Synthesis of iron-containing nitrogen-doped titania by hydrothermal method and its photocatalytic activity

By a hydrothermal method, iron and nitrogen co-doped TiO₂ and iron oxide impregnated nitrogen-doped TiO₂ were prepared. The obtained Fe and N co-doped TiO₂ showed mixed anatase, rutile, and brookite phases, and high specific surface areas above 160 m²/g. The Fe co-doping was proved to be effective to enhance the visible light absorption ability; however, the photocatalytic activity in deNO _x experiment decreased due to the increase in the amount of lattice vacancy. On the other hand, the photocatalytic activity of N-doped TiO₂ was improved by the impregnation of iron oxide.     

Synthesis and photocatalytic activity of nanocrystalline TiO2 co-doped with nitrogen and cobalt(II)

Nitrogen-modified cobalt-doped TiO₂ materials were successfully prepared via a modified sol–gel method. The structure and properties of the catalysts were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM, ultraviolet–visible light diffuse reflectance spectra (UV–Vis DRS), N₂ adsorption–desorption isotherms, and energy-dispersive X-ray spectroscopy. The XRD patterns of the pure and co-doped TiO₂ samples indicate that the predominant phase was anatase. The average grain size obtained from TEM was approximately 10 nm. The Brunauer–Emmett–Teller analysis results indicate that the specific surface area was 77.7 m² g^?1. The UV–Vis DRS results for the co-doped sample reveal an absorption edge that had been red-shifted to 500 nm. The photocatalytic activities of the samples were evaluated through photodegradation of papermaking wastewater under UV and visible light irradiation. Compared with the cobalt-doped TiO₂ sample and Degussa P25, the 3 mol% N-doped mesoporous N/Co-TiO₂ photocatalyst exhibited the highest photocatalytic activity, which can be ascribed to the synergistic effect of the N and Co co-doping.     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Sol–gel preparation and characterization of Ag and Mg co-doped nano TiO<Subscript>2</Subscript>: efficient photocatalytic degradation of C.I. Acid Red 27

In this study, we successfully prepared pure, mono-doped, and Ag, Mg co-doped TiO₂ nanoparticles using the sol–gel method, with titanium tetraisopropoxide as the Ti source. The prepared samples were characterized by X-ray powder diffraction (XRD), specific surface area and porosity (BET and BJH) measurement, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence, and energy dispersive X-ray spectroscopy techniques. The XRD data showed that the prepared nanoparticles had the same crystals structures as the pure TiO₂. Also, DRS results indicated that the band gap of co-doped photocatalyst was smaller than that of the monometallic and undoped TiO₂ and that there was a shift in the absorption band towards the visible light region. Furthermore, the photocatalytic activity of the prepared catalysts was evaluated by the degradation of C.I. Acid Red 27 in aqueous solution under visible light irradiation. The results showed that Ag (0.08 mol%), Mg (0.2 mol%) co-doped TiO₂ had the highest photoactivity among all samples under visible light. It was concluded that co-doping of the Ag and Mg can significantly improve the photocatalytic activity of the prepared photocatalysts, due to the efficient inhibition of the recombination of photogenerated electron–hole pairs. The optimum calcination temperature and time were 450 °C and 3 h, respectively.     

Biogenic synthesis from <Emphasis Type="Italic">Prunus</Emphasis> × <Emphasis Type="Italic">yedoensis</Emphasis> leaf extract,characterization, and photocatalytic and antibacterial activity of TiO<Subscript>2</Subscript> nanoparticles

Green synthesis of TiO₂ nanoparticles (NPs) from Prunus × yedoensis leaf extract (PYLE), and their application for removal of phosphate and their antibacterial activity, were studied for the first time. NPs were obtained using a green chemistry approach from 0.1 M TiO₂ and PYLE at ratio of 1:1 (v/w). Initial confirmation of production of TiO₂ NPs was provided by a color change from white to light yellow, then calcination was performed at 500 °C for 1 h. The TiO₂ NPs were characterized using various analytical techniques such as ultraviolet–visible (UV–Vis) spectroscopy, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicated that the optimal amount of TiO₂ NPs for removal of phosphate was 10 mg/l (10 ppm) with duration of 25 min. Furthermore, the antibacterial activity of TiO₂ NPs was also investigated using two different bacteria (Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli) in aqueous medium. The results revealed highly efficient sunlight-driven photocatalytic and antibacterial activity of TiO₂ NPs.     

An ambient temperature aqueous sol–gel processing of efficient nanocrystalline doped TiO2-based photocatalysts for the degradation of organic pollutants

An environmentally-friendly aqueous sol–gel process for producing undoped and Cu²⁺, Ni²⁺, Zn²⁺ or Pb²⁺-doped TiO₂ photocatalysts exhibiting a remarkably high photocatalytic activity without requiring any calcination step has been developed. The physicochemical properties of the catalysts were characterized by ICP-AES, XRD, UV–Vis spectroscopy and nitrogen adsorption–desorption. It has been found that the catalysts are composed of nanocrystallites of anatase with a size of 6–7 nm and a specific surface area varying from 184 to 275 m² g^?1. A screening of the photocatalytic activity of the undoped and doped photocatalysts has been performed by evaluating the degradation of 4-nitrophenol under artificial light (330 nm < λ < 800 nm) after 7 h of illumination using a custom-designed multisample photoreactor. The activity measured for the TiO₂-Undoped catalyst was found to be five times higher than the activity measured for uncalcined TiO₂ catalysts produced by other sol–gel methods. We propose that this interesting result is due to the particular morphology of the xerogels obtained. It has also been demonstrated that the presence of the dopant leads to an enhancement of the photocatalytic activity in all cases. The role of particular dopants in modulating the photocatalytic activity will be discussed. Finally, the possibility of producing undoped and Zn²⁺-doped films presenting a higher activity than the commercial photocatalytic coating (Saint Gobain Glass Bioclean^®) without requiring any calcination step has been demonstrated. These preliminary results constitute an important step forward in the development of photocatalytic films using a sol–gel process compatible with the constraints associated with large-scale industrial processing.     

The structural, morphological, and surface properties of tungsten-doped TiO2 nanopowders and their contribution to the photocatalytic activity

Tungsten-doped TiO₂ nanopowders (W-TiO₂) were prepared by chemical vapor synthesis and the effects of a post-heat treatment on their physical, surface, and photocatalytic properties were investigated. The W-TiO₂ nanopowders containing about 1.0 mol % of tungsten were obtained and annealed from 400 to 700 °C. The as-synthesized and annealed W-TiO₂ nanopowders were carefully examined for their crystalline and opto-electronic structure and morphology by means of X-ray diffraction, UV–Vis spectroscopy, and transmission electron microscopy. In addition, the surface condition was investigated by X-ray photoelectron spectroscopy. The photocatalytic activities were studied by the oxidative degradation of 2-propanol under UV light irradiation. We found that the photocatalytic activity of W-TiO₂ varied significantly with the temperature of the heat treatment, exceeding the performance of P25 after annealing at 600 °C. Interestingly, the chemical composition of titanium and tungsten of W-TiO₂ played a crucial role to its photocatalytic activity as the mixed valence states, Ti ⁿ⁺ (n = 4, 3, 2, 0) and W ⁿ⁺ (n = 6, 5, 4), were found in accordance with altering the annealing temperature.     

Excellent degradation performance of azo dye by metallic glass/titanium dioxide composite powders

The metallic glass/titanium dioxide powders (MG/TiO₂) with enhanced photocatalytic oxidation activity were synthesized, which exhibit a higher efficiency in decolorizing methylene blue solutions (MB). Compared with the pure TiO₂ and crystalline alloy/TiO₂ (CA/TiO₂) under the same circumstances, its degradation rate was 60 % and 30 % higher, respectively. Furthermore, compared with the CA/TiO₂, the MG/TiO₂ photocatalytic rate was three times faster when decolorizing MB. Considering the excellent intrinsic high-performance photocatalytic degradation under visible light irradiation, these novel powders were proven to have potential applications in water purification industry.     

Photocatalytic performance of silver-modified TiO2 embedded in poly(ethyl-acrylate-co-methyl metacrylate) matrix

The plasmonic Ag-TiO₂ (with 0.5 wt% Ag) photocatalyst was prepared on P25 TiO₂ surface. The presence of AgNPs on the titania was indicated by the UV–vis spectrum, which showed a plasmonic absorbance band in the visible range (λ _max?=?455 nm). XPS measurements suggested that Ag was in metallic (Ag) and in oxide forms on TiO₂. Ag-TiO₂ photocatalyst and TiO₂ were embedded in [poly(ethyl acrylate-co-methyl methacrylate; p(EA-co-MMA)] copolymer to attain mechanically stable, photocatalytically active nanocomposite films. The photooxidation of ethanol was slower on the photocatalyst/polymer nanocomposites, but it could be significantly improved by irradiating them with UV light. The photoaging was applied as a post-preparation treatment to improve the photocatalytic activity of the nanocomposite films. Changed surface morphology and the partial destruction of the polymer were supported by AFM and FTIR results. Contact angle measurements were used to determine the surface free energies of the prepared and the photoaged nanocomposite films.     

Light expanded clay aggregate (LECA) as a support for TiO<Subscript>2</Subscript>, Fe/TiO<Subscript>2</Subscript>, and Cu/TiO<Subscript>2</Subscript> nanocrystalline photocatalysts: a comparative study on the structure,morphology, and activity

In this work, TiO₂ and doped TiO₂ photocatalysts (Fe/TiO₂ and Cu/TiO₂) were synthesized by the sol–gel method. The main objective of this study was to investigate the influence of dopants on the structure, morphology, and activity of the catalysts in powder and immobilized states. XRF, XRD, and SEM methods were used to characterize the catalysts. The structure and phase distribution of the nanocrystalline powders were identified by XRD. Nanoparticles crystallite size and the degree of crystallinity were affected by doping. The anatase contents of catalysts were achieved as follows: TiO₂ (5.89 %) < Fe/TiO₂ (42.17 %) < Cu/TiO₂ (70.28 %). It was indicated that the activity of the catalysts strongly depends on the anatase content. Under the same circumstances, copper-modified TiO₂ exhibited a twofold higher photocatalytic activity compared with TiO₂. The nanostructured catalysts were immobilized on light expanded clay aggregate (LECA) granules in order to investigate the effect of a novel support on the activity of the catalysts. Morphological changes are recognizable in the SEM images. Activity tests indicated that the best catalytic performance was assigned to Cu/TiO₂/LECA. After 120 min of irradiation, 61 % degradation of phenol in synthetic wastewater was achieved. The high photocatalytic activity of Cu/TiO₂/LECA confirms that LECA is as an excellent support.     

Persistent photocatalysis of continuously flowing gas-phase nitric oxide using CaAl2O4:(Eu,Nd)/rutile phase TiO2−x N y composites

CaAl₂O₄:(Eu,Nd)/rutile phase TiO_2?x N _y composites were synthesized via a two-step method, i.e. a solvothermal reaction followed by a mechanochemical treatment. The photocatalytic deNO _x activity of the composites was evaluated under UV light (λ > 290 nm) irradiation and after turning off the UV light. It was confirmed that rutile phase TiO_2?x N _y nanoparticles could be uniformly dispersed on the surface of CaAl₂O₄:(Eu,Nd) after planetary ball milling treatment. The composites prepared by this two-step method had high photocatalytic activity and good prolonged catalysis time even after turning off the light.     

Mesoporous TiO2−xAy (A = N,S) as a visible-light-response photocatalyst

Mesoporous TiO_2?xA_y (A = N, S) thin films were fabricated using thiourea as a doping resource by a combination of sol-gel and evaporation-induced self-assembly (EISA) processes. The results showed that thiourea could serve two functions of co-doping nitrogen and sulfur and changing the mesoporous structure of TiO₂ thin films. The resultant mesoporous TiO_2?xA_y (A = N, S) exhibited anatase framework with a high porosity and a narrow pore distribution. The formation of the O–Ti–N and O–Ti–S bonds in the mesoporous TiO_2?xA_y (A = N, S) were substantiated by the XPS spectra. A new bandgap in visible light region (520 nm) corresponding to 2.38 eV could be formed by the co-doping. After being illuminated for 3 h, methyl orange could be degraded nearly completely by the co-doped sample under both ultraviolet irradiation and visible light illumination. While pure mesoporous TiO₂ could only degrade 60% methyl orange under UV illumination and showed negligible photodegradation capability in the visible light range. Furthermore, the photo-induced hydrophilic activity of TiO₂ film was improved by the co-doping. The mesoporous microstructure and high visible light absorption could be attributed to their good photocatalytic acitivity and hydrophilicity.     

Enhanced photocatalytic reduction of Cr(VI) by manganese-doped anatase titanium dioxide

Nano-TiO₂ is frequently used as an optimal photocatalyst, since it is nontoxic, low cost, and environmentally friendly, especially for its photocatalytic oxidation action. However, its photocatalytic reducing action has not been widely researched. In this study, TiO₂ doped with different concentrations of manganese was prepared by the sol–gel method and characterized using different techniques to analyze the surface structure, phase composition, and surface elements of the different materials. To investigate the photocatalytic activity, Mn–TiO₂ was used for photocatalytic reduction of Cr(VI). Moreover, various organic pollutants were added to determine whether they enhanced the photocatalytic reduction of Cr(VI). The experiments indicated that the presence of Mn in TiO₂ could enhance its photocatalytic reduction action, especially at 0.02 % molar ratio. Manganese ions doped in TiO₂ behaved as electron accumulation sites. In addition, pH value, and photocatalyst dosage were investigated to analyze their effects on the photocatalytic reduction action. The results show that lower pH value improved the efficiency of photocatalytic reduction; there were no significant changes in the photocatalytic reduction rate with dosage above 1.0 g/L. In the presence of different electron donors (organic pollutants as hole scavengers), the photocatalytic reduction of Cr(VI) was generally improved. In short, manganese-doped TiO₂ exhibited improved photocatalytic reduction activity, especially in cooperation with various organics.     

Solvothermal preparation of copper(II) porphyrin-sensitized mesoporous TiO<Subscript>2</Subscript> composites: enhanced photocatalytic activity and stability in degradation of 4-nitrophenol

Four new copper(II) porphyrins CuPp(1, 2, 3, 4) with a different number of peripheral ester groups were synthesized and used to sensitize the mesoporous TiO₂ under solvothermal condition, and accordingly, four mesoporous CuPp(1, 2, 3, 4)/TiO₂ composites were obtained. These composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, BET nitrogen adsorption–desorption isotherms (BET), UV–vis diffuse reflectance spectroscopy (UV–vis-DRS), and Fourier-transform infrared spectroscopy (FT-IR). The results showed the crystal structure and morphology of mesoporous TiO₂ were not affected by the porphyrin existence on its surface. The photocatalysis properties of mesoporous TiO₂ and CuPp(1, 2, 3, 4)/TiO₂ have been evaluated by conducting the photocatalytic degradation of 4-nitrophenol (4-NP) under visible-light irradiation, and the result showed their higher photocatalytic activities and the order is: CuPp(4)/TiO₂ > CuPp(3)/TiO₂ > CuPp(2)/TiO₂ > CuPp(1)/TiO₂ ? TiO₂. The probable reasons are their large surface area and different number of peripheral groups in CuPp, which separate electron–hole pairs efficiently. The repetition test of CuPp(1, 2, 3, 4)/TiO₂ composites demonstrated that they still maintained superior photocatalytic activity over six recycles.     

可见光响应的镍硅共掺杂二氧化钛及其光催化性能

为了更好地利用太阳光和提高二氧化钛的光催化性能,以钛酸四正丁酯、正硅酸乙酯、六水合硝酸镍为原料,在高压釜中140℃非水溶剂热反应,所得材料经400℃焙烧制得镍硅共掺杂的二氧化钛光催化剂.所得材料用X射线衍射、氮吸附、透射电镜、X射线光电子能谱、傅里叶变换红外光谱、紫外漫反射等测试手段分析,结果显示所有样品均为锐钛矿型二氧化钛,Si和Ni均掺杂到TiO2体相中,样品具有较大的比表面积,其最大达303.3m2·g-1.在可见光照射下,以降解罗丹明-B为探针反应研究其可见光催化性能,与未掺杂和镍掺杂的二氧化钛相比较,共掺杂的二氧化钛具有更高的可见光催化性能,当Ni/Ti和Si/Ti的物质的量的比分别为0.01和0.20时,可见光催化性能最好.可见光催化性能的提高归因于镍和硅的协同作用.     

TiO2-assisted photocatalytic degradation of diclofenac, metoprolol, estrone and chloramphenicol as endocrine disruptors in water

The photocatalytic oxidation of diclofenac, metoprolol, estrone and chloramphenicol was tested in the tube reactor using different commercially available TiO₂. The photocatalysts were characterized using BET, XRD and SEM. The studied photocatalysts differed in S_BET, pore volume and rutile presence. It was observed that generally anatase TiO₂ possessed the highest activity in the photocatalytic oxidation of diclofenac, chloramphenicol and estrone. The presence of rutile enhanced the photooxidation of metoprolol. In case of the other pollutants, however, rutile diminished the photooxidation efficiency. The most effective in the reduction of the COD parameter of treated water was anatase with 21 nm crystals. The photooxidation of all studied pollutants can be described by the pseudo-first order kinetics with the values ranging from 0.46 × 10^?2 min^?1 in case of estrone removal over Tytanpol (Z.A. Police, Poland) to 1.87 × 10^?2 min^?1 for the removal of chloramphenicol over TiO₂ 21 nm (Sigma-Aldrich). The highest initial reaction rates were obtained for metoprolol removal over TiO₂ 21 nm (Sigma-Aldrich) 1.9 × 10^?6 mol dm³ min^?1 being three times higher than that determined for estrone photocatalytic oxidation over TiO₂ (Sigma-Aldrich).     

A new perspective for effect of S and Cu on the photocatalytic activity of S,Cu-codoped nano-TiO2 under visible light irradiation

Sulfur and copper codoped TiO₂ nanoparticles were prepared by sol-hydrothermal process. And the samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectra analysis, scanning electron microscopy, Brunauer Emmett Teller analysis, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectra and X-ray fluorescence analysis. It was found that the S, Cu-codoped TiO₂ became amorphous with the increase of Cu content, and copper on the surface of TiO₂ existed in the oxidation state of Cu(II) while S in the form of S⁶⁺ species. And the codoped particles had higher surface area, smaller particle size, stronger spectral response in visible region compared with pure TiO₂. The effects of doping amount in a wide range, catalyst dosage, and recycle on the photocatalytic activity of the codoped catalysts were investigated with Acid Orange 7 as the model compound under visible light illumination (λ > 447 nm). The results showed that S (2.0 %), Cu (5.0 %) codoped TiO₂ had the highest visible light photocatalytic activity and good reusability performance. The kinetic study showed that this photocatalytic process coincided with the Langmuir–Hinshelwood pseudo first order reaction model.     

Charge separation by tetrahexahedron-SrTiO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> heterojunction as an efficient photocatalyst

Charge separation plays a key role in the conversion of solar energy into chemical energy for use in the redox reaction and as well as in the photocatalytic activity. In this study, SrTiO₃ particles with different morphologies including irregular, tetrahexahedron, and cube were synthesized by an in situ solvothermal method. The photocatalytic activity of the synthesized nanoparticles was investigated in the photocatalytic decomposition of methylene blue under UV light irradiation. Tetrahexahedron SrTiO₃ particles exhibited high decomposition activity (70 %), which is about two times higher than those of the irregular and cubic SrTiO₃ particles. The high decomposition activity of tetrahexahedron SrTiO₃ particles could be attributed to the improvement of charge separation achieved on different crystal facets. To reach a good charge separation, tetrahexahedron SrTiO₃/TiO₂ coupled nanoparticles were fabricated by impregnation method. Results showed that coupling tetrahexahedron SrTiO₃ with TiO₂ could produce efficient charge separation between tetrahexahedron SrTiO₃ and TiO₂ due to their matched band edges. In order to achieve better charge separation, the tetrahexahedron SrTiO₃/90 %TiO₂ sample was calcined at different temperatures in the 450–750 °C range. Tetrahexahedron SrTiO₃/90 %TiO₂ coupled nanoparticles calcined at 650 °C show high photocatalytic activity compared with other samples. The prepared samples were characterized by using various techniques such as X-ray diffraction, scanning electron microscopy, photoluminescence emission spectra, and UV–Vis diffuse reflectance spectroscopy.     

TiO2/EDTA-rich carbon composites: Synthesis,characterization and visible-light-driven photocatalytic reduction of Cr(VI)

TiO₂/EDTA-rich carbon composites exhibits excellent photoreduction of Cr(VI) activity via ligand-to-metal charge transfer process.     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.