Unmodified TiO2 Research Articles

Effects of Cu addition on CO gas-sensing properties of TiO2 prepared by oxidizing mechanically-synthesized TiN composites

TiN–Cu composites were synthesized in a pressurized N2 atmosphere using a ball milling process. TiO2 sensing materials were added with 0–8at% Cu, which was prepared via oxidation at temperatures of 600 and 800°C. Structural characterization was performed using X-ray diffraction, Field emission scattering electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). Cu addition promoted anatase-to-rutile transformation and grain growth, and the responses of the samples that were oxidized at 600°C with CO gas were enhanced by adding Cu to TiO2 compared with the unmodified TiO2. The TiO2 materials with 4% Cu showed the greatest response to CO of 4.1 at 1000ppm of CO gas, which can be compared to the response value of 1.2 of unmodified TiO2–CO gas under identical conditions. The enhancement of TiO2 sensitivity to CO gas is believed to originate from well-dispersed metallic and Cu oxides, which are known catalysts for the oxidation of CO gas. When the oxidation temperature was increased to 800°C, the strongly bound CuO particles dissociated, and the response changed to p-type. It is proposed that the segregation induces a conduction pathway through CuO.

Simplified sonochemical preparation of titania embedded with selected metals for purification of benzene and toluene

Titania (TiO2) photocatalysts, each embedded with one of six metals (Ag, Ce, Co, Fe, Mg, and Mn), were prepared using a simplified ultrasonic process. The characteristics of the prepared metal-embedded TiO2 (metal–TiO2) were determined using transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, photoluminescence emission spectroscopy, UV–visible spectroscopy, and nitrogen adsorption–desorption. Except for Co–TiO2, the metal–TiO2 photocatalysts showed improved performance for the decomposition of gaseous benzene and toluene, which are two of the most problematic indoor air pollutants that can cause a variety of adverse health symptoms, under daylight lamp irradiation. Photocatalytic activity was greatest for the Mg–TiO2 sample, followed by, in order, the Ag–TiO2, Ce–TiO2, Fe–TiO2, Mn–TiO2, unmodified TiO2, and Co–TiO2 samples. Although Mg–TiO2 showed the least redshift in its light absorption and the highest electron–hole recombination rate among the metal–TiO2 photocatalysts, it yielded the highest photocatalytic activity, likely because of its increased adsorption capacity and anatase composition. The degradation of benzene and toluene over Mg–TiO2 improved as ultrasound treatment amplitude increased from 20 to 37μm, then decreased gradually as amplitude was further increased to 49μm. Degradation efficiency also improved as ultrasound operation time increased from 30 to 60min, then decreased gradually as amplitude was further increased to 90min. Overall, this process could be utilized to prepare metal–TiO2 photocatalysts with improved performance for the decomposition of gas phase pollutants under daylight lamp irradiation.

Transparent and flexible films of new segmented polyurethane nanocomposites incorporated by NH2-functionalized TiO2 nanoparticles

Abstract In this work, TiO 2 nanoparticles are surface modified by NH 2 -terminated organic moieties arised from 4,4′-methylene diphenyl diisocyanate (MDI). These nanoparticles are incorporated into ether-based segmented polyurethane (SPU) matrix. MDI is utilized as monomer together with poly(tetramethylene oxide) (PTMO) comonomer for preparing the final polymer as well. The NH 2 -functionalized TiO 2 nanoparticles are covalently linked to the NCO terminals of the resulting SPU macromolecules during film preparation stage. Therefore, in addition to butylene glycol, these surface modified nanoparticles with enhanced organophilicity could play the role of the second chain extender of NCO-capped SPU macromolecules through formation of urea linkages. Optical and thermal behaviors of the transparent and flexible film (SPU/TiO 2 –MDI) is compared with those of unmodified TiO 2 (SPU/TiO 2 ) and TiO 2 -unloaded SPU films. Though the particle loading is only 5 wt.%, incorporation of TiO 2 and TiO 2 –MDI nanoparticles into the SPU polymer enhances significantly the light absorption in UV region at 300–400 nm. SEM images of the prepared films clearly show a considerable decrease in particle aggregation for TiO 2 –MDI into SPU matrix compared to that of unmodified TiO 2 . TG analyses indicate a one-step decomposition pattern with onset temperatures of about 360 and 380 °C for neat SPU and SPU/TiO 2 –MDI, respectively. Moreover, DTA thermograms of both nanocomposites show obviously two exothermic phase transitions in the thermal range of 330–440 °C.

Photocatalytic Removal of 2,4-D Herbicide on Lanthanum Oxide-Modified Titanium Dioxide

Titanium dioxide (TiO2) has been recognized as an active photocatalyst for degradation of various organic pollutants. In this study, in order to improve the photocatalytic activity of TiO2, the effect of lanthanum oxide modification was investigated by using commercial P25 as the benchmark. Lanthanum oxide/P25 TiO2 composites with 0.1, 0.5, 1 and 5 mol% of La loadings were prepared via an impregnation method. The resultant composites were characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and electrochemical impedance spectroscopy (EIS). It was confirmed that the addition of lanthanum oxide did not much affect the crystallinity, crystal structure and the morphology of P25 TiO2. The catalytic activities of the lanthanum oxide/P25 TiO2 catalysts were tested by using 2,4-dichlorophenoxyacetic acid (2,4-D) as the test pollutant and UV light as the irradiation source. The reaction was caried out for 1 hour at room temperature and the percentage removal was determined using a UV spectrophotometer. The results showed that La loading was an important factor that influenced the photocatalytic activity of the composites. After 1 hour reaction, the best catalyst with 0.1 mol% of La loading showed 24% higher photocatalytic activity than the unmodified P25 TiO2 catalyst. It is shown by EIS that the enhanced photocatalytic activity of the composites was due to the ability of lanthanum oxide in improving the charge separation of the photogenerated electron-hole pairs in TiO2.

Boosting Photovoltaic Performance of Dye-Sensitized Solar Cells Using Silver Nanoparticle-Decorated N,S-Co-Doped-TiO2 Photoanode.

A silver nanoparticle-decorated N,S-co-doped TiO2 nanocomposite was successfully prepared and used as an efficient photoanode in high-performance dye-sensitized solar cells (DSSCs) with N719 dye. The DSSCs assembled with the N,S-TiO2@Ag-modified photoanode demonstrated an enhanced solar-to-electrical energy conversion efficiency of 8.22%, which was better than that of a DSSC photoanode composed of unmodified TiO2 (2.57%) under full sunlight illumination (100 mWcm−2, AM 1.5 G). This enhanced efficiency was mainly attributed to the reduced band gap energy, improved interfacial charge transfer, and retarded charge recombination process. The influence of the Ag content on the overall efficiency was also investigated, and the optimum Ag content with N,S-TiO2 was found to be 20 wt%. Because of the enhanced solar energy conversion efficiency of the N,S-TiO2@Ag nanocomposite, it should be considered as a potential photoanode for high-performance DSSCs.

ChemInform Abstract: Visible Light Mediated Cyclization of Tertiary Anilines with Maleimides Using Nickel(II) Oxide Surface‐Modified Titanium Dioxide Catalyst

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Enhanced photoelectrocatalytic hydrogen production activity of SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays

SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays (ST–TiO2 NTAs) were constructed by following these steps: firstly, highly ordered TiO2 nanotube arrays (TiO2 NTAs) were synthesized directly on Ti foils through electrochemical oxidation, then SrTiO3–TiO2 nanoparticles were deposited on the TiO2 NTAs using two-step hydrothermal treatment. SrTiO3–TiO2 nanotube arrays (S–TiO2 NTAs) were also prepared by directly hydrothermal treatment of TiO2 NTAs for comparison. The photoelectrocatalytic hydrogen production activities of all the samples were evaluated by using ethylene glycol as a sacrificial reagent in water under a 300 W xenon arc lamp. The photoelectrocatalytic hydrogen production rate of TiO2 NTAs can be significantly improved by modifying SrTiO3–TiO2 hetero-nanoparticles and achieved a greatly promoted value of 314.9 μmol cm−2 h−1 which was 2.1 times higher than that of the unmodified TiO2 NTAs. Compared to S–TiO2 NTAs, ST–TiO2 NTAs showed a 32.8% increase in hydrogen production rate. Furthermore, SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays exhibited excellent stability and was facile to be safely reused. The improvement of photocatalytic hydrogen production efficiency is attributed to the difference of the conduction band potential between TiO2 and SrTiO3 in SrTiO3–TiO2 hetero-nanoparticles, thereby boosting the transfer and separation of the photogenerated electron–hole pairs.

Synthesis and optimization of Ag–TiO2 composite nanofibers for photocatalytic treatment of impaired water sources

In this work, Ag–TiO2 composite nanofibers were fabricated by electrospinning, where the composition and crystallinity were tuned by controlling the precursor composition and annealing conditions. Characterization revealed that bulk–embedded Ag nanoparticles inhibited anatase-to-rutile phase transformation and a decrease in band gap from 3.2 down to 2.8eV with increase in the Ag content. The photocatalytic activity of 0.5at.% Ag–TiO2 nanofibers toward phenol degradation was the greatest, outperforming both unmodified TiO2 nanofibers and commercially available TiO2 Aeroxide® P25 by a factor of ∼3. The high reactivity of the low content Ag–TiO2 nanofibers can be attributed to the addition of electron traps, which provide efficient carrier separation and, therefore, decreased recombination. However, further increase in Ag content led to lower photoreactivity, most likely due to the growth of the Ag nanoparticles, which suggests an optimal size of 2 to 3nm for the Ag nanoparticles at 0.5at.% provided the greatest photoreactivity. Ag–TiO2 nanofibers show great promise as innovative and highly performing nanomaterials for future nanotechnology-based treatment systems, particularly when the photoreactivity demonstrate herein is used in synergy with the established antimicrobial activity of nano-Ag.

Controlled Growth of WO<sub>3</sub>-Loaded TiO<sub>2</sub> Nanotubes for Tandem Solar-Driven Water Splitting Cell

Nowadays, hydrogen production using solar-driven photoelectrochemical (PEC) water splitting has attracted considerable attention since the introduction of TiO2 photoelectrodes. However, TiO2 is not able to split water on its own because the cleavage requires more than 1.4 V or even up to 1.9 V, including the redox potential of water (1.23 V) and unavoidable over-potentials. Many semiconductors have been studied, but only a very few large band gap materials can generate enough photo-voltage to cleave water for a single photoelectrode PEC water splitting cell especially processing under solar illumination. In the present study, development of WO3-loaded TiO2 nanotubes (WTNT) is a possible solution to generate a voltage that is high enough to split the water while absorbing more light (photons) from a greater part of solar spectrum. Furthermore, WTNT offered several advantages over the pure TiO2 photoelectrode, such as excellent chemical and thermal stability, active at room temperature as well as responsive to UV and visible illumination. The paper concludes by presenting the comparison results between unmodified TiO2 and WTNT photoelectrode in term of morphology, phase, elemental analysis, electrical properties, and electrochemical properties for the tandem solar-driven water splitting cell.

Visible-light driven C@TiO2 porous films: Enhanced photoelectrochemical and photoelectrocatalytic performance

Visible-light driven C-modified TiO2 film (C@TiO2 film) was prepared on a conducting substrate and studied as photoanode for photoelectrochemical and photoelectrocatalytic (PEC) properties. The as-prepared material was characterized by SEM, TEM, XRD, and diffuse reflectance spectra. The C@TiO2 film with multiporous structure exhibited enhanced electrochemical properties and excellent PEC performance, with a seven-fold improvement of photocurrent intensity as compared to unmodified TiO2. The PEC improvement may be resulting from extended visible light-harvesting, low electron transfer resistance, and promoted photocurrent response. This study could provide a new perspective on preparing high performance photoelectric catalyst films.

Solid state metal-free eosin-Y dye sensitized solar cell based on PVdF-HFP electrolytes: combined effect of surface modified TiO2 and plasticizer on electrochemical and photovoltaic properties

The hybrid polymer nanocomposites based on poly(vinylidene fluoride-co-hexaflouro propylene) (PVdF-HFP) as a host matrix, propylene carbonate as the plasticizer, and surface modified and unmodified TiO2 nanoparticles as fillers for dye-sensitized solar cell applications have been prepared using a solvent casting technique. The surface of TiO2 was modified using aminopropyltrimethoxysilane (APS), and its organic functional groups on TiO2 were confirmed by Fourier transform infrared (FTIR) spectroscopy. The PVdF-HFP membranes were characterized by FTIR, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), atomic force microscopic (AFM), and ultraviolet–visible (UV-Vis) spectroscopic techniques. It was found a new interaction of APS molecules on TiO2 surface with matrix as well as electrolyte salt. The experimental observations indicated a noticeable improvement in ionic conductivity of modified TiO2 of about 6.7 × 10−4 S/cm when compared with unmodified counterpart (TiO2) as the filler within PVDF-HFP matrix. The solid state dye-sensitized solar cell has been fabricated by using silane-modified TiO2/PVdF-HFP nanocomposite electrolyte and eosin-Y as sensitizer, and its photoconversion efficiency is measured about 1.47 %.

Photocatalytic Nanocomposite Polymers for Enhanced Water Purification Applications

The need for clean and drinkable water cannot be understated as it is the prerequisite for all human and economic development. Unfortunately, 780 million people do not have access to clean water, resulting in the death of over 2 million children every year. Literature has shown that photocatalytic nanoparticles enhance the chemical degradation of organic pollutants when exposed to UV light. The major limitation in this application is due to lack of availability of a UV radiation. This research developed a cellulose based nanocomposite film that uses visible light to degrade simulated organic pollutants through catalytic photo-redox reactions. Increasing the redox potential will also increase the potency of the nanocomposite, so various methods of enhancing electron transfer were implemented. Dye sensitization, surface modifications, and metal deposition on the nanoparticles were found to improve the transfer of electrons from the semiconductor to the pollutant. In addition to increasing the rate of reaction, Ag-functionalized TiO2 nanoparticles resulted in a synergistic antimicrobial effect, which eliminated E. Coli and S. Aureus from the water samples. Both dye sensitization and noble metal deposition showed a 25% increase in the amount of pollutant that was chemically degraded in comparison to unmodified TiO2. Additionally, surface modifications of the nanoparticles by covalently bonding new functional groups to the nanoparticle surface facilitate metal complexation, removing heavy metal ions from the sample.

Photocatalytic degradation of methylene blue and inactivation of pathogenic bacteria using silver nanoparticles modified titanium dioxide thin films

Titanium dioxide (TiO2) is a well-studied photocatalyst that is known to break down organic molecules upon ultraviolet irradiation. TiO2 thin films were fabricated on glass substrates using the doctor-blade procedure, the film surface was modified with silver nanoparticles to increase its visible light response. The Ag-TiO2 films were characterized by transmission electron microscopy, scanning electron microscopy equipped with energy dispersive spectrometry and X-ray diffraction. The photocatalytic degradation of methylene blue (MB) and inactivation of Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus were studied. The modified films presented enhanced photocatalytic efficiency and can decompose MB solution two-times faster than the unmodified TiO2 films, under illumination of sunlight. A nominal degradation (15 %) was observed in control MB under sunlight. The degradation efficiency of Ag-TiO2 films slightly decreased after five consecutive experiments. Ag-TiO2 films revealed very effective bactericidal activity against both E. coli and S. aureus. The photocatalytic inactivation toward E. coli and S. aureus showed a similar trend with much higher effectiveness toward E. coli under the same experimental conditions. The inactivation efficiency was maximized and reached 95 % for S. aureus and 97 % for E. coli, after 180 min incubation. These results demonstrate the potential of application of Ag-TiO2 photocatalysis as a method for treatment of diluted waste waters in textile industries.

Rapid removal and subsequent low-temperature mineralization of gaseous acetaldehyde by the dual thermocatalysis of gold nanoparticle-loaded titanium(IV) oxide

Under ambient humid conditions, the adsorption of acetaldehyde on unmodified TiO2 is small and weak. In contrast, loading Au particles smaller than 3nm on TiO2 with surface area larger than 17.5m2g−1 (Au/TiO2) causes the rapid and strong adsorption of gaseous acetaldehyde from a closed space. This striking adsorption phenomenon initiates from the aerobic oxidation of acetaldehyde to acetic acid by the thermocatalysis of Au/TiO2 at room temperature. Acetic acid is moved to the TiO2 surface to be dissociated to acetate ion and proton, which are adsorbed on the Lewis acid and base sites on the surface, respectively. The resulting reproduction of the catalytic sites for the acetaldehyde oxidation enables the continuous removal of acetaldehyde without the release of the harmful product. Further, the adsorbed species on Au/TiO2 are completely oxidized to CO2 by the post-heating at 548K, whereas the oxidation degree of acetate adsorbed on unmodified TiO2 remains several % even at 570K with harmful products (Quah et al., 2010).

Visible light mediated cyclization of tertiary anilines with maleimides using nickel(II) oxide surface-modified titanium dioxide catalyst.

Surface-modified titanium dioxides by highly dispersed NiO particles have an extended absorption in the visible light region and a reduced hole-electron pair recombination than unmodified TiO2. They have now been successfully applied as highly active heterogeneous photocatalysts in the visible light mediated direct cyclization of tertiary anilines with maleimides to give tetrahydroquinoline products in moderate to high yields at ambient temperature. In contrast with unmodified titanium dioxide catalysts that are conventionally used in a stoichiometric amount in combination with UVA light, only a catalytic amount (1 mol %) of the surface-modified TiO2 catalyst is needed along with visible light to efficiently catalyze the reaction. Compared with transition-metal complexes such as Ru(bpy)3Cl2 or Ir(ppy)2(dtbbpy)PF6, advantages of these surface-modified titanium dioxides as photocatalyst include high catalytic activity, low cost, ease of recovering, and being able to be used for at least nine times without significant decay of catalytic activity.

Hot plasmonic electrons for generation of enhanced photocurrent in gold-TiO2 nanocomposites.

In this manuscript, for the first time, we report a combination of electrophoretic and sintering approaches for introducing gold nanoparticles into nanoporous TiO2 films to generate ‘hot’ electrons resulting in a strong enhancement of photocurrent. The Au-TiO2 nanocomposite material was prepared by the electrophoretic deposition of gold nanoparticles into a porous nanoparticulate titanium dioxide film, creating a photoactive electrode. The composite film demonstrates a significant increase in the short circuit current (Isc) compared to unmodified TiO2 when excited at or close to the plasmon resonance of the gold nanoparticles. Then, we employed a thermal ripening process as a method of increasing the Isc of these electrodes and also as a method of tuning the plasmon peak position, with a high degree of selectivity. Photo-electrochemical investigations revealed that the increase in photocurrent is attributed to the generation and separation of plasmonically generated hot electrons at the gold/TiO2 interface and also the inter-band generation of holes in gold nanoparticles by photons with λ < 520 nm. Theoretical modelling outputs perfectly match our results obtained from photo-physical studies of the processes leading to enhanced photocurrent.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-014-0710-5) contains supplementary material, which is available to authorized users.

Reduced graphene oxide-titania nanocomposite-modified photoanode for efficient dye-sensitized solar cells

Summary We report the successful application of reduced graphene oxide–titania (rGO–TiO2) nanocomposite as an efficient photoanode for dye-sensitized solar cell (DSSC). The DSSC assembled with the rGO–TiO2-modified photoanode demonstrated an enhanced solar to electrical energy conversion efficiency of 4.74% compared with the photoanode of DSSC composed with unmodified TiO2 (2.19%) under full sunlight illumination (100 mW/cm2, AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduced the back electron transfer process. Influence of the rGO content on the overall efficiency was also investigated, and the optimal rGO content for TiO2 was 0.5 mg. Further, the modification of rGO–TiO2 on the compact layer TiO2 surface led to an increase in efficiency to 5.83%. The superior charge collection and enhanced solar energy conversion efficiency of the rGO–TiO2 nanocomposite makes it to be used as a promising alternative to conventional photoanode-based DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.

Tailored synthesis of photoactive TiO ₂ nanofibers and Au/TiO ₂ nanofiber composites: structure and reactivity optimization for water treatment applications.

Titanium dioxide (TiO2) nanofibers with tailored structure and composition were synthesized by electrospinning to optimize photocatalytic treatment efficiency. Nanofibers of controlled diameter (30-210 nm), crystal structure (anatase, rutile, mixed phases), and grain size (20-50 nm) were developed along with composite nanofibers with either surface-deposited or bulk-integrated Au nanoparticle cocatalysts. Their reactivity was then examined in batch suspensions toward model (phenol) and emerging (pharmaceuticals, personal care products) pollutants across various water qualities. Optimized TiO2 nanofibers meet or exceed the performance of traditional nanoparticulate photocatalysts (e.g., Aeroxide P25) with the greatest reactivity enhancements arising from (i) decreasing diameter (i.e., increasing surface area), (ii) mixed phase composition [74/26 (±0.5) % anatase/rutile], and (iii) small amounts (1.5 wt %) of surface-deposited, more so than bulk-integrated, Au nanoparticles. Surface Au deposition consistently enhanced photoactivity by 5- to 10-fold across our micropollutant suite independent of their solution concentration, behavior that we attribute to higher photocatalytic efficiency from improved charge separation. However, the practical value of Au/TiO2 nanofibers was limited by their greater degree of inhibition by solution-phase radical scavengers and higher rate of reactivity loss from surface fouling in nonidealized matrixes (e.g., partially treated surface water). Ultimately, unmodified TiO2 nanofibers appear most promising for use as reactive filtration materials because their performance was less influenced by water quality, although future efforts must increase the strength of TiO2 nanofiber mats to realize such applications.

Self-cleaning properties of cement plates loaded with N,C-modified TiO2 photocatalysts

The photocatalytic activity of cement pastes containing nitrogen and carbon co-modified TiO2 photocatalysts (TiO2-N,C) were evaluated trough the degradation of model organic water contaminate (Reactive Red 198) under UV–vis light source. It was found that cement plates containing TiO2-N,C photocatalysts exhibited higher photocatalytic efficiency than those containing unmodified TiO2.

First principles investigation of anion-controlled red shift in light absorption in ZnX (X = O, S, Se) nanocluster modified rutile TiO2

There is significant interest in finding new approaches to modifying TiO2 in order to endow it with visible light driven photocatalytic activity. To date, the most widely studied approach is to dope TiO2 with metals, non-metals or both simultaneously. However, there are some serious issues associated with doping of TiO2. We have studied an alternative approach in which TiO2 surfaces are modified with nanoclusters of metal oxides and have shown that this can introduce new states into the original TiO2 band gap that permits a red shift to induce visible light absorption while enhancing the photocatalytic activity over unmodified TiO2. In this paper we extend this idea to modification of rutile TiO2 with nanoclusters of ZnO, ZnS and ZnSe, which allows us to explore the possibility of tuning the magnitude of the red shift in modified TiO2 through the choice of anion in the nanocluster modifier. We find that the adsorption energies of the nanoclusters and the interfacial geometry are strongly influenced by the nature of the anion, with the ZnSe nanoclusters the most weakly bound, arising from the large ionic radius of Se giving longer surface–nanocluster distances and thus weaker binding. The magnitude of the red shift compared to unmodified rutile (110) can be over 1 eV and is tuned by the size (or surface loading) of the nanocluster and the anion in the nanocluster. Finally, a model of the photoexcited state shows that holes localised onto low coordinated anion sites on the adsorbed nanoclusters and electrons localise onto the TiO2 surface which will reduce charge recombination and enhance the photocatalytic activity. This concept of an anion controlled red shift in light absorption in nanocluster-modified TiO2 should be extendable to other metals such as tin or lead chalcogenides.