Formation of Oxynitride as the Photocatalytic Enhancing Site in Nitrogen‐Doped Titania Nanocatalysts: Comparison to a Commercial Nanopowder

A nitrogen‐doped TiO₂ nanocolloid has been successfully prepared and its properties compared with the commercially available TiO₂ nanomaterial, Degussa P25. Several characterization techniques, X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM), Fourier transform infrared (FT‐IR) spectroscopy, Raman scattering, and UV‐visible reflectance spectra, are combined in order to determine the crystal phase and grain size, shape, degree of nitrogen incorporation, and nature of the resultant oxynitride chemical bonding on the surface and in the bulk. The high relative photocatalytic activity of the nitrogen doped‐TiO₂ nanocolloid is evaluated through a study of the decomposition of methylene blue under visible light excitation. The ease and degree of substitutional‐insertional nitrogen doping is held accountable for the significant increase in photocatalytic activity in the porous nanocolloid versus the nitrided commercial nanopowder. It is suggested that the nitrogen incorporation produces an NO bonding region as evidenced by the resulting XPS spectrum.     

Sonocatalytic activity of Yb,B, Ga-codoped Er3+:Y3Al5O12/TiO2 in degradation of organic dyes

A series of Yb, B and Ga doped Er³⁺:Y₃Al₅O₁₂ (Er:YAG) as up-conversion luminescence agents were synthesized using sol–gel method. After that, their corresponding TiO₂ coated composites (Er³⁺:Y₃Al₅O₁₂/TiO₂ (Er:YAG/TiO₂), Yb-doped Er³⁺:Y₃Al₅O₁₂/TiO₂ (YbEr:YAG/TiO₂), Yb and B-doped Er³⁺:Y₃Al₅O₁₂/TiO₂ (YbEr:(B)YAG/TiO₂), Yb and Ga doped Er³⁺:Y₃Al₅O₁₂/TiO₂ (YbEr:(Ga)YAG/TiO₂) and Yb, B and Ga doped Er³⁺:Y₃Al₅O₁₂/TiO₂ (YbEr:(B,Ga)YAG/TiO₂)) as sonocatalysts were prepared by sol–gel coating process. The up-conversion luminescence agents and their coated composites were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). And that, the sonocatalytic activities were detected through the degradation of some organic dyes as model pollutants by UV–vis spectroscopy under ultrasonic irradiation. The influencing factors such as heat-treated temperature and heat-treated time on the sonocatalytic activity of YbEr:(B,Ga)YAG/TiO₂ coated composite were studied. In addition, the effects of ultrasonic irradiation time and initial dye concentration on the sonocatalytic degradation were also reviewed. The experimental results showed that the doping of Yb, B and Ga into Er:YAG/TiO₂ significantly enhanced its up-conversion luminescence capability, therefore, improved the sonocatalytic activity of Er:YAG/TiO₂ coated composite in the degradation of organic dyes. Particularly, YbEr:(B,Ga)YAG/TiO₂ coated composites with 3:7 mass ratio heat-treated at 550 °C for 60 min displayed the highest sonocatalytic activity. At last, the experiments indicated that the YbEr:(B,Ga)YAG/TiO₂ coated composite has also a good sonocatalytic activity to degrade other organic dyes under ultrasonic irradiation.     

Nitrogen doped anatase TiO2 sheets with dominant {001} facets for enhancing visible-light photocatalytic activity

The photocatalytic activity of TiO₂ can be mainly improved from three approaches: (1) enhancing surface energy; (2) increasing availability of visible light and (3) improving the separation efficiency of photo-induced electrons and holes. Here, we report a one-step route to obtain nitrogen (N) doped TiO₂ sheets with dominant {001} facets by a hydrothermal process. The XRD patterns confirm the better crystallinity. XPS spectrums show nitrogen acting as interstitial N or an O–Ti–N structure in TiO₂ sheets. Compared with that of TiO₂ sheets, the N doped TiO₂ sheets not only absorb visible light, but also have a large percentage of high reactive {001} facets, so the photocatalytic activities are greatly enhanced, as confirmed by the decomposition of methylene orange.     

Sol gel synthesis of cobalt doped TiO2 and its dye sensitization for efficient pollutant removal

This study was concentrated on the synthesis of new cobalt doped (Co-TiO₂) photocatalyst via sol-gel method in the presence of surfactant Triton X100 or Tween 20. Surfactant was used to obtain smaller particles and enhance the photocatalytic action of the catalyst. Co-TiO₂ catalyst was further modified with a phthalocyanine for dye sensitization that facilitates electron transfer. A peripherally tetra 12-crown-4 substituted metal free phtalocyanine (Pc) derivative was first time synthesized and used as dye sensitizer employing same sol-gel method in the presence and absence of above surfactants (Pc/Co-TiO₂). The as-synthesized photocatalysts were characterized by XRD, TGA, SEM, EDX, TEM, BET and UV–vis diffuse reflectance spectroscopy (DRS). The results revealed that the both cobalt and Pc had been successfully immobilized on the TiO₂ nanoparticles and the nanocomposite had the anatase structure. Incorporation of Pc into TiO₂ structure caused significant shift of absorption edge into visible range due to strong absorbance of Pc. Apart from this particle size of Pc immobilized TiO₂ was dramatically decreased particularly in the presence of surfactant. The photocatalytic degradation of methyl orange (MO) dye solution (10 mg/L) and the photocatalytic reduction of Cr(VI) ions (10 mg/L) using Pc/Co-TiO₂ (2 g/L) was investigated under UV light irradiation (λ=365 nm). Photocatalytic studies revealed that the Pc/Co-TiO₂ prepared in the presence of Tween 20 has shown much higher photocatalytic activity than the other catalysts. After 150 min of irradiation, the photocatalytic activity of the catalysts follows the order: Pc/Co-TiO₂-T20>Pc/Co-TiO₂-TX100>Pc/Co-TiO₂>Co-TiO₂-T20>Co-TiO₂-TX100>Co-TiO₂. It was found that about 60.3% of the MO was removed and 71.3% of the Cr(VI) ions were reduced by Pc/Co-TiO₂ after 150 min under 365 nm light irradiation.     

Photocatalytic elimination of bisphenol A under visible light using Ni-doped TiO2 synthesized by microwave assisted sol-gel method

In this work, heterogeneous photocatalysis under visible light was applied as treatment to degrade bisphenol A (BPA) using Ni-TiO₂ catalysts with different Ni contents (0.5 and 1.0 wt%). The materials were synthesized by rapid microwave assisted sol-gel process (MW). For comparison, 1.0% Ni-TiO₂ by conventional sol-gel method (CM) was prepared. Semiconductors were characterized by various analytical techniques. Diffuse reflectance spectroscopy studies indicated a red shift in the band gap absorption to the visible region when nickel was incorporated while results from powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed the substitution of sites of Ti⁴⁺ ions by Ni²⁺ ions into the crystal lattice of anatase TiO₂. The best results in BPA degradation were obtained at solution pH 9 in the follow order 1.0% Ni-TiO₂ MW > 0.5% Ni-TiO₂ MW > 1.0% Ni-TiO₂ CM > TiO₂ MW. This behavior was explained by the lower band gap (Eg) value, smaller crystallite size and the inhibition in recombination of the electron/hole pairs, caused by nickel incorporation. Using 1.0% Ni-TiO₂ MW as catalyst, complete BPA degradation, and 77% mineralization were achieved in 210 min. The toxicity of the final solution was also evaluated by means of the marine bacteria Vibrio fischeri.     

Hybridized Nanowires and Cubes: A Novel Architecture of a Heterojunctioned TiO2/SrTiO3 Thin Film for Efficient Water Splitting

A unique morphology of SrTiO₃ nanocubes precipitated on TiO₂ nanowires is successfully synthesized in the form of a thin‐film heterojunctioned TiO₂/SrTiO₃ photocatalyst using facile hydrothermal techniques. The formation mechanisms of the synthesized photocatalysts are meticulously studied and described. Growth of SrTiO₃ single crystal nanocubes (≈50 nm in width) on anatase polycrystalline nanowires follows an in situ dissolution‐precipitation pathway. This is consonant with the classic LaMer model. By analyzing the results of field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), X‐ray diffraction (XRD), energy dispersive X‐ray (EDX) spectroscopy, X‐ray photoelectron spectroscopy (XPS), and UV‐vis spectrophotometry, a comprehensive structural and morphological characterization of the photocatalysts is established. FESEM images reveal that the anatase film comprises mainly of nanowires bristles while the tausonite film is primarily made up of nanocube aggregations. In comparison to the respective pristine semiconductor photocatalysts, the heterostructured photocatalyst demonstrates the highest efficiency in photocatalytic splitting of water to produce H₂, 4.9 times that of TiO₂ and 2.1 times that of SrTiO₃. The enhanced photocatalytic efficiency is largely attributed to the efficient separation of photogenerated charges at heterojunctions of the two dissimilar semiconductors, as well as a negative redox potential shift in the Fermi level.     

Synthesis of mesoporous titania–graphite composite templated by hypocrellins for visible-light photocatalytic degradation of acetaldehyde

A photoactive compound extracted from a fungus (Hypocrella bambuase), named hypocrellins, was used as template to synthesize thermally stable mesoporous materials. The synthesized mesoporous titania samples were characterized using a combination of various physicochemical techniques, such as N₂ adsorption/desorption measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The results of physicochemical characterizations showed that the as-synthesized sample was a composite of highly crystalline mesoporous anatase titania and graphitic carbon (gc–MTiO₂), which implies the dual function of hypocrellins as template and “dopant”. The in situ doped graphitic carbon significantly increased the visible-light absorbance of TiO₂. The gc–MTiO₂ exhibited efficient photocatalytic activity under visible-light for photodegradation of acetaldehyde, a common indoor air pollutant. The photophysics and electron dynamics in this photocatalytic process were studied by time-resolved FT-IR spectra, in particular on the nano- to milli-second time scale. It is observed that electrons were injected into the conduction band of gc–MTiO₂ and they were decayed to deep traps caused by graphitic carbon. The reported strategies could open up new uses for mesoporous titania self-doped with carbon in applications such as solar cells, photocatalysts, photoelectrical devices, and photo-induced sensors.     

Zero-valent nanophase iron and nitrogen co-modified titania nanotube arrays: Synthesis,characterization, and enhanced visible-light photocatalytic performance

We prepared nano-zero-valent iron (nZVI) and N co-modified TiO₂ (nZVI/N–TiO₂) nanotube arrays as an enhanced visible-light photocatalyst. The TiO₂ nanotube arrays were synthesized by electrochemical anodization of Ti foil in a two-electrode system. Amorphous TiO₂ nanotube arrays were immersed in ammonia and then annealed to produce crystalline N-doped TiO₂ (N–TiO₂) nanotube arrays. nZVI spheres were directly deposited on the N–TiO₂ nanotube arrays by borohydride reduction. The photocatalysts were characterized by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and electrochemical impedance spectroscopy (EIS). The environmental applicability and photocatalytic activity of the proposed nZVI/N–TiO₂ nanotube arrays were tested by phenol degradation in an aqueous system under UV and visible light irradiation. The phenol degradation rate constants of each sample under visible light irradiation were in the following order: nZVI/N–TiO₂ (k_obs=0.006 min⁻¹⁾>N–TiO₂ (k_obs=0.002 min⁻¹) ⪢ nZVI/TiO₂ (k_obs=0.0003 min⁻¹)>TiO₂ (k_obs=0.0001 min⁻¹). This result can be attributed to the synergistic effect of the N–TiO₂ nanotubes with lower energy band gap and the electron transfer from the conduction band (CB) of N–TiO₂ to nZVI spheres highly-dispersed on the N–TiO₂ for enhanced separation of photogenerated electrons and holes.     

Visible-light-driven composite La2O3/TiO2 nanotube arrays: Synthesis and improved photocatalytic activity

In this work, using a lanthanum nitrate solution as lanthanum source, a visible-light responsive La₂O₃/TiO₂ nanotube arrays (TNTs) composite was synthesized by a facile impregnation-calcinations technique. The as-synthesized samples were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy and photocurrent tests. The photocatalytic activity of the La₂O₃/TNTs composite under visible-light irradiation (λ>420 nm) was evaluated by the degradation of Rhodamine B (RhB). The results revealed one part of La was doped, and the other part was dispersed on the TNTs surface in the form of La₂O₃. La-doping narrowed the band gap and La₂O₃ modification accelerated the separation of photo-induced electron-hole pairs. Consequently, the as-prepared La₂O₃/TNTs composite exhibited much higher photocatalytic activity than pure TNTs. The photocatalytic activity of the composite was related to impregnation time of lanthanum nitrate solution, and an optimal time was 2 h. The activity of 2-La₂O₃/TNTs displayed 3.7 times as high as that of pure TNTs. A possible mechanism on the La₂O₃/TNTs photocatalytic activities is suggested. The composite, as promising materials, could be used to degrade dye wastewater or other organic pollutants.     

Synergistic Effect of Si Doping and Heat Treatments Enhances the Photoelectrochemical Water Oxidation Performance of TiO2 Nanorod Arrays

TiO₂ is a very promising photocatalytic material due to its merits including low cost, nontoxicity, high chemical stability, and photocorrosion resistance. However, it is also known that TiO₂ is a wide bandgap material, and it is still challenging to achieve high photocatalytic performance driven by solar light. In this paper, silicon‐doped TiO₂ nanorod arrays are vertically grown on fluorine‐doped tin oxide substrates and then are heat treated both in air and in vacuum. It is found that the silicon doping together with the heat treatment brings synergic effect to TiO₂ nanorod films by increasing the crystallinity, producing abundant oxygen vacancies, enhancing the hydrophilicity as well as improving the electronic properties. When used as photoanodes in photoelectrochemical water splitting, under the condition of AM 1.5G simulated solar irradiation and without using any cocatalysts, these nanorod films show photocurrent density as high as 0.83 mA cm^?2 at a potential of 1.23 V versus reversible hydrogen electrode, which is much higher than that of the TiO₂ nanorod films without doping or heat treating. The silicon‐doped TiO₂ nanorod array films described in this paper are envisioned to provide valuable platforms for supporting catalysts and cocatalysts for efficient solar‐light‐assisted water oxidation and other solar‐light‐driven photocatalytic applications.     

An enhanced visible light active rutile titania–copper/polythiophene nanohybrid material for the degradation of rhodamine B dye

A novel copper doped TiO₂ (TiO₂–Cu)/polythiophene (PTh) nanohybrid material with discrete polymer concentrations is devised by a modified sol–gel technique at low temperature. The XRD outcome revealed that the polythiophene and copper contents do not affect the crystal structure of TiO₂. SEM and TEM images of the TiO₂–Cu and nanohybrid denoted the presence of a nanoparticle sized core–shell structure. UV–visible absorption spectra of nanohybrid catalyst with diverse polymer concentrations broadcasted a broad and strong absorption in the visible region. A strong interaction between the interface of PTh and TiO₂–Cu was confirmed by FT-IR. The presence of Cu²⁺ ion and positively charged sulfur (polarons) throughout the polymer carbon content was manifested by XPS spectra. The photocatalytic activity of nanohybrid catalyst has been evaluated by degradation of Rhodamine B (RhB) under visible light irradiation. The effect of solution pH, catalyst dosage and initial concentration of RhB on the photocatalytic activity of TiO₂–Cu/PTh nanohybrid with different loadings is studied. It has been observed that the rate of degradation of RhB over TiO₂–Cu/PTh nanohybrid is better than TiO₂–Cu metal oxide under visible light irradiation.     

Anatase titania nanorods by pseudo-inorganic templating

A novel, facile and cost-effective single step aqueous sol–gel method for the synthesis of anatase TiO₂ nanorods without the assistance of structure-directing organic/inorganic templates is reported. We specifically demonstrate a pseudo-inorganic templating method using ammonium iron (III) sulfate. Highly thermal stable anatase TiO₂ nanorods were obtained using titanium oxysulfate and ammonium iron (III) sulfate as precursors. The structural, microstructural and chemical analyses of the nanorods synthesized, strongly supported the pseudo inorganic templating role of ammonium iron (III) sulfate on the formation of nanorod morphology. The materials have been characterized using different techniques such as TEM, XRD, BET surface area measurement, diffuse reflectance spectra and XPS. TEM study confirmed the rod shape of nano-anatase TiO₂, having a diameter in the range of 20–40 nm and a length of 100 nm. XPS investigation showed that along with Fe³⁺, nitrogen and sulfur were also been doped into the TiO₂ lattice from the single source dopant precursor ammonium iron (III) sulfate. Moreover, UV/vis diffuse reflectance spectra of nanorods showed red-shifts towards visible light and a corresponding decrease in band-gap energies consistent with an n-type doping of the anatase TiO₂ matrix. This aqueous sol–gel synthesis of anatase nanorod with pseudo inorganic templating explores the advantages of inexpensive precursors, control over the powder morphology and optical properties, and distribution of the dopants over TiO₂ at nano level due to homogeneous mixing of the precursors. Finally the photocatalytic analysis showed that the TiO₂ nanorod have two times higher activity than the commercially available Degussa P 25.     

Reactive pulsed laser deposited N–C codoped TiO2 thin films

TiO₂ is a large bandgap chemically stable oxide useful for several applications that involve photo-activated processes, including photocatalysis, photovoltaics, photoelectrolysis, etc. However, the large band gap renders this material not a very efficient absorber of the solar spectrum. Various schemes of cation and anion doping have been utilized that reduce this deficiency to a certain extent. In this paper we present the results of N–C codoping of TiO₂ thin films deposited by a reactive pulsed laser deposition technique. These films were compared for their optical and structural properties with undoped, N doped and C doped TiO₂ films prepared by the same technique. While all samples contained polycrystalline anatase phase, varying N₂ and CH₄ partial pressures resulted in change in TiO₂ lattice parameters due to codoping. X-ray diffraction high-resolution scans show the evidence of C incorporation into TiO₂ lattice by 2θ shift in (101) reflections due to large ionic radius of C. N doping was confirmed by XPS analyses. Direct relationship between oxygen vacancies and doping concentration was established by the deconvolution of XPS peaks. Considerable bandgap reduction occurred that was measured by using UV–vis diffuse reflectance spectroscopy. Results show that reactive pulsed laser deposition is indeed a useful method for the synthesis of codoped TiO₂ thin films as bandgap reduction of ~1.00 eV via N–C codoping was successfully achieved.     

Fabrication and enhanced performance of calcium metasilicate-stabilized silver-promoted anatase photocatalysts

A range of calcium metasilicate–silver promoted-anatase (Ag–TiO₂–CaSiO₃) photocatalysts was obtained by photoreduction and physisorption methods. The calcium metasilicate (CaSiO₃) materials were prepared by chemical precipitation technology. The structure and morphology of photocatalysts were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) characterization methods. The results show that the anatase (TiO₂) and silver promoted-anatase (Ag–TiO₂) particles were evenly distributed on the surface of calcium silicate material. After the activity of photocatalysts was evaluated through the degradation rate of methyl orange (MO), the results showed that the 4% Ag–TiO₂/CaSiO₃ products have higher activity during the reaction, and the products showed excellent reusability after that these were repeated five times. The sample of Ag–TiO₂/CaSiO₃ exhibits activity of MO degradation under visible light (λ >400 nm) because of the active sites of Ag nanoparticles. The novel composite photocatalysts might have potential applications in the treatment of environmental pollution.     

Effects of silver substrates on the visible light photocatalytic activities of copper-doped titanium dioxide thin films

Novel copper-doped titanium dioxide (Cu-doped TiO₂) thin films on silver (Ag) substrates with different thicknesses were prepared by sol–gel and magnetron sputtering methods. The influences of the Ag substrate thickness on the morphology and performance of the films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV–visible spectroscopy, and photocatalytic degradation testing with methylene blue aqueous solution under visible light irradiation. The results indicated that Ag substrates with an optimal thickness of 30 nm not only maintained the tiny nanocrystals but also greatly improved dispersion of the nanoparticles on the surface of the nanofilms. Furthermore, during the calcination process, part of the Ag atoms diffused from the substrates into the Cu–TiO₂ films and substituted for the Cu ions to form Ag–TiO₂. A proper Ag substrate thickness (30 nm) greatly improved the photocatalytic properties of TiO₂ with photocatalytic efficiency, reaching approximately 86% in 300 minutes under visible light irradiation. However, an excess of Ag substrate not only led to the Cu ion separating out in the form of CuO but also resulted in the agglomeration of TiO₂ particles on the surface, which were detrimental to photocatalytic activities.     

Enhanced properties for visible-light-driven photocatalysis of Ag nanoparticle modified Bi2MoO6 nanoplates

The visible light driven Bi₂MoO₆ photocatalyst doped with different contents of Ag nanoparticles was successfully synthesized by a combination of hydrothermal and sonochemical methods. The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM) and UV–visible spectroscopy to investigate crystalline structure, morphology, composition and photocatalytic properties. XRD patterns and TEM images of the samples revealed pure phase orthorhombic Bi₂MoO₆ nanoplates without any detection of Ag dopant due to its low concentration and very tiny particle size. TEM images showed that Ag nanoparticles with the size of 10–15 nm were dispersed randomly on the surface of Bi₂MoO₆. The XPS analysis of Ag/Bi₂MoO₆ nanocomposites revealed the presence of additional metallic Ag. Photocatalytic activities of the Ag/Bi₂MoO₆ nanocomposites were evaluated by determining the degradation of rhodamine B (RhB) under visible light radiation. In this research, the 10 wt% Ag/Bi₂MoO₆ nanocomposites showed the best photocatalytic activity. The results suggest that the dispersion of Ag nanoparticles on the surface of Bi₂MoO₆ significantly enhances its photocatalytic activity.     

Improved performance of surface functionalized TiO2/activated carbon for adsorption–photocatalytic reduction of Cr(VI) in aqueous solution

TiO₂ coated on activated carbon (TiO₂/AC) was synthesized by a facile sol-hydrothermal preparation. The as-prepared TiO₂/AC was modified by sequential treatment of nitric acid and thionyl chloride, followed by surface attaching of diethylenetriamine. The obtained materials were characterized by transmission electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, BET adsorption, and their adsorption–photocatalytic reduction activities were evaluated by the removal of aqueous Cr(VI). The results showed that TiO₂ particles were homogeneously deposited on the surface of activated carbon, and diethylenetriamine was grafted covalently onto the surface of TiO₂/AC through amide linkage. The diethylenetriamine-functionalized TiO₂/AC (TiO₂/AC-DETA) exhibits high adsorption capability for Cr(VI) through electrostatic, coordinative and hydrogen bonding interactions. The significant enhancement of photocatalytic activity of TiO₂/AC-DETA for reduction of Cr(VI) was observed, which was mainly attributed to the enrichment of Cr(VI) onto the surface of AC and successive fast interfacial transfer of Cr(VI) and photogenerated electrons resulted from the intimate contact between AC and TiO₂ through dense heterojunctions by forming of C–O–Ti linkages.     

WO3/TiO2 nanocomposites: Salt–ultrasonic assisted hydrothermal synthesis and enhanced photocatalytic activity

A series of WO₃/TiO₂ composite photocatalysts were fabricated via a facile salt–ultrasonic assisted hydrothermal process. The obtained samples were characterized by X-ray diffraction, scanning eletron microscopy, energy dispersive X-ray spectroscopy and UV–vis diffused reflectance spectroscopy. It was confirmed that anatase TiO₂ and monoclinic WO₃ coexisted in the composites. The photocatalytic activity of as-prepared WO₃/TiO₂ composites for degradation of Rhodamin B (RhB) under visible light irradiation was investigated. The results showed that WO₃/TiO₂ composites have a higher photocatalytic activity than those of pure TiO₂ and pure WO₃. First-principle calculations based on density functional theory were performed to explore the electronic structure and illustrate the photocatalytic mechanism of WO₃/TiO₂. The calculated energy gap was 2.53 eV, which was close to the experimental observation (2.58 eV). Due to the combination of WO₃/TiO₂, the photoinduced electrons and holes transfer between the WO₃ and TiO₂ in opposite directions, thus providing sufficient charge separation, which contributed to the photocatalytic activity enhancement.     

Design of conduction band structure of TiO2 electrode using Nb doping for highly efficient dye‐sensitized solar cells

A barrier layer of undoped TiO₂ was deposited on the Nb‐doped TiO₂ electrode to suppress the recombination at the Nb‐doped TiO₂/dye–electrolyte interface for highly efficient dye‐sensitized solar cells (DSCs). The Nb content in TiO₂ was varied in a range of 0.7–3.5 mol% to modify the TiO₂ energy‐band structure. Nb‐doped TiO₂/dye interfaces were characterized by a combination of ultraviolet photoemission spectroscopy and optical absorption spectroscopy measurements, allowing the determination of the conduction band minimum (CBM) of the TiO₂ electrode and the lowest unoccupied molecular orbital of the N719 dye. The lowering of TiO₂ CBM by Nb doping induced the increase in short‐circuit current of DSCs. However, open‐circuit voltage and fill factor are decreased, and this result was ascribed to the enhanced recombination at the Nb‐doped TiO₂/dye–electrolyte interface. The effect of doping on charge transport in DSCs was analyzed using electrochemical impedance spectroscopy. We have shown that by introducing of TiO₂ barrier layer, the Nb doping content, which results in DSC highest efficiency, can be increased because of the suppression of the dopant‐induced recombination. The energy conversion efficiency of the solar cells increased from 7.8% to 9.0% when undoped TiO₂ electrode is replaced with electrode doped with 2.7 mol% of Nb because of the improvement of the electron injection and collection efficiencies. The correlation between the electronic structure of the TiO₂ electrode, charge transfer characteristics, and photovoltaic parameters of DSCs is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Solid state synthesis of erbium doped ZnO with excellent photocatalytic activity and enhanced visible light emission

The doped ZnO crystals with different erbium content were prepared by solid state reaction technique. The method is simple, relatively less expense and enables the production in large scale. The samples were characterised by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV/vis diffuse reflectance spectroscopy and photoluminescence techniques. Photocatalytic activity of samples was investigated by the degradation of methylene blue under UV light irradiation and was observed that, small fractions of erbium incorporation have a significant role in the enhancement of photocatalytic activity of ZnO. And the good stability of prepared catalysts makes them suitable for practical applications. Fluorescent property studies of erbium doped ZnO at room temperature show enhanced visible light emission due to the production of induced defects like antisite oxygen O_Zn and interstitial oxygen O_i. This work reports the co-existence of two mutually exclusive properties such as fluorescence and photocatalytic activity at their best in 0.6 wt% erbium doped ZnO.