Surface Of TiO2 Particles Research Articles

Fabrication of highly dispersed NiTiO3@TiO2 yellow pigments with enhanced NIR reflectance

The highly dispersed NiTiO3@TiO2 yellow pigments with core-shell structure were prepared through calcinations of precursors obtained from the precipitation of Ni2+ on the surface of TiO2 particles. The synthesized pigments were characterized by XRD, SEM, TEM, UV–vis-IR spectroscopy. The results showed that the pigments were consisted of TiO2 core and outer ilmenite NiTiO3 shell. UV–vis diffuse reflectance spectroscopy results showed the enhance reflection peak at ∼580nm of the NiTiO3@TiO2 pigments result in a better yellow color than that of the pure NiTiO3 pigments. Compared with pure NiTiO3 pigments, the NiTiO3@TiO2 pigments also presented a much higher NIR reflectance. The mechanism analyzed results indicated that the reason was attributed to the special core-shell structure. The solar reflective coating colored by the NiTiO3@TiO2 pigments reduced the inner surface temperatures of glass plates by approximately 8.7°C.

Synthesis and coloration of highly dispersed NiTiO3@TiO2 yellow pigments with core-shell structure

The highly dispersed NiTiO3@TiO2 yellow pigments with core-shell structure were prepared through calcinations of precursors obtained from the precipitation of Ni2+ on the surface of TiO2 particles. The synthesized pigments were characterized by XRD, SEM, TEM, Uv–vis spectroscopy and colorimetry. The pigments were found to consist of TiO2 core and outer ilmenite NiTiO3 shell. The optical absorption of Ni2+ in octahedral coordination produced intense yellow colors. Compared with pure NiTiO3, the NiTiO3@TiO2 pigments presented higher yellow and lower red hues, resulted in intense yellow colors. The particle size distribution of the prepared pigments and ζ potential measurement indicated that the NiTiO3-0.75@TiO2 pigments were uniform and well-dispersed in glycol solvents, and they form relatively more stable suspension than pure NiTiO3 pigments. Meanwhile, these pigments were stable in commercial low–temperature ceramic glazes, possessed more brilliant yellowish colors than pure NiTiO3 prepared by sol-gel method.

Properties of AlPO4/CePO4 hybrid coating on rutile TiO2

A dense and amorphous AlPO4/CePO4 film was prepared on the surface of rutile TiO2 particles by chemical deposition method. Compared with plain rutile TiO2 particles, the water dispersibility, whiteness and brightness were obviously improved. The fabricated CePO4/AlPO4 hybrid layer effectively suppressed the photo-catalytic activity of rutile TiO2 particles. Optimum cerium phosphate content (counted by CeO2) of hybrid coating should not exceed 0.5 wt-% when AlPO4 (counted by Al2O3) was 2 wt-% to effectively balance the whiteness, brightness and photo-stability.

Effects of release agents on the film morphology of TiO2 photoanodes for FDSSCs by the roll-to-roll method

Flexible dye-sensitized solar cells (FDSSCs) are dye-sensitized thin-film solar cells constructed on flexible substrate with the advantages of eco-friendly, ease of fabrication, low cost and light weight. FDSSCs exhibit extensive application prospect. Herein, FDSSCs were constructed by the roll-to-roll method using terpineol and silicone oil as the release agent. Three-dimensional profile measurement is taken directly on nanocrystalline-TiO2 photoanodes. The phase composition and surface micro-morphology indicate that relatively large grain sizes and uniform surface of TiO2 particles are obtained. A layer of amorphous SiO2 exists on the nanocrystalline-TiO2 photoanode owing to the release agent (silicon oil), which hinders electrons to travel, thus the photoelectric conversion efficiency is low. However, nanocrystalline-TiO2 photoanodes with uniform particles, good density and high porosity are achieved by using the release agent of terpineol, and the energy conversion efficiency of 2.97% was obtained.

Anchoring Nitrogen-Doped TiO2 Nanocrystals on Nitrogen-Doped 3D Graphene Frameworks for Enhanced Lithium Storage.

An advanced architecture design of nitrogen-doped TiO2 anchored on nitrogen-doped 3D graphene framework composites (denoted as N-TiO2 /N-3D GFs) have been fabricated by a facile template process and further NH3 treatment. The 3D graphene framework allows the electrolyte to penetrate into the inverse opal structure, and possesses high electronic conductivity. The close contact between the N-TiO2 and the graphene suppresses the growth and aggregation of TiO2 nanoparticles during heating process, leading to decreased Li+ diffusion length. The N-doping in both TiO2 and the graphene matrix could improve the electronic conductivity on the TiO2 particle surface and between adjacent particles. As expected, when used as an anode for Li-ion batteries (LIBs), the N-TiO2 /N-3D GFs composite delivers an excellent reversible capacity of 165 mA h g-1 after 200 cycles at 100 mA g-1 and an outstanding rate capability of 114 mA h g-1 after 1000 cycles at 1 Ag-1 . With rational design, this strategy could be extended to other electrode materials that may hold great promise for the development of high energy storage systems.

Influence of aggregate size on photoactivity of N-doped TiO2 particles in aqueous suspensions under visible light irradiation

Abstract This work is focused on the study of the correlation between the photocatalytic activity of N-doped TiO2 particles, achieved by a designed synthesis, and their degree of aggregation in aqueous suspension. N-doped TiO2 photocatalyst particles, suspended in bidistilled water, presented a trimodal (in the nano-micro metric range) aggregate size distribution. This distribution resulted monomodal, in the nanometric range, when in the aqueous solution was added an organic dispersing agent (azulene). This behavior was associated to the presence, on the N-doped TiO2 particle surfaces, of an organic phase which was detected by thermal and infrared analysis. This organic phase was assumed to have a stabilizing function for nanoparticles. The influence of aggregate size of N-doped TiO2 photocatalyst on the photocatalytic degradation of methylene blue has been studied. The aggregate size distribution of photocatalyst influenced the amount of methylene blue adsorbed on catalyst surface and increased the photocatalytic activity. The influence of operating parameters such as the amount of dispersing agent and the amount of photocatalyst in aqueous suspensions has also been examined.

Surface Organic Modification of TiO2 Powder and Relevant Characterization

Surface organic modification was conducted to TiO2 with modifiers to improve the dispersity and comparability of pigment TiO2 in application system by adjusting particle surface characteristics. Then, modification effects were characterized according to the changes in wetting contact angle and activation index of TiO2 before and after modification. Moreover, the modification mechanisms of sodium stearate and sodium oleate were studied by analyzing the characteristics of TiO2 surface functional groups in modification system and effects of modifiers. The results showed that, after being wet-processed with sodium stearate and sodium oleate, TiO2 could turn from surface hydrophilic to inductive hydrophobic with controllable degree. The wetting contact angle of modified TiO2 increased from 7° to 125.6° and 121.3°, respectively. The dispersity of TiO2 in organic medium was stronger than that in inorganic medium. The modifiers formed absorption with chemical property on TiO2 particle surface, so the inductive hydrophobicity of surface was stable.

Direct combination of hydrogen evolution from water and methane conversion in a photocatalytic system over Pt/TiO2

The CH4 conversion under ambient condition remains a challenge over the past years, and the production of the ideal clean energy of H2 is considered as an alternative method to meet the requirement of sustainable development. Herein, a new photocatalytic reaction system involved H2 evolution from aqueous water and CH4 conversion is established over Pt/TiO2. The synergistic effect between the two reactions of H2 production and CH4 conversion brings up the considerable quantum efficiencies of H2 production to 4.7% without sacrificial agent and CH4 conversion (the main products are C2H6 and CO2) to 3.3% simultaneously. The introduction of Pt on the surface of TiO2 particles facilitates the activation of CH4 and OH that can assist to produce methyl radical (CH3), afterwards more C2H6 (61.7% selectivity) is formed.

Characterization of Interfacial Charge‐Transfer Photoexcitation of Polychromium‐Oxo‐Electrodeposited TiO2 as an Earth‐Abundant Photoanode for Water Oxidation Driven by Visible Light

Polychromium-oxo-deposited TiO2 (CrIII x Oy /TiO2 ) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth-abundant photoanodes for visible-light-driven water oxidation. The high-resolution transmission electron microscopy (HR-TEM) observation illustrated that an CrIII x Oy layer with approximately 2-3 nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the CrIII x Oy /TiO2 electrodes. However, the wavelength (below 620 nm) for photocurrent generation at CrIII x Oy /TiO2 -rutile was longer than that (below 560 nm) at CrIII x Oy /TiO2 -P25 by 60 nm, which is in agreement with the difference (0.2 eV) in the conduction band (CB) edge energy between rutile and anatase TiO2 . This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr 3d of the deposited CrIII x Oy layer to the TiO2 CB. The photocurrent generated for CrIII x Oy /TiO2 -rutile was higher than that for CrIII x Oy /TiO2 -anatase, which is ascribed to 1) more effective CrIII x Oy deposition on the rutile particles, 2) a larger electrolyte/CrIII x Oy interface for water oxidation as a result of smaller rutile particles (ca. 30-40 nm) compared with larger P25 particles (ca. 40-80 nm), and 3) more effective use of visible light owing to the low energy IFCT transition of rutile.

Cu and Zr surface sites in the photocatalytic activity of TiO2 nanoparticles.

The rate of methylene blue and terephthalic acid degradation assisted with double metal-modified catalyst (0.1mol% Cu and 1.0mol% Zr) was enhanced as compared with single metal-modified catalysts (0.1, 0.5mol% Cu and 1.0mol% Zr). The wet impregnation method was used for copper and zirconium modification of the surface of Aeroxide P25 TiO2 particles. Simultaneous loading of both metals on the surface of P25 leads to an increased specific surface area of the obtained material despite negative Cu influence. The tendency of stabilization and agglomerate size rising with the time for Cu and Zr-modified catalysts were traced by dynamic light scattering (DLS) measurements. The observed optical characteristics suggest that Cu compensated the broadening of band gap caused by Zr loading. Crystal structure of obtained photocatalysts was explored by XRD; morphological data and particle size were obtained by SEM. EDX was used for Zr and Cu content determination. Cu K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analytical techniques were used to investigate the local Cu neighbourhood in the samples and to identify copper coordination and valence state of copper species in the synthesized nanocomposites.

Effects of porous films on the light reflectivity of pigmentary titanium dioxide particles

The light reflectivity of the film-coated titanium dioxide particles (TiO2) as a function of the film refractive index was derived and calculated using a plane film model. For the refractive index in the range of 1.00–2.15, the lower the film refractive index is, the higher is the light reflectivity of the film. It is inferred that the lower apparent refractive index of the porous film resulted in the higher reflectivity of light, i.e., the higher hiding power of the titanium dioxide particles. A dense film coating on TiO2 particles with different types of oxides, i.e., SiO2, Al2O3, MgO, ZnO, ZrO2, TiO2, corresponding to different refractive indices of the film from 1.46 to 2.50, was achieved, and the effects of refractive index on the hiding power from the model prediction were confirmed. Porous film coating of TiO2 particles was achieved by adding the organic template agent triethanolamine (TEA). The hiding power of the coated TiO2 particles was increased from 88.3 to 90.8 by adding the TEA template to the film coating (5–20wt%). In other words, the amount of titanium dioxide needed was reduced by approximately 10% without a change in the hiding power. It is concluded that the film structure coated on TiO2 particle surface affects the light reflectivity significantly, namely, the porous film exhibits excellent performance for pigmentary titanium dioxide particles with high hiding power.

Development of linear and threshold no significant risk levels for inhalation exposure to titanium dioxide using systematic review and mode of action considerations

Titanium dioxide (TiO2) has been characterized as a poorly soluble particulate (PSP) with low toxicity. It is well accepted that low toxicity PSPs such as TiO2 induce lung tumors in rats when deposition overwhelms particle clearance mechanisms. Despite the sensitivity of rats to PSPs and questionable relevance of PSP-induced tumors to humans, TiO2 is listed as a possible human carcinogen by some agencies and regulators. Thus, environmental toxicity criteria for TiO2 are needed for stakeholders to evaluate potential risks from environmental exposure and regulatory compliance. A systematic review of the literature was conducted to characterize the available data and identify candidate datasets upon which toxicity values could be derived. Key to this assessment, a survey of mechanistic data relevant for lung cancer was used to support quantitative inhalation risk assessment approaches. A total of 473 human studies were identified, 7 of which were epidemiological studies that met inclusion criteria to quantitatively characterize carcinogenic endpoints in humans. None of these studies supported derivation of toxicity criteria; therefore, animal data were used to derived safety values for TiO2 using different dose-metrics (regional deposited dose ratios, TiO2 particle surface area lung burden, and volumetric overload of alveolar macrophages), benchmark dose modeling, and different low-dose extrapolation approaches. Based on empirical evidence and mechanistic support for nonlinear mode of action involving particle overload, chronic inflammation and cell proliferation, a no significant risk level (NSRL) of 300 μg/day was derived. By comparison, low-dose linear extrapolation from tumor incidence in the rat lung resulted in an NSRL value of 44 μg/day. These toxicity values should be useful for stakeholders interested in assessing risks from environmental exposure to respirable TiO2.

The effect of mesoporous TiO2 pore size on the performance of solid-state dye sensitized solar cells based on photoelectrochemically polymerized Poly(3,4-ethylenedioxythiophene) hole conductor

Photoelectrochemical polymerization of poly(3,4-ethylenedioxythiphene) (PEDOT) has recently been introduced and widely investigated for fabrication of the hole transporting material (HTM) in highly efficient solid state dye sensitized solar cells (sDSCs). In this work, the effects of the surface area and pore size of TiO2 film were for the first time investigated in the sDSCs employing the in-situ polymerizated PEDOT HTM. Three different varieties of mesoporous TiO2 particles with controllable surface area and pore size were synthesized through the basic route in order to study the corresponding sDSC photovoltaic performances. It was found that the pore size plays an important role in the kinetics of the photoelectrochemical polymerization (PEP) process and the formation of the PEDOT capping layer. Larger pore sizes provided a more favourable pathway for the precursor diffusion through the mesoporous pores during the PEP process, which contributed towards a more efficient PEP. However, the interfacial contact area between the formed polymer and the dyes on the surface of TiO2 particle would be lower in the case of larger pore sizes, which consequently caused a less efficient dye regeneration process. Electronic diffusion on the other hand was improved for larger particle sizes. Employing an organic dye LEG4 and the self-made TiO2 with an optimal pore size of 25nm and particle size of 24nm, the sDSCs showed a promising power conversion efficiency (PCE) of 5.2%, higher than 4.5% for the commercial TiO2 Dyesol DSL-30. By measuring the dye regeneration yield and the kinetics through photoinduced absorption, it was observed that the homemade TiO2 based device had more efficient dye regeneration compared to the Dyesol based device, which could result from the better interfacial contact between the PEDOT and the dye. This work provides important information on the effect of meso-pore size on sDSCs and points to the necessity of further photoanode optimization toward the enhancement of the PCE of polymeric hole conductor-based DSCs.

Catalytic Properties of Polyvanadate Xerogels Supported to Anatase in Decomposition of Hydrogen Peroxide and Oxidation of o‐Xylene

SummaryThe present work deals with evaluation of the catalytic properties of polyvanadate xerogels deposited on titanium dioxide (anatase). Xerogels of polyvanadates in the form of nanofibers were obtained by sol‐gel method. The average sizes of polyvanadate nanoparticles in aqueous solution determined by DLS were equal to 7 and 50 nm. TEM results reveal the formation of nanostructured thin layers of polyvanadates on the surface of TiO2 particles. The catalytic properties of polyvanadates deposited on the surface of anatase by impregnation method were studied with respect to decomposition of hydrogen peroxide and oxidation of o‐xylene under mild conditions.

Preparation of paraffin/porous TiO2 foams with enhanced thermal conductivity as PCM, by covering the TiO2 surface with a carbon layer

In the present study, porous TiO2 foams (PTF) were prepared by particle-stabilized emulsion method. The samples having solid contents ranging from 20wt.% to 35wt.% were prepared and successfully impregnated with paraffin without using a surfactant. SEM images showed that the prepared PTFs had three-dimensional interpenetrating structures with good porosities. The pore structure and morphology of PTF was markedly influenced by the solid content. With increase in solid content, porosity decreased, along with a decrease in the homologous encapsulation ratio of paraffin. Differential scanning calorimetry (DSC) evaluated the thermal properties of the paraffin/PTF (PTFP) composites. DSC results showed that with a solid content of 20wt.%, the paraffin adsorption reached 62vol.% and latent heat of the composite PCM was 94.05J/g after 200 melting/freezing cycles. TGA results showed that the form-stable composite PCMs had good thermal stabilities. In order to further enhance the thermal conductivity and improve the adsorption capacity of PTF, sucrose was added to the emulsion and carbonized in situ to form carbon/PTF (PTFC). This could also be successfully impregnated with paraffin to obtain the form-stable composite paraffin/PTFC (PTFCP). The TEM images and results of XPS analysis confirmed that the surfaces of TiO2 particles were covered with a 2nm thick carbon film (C/TiO2). The thermal conductivity of PTFCP increased from 0.302W/mK to 1.059W/mK compared to PTFP, along with a further improvement in adsorption capacity. Furthermore, the results of FT-IR analysis and thermal cyclic tests showed that the form-stable composite PCMs had good chemical stability and thermal reliability after 200melting/freezing cycles. Therefore, the prepared form-stable composite PCMs having excellent pore structures, thermal properties, thermal reliabilities, and chemical stabilities are promising PCM candidates for heat energy storage applications.

Amorphous TiO2 Buffer Layer Boosts Efficiency of Quantum Dot Sensitized Solar Cells to over 9%

Charge recombination at an electrode/electrolyte interface is the main factor to limit the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we present a novel and facile strategy based on successive coating of a sensitized electrode with a combination of blocking layers in appropriate sequence for suppressing the charge recombination. In this scenario, modification of the exposed surface of both TiO2 particles and QDs with an amorphous TiO2 (am-TiO2) layer via a classical TiCl4 hydrolysis treatment plays a fundamental role to enhance the effectiveness of a recombination blocking ZnS/SiO2 barrier layer. This strategy allows construction of CdSe0.65Te0.35 QD based champion QDSCs exhibiting a new PCE record of 9.28% and a certified PCE of 9.01% under full one sun illumination. The specific nature and sequence of the layering process is critical for the gain of photovoltaic performance. Control experiments indicate that the am-TiO2 is superior to a crystalline TiO2 laye...

Modification of TiO2 powder via atmospheric dielectric barrier discharge treatment for high performance lithium-ion battery anodes

The main objective of this study is to improve the electrochemical performances of TiO2 Li-ion anode material by introducing plasma treatment on TiO2 powder. A specially designed atmospheric dielectric barrier discharge plasma generator feasible to modify powders is proposed. The rate capacity of 20min plasma-treated TiO2 anode revealed nearly 20% increment as compared to that of pristine TiO2 at the rates of 0.5, 1, 2, 5, 10C. As-treated TiO2 was first analyzed by the X-ray diffractometer and high resolution transmission electron microscope confirmed that there was no noticeable surface morphology and microstructure change from plasma treatment. In addition, plasma-treated TiO2 was reduced with increasing treatment duration. Significant amount of excited argon (Ar∗) and excitation of a nitrogen second positive system (N2∗) were discovered using optical emission spectroscopy (OES). It was believed that Ar∗ and N2∗ contributed to TiO2 surface reduction as companied by formation of oxygen vacancy. A higher amount of oxygen vacancy increases the chance of allowing excited nitrogen to dope onto surface of TiO2 particle. Electrochemical properties of TiO2 were raised due to the production of oxygen vacancy and nitrogen doping. These findings enhance the understanding of the atmospheric plasma treatment on the potential application of TiO2 anode material in Li-ion battery.

Influence of Carbon Nanotubes on Photocatalytic Activities of Titanium Dioxide Nanocomposite Powders

This research aims to produce TiO2-based composite powder by growing of carbon nanotubes (CNTs) on the surface of micron-sized TiO2 particles using a chemical vapor deposition (CVD) technique. This nanocomposite powder will be further used as feedstock powder to build up as a coating using a thermal spray technique. This coating is expected to have better photocatalytic efficiency over that of pure TiO2 coating. For composite powder preparation, rutile-phase of TiO2 powder with particle size in a range of 25 – 45 µm was used as a starting powder. The powder was placed in a CVD apparatus under ethanol atmosphere as a carbon source. The best CNTs growing condition was found to be 650°C for 60 min. The starting powder and as-synthesized composite powders were characterized by scanning electron microscopy, energy dispersive spectrum, Raman spectroscopy and UV-vis spectroscopy. The results showed that CNTs were successfully grown in-situ on the surface of TiO2 particles. The photocatalytic activities under visible-light were examined based on a degradation of methylene blue. The degradation efficiency of the TiO2/CNTs composite powder was found to be higher than that of pure TiO2. It is expected that the TiO2/CNTs nanocomposite powder could be further used to fabricate various of nanocomposite products.

Biotechnologically obtained nanocomposites: A practical application for photodegradation of Safranin-T under UV-Vis and solar light

This research was undertaken to determine the potential of biologically obtained ZnS-TiO2 nanocomposites to be used as catalysts in the photodegradation of organic pollutants, namely, Safranin-T. The photocatalysts were prepared by modifying the surface of commercial TiO2 particles with naturally produced ZnS, using sulfide species produced by sulfate-reducing bacteria and metal contaminated wastewaters. Comparative studies using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), prior and after photodegradation, were carried out in order to monitor possible structural and morphological changes on the particles. Adsorption properties and specific areas were determined by the Brunauer–Emmet–Teller (BET) method. The final solutions were characterized by UV-Vis and chemical oxygen demand (COD) content in order to determine Safranin-T concentration and toxicity. The influence of the catalyst amount, initial pH and dye concentration was also evaluated. Finally, the efficiency of the precipitates as catalysts in sunlight-mediated photodegradation was investigated, performing two scale experiments by using different volumes of dye-contaminated water (150 mL and 10 L). All tested composites showed potential to be used as photocatalysts for the degradation of Safranin-T, although the ZnS-TiO2_0.06 composite (0.06 g of TiO2 per 50 mL of the zinc solution) was the most effective. This substantiates the applicability of these biologically obtained materials as efficient photocatalysts for the degradation of organic pollutants, in laboratorial conditions and under direct sunlight.

The Effect of Synthesis Conditions on Mesoporous Structure and the Photocatalytic Activity of TiO2 Nanoparticles.

Mesoporous TiO2 nanoparticles have been synthesized by sol-gel method in different preparation conditions to investigate the effect of triblock copolymer, acetic acid and water on mesoporous structure and the photocatalytic activity. The synthesized photocatalysts were characterized by means of X-ray powder diffraction, Nitrogen adsorption/desorption studies, High resolution transmission electron microscopy, Scanning electron microscopy, Diffuse reflectance UV-Vis spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis. Among the various synthesized materials, mesoporous TiO2 synthesized using triblock copolymer as a structure directing template in acetic acid medium with high water ratio calcined at 400 degrees C was found to have the highest photocatalytic activity due to the enhanced band gap energy, high specific surface area and high average pore size. The large mesopores provide more pathways for the reactants to enter and products to escape and enhances the adsorption of methylene blue. The photocatalytic activity decreases with increase of solution pH. The rate of *OH formation is high at lower pH, which enhances the photocatalytic activity was revealed by photoluminescence technique. In addition, the adsorbed hydroxyl groups on the surface of mesoporous TiO2 particles can interact with photogenerated holes to produce more *OH radicals, which enhances charge transfer efficiency and enhances the rate of *OH formation.