Photocatalytic Activity Of Anatase TiO2 Research Articles

A particular mechanism of the effect of lone pair E TeIV dopant atoms on visible-light photocatalytic activity of anatase TiO2

It was found that small additives of E TeIV species (< 1 at%) notably enhance the visible-light photocatalytic activity of polycrystalline anatase TiO2. This effect can tentatively be attributed to the neutralization of the neighboring surface- located oxygen vacancy, acting as a recombination center for photogenerated holes and electrons, by the dopant stereochemically active lone electron pair E.

Synthesis of Tio2 photocatalyst with tunable optical properties and exposed facet for textile wastewater treatment

TiO2 semiconductor plays a paramount important as an active photocatalyst mainly due to its photo-induced electron transfer properties. The metastable anatase in particular are widely accepted to have the most photoactive activity in catalytic application as opposed to rutile TiO2. This is majorly due to the significantly lower recombination rate of electron pair possesses by anatase TiO2. Unfortunately, high recombination rate in anatase TiO2 hinders its application as a functional photocatalyst. Therefore, it is crucial to further enhance the photocatalytic activity of anatase TiO2, by modifying its optical properties, morphological properties, and crystal facet. The study aims to provide a benign synthesis method for TiO2 with a co-exposed {001}/{100} anatase TiO2 facet. The synthesis was conducted via one-pot reflux condensation method. A concise evaluation upon the effect of different synthesis heating duration, temperature and doping materials towards the crystal phase, morphology, and photocatalytic performance of TiO2 were conducted. Anatase TiO2 with high percentage of the high-energy {001} facet have the ability to boost the adsorption and photocatalytic performance as opposed to anatase TiO2 dominated with a thermodynamically stable {101} facet. The incorporation of non-metal dopant (HF) acts as surface modifier which leads to the enhancement of {001} facet percentage. This study further evaluates the functionalities of HCl in paving way towards the formation of mid-gap state, hence improving Anatase TiO2 optical properties. The reduction of band gap of the anatase TiO2 can clearly be identified from the shifts in the adsorption band towards higher wavelength. From the findings, it was found that the synergistic effect upon co-doping anatase TiO2 with the two non-metal dopants plays an important role in altering the ratio of exposed facet hence leading towards improving the photocatalytic efficiency of the nanomaterial. To evaluate the photocatalytic performance of the synthesized TiO2, Remazol Brilliant Blue (0.01 g/L) was chosen as the target pollutant. The enhanced photodegradation of co-doped F/Cl-TiO2 was evaluated and it was found that 87.21% and 43.21% of Remazol Brilliant Blue had successfully been degraded within 120 min with irradiation of broad spectrum and blue light (475 nm) respectively. This is mainly attributed to the co-exposed {001}/{100} anatase TiO2 facet presence in the F/Cl-TiO2 sample.

Water effect on the band edges of anatase TiO2 surfaces: A theoretical study on charge migration across surface heterojunctions and facet-dependent photoactivity.

The charge migration mechanism across the surface heterojunction constructed on an anatase TiO2 nanocrystal is still under debate. To solve this longstanding question, we present a systematic study of the band edges (vs. standard hydrogen electrode, SHE) of aqueous TiO2 interfaces with anatase (101), (100) and (001) surfaces, using a combination of density functional theory-based molecular dynamics (DFTMD) and efficient computational SHE (cSHE) methods. Our calculations show that the conduction band minimum (CBM) of the (101) surface is lower than that of (001) and (100) surfaces, which is thermodynamically favorable for electrons migrating to the (101) surface through the surface heterojunction, while the hole preferentially accumulates on the (100) surface due to its highest valence band minimum (VBM). In addition, we qualitatively explore the facet-dependent photocatalytic activity of anatase TiO2. Due to the possession of both the beneficial atomic structure (with 100% undercoordinated Ti5c atoms at the surface) and electronic structure (more strongly oxidizing holes in the VBM and efficient electron-hole spatial separation separation), the (001) surface exhibits the most efficient photocatalytic performance for water oxidation. Furthermore, it is confirmed that the use of simplified theoretical models neglecting the detailed atomic structures of water at the aqueous interface is inadequate to predict the band alignment of semiconductors relative to water redox potentials, so that it may result in substantial errors in evaluating the photocatalytic performance of materials to be used for water splitting.

119Sn Mössbauer spectroscopic insight into the effect of surface-located tin dopant cations on the visible-light photocatalytic activity of anatase TiO2

The presence of Sn4+ dopant ions on the surfaces of titania crystallites results in a nearly fourfold increase in the rate constant of a white-light photocatalytic bleaching reaction of methyl orange. Thus, the positive effect of a SnII electronic lone pair, which was theoretically predicted in 2013 by Iwaszuk and Nolan for a SnO-nanocluster modified anatase model, can be experimentally revealed using catalyst powders containing surface-located oxidized Sn4+ species.

Hollow TiO2 Microsphere/Graphene Composite Photocatalyst for CO2 Photoreduction

In an attempt to improve the photocatalytic activity of anatase TiO2, we developed a composite photocatalyst composed of hollow TiO2 microspheres (hTS) and graphene. The hTS were prepared through a two-step hydrothermal process, where SiO2 microspheres with desirable diameters of 100–400 nm were used as sacrificial templates. Accordingly, the effect of the hTS cavity size on the activity of the catalyst in wet CO2 photoreduction (CO2PR) was studied. Furthermore, it was established that the hydrothermal pH value crucially influences the photocatalytic activity of the hTS photocatalyst, as well as its composition and microstructure. The hTS photocatalyst was also combined with graphene (0–90 wt%) to improve its photocatalytic activity. This study provides insight into the optimal microsphere diameter, hydrothermal pH value, and graphene/hTSx ratio required for designing hollow microsphere-based photocatalysts with enhanced CO2PR performances.

Electronic and optical properties of mono and co-doped anatase TiO2: First principles calculations

Density functional theory-based calculations are adopted for clarifying the validity of mono-dopant (Co, Cr, B), co-dopant (Co/B, Cr/B), and oxygen deficiency on the photocatalytic activity of anatase TiO2. The crystal structure, formation energies, electronic, and optical properties are calculated in the framework of HSE06 hybrid functional. The impurity states appear in the band gap region, thus changing the electronic structures and resulting in red shift of the absorption edge in the defected systems. Furthermore, the main band gap is narrowed for all defected systems except for Co mono-doping and oxygen vacancy. The deep impurity states on mono-doping, could affect the recombination of photo-excited electron-hole pairs, while the charge separation efficiency could be enhanced on Cr/B co-doping by shallow receptor state. The calculated optical properties emphasize the enhanced absorption efficiency and the extended absorption edge to the visible light on Cr/B co-doping. The findings in this paper could suggest the Cr/B co-doped anatase TiO2 as a good photocatalyst with longer life of the photogenerated charge carriers.

Role of molecular oxygen on the synthesis of Ni(OH)2/TiO2 photocatalysts and its effect on solar hydrogen production activity

Molecular oxygen performs a vital role in the photocatalytic activity of anatase TiO2, but there is a little experimental insight into the role of molecular oxygen on the synthesis of TiO2 based photocatalysts. Herein, we have shown that Ni(OH)2/TiO2 prepared in the presence and absence of molecular oxygen results in significantly varied hydrogen production activity. The sample synthesized in the presence of O2 and N2 produced 6624 μmol/h/g and 4468 μmol/h/g of hydrogen under direct solar light exposure. Additionally, the samples prepared in the presence of light irradiation produced 8289 μmol/h/g of hydrogen, a 72 fold jump in hydrogen production compared to TiO2. XPS, FTIR, Raman, and ESR measurements were carried out to investigate the underlined mechanism for such variation in the photocatalytic activity. Our results suggest that the presence of molecular oxygen during Ni(OH)2/TiO2 synthesis causes the formation of terminal OH and reduced the oxygen vacancies on the surface of TiO2, which can significantly alter the H2 production. Also, the reusability of the photocatalysts is greatly affected by the synthesis conditions, namely the presence of light and molecular oxygen.

Surface Defect-Controlled Growth and High Photocatalytic H2 Production Efficiency of Anatase TiO2 Nanosheets.

Facet engineering of anatase TiO2 by controlling the {001} exposure ratio has been the focus of numerous investigations to optimize photocatalytic activity. In particular, an introduction of fluoride ions during the crystal growth has been demonstrated to be very effective and decisive in realizing the facet exposure of the crystals. However, a key role of fluoride ions in stabilizing {001} exposure and improving subsequent photocatalytic activity of anatase TiO2 remains unclear up to date. Herein, a controlled thickness of anatase TiO2 nanosheets has been realized by introducing different amounts of ethanol into a HF acid-assisted hydrothermal reaction. The thinnest nanosheets with a thickness of ∼2.9 nm were evaluated to have the highest H2 production rate of 41.04 mmol·h-1·g-1 under ultraviolet light irradiation, and the corresponding quantum efficiency was determined to be 41.6% (λ = 365 nm). Moreover, it is proved for the first time that fluoride ions are bonded with Ti vacancies on {001} facets, and such defects are crucial for stabilizing the ultrathin nanosheets and improving their electron-hole separation, therefore leading to a highly efficient photocatalytic activity. The findings offer an opportunity to engineer facets and functionality of anatase TiO2 by controlling surface defects.

TiO2 nanotree films for the production of green H2 by solar water splitting: From microstructural and optical characteristics to the photocatalytic properties

Green H2 production by solar water splitting relies entirely on the intrinsic properties of the photocatalyst. In this study the impact of these intrinsic properties on the photocatalytic activity of anatase TiO2, the quintessential component of state of the art photocatalytic systems was explored at the nanoscale. The exploration involved a holistic microstructural and optical characterization of fully crystallized anatase thin films synthetized by metalorganic chemical vapor deposition. A combination of electron microscopy, spectroscopic ellipsometry, and infrared spectroscopy revealed that when the deposition temperature increased, the morphology evolved from dense to porous and columnar nanostructures. Interestingly, the columns with a complex, tree-like nanostructure photogenerated 18 times more H2 than the densest sample. This result shows that the beneficial effect of the morphological nano-complexification and crystallographic diversification of the exchange facets on the photocatalytic performance outweighs the detrimental aspects inherent to this evolution, namely the drop of the charge carrier transport and the increase of residual stress.

Synthesis of oxygen-deficient blue titanium oxide by discharge plasma generated in aqueous ammonia solution

Abstract When discharge plasma was generated in an aqueous ammonia solution containing titanium dioxide (TiO2) powder, blue TiO2 was obtained. The blue TiO2 contained oxygen defects and Ti3+ formed by the plasma treatment; i.e., reducing species such as hydrogen radicals generated in situ during ammonia decomposition by plasma were considered to reduce TiO2. No marked changes in the crystallographic structure and specific surface area of TiO2 were observed after the plasma treatment, indicating that TiO2 was not exposed to high temperature. In addition, the plasma-treated TiO2 remained blue when exposed to air for several months. The photocatalytic activity of anatase TiO2 under visible light irradiation was enhanced after plasma treatment. In contrast, the plasma-treated rutile TiO2 showed inferior photocatalytic activity under visible light irradiation compared with that of the untreated rutile TiO2.

Evolution of photovoltaic and photocatalytic activity in anatase-TiO2 under visible light via simplistic deposition of CdS and PbS quantum-dots

Abstract A simple approach to deposit metal chalcogenide-based quantum-dots on TiO2 (anatase) nanoparticles via pseudo-successive ionic layer adsorption and reaction (p-SILAR) was opted to design and investigate the corresponding photoactivity under visible light. We used TiO2/PbS and TiO2/CdS nanocomposites for photocatalysis after which we prepared solar paints from them to put side by side the resultant photovoltaic performance. We developed solar paint type quantum-dot-sensitized solar cells (QDSCs) from TiO2/PbS and TiO2/CdS nanocomposites to divulge electron-hole generation, electron-hole recombination, and resistance against photo-corrosion. TiO2/PbS exhibited higher electron-hole generation than TiO2/CdS owing to its efficient visible light harvesting capability which resulted in higher photocurrent density (JSC) and thus higher power conversion efficiency (PCE) for respective QDSC; however, it had inferior resistance against photo-corrosion. Additionally, the degradation of an azo-based dye (acid orange-56) reflected an effectual increase in the photocatalytic activity of anatase-TiO2 as a result of deposition of PbS and CdS QDs. TiO2/PbS performed better than TiO2/CdS as a photocatalyst under visible light irradiation.

Visible-light responsive boron and nitrogen codoped anatase TiO2 with exposed {0 0 1} facet: Calculation and experiment

To fully understand the synergistic effect of B/N codoping on the visible-light photocatalytic activity of anatase TiO2 with exposed {0 0 1} facet, a combination of Density Functional Theory (DFT) calculation by GGA + U method and experiment has been performed. Bader charge and Electronic Location Function (ELF) analysis reveal that there is free electron-gas like behavior around N and neighbor B for B/N-codoped anatase TiO2 with exposed {0 0 1} facet, and its visible-light absorbance increases, which may promote Ti4+ reduction to Ti3+. The results of calculation and experiment demonstrate that B/N codoping leads to the shift of the absorption edge of the TiO2 to lower energy region, and thus makes its photocatalysis active within the wavelength of 600 nm.

Structure and Reactivity of a Model Oxide Supported Silver Nanocluster Catalyst Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy

The photocatalytic activity of anatase TiO2 decorated with metal clusters has been widely documented, but the nature of the metal–metal oxide interface and reaction intermediates in catalytic processes are still not well understood. This in part is due to the fact that use of photoelectron spectroscopy to deduce the surface chemistry of catalytic systems has long been hampered by the huge pressure difference between real-world operation and the requirement of high vacuum for electron detection. Here, the in situ growth of silver nanoparticles on a model metal-oxide catalyst support and their reactivity with a CO/H2O gas mixture has been investigated in detail. Using synchrotron X-ray photoelectron spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, and scanning tunneling microscopy, the interaction of Ag with the anatase TiO2 surface leads to metal-surface charge transfer and low mobility of Ag on the surface. Upon exposure to a 1.5 mbar CO/1.5 mbar H2O gas mixture, partial oxidation of ...

Elastic, electronic and optical properties of anatase TiO2 under pressure: A DFT approach

The first principle pseudopotential method within the generalized gradient approximation (GGA) and the local density approximation (LDA) have been applied to investigate the electronic, elastic and optical properties plus the acoustic wave velocities of anatase TiO2 under high pressure (0–80 GPa). The calculated bulk moduli (177 GPa and 181 GPa) are in excellent agreement with experimental results (179 GPa and 178 GPa). Anatase TiO2 is found to be mechanically stable under high pressure (0–80 GPa) by applying the Born stability criteria. Acoustic wave speeds are predicted in the [100], [010], [001],[11¯0], [110] and [101¯] directions by using the calculated elastic constants. An underestimated band gap (2.174 eV (GGA), 2.113 eV (LDA)) is obtained, and it shows no change when the pressure is varied from 0–10 GPa. The bandgap reduction is caused by the decrease of the lattice constants and volume and an increase of the internal parameters as a function of pressure. The dielectric constant ε (ω) and the refractive index show a good agreement with the experimental results. From the absorption spectrum, it is found that the photocatalytic activity of anatase TiO2 decreases with an increase of pressure. The pressure effect on the energy loss function appears in the form of new peaks in the energy loss spectra.

The effect of surface heterojunction between (0 0 1) and (1 0 1) facets on photocatalytic performance of anatase TiO2

To explore the effect of surface heterojunction between (001) and (101) planes on photocatalytic activity of anatase TiO2, the anatase TiO2 photocatalysts with different ratio of (001) and (101) planes were prepared via a facile hydrothermal method. The as-prepared photocatalysts were characterized by XRD, TEM, HRTEM, UV–vis, and PL to explore the optimal ratio of these facets. Meanwhile, the as-prepared samples were used to photocatalytically remove elemental mercury under UV lamp irradiation. The results indicated that the removal efficiency was different and the percentage of (001) was 32% exhibiting the best photocatalytic activities. It can be attribute to the surface heterojunction between (001) and (101) planes and the optimal ratio of these facets, which can suppress the recombination of photoexcited electron-hole pairs.

Enhanced optical absorption and photocatalytic activity of anatase TiO2 through C[sbnd]Nd-codoped: A DFT+U calculations

The electronic and optical properties are investigated using density functional theory plus U approach in CNd monodoped and codoped anatase TiO2. The calculated results indicate that C dopant can enhance the intensity of optical absorption and Nd dopant can extend the optical absorption range into the whole visible spectrum in CNd-codoped anatase TiO2, and the Nd 4f states can effectively reduce the recombination of photo-excited electron-hole pairs thus achieving higher visible light photocatalytic activity for hydrogen production by water splitting than pure TiO2. Moreover, we also study the effects of doping concentration and impurity distance in CNd-codoped anatase TiO2 system, finding that the higher doping concentration, the stronger absorption activity, and absorption activity increases with the shortness of impurity distance due to the assemblage of impurity states.

First-principles study on codoping effect to enhance photocatalytic activity of anatase TiO2

Codopant is an effective approach to modify the bandgap and band edge positions of transition metal oxide. Here, the electronic structures as well as the optical properties of pristine, mono-doped (N/P/Sb) and codoped (Sb, N/P) anatase TiO2 have been systematically investigated based on density functional theory calculations. It is found that mono-doped TiO2 exhibits either unoccupied or partially occupied intermediate state within the energy gap, which promotes the recombination of electron-hole pairs. However, the presence of (Sb, N/P) codopant not only effectively reduces the width of bandgap by introducing delocalized occupied intermediate states, but also adjusts the band edge alignment to enhance the hydrogen evolution activity of TiO2. Moreover, the optical absorption spectrum for (Sb, N/P) codoped TiO2, which is favored under oxygen-rich condition, demonstrates the improvement of its visible light absorption. These findings will promote the potential application of (Sb, N/P) codoped TiO2 photocatalysis for water splitting under visible light irradiation.

Synergetic Effect of Pt and Borate on the TiO2-Photocatalyzed Degradation of Phenol in Water

It has been reported that Pt and borate can promote the TiO2-photocatalyzed degradation of phenol in an aerated aqueous suspension, respectively. Herein, we report a synergism between Pt and borate greatly improving the photocatalytic activity of anatase TiO2. The rate of phenol degradation was dependent on Pt loading, borate concentration, and solution pH. A maximum rate of phenol degradation was observed at 0.52 wt % Pt, 3.0 mM Na2B4O7, and initial pH 9.0, respectively. Under such conditions, the rates of phenol degradation, upon the addition of Pt, borate, and Pt plus borate, were increased by 1.34, 0.22, and 4.87 times, respectively. This mutual action of Pt and borate were also observed from the photocatalytic degradation of 4-chlorphenol, and 2,4-dichlrophenol. A separate experiment with the TiO2 and Pt/TiO2 film electrodes showed that borate could mediate the hole oxidation of phenol, but not water. Furthermore, the electrochemical reduction of O2 over TiO2 and Pt/TiO2, upon addition of borate, bec...

Rapid removal and decomposition of gaseous acetaldehyde by the thermo- and photo-catalysis of gold nanoparticle-loaded anatase titanium(IV) oxide

Gold nanoparticles (NPs) with a mean particle size ranging from 2.1 to 7.4nm were loaded on anatase TiO2 particles (Au/TiO2) by the heating temperature-varied deposition precipitation technique. This study has shown that Au/TiO2 with Au particle size <3nm and TiO2 surface area >50m2g−1 can be a promising environmental catalyst for the rapid removal and decomposition of gaseous acetaldehyde in a closed space. The Au loading on TiO2 causes a drastic enhancement of the acetaldehyde adsorption in the dark, and the adsorption amount increases as the Au particle size decreases. This result originates from the thermocatalytic activity of Au/TiO2 for the oxidation of acetaldehyde to acetic acid under ambient conditions. The resulting acetic acid spontaneously moves to the TiO2 surface due to the great adsorptivity for the carboxyl group. Consequently, the acetaldehyde adsorption amount strongly depends on the TiO2 surface area in addition to the Au particle size. UV-light irradiation of acetaldehyde (or acetate)-adsorbed Au/TiO2 leads to the complete decomposition to carbon dioxide by the high photocatalytic activity of anatase TiO2.

Fabrication and Photocatalytic Activity of Photocatalyst Coatings by Mechanical Coating Technique and the Oxidation at Relatively Low Temperatures

Titanium (Ti) coatings on alumina (Al2O3) balls fabricated by mechanical coating technique (MCT) were oxidized at relatively low temperatures. Crystal structure and microstructure of the coatings were investigated. Photocatalytic activity of the coatings was evaluated and discussed. The results showed that TiO2 films on Ti or Ti/TiO2 coatings were fabricated by the MCT and subsequent heat oxidation. The TiO2 is anatase phase if the heat oxidation temperature is under 773 K. The TiO2 is the mixed phases of anatase and rutile if the heat oxidation temperature is in the range of 673–973 K. Besides, rutile TiO2 is formed if the heat oxidation temperature is beyond 1073 K. Photocatalytic activity of anatase TiO2 is higher than rutile TiO2.