Simple fabrication of rod-like N-doped TiO2/Ag with enhanced visible-light photocatalytic activity

Rod-like N-doped TiO₂/Ag composites were successfully synthesized by a modified sol–gel method, without adding any surfactants. The entire preparation differs from the traditional sol–gel synthesis of TiO₂ that the reaction can get controlled by adjusting the flow speed of water vapor and NH₃. Characterization results show that as-prepared samples were uniform nanorods with an average length of ca. 3 µm and a cross section diameter of ca. 150 nm. The rod-like structure was formed during the annealing process. A possible mechanism was proposed to illustrate the formation of rod-like Ag–N–TiO₂. The degradation of methylene blue performed under visible light with the prepared nanorods as the photocatalyst demonstrated the photocatalytic activities of TiO₂ can be improved by the synergistic effect of N doping and Ag modification. In addition, as-prepared TiO₂-based photocatalyst exhibits a significantly enhanced photo-chemical stability after 5 catalytic cycles mainly due to the rod-like morphology. This indicated that they have some potential value in practical application.     

Effect of hydrodynamics during sol–gel synthesis of TiO2 nanoparticles: From morphology to photocatalytic properties

In this study, the role of mixing hydrodynamics during the sol–gel synthesis of titania nanoparticles and the consequences on their photocatalytic properties were investigated. For the first time three different T-mixer geometries were tested. Alcoholic solutions of titanium tetra-isopropoxide and water were mixed in three different T-mixers with turbulence promoters and thus different mixing characteristics. The changes of nanoparticle sizes during the induction time of the sol–gel process were followed by dynamic light scattering and velocity and turbulence fields were simulated by Computational Fluid Dynamics (CFD) for the three T-mixer geometries. The results indicated that macro-mixing is crucial during the first step as it determines the nucleation rate and then the primary particle size. The micro-mixing has an influence on particle properties, especially on particle stability. Titanium dioxide nanoparticles synthesized by the sol–gel process were deposited on alumina supports. A homogeneous film of about 200 nm was deposited in all cases. Degradation of Acid Orange 7 (AO7) was used to evaluate the photocatalytic activity of TiO₂ coatings. No difference was observed between the photoactivity of synthesized TiO₂. Total mineralization of the dye occurred after 24 h irradiation.     

ZrO2 sol–gel pre-treatments doped with cerium nitrate for the corrosion protection of AA6060

Sol–gel coatings represent an alternative corrosion protection method to the chromate based systems which must be replaced. Recently, it was shown that ZrO₂ based sol–gel coatings deposited on AA6060 can provide a good corrosion protection to AA6060. However, ZrO₂ based sol–gel systems are not able to provide the self-healing effect which is instead the peculiar property of chromate conversion coatings. The structure of the ZrO₂ based sol–gel systems does not contain species able to restore the barrier properties when defects or damages impair the coating protection.     

Effect of sintering temperature on microstructure and transport properties of Li3xLa2/3−xTiO3 with different lithium contents

Li_3xLa_2/3−xTiO₃ (LLTO) powder with different lithium contents (nominal 3x = 0.03–0.75) was synthesized via a simple sol–gel route and then calcination of gel-derived precursor at 900 °C which was much below the calcination temperature required for synthesizing the LLTO powder via solid state reaction route. The LLTO powder of sub-micron sized particles, derived from such sol–gel method, showed almost no aggregation. Starting from the sol–gel-derived powder, the LLTO ceramics with different lithium contents were prepared at different sintering temperatures of 1250 and 1350 °C. It demonstrated that our sol–gel route is quite simple and convenient compared to the previous sol–gel method and requires lower temperature for the LLTO. Our results also illustrated that lithium content significantly affects the structure and ionic conductivity of the LLTO ceramics. The dependence of the ionic conductivity on the lithium content, lattice structure, microstructure and sintering temperature was investigated systematically.     

Elaboration of pure and doped TiO2 nanoparticles in sol–gel reactor with turbulent micromixing: Application to nanocoatings and photocatalysis

Pure and doped nanocoatings were prepared of from chemically active TiO₂ colloids. The colloids are generated in sol–gel reactor with turbulent mixing of two reactive fluids, containing titanium tetra-isopropoxide and water, in T-mixer. The particle size is measured by the light-scattering technique using optical-fibre probe. The TiO₂ nanoparticles doped with nitrogen are obtained by the injection of a doping agent into the reaction zone at the mixing stage. The mixing at the nucleation stage has a strong impact on the nanoparticles polydispersity and mean size. The prepared nanocoatings show photocatalytic activity under UV and visible light illumination.     

Electrochemical investigation of high-performance silane sol–gel films containing clay nanoparticles

Silane sol–gel coatings are widely used as adhesion promoters between inorganic substrates, such as metals, and organic coatings. The aim of these pre-treatments is to enhance the corrosion protection performance of the organic coating improving the adhesion to the substrate and acting as a barrier against water and aggressive ions diffusion. It is a matter of fact that the silane sol–gel pre-treatments do not provide an active protection against corrosion processes except for the partial inhibition of the cathodic reaction. Inorganic pigments can improve the barrier properties of the silane sol–gel film, enhancing the resistance against corrosion. In this study, different amounts of montmorillonite nanoparticles were added to a water based silanes mixture in order to improve the barrier properties of the sol–gel coating. Hot dip galvanized steel was used as substrate. The sol–gel film consists of a combination of three different silanes, GPS, TEOS and MTES. The clay nanoparticles used in this study were mainly neat montmorillonite. The proper concentration of filler inside the sol–gel films was determined comparing the corrosion resistance of silane layers with different nanoparticles contents. Additionally, the effect of CeO₂ and Ce₂O₃ enriched montmorillonite particles. The EIS analysis and the polarization measurements demonstrated that the optimal amount of neat montmorillonite nanoparticles is about 1000 ppm. The same electrochemical techniques highlighted the limited effect of the cerium oxides grafted to the clay nanoparticles on the corrosion resistance of the silane sol–gel film. The TEM analysis proved the presence of a nano-crystalline structure inside the silane sol–gel film due to the formation of crystalline silica domains.     

Synthesis and electrochemiluminescence of the CeO2/TiO2 composite

CeO₂/TiO₂ composite with kernel–shell structure was synthesized by a sol–gel process. The characterization results show that the composite is made up of anatase phase TiO₂ and cubic system CeO₂. The electrochemiluminescence (ECL) behavior of the CeO₂/TiO₂ composite was studied by a cyclic voltammetry in the presence of persulfate, and the effect factors on ECL emission were discussed. Based on a series of experiments, it is proposed that the strong dual ECL emission produced by the CeO₂/TiO₂ composite resulted from the benefit ECL effect of interface heterojunction in composite.     

Investigation of phase separation of nano-crystalline anatase from TiO2SiO2 thin film

In this work, a set of SiO₂–TiO₂ mixed oxides was prepared by the polymeric sol–gel route and deposited on glass substrate through the dip coating technique. Then, the effect of different important preparation parameters (sol–gel stabilizers, Ti content, and heat treatment) on the phase separation was investigated. The developed films were heat treated at 500 °C and characterized using TGA/DTA, FTIR, XRD, SEM, and AFM. The results showed that TiO₂ segregation can be controlled by selecting an appropriate composition of diethanolamine (DEA) and methyl methacrylate (MMA) for preparation of polymeric silica–titania sol. Besides, anatase phase in the samples were crystallized without any stabilizers within heat treatment procedure at 500 °C; however, using appropriate composition of DEA and MMA crystallization rate significantly decreased.     

Visible light photocatalytic degradation of thiophene using Ag–TiO2/multi-walled carbon nanotubes nanocomposite

Ag–TiO₂ nanocatalyst, supported on multi-walled carbon nanotubes, was synthesized successfully via a modified sol–gel method, and the prepared photocatalyst was used to remediate aqueous thiophene environmentally by photocatalytic oxidation under visible light. The prepared Ag–TiO₂/multi-walled carbon nanotubes nanocomposite photocatalyst was characterized through X-ray diffraction, Brunauer–Emmett–Teller (BET), transmission electron microscopy, and UV–vis spectra (UV–vis). The results showed that both Ag and TiO₂ nanoparticles were well-dispersed over the MWCNTs and formed a uniform nanocomposite. Ag doping can eliminate the recombination of electron–hole pairs in the catalyst, and the presence of MWCNTs in the TiO₂ composite can change surface properties to achieve sensitivity to visible light. The optimum mass ratio of MWCNT:TiO₂:Ag was 0.02:1.0:0.05, which resulted in the photocatalyst's experimental performance in oxidizing about 100% of the thiophene in a 600 mg/L solution within 30 min and with 1.4 g L⁻¹ amount of catalyst used.     

Mortality response of folate receptor-activated,PEG–functionalized TiO2 nanoparticles for doxorubicin loading with and without ultraviolet irradiation

TiO₂ nanoparticles (NPs) were synthesized by hydrothermal assisted sol–gel technique. In the next step, as-synthesized NPs were modified by poly ethylene glycol (PEG). Then, folic acid (FA) was conjugated to TiO₂–PEG. Finally, Doxorubicin (Dox) as an anticancer drug was loaded on as-prepared TiO₂–PEG–FA nanocarrier. The optimization of TiO₂ and FA concentration and the influence of ultraviolet (UV) irradiation on photocatalytic activity of nanocarrier and Dox loaded carrier were assessed by utilizing the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT)-assay method.     

Weathering performance of spruce coated with water based acrylic paint modified with TiO2 and clay nanoparticles

This work examines the effect of wood specimens coated with water based acrylic coatings modified with TiO₂ and clay nanoparticles against weathering strain. The long-term durability of the specimens towards climate strain was studied within a relatively short time frame by accelerated climate ageing. The surface changes that occurred as a result of photodegradation of the specimens subjected to accelerated climate exposures were studied using colour measurements and Fourier transform infrared (FTIR) spectroscopy. The results revealed a significant decrease in the intensity of lignin bands attributed to degradation of the lignin component of the wood. However, the intensity of the lignin photodegradation was lower for coated specimens, with slightly lower degradation for the specimens coated with paints modified with TiO₂ and unmodified montmorillonite clay nanoparticles.     

Performance enhancement of dye-sensitized solar cells using nanostructural TiO2 films prepared by a graft polymerization and sol–gel process

Nanostructural TiO₂ films with large surface areas were prepared by the combined process of graft polymerization and sol–gel for use in dye-sensitized solar cells (DSSCs). The surface of the TiO₂ nanoparticles was first graft polymerized with photodegradable poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP), after which the particles were deposited onto a conducting glass. The PMMA chains were removed from the TiO₂ films by UV irradiation to generate secondary pores, into which titanium isopropoxide (TTIP) was infiltrated. The TTIP was then converted into small TiO₂ particles by calcination at 450 °C, as characterized by energy-filtering transmission electron microscopy (EF-TEM) and field emission scanning electron microscopy (FE-SEM). The nanostructural TiO₂ films were used as a photoelectrode in solid-state DSSCs; the energy conversion efficiency was 5.1% at 100 mW/cm², which was higher than the values achieved by the pristine TiO₂ (3.8%) and nongrafted TiO₂/TTIP photoelectrodes (3.3%). This performance enhancement is primarily due to the increased surface area and pore volume of TiO₂ films, as revealed by the N₂ adsorption–desorption isotherm.     

Preparation and characterization of TiO2, ZnO,and TiO2/ZnO nanofilms via sol–gel process

The preparation of the TiO₂, ZnO, and TiO₂/ZnO nanofilms was conducted on glass via sol–gel process. The prepared film was detailedly characterized by means of OM, SEM, XRD, and EDS. The results showed that the obtained pure TiO₂ was composed of nanoparticles. For pure ZnO it consisted of nanoparticles and large agglomerates. Both the microstructural morphology and the crystallization of the prepared TiO₂/ZnO composite film were strongly related to the Ti/Zn ratio in the film. With a Ti/Zn ratio less than 1/1, the composite film was absence of cracks. Poor crystallization was definitely observed for the composite film with Ti/Zn ratio of 3/1 and 1/1. The EDS analysis revealed homogeneous distribution of Ti and Zn elements in the film.     

Synthesis of novel UV-curable difunctional thiourethane methacrylate and studies on organic–inorganic nanocomposite hard coatings for high refractive index plastic lenses

This study relates to the development of ultraviolet (UV)-curable, organic–inorganic nanocomposite hard coatings for plastic lens substrates, especially for polythiourethane (PTU) and polycarbonate (PC). Novel difunctional thiourethane methacrylate (mercaptoethylsulfide-thiourethane methacrylate: coded MES-TUMA and isophorone diisocyanate-mercaptoethylsulfide-thiourethane methacrylate: coded IPDI-MES-TUMA) was synthesized to enhance the adhesive strength for PTU. On the basis of IR, ¹H NMR, electron spray ionisation-mass spectrometry (ESI-MS) analysis and gel permeation chromatography (GPC), the expected structures were confirmed. These difunctional thiourethane methacrylates were easily mixed with multifunctional urethane acrylate, surface-modified ZrO₂–TiO₂ nanoparticles and photoinitiator in coating formulations. The UV-cured organic–inorganic nanocomposites were very useful as hard coatings for high refractive index plastic lenses such as PTU and PC.     

Characterisation of urushiol formaldehyde polymer/multihydroxyl polyacrylate/SiO2 nanocomposites prepared by the sol–gel method

Novel anti-ultraviolet UFP/MPA/SiO₂ nanocomposite coatings were prepared from urushiol formaldehyde polymer (UFP) and multihydroxyl polyacrylate resin (MPA) via the sol–gel process. FT-IR spectroscopy was employed to reveal the nanocomposite structure between UFP/MPA and nano-SiO₂. TEM was used to observe the size scale and the distribution of nanoparticles throughout the polymer matrix. Simultaneously, the dynamic mechanical properties were characterised through dynamic mechanical thermal analysis (DMTA). The influence of the SiO₂ content on the physical mechanical and anticorrosive properties of UFP/MPA/SiO₂ nanocomposites was investigated. Moreover, the 1000 h anti-ultraviolet tests showed that the ultraviolet resistance of UFP/MPA/SiO₂ coatings improved. The best anti-ultraviolet and anticorrosive properties were achieved when the SiO₂ content was 5 wt.%.     

Application of the statistical Taguchi method to optimize TiO2 nanoparticles synthesis by the hydrothermal assisted sol–gel technique

TiO₂ nanoparticles were synthesized by hydrothermal assisted sol–gel technique. The preparation parameters including pH value, the amount of water, titanium tetra isopropoxide content, temperature and time of hydrothermal process were investigated by Taguchi statistical experiments to determine the influence of synthesizing variables on the optimal conditions and to realize the highest degree of crystallinity or smallest crystallite size. X-ray diffraction (XRD) analysis and direct band gap energy (E_g) values, measured via diffuse reflectance spectra (DRS), proved that all the samples consist of anatase as a unique phase. Transmission electron microscopy (TEM) and specific surface area values showed that the sample with the smallest crystallite size could exert more effective photoactivity confirmed by measuring the decomposition rate of methylene blue. The apparent photodegradation rate constant of the sample with the smallest crystallite size was about five times greater than that of commercial TiO₂.     

Novel porous TiO2 glass-ceramics with highly photocatalytic ability

A porous TiO₂ glass-ceramics with high photo-oxidative activity was successfully obtained from the SiO₂–Al₂O₃–B₂O₃–CaO–TiO₂ glass system. Rutile-type TiO₂ was observed in the crystallization temperature range of 973–1173 K. The band gap of the glass-ceramics coincided approximately with that of rutile-type TiO₂. The photocatalytic activity of this glass-ceramics was about four times larger than that of a TiO₂-coated photocatalyst fabricated by the sol–gel process. Furthermore, as this porous TiO₂ glass-ceramics contained TiO₂ in composition form, it could prevent peeling of the TiO₂ from the substrate. As well, this glass-ceramics can be easily shaped into sheets, tubes, rods, etc.     

Effect of silica on the microstructure and photocatalytic properties of titania

A series of TiO₂/SiO₂ composite with different Ti/Si ratios were prepared by sol–gel technique. The samples were characterized by different analytical techniques such as XRD, FT-IR, BET and XPS. Grain size of anatase TiO₂ calculated using Scherrer's formula was found to be in the range of 2.1–8.7 nm, and the content of anatase phase in TiO₂ ranges from 45% to 40.1%. The photocatalytic properties on methyl orange (MO) solution were also studied. The degradation rate of the composite is much higher than that of the pure TiO₂ in the same conditions.     

Preparation and Characterization of Nanostructured TiO2/Epoxy Polymeric Films

Summary: Titania‐containing coatings were prepared by cationic photopolymerization of an epoxy resin either by dispersion of preformed TiO₂ nanoparticles or by their in‐situ generation through a sol‐gel dual‐cure process. The kinetics of photopolymerization was evaluated by real‐time FT‐IR, studying the effect of the TiO₂ concentration. The properties of cured films were investigated, showing an increase of hydrophilicity on the surface of the coatings with increasing TiO₂ content. TEM analysis demonstrated that it is possible to achieve a significantly better control of the dispersion of the inorganic particles within the organic matrix by in‐situ generation of TiO₂, thus completely avoiding macroscopic phase separation and obtaining homogeneous, transparent coatings.

Bright‐field TEM micrograph for TIP20 dual‐cured film.     

Photocatalytic activity of thin TiO2 films deposited using sol–gel and plasma enhanced chemical vapor deposition methods

Thin titanium dioxide films, deposited using RF PECVD and sol–gel techniques, were studied comparatively with respect to their bactericidal as well as self-cleaning properties. The effect of the deposition process on film morphology, chemical and crystalline structure, bactericidal activity and hydrophilic properties was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), surface profilometry, optical microscopy and contact angle measurements. It was found that the bactericidal activity of amorphous TiO₂ films, produced using the RF PECVD method, as either comparable to or better than those of crystalline (anatase) films deposited by means of the sol–gel technique. One reason for such advantageous behavior of plasma deposited materials is thought to be their substantially higher surface roughness, as revealed by AFM measurements. The hydrophilic effect, induced with UV irradiation, was strongest in the case of sol–gel films, but the RF PECVD synthesized coatings were found to be only slightly less hydrophilic. The conclusion follows that both sol–gel and RF PECVD techniques are equally capable of producing titanium dioxide films of high photocatalytic quality.