Nanocrystalline TiO2 Particles Research Articles

A novel structure of cellulose-TiO2 nanocomposite for ultra-fast and recyclable organic dyes degradation in wastewater

TiO2-based nanocomposites have been widely used for wastewater treatment due to their photocatalytic activities and applications. In this work, cellulose-TiO2 nanocomposite powder with a novel structure was successfully prepared by non-sintering low-temperature sol-gel and co-precipitation methods to clean the dye-containing wastewater. The facet {010} of spherical nanocrystalline TiO2 particles was covered by cellulose molecules to improve the adsorption speed and reusability of dye adsorption. The cellulose-TiO2 nanocomposite powder unveiled 100% removal rate of dyes within 30 s under different temperatures and pH conditions, which was quicker than all existing methods to date. This nanocomposite powder also exhibited excellent recyclable performance and adsorbed dyes from dyeing wastewater which could restore the function of adsorbing dye molecules after being irradiated by ultraviolet light or even sunlight. After 7 times of duty-cycle operation, the dye removal rate remained at 72%, which aided high economic value and, thus, it was excellent in practical applications. Moreover, this work introduced a sono-synthesis approach for the production of a cellulose-TiO2 nanocomposite adsorbent, which offered rapid cleaning of various organic dyes from wastewater due to its unique structure. Thus, the present fabricated cellulose-TiO2 nanocomposite powder could be an excellent candidate using dying wastewater treatment for collecting and degrading organic dyes and excellent repeatable performances.

SORPTION PROPERTIES OF RUTILE PHASE TiO2 NANOPARTICLES

There are many scientific studies on phenol adsorption. Sorption of phenol in the presence of activated carbon, graphite oxide and other adsorbents is very common. This article is the first to study the sorption properties of TiO2nanoparticles with a rutile phase; TiO2 nanoparticles with a rutile phase were synthesized by the sol-gel method and used as an adsorbent. Later the process of adsorption of a 1 mgL-1 phenol solution in the presence of rutile TiO2 nanoparticles was studied. The adsorption process lasted 2 hours at a temperature of 25°C.Although the rutile TiO2 phase is a very good photocatalyst it has been shown to be a weak adsorbent. Nano crystalline TiO2 particles of the rutile phase were characterized by powder X-ray diffraction (XRD).The course of adsorption was studied on the device "Varian Cary 50". Based on the curves plotted on the “Varian Cary 50” it was determined that adsorption was incomplete. At the end of the process judging by the graph we can say that the amount of phenol in the solution decreased but phenol still remained which indicates incomplete adsorption. Mathematical modeling of the process has been developed using both logistic and exponential methods. Keywords: nano-TiO2, phenol, adsorption, XRD, TEM.

Expression of Concern: Influence of iron doping on the photocatalytic activity of nanocrystalline TiO2 particles fabricated by ultrasound method for enhanced degradation of organic dye

Expression of Concern: Influence of iron doping on the photocatalytic activity of nanocrystalline TiO2 particles fabricated by ultrasound method for enhanced degradation of organic dye

Fretting damage of Ni-rich ultrafine grained NiTi superelastic wires

The effects of fretting on Ni-rich ultra-fine grained NiTi superelastic wires have been characterized. Fretting tests have been performed using wire on wire in 90° cross-cylinder configuration until 105 cycles in air at 25 °C. Constant displacement amplitude of 50 µm and normal loads of 10, 20 and 50 N were considered. For a normal load of 10 N, the tribosystem performed in Gross Slip Regime and the predominance of wear damage was observed. Mixed Fretting Regime was instead observed for normal loads of 20 N and 50 N. In these cases, the predominant damage mechanism was crack formation with the cracks oriented normal to the displacement direction. Occurrence of martensitic transformation in the contact region was inferred from the particular shape of the fretting loops. Due to their possible impact on biocompatibility, the debris detached from the tribosystem during the different experiments were collected and characterized by TEM. They consisted in agglomerations of nano-crystalline TiO2 (rutile) and NiO oxide particles sized between 10 and 20 nm.

Enhanced electrochromic properties of TiO2 nanocrystal embedded amorphous WO3 films

We investigated the effect of nanocrystalline TiO2 doping on the electrochromic properties of tungsten trioxide (WO3) films. Here, we prepared various TiO2 nanocrystal-embedded amorphous WO3 films by a simple one-step dip-coating method. XRD data of the films show amorphous nature for both undoped and nanoparticle TiO2 doped WO3 films with anatase phase of TiO2 having (101) plane, which were further confirmed by TEM measurements. XPS of TiO2 doped WO3 film shows +6 oxidation state of W atom, implying the stoichiometric WO3 composition. The electrochromic properties of the films were investigated by in situ spectroelectrochemical methods, showing the markedly different behaviors of the films depending on the amount of nanocrystalline TiO2 doped. In particular, charge deintercalation kinetics of the films were significantly affected by the content of nanocrystalline TiO2 in amorphous WO3 matrix with 7 times faster deintercalation process by 30 wt% of TiO2 doping into WO3 at the expense of the reduced bleaching transmittance. This phenomenon may be associated with the effect of nanocrystalline TiO2 particles on blocking accessibility of Li ions to the trapping sites which has to be de-trapped if the ions are to be released.

Synthesis of Si, N co-Doped Nano-Sized TiO₂ with High Thermal Stability and Photocatalytic Activity by Mechanochemical Method.

Τhe photocatalytic activity in the range of visible light wavelengths and the thermal stability of the structure were significantly enhanced in Si, N co-doped nano-sized TiO2, and synthesized through high-energy mechanical milling of TiO2 and SiO2 powders, which was followed by calcination at 600 °C in an ammonia atmosphere. High-energy mechanical milling had a pronounced effect on the mixing and the reaction between the starting powders and greatly favored the transformation of the resultant powder mixture into an amorphous phase that contained a large number of evenly-dispersed nanocrystalline TiO2 particles as anatase seeds. The experimental results suggest that the elements were homogeneously dispersed at an atomic level in this amorphous phase. After calcination, most of the amorphous phase was crystallized, which resulted in a unique nano-sized crystalline-core/disordered-shell morphology. This novel experimental process is simple, template-free, and provides features of high reproducibility in large-scale industrial production.

Influence of iron doping on the photocatalytic activity of nanocrystalline TiO2 particles fabricated by ultrasound method for enhanced degradation of organic dye

Synthesis and characterization of Fe doped TiO2 composite with iron concentration varying from 0 to 7% as a photocatalyst in the photodegradation of methylene orange on UV–Vis light irradiation in a closed reactor has been carried out. Synthesis was conducted by the ultrasound method at room temperature using tetrabutyl titanate and iron(III)chloride 6-hydrate as a precursor, followed by thermal treatment at a temperature of 600 °C. The characterizations were performed using X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy (SEM), FT-IR spectrometry, thermal analysis, UV–Vis diffuse reflectance spectrophotometer, photoluminescence and Brunauer–Emmett–Teller (BET). XRD spectra revealed that samples crystallized in the anatase phase at 600 °C. The transmission and SEM were used to detect the morphology of synthesized nanoparticles, which sizes changed with the altitude in the doping concentration to 7%. FTIR spectra exhibit broad peaks where anatase phases of TiO2 demonstrate very sharp peaks. In accordance with UV–Vis absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.21 eV, for undoped TiO2, to 2.46 eV, for TiO2 doped at 7%. The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. The maximum photoconversion efficiency was 2.5%, which was six times the photoconversion efficiency of undoped TiO2. Finally, the prepared materials were used to photocatalyse the decolourization of methylene orange in aqueous medium as a model compound under the illumination of visible light (λ = 420 nm).

Temperature-dependent phase transformation of TiO2 nanoparticles synthesized by sol-gel method

Nanocrystalline TiO2 particles were prepared to study the calcination temperature dependent phase transformation. X-ray diffraction (XRD) patterns showed the strong Bragg peaks correspond to anatase (101) and rutile (110) phases with their crystallite size 12 and 49 nm for the samples T1 and T2 calcined at 450 and 700 °C respectively. Raman spectroscopy investigation showed the phase transformation with the dominating rutile peaks from the pure-anatase phase. By UV–vis absorption spectroscopy, the strong ultraviolet-light absorption below 400 nm was observed. Using Kubelka-Munk function, the estimated band gap values were found to be 3.38 and 3.03 eV. The transmission scanning microscopy (TEM) images exhibited the slightly agglomerated nanoparticles while the selected area diffraction (SAED) patterns endorsed the polycrystalline nature.

Electrophoretic deposition of nanocrystalline TiO2 particles on porous TiO2-x ceramic scaffolds for biomedical applications

Nanocrystalline TiO2 coated scaffolds offers the possibility to be used in bone tissue regeneration providing not only space for new tissue formation, but also to enhance bioactivity of the implant. In the present study, direct current electrophoretic deposition (EPD) was chosen as simple and low cost technique to coat 3D porous structure of TiO2-x ceramic. Suspension for EPD was prepared suspending nanocrystalline TiO2 particles in isopropanol and adding triethanolamine as dispersant. TiO2 particles were electrophoretically deposited on the surface of TiO2-x scaffolds through varying EPD time and applied voltage. The scaffold pore structure was maintained after applying the coating by EPD. The deposition of nanocrystalline TiO2 coating can be a smart strategy to impart bioactive properties to the 3D scaffold, allowing formation of spherical hydroxyapatite particles on the coated scaffolds after immersion in simulated body fluid. In vitro cell studies does not show cytotoxic effect of nanocrystalline TiO2 coated scaffolds.

Sandwich-like design of TiO2 electrodes containing multiple light scattering layers for dye-sensitized solar cells applications

This study comes up with a new architecture of multi-layered photoanode electrodes containing three thick layers (i.e., 4μm) of nanocrystalline TiO2 particles and three thin layers (i.e., 1μm) of uniform TiO2 aggregates, which are alternately deposited. The aggregates layers are deposited by a straightforward gel process, developed for the preparation of uniform and sponge-like light scattering layer for dye-sensitized solar cells (DSCs) applications. The aggregates layers are composed of uniform spherical particles with average diameter of 2μm, containing small nanoparticles with the average grain size of 20nm. The nanocrystalline layers contain 20-nm-diameter TiO2 nanoparticles. X-ray diffraction (XRD) reveals that the nanocrystalline layers have a pure anatase phase, whereas the aggregates layers show a mixture of anatase and rutile phases. Diffuse reflectance spectroscopy (DRS) demonstrates that the multi-layered electrode enjoys better light scattering ability than that of mono-layered electrode due to the incorporation of a thin light scattering layer into the nanocrystalline film. The multi-layered DSC shows the highest power conversion efficiency of 7.85% as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy (EIS). From IPCE measurement, the external quantum efficiency of the multi-layered cell at 530nm is equal to 89%, which is higher than that of mono-layered cell (i.e., 78%).

Multi-layered architecture of electrodes containing uniform TiO2 aggregates layers for improving the light scattering efficiency of dye-sensitized solar cells

This study comes up with a new architecture of multi-layered photoanode electrodes containing two thick layers (i.e., 6 µm) of nanocrystalline TiO2 particles and two thin layers (i.e., 1 µm) of uniform TiO2 aggregates, which are alternately deposited. The aggregates layers are deposited by a straightforward gel process, developed for the preparation of uniform and sponge-like light scattering layer for dye-sensitized solar cells (DSSCs) applications. The aggregates layers are composed of uniform spherical particles with average diameter of 2 µm, containing small nanoparticles with the average grain size of 20 nm. The nanocrystalline layers contain 20-nm-diameter TiO2 nanoparticles. X-ray diffraction reveals that the nanocrystalline layers have a pure anatase phase, whereas the aggregates layers show a mixture of anatase and rutile phases. Diffuse reflectance spectroscopy demonstrates that the multi-layered electrode enjoys better light scattering ability than that of mono-layered electrode due to the incorporation of a thin light scattering layer into the nanocrystalline film. The multi-layered DSSC shows the highest power conversion efficiency of 7.69 % as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy. From IPCE measurement, the external quantum efficiency of the multi-layered cell is equal 88 %, which is higher than that of mono-layered cell (i.e., 78 %).

Adsorption and photocatalysis of nanocrystalline TiO2 particles for Reactive Red 195 removal: effect of humic acids, anions and scavengers.

In the present study, the coupling of adsorption capacity and photocatalytic efficiency of two different industrially produced titania catalysts was investigated and compared. The azo dye Reactive Red 195 was selected as a model compound. The tested catalysts, PK-10 and PK-180, exhibited different adsorption capacities due to their significant difference in their specific surface, but both have proven to be effective photocatalysts for photodegradation of the studied dye. PK-10 exhibited strong adsorption of the studied dye due to its high specific surface area, while the second studied catalyst, PK-180, demonstrated negligible adsorption of Reactive Red 195. The effect of the pH, the concentration of the catalyst and the initial concentration of the dye appear to affect the photocatalytic rate. The effect of the presence of humic acids and inorganic ions was also examined, while the contribution of various reactive species was indirectly evaluated through the addition of various scavengers. To evaluate the extent of mineralisation of the studied dye, total organic carbon (TOC) measurements during the experiment were also conducted. Besides total colour removal, evident reduction of TOC was also achieved using both catalysts.

Anatase nanoparticles surface modified with fused ring salicylate-type ligands (1-hydroxy-2-naphthoic acids): A combined DFT and experimental study

Sensitization of TiO2 crystals and nanoparticles with appropriately chosen organic molecules can lead to a significant shift of their absorption threshold from the UV to the visible, thus improving the absorption of the solar spectrum as well as the efficiency of photocatalytic and photovoltaic devices. Herein, the surface modification of nanocrystalline TiO2 particles (45Å) with salicylate-type ligands consisting of an extended aromatic ring system, specifically 1-hydroxy-2-naphthoic acid and 1,4-dihydroxy-2-naphthoic acid, was found to alter the optical properties of nanoparticles in a similar way to salicylic acid. From both absorption measurements and steady-state quenching measurements of modifier fluorescence upon binding to TiO2 in methanol/water=90/10 solutions, stability constants in the order of 103M−1 have been determined at pH 2. Fluorescence lifetime measurements, in the presence and absence of colloidal TiO2 nanoparticles, indicated that the fluorescence quenching process is primarily static quenching, thus proving the formation of a nonfluorescent charge-transfer (CT) complex. The binding structures were investigated by using FTIR spectroscopy. Thermal stability of CT-complexes was investigated by using TPD analysis (TG/DTA/MS). Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain the vibrational frequencies of charge transfer complexes, and the calculated values were compared with the experimental data. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of a salicylate type (binuclear bidentate binding–bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. The formation of the inner-sphere CT-complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and a reduction in the band gap upon the increase in the electron delocalization when including an additional ring.

New Nanocomposite Materials by Incorporation of Nanocrystalline TiO2 Particles into Polyaniline Conductive Films

This work is focused on the combination of two building-blocks, nanocrystalline TiO2 particles and polyaniline conductive films (PAni). The preparation of new nanostructured composite materials, displaying electron- and proton-conductive properties, to be used for the fabrication of new and superior energy storage devices was envisaged. The semiconducting TiO2 nanoparticles were obtained by means of a hydrothermal route. The PAni films were prepared on glassy carbon electrodes by electrochemical polymerization, under potential dynamic conditions. After characterization by X-ray diffraction, transmission electron microscopy or scanning electron microscopy and electrochemical techniques, the nanocrystalline particles were immobilized in the polymer matrix. The incorporation of the TiO2 was achieved using two distinct approaches: during the polymer growth or by deposition over previously prepared PAni films. The results demonstrate that the PAni morphology depends on the experimental conditions used during the polymer growth. After TiO2 immobilization, the best electrochemical response was obtained for the nanocomposite structure produced through the TiO2 incorporation after the PAni film synthesis. The modified electrodes were structurally and morphologically characterized and their electro-catalytic activity towards the hydrogen evolution reaction was analyzed. A new electrochemical performance related with the oxidation of molecular hydrogen entrapped in the PAni-TiO2 matrix was observed for the modified electrode after TiO2 incorporation. This behavior can be directly associated with the synergetic combination of the TiO2 and PAni, and is dependent on the amount of the semiconductor.

Effects of Calcination Condition on Photocatalytic Properties of Nano-TiO$lt;inf$gt;2$lt;/inf$gt;/Opal Composite and Its Mechanism

Nanocrystalline TiO2 particles immobilized on opal by a hydrolysis precipitation method are used as a novel catalyst in photocatalysis. Effects of crystalline and size, BET specific surface area and porous properties on the photoactivity were investigated by characterizing samples obtained under various calcination temperatures and periods. Results reveal that there is still no evidence of rutile phase in XRD patterns when the calcination temperature increases to 800℃. This indicates that the opal support impedes the phase transformation. The photocatalytic reactivity of this nano-TiO2/opal composite catalyst was evaluated by degrading Rhodamine B (RhB) under ultraviolet light. The sam- ple calcined at 600℃ for 2 h exhibits the smaller crystalline size and larger specific surface area with a concomitant higher activity of 97.24% for RhB degradation by 4 h irradiation under 250 W Hg lamp.

Mo, Mn and La doped TiO2: Synthesis, characterization and photocatalytic activity for the decolourization of three different chromophoric dyes

Nanocrystalline TiO2 particles doped with different concentrations of Molybdenum (Mo), Manganese (Mn) and Lanthanum (La) (0.25–1.0%) were synthesized using sol–gel method and characterized by standard analytical techniques such as X-ray diffraction (XRD), UV–Vis spectroscopy and Scanning Electron Microscopy (SEM). The XRD analysis shows the partial crystalline nature and anatase phase. The SEM images of undoped and doped TiO2 at different magnifications also show the partial crystalline nature with rough surfaces. The photocatalytic activity of the synthesized particles (TiO2 doped with Mo, Mn and La) was tested by studying the decolourization of three different chromophoric dyes such as Acid Red 88 (azo dye), Gentian Violet (triphenylmethane dye) and Remazol Brilliant Blue R (anthraquinone dye) as a function of time on irradiation in aqueous suspension in an immersion well photochemical reactor with a 500 W halogen linear lamp in the presence of atmospheric oxygen. The results indicate that TiO2 with dopant concentration of 0.75% (Mo) and 1.0% (Mn, La) showed the highest photocatalytic activity as compared to the other dopant concentrations for the decolourization of all the dyes.

Surface modification of anatase nanoparticles with fused ring salicylate-type ligands (3-hydroxy-2-naphthoic acids): a combined DFT and experimental study of optical properties

The surface modification of nanocrystalline TiO2 particles (45 Å) with salicylate-type ligands consisting of an extended aromatic ring system, specifically 3-hydroxy-2-naphthoic acid, 3,5-dihydroxy-2-naphthoic acid and 3,7-dihydroxy-2-naphthoic acid, was found to alter the optical properties of nanoparticles in a similar way to salicylic acid. The formation of the inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and a reduction in the band gap upon the increase in the electron delocalization when including an additional ring. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of a salicylate-type (binuclear bidentate binding-bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. From both absorption measurements in methanol/water = 90/10 solutions and steady-state quenching measurements of modifier fluorescence upon binding to TiO2 in aqueous solutions, stability constants in the order of 10(3) M(-1) have been determined at pH 2 and pH 3. Fluorescence lifetime measurements, in the presence and absence of colloidal TiO2 nanoparticles, indicated that the fluorescence quenching process is primarily static quenching, thus proving the formation of a nonfluorescent CT complex. The binding structures were investigated by using FTIR spectroscopy. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain the vibrational frequencies of charge transfer complexes, and the calculated values were then compared with the experimental data.

Fine size-regulation of nanocrystalline anatase-TiO2via sol–gel synthesis and subsequent phase transformation by calcination

Nanocrystalline TiO2 particles were prepared via the sol–gel process. The particle size and nanostructure of the TiO2 sol were controlled through the ageing process accompanied by hydrolysis–polycondensation. The resultant TiO2 particles were analysed by BET, HR-TEM, PSA, TGA, turbidity, XRD, and zeta potential analyses. The TiO2 size increased with increasing ageing time and reaction temperature. A phase transformation from anatase to rutile occurred with heat treatment at 500 °C. The phase transformation is strongly influenced by the primary particle sizes of TiO2, which were characterised via XRD and Raman spectroscopic analyses.

Influence of Ce Doping on the Electrical and Optical Properties of TiO2and Its Photocatalytic Activity for the Degradation of Remazol Brilliant Blue R

Nanocrystalline TiO2particles doped with different concentrations of Cerium (Ce, 1–10%) have been synthesized using sol-gel method. The prepared particles were characterized by standard analytical techniques such as X-ray diffraction (XRD), FTIR and Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The XRD analysis shows no change in crystal structure of TiO2after doping with different concentrations of Ce, which indicates the single-phase polycrystalline material. The SEM analysis shows the partial crystalline nature of undoped, and doped TiO2and TEM analysis shows the particle sizes were in the range of 9–14 nm in size. The a.c. analysis shows that the dielectric constantεand dielectric loss tanδdecrease with the increase in frequency. The dielectric property decreases with the increase in dopant concentration. It is also observed that the impedance increases with an increase in dopant concentration. The photocatalytic activity of the synthesized particles (Ce-doped TiO2) with dopant concentration of 9% (Ce) showed the highest photocatalytic activity for the degradation of the dye derivative Remazol Brilliant Blue R in an immersion well photochemical reactor with 500 W halogen linear lamp in the presence of atmospheric oxygen.

Preparation of a working electrode with a conducting PEDOT:PSS film and its applications in a dye-sensitized solar cell

This study investigates the applicability of a working electrode with a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) film on a dye-sensitized solar cell (DSSC). This working electrode was designed and fabricated by inserting a PEDOT:PSS film between a fluorine-doped tin oxide (FTO) glass substrate and a layer of nanocrystalline TiO2 particles (P-25). This study also examines the effects of annealing temperature and duration on the transmittance and microstructure of a PEDOT:PSS film as well as the power conversion efficiency of DSSC with this film. The power conversion efficiency of a DSSC with a PEDOT:PSS film (6.37%) substantially exceeds that of a conventional DSSC (4.24%). This result is attributed to the fact that this transparent and conductive PEDOT:PSS film deposited on the FTO glass substrate using a simple spin coating method substantially improves the short-circuit photocurrent per unit area and the fill factor of DSSC.