Preparation and characterization of a novel activated carbon‐supported N‐doped visible light response photocatalyst (TiO2−xNy/AC)

A photocatalyst, TiO_2?xN_y/AC (activated carbon (AC) supported N‐doped TiO₂), highly active in both the Vis and UV range, was prepared by calcination of the TiO₂ precursor prepared by acid‐catalyzed hydrolysis in an ammonia atmosphere. The powders were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, X‐ray diffraction, N₂ adsorption, Fourier transform infrared spectroscopy and phenol degradation. The doped N in the TiO₂ crystal lattice creates an electron‐occupied intra‐band gap allowing electron‐hole pair generation under Vis irradiation (500–560 nm). The TiO_2?xN_y/AC exhibited high levels of activity and the same activity trends for phenol degradation under both Vis and UV irradiation: TiO_2?xN_y/AC calcined at 500 °C for 4 h exhibited the highest activity. The band‐gap level newly formed by doped N can act as a center for the photo‐generated holes and is beneficial for the UV activity enhancement. The performance of the prepared TiO_2?xN_y/AC photocatalyst revealed its practical potential in the field of solar photocatalytic degradation of aqueous contaminants. Copyright © 2007 Society of Chemical Industry     

Nanostructured Solids from Freeze‐Dried Precursors: Multigram Scale Synthesis of TiO2‐Based Powders

Nanocrystalline TiO₂ and Ti_1?xV_xO₂ (x = 0.01) powders have been prepared by thermal decomposition, in air, of amorphous precursors resulting from the freeze‐drying of appropriate solutions. In addition, TiO_2?xN_y (anatase and rutile) and TiO_xN_y (rock‐salt) have been prepared by thermal treatment in ammonia of a crystalline precursor (TiO₂ obtained at 673 K). TEM and SEM images, as well as the analysis of the X‐ray diffraction (XRD) patterns, show the nanoparticulated character of those solids obtained at low temperatures, with typical particle sizes in the 10–20 nm range when prepared at 673 K. The UV–Vis results indicate both the insertion of V in the anatase lattice and the feasibility of nitridation at low temperatures. The photocatalytic properties of these materials (as prepared and after their incorporation to mortar samples) in the degradation of nitrogen oxides have been preliminary evaluated. Although N‐doping enhances the photocatalytic activity of the TiO₂ matrix, V‐doping worsens it.     

Persistent deNOx Ability of CaAl2O4:(Eu, Nd)/TiO2-x N y Luminescent Photocatalyst

Abstract  

CaAl₂O₄:(Eu, Nd)/TiO_2-x N _y composite luminescent photocatalyst was successfully synthesized by a simple planetary ball milling process. Improvement of photocatalytic deNOx ability of TiO_2-x N _y , together with the persistent photocatalytic activity for the decomposition of NO after turning off the light were realized, by coupling TiO_2-x N _y with long afterglow phosphor, CaAl₂O₄:(Eu, Nd). The novel persistent photocatalytic behavior was related to the overlap between the absorption wavelength of TiO_2-x N _y and the emission wavelength of the CaAl₂O₄:(Eu, Nd). It was found that CaAl₂O₄:(Eu, Nd)/TiO_2-x N _y composites provided the luminescence to persist photocatalytic reaction for more than 3 h after turning off the light.     

Highly active TiO2−x−yNxFy visible photocatalyst prepared under supercritical conditions in NH4F/EtOH fluid

A novel N and F co-doped TiO₂ (TiO_2−x−yN_xF_y) photocatalyst is prepared by treating the TiO₂ precursor in NH₄F/ethanol fluid under supercritical conditions. During photocatalytic degradation of methylene blue under visible light irradiation, the as-prepared TiO_2−x−yN_xF_y exhibits higher activity than the undoped TiO₂, N-doped TiO₂ (TiO_2−xN_x), and F-doped TiO₂ (TiO_2−yF_y). Based on the characterizations including XRD, Raman, FTIR, TEM, PLS, UV–vis DRS, N₂ adsorption–desorption isotherms, XPS and NH₃-TPD, the synergetic promotions of N- and F-dopants incorporated into the TiO₂ lattice are discussed based on the enhanced spectral response in visible region, oxygen vacancies, and surface acidic sites. Meanwhile, the supercritical treatment also promotes the activity owing to the increase in both the surface area and the crystallization degree of anatase, and the enhanced incorporation of N- and F-dopants into the TiO₂ lattice.     

Defective Y2O3−x–driven anomalous photocatalytic enhancement using Y2O3−x–TiO2−x nanorod composite composition spreads

Synergistic photocatalysis is reported, using the optimal amounts of oxygen vacancies of high‐k materials and nanoarchitecture maneuvering by employing a combinatorial sputtering approach. The highlights include (i) the successful fabrication of samples using combinatorial sputtering; (ii) a systematic investigation of the coupling effect between Y₂O_3?x and TiO_2?x; (iii) elucidating charge carrier transport through current‐voltage (I‐V) and capacitance‐voltage (C‐V) characterizations; and (iv) providing an alternative application for high‐dielectric constant (high‐k) materials in photocatalysis. The simple yet effective composition spread technique rapidly determined that Sample 6 (4 at% Y₂O_3?x‐96 at% TiO_2?x, TiO_2?x‐rich on the Y₂O_3?x–TiO_2?x nanorod composite composition spread) exhibited the highest photocatalytic efficiency (i.e., approximately 3.4 times and 1.4 times higher than that of P25 and pure TiO_2?x nanorods, respectively). The predominant factor was determined to be electron migration along defective Y₂O_3?x nanorods to the sample surface. The extracted mobility was discovered to be an order of magnitude greater than that of pure TiO_2?x. The photoelectrochemical stability and reusability were also demonstrated.     

Preparation of aerochitin‐TiO2 composite for efficient photocatalytic degradation of methylene blue

An aerochitin–titania (TiO₂) composite was successfully synthesized and characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, field emission scanning electron microscopy, and N₂ adsorption isotherms. The photocatalytic activity of the composite was investigated on the degradation of the model organic pollutant, methylene blue (MB) dye, under UV irradiation. The aerochitin–TiO₂ composite showed excellent adsorptive and photocatalytic activity with a degradation degree of 98% for MB. The first‐order rate constants for the photodegradation MB by TiO₂ nanoparticles and aerochitin–TiO₂ composite were found to be (3.49 ± 0.04) × 10^?3 and (1.82 ± 0.02) × 10^?2 min^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45908.     

Structural and Thermodynamics Properties of TiC1−xNx–TiO1−xNx Solid Solutions: X‐ray Diffraction and First‐Principles Approaches

The structural properties and mixing thermodynamic of TiC_1?xN_x and TiO_1?xN_x (0 ≤ x ≤ 1) solid solutions have been studied by X‐ray diffraction method and first‐principles calculations. The TiC_1?xN_x and TiO_1?xN_x compounds were synthesized via solid‐state reaction and the analysis of XRD patterns show the properties of continuous solid solutions over the whole composition range. Thermodynamic analyses and structural stability studies were performed based on the mixing enthalpies and electronic structures. The mixing enthalpies of TiC_1?xN_x and TiO_1?xN_x can be fitted using a second‐degree polynomial with the increasing of supercell. The first‐principles calculations results reveal that the TiO_1?xN_x shows large number vacancies segregated in TiO‐part. The charge redistributed around Ti vacancy constitutes the main contribution to the stabilization rather than the Ti–Ti bond across the O vacancy through analyzing the electron density difference plots and PDOS . These results provide theoretical basis for the development and application of the TiC_1?xN_x and TiO_1?xN_x solid solutions.     

A novel TiO2 − xNx/BN composite photocatalyst: Synthesis,characterization and enhanced photocatalytic activity for Rhodamine B degradation under visible light

A novel TiO_2 − xN_x/BN composite photocatalyst was prepared via a facile method using melamine–boron acid adducts (M·2B) and tetrabutyl titanate as reactants. The morphological results confirmed that nitrogen-doped TiO₂ nanoparticles were uniformly coated on the surface of porous BN fibers. A red shift of absorption edge from 400 nm (pure TiO₂) to 520 nm (TiO_2 − xN_x/BN composites) was observed in their UV–Vis light absorption spectra. The TiO_2 − xN_x/BN photocatalysts exhibited enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) and the highest photocatalytic degradation efficiency reached 97.8% under visible light irradiation for 40 min. The mechanism of enhanced photocatalytic activity was finally proposed.     

Microwave photocatalysis III. Transition metal ion‐doped TiO2 thin films on mercury electrodeless discharge lamps: preparation,characterization and their effect on the photocatalytic degradation of mono‐chloroacetic acid and Rhodamine B

BACKGROUND: Mercury electrodeless discharge lamps (Hg‐EDLs) were used to generate UV radiation when exposed to a microwave field. EDLs were coated with doped TiO₂ in the form of thin films containing transition metal ions Mⁿ⁺ (M = Fe, Co, Ni, V, Cr, Mn, Zr, Ag). Photocatalytic degradation of mono‐chloroacetic acid (MCAA) to HCl, CO₂, and H₂O, and decomposition of Rhodamine B on the thin films were investigated in detail. RESULTS: Polycrystalline thin doped TiO₂ films were prepared by dip‐coating of EDL via a sol–gel method using titanium n‐butoxide, acetylacetone, and a transition metal acetylacetonate. The films were characterized by Raman spectroscopy, UV/Vis absorption spectroscopy, X‐ray photoelectron spectroscopy (XPS), electron microprobe analysis and by atomic force microscopy (AFM). The photocatalytic activity of doped TiO₂ films was monitored in the decomposition of Rhodamine B in water. Compared with the pure TiO₂ film, the UV/Vis spectra of V, Zr and Ag‐doped TiO₂ showed significant absorption in the visible region, and hence the photocatalytic degradation of MCAA had increased. The best apparent degradation rate constant (0.0125 min^?1), which was higher than that on the pure TiO₂ film by a factor of 1.7, was obtained with the Ag(3%)/TiO₂ photocatalyst. The effect of doping level of vanadium acetylacetonate on the photocatalytic efficiency of the V‐doped TiO₂ was determined. CONCLUSIONS: Transition metal ion‐doped TiO₂ thin films showed significant absorption in the visible region. The metal doped TiO₂ photocatalyst (with an appropriate amount of V, Zr and Ag) on the Hg‐EDLs increased the degradation efficiency of MCAA in a microwave field. Copyright © 2009 Society of Chemical Industry     

A Visible Light Photocatalyst of Carbonate‐Like Species Doped TiO2

Carbon‐doped TiO₂ nanomaterials have been successfully synthesized via an effective two‐step procedure involving hydrothermal method and followed by a low‐temperature calcination treatment process, through which a controllable amount of carbonate‐like species could be incorporated into TiO₂. First‐principles calculations suggest the TiO₂ doped with carbon in form of carbonate‐like species can effectively extend the adsorption of the material from ultraviolet region to visible light. And it is experimentally found that carbon‐doped TiO₂ nanomaterials exhibit much higher photocatalytic activity than reference P25 and TiO_2?xN_x catalysts toward the liquid‐phase degradation of organic pollutants under visible light (420 nm < λ < 800 nm) irradiation. The presence of synergic effect between carbonate‐like doping and anatase TiO₂ is believed to play an essential role in affecting the photocatalytic reactivity, and the response to the visible light is ascribed to the narrowed band gap energy controlled by carbon doping. Moreover, the roles of active species in the photocatalytic process are compared using different types of active species scavengers. Meanwhile, the degradation mechanism of the photocatalysis is proposed. It is hoped that our work could provide valuable information on the design of carbonate‐like doped semiconductor with more excellent properties and set the foundation for the further industrial application.     

Characterizations of TiO2/SiO2/Ni–Cu–Zn Ferrite Composite for Magnetic Photocatalysts

The TiO₂/SiO₂/Ni–Cu–Zn ferrite composite for magnetic photocatalysts with high photocatalytic activity is successfully prepared in this study. The composite are composed of spherical or elliptical Ni–Cu–Zn ferrite nanoparticles about 20–60 nm as magnetic cores, silica as barrier layers with thickness of 15 nm between the magnetic cores and titania shells with thickness approximately 1.5 nm. Photodegradation examination of TiO₂/SiO₂/ Ni–Cu–Zn ferrite composite was carried out in methylene blue (MB) solutions illuminated under a Xe arc lamp with 35 W and color temperature of 6000 K. The results indicated that about 47.1% of MB molecules adsorbed on the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite within 30 min mixing due to it higher pore volume of 0.034 cm³/g, and after 6 h Xe lamp irradiation, 83.9% of MB 16.1% was photodegraded. Compared with the TiO₂ /Ni–Cu–Zn ferrite composite, the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite with silica barrier layer prohibited the photodissolution and enhanced the photocatalytic ability. The magnetic photocatalyst shows high photocatalytic efficiency that the apparent first‐order rate constant k_obs is 0.18427 h^?1, and good magnetic property that the saturation magnetization (M_s) of is 37.45 emu/g, suggesting the magnetic photocatalyst can be easily recovered by the application of an external magnetic field.     

Synthesis of Ti1−xSnxO2 nanosized photocatalysts in reverse microemulsions

The preparation of Ti_1−xSn_xO₂ nanocrystalline photocatalysts in reverse microemulsions is reported in this work. The obtained materials have been characterised by total reflection X-ray fluorescence (TXRF), X-ray diffraction (XRD) and Raman and UV–vis spectroscopies. Very good accordance between calculated and obtained compositions is observed. Undoped TiO₂ prepared in this way crystallises in the anatase phase. Tin-doped anatase is formed with x < 0.05, while both anatase and rutile phases crystallise when x ≥ 0.05. When both phases coexist, a preferential doping of rutile seems to occur. When x = 0.10, a multiphase mixture containing TiO₂(anatase), TiO₂(rutile) and SnO₂ was formed. No significant modification of the band gap is found in any case. The photocatalytic activity of the obtained catalysts is compared employing the trichloroethylene photocatalytic degradation as a test reaction. The beneficial effect of Sn⁴⁺ in the activity of TiO₂ appears to be related to the formation of anatase–rutile mixtures, leading to the highest specific photocatalytic activity in the sample of composition Ti_0.93Sn_0.07O₂, with anatase:rutile ratio close to 3.     

Triggering efficient photocatalytic water oxidation reactions over BaNbO2N by incorporating Ca at B site

Although BaNbO₂N has visible light absorption as far as 740 nm, its photocatalytic activity is generally very poor under ordinary conditions, being incommensurate to its light absorption properties. In this work, we introduce Ca into the B site of BaNbO₂N to form a complex perovskite BaNb_1−x/3Ca_x/3O_2+yN_1−y (0 ≤ x, y ≤ 1). The presence of Ca in BaNbO₂N has great impact on a number of important properties such as band gap value, nitrogen content, surface hydrophilicity, and defects levels. In particular, defects such as Nb⁴⁺ species are effectively suppressed in Ca-modified BaNbO₂N. More importantly, photocatalytic activity of BaNbO₂N for water oxidation reactions is substantially improved after Ca modifications. Compared with pristine BaNbO₂N, more than twofold enhancement in photocatalytic oxygen evolution is observed for BaNb_0.8Ca_0.2O_2+yN_1−y (x = 0.6). Such improvements probably stem from the suppression of Nb⁴⁺ species in the structure as well as enhanced surface hydrophilicity after Ca modification. The facile approach by incorporating alkaline earth cations into crystal structure can be well extended to other perovskite oxynitrides whose photocatalytic activity is subject to those defective species.     

A multifunctional Ag/TiO2/reduced graphene oxide with optimal surface-enhanced Raman scattering and photocatalysis

A multifunctional Ag/TiO₂/reduced graphene oxide (rGO) ternary nanocomposite was prepared by a one-step photochemical reaction with TiO₂ and Ag nanoparticles successively deposited on reduced graphene oxide. The structure, morphology, composition, optical, and photoelectrochemical properties of Ag/TiO₂/rGO were investigated in detail. Meanwhile, the ternary nanocomposite possessed much higher adsorption capacity to organic dyes compared with bare TiO₂ and binary Ag/TiO₂, which would help to its use for surface-enhanced Raman scattering detection and photocatalytic degradation. Due to the charge transfer between rGO and organic dyes and enhanced electromagnetic mechanism of Ag, Ag/TiO₂/rGO nanocomposites as surface-enhanced Raman scattering substrates demonstrated dramatically improved sensitivity and good uniformity. The detection limit of rhodamine 6G (R6G) was as low as 10⁻⁹ mol/L, and the relative standard deviation values of the intensities remained below 5%. Most importantly, the synergistic coupling effect of three components extended the photoresponse range and accelerated separation of the electron-hole pairs, leading to greatly improved photocatalytic activity under simulated sunlight. The maximum rate constant (k, 0.06243 min⁻¹) of Ag/TiO₂/rGO was 50 and four times higher than that of TiO₂ and Ag/TiO₂, respectively.     

Visible light induced self-cleaning performance of iron-doped TiO2 nanoparticles for surface applications

This study aimed to enhance the visible light photosensitivity of TiO₂ nanoparticles for self-cleaning applications by doping with Fe³⁺. Nanocrystalline undoped and Fe-doped TiO₂ (Ti_1 − xFe_xO₂, x = .01–.04) were synthesized via sol–gel method. The results demonstrated that Fe-doped TiO₂ nanoparticles exhibited visible light sensitivity and self-cleaning properties. An increased Fe concentration resulted in a red shift in the absorption band edge. Fe_0.03-doped TiO₂ with an average particle size of ∼21 nm, a crystallite size of ∼12 nm, and a band gap of ∼2.86 eV showed the highest photocatalytic activity (60% methylene blue degradation) and super-hydrophilicity (water droplet contact angle 9°) under visible light radiation. These findings highlight the potential of Fe-doped TiO₂ nanoparticles as a promising material for self-cleaning applications.     

The oxygen reduction reaction on Pt/TiO x N y -based electrocatalyst for PEM fuel cell applications

Titanium oxy-nitride was developed for the first time as Pt electrocatalyst support for the ORR in PEM fuel applications. The conditions of the support preparation and the Pt/TiO _x N _y -based electrodes’ elaboration by chemical reduction method were determined. Comparison of the polarization curves of the carbon and the TiO _x N _y supported how clearly TiO _x N _y was more stable than the Vulcan XC-72R. It was found that the 40 wt% Pt/TiO _x N _y -based electrocatalyst is active for the ORR in acid medium, but the activity was less than that of Pt/C. The normalized electrochemical surface area degradation of Pt/TiO _x N _y was significantly less than that of Pt/C. The kinetics of the ORR on Pt/TiO _x N _y proceeded through a four-electron transfer process. The single-cell hydrogen/oxygen PEM fuel cell performances based on Pt/TiO _x N _y cathode electrocatalyst exhibited the same range of characteristics as those based on Pt/C.     

One-step preparation of size-defined aggregates of TiO2 nanocrystals with tuning of their phase and composition

One-step route based on the thermal decomposition of the double salt (NH₄)₂TiO(SO₄)₂ (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO₂, nitrogen-doped TiO₂, TiN_xO_1−x, to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO₂ in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO₂, TiN_xO_1−x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH₃ gas by varying the temperatures. The network of anatase TiO₂ with a specific surface area up to 64 m² g⁻¹ contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO₂ and nitrogen-doped TiO₂ under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO₂ nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO₂ powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.     

Effect of the status of Sm on the properties of Sm contained N doped TiO2 photocatalysts

Nitrogen-doped TiO₂ (TiO_2?xN_y) nanoparticles with and without adding Sm³⁺ were synthesized by thermohydrolysis of TiCl₃. The samples were characterized by X-ray diffraction, specific surface area determination, UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity of the sample was investigated by employing the oxidative destruction of nitric oxide as a probe reaction using a flow reactor. Although the doping of Sm³⁺ in the lattice of titania was not useful to improve the photocatalytic activity, loading of samarium oxides on the surface of titania resulted in an improvement of the photocatalytic activity of the nitrogen-doped TiO₂. The beneficial effect was explained by an increased separation efficiency of the photogenerated electron–hole pairs.     

Visible-light-induced photocatalytic activity of TiO2−xNy prepared by solvothermal process in urea–alcohol system

Nitrogen-doped anatase, rutile and brookite titania photocatalyst TiO_2−xN_y which can be excited by visible light were prepared by mixing aqueous TiCl₃ solutions with urea ((NH₂)₂CO) and various type of alcohols followed by solvothermal treatment at 190 °C. The phase composition, crystallinity, microstructure and specific surface area of titania powders greatly changed depending on the pH and type of solvents. Violet, yellowish and grayish TiO_2−xN_y with excellent visible light absorption and photocatalytic activity were prepared. The TiO_2−xN_y powders prepared in urea–methanol solution showed excellent photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light λ > 510 nm.     

Effect of electrolyte addition on activity of (Ga1−xZnx)(N1−xOx) photocatalyst for overall water splitting under visible light

Effects of electrolyte addition on photocatalytic activity of (Ga_1−xZn_x)(N_1−xO_x) modified with either Rh_2−yCr_yO₃ or RuO₂ nanoparticles as cocatalysts for overall water splitting under visible light (λ > 400 nm) are investigated. The cocatalyst Rh_2−yCr_yO₃ is confirmed to selectively promote the photoreduction of H⁺, while RuO₂ functions as both H₂ evolution sites and as efficient O₂ evolution sites. The activity of Rh_2−yCr_yO₃-loaded (Ga_1−xZn_x)(N_1−xO_x) is found to be suppressed in the presence of Cl⁻, which undergoes oxidation by photogenerated holes in the valence band of (Ga_1−xZn_x)(N_1−xO_x). Alkaline- and alkaline earth-metal cations in the reactant solution compensate the negative effect of Cl⁻ to a certain extent depending on the metal cation employed. Among the electrolytes examined, the addition of an appropriate amount of NaCl or A₂SO₄ (A = Li, Na, or K) to the reactant solution without pH control is found to increase activity by up to 75% compared to the case without additives. Direct splitting of seawater to produce H₂ and O₂ is also demonstrated using Rh_2−yCr_yO₃-loaded (Ga_1−xZn_x)(N_1−xO_x) catalyst under visible light.