Surface Of TiO2 Particles Research Articles

Synthesis and Characterization of Hollow TiO2 Particles Coated with Polyimide Brushes by Click Chemistry

In order to improve the compatibility between nanoparticles and polymer matrix, a feasible processing way for grafting polyimides (PI) on the surface of hollow TiO2 particles was developed. Hollow TiO2 spheres were prepared by using polystyrene-methyl acrylic acid latex as a template starting from tetrabutyl titanate. Surface graft of azide-decorated hollow TiO2 spheres with well-defined alkyne-terminated PI were achieved by "click" chemistry in three steps: (1) choloromethylation and azidization of hollow TiO2, (2) preparation of alkyne-terminated PI by polycondensation, (3) click coupling between the azidized hollow TiO2 and the alkyne-terminated PI under the catalysis of CuSO4/sodium ascorbate. Fourier transform infrared (FTIR) and Nuclear Magnetic Resonance (1HNMR) spectra were used to illustrate quantitative transformation of the PI brushes on hollow TiO2 particles into the desired functional group. The morphology of hollow TiO2-PI composite particles was characterized by transmission electron microscopy (TEM) which showed the irregular hollow structure. The results indicate that the grafting of polymer chains with thermostability and flame retardance on the surface of hollow TiO2 sphere is successful.

A comparative study about the influence of metal ions (Ce, La and V) doping on the solar-light-induced photodegradation toward rhodamine B

Water contamination by the textile dye effluents has become a serious environmental issue, which are threatening to the human health and biological diversity. The TiO2 photocatalysis has been proven to be used to remove textile dyes in water. In order to improve its solar-light activity, three metal ions, including cerium (Ce), lanthanum (La) and vanadium (V), were selected as dopants to prepare metal ions doped TiO2 particles by sol–gel method. The synthesized particles were characterized by X-ray diffraction, field scanning electron microscopy, UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Through the physicochemical properties of the resulting metal ions doped TiO2 particles, we found that characteristics of dopants could strongly affect the crystalline phase and crystallite size, the optical absorption spectrum and the bandgap energy of the modified TiO2 catalysts, and consequently influence the photocatalytic ability. We investigated the link between dopant’s characteristics and photoactivity of the doped catalysts, and deduced that the existence of dopant in the modified catalysts is crucial. In the case of Ce or La doping, the dopants homogeneously dispersed on the surface of TiO2 particles as oxides and interacted with TiO2 particles via REOTi bond. Nevertheless, the V species successfully entered the TiO2 lattice and substituted for Ti4+ due to its similar ionic radius with Ti. The photocatalytic activities of Ce-, La-, or V-doped TiO2 photocatalysts were evaluated by the degradation of rhodamine B under simulated solar-light illumination. In our case, only the doping of Ce or V could drive efficient solar-light activity. The bandgap energy of 1.0%-Ce–TiO2 was narrowed to 2.70eV and the removal ratio for dye could raise up to 83% with a relatively high calcination temperature.

Dispersion of TiO2 particles and preparation of SiO2 coating layers on the surfaces of TiO2

Fine TiO2 has been widely used as a white pigment, but the aggregation of TiO2 particles related to the high specific surface area makes it a challenge to modify its surface. In this paper, NaOH and Na2SiO3 were adopted as regulators for the pH of TiO2 aqueous dispersion. It was discovered that when the pH is 12, the TiO2 particles have the maximum zeta potential and the repulsive force between two TiO2 particles is also at the maximum, which is favourable for the dispersion of TiO2. In terms of the modifying the surface, it was proved that a continuous and compact film of hydrous silica on the surface of TiO2 particles is produced by coprecipitation of Na2SiO3 and H2SO4 when the TiO2 particles are adequately dispersed by ultrasound at pH 12. Furthermore, it was found that the morphology of SiO2 is different when Na2SiO3 and H2SO4 solutions are added in different ways.

Alumina Surface Treated TiO2 - From Process to Application

Titanium dioxide (TiO2) has found widespread use. Typically it is used in another matrix to impart certain properties. For example, it is widely used as a white pigment for paints and polymers. The aim of this research work was to achieve improvements in the sense of processability as well as the dispersion performance of alumina surface treated pigmentary TiO2in polymer matrix. Wet chemical method was used to modify the surface of the TiO2 pigment. Surface treatment included precipitation of hydrous oxides of aluminium on the surface of TiO2 particles. During controlled surface treatment, agglomeration has been avoided, which has been proved to improve applicative properties of TiO2 particles. In addition to that, organic additives were applied to enhance performance attributes of the pigmentary TiO2. The effectiveness of surface treatment was determined using scanning-transmission (STEM) and transmission (TEM) electron microscopy. Quantitative evaluation of quality and dispersion of the pigments has been performed using Filter pressure test. Lower pressure generated during filter pressure test when particles were well dispersed in a polymer matrix. Surface treatment also affected pigment processibility; i.e. filterability and settling, which is of high importance for process planning.

Characterization and improved solar light activity of vanadium doped TiO2/diatomite hybrid catalysts.

V-doped TiO2/diatomite composite photocatalysts with different vanadium concentrations were synthesized by a modified sol-gel method. The diatomite was responsible for the well dispersion of TiO2 nanoparticles on the matrix and consequently inhibited the agglomeration. V-TiO2/diatomite hybrids showed red shift in TiO2 absorption edge with enhanced absorption intensity. Most importantly, the dopant energy levels were formed in the TiO2 bandgap due to V(4+) ions substituted to Ti(4+) sites. The 0.5% V-TiO2/diatomite photocatalyst displayed narrower bandgap (2.95 eV) compared to undoped sample (3.13 eV) and other doped samples (3.05 eV) with higher doping concentration. The photocatalytic activities of V doped TiO2/diatomite samples for the degradation of Rhodamine B under stimulated solar light illumination were significantly improved compared with the undoped sample. In our case, V(4+) ions incorporated in TiO2 lattice were responsible for increased visible-light absorption and electron transfer to oxygen molecules adsorbed on the surface of TiO2 to produce superoxide radicals ˙O2(-), while V(5+) species presented on the surface of TiO2 particles in the form of V2O5 contributed to e(-)-h(+) separation. In addition, due to the combination of diatomite as support, this hybrid photocatalyst could be separated from solution quickly by natural settlement and exhibited good reusability.

Reaction of human macrophages on protein corona covered TiO2 nanoparticles

The cytokine secretion of primary cells of human macrophages during the interaction of TiO2 nanoparticles (with an average primary size of 100-120nm) is investigated down to concentration levels suggested to be relevant for in vivo conditions. We find that high TiO2 concentrations induce the cytokines Interleukin IL-1β, IL-6, and IL-10 secretion, while at low concentrations only IL-6 secretion is observed. To obtain further evidence on in vivo conditions we investigated the development and structure of the protein corona of the nanoparticles. We demonstrated that the surface of TiO2 particles attract preferably secondary modified proteins which then induce cytokine secretion of macrophages. Our results indicate that concentration of corona covered TiO2 particles below 1μg/ml induce IL-6 secretion which is reported to be responsible for the development of autoimmune diseases as well as for the secretion of acute phase proteins. From the Clinical EditorThis study investigates the effects of protein corona covered titanium dioxide nanoparticles on human macrophages, concluding that concentration of such particles below 1 μg/ml induces IL-6 secretion, which may be responsible for the development of autoimmune diseases as well as for the secretion of acute phase proteins. This finding has important implications on future applications of such nanoparticles.

Catalytic Behavior of Flame-Made Pd/TiO2 Nanoparticles in Methane Oxidation at Low Temperatures

A controlled one-step synthesis of titania-supported palladium (Pd/TiO2) nanoparticles is demonstrated by using a premixed stagnation swirl flame with an ultrafine spray feeding system. The new method produces well-dispersed palladium clusters on the surface of TiO2 particle. The low-temperature methane catalytic oxidation indicates that the flame-made Pd/TiO2 possesses activity apparently higher than that of the impregnated one under the same Pd loading. For the first time, we observe a special pinched hysteresis loop of catalytic activity of Pd/TiO2 nanoparticles from the curves of CH4 conversion versus temperature during heating–cooling cycles. Thermal stability analysis confirms the complex coexistence and transformation of metallic Pd and PdO in Pd/TiO2 particles. Further morphological characterization reveals the oxidation rate is controlled by the metallic Pd content on the particle surface, whereas the deactivation of the catalysts is mainly due to the Pd dispersion decrement. The competition between the Pd dispersion decrement and the PdO reduction at the surface may result in the pinched hysteresis loop of Pd/TiO2 catalysts during low-temperature methane combustion.

Efficient Visible-Light-Driven Photocatalytic Degradation with Bi2O3 Coupling Silica Doped TiO2

A new TiO2-based visible light photocatalyst (Bi2O3/Si–TiO2) was synthesized by both Bi2O3 coupling and Si doping via a two-step method. The structural, morphological, light absorption, and photocatalytic properties of as-prepared samples were studied using various spectroscopic and analytical techniques. The results showed that Bi2O3/Si–TiO2 catalysts held an anatase phase and possessed high thermal stability. The doped Si was woven into the lattice of TiO2, and its content had a significant effect on the surface area and the crystal size of Bi2O3/Si–TiO2. The introduced Bi species mainly existed as oxides on the surface of TiO2 particles, and the Bi2O3 photosensitization extended the light absorption into the visible region. Bi2O3 coupling also favored the separation and transfer of photoinduced charge carriers to inhibit their recombination and Si doping enlarged the surface area of photocatalysts. Compared to bare TiO2, Bi2O3/TiO2, and Si–TiO2, Bi2O3/Si–TiO2 samples showed better activities for the degradation of methyl orange (MO) and bisphenol A (BPA) under visible light irradiation (λ > 420 nm). The highest activity was observed for 1.0% Bi2O3/15% Si–TiO2 calcined at 500 °C. The superior performance was ascribed to the high surface area, the ability to absorb visible light, and the efficient charge separation associated with the synergetic effects of appropriate amounts of Si and Bi in the prepared samples. The adsorbed hydroxyl radicals (•OH) were also found to be the most reactive species in the photocatalytic degradation.

Direct synthesis of supported palladium catalysts for methane combustion by stagnation swirl flame

The titania supported palladium nano catalysts (Pd/TiO2) are synthesized in one-step using a premixed stagnation swirl flame (SSF) with ultra-fine spray system. This novel SSF method, with features of short residence time and fast quenching, produces nanosized (<2.5nm) palladium particles being well dispersed on the 7–8nm TiO2 particle surface, with an overall specific surface area of 210–220m2/g. The X-ray photoelectron spectroscopy (XPS) results indicate that the collected palladium particles are a mixture of both Pd and PdO, whereas the TiO2 support is mainly in anatase phase by X-ray diffraction (XRD). A revised population balance model (PBM) by incorporating coagulation, sintering and scavenging of the binary system (Pd and TiO2) is developed to explain the in situ doping mechanism of Pd/TiO2 composites in the flame domain. Then, we use the synthesized nano catalyst to conduct the catalytic combustion of methane under 5–15% Pd loadings. It exhibits more excellent activity than those in the literature under identical temperatures. The T20, as 20% methane conversion temperature, can reduce to as low as 293°C at 15% Pd loading. It is because that the Pd/TiO2 catalysts made from the stagnation flame show a good dispersion of size-controlled palladium on TiO2 which may not be accessible by wet-chemistry and even other flame synthesis routes.

Improving stability of TiO2 particles in water by RF-plasma polymerization of poly(acrylic acid) on the particle surface

The stability of TiO2 particles in water was increased through plasma polymerization of acrylic acid (AA) onto the particles surface. The polymerization was carried out directly upon TiO2 powder by using two radiofrequency (RF) plasma reactors: one inductively coupled and another capacitively coupled. In both cases, a cross-linked polyacrylic acid (PAA) film was formed on TiO2 particles surface, which was characterized by Energy Dispersive Spectroscopy (EDS), Fourier-transformed infrared spectroscopy, (FTIR), Raman Spectroscopy, and X-ray photoelectron spectroscopy (XPS). The stability of the PAA-coated TiO2 particles was determined by their precipitation in water. It was found that a moderate plasma treatment effectively improved the stability of PAA-coated TiO2 particles. At low levels of AA polymerization, the TiO2 particles surface was not modified enough to improve their stability in water; on the other hand, a high degree of AA polymerization led to the formation of large agglomerates, induced by the PAA film, and these particles were not stable. As expected, the particle size and the Z-potential of the PAA-coated particles determined their stability in water. Under the optimum operating conditions of this study, the treated TiO2 particles showed stability as good as that of TiO2 particles modified with a dispersant.

Dye-Sensitized Solar Cells: Physically Stable Polymer-Membrane Electrolytes for Highly Efficient Solid-State Dye-Sensitized Solar Cells with Long-Term Stability (Adv. Energy Mater. 3/2014)

A highly stable, solid-state dye-sensitized solar cell with excellent power conversion efficiency is demonstrated using a novel 3D polymer network membrane (3D-PNM) electrolyte. As reported by Taiho Park and co-workers in article number 1300489, a one-pot, in situ cross-linking polymerization on the surface of TiO2 particles in the presence of redox species encapsulates with a thin porous membrane layer and leads to great physical stability for the 3D-PNM on the surface of the TiO2 electrode.

An N-doped anatase/rutile TiO2hybrid from low-temperature direct nitridization: enhanced photoactivity under UV-/visible-light

Colloidal N-doped TiO2 nanocrystals are successfully synthesized by low-temperature direct nitridization in triethylamine solution during hydrolysis of tetrabutyl titanate, followed by acidic peptization at 70 °C. Through adjusting the acid concentration and peptization time, the N-doped samples consisting of different proportions of anatase and rutile phases are obtained. Several characterization techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy are employed to determine the crystal phase, morphology, degree of nitrogen incorporation and optical properties of the products. The high resolution XPS spectrum of the N 1s region confirms the substitutional nitrogen doping of lattice oxygen in TiO2 crystals. For comparison, it is found that most of the N species are chemisorbed on the surface of TiO2 particles if the N-source is introduced after crystallization. The light response in the range of 400–500 nm is obviously improved by N doping, which facilitates the absorption of photons to produce e−–h+ pairs under visible irradiation. On the other hand, nitrogen doping also inhibits the recombination of the photoinduced carriers and therefore increases the quantum efficiency of the TiO2 photocatalyst. As a result, the as-synthesized N-doped TiO2 nanomaterials exhibit higher photocatalytic activity both in the UV- and visible-light region in contrast to the non-doped TiO2. The hybrid containing 63.1% anatase shows the highest photocatalytic activity, which is due to a synergistic effect between anatase and rutile.

New understanding of the difference of photocatalytic activity among anatase, rutile and brookite TiO2.

In general, anatase TiO2 exhibits higher photocatalytic activities than rutile TiO2. However, the reasons for the differences in photocatalytic activity between anatase and rutile are still being debated. In this work, the band structure, density of states, and effective mass of photogenerated charge carriers for anatase, rutile and brookite TiO2 are investigated by the first-principle density functional theory calculation. The results indicate that anatase appears to be an indirect band gap semiconductor, while rutile and brookite belong to the direct band gap semiconductor category. Indirect band gap anatase exhibits a longer lifetime of photoexcited electrons and holes than direct band gap rutile and brookite because the direct transitions of photogenerated electrons from the conduction band (CB) to valence band (VB) of anatase TiO2 is impossible. Furthermore, anatase has the lightest average effective mass of photogenerated electrons and holes as compared to rutile and brookite. The lightest effective mass suggests the fastest migration of photogenerated electrons and holes from the interior to surface of anatase TiO2 particle, thus resulting in the lowest recombination rate of photogenerated charge carriers within anatase TiO2. Therefore, it is not surprising that anatase usually shows a higher photocatalytic activity than rutile and brookite. This investigation will provide some new insight into understanding the difference of photocatalytic activity among anatase, rutile and brookite.

CeO2가 졸겔법으로 합성한 CeO2-TiO2계 SCR용 촉매의 활성에 미치는 물리화학적 영향

The effects of CeO2 on catalytic activity of CeO2-TiO2 for the selective catalytic reduction (SCR) of NOx were investigated in terms of structural, morphological, and physico-chemical analyseis. CeO2-TiO2 catalysts were synthesized with three different additions, 10, 20, and 30 wt% of CeO2, by the sol-gel method. The XRD peaks of all specimens were assigned to a TiO2 phase (anatase) and the peaks became broader with the addition of CeO2 because it was dispersed as an amorphous phase on the surface of TiO2 particles. The specific surface area of TiO2 increased with the addition of CeO2 from 60.6306 m 2 /g to 116.2791 m 2 /g due to suppression of TiO2 grain growth by CeO2. The 30 wt% CeO2-TiO2 catalyst, having the strongest catalytic acid sites (BrΦnsted and Lewis), showed the highest NOx conversion efficiency of 98 % at 300 o C among the specimens. It was considered that CeO2 contributes to the improvement of the NOx conversion of CeO2-

On the influence of the microwaves’ thermal and non-thermal effects in titania photoassisted reactions

In this paper we contend that the microwaves’ non-thermal effect(s) is an important factor in the enhancement of TiO2 photoassisted reactions involving the decomposition of organic pollutants in model wastewaters by an integrated microwave-/UV-illumination method (UV/MW). This method proved far superior in degrading organic pollutants than the more traditional TiO2-assisted photodegradations under UV irradiation alone (UV method). For instance, all the functions in the rhodamine-B (RhB) dye structure decompose competitively by the UV method for which the transformation of the nitrogen atoms was not an insignificant part of the process; however, their transformation to NH4+ ions (and some NO3−ions) was significantly enhanced by the UV/MW method. The latter also proved far superior to the UV method in the degradation of 1,4-dioxane under identical temperature conditions as for the UV/MW method but with conventional heating (UV/CH). In addition, the microwave-assisted photodegradation of bisphenol-A (BPA) was shown to be not only due to a microwave thermal effect, but also to a significant non-thermal effect that might implicate hot spots on the TiO2 particle surface when MW irradiated leading to enhanced photodegradation at near-ambient temperatures. Such enhancements in process dynamics may be due to enhanced formation of OH radicals under UV/MW irradiation, at least for the Evonik P25 titania system. The response of this metal oxide specimen to the microwave non-thermal effect(s) has been correlated to changes in lattice distortions in the TiO2 crystalline structure.

One-pot synthesis of TiO2–WO3 composite nanocrystallites with improved photocatalytic properties under natural sunlight irradiation

TiO2–WO3 composite crystallites were prepared by a one-pot synthesis via hydrothermal reaction using Ti(SO4)2 and Na2WO4·2H2O as source materials. The samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectrometer (EDS) methods. Results reveal that the WO3 particles are uniformly dispersed on the surface of TiO2 particles without any detectable change in crystal structure and morphology of the TiO2–WO3 composite nanocrystallites. Corresponding photocatalytic properties of the pure TiO2 and TiO2–WO3 crystallites are found to increase first and then decrease with increasing W/Ti molar ratios. The sample with a W/Ti molar ratio of 1:99 shows the highest photodegradation rate (95.8%) for Rhodamine B under natural sunlight irradiation.

Physically Stable Polymer‐Membrane Electrolytes for Highly Efficient Solid‐State Dye‐Sensitized Solar Cells with Long‐Term Stability

A 3D polymer‐network‐membrane (3D‐PNM) electrolyte is described for highly stable, solid‐state dye‐sensitized solar cells (DSCs) with excellent power‐conversion efficiency (PCE). The 3D‐PNM electrolyte is prepared by using one‐pot in situ cross‐linking polymerization on the surface of dye‐sensitized TiO2 particles in the presence of redox species. This method allows the direct connection of the 3D‐PNM to the surface of the TiO2 particles as well as the in situ preparation of the electrolyte gel during device assembly. There are two junction areas (liquid and solid‐state junctions) in the DSCs that employ conventional polymer electrolytes, and the major interface is at the liquid‐state junction. The solid‐state junction is dominant in the DSCs that employ the 3D‐PNM electrolyte, which exhibit almost constant performance during aging at 65 °C for over 700 h (17.0 to 17.2 mA cm–2). The best cell performance gives a PCE of 9.1%; this is slightly better than the performance of a DSC that employs a liquid electrolyte.

Combined embedding of N-doping and CaCO3 surface modification in the TiO2 photoelectrodes for dye-sensitized solar cells

A successive embedding of N-doping and CaCO3 surface modification was carried out in the TiO2 photoelectrodes for dye-sensitized solar cells (DSSCs). The combined effect was revealed with the great increase of the open-circuit voltage (Voc), short-circuit current (Jsc), and photoelectric conversion efficiency (η) of the prepared cells; the efficiency (η) was improved from 5.42% of a commercial TiO2 photoelectrode to 7.47% of an unmodified N-doped electrode, and to 9.03% of a N-doped and CaCO3 surface modified electrode. An enhanced photoresponse in N-doped TiO2 nanoparticles generate more photo-excited electrons in adsorbed dye, as supported by measured UV–vis diffuse reflectance spectra and incident photon to current conversion efficiency (IPCE). A successive CaCO3 surface modification then form a barrier on the surface of N-doped TiO2 particles, suppressing charge recombination of photo-generated electrons from N-doped TiO2 to dye or electrolyte, and thus extending their life time in the electrode, as supported by electron impedance spectroscopy (EIS). Furthermore, the higher basicity of the CaCO3 modified TiO2 facilitates the dye adsorption, as supported by the direct measurement of the amount of adsorbed dye.

Organic Pollutants Decomposition by TiO&lt;sub&gt;2&lt;/sub&gt; Visible-Light Photocatalysis with H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2 &lt;/sub&gt;Assistance&lt;i&gt;&lt;/i&gt;

The effects of crystalline structure (Anatase and Rutile) and H2O2 addition on TiO2 visible-light photocatalysis were studied, which used reactive brilliant red X-3B and phenol as model pollutants. The results indicated that reactive brilliant red X-3B could be degradated by the two form TiO2(anatase or rutile) under visible-irradiation with the assistance of H2O2, however, when the surface sites of TiO2 photocatalysts were preeminently occupied by CO32-, photodecomposition could not be processed. Phenol could also be degradated by the two form TiO2 under visible-irradiation with the assistance of H2O2, rutile TiO2 exhibited a better photocatalytic activity, and its degradation ratio could be 80% after 120 min of reaction. The concentration of the ring intermediates detected during phenol decomposition was evidently higher when using rutile TiO2 as photocatalyst, and the presence of hydroxyl radical inhibitor (tert-butyl alcohol or methanol) had great effects on the degradation efficiency of rutile TiO2, but had less effects on anatase TiO2. The degradation of phenol occurred mainly in the solution when using rutile TiO2 as photocatalyst, and in contrast, the degradation occurred mainly at the TiO2 particles surface when using anatase TiO2 as photocatalyst.

Effect of Surface Fluorination on the Charge/Discharge Properties of High Potential Negative Electrode TiO&lt;sub&gt;2&lt;/sub&gt;(B) for LIBs

Surface fluorination of TiO2(B) powder was conducted by pure F2 gas at room temperature for 1 h and the effect on the charge/discharge properties was examined as a negative electrode of Li-ion batteries (LIBs). X-ray diffraction (XRD) pattern was not changed before and after the surface fluorination though the peak intensities became weaker than that of the pristine sample, indicating the etching of the surface of SF-TiO2(B) power. This was supported by scanning electron microscopy (SEM) observation. However, X-ray photoelectron spectroscopy (XPS) analysis clearly revealed that F atoms exist on the surface of TiO2(B) particles and probably were covalently bonded with Ti atoms near the surface. From the charge/discharge tests at a C/6 rate, the SF-TiO2(B) exhibited a higher 1st discharge (203 mAh g-1) than the pristine sample (181 mAh g-1) with a good cycleability. Impedance analysis revealed that both resistances of solid electrolyte interphase (SEI) film and charge transfer at the SEI /active material interface were reduced by surface fluorination, implying the improvement of SEI film and permeability of the electrolyte solution to the interphase. The rate capability was improved by the surface fluorination up to 1C rate, at which the SF-TiO2(B) exhibited a high discharge capacity of around 150 mAh g-1.