysis showed that all the TiO2:Nb(V) films were nanocrystalline in the anatase phase, with a uniform and compact microstructure and a homogeneous superficial structure of small grains with diameters in the range of 13-19 nm. For the electrical characterization, the TiO2:Nb(V) films were incorporated in Metal-Insulator-Semiconductor (MIS) structures. The specific resistivity is of the order of 104 Ωcm and its value decreases with increasing the electrical field, which testifies to the injection of electrons into these layers. From the analysis of the current-voltage curves taken at different temperature- and frequency-dependent capacitance-voltage and conductance-voltage characteristics, the density and parameters of deep levels in these TiO2 films are evaluated and the electron charge transport mechanism is established. It was shown that the current in these TiO2:Nb(V)-Si MIS structures is mainly carried out by inter-trap tunneling via deep levels energetically distributed in the TiO2 bandgap. Testing these sol-gel TiO2:Nb(V) layers for gas sensing and photocatalytic capabilities proved that they could serve such purposes. In particular, the results of the V-doped sol-gel TiO2 film confirm its CO detection capability, which is rarely reported in the literature. For the photodegradation of methylene blue, the Nb-doped TiO2 samples were superior, with nearly double the photocatalytic efficiency of undoped TiO2.

The Solvent Role for the Decomposition of Paracetamol in Distilled and Drinking Water by Pure and Ag-Modified TiO2 Sol-Gel Powders.

In this study, pure TiO2 gels were synthesized by applying the sol-gel method, using Ti(IV) butoxide with the addition of two different solvents, namely ethylene glycol (EG) and isopropanol (isop), with only air moisture present. It was established using XRD that the gel prepared with the addition of EG was amorphous even at 400 °C, while the other gel was amorphous up to 300 °C. It was found that TiO2 (anatase) had a dominant crystalline phase during heating to 600 °C, while at 700 °C, TiO2 (rutile) appeared. The as-obtained powdered materials were annealed at 500 °C and subsequently underwent photocatalytic tests with paracetamol. Additionally, the TiO2 samples were modified with Ag+ co-catalysts (10-2 M), using photofixation by UV illumination. The photocatalytic activity of the Ag-modified powders was also tested in the photodegradation of a commonly used paracetamol in aqueous solution under UV light illumination. The obtained data exhibited that the annealed samples had better photocatalytic efficiency and decomposed paracetamol faster in comparison to the non-annealed sol-gel powders. The highest degradation efficiency was observed for the TBT/isop/Ag material, with degradation efficiencies average values of 65.59% and 75.61% paracetamol achieved after the third cycle of photocatalytic treatment. The co-catalytically modified powders had higher photocatalytic efficiency in comparison to the pure nanosized powders. Moreover, the sol-gel powders of TBT/EG, TBT/EG/Ag (10-2 M), TBT/isop, and TBT/isop/Ag (10-2 M) demonstrated the ability to retain their photocatalytic activity even after three cycles of use, suggesting that they could find practical use in the treatment of pharmaceutical wastewater. The observed photocatalytic efficiency and positive impact of silver make the prepared powders a desirable choice for pharmaceutical drug degradation, helping to promote environmentally friendly and effective wastewater treatment technology.

Enhancing the Photocatalytic Activity of Immobilized TiO2 Using Laser-Micropatterned Surfaces

In the past, the application of TiO2 slurry reactors has faced difficulties concerning the recovery and reusability of the catalyst. In response to these challenges, immobilized photocatalyst systems have been investigated, wherein the catalyst is fixed onto a solid support, frequently with reduced photocatalytic performance. In the present study, thin TiO2 films were developed in the anatase phase by the sol-gel process and spin-cast on laser-microstructured silicon substrates, to form photocatalytic surfaces of increased activity. The TiO2 films were thoroughly characterized using SEM-EDX, XRD, UV–Vis spectroscopy, and Raman spectroscopy. The photocatalytic activity of these surfaces was evaluated by the degradation of atrazine in aqueous solution under UV irradiation. Their photocatalytic activity was found to be significantly enhanced (mean kobs 24.1 × 10−3 min−1) when they are deposited on laser-microstructured silicon compared with flat silicon (mean kobs 4.9 × 10−3 min−1), approaching the photocatalytic activity of sol-gel TiO2 fortified with Degussa P25, used as a reference material (mean kobs 32.7 × 10−3 min−1). During the photocatalytic process, several transformation products (TPs) of atrazine, namely 2-chloro-4-(isopropylamino)-6-amino-s-triazine (CIAT), 2-chloro-4-amino-6-(ethylamino)-s-triazine (CAET), and 2-chloro-4.6-diamino-s-triazine (CAAT), were identified with LC–MS/MS. The stability of the photocatalytic surfaces was also investigated and remained unchanged through multiple cycles of usage. The surfaces were further tested with two other pollutants, i.e., 2,4,6-trichlorophenol and bisphenol-a, showing similar photocatalytic activity as with atrazine.

Hydrophilic sol-gel TiO2 coating on procaine-loaded injector needle for painless clinical treatments

Titanium dioxide (TiO2) coatings are demanded in clinical applications due to their biocompatible, porosity, and semiconducting properties. Drug release studies take advantage of these unique aspects of TiO2 for painless injection for those who have to take medicine through the injection frequently. In this study, TiO2 was prepared via the sol-gel method with Titanium tetra isopropoxide (TTIP) precursor in alcohol solvent for pH 3, 4, and 5 values. The prepared solution was coated on stainless steel substrates and injectors via dip coating. Following these steps, samples were calcinated at various temperatures (100°C, 300°C, 500°C, 700°C). The structural, physical, and chemical composition, chemical bond, wettability, and drug-release properties of coated samples were researched. Contact angle values affirmed that high temperatures and ultraviolet (UV)-light irradiation made samples more hydrophilic (26°±5° at 700°C for pH 4). Procaine, a short-time period local anaesthetic, was chosen as a model drug. Increased calcination temperature and raised hydrophilicity led to improve the released drug amount. Drug release studies were carried out using Franz diffusion cells at 36.5°C. Samples at 500°C calcinated released the highest amount of drug (90%) for 45 sec injection time. This study shed light on how TiO2 coating can be successfully utilized for clinical applications in the future.

Investigation of the anatase-to-rutile transition for TiO2 sol-gel coatings with refractive index up to 2.7

This work describes the elaboration of rutile titanium dioxide films with high refractive indices and low scattering losses by sol-gel process and controlled crystallization. The evolutions of the optical properties and crystalline structure of sol-gel processed titania coatings on fused silica were investigated for different thermal budgets of the annealing post-treatment using ellipsometry, spectrophotometry, X-ray diffraction and electronic microscopy. It reveals that anatase and rutile coatings with refractive indices of 2.51 and 2.73 can be prepared with associated optical loss of 0.5 % and 1 %, respectively, which are an excellent compromise for applications in integrated photonics. These evolutions are associated to the thermally induced mass transfer and phase transitions occurring during thermal annealing that involves first the nucleation growth and sintering of anatase polyoriented nanocrystals, followed by the transformation into rutile polyoriented nanocrystals. Concomitantly, rutile crystals with (110) faces parallel to the surface consume surrounding anatase and rutile nanocrystals by diffusive sintering to yield micron-size rutile monocrystalline and monooriented platelets patchwork, exhibiting refractive index of 2.73 and 1.2 % optical loss. The formation of these platelets is governed by surface energies and is responsible for the increase in optical loss.

Synthesis of sol-gel TiO2 nanoparticles and assessment of their antifungal activity for the eventual conservation of historical documents

One of the main causes of deterioration of ancient documents is the presence of microorganisms, especially fungi. In this study, we report on the detection of microbiological contamination in ancient books from the Franciscan Library of San Pedro Cholula, in the state of Puebla, Mexico. The microscopic observation of different organic pigments and in vitro assays indicated the presence of Rhizopus sp., Mucor sp., and Alternaria sp. on the papers. The fungicidal activity of TiO2 nanoparticles (NPs), synthesized by the sol gel process, was then evaluated against these strains by two different methods: i) the agar well diffusion method using Petri dishes and ii) in pieces of old book pages, where the strains had been previously incubated. From TEM measurements, it was determined that the TiO2 NPs had a diameter of 70 nm. Anatase TiO2 NPs were synthesized as indicated by Raman spectroscopy and XRD. From UV–Vis spectroscopy and the Tauc´s method for an indirect band-gap semiconductor, a band-gap energy value of 2.9 eV was obtained. The surface chemistry of the TiO2 NPs/paper substrates was analyzed by XPS. In addition, a core-level XPS analysis of the O 1s and C 1s orbitals was used to identify signals related to cellulose. The antifungal activity of TiO2 NPs was demonstrated for the investigated fungi. A higher inhibition occurred for Rhizopus sp., followed by Mucor sp., and Alternaria sp. with inhibition halos of 26, 24, and 18 % in diameter, respectively. This work used highly sensitive techniques with the aim of proposing methodologies that contribute to the preservation of historical documents.

Effect of sintering aid combined vacuum infiltration on the properties of Al2O3-based ceramics via binder jetting

Binder Jetting (BJ) technology enables cost-effective and efficient fabrication of complex Al2O3-based ceramic components. However, in the process of manufacturing Al2O3-based ceramics using BJ, issues such as high sintering temperatures and relatively low sintered strength and relative density are encountered. In this study, we investigated the MnO2 sintering aid in combination with TiO2 sol-gel vacuum infiltration to introduce a MnO-TiO2-Al2O3 ternary sintering system, which could reduce the sintering temperature and enhance the strength and relative density of Al2O3-based ceramics. Through single-factor and response surface experiments, the effects of MnO2 addition, green body sintering temperature, infiltration time, and infiltration vacuum level on the properties and reinforcement mechanism of BJ Al2O3-based ceramics were studied. The research results revealed that with 10% MnO2 addition, a sintering temperature of 1450 °C, infiltration time of 60 s, and infiltration vacuum level of 24 KPa, the bending strength and sintered relative density of Al2O3-based ceramics reached 113.79 MPa and 78.13%, respectively. The bending strength was 48 times higher than that of the Al2O3 ceramic samples without sintering aid composite infiltration treatment, and the sintered relative density was improved by 41.85%.

Sol–gel catalysts immobilized on stainless steel meshes for Ba2+ removal in a continuous flow process: An experimental design

Abstract This study describes the use of a continuous flow system for photocatalytic reactions employing a TiO2 sol–gel structured catalyst. The catalyst was immobilized on various stainless steel meshes to investigate the barium(II) removal. To verify its photocatalytic activity, batch tests were carried out and the results were compared to the commercial catalyst P25. Effects of thermal treatment on the structured catalyst were investigated. The continuous flow photocatalytic tests were conducted under different experimental conditions through an experimental design to verify the effect of the parameters (pH and volume flow). The results of the batch tests indicated that the TiO2 sol–gel catalyst showed very similar activity to the TiO2 P25 when used in powder suspension (32% reduction of Ba2+). In the continuous flow process, maximum adhesion of catalysts on meshes was found at a calcination temperature of 623 K. The experimental design indicated the pH as a significant parameter in the studied conditions. It was observed that at pH levels close to 7, also indicated by the study of the zero charge point and lower flow rates, it was possible to obtain ∼20% removal of Ba2+ ions, in a continuous flow reactor with a residence time of 83 min.

Selectivity of Sol-Gel and Hydrothermal TiO2 Nanoparticles towards Photocatalytic Degradation of Cationic and Anionic Dyes.

Titanium dioxide (TiO2) nanoparticles have been extensively studied for catalyzing the photo-degradation of organic pollutants, the photocatalyst being nonselective to the substrate. We, however, found that TiO2 nanoparticles prepared via the sol-gel and hydrothermal synthetic routes each possess a definite specificity to the charge of the substrate for photodegradation. The nanoparticles were characterized by SEM, FTIR, XRD, TGA, and UV-visible spectra, and the photocatalytic degradation under UV-B (285 nm) irradiation of two model compounds, anionic methyl Orange (MO) and cationic methylene blue (MB) was monitored by a UV-visible spectrophotometer. Untreated sol-gel TiO2 nanoparticles (Tsg) preferentially degraded MO over MB (90% versus 40% in two hours), while after calcination at 400 °C for two hours (Tsgc) they showed reversed specificity (50% MO versus 90% MB in one hour). The as-prepared hydrothermal TiO2 nanoparticles (Tht) behaved in the opposite sense of Tsg (41% MO versus 91% MB degraded in one and a half hours); calcination at 400 °C (Thtc) did not reverse the trend but enhanced the efficiency of degradation. The study indicates that TiO2 nanoparticles can be made to degrade a specific class of organic pollutants from an effluent facilitating the recycling of a specific class of pollutants for cost-effective effluent management.

Inverse effects of lanthanide co-doping on the photocatalytic hydrogen production and dye degradation activities of Cu doped sol-gel TiO2

Copper doped and lanthanide-copper co-doped titania powders were prepared by sol–gel technique and the effects of co-doping on the photocatalytic reduction and oxidation activities of titania were investigated in this work. Characterization studies indicated that a reduced structure was formed due to the presence of Ti3+ species in copper doped titania powder and a more stable structure was formed when lanthanides were used as co-dopants. Copper doped powder had a significantly higher activity in photocatalytic hydrogen production (1037 μmol/g/h) than the co-doped powders (∼400 μmol/g/h). The oxidation activities of co-doped powders however were determined to be about 2 times higher than that of the copper doped powder. The decrease in the reduction activity was attributed to the decrease in the number of Ti3+ sites, whereas the increase in oxidation activity was probably a result of the increase in the surface area and dye adsorption due to lanthanide co-doping.

Induced surface photovoltage in TiO2 sol-gel nanoparticles

Induced surface photovoltage in TiO2 sol-gel nanoparticles

Ti doped hematite photoanodes: Protective coverage by titania overlayers

In this work, the photoresponse of Ti doped hematite electrodes was optimized by adjusting the thickness and the level of doping. The electrodes were then covered by a TiO2 overlayer by dip coating (DC) or by atomic layer deposition (ALD) to improve chemical stability. Coverage of hematite by a dip-coated sol–gel TiO2 film of thickness up to 135 nm resulted only in a small decrease in photocurrent (by about 30 %). A similar decrease in photocurrent (about 25 %) was observed after the coverage by a very thin (2 nm) ALD TiO2 film while the increase of the thickness to 8 nm led to almost complete suppression of photocurrent. This behaviour can be explained by the different morphology and structure of the overlayers. Although the surface morphology of sol–gel TiO2 films was very smooth and dense, penetration of such films by the electrolyte occurred even for a thickness of 135 nm. On the other hand, much thinner ALD TiO2 films (8 nm) exhibited almost no electrolyte penetration. Such different blocking properties of the two TiO2 overlayers are in direct agreement with the observed dissolution rate in acidic media – the better the blocking properties of an overlayer the better the chemical stability of stratified hematite/titania photoelectrode.