Surface Of TiO2 Particles Research Articles

Sequential ionic layer adsorption reaction formation of LaVO4–TiO2 nanocomposites for photocatalytic water treatment

Lanthanum vanadate (LaVO4) has been deposited onto the surface of P25 TiO2 particles immobilized on glass beads for photocatalytic water treatment.

Bcl Morphology Formation Strategy on Nanostructured Titania via Alkaline Hydrothermal Treatment

Titanium dioxide (TiO2) is a semiconductor material that plays an important role in photocatalysis. Bicontinuous concentric lamellar (bcl) is an interesting morphology with an open channel pore structure that has been successfully synthesized on silica-based materials. If bcl morphology can be applied in TiO2 system, then many surface properties of TiO2 can be enhanced, i.e. photocatalytic activity. A simple and effective strategy has been demonstrated to transform aggregated and spherical TiO2 particles to bcl morphology via alkaline hydrothermal route. Alkaline hydrothermal treatment successfully transforms TiO2 particle surface to have bcl morphology through swelling with ammonia then followed by phase segregation process. We proposed this strategy as a general pathway to transform the particle surface with any shape to have bcl morphology.

Diffusion mechanism and release profile of a multivitamin from TiO2 hollow particles

The present study aimed to control the release rate profile of a multivitamin that has hydrophilic and hydrophobic properties and to investigate its diffusion rate from titanium dioxide (TiO2) hollow particles. The TiO2 hollow particles encapsulating the vitamins C and E were prepared via a sol-gel process using an inkjet nozzle. The obtained particles were evaluated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The sustained release rate was estimated by the dialysis bag method. Additionally, a diffusion mechanism for the multivitamin from the TiO2 hollow particles was proposed.TiO2 particles prepared by this method exhibited spherical porous structures. The TiO2 hollow particles were successful in encapsulating both the hydrophilic vitamin C and the hydrophobic vitamin E, resulting in a sustained release profile for these two components from the TiO2 hollow particles. The release behavior of the multivitamin was quite different from that of each single vitamin. This is related to the adsorption state of each vitamin on the TiO2 particle surface. The effective diffusion coefficient of VC derivative (8.403 × 10−13 cm2/s) was faster than that of VE derivative (1.671 × 10−13 cm2/s). This tendency may be attributed to the difference between hydrophilic and hydrophobic properties. Additionally, the value of effective diffusion coefficient in multi-component was always larger than that in single component. The value of Knudsen diffusion coefficient in VC and VE derivative was 2.684 × 10−3 and 2.264 × 10−3 cm2/s, respectively. In all samples, Knudsen diffusion coefficient was larger than molecular diffusion coefficient. The diffusion mechanism of the active ingredients likely depends on the pore size of TiO2 and the molecular size of the active ingredients.

Mussel adhesive protein-coated titanium oxide nanoparticles for effective NO removal from versatile substrates

Titanium dioxide (TiO2)-based photocatalysis has been adopted to decrease nitrogenous oxides levels in air. However, the low binding abilities of polymeric binders used to bind TiO2 particles to various substrates in wet conditions, and the formation of large agglomerates of TiO2 particles due to poor the adhesion between polymeric binders and TiO2 particles have obstructed various indoor and outdoor applications of TiO2. In this study, we demonstrated an effective method of dispersing TiO2 particles in an aqueous solution with the help of mussel adhesive protein (MAP). The MAP was homogeneously coated on the surfaces of TiO2 particles with a thickness of 3–4 nm. The MAP acted as a dispersing agent for the TiO2 particles and enabled strong and stable adhesion between TiO2 and the substrates. Moreover, the homogeneously coated MAP layer did not affect the intrinsic photocatalytic activity of the TiO2 particles. Notably, the MAP/TiO2 nanoparticle-coated stainless steel sample exhibited a superior NO removal rate to mortar, glass, and wood-containing samples because of the enhanced efficiency of the photocatalytic redox process. The developed protein-based suspension could be successfully applied to various construction materials including cement, glass, wood, and stainless steel because of the strong binding ability of MAP, especially in wet conditions.

Influence of relative humidity on SO2 oxidation by O3 and NO2 on the surface of TiO2 particles: Potential for formation of secondary sulfate aerosol.

The heterogeneous reactions of SO2/O3 and SO2/NO2 with TiO2 particles were studied as a function of relative humidities (RHs). An in situ microscopic Fourier transform infrared (micro-FTIR) spectrometer was used to monitor the reaction kinetics. Rapid conversion of SO2 to sulfate occurs on the surface of TiO2 particles in the presence of O3 or NO2, which is sensitive to RHs. For unreacted (fresh) particles, the uptake coefficients for SO2 in initial stage are both obviously enhanced over four times with the increasing RH from ~4% to ~85%. Moreover, the uptake coefficient in the system of SO2/O3 is about 40% higher than that of SO2/NO2 on TiO2 particles at the similar RH conditions. For TiO2 after exposure to SO2/O3 or SO2/NO2 (sulfated) particles, the uptake coefficients for SO2 in moisture absorption stage are all higher than that on fresh particles in initial stage at the similar RH, indicating rapid mixture gases adsorption with particle hygroscopic growth. The high production of the secondary sulfate for heterogeneous reaction of mixture gases on TiO2 surface from arid region to humid region provides new insights for better understanding the severe haze under the humid condition.

Dark brown Cr doped CaTiO3 pigments with high NIR reflectance

Some brown CaTiO3 pigments have been synthesized by calcining the depositions of CaCO3 and Cr dopant on the surface of TiO2 particles. The pigments have a pure phase composition of perovskite and a narrow size distribution ranging from 0.5 to 1.5 μm. These pigments have a low lightness and exhibit dark brown color due to the presence of Cr6+.The doped CaTiO3 pigment with 1% Cr has high NIR reflectance of 79.7% and high solar reflectance of 58%, and the doped pigment coating can lower 8.9 °C for the inner surface of ceramic tiles.

Particulars of the Sol-Gel Synthesis of Titanium Oxide Micro- and Nanoparticles for Creating a Composite Hybrid Antireflection Coating on Float-Glass

Sol-gel processes occurring during hydrolysis in the presence of the surfactant diethylamine were studied. It is shown that the rate of the hydrolysis of tetrabutoxytitanium with minimal water and in the presence of dimethylamine is determined by the competition between the process of condensation of TiO2 nanoparticles and the process of adsorption of dimethylamine on the surface of TiO2 particles.

Impact of Titanium Dioxide on the Bioaccessibility of β-Carotene in Emulsions with Different Particle Sizes

Commercial, titanium dioxide (TiO2) ingredients used as color additives (E171) in foods and beverages contain an appreciable fraction of particles in the nanoscale range. At present, little information is available regarding the potential impact of food-grade TiO2 nanoparticles on the gastrointestinal fate of co-ingested bioactives, such as nutraceuticals. In this study, the impact of TiO2 on the bioaccessibility of β-carotene solubilized in model food emulsions was investigated using a simulated gastrointestinal tract model. Raman spectroscopy showed that there was no charge transfer between β-carotene and TiO2 but that some β-carotene absorbed to the surface of TiO2 particles. The initial particle size of the food emulsion did not significantly affect β-carotene bioaccessibility, probably because the same amount of free fatty acids (FFAs) was released by the end of digestion. The addition of TiO2 at levels typically found in foods also had no significant impact on β-carotene bioaccessibility and FFA release, which suggested that this type of inorganic particle does not interfere with the gastrointestinal fate of these lipophilic bioactive agents. This information is important for ensuring the safety of inorganic nanoparticle utilization within the food industry.

Photocatalytic activity of gadolinium doped TiO2 particles for decreasing heavy metal chromium (VI) concentration

Titanium dioxide (TiO2) is among the most potential photocatalyst. However, TiO2 only works under UV light due to the relatively wide band gap energy. To overcome this, TiO2 is infiltrated (doped) by rare earth elements such as gadolinium (Gd). TiO2 was synthesized using sol gel method, while Gd/TiO2 photocatalyst was synthesized by the mixing methods of sol-gel and impregnation. The crystals are then characterized using XRD and SEM-EDX. The XRD diffractogram demonstrated that the crystallinity synthesized of TiO2 had an anatase structure similar to the structure of anatase P-25 as references. The SEM-EDX showed that Gd ion could not enter the crystal lattice, but only dispersed on the surface of TiO2 particles. The optimum result of decreased Cr(VI) concentration was reported using Gd/TiO2 1% w/w by a decrease of up to 94%, after irradiated with ultraviolet for one hour.

Ultrafast sonochemistry-based approach to coat TiO2 commercial particles for sunscreen formulation

TiO2 is a common inorganic filter used in sunscreens due to its photoprotective effect on the skin against UV radiation. However, the use of this kind of material in cosmetics is limited by its inherent photocatalytic activity. It is known that coating on TiO2 surface can improve some features. Although, many of the methodologies used for this purpose are still laborious and time-consuming. Thus, this work reports a novel, easy, cheap and fast strategy to coat TiO2 particles by using a sonochemistry approach, aiming to decrease photocatalytic activity and to enhance colloidal stability. For this proposal, SiO2, Al2O3, ZrO2 and sodium polyacrylate (PAANa) were used to tune the surface of commercial TiO2 particles and they were applied in a sunscreen formulation. The samples were characterized by XRPD, FT-IR, DLS, EDS, SEM and TEM. The photocatalytic activity and UV-shielding ability were also evaluated. The sunscreen formulations were prepared and characterized by zeta potential, DLS, and Sun Protection Factor (SPF). FT-IR, EDS, and charge surface of the particles confirmed the success of the sonochemistry coating. Additionally, TiO2@Al2O3, TiO2@SiO2 and TiO2@PAANa show a lower photocatalytic activity than original TiO2 with similar UV-shielding ability. The sunscreens produced with the coated TiO2 have similar SPF to the one with commercial TiO2. Specifically, the sunscreen with TiO2@PAANa shows an increase in colloidal stability. Herein, the incorporation of the sonochemical-coated TiO2 particles in sunscreen formulations may produce sunscreens with better aesthetic appearance and a greater health security due to its lower free radicals production.

Suppression of TiO2 Photocatalytic Activity by Low-Temperature Pulsed CVD-Grown SnO2 Protective Layer

TiO2 pigments are widely used in paint industries. Inert coating layers were usually deposited on the TiO2 pigments to suppress the photocatalytic activity of TiO2, which can prevent the degradation of surrounding polymer molecules. However, the traditional wet chemical methods normally form thick films, which would impair the pigment properties of TiO2. In this work, SnO2 and SiO2 protective layers were grown on the TiO2 particle surface by low-temperature pulsed chemical vapor deposition. At temperatures <60 °C, thin and uniform amorphous SnO2 films were obtained. The photocatalytic activities of both TiO2/SnO2 and TiO2/SiO2 core–shell particles were suppressed, and TiO2/SnO2 core–shell particles showed higher lightening power than TiO2/SiO2. According to transient fluorescence, photocurrent, and electrochemical impedance spectroscopy measurements, the low electron mobility of amorphous SnO2 and SiO2 films led to fast recombination of photogenerated electrons and holes, thus preventing their migration t...

A simple post-treatment with urea solution to enhance the photoelectric conversion efficiency for TiO2 dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are performed using C3N4 post-treated TiO2 particles as photoanode materials. The photoanode materials were synthesized via a simple method by which a thin layer of C3N4 was coated onto the surface of TiO2 particles after the TiO2 was dipped in urea solution followed by calcination properly. The experimental results show that the photoelectric conversion efficiency of the TiO2 DSSCs is remarkably improved. The measurements of I-V characteristic along with the analysis of electrochemical impedance spectroscopy indicate that the C3N4 layer can expand the visible light absorption, suppress the recombination reaction of the e−-h+ pair and increase both the open circuit voltage and the short-circuit photocurrent density. The mechanism of the improved performance of TiO2 DSSCs by C3N4 coating coating is proposed. The post-treatment method recorded in this work can be easily operated and achieve an enhanced photoelectric performance of DSSCs.

Graphitic carbon nitride nanosheet wrapped mesoporous titanium dioxide for enhanced photoelectrocatalytic water splitting

We report a new strategy to fabricate a core-shell TiO2@g-C3N4 composite for photoelectrochemical water splitting. The heterojunction structure is prepared by chemically wrapping exfoliated thin layer g-C3N4 nanosheets on the surface of anatase TiO2 particles. The TiO2@g-C3N4 sample demonstrates high visible-light photoactivity towards water splitting, resulting in an increase in photocurrent density by a factor of 2.5 times compared to the bare TiO2. This is ascribed to the inhibition of electron-hole pair recombination due to the synergistic effect between TiO2 and g-C3N4, which enhances the charge transfer and separation. The prolonged lifetime of the charges is confirmed by using the transient absorption spectroscopic measurements.

Synthesis and color properties of the TiO2@CoAl2O4 blue pigments with low cobalt content applied in ceramic glaze

AbstractThe TiO2@CoAl2O4 complex blue pigments with low cobalt content were synthesized through calcinations of the precursor obtained from coprecipitating Co2+ and Al3+ to form Co‐Al LDHs (layered double hydroxides) on the surface of TiO2 particles. The structure and the properties of the synthesized pigments were characterized by XRD, SEM, TEM, UV‐Vis spectroscopy, XPS, and colorimeter. The precursors of the blue TiO2@CoAl2O4 complex pigments were consisted of LDHs shell layer encapsulated TiO2 microsphere. After calcinations at 1100°C, the LDHs shell layer were absolutely transformed to the spinel CoAl2O4, and the pigments presented a core‐shell structure and uniform sphere morphology (the diameter of microsphere was about 780 nm). The absorption bands at around 547, 584, and 624 nm in the Uv‐Vis absorption spectra of the TiO2@CoAl2O4 complex pigments were corresponded to the characteristic absorption bands of the spinel CoAl2O4, revealed the pigments with a bright blue hue. In addition, as the mass ratio of CoAl2O4/TiO2 increased to 0.4, the blue component of the pigments reached to 27.89 and slight color variation with the increase in the CoAl2O4 content in a range, possessed low cobalt content and exhibited a stabile performance in commercial low‐temperature ceramic glazes. The XGT results showed that the TiO2@CoAl2O4 complex pigments with low cobalt content presented bright color in ceramic glaze. Especially, the synthesized pigments reduced the usage and toxicity of cobalt, which were efficiency for economy and environmental protection.

Potential impact of inorganic nanoparticles on macronutrient digestion: titanium dioxide nanoparticles slightly reduce lipid digestion under simulated gastrointestinal conditions

Titanium dioxide (TiO2) particles are used in some food products to alter their optical properties, such as whiteness or brightness. These additives typically contain a population of TiO2 nanoparticles (d < 100 nm), which has led to concern about their potential toxicity. The objective of this study was to examine the impact of TiO2 particles on the gastrointestinal fate of oil-in-water emulsions using a simulated gastrointestinal tract (GIT) that includes mouth, stomach, and small intestine phases. Theoretical predictions suggested that TiO2 nanoparticles might inhibit lipid digestion through two physicochemical mechanisms: (i) a fraction of the lipase adsorbs to TiO2 particle surfaces, thereby reducing the amount available to hydrolyze lipid droplets; (ii) some TiO2 particles adsorb to the surfaces of lipid droplets, thereby reducing the lipid surface area exposed to lipase. The importance of these mechanisms was tested by passing protein-coated lipid droplets (2%, w/w) through the simulated GIT in the absence and presence of TiO2 (0.5%, w/w) nanoparticles (18 nm) and fine particles (167 nm). Changes in particle characteristics (size, organization, and charge) and lipid digestion were then measured. Both TiO2 nanoparticles and fine particles had little impact on the aggregation state and charge of the lipid droplets in the different GIT regions, as well as on the rate and extent of lipid digestion. This suggests that the theoretically predicted impact of particle size on lipid digestion was not seen in practice.

Two‐Electron Oxidation of Water Through One‐Photon Excitation of Aluminium Porphyrins: Molecular Mechanism and Detection of Key Intermediates

AbstractThe reaction mechanism of photochemical water oxidation catalyzed by AlIII porphyrins (AlTIIIMPyP(OH)2) covalently adsorbed through the coordination of one axial OH group on the surface of TiO2 particles was investigated by time‐resolved nanosecond laser flash photolysis (NLFP). Three types of transient species with completely different absorption and decay characteristics were detected by means of NFLP, demonstrating that the photochemical production of H2O2 from water is initiated only by one‐photon excitation of the catalyst followed by stepwise two‐electron conversion processes, providing a promising model for photochemical water oxidation. Laser flash excitation of AlIIITMPyP adsorbed on a transparent TiO2 film leads to the formation of the AlTMPyP(OH) radical cation through one‐electron injection from the excited singlet state of the catalyst to the conduction band of TiO2. The radical cation is subsequently deprotonated into AlTMPyP(O.), which further reacts with OH−/H2O to form a key intermediate, the radical anion of AlTMPyP(O‐OH), having a characteristic O−O bond at the axial position within a delay time of 2–3 μs. Thereafter the radical anion efficiently transfers a second electron to TiO2 leading to the formation of AlTIIIMPyP(O‐OH) (≈67 μs), which reacts further with OH−/H2O to liberate free hydrogen peroxide as an end‐product with regeneration of the starting catalyst, AlTIIIMPyP(OH), (≈500 μs).

Preparation of TiO2-coated barite composite pigments by the hydrophobic aggregation method and their structure and properties

We obtained hydrophobic barite (BaSO4) and rutile titanium dioxide (TiO2) particles (as raw materials) by organic surface modification. Subsequently, TiO2-coated barite composite pigments were prepared via the hydrophobic aggregation of heterogeneous particles in a water medium. The pigment properties of the TiO2-coated barite composite pigments were characterized and evaluated by determining their hiding power, oil absorption value and whiteness. The optical properties were determined by obtaining their UV-vis diffuse reflectance spectra and using the CIE-L*a*b* method. The morphology and bonding properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (IR). The results show the similarity between the composite pigment and pure rutile TiO2: when the mass ratio of rutile TiO2 in the composite pigment was 60%, the hiding power of the TiO2-coated barite composite pigment was 90.81% of that of pure rutile TiO2. Moreover, the surfaces of the barite particles were uniformly and firmly coated by TiO2, with a hydrophobic association occurring between the hydrophobic carbon chains on the surfaces of barite and TiO2 particles.

Sulfur-Doped TiO2: Structure and Surface Properties

A comprehensive study on the sulfur doping of TiO2, by means of H2S treatment at 673 K, has been performed in order to highlight the role of sulfur in affecting the properties of the system, as compared to the native TiO2. The focus of this study is to find a relationship among the surface, structure, and morphology properties, by means of a detailed chemical and physical characterization of the samples. In particular, transmission electron microscopy images provide a simple tool to have a direct and immediate evidence of the effects of H2S action on the TiO2 particles structure and surface defects. Furthermore, from spectroscopy analyses, the peculiar surface, optical properties, and methylene blue photodegradation test of S-doped TiO2 samples, as compared to pure TiO2, have been investigated and explained by the effects caused by the exchange of S species with O species and by the surface defects induced by the strong H2S treatment.

Effects of Molecular Structure and Solvent Polarity on Adsorption of Carboxylic Anchoring Dyes onto TiO2 Particles in Aprotic Solvents.

Interactions of molecules with the surface of TiO2 particles are of fundamental and technological importance. One example is that the adsorption density and energy of the dye molecules on TiO2 particles affect the efficiency of dye-sensitized solar cells (DSSC). In this work, we present measurements characterizing the adsorption of the two isomers, para-ethyl red (p-ER) and ortho-ethyl red (o-ER), of a dye molecule potentially applicable for DSSC onto TiO2 particles by second harmonic scattering (SHS). It is found that while at the wavelengths used here o-ER has a much bigger molecular hyperpolarizability, p-ER exhibits strong SHS responses but o-ER gives no detectable SHS when the dyes are added to the TiO2 colloids, respectively. This observation indicates that o-ER does not adsorb onto TiO2, likely due to steric hindrance. Furthermore, we investigate how solvents affect the surface adsorption strength and density of p-ER onto TiO2 in four aprotic solvents with varying polarity. The absolute magnitude of the adsorption free energy was found to increase with the specific solvation energy that represents the ability of accepting electrons and solvent polarity. It is likely that resolvation of the solvent molecules displaced by the adsorption of the dye molecule at the surface in stronger electron-accepting and more polar solvents results in a larger adsorption free energy for the dye adsorption.

Fabrication of transparent metal mesh electrode by using silver-metal oxide nanoparticles for application to touch screen panel

ABSTRACTIn this work core-shell type Ag-metal oxide particles were synthesized by coating of Ag metal on the surface of SiO2, ZnO and TiO2 particles utilizing alkylamine silver complex as Ag source. The resulting Ag-SiO2, Ag-ZnO and Ag-TiO2 nano particles were used to make Ag-metal oxide paste with the epoxy resin as binder polymer, ethylcarbitol acetate as solvent and polymeric wetting agent as rheological additive. The micron sized trench pattern was fabricated on polyethylene terephthalate(PET) film by UV imprinting method utilizing the mold with embossed trench layer pattern. The nano-sized silver paste was filled into trench layer patterned on PET film by using a screen printer type filling machine. The silver metal mesh transparent conducting electrode touch sensor showed high visible light transmittance(∼90%) and low resitivity of 3.6 × 10−4 Ωcm required in the practical applications.