Mixed-phase TiO2 Nanoparticles Research Articles

Enhancing photocatalytic performance of iron-doped TiO2 nanoparticles: Effects of annealing temperature on anatase-rutile mixed phase structure

The photocatalytic activity of the methylene blue in metal oxide anatase-rutile mixed phase TiO2 nanoparticles doped with iron after annealing at various temperature has been investigated. The ratio Fe/Ti (wt 3 %) was prepared using the conventional co-precipitation technique with annealing treatment. X-ray Diffraction (XRD) analysis showed anatase (∼25 %) and rutile (∼75 %) phase structures, and the crystallite size increased with increasing temperature. The Fourier transform infrared (FTIR) transmittance band at 517 cm−1 for TiO2 stretching vibration mode was examined using Kramer-Kronig relation for determining the optical characteristic such as the refractive index (n), the extinction coefficient (k), the dielectric function, and the energy loss function. Further analysis of the optical properties of Fe-doped TiO2 NPs shows the Δ (LO−TO) is shrinker after annealing above 200oC that indicated more stable bonding. The field emission scanning electron microscopy (FESEM) micrographs show agglomerations formed into clusters like as edelweiss flowers and roses on the surface. UV–Vis measurement reveals that the optical energy gap decreased from 3.05 eV annealed at 200oC to 2.88 eV annealed at 500oC. The UV–Vis absorbance with varying the time from 30 to 120 min to MB as a pollutant is reduced as time irradiation increases with photocatalytic rates for annealing at 500oC is 0.0071/min. The predominant anatase phase alignment, stable bonding, and unique surface make iron doped TiO2 NPs a promising catalyst.

Tailoring performance of hybrid supercapacitors by fluorine-rich block copolymer-derived carbon coated mixed-phase TiO2 nanoparticles

Hybrid supercapacitors can function as both batteries and supercapacitors owing to their high specific energy and capacitive power, respectively. Transition metal oxide-based electrodes exhibit a high theoretical specific capacitance, but their large-scale application in charge storage devices is limited by their low conductivity and electrical stability. To address this problem, we introduced a highly conductive carbon coating over mixed-phase titanium dioxide (C/TiO2) using a novel carbon-rich polyacrylonitrile block copolymer containing an active pentafluorophenyl acrylate ester block (PAN-b-PFPA). The LiFePO4 (LFP) positrode and C/TiO2 negatrode assembled hybrid LFP║C/TiO2 @ 800 supercapacitor exhibited a high specific capacitance of 227 F/g (current density of 1 A/g), power density of 500 W/kg, and energy density of 32 W h/kg. Importantly, higher specific capacitance (∼84%) and Coulombic efficiency (∼96%) were maintained over 5000 charge–discharge cycles. The improved performance of hybrid LFP║C/TiO2 @ 800 supercapacitor is attributable to (1) selectively mixed anatase–rutile TiO2 phases that led to additional Ti3+ oxidation state formation, (2) firm porous carbon coating resulting from the surface anchoring of PAN-b-PFPA copolymer, and (3) fluorine/sulfur impurities from pyrolysis residues. The carbon coating of transition metal oxides from the pyrolysis of PAN-b-PFPA copolymers can facilitate the large-scale development of energy storage materials.

Synthesis of anatase and rutile mixed phase titanium dioxide nanoparticles using simple solution combustion method

In this present study, anatase and rutile mixed phase TiO2 nanoparticles have been prepared by an eco-friendly simple solution combustion method in a single step. Ethylene glycol and Ethanol were used as fuel for the combustion of titanium precursor. The prepared nanoparticles were subjected to UV–vis diffuse reflectance spectra, XRD, TEM and FTIR characterizations. The XRD reveals that the prepared TiO2 nanoparticles were in crystalline nature with various amounts of anatase and rutile phases. The weight fractions of anatase and rutile phases were controlled by varying the amount of titanium precursor. The TEM images exhibits that the prepared TiO2 are in size in the range of 20–40 nm.

Photocatalytic Activity Enhancement of Anatase/Rutile‐Mixed Phase TiO2 Nanoparticles Annealed with Low‐Temperature O2 Plasma

Photodecomposition and photobactericidal activities of anatase/rutile‐mixed phase TiO2 nanoparticles annealed with low‐temperature O2 plasma are clarified by comparing them with those annealed in ambient air. The photocatalytic activities of plasma‐assisted‐annealed sample greatly enhance as compared with the untreated sample, under not only UV irradiation but also visible‐light irradiation. The photocatalytic activities of air‐annealed samples do not enhance under UV irradiation but enhance under visible‐light irradiation. The enhanced photocatalytic activities due to the plasma‐assisted annealing (PAA) originate from the increased photoexcited carrier concentration. This enhancement is discussed from PAA‐induced characteristic factors. PAA facilitates the phase transformation to anatase, contributing directly to extending the photoexcited carrier lifetime. PAA introduces more oxygen vacancies, contributing to trapping more photogenerated electrons. PAA also introduces more bridging/terminal oxygen groups adsorbed on the surface, increasing the upward band‐bending, the depletion layer width at the surface, and the charge transfer from rutile to anatase. These two introductions contribute to facilitating the separation of photoexcited carriers. Furthermore, PAA reduces the aggregate size of TiO2 nanoparticles formed on the surface, contributing to increasing optical absorptions. More reactive oxygen species produced from the bridging/terminal oxygen groups by the photoexcited carriers will also enhance the photocatalytic activities.

Acid-assisted synthesis of TiO2 nanoparticles for enhancement of visible light photocatalytic efficiency

Compared with pure phase TiO2, the mixed-phase TiO2 nanoparticles with oxygen vacancies can help to reduce the carrier recombination rate and band gap, which is contribute to the visible light photocatalysis performance. In this study, three kinds of acid were separately used to prepare TiO2 nanoparticles by hydrothermal method without any post-heat treatment for enhancement of visible light photocatalytic efficiency. When utilized to assist photocatalysis degradation of methyl orange in water under visible light irradiation, the TiO2 nanoparticles obtained from HCl (H-TiO2) and CH3COOH (A-TiO2) showed stable photocatalysis performance for increasing the cycles up to ten times while only five cycles for TiO2 nanoparticles obtained by HNO3-assisted (N-TiO2). The photocatalysis performance of H-TiO2 powder and A-TiO2 powder are both better than that of the N-TiO2 powder. Therefore, the TiO2 samples prepared by HCl- and CH3COOH-assisted method in this work are regarded as excellent photocatalysts for water cleaning.

Facile Formation of Anatase/Rutile TiO2 Nanocomposites with Enhanced Photocatalytic Activity.

Anatase/rutile mixed-phase TiO2 nanoparticles were synthesized through a simple sol-gel route with further calcination using inexpensive titanium tetrachloride as a titanium source, which effectively reduces the production cost. The structural and optical properties of the prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-vis adsorption. The specific surface area was also analyzed by Brunauer–Emmett–Teller (BET) method. The anatase/rutile mixed-phase TiO2 nanocomposites containing of rod-like, cuboid, and some irregularly shaped anatase nanoparticles (exposed {101} facets) with sizes ranging from tens to more than 100 nanometers, and rod-like rutile nanoparticles (exposed {110} facets) with sizes ranging from tens to more than 100 nanometers. The photocatalytic activities of the obtained anatase/rutile mixed-phase TiO2 nanoparticles were investigated and compared by evaluating the degradation of hazardous dye methylene blue (MB) under ultraviolet light illumination. Compared to the commercial Degussa P25-TiO2, the mixed-phase TiO2 nanocomposites show better photocatalytic activity, which can be attributed to the optimal anatase to rutile ratio and the specific exposed crystal surface on the surface. The anatase/rutile TiO2 nanocomposites obtained at pH 1.0 (pH1.0-TiO2) show the best photocatalytic activity, which can be attributed to the optimal heterojunction structure, the smaller average particle size, and the presence of a specific exposed crystal surface. The enhanced photocatalytic activity makes the prepared anatase/rutile TiO2 photocatalysts a potential candidate in the removal of the organic dyes from colored wastewater.

Direct nanocrystallite size investigation in microstrained mixed phase TiO2 nanoparticles by PCA of Raman spectra

Mixed phase anatase and rutile TiO2 nanoparticles (30–67% R/A) have been synthesized by single step laser pyrolysis. Parallel studies by XRD and Raman spectroscopy suggested possible deforming microstress inside certain samples, due to boundary interactions between neighbouring nanocrystallites in nanoparticles, phase instabilities and/or O/C contents. Microstress in nanoparticles supports anatase phase stability in competition with rutile phase. Williamson-Hall plot was used to evaluate crystallite size and strain. A tensile global microstrain in anatase crystallites, was observed for elevated C content titania nanoparticles, together with compressive microstrain in crystallites within O deficient TiO2 nanoparticles. XPS and TEM characterization opens insights regarding the processes behind this type of behaviour. Principal Component Analysis of Raman spectra was applied for batch auto-characterization of mixed phase nanoparticles, with emphasis upon the method ability to simultaneously appreciate crystallite size for both anatase and rutile phase. The method focuses on covariational matrix of multiple samples Raman spectra. It provides results in good agreement with XRD calculated crystallite dimensions for unstrained titania, while for samples with microstrains it returns the size closer to the one predicted by Williamson-Hall plot.

Premixed Stagnation Flame Synthesized TiO2 Nanoparticles with Mixed Phases for Efficient Photocatalytic Hydrogen Generation

Mixed-phase TiO2 nanoparticles (10–20 nm) composed of rutile, anatase, and srilankite phases are prepared through a one-step flame synthesis method. The phase composition of TiO2 nanoparticles can be easily tuned by changing the flame conditions such as the gas flow rates of the fuel, oxygen, and argon carrier. The optimized anatase/rutile/srilankite TiO2 sample with as low as 0.1 wt % of Pt cocatalyst exhibits remarkable photocatalytic H2 generation rate of 21.9 mmol h–1 g–1 and an apparent quantum efficiency (AQE) of 39.4% at 360 nm, higher than those of anatase/rutile or anatase TiO2. The less studied srilankite phase is first time investigated for photocatalytic H2 generation. It is revealed that the relatively low content of srilankite phase in TiO2 could efficiently promote charge separation and transportation. It is remarkable that, compared to the commercial P25 TiO2, the flame-made TiO2 significantly improves Pt reduction and dispersion owing to the oxygen vacancies and surface defects. The optim...

A magnetically separable SO4/Fe-Al-TiO2 solid acid catalyst for biodiesel production from waste cooking oil

A novel magnetic SO4/Fe-Al-TiO2 solid acid catalyst was synthesized for biodiesel production via the (trans)esterification of waste cooking oil (WCO). The nanocomposite catalyst was prepared by the sequential functionalisation of commercial rutile/anatase mixed phase TiO2 nanoparticles (NPs) with alumina as a buffer layer, and subsequently hematite to impart magnetic character, prior to sulfation with chlorosulfonic acid to introduce Brønsted acidity. XRD showed that the SO4/Fe-Al-TiO2 catalyst comprised titania (rutile and anatase phases), aluminium sulphate, and hematite nanoparticles, while electron microscopy revealed the layer-by-layer assembly of these components within the SO4/Fe-Al-TiO2 catalyst. FTIR confirmed the presence of surface sulphate groups SO42− and S2O72−/S3O102−, creating a predominantly Brønsted acid catalyst with high acid loading. The catalyst achieved 96% fatty acid methyl ester (FAME) yield from WCO after 2.5 h of reaction at 90 °C, using 3 wt% of the magnetic catalyst, and a methanol:oil molar ratio of 10:1. SO4/Fe-Al-TiO2 was also effective for feedstocks containing up to 20 wt% of free fatty acid (FFA), and showed excellent stability for WCO (trans)esterification over 10 recycles.

Effect of porphyrin on photocatalytic activity of TiO2 nanoparticles toward Rhodamine B photodegradation

As known, porphyrins have central role in photosynthesis, biological oxidation and reduction and oxygen transport beside to their intensive color which qualify them to be good photosensitizers. Herein, tetra (4-carboxyphenyl) porphyrin (TCPP) was prepared by a simple one-pot synthesis to use as a visible antenna for TiO2 nanoparticles that were prepared via a simple template-free sol-gel method. Various loading percentages of TCPP (0.05–1%) were incorporated on the surface of TiO2 as photosensitizer for photocatalytic degradation of Rhodamine B (Rh B) dye as a primary cationic pollutant model. Among them, 0.1% TCPP-TiO2 was the most reactive sample. It was found that the photoactivity of 0.1% TCPP-TiO2 sample (0.5g/L) was approximately 1.5 times greater than that of pure TiO2 (0.5g/L) toward the degradation of Rh B (1×10−5M) under UV-A irradiation. Transient fluorescence decay measurements showed that the life time of TiO2 excited state has doubled after anchoring TCPP, thus the probability of electron-hole recombination has decreased. The samples were characterized by XRD, HR-TEM, DRS and N2 adsorption-desorption isotherms. The XRD patterns confirmed the successful preparation of TiO2 nanoparticles with average crystalline size of 25.7nm. Also, XRD patterns suggested the presence of mixed phase TiO2 nanoparticles of 77% anatase and 23% rutile. DRS showed that the characteristic peaks of TCPP covered the whole visible range 400–700nm. HR-TEM images showed the spheroids shape of TiO2 nanoparticles and confirmed the presence of anatase and rutile phases as suggested from XRD data. The different parameters affecting the photodegradation of Rh B dye such as catalyst dose, dye concentration and pH were studied to obtain the optimum conditions. Almost complete degradation of Rh B was obtained which confirmed by HPLC and TOC measurements. The effect of scavengers was studied to indicate the most active species. TCPP-TiO2 gave a good response toward the photodegradation of Rh B under visible irradiation. Finally, the mechanism of photocatalytic degradation process was suggested.

Synergistic Effects of Sm and C Co-Doped Mixed Phase Crystalline TiO₂ for Visible Light Photocatalytic Activity.

Mixed phase TiO2 nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO2 was shifted to the visible-light region, which was attributed to incorporation of samarium and carbon into the TiO2 lattice during high-temperature reaction. Samarium effectively decreased the anatase-rutile phase transformation. The grain size can be controlled by Sm doping to achieve a large specific surface area useful for the enhancement of photocatalytic activity. The photocatalytic activities under visible light irradiation were evaluated by photocatalytic degradation of methylene blue (MB). The degradation rate of MB over the Sm-C co-doped TiO2 sample was the best. Additionally, first-order apparent rate constants increased by about 4.3 times compared to that of commercial Degusssa P25 under the same experimental conditions. Using different types of scavengers, the results indicated that the electrons, holes, and •OH radicals are the main active species for the MB degradation. The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure.

Synthesis of nanostructured TiO2 thin films with highly enhanced photocatalytic activity by atom beam sputtering

Nanostructured TiO2 thin films with highly enhanced photocatalytic activity were prepared by atom beam sputtering technique. The effects of thermal annealing on the structural, morphological and photocatalytic properties of TiO2 thin films were investigated using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, Raman spectroscopy and UV-visible absorption spectroscopy. X-ray diffraction studies showed that the as-deposited TiO2 thin films made up of anatase TiO2 nanoparticles transformed into anatase/ rutile mixed-phase TiO2 nanoparticles upon annealing. Field emission scanning electron microscopy and atomic force microscopy studies revealed growth of TiO2 nanoparticles from 16 nm to 29 nm upon annealing at 600 o C. The photocatalytic activities of the nanostructured TiO2 thin films were studied by monitoring photocatalytic degradation of methylene blue in water. Our results showed that the as-deposited nanostructured TiO2 thin films exhibited highly enhanced photocatalytic efficiency as compared to the annealed samples. The mechanism underlying the enhanced photocatalytic activity of nanostructured TiO2 thin film is tentatively proposed.

Preparation, characterization, and kinetic and thermodynamic studies of mixed-phase TiO2 nanoparticles prepared by detonation method

Although detonation method has been reported to prepare TiO2 nanoparticles, phase transformation and crystal growth of detonation-prepared TiO2 nanoparticles have not been explored extensively. In this study, mixed-phase TiO2 nanoparticles, consisting of anatase (34.8wt%, ∼9.4nm) and rutile (65.2wt%, ∼18.2nm), were prepared by the detonation method. The phase transformation in the TiO2 sample at different annealing temperatures was modeled to understand the transformation behaviors. Thermal treatment experiments of the detonation-prepared TiO2 nanoparticles indicated that the initial process involved an anatase-to-rutile transformation. The TiO2 grains coarsened drastically after thermal treatment at 600°C for 1h. In contrast to a normal transformation, the anatase-to-rutile transformation was followed by conversion of rutile to anatase in large crystals. Moreover, smaller TiO2 particles could gain more kinetic energy and combine rapidly with the increase in temperature, forming larger particles. Anatase was transformed completely to rutile after thermal treatment at 720°C for 3.5h. The transformation temperature from anatase to rutile of the detonation-prepared TiO2 nanoparticles was approximately 80°C lower than that of TiO2 prepared by conventional methods. Therefore, thermal treatment may be employed to control the particle size and phase content of detonation-prepared TiO2 nanoparticles.

Toward a Visible Light-Driven Photocatalyst: The Effect of Midgap-States-Induced Energy Gap of Undoped TiO2 Nanoparticles

TiO2 is one of the most promising candidate materials for clean-energy generation and environmental remediation. However, the larger-than 3.1 eV bandgap of perfectly crystalline TiO2 confines its application to the ultraviolet (UV) range. In this study, the electronic and the optical properties of undoped mixed-phase TiO2 nanoparticles were investigated using UV and inverse photoemission, low intensity X-ray photoelectron (XP), and diffused reflectance spectroscopy methods. The facile solution-phase synthesized nanoparticles exhibited a midgap-states-induced energy gap of only ∼2.2 eV. The diffused reflectance spectrum showed sub-bandgap absorption due to the existence of a large Urbach tail at 2.2 eV. The UV photoemission spectrum evidenced the presence of midgap states. The 2.2 eV energy gap enables the nanoparticles to be photoactive in the visible energy range. The gas-phase CO2 photoreduction test with water vapor under visible light illumination was studied in the presence of the synthesized TiO2 na...

Hierarchical assembly of BiOCl nanosheets onto bicrystalline TiO2 nanofiber: Enhanced photocatalytic activity based on photoinduced interfacial charge transfer

One-dimensional ternary hierarchical heterostructures based on BiOCl nanosheets and bicrystalline TiO2 nanofiber frameworks that consist of anatase–rutile (AR) mixed phase TiO2 nanoparticles were successfully designed by combining the electrospinning technique and solvothermal method. The BiOCl nanosheets were uniformly grown onto the electrospun TiO2 nanofibers, and the density of the secondary BiOCl nanosheets could be controlled by adjusting the precursor concentration. Photocatalytic tests displayed that the ternary BiOCl/TiO2 (AR) hierarchical heterostructures possessed a much higher degradation rate than the bare bicrystalline TiO2 (AR) nanofibers, BiOCl/TiO2 (A) or BiOCl/TiO2 (R) composite. It is mainly attributed to the photogenerated interfacial charge transfer based on the photosynergistic effect of the heterojunctions, which results in the high separation efficiency of photogenerated electron–hole pairs.

The Effect of Heat Treatment of TiO2 Nanoparticles on Photovoltaic Performance of Fabricated DSSCs

The present work focuses on the synthesis of mixed phase TiO2 nanoparticles with reduced band gaps without even being doped. The synthesis was carried out by chemical route followed by heat treatments at different temperatures to favor rutile incorporation in anatase network. The significance of different heat treatment temperatures on the phase composition of TiO2 nanoparticles and its effect on optical band gap and the photovoltaic performance are analyzed. The thermal analysis, phases, morphology, and energy band gap of as-synthesized TiO2 nanoparticles have been characterized by DTA/TG, x-ray diffraction, field-emission scanning electron microscope, transmission electron microscope, and UV-Vis-NIR, respectively. The results show the presence of rutile (~15 nm) and anatase phases (~17 nm) in “as-synthesized” TiO2 nanoparticles. TiO2 nanoparticles are heat treated for 2 h at 200, 400, and 600 °C in air. It is observed that heat treatment results in higher photoactivity in visible region of the solar radiation and the material demonstrated high photovoltaic performance in conjunction with N-719. The optical band gap values are found to be in the range of 2.59-2.88 eV. The dye-sensitized solar cells (DSSCs) fabricated by TiO2 nanoparticles, heat treated at 600 oC show the energy conversion efficiency (η) of 6.08% with high photo current density (Jsc) of 11.76 mA/cm2. The work highlighted in this paper represents the realization of simple method of achieving low band gap semiconductors without being doped, for DSSCs applications.

Study on crystallinity and morphology controlling of titania using acrylamide gel method and their photocatalytic properties

In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO2 nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO2 nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO2 nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450°C have pure anatase and anatase–rutile mixed structures. The prepared samples having crystallite size between 5nm and 60nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TECI), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75min.

Preparation of Anatase/Rutile Mixed-Phase Titania Nanoparticles for Dye-Sensitized Solar Cells

Acid-labile high surface mesoporous ZnO/Zn(OH)2 composite material is used as a novel hard template for the preparation of mesoporous amorphous TiO2. The template-free amorphous TiO2 material is then thermally crystallized at suitable temperature to control the relative ratio of anatase and rutile phases in a particle. Four different anatase/rutile (AR) mixed-phase TiO2 nanoparticles (AR-3, AR-15, AR-20, and AR-23 denoted for the samples of 3%, 15%, 20%, and 23% rutile phase, respectively) are prepared and characterized by powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). The coexistence of anatase and rutile phases in a TiO2 nanoparticle is visually confirmed by HRTEM analysis. These mixed-phase TiO2 nanoparticles are examined as candidates for photoelectrodes of dye-sensitized solar cells (DSSCs). The J-V curves and IPCE spectra for the DSSCs prepared from the mixed-phase TiO2 nanoparticles are obtained, and their photovoltaic properties are investigated. The photo-conversion efficiency (eta) indicates the highest value of 5.07% for AR-20. The synergistic effect of coexisting anatase and rutile phases with an optimal ratio in a TiO2 nanoparticle of AR-20 for an efficient interfacial transfer of photo-generated electrons is likely to lead to the highest efficiency among the AR-n samples.

Hierarchical assembly of ultrathin hexagonal SnS2nanosheets onto electrospun TiO2nanofibers: enhanced photocatalytic activity based on photoinduced interfacial charge transfer

Well-designed hierarchical nanostructures with one dimensional (1D) TiO(2) nanofibers (120-350 nm in diameter and several micrometers in length) and ultrathin hexagonal SnS(2) nanosheets (40-70 nm in lateral size and 4-8 nm in thickness) were successfully synthesized by combining the electrospinning technique (for TiO(2) nanofibers) and a hydrothermal growth method (for SnS(2) nanosheets). The single-crystalline SnS(2) nanosheets with a 2D layered structure were uniformly grown onto the electrospun TiO(2) nanofibers consisted of either anatase (A) phase or anatase-rutile (AR) mixed phase TiO(2) nanoparticles. The definite heterojunction interface between SnS(2) nanosheets and TiO(2) (A or R) nanoparticles were investigated by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Moreover, the as-prepared SnS(2)/TiO(2) hierarchical nanostructures as nanoheterojunction photocatalysts exhibited excellent UV and visible light photocatalytic activities for the degradation of organic dyes (rhodamine B and methyl orange) and phenols (4-nitrophenol), remarkably superior to the TiO(2) nanofibers and the SnS(2) nanosheets, mainly owing to the photoinduced interfacial charge transfer based on the photosynergistic effect of the SnS(2)/TiO(2) heterojunction. Significantly, the SnS(2)/TiO(2) (AR) hierarchical nanostructures as the tricomponent heterojunction system possessed stronger photocatalytic activity than the bicomponent heterojunction system of SnS(2)/TiO(2) (A) hierarchical nanostructures or TiO(2) (AR) nanofibers, which was discussed in terms of the three-way photosynergistic effect between SnS(2), TiO(2) (A) and TiO(2) (R) component in the SnS(2)/TiO(2) (AR) heterojunction resulting in the high separation efficiency of photoinduced electron-hole pairs, as evidenced by photoluminescence (PL) and surface photovoltage spectra (SPS).

Effect of annealing temperature on Raman spectra of TiO2 nanoparticles

Sol–gel method has been used to prepare pure anatase and anatase–rutile mixed phase TiO2 nanoparticles by calcination at different temperatures. The influences of calcination temperature on structure, band gap, luminescence properties and Raman spectra have been investigated. A clear evidence of structural transformation from pure anatase to anatase–rutile mixed phase structures has been confirmed by X-ray diffraction (XRD). Photoluminescence spectroscopy (PL) shows that the change in structure is also responsible for exhibiting the change in PL intensity. The Raman spectroscopy exhibits the anomalous behavior for band broadening and shifting of Raman bands with increasing crystallite size.