Surface Of TiO2 Powder Research Articles

Surface modification of TiO2 with a less expensive metal (iron) to exploit solar energy in photocatalysis: An ecological and economical solution

To degrade the tryptophan molecule through photocatalysis, the exploitation of solar energy in the present study necessitated the use of visible light active photocatalysts. Iron-transition metal nanoparticles were deposited on the surface of TiO2 powders through an impregnation method to obtain X%Fe-TiO2 for the purpose of improving the optical absorption of TiO2 in the visible light region. The effects of iron percentage (X%: 2,4 and 5), iron oxidation state and pH on the photocatalytic performance of TiO2 modified under solar irradiation were thoroughly studied. The characterization results by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) indicate that iron nanoparticles were successfully fixed on the TiO2 surface. The absorption wavelengths of all X%Fe-TiO2 photocatalysts shifted towards the visible, confirming successful modification of the TiO2 surface with iron. Based on the empirical results, X%Fe-TiO2 nanomaterials demonstrate a higher activity compared with the unmodified TiO2 under solar irradiation. The 4%Fe(III)-TiO2 photocatalyst, in particular, displayed the highest photocatalytic activity at natural pH. The degradation was complete in 60 min. Therefore, it is interesting to note that iron had more functions and benefits than noble metals. The mechanism of the Fe-TiO2 system has been proposed in detail.

Synthesis of a Gold-Inserted Iron Disilicide and Rutile Titanium Dioxide Heterojunction Photocatalyst via the Vapor-Liquid-Solid Method and Its Water-Splitting Reaction.

A solid-state Z-scheme system is constructed whereby rutile titania (TiO2) and beta-iron disilicide (β-FeSi2) were combined to act as oxygen (O2)- and hydrogen (H2)-evolution photocatalysts, respectively, connected by gold (Au). β-FeSi2 island grains with diameters in the 0.5-2 μm range were formed on the surface of Au-coated TiO2 powder by the co-sputtering method. On the surface of TiO2 powder, the Au-Si liquidus phase was obtained via a Au-Si eutectic reaction, which contributed to the selective deposition and crystallization of β-FeSi2 island grains onto Au. After the loading of the H2-evolution cocatalysts platinum and chromium oxide onto β-FeSi2, the system obtained catalyzed the evolution of H2 and O2 in a stoichiometric ratio from pure water under ultraviolet light irradiation. The transfer of photoexcited electrons in the conduction band (CB) of β-FeSi2 to Pt causes the reduction of protons to H2, and the photogeneration of holes in the valence band (VB) of TiO2 causes the oxidation of water to O2. In addition, the photogenerated holes in the VB of β-FeSi2 and the photoexcited electrons in the CB of TiO2 combined with each other in the Au layer, affording the completion of the overall photocatalytic water-splitting.

Simultaneous Second Harmonic Generation and multiphoton excited photoluminescence in anatase TiO2 nano powders

Second Harmonic Generation (SHG) and Multiphoton Excited Photoluminescence (MEPL) are observed in retro-reflection mode from a 22 nm diameter anatase TiO2 nanoparticle powder. Depth intensity profiles are obtained by scanning the fundamental beam focal point through the TiO2 powder surface into its volume for the energy of the incident photons tuned around the anatase TiO2 band-gap energy of 3.2 eV. Evidence for the appearance of both SHG and MEPL is presented, their relative contribution depending on the conditions of photo-excitation, in particular the fundamental wavelength and the focal point depth location. MEPL dominates at fundamental photon energies matching the band-gap energy whereas below and above the band-gap SHG is clearly seen. Depth intensity profiles exhibiting a rising edge determined by the fundamental laser beam focusing conditions and a decreasing edge determined by extinction and multiphoton scattering strongly differ between SHG and MEPL, SHG profiles being by far narrower than that of MEPL. Re-absorption of the emitted SHG and MEPL light occurs due to the spectral proximity with the TiO2 band gap energy but excitation with fundamental light below band-gap further suggests that the intrinsic difference between the two SHG and MEPL processes is responsible for the contrasted depth profiles. This combined study where both SHG and MEPL occur presents perspectives in the study of the photonic properties of powder materials.

Interfacial charge transfer complex between TiO2 and non-aromatic ligand squaric acid

The attachment of squaric acid, a non-aromatic molecule, to the surface of TiO2 powder induced the optical absorption of the obtained hybrid material in the visible spectral range due to the interfacial charge transfer complex formation. The optical characterization of the hybrid is supported by the density functional theory calculations of the model cluster. The paramagnetic species generated upon excitation with ultraviolet or visible light, in both TiO2 powders, pristine and surface-modified, were identified conducting low-temperature solid-state and indirect electron paramagnetic resonance (EPR) spectroscopy experiments (spin trapping and spin scavenging). The solid-state EPR experiments indicated the promotion of electrons from the organic moiety to the titania conduction band under visible-light excitation of hybrid. Also, the spin scavenging experiments showed that the electrons generated in the hybrid upon the visible-light activation facilitate the reduction of the radical cations present in the dispersion, while these effects are not observed for pristine TiO2.

Photodeposited IrO2 on TiO2 support as a catalyst for oxygen evolution reaction

A simple, alternative, catalyst preparation method was proposed in order to combine the properties of photoactive and stable TiO2 with state-of-the art of IrO2 for the oxygen evolution reaction (OER). IrO2 nanoparticles were obtained in the process of photodeposition on the surface of TiO2 powder by UV illumination from appropriate Ir salt aqueous solution. Physicochemical characterization of the resulting IrO2/TiO2 composite, containing 25% w/w Ir, was carried out by transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the prepared IrO2/TiO2 catalyst was compared with that of commercial unsupported IrO2. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to identify the surface electrochemistry and OER of the IrO2/TiO2 catalyst. Electrochemical impedance spectroscopy (EIS) was used to determine uncompensated and charge transfer resistance. CA experiments were carried out in order to evaluate the stability of the IrO2/TiO2 composite during OER in the dark and under UV light irradiation. The photodeposition method on a TiO2 support resulted in 1–2 nm Ir nanoparticles, very well dispersed on the surface and in their oxidized state (IrO2). Electrochemical results indicated that despite its lower conductivity, the IrO2/TiO2 composite exhibits comparable intrinsic electrocatalytic activity for OER with that of the commercial IrO2 catalyst. It was found that under UV light irradiation there has been improvement of the stability of the IrO2/TiO2 performance during oxygen evolution (presumably due to sustained activation of reactive species via photogenerated holes or OH radicals) as well as current enhancement (due to the interaction between the photogenerated holes in TiO2 support and IrO2 nanoparticles). These would be beneficial effects in prolonged water photo-electrolysis.

Fabrication of Yb-doped TiO2 using liquid phase plasma process and its photocatalytic degradation activity of naproxen

Photocatalysts responding to visible light were prepared by doping ytterbium (Yb) to TiO2 powder by LPP method. Yb2O3 nanoparticles were uniformly precipitated on the surface of TiO2 powder, and when the precursor concentration was increased, the precipitated Yb2O3 nanoparticles increased. The precipitated Yb element lowered the band gap energy of Yb-doped TiO2 photocatalyst (YTP) by 0.07 to 0.14 eV compared to bare TiO2. YTPs degraded naproxen (NPX) better than bare TiO2, especially under blue LED light (maximum wavelength 470 nm), and YTP containing higher Yb elements showed higher decomposition activity. NPX was decomposed into CO2 and H2O by decarboxylation and demethylation by hydroxyl radicals generated from TiO2 photocatalysts, suggesting a degradation pathway based on the three intermediates detected by LC/MS analysis.

Immobilization of dextransucrase on functionalized TiO2 supports

The TiO2 based hybrid supports with different functional groups (amino, glutaraldehyde or epoxy) were prepared and their influence on immobilization of dextransucrase (DS) was studied. Novel synthetic route for surface modification of TiO2 with amino and glutaraldehyde groups was developed taking advantage of charge transfer complex (CTC) formation between surface Ti atoms and salicylate-type of ligand (5‑aminosalicylic acid (5-ASA)). The proposed coordination of 5-ASA to the surface of TiO2 powder and optical properties of CTC was presented. The pristine TiO2 and amino functionalized TiO2 have higher sorption capacity for DS (12.6 and 12.0mgg−1, respectively) compared to glutaraldehyde and epoxy activated supports (9.6 and 9.8mgg−1, respectively). However, immobilized enzyme to either glutaraldehyde or epoxy functionalized TiO2 have almost two times higher expressed activities compared to pristine TiO2 support (258, 235 and 142IUg−1, respectively). Thermal stability of enzyme immobilized on glutaraldehyde and epoxy functionalized supports was studied at 40°C, as well as operational stability under long-run working conditions in repeated cycles. After five cycles, DS imobilized on glutaraldehyde activated support retained almost 70% of its initial expressed activity, while, after five cycles, performance of DS immobilized on epoxy activated support was significantly lower (15%).

Formation of submicrometer titanium carbide from a titanium dioxide encapsulated in phenolic resin

A novel synthesis process has been developed to produce high-purity and submicrometer titanium carbide powders from a titanium dioxide encapsulated in phenol resin. The precursor powders were produced by coating titanium dioxide powders with phenolic resin shells. Then the precursor powders were roasted at various temperatures from 1373 to 1873 K for 2 h in a flowing Ar atmosphere. The decomposed carbon from phenolic resin could be used to reduce TiO2. X-ray diffraction, field emission scanning electron microscope, and thermogravimetric and differential thermal analyses were employed to characterize the phase composition, microstructure, and reaction mechanism. The phenol resin was decomposed completely into pyrolytic carbon below 1200 K. The pyrolytic carbon with high activities deposited on the surface of TiO2 powders evenly, which formed carbon shells and provided a close contact with TiO2 particles. γ-Ti3O5, λ-Ti3O5, Ti2O3, TiCxOy, and TiC were continuously formed during the carbothermic reduction. It is found that the titanium carbide powders with a lattice parameter of 4.311 A were finally synthesized at 1873 K when the molar ratio of titanium dioxide to phenolic resin was 1:0.6. The particle size of the obtained titanium carbide powders was about 0.4 μm.

Titanium dioxide modification with cobalt oxide nanoparticles for photocatalysis

Liquid phase plasma (LPP) method was used to synthesize a photocatalyst that can respond to visible light by precipitating cobalt oxide nanoparticles on the surface of TiO2 powders. Uniform precipitation of cobalt oxide nanoparticles on the surface of TiO2 powders was observed, resulting in successful synthesis of Co oxide nanoparticles on TiO2 photocatalysts (CTP). The CTP synthesized in this study showed a photocatalytic activity under visible blue light. However, its photocatalytic activity was lower than that of bare TiO2 under UV light because the cobalt oxide precipitate acted as crystal defects deteriorating the catalytic activity.

Preparation of solid acid carbon coating on the surface of TiO2 by photo-CVD of gaseous aromatic hydrocarbons

Abstract Properties of a solid acid carbon coating prepared on TiO2 powder surface using photochemical vapor deposition (photo-CVD) were evaluated. The TiO2 powder surface became brown during UV illumination under a flowing xylene and xylene sulfonic acid mixture. Observation by TEM revealed an amorphous carbon coating on the TiO2 powder. Sulfonate groups were identified on the coating using FT-IR. A chart of NH3-TPD measurements showed two peaks: that at high temperature was attributed to the coating’s strong acid. The carbon coating’s acidity was equivalent to that of the solid superacid carbon powder and the carbon-coated TiO2 decomposed cellulose.

Preparation, characterization and photocatalytic property of Ag-loaded TiO2 powders using photodeposition method

The Ag particles were photodeposited on TiO2 powder surface. The X-ray diffraction (XRD), Raman spectroscopy, transmittance electron microscopy (TEM), UV-vis diffused reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectrophotoscopy were used to investigate the structure and morphologies of the samples. It is found that the loaded Ag particles have no effect on the XRD patterns, and the Raman scattering becomes much stronger due to the surface Raman enhancing effect. The TEM images show that the TiO2 grains are in the shape of short sticks, and the spherical Ag particles with hexagonal structure are adhered to the TiO2 grain surface tightly. XPS result shows that the loaded Ag particles can not affect the chemical states of Ti and O, and they are mainly in the form of metal Ag. A wide plasmon absorption appears on the UV-vis spectra after Ag photodeposition. The loaded Ag further greatly decreases the PL intensity, which partly indicates the electron transfer from TiO2 to Ag. The photocatalytic activities firstly increase with the content of loaded Ag, and then sharply decrease. Finally, the photocatalytic mechanism related to Ag-loaded TiO2 powders was discussed in detail.

Preparation of nanocrystalline Fe-doped TiO2 powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO2 powders were prepared using TiOSO4, urea, and Fe(NO3)3 · 9H2O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO2, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m2/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe3+ and Fe2+ have been detected on the surface of TiO2 powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO2 powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO2 was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO2 powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.

Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route

A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy=0.02 eV and freezing temperature=362 °C. All these measurements confirmed its relaxorlike phase transition.

Surface Coating of TiO<sub>2</sub> Powder

SiO2 nano-scale films were coated on the surface of TiO2 powder by liquid phase deposition. The morphology and the composition of coated TiO2 were studied by transmission electron microscopy (TEM), X-ray photoelectronic spectrscopy (XPS), and X-ray fluorescence (XRF). The study showed that a continuous SiO2 nano-scale film was coated on the TiO2 particles, and the element Si was bonded to the surface of TiO2 in the form of the Ti-O-Si bond. The most suitable conditions for coating are: 0.5 mol•L-1 of C ; pH value of 9.5; 200 g•L-1 of C , reaction time of 5 h at 85 °C.

Complete Decomposition of Benzene, Toluene, and Particulate Matter Contained in the Exhaust of Diesel Engines by Means of Thermally Excited Holes in Titanium Dioxide at High Temperatures

We previously reported on a decomposition system of organic wastes by the use of thermally excited holes in TiO2 at high temperatures. A good feature of our system is that it makes use of a large number of holes formed, for example, at 350 °C for the oxidation of organic wastes. In this investigation, we aim at applying this technology to the complete decomposition of benzene, toluene, and particulate matter (PM) included in the exhaust of diesel engines. Special attention has been paid to the adsorption process of benzene and toluene onto the surface of TiO2, as well as to their subsequent decomposition, as studied by thermal analysis, Raman spectroscopy, and ESR in consideration of the specific surface of TiO2 powders. Both benzene and toluene are found to completely decompose into H2O and CO2 at about 350 °C, via fragments of ethylene, butene, propene, and butadiene. On the other hand, PM appears more difficult to decompose due to its powdered form. However, PM was finally confirmed to be decomposed when the mixture of PM and TiO2 was heated under a pressure of about 280 N/m2 at about 350 °C.

Effect of Low Frequency and Power Ultrasonic Treatment on the Surface Adsorbed Organics and Visible Light Photocatalysis Activity of Nanosized TiO<sub>2</sub> Photocatalyst

The effect of ultrasonic treatment under low frequency and power condition on the surface adsorption state and photocatalysis activity of nanosized TiO2 photocatalyst was studied. Results obtained from UV-Vis absorption spectra revealed that obvious differences of adsorption state on TiO2 powder surface were found after ultrasonic treatment, which agreed with the DTA-TG results that the thermal peaks varied with increasing ultrasonic treatment time. Furthermore, the photocatalysis activity for methyl-orange solution under visible light irradiation (≥450 nm) varied in a similar way with increasing ultrasonic treatment time. Present study revealed that the ultrasonic treatment was an effective way to study the relation between the surface adsorption state and photocatalysis activity of present nanosize TiO2 photocatalyst.

Complete decomposition of benzene, toluene and particulate matter (PM) contained in the exhaust of diesel engines by means of thermally-excited holes in TiO<sub>2</sub> at high temperatures

Titanium dioxide was once extensively investigated as a photoconductor for the electrophotographic photorecptor at its incunabula. Nowadays, it has attracted attention as a material for photocatalyzers, solar cells as well as their related areas. We report here another application of titanium dioxide. Our motivation is to make use of thermally-generated holes for decomposition of organic compounds. We have previously reported on a decomposition system of organic wastes by use of thermally-excited holes in TiO2 at high temperatures (about 350-500 °C). In the present investigation, we aim at applying this technology to complete decomposition of benzene, toluene and particulate matter (PM) contained in the exhaust of diesel engines. Special attention has been paid to the adsorption process of benzene and toluene onto the surface of TiO2, as well as to their subsequent decomposition, as studied by thermal analysis, Raman and ESR spectra in consideration of the specific surface of TiO2 powders. Both benzene and toluene are found to completely decompose into H2O and CO2 at about 350 °C, via fragments of ethylene, butene, propene and butadiene. On the other hand, PM appears more difficult to decompose due to its powdered form. However, PM was finally confirmed to be decomposed when the mixture of PM and TiO2 was heated under pressure of about 280 N/m2 at about 350 °C.

Comparison of Different Photocatalytic Systems for Acetonitrile Degradation in Gas–solid Regime

Photocatalytic degradation of acetonitrile was carried out in gas–solid regime by using two commercial TiO2 samples (Merck and Degussa P25) irradiated in two continuous annular photoreactors. The inlet gas flow consisted of oxygen, nitrogen, acetonitrile and water vapours. The influence on the photodegradation rate of gas flow rate, acetonitrile, oxygen and water concentrations and photon flux was investigated. The degradation products of acetonitrile were carbon dioxide and hydrogen cyanide. The photocatalysts performance was not affected by the presence or absence of water vapour in the reacting mixture. The Langmuir–Hinshelwood model describes adequately the photoreactivity results and provides the values of kinetic and equilibrium adsorption constants. FT-IR spectroscopy was used to investigate the adsorption patterns and photo-oxidation intermediates of acetonitrile on fully hydrated surface of TiO2 powders. Acetonitrile was adsorbed on Ti4+ surface ions and hydroxyl groups for both types of TiO2. In the absence of UV light this interaction was completely reversible for Merck catalyst whereas for Degussa P25 part of adsorbed acetonitrile molecules reacted to form acetamide-like species.

Effects of the oxygen vacancy on NO adsorption at the TiO2 surface

The desorption spectrum of NO adsorbed on the surface of TiO2 powder was determined by temperature programmed desorption. The molecular orbital theory was u tilized to investigate the crystal cluster model of NO adsorbed on TiO2 and th e change of band gap in the adsorption process. The results indicate that there exist two peak temperatures, 450 and 980K, as N2 desorption followed by the NO adsorption on TiO2 The intensity of N2 desorption decre ases if the TiO2 powder is pretreated in an O2 atmosphere. The nitrogen atoms of the adsorbed NO gas recombine into N2 for desorption while oxygen atoms occupy th e oxygen vacancies in the TiO2 surface. The calculation analysis from the mole cular orb ital theory supports the deduction that the existence of oxygen vacancy on TiO2(110) surface offers a suitable condition of crystal surface for NO ad sorption.

Influences of Adsorption on TiO2 Photocatalytic One-Electron Oxidation of Aromatic Sulfides Studied by Time-Resolved Diffuse Reflectance Spectroscopy

TiO2 photocatalytic one-electron oxidation of 4-methyl-p-tolylsulfide (MTS), 4-(methylthio)phenyl methanol (MTPM), 4-(methylthio)benzoic acid (MTBA), and 4-(methylthio)phenyl acetic acid (MTPA) adsorbed on the surface of TiO2 powder slurried in acetonitrile (CH3CN) has been investigated by time-resolved diffuse reflectance spectroscopy. As compared to MTS, high concentrations of the adsorbed MTPM, MTBA, and MTPA determined by UV absorption spectral measurements clearly indicate that −OH and −COOH groups play an important role in being adsorbed on the surface of TiO2 particles. From Langmuir-type adsorption/desorption plots, the apparent equilibrium constants (Kad) of 20, 60, 2.3 × 104, and 1.1 × 104 M-1 were determined for MTS, MTPM, MTBA, and MTPA, respectively. The difference in the Kad values clearly indicates that −COOH and −CH2COOH groups are strongly adsorbed on the TiO2 surface compared with −CH2OH and −CH3 groups. The initial concentration of the radical cations generated from oxidation reactions ...