Sol-gel Dip-coating Technique Research Articles

Solar-Induced Photocatalytic Degradation of Reactive Red and Turquoise Dyes Using a Titanium Oxide/Xanthan Gum Composite

The present study explores the solar-induced photocatalytic degradation of reactive red (RR) and reactive turquoise (RT) dyes in a single system using TiO2 immobilized in xanthan gum (TiO2/XG), synthesized using the sol–gel dip-coating technique for direct precipitation. SEM-EDX, XRD, FTIR, and UV–Vis were used to assess the characteristics of the resulting catalyst. Moreover, the effects of different operating parameters, specifically pH, dye concentration, TiO2/XG concentration, H2O2 concentration, and contact time, were also investigated in a batch photocatalytic reactor. The immobilized TiO2/XG catalyst showed a slight adsorption degradation efficiency and then improved the RR and RT dye degradation activity (92.5 and 90.8% in 120 min) under solar light with a remarkable Langmuir–Hinshelwood pseudo-first-order degradation rate of 0.0183 and 0.0151 min−1, respectively, under optimum conditions of pH 5, dye concentration of 25 mg/L, TiO2/XG concentration of 25 mg/L, H2O2 concentration of 400 mg/L, and reaction time of 120 min. The improved photocatalytic ability was ascribed to the impact of TiO2/XG nanoparticles with a high surface area, and lower band gap energy. Solar light energy has significant potential for addressing energy deficit and water pollution concerns.

Fabrication of ordered layered SnO2/TiO2 heterostructures and their photocatalytic performance for methyl blue degradation.

The rapid growth in population and industrialization has given rise to serious environmental issues, especially the water pollution. Photocatalysis with the assist of semiconductor photocatalysts has been considered as an advanced oxidation technique for degrading a variety of pollutants under solar irradiation. In this work, we have fabricated SnO2-TiO2 heterostructures with different ordered layers of SnO2 and TiO2 via the sol-gel dip-coating technique and utilized in photocatalysis for degradation of methyl blue dye under UV irradiation. The influence of the layer's position on SnO2 and TiO2 properties is investigated via the various techniques. The grazing incidence X-ray diffraction (GIXRD) analysis reveals that the as-prepared films exhibit pure anatase TiO2 and kesterite SnO2 phases. The 2SnO2/2TiO2 heterostructure exhibit the maximum crystallite size and smallest deviation from the ideal structure. Scanning electron microscopy cross-section images manifest good adhesion of the layers to each other and to the substrate. Fourier transform infrared spectroscopy reveals the characteristic vibration modes of SnO2 and TiO2 phases. UV-visible spectroscopy measurements indicate that all films exhibit high transparency (T = 80%) and the SnO2 film reveals a direct band gap of 3.6eV, while the TiO2 film exhibits an indirect band gap of 2.9eV. The optimal 2SnO2/2TiO2 heterostructure film revealed best photocatalytic degradation performance and the reaction rate constant for methylene blue solution under UV irradiation. This work will trigger the development of highly efficient heterostructure photocatalysts for environmental remediation.

Zinc Oxide Films Fabricated via Sol-Gel Method and Dip-Coating Technique-Effect of Sol Aging on Optical Properties, Morphology and Photocatalytic Activity.

Zinc oxide layers on soda-lime glass substrates were fabricated using the sol-gel method and the dip-coating technique. Zinc acetate dihydrate was applied as the precursor, while diethanolamine as the stabilizing agent. This study aimed to determine what effect has the duration of the sol aging process on the properties of fabricated ZnO films. Investigations were carried out with the sol that was aged during the period from 2 to 64 days. The sol was studied using the dynamic light scattering method to determine its distribution of molecule size. The properties of ZnO layers were studied using the following methods: scanning electron microscopy, atomic force microscopy, transmission and reflection spectroscopy in the UV-Vis range, and the goniometric method for determination of the water contact angle. Furthermore, photocatalytic properties of ZnO layers were studied by the observation and quantification of the methylene blue dye degradation in an aqueous solution under UV illumination. Our studies showed that ZnO layers have grain structure, and their physical-chemical properties depend on the duration of aging. The strongest photocatalytic activity was observed for layers produced from the sol that was aged over 30 days. These layers have also the greatest porosity (37.1%) and the largest water contact angle (68.53°). Our studies have also shown that there are two absorption bands in studied ZnO layers, and values of optical energy band gaps determined from positions of maxima in reflectance characteristics are equal to those determined using the Tauc method. Optical energy band gaps of the ZnO layer fabricated from the sol aged over 30 days are EgI = 4.485 eV and EgII = 3.300 eV for the first and second bands, respectively. This layer also showed the highest photocatalytic activity, causing the pollution to degrade 79.5% after 120 min of UV irradiation. We believe that ZnO layers presented here, thanks to their attractive photocatalytic properties, may find application in environmental protection for the degradation of organic pollutants.

Structural and Optical Properties of TiO<sub>2</sub> Thin Films prepared by the Dip-Coating Method: Effect of Thickness and Annealing Temperature

In this work, the Sol-Gel dip-coating technique is used to report the effect of thickness and annealing temperature on structural and optical properties of TiO2 thin films. To study the effect of the annealing temperature, the prepared samples were annealed at different temperatures: 300, 400, and 500 °C for 1 h. By increasing the annealing temperature, an amelioration of the crystalline quality is observed. The best crystalline quality was obtained at 500 °C. Additionally, the band gap value Eg, evaluated from transmission spectra, does not vary with the increasing of the annealing temperature. All the films with different thicknesses present crystalize in the Anatase structure, and the crystallite size value does not practically change with thickness increase. It was also found that the TiO2 film band gap value decreases with the film thickness increase, demonstrating the possibility of band gap tuning by varying the TiO2 film thickness.

Numerical scrutiny of a silica-titania-based reverse rib waveguide with vertical and rounded sidewalls.

In this work, a modal analysis of reverse rib waveguide (RRW) structures based on a silica-titania platform is carried out. The silica-titania waveguide films can be deposited via the sol-gel method and dip-coating technique. To combine this low-cost deposition technique with the economical fabrication method, we propose to structure the samples via wet-chemical etching. Due to the isotropic nature of wet etching, the waveguide architecture with rounded sidewalls is considered to model the RRW. Additionally, the modal conditions and bending loss are compared with the RRW with vertical sidewalls. It is assumed that this study will be beneficial for comprehending the modal conditions of waveguide structures with perfectly vertical and rounded sidewalls.

Fabrication of porous and visible light active ZnO nanorods and ZnO@TiO2 core-shell photocatalysts for self-cleaning applications.

Highly transparent and self-cleaning ZnO nanorods (NRs) and ZnO@TiO2 core-shell (CS) nanoarrays were fabricated using the sol-gel dip-coating technique. TiO2 nanoparticles (NPs) were coated as a shell layer over the hydrothermally grown ZnO NRs. The number of shell layers on the ZnO NRs was varied by modulating the number of dipping cycles from 1 to 3 to optimize their transmittance. The optimized CS nanoarrays with two dipping cycles display a 2% enhancement of optical transmission compared to the ZnO NRs. In addition, superhydrophilicity (contact angle ∼of 12°) stimulates the self-cleaning nature of the thin films. A water contact angle of 12° was noted for the ZnO@TiO2: 2 cycle sample, indicating their superhydrophilic nature. Moreover, the photocatalytic activity of the pristine ZnO NRs and ZnO@TiO2 CS nanoarrays was tested under UV and direct sunlight through the dye degradation of methylene blue (MB). Based upon the TiO2 morphology and accessibility of the ZnO@TiO2 heterojunction interface, CS nanoarrays with two shell layers exhibit the highest degree of dye photodegradation efficiency of 68.72% and 91% under sunlight and UV light irradiation, respectively. The CS nanoarrays demonstrate medium sunlight and excellent UV-light-driven photocatalytic activity. Our findings suggest that the ZnO@TiO2 CS nanoarrays are potential photocatalysts for dye degradation and self-cleaning applications in solar cell coverings.

New approach for designing wrinkled and porous ZnO thin films for photocatalytic applications

A new template-free, porous, and wrinkled ZnO thin films were designed by sol-gel dip-coating technique for enhancing the photocatalytic degradation of organic pollutants in water. The spontaneous formation of such nanostructure represents a certain type of instability-driven organization under intrinsic stress, such as thermal compression. The surface evolution was tracked by in situ thermo-ellipsometry technique through the changes in the film’s thickness and refractive index. The engineered nanostructure was obtained by a pre-heat treatment at 150 ⁰ C in the infrared chamber of the dip-coater followed by a post-annealing in the air at 450 ⁰ C for 1 h. A wrinkled structure with a porosity of ∼ 22–25% and an average pore Ferret diameter of ∼24 nm were revealed, promoting the adsorption of pollutants onto the films' surface. The photocatalytic activity of ZnO films was tested via the degradation of methylene blue probe molecule under two different irradiation sources. A high removal efficiency above 92% and degradation rate constants of 0.0049 min−1 and 0.0121 min−1 were registered under UVA and visible light respectively.

Smooth semicompact multilayer coating of TiO2 obtained by combining anodic oxidation and sol-gel techniques

Titanium oxide provides biological and hemocompatible properties to different biomedical devices made of titanium or its alloys. However, since this oxide naturally has a very low thickness and low tribological performance, it would be interesting to obtain thicker and more resistant oxides. In this work, a nanoporous/compact titanium oxide coating was synthesized on the Ti-6Al-4V alloy by combining the anodic oxidation and sol-gel dip-coating techniques. This coating was characterized by optical microscopy, scanning electron microscopy, atomic force microscopy, profilometry and X-ray diffraction. A ~600 nm-thick coating with low roughness (Ra ≅ 50 nm and Sa ≅ 57 nm) and free of cracks was obtained. The coating does not hide the nano- and micro-roughness of the substrate on which it was synthesized. The crystalline structure of the coating is anatase and rutile, but, superficially (~100 nm), it is only anatase.

Low-temperature electrical transport and tunable optical properties of Mo-doped V2O3 thin films

This work reports the structural and low-temperature electrical transport properties of Mo doped V2O3 single-layer thin films (i.e., with compositions between Mo and V2O3 [V2−xMoxO3−δ (x = 0, 0.05–0.1)]) deposited on alumina (Al2O3) substrates by sol–gel dip-coating technique. The crystallinity of the V2O3 films is modified with the high concentration of Mo doping and exhibits a relatively defective structure compared to that of pure V2O3 films. The low temperature (i.e., over a temperature range of 253.15 to 273.15 K) electrical hysteresis curves reveal that the triggering of metal–insulator transition at low temperatures. The metal–insulator transition (MIT) temperature (Tc) values are found to be 258.49 and 261.11 K for 8 and 10 mol% Mo doped V2O3 films, respectively, which are higher than that of undoped V2O3 (Tc = 253.09 K). The experimental results contribute a promising method to develop a novel material for high-performance low-temperature engineering applications.

Sol-Gel Derived Silica-Titania Waveguide Films for Applications in Evanescent Wave Sensors-Comprehensive Study.

Composite silica-titania waveguide films of refractive index ca. 1.8 are fabricated on glass substrates using a sol-gel method and dip-coating technique. Tetraethyl orthosilicate and tetraethyl orthotitanate with molar ratio 1:1 are precursors. Fabricated waveguides are annealed at 500 °C for 60 min. Their optical properties are studied using ellipsometry and UV-Vis spectrophotometry. Optical losses are determined using the streak method. The material structure and chemical composition, of the silica-titania films are analyzed using transmission electron microscopy (TEM) and electron dispersive spectroscopy (EDS), respectively. The surface morphology was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods. The results presented in this work show that the waveguide films are amorphous, and their parameters are stable for over a 13 years. The optical losses depend on their thickness and light polarization. Their lowest values are less than 0.06 dB cm-1. The paper presents the results of theoretical analysis of scattering losses on nanocrystals and pores in the bulk and interfaces of the waveguide film. These results combined with experimental data clearly indicate that light scattering at the interface to a glass substrate is the main source of optical losses. Presented waveguide films are suitable for application in evanescent wave sensors.

Thermal neutrons effect on improvement of electrical properties at CIGS thin film derived by sol-gel dip coating technique

The thermal neutron effect on the copper indium gallium (di)selenide thin film synthesized by the sol-gel dip-coating technique has explained the novel use of this film under extreme conditions (such as neutron irradiation fields). The thin film samples were treated by using the reactor neutrons to obtain the optimum neutron treatment for the determination of the variations in the structural characteristics. The gamma filter system has provided the evaluation of the high thermal neutron flux effect on the thin film samples by using the tangential beam tube of ITU TRIGA Mark–II reactor. The influence of the neutron effect on the electrical and optical features was explained by the rise of selenium amount in the thin film. The neutron-treated thin film samples (at 50 at. % Se) had a significant effect on the lowest electrical resistivity depending on the increase of the film density. The equivalent gamma dose of the neutron-treated thin film was determined as a 0.024 Gy dose level for neutron irradiation. The neutron treatment was significant to evaluate the decrease in the sheet resistivity of the thin film at this dose level. The neutron dose has led to a slight decrease in the optical band gap as the result of the thermal and epithermal neutrons' effects on the thin film.

Impact of Cu on structural, optical, dielectric properties and antibacterial activity of TiO2 thin films

In this work, Copper-doped TiO2 thin films were synthesized on glass substrates using a sol-gel dip-coating technique with varied molar concentrations of copper precursor (1,3,5,7,9 at. wt. %). Cu affected the structural, morphological, dielectric, antibacterial, and optical properties of TiO2 films. The formation of the anatase phase was confirmed by XRD. The morphology of all synthesized thin films was spherical grains with slight aggregation. The hopping process explained dielectric characteristics that obeyed the Maxwell-Wagner model and Koop's theory. These films were ideal for high-frequency devices because of their low dielectric constant. It was observed that as Cu concentration increased, the optical band gap energy reduced, which was beneficial for improving solar cell efficiency. Cu-doped TiO2 produced the best antibacterial agent. The photocatalysts with the highest photo activities were those containing 9 wt% Cu. The increased light absorption in the UV-VIS range and the lower recombination rate of the photoinduced electron hole pair of Cu-doped TiO2 thin films were responsible for the improved photocatalytic activity. Methylene blue degraded in the presence of sunshine, making it a potential material for the treatment of water.

Influence of Al content on microstructure and optical transmittance of sol-gel dip-coated ZnO films

Aluminum-doped zinc oxide thin film (Al:ZnO) was derived by the sol-gel dip-coating technique to analyze the doping effect on the film’s crystal structure and optical transparency. The surface structure of the thin film had the particles in the nano-spherical form. Al amount changed surface roughness with the variation of the grain size. The crystal structure of ZnO was wurtzite (in XRD analysis). The surface morphology of the film was also examined with SEM images. The effect of Al doping was investigated to evaluate the necessary amount of Al on the optical properties. The films show high optical transparency (~85%) at specific Al doping amounts (0.8-1.6%).

Study on the role of rGO in enhancing the electrochromic performance of WO3 film

In the present work, an improved electrochromic thin film has been developed with faster color switching time on incorporation of rGO in WO3 film. Here, pristine WO3 and rGO-WO3 (rGO concentration varying from 1–7wt%) based nanocomposite electrochromic films were fabricated on ITO coated glass substrate, by utilizing a facile sol-gel dip-coating technique. Detailed structural and morphological analyses of the films were carried out using XRD, FESEM, TEM and Raman Spectroscopy. Assimilating the electrochromic properties of all the films showed that, 5wt% rGO incorporated WO3 film gave a maximized electrochemical performance with minimum degradation in optical transmittance. The film also exhibited an optical modulation of ∼ 50% and a better switching response having coloration time (tc) ~ 5.3 s and bleaching time (tb) ~ 6.2 s as compared to the pristine film (tc~ 9.6 s, tb ~ 10.4 s). Incorporation of rGO also resulted in an enhancement of coloration efficiency from ∼ 81 to ∼ 386 cm2/C. The Electrochemical Impedance Spectroscopy (EIS) analysis of pristine and rGO loaded film clearly revealed better charge transfer on incorporation of rGO. The cyclic stability study exhibited ∼ 25% deterioration in optical transparency of the bare WO3 film which was < 10% for the rGO impregnated film. An ex-situ XRD analysis demonstrated that a crystal dislocation occurring in pristine WO3 sample was responsible for the same.

Zirconium oxide film deposition properties to build transparent electronic devices in conjunction with tin dioxide

ZrO2 thin films are deposited by the sol–gel dip-coating technique where the thermal annealing temperature and the number of deposited layers determine the properties of this material concerning the application in field-effect transistor (FET) devices in conjunction with SnO2 layer, also produced by sol–gel dip-coating. The best annealing temperature for the ZrO2 film was found as 400°C, along with a small number of layers and the position of the layer inside the oven, which determines the dominant heat transport mechanism of conduction or convection phenomena. The electrical insulating property of ZrO2 layers was confirmed with the current in the order of pA, even for layers about 100 nm thick. The temperature of 400°C also leads to a lower leak current through the gate in the device, which is three orders of magnitude lower than the source-drain current (in the order of a tenth of [Formula: see text]A).

Towards facile fabrication of photonics components from inorganic and hybrid sol-gel films. Preparation and optical properties characterization

New trends towards development of integrated optics and miniaturization of photonic devices require fabrication of miniaturized photonic components. Fabrication of waveguiding films with designed optical properties is a fundamental process for production of planar integrated devices.We report here preparation of thin layers based on TiO2 precursor (TET – titanium(IV) ethoxide) and SiO2 precursors, namely inorganic (TEOS – tetraethyl orthosilicate) or organically modified (GLYMO − 3-glycidoxypropyltrimethoxysilane) as candidates for potential application in the planar integrated circuits.The thin layers were deposited on soda-lime glass substrates using the sol-gel method and dip-coating technique and processed at relatively low temperature (up to 300 °C). Several parameters e.g. a) the type of SiO2 precursor, b) the presence of complexing agent for TET and c) heat treatment temperature were tested for their influence on thickness and refractive index of the obtained films.Furthermore, a few series of sol-gel films activated with luminescent dye (Rhodamine B) was fabricated. The influence of the above-listed parameters on luminescent properties of the films was characterized because of lack of systematic study in the literature in this aspect. Moreover, a spectrum of the light at the output of a chosen luminescent dye-doped waveguiding film excited by laser source was investigated.In addition, the subject of our investigations were films prepared at 200 °C with various amounts of TET and organically modified SiO2 precursor in concentration range not presented before. Their optical properties such as homogeneity and values of optical band gap of TiO2 clusters were explored. For selected samples the waveguide properties including the optical losses were evaluated. For the first time, hybrid films with presented composition and refractive index in range of 1.59–1.71 were used for patterning by nanoimprint technique allowing for reproduction of periodic structures, which may serve for example as grating couplers or DFB (distributed feedback) resonators.

Cerium and europium doped TiO2 thin films deposited by a sol-gel dip-coating process: characterization and photocatalytic activity toward dye degradation

Cerium (Ce) and europium (Eu)-doped TiO2 thin films were obtained by sol-gel dip-coating technique. SEM micrographs showed that the surfaces are covered by agglomerated particles due to the repeating coating process. XRD patterns showed the presence of TiO2 anatase phase. Raman spectra revealed that the peaks recorded at 146 cm-1(Eg) and 397 cm-1(B1g) were related to the anatase phase. EIS measurements proved that Ce-TiO2 (1wt%) and Eu-TiO2 (0.1wt%) photocatalysts possessed a lower electron transfer resistance than pure TiO2, which can lead to effective separation of electron/ hole pairs during the photoreactions. The photoactivity of Ce and Eu-doped TiO2 was investigated by the degradation of amido black10B dye (AB) under UV excitation and varying the initial pH and concentrations. It was found that Eu-TiO2 (0.1wt%) exhibited higher photocatalytic activity, reaching a first-order reaction rate of kapp(0.036min-1), t1/2 was around 12 min and AB removal was 98.94%, under optimal pH of 3.5 and AB concentration of 10ppm compared to (t1/2 = 45 min, t1/2=30 min), (kapp = 0.022 min-1, kapp = 0.026min-1) and AB removal (94.78%, 96.44%), respectively for pure TiO2 and Ce-TiO2 (1wt%). Further increase in Eu/Ce amount up to optimal concentration (1wt% Ce and 0.1wt% Eu) led to a decrease in the AB removal. The mineralization of AB using Eu-TiO2 photocatalyst was confirmed by HPLC analysis.

Nanostructured Ga doped ZnO thin films prepared by Sol-Gel spin-Coating / Filmes finos de ZnO NanoestruturadoS Ga doped preparados por sol-Gel spin-Coating

ZnO nanostructures are used in device systems such as photodetectors, gas sensors,photoemission devices, UV-photosensors and many others in Optoelectronics.In the present work we studied nanocrystalline ZnO:Ga thin films prepared by the sol–gel dip-coating technique. Samples were characterized by Grazing Incidence X-ray Diffraction(GIXD), X-ray Reflectivity (XR) and Grazing Incidence Small-Angle X-ray Scattering(GISAXS) methods and Field Effect Scanning Electronic Microscopy (FESEM). Characterization of the samples shows that the obtained films were uniform, continuous, with a crystallite size around 12 nm, an average pores size of around 3.5nm, and a volume fraction of nanoporosity between 0.18 and 0.3. Comparison of densities between doped and undoped films is discussed.

Effects of withdrawal speed on the structural, morphological, electrical, and optical properties of CuO thin films synthesized by dip-coating for CO2 gas sensing

Copper oxide (CuO) thin films have been deposited on glass substrates by a facile sol–gel dip-coating technique with varying withdrawal speeds from 0.73 to 4.17 mm/s. The variation in the film thickness manifested by dip-coating withdrawal speeds was investigated in detail to investigate its effect on the structural, morphological, opto-electrical, and wettability properties of CuO thin films for carbon dioxide (CO2) gas-sensing applications. The crystallinity, as well as phase purity of dip-coated CuO, was confirmed by both x-ray diffraction (XRD) and Raman spectral analyses. The surface morphology of the films characterized by scanning electron microscopy revealed that pore density decreases with increasing withdrawal speeds and the grain size is found to increase with the increasing film thickness corroborating the XRD results. The optical bandgap of dip-coated CuO films was estimated in the range of 1.47–1.52 eV from the UV–vis–NIR transmission data, and it is found to decrease with the increase in Urbach tail states accompanied by the increase in the film thickness. The ratio of the electrical and optical conductivity of CuO films was found to decrease with increasing withdrawal speeds due to the variation in the carrier concentration. Among all the studied films, the sample deposited at a 0.73 mm/s withdrawal speed exhibited the highest crystallinity, porous morphology, highest pore density, opto-electrical conductivity, as well as water contact angle and, therefore, the maximum gas sensing response of CO2 vapor in the air recorded at room temperature.

Design and validation of additive manufactured catalytic converter for the control of regulated and unregulated emissions of a gasohol fuelled spark ignition engine

In recent years, there have been many investigations carried on the regulated emissions in SI engines using gasohol fuels. However, there has been a lack of research on unregulated emissions, the technique required to reduce unregulated emissions, and cold start emissions at gasohol fuels. In this research work, a unique design for substrate in the catalytic converter is proposed to increase the conversion efficiency and reduce both regulated and unregulated emissions. The Computational Fluid Dynamics (CFD) results show that unique design has 10.4% greater surface area, 1.29 times higher cell density, with the more uniform flow, greater pressure drop, and lesser exit velocity than conventionally shaped substrate. The novel design of substrate is fabricated using an additive manufacturing (AM) process with Stainless Steel (SS) 316L material to have high mechanical and thermal strength. The AM substrate and conventional shaped substrate are coated with non – Platinum Group Metal (PGM) catalysts such as cobalt oxide and vanadium pentoxide as catalysts using sol–gel dip-coating technique. Both the catalytic converters are tested with gasoline, E10, and E20 blends in SI engine. The emission results show 17.39% higher conversion efficiency than conventional shaped Three-way catalytic converter (TWC). The catalytic converter with the novel shaped substrate is insulated with Phase Change Material (PCM) to reduce cold-start emissions. From the cold start study, it was concluded that the PCM-KOH insulated catalytic converter is found to be the most efficient way to resolve the cold start emissions with 75% higher conversion efficiency than a conventional TWC.