Efficient visible light-induced degradation of phenol on N-doped anatase TiO2 with large surface area and high crystallinity

The N-doped anatase TiO₂ photocatalysts were prepared via solvothermal and ethylenediamine reflux treatment, followed by the sequential calcination in air and NH₃/N₂ atmosphere. The resulting photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and UV-vis diffuse reflectance spectra. The results revealed that the prepared N-doped anatase TiO₂ had characteristics of small crystallite size, large surface area, high crystallinity and visible light response. The prepared N-doped anatase TiO₂ photocatalysts showed much higher photocatalytic activity than N-doped Degussa P25 for the degradation of phenol under both ultraviolet and visible light irradiation, owing to more highly oxidizing hydroxyl radical which was the main oxidative species responsible for the degradation of phenol.     

铈和磷钨酸共掺杂纳米二氧化钛中空纤维的制备及其光催化活性

以棉花纤维为模板,以钛酸四正丁酯、硝酸铈铵和磷钨酸为原料采用模板法制备了一系列铈和磷钨酸共掺杂的、具有中空纤维结构的TiO₂光催化材料, 利用扫描电子显微镜、X射线衍射、BET和紫外-可见光谱等技术对其形貌、晶体结构及表面结构、光吸收特性等进行了表征. 以苯酚溶液的光催化降解为模型反应,考察了不同掺杂量的样品在紫外和可见光下的光催化性能. 结果表明,用模板法制备的TiO₂纤维材料具有中空结构,共掺杂的TiO₂纤维在紫外和可见光条件下较纯TiO₂纤维和单掺杂TiO₂纤维对苯酚溶液具有更好的光催化降解效果, 且铈和磷钨酸的掺杂量显著影响该纤维材料的催化性能;当铈掺杂量为0.3mol%和磷钨酸掺杂量为2mol%,在500 oC焙烧2 h所得中空纤维材料的催化性能最佳,4 h即可使苯酚溶液的降解率达98.5%;重复使用4次仍可使苯酚溶液的降解率保持在87%以上,且该催化剂材料易于离心分离去除.     

Enhanced visible light photocatalytic properties of Fe-doped TiO2 nanorod clusters and monodispersed nanoparticles

In order to get photocatalysts with desired morphologies and enhanced visible light responses, the Fe-doped TiO₂ nanorod clusters and monodispersed nanoparticles were prepared by modified hydrothermal and solvothermal method, respectively. The microstructures and morphologies of TiO₂ crystals can be controlled by restraining the hydrolytic reaction rates. The Fe-doped photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy (UV-vis), N₂ adsorption-desorption measurement (BET), and photoluminescence spectroscopy (PL). The refinements of the microstructures and morphologies result in the enhancement of the specific surface areas. The Fe³⁺-dopants in TiO₂ lattices not only lead to the significantly extending of the optical responses from UV to visible region but also diminish the recombination rates of the electrons and holes. The photocatalytic activities were evaluated by photocatalytic decomposition of formaldehyde in air under visible light illumination. Compared with P25 (TiO₂) and N-doped TiO₂ nanoparticles, the Fe-doped photocatalysts show high photocatalytic activities under visible light.     

Synthesis of efficient TiO2-based photocatalysts by phosphate surface modification and the activity-enhanced mechanisms

A simple strategy to greatly increase the thermal stability of nanocrystalline anatase has been put forward to fabricate efficient TiO₂-based photocatalysts under ultraviolet irradiation, via the surface modification with phosphate anions. The results show that the increased anatase thermal stability is attributed to the roles of the phosphate modification effectively inhibiting the contacts among anatase nanocrystals. Compared to un-modified TiO₂, the modified TiO₂ calcined at high temperature (over 700 °C) exhibits much high photocatalytic activity for degrading Rhodamine B (or phenol) solution, even superior to the commercial P25 TiO₂. The activity enhancement is mainly attributed to the increased separation rate of photogenerated charge carriers on the basis of the measurements of steady state- and transient state-surface photovoltage spectroscopy. This work would provide a practical route to reasonably design and synthesize high-performance TiO₂-based nanostructured photocatalysts with high anatase thermal stability.     

Preparation and characterization of nitrogen-doped TiO2 nanoparticles by the laser pyrolysis of N2O-containing gas mixtures

Nitrogen-doped TiO₂ nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl₄ (vapors) and N₂O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18 nm in case of the almost pure anatase sample to about 13 nm in case of the anatase-rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process.     

Fabrication of nitrogen-doped TiO2 layer on titanium substrate

In this paper, macropores TiO₂ layer was fabricated on titanium substrates based on plasma based ion implantation (PBII). In order to increase the photodegradation efficiency of fabricated TiO₂ layer, two approaches are used: (1) preparation of macropores on TiO₂ layer to increase the total photodegradation area and (2) nitrogen doping (N-doping) to increase light absorption efficiency. The fabrication process of the N-doped macropores TiO₂ layer comprises four steps: firstly, helium plasma based ion implantation (He-PBII) is employed to generate He bubbles in substrate; secondly, oxygen plasma based ion implantation (O-PBII) and a followed annealing in air are executed to obtain rutile and anatase mixture TiO₂ phases; thirdly, He bubbles are exposed to the surface via an Ar ion sputter process; lastly, the samples are doped by nitrogen PBII (N-PBII). The photodegradation of Rhodamine B solution under Xe lamp indicates that the TiO₂ layer with surface macropores and N-doping has higher light photocatalysis efficiency.     

Characteristics of N-doped TiO2 thin films grown on unheated glass substrate by inductively coupled plasma assisted dc reactive magnetron sputtering

N-doped TiO₂ thin films have been deposited on unheated glass substrates by an inductively coupled plasma (ICP) assisted direct current (dc) reactive magnetron sputtering. All films were produced in the metallic mode of sputtering in order to achieve a high deposition rate. The structures and properties of the N-doped TiO₂ films were studied by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, field emission scanning electron microscopy and UV–Vis spectrophotometer. Experimental results show that we can obtain well crystallized N-doped anatase phase TiO₂ thin films at low deposition temperature and at high deposition rate by using the ICP assisted dc reactive magnetron sputtering process. The doping of nitrogen into TiO₂ lattices leads to a smooth shift of the absorption band toward visible light regions.     

Preparation of TiO2 thin films from autoclaved sol containing needle-like anatase crystals

A new inorganic sol-gel method was introduced in this paper to prepare TiO₂ thin films. The autoclaved sol with needle-like anatase crystals was synthesized using titanyl sulfate (TiOSO₄) and peroxide (H₂O₂) as starting materials. The transparent anatase TiO₂ thin films were prepared on glass slides from the autoclaved sol by sol-gel dip-coating method. A wide range of techniques such as Fourier transform infrared transmission spectra (FT-IR), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), scanning electron microscopes, X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectrum were applied to characterize the autoclaved sol and TiO₂ thin films. The results indicate that the autoclaved sol is flavescent, semitransparent and stable at room temperature. The anatase crystals of TiO₂ films connect together to form net-like structure after calcined and the films become uniform with increasing heating temperature. The surface of the TiO₂ films contain not only Ti and O elements, but also a small amount of N and Na elements diffused from substrates during heat treatment. The TiO₂ films are transparent and their maximal light transmittances exceed 80% under visible light region.     

Synthesis, characterization and degradation of Bisphenol A using Pr, N co-doped TiO2 with highly visible light activity

Praseodymium and nitrogen co-doped titania (Pr/N-TiO₂) photocatalysts, which could degrade Bisphenol A (BPA) under visible light irradiation, were prepared by the modified sol-gel process. Tetrabutyl titanate, urea and praseodymium nitrate were used as the sources of titanium, nitrogen and praseodymium, respectively. The resulting materials were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption isotherm and Fourier transform infrared spectra (FTIR). It was found that Pr doping inhibited the growth of crystalline size and the transformation from anatase to rutile. The degradation of BPA under visible light illumination was taken as probe reaction to evaluate the photo-activity of the co-doped photocatalyst. In our experiments, the optimal dopant amount of Pr was 1.2 mol% and the calcination temperature was 500 °C for the best photocatalytic activity. Pr/N-TiO₂ samples exhibited enhanced visible-light photocatalytic activity compared to N-TiO₂, undoped TiO₂ and commercial P25. The nitrogen atoms were incorporated into the crystal of titania and could narrow the band gap energy. Pr doping could slow the radiative recombination of photogenerated electrons and holes in TiO₂. The improvement of photocatalytic activity was ascribed to the synergistic effects of nitrogen and Pr co-doping.     

Doping mode, band structure and photocatalytic mechanism of B-N-codoped TiO2

The photocatalyst B and N codoped TiO₂ (B-N-TiO₂) was prepared via the sol-gel method by using boric acid and ammonia as B and N precursors. The doping mode, band structure and photocatalytic mechanism of B-N-TiO₂ were investigated well and elucidated in detail. B-N-TiO₂ showed the narrowed band gap and thus extended the optical absorption due to interstitial N and [NOB] species in the TiO₂ crystal lattice. The coexistence of interstitial N and [NOB] species in the TiO₂ crystal lattice and surface NO_x species allowed the more efficient utilization of visible light. Simultaneously, interstitial [NOB] and N species and surface B₂O₃ and NO_x species facilitated the separation of photo generated electrons and holes and suppress their recombination effectively. Hence, B-N-TiO₂ showed a higher photocatalytic activity than pure TiO₂, N-doped TiO₂ (N-TiO₂) and B-doped TiO₂ (B-TiO₂) under both UV and visible light irradiation.     

低成本溶胶-凝胶法制备SiO2/TiO2双层膜的减反射与自清洁性能

将玻璃基底依次在低成本的SiO₂溶胶和TiO₂溶胶中浸渍后,在500 oC下煅烧制备了同时具备减反射与自清洁性能的SiO₂/TiO₂双层膜．该膜的光学性能与结构特征分别通过紫外-可见分光光度计和场发射扫描电镜进行了表征．同时,源于超亲水性和光催化作用的自清洁性能也凸显出来．实验结果表明制备SiO₂/TiO₂双层膜对光的透射率最高可达到95%,同时具备自清洁性能．     

Preparation and characterization of visible light responsive Fe2O3-TiO2 composites

In this study we present the effects of iron oxide (Fe₂O₃) on titanium dioxide (TiO₂) in synthesising visible-light reactive photocatalysts. A Fe₂O₃-TiO₂ composite photocatalyst was synthesized from Fe₂(SO₄)₃ and Ti(SO₄)₂ by a ethanol-assisted hydrothermal method. The preparation conditions were optimized through the investigation of the effects of hydrothermal temperature and time as well as molar ratio of Ti to Fe on the photocatalytic activity. The visual, physical and chemical properties of the Fe₂O₃-TiO₂ composites were investigated. The results showed that α-Fe₂O₃ and anatase TiO₂ were present in the composites. The Fe₂O₃-TiO₂ synthesized under optimum condition consisted of mesoporous structure with an average pore size of 4 nm and a surface area of 43 m²/g. Under visible and solar light irradiation, the photocatalytic activity of optimized sample was significantly higher than that of pure TiO₂. This sample led to a photodegradation efficiency of 90% and 40% of auramine under visible light and solar light, respectively.     

An efficient composite growing N-doped TiO<Subscript>2</Subscript> on multi-walled carbon nanotubes through sol–gel process

High-activity, visible-light-driven photocatalysts were prepared by forming N-doped TiO₂ on multi-walled carbon nanotubes (MWCNTs). The use of MWCNTs as the support in a N-doped TiO₂ system favored electron trapping, because the recombination process could be retarded, thus promoting photocatalytic activity. The prepared photocatalysts were systematically characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunaure–Emmett–Teller (BET) spectroscopy, and UV–Vis diffuse reflectance spectroscopy (UV–Vis/DRS). The results indicated that the N-doped TiO₂ coated on MWCNTs improved the surface area and slightly modified the optical properties of the composite. The activities of the photocatalysts were probed by photodegradation of methanol in the presence of visible light irradiation. The experimental results revealed that the strong interphase linkage between the MWCNTs and the N-doped TiO₂ played a significant role in improving photocatalytic activity. However, the mechanical process for MWCNT–TiO_2-x N _x mixtures showed lower activity than just pure N-doped TiO₂. In this study, N-doped TiO₂ precursors coated with pretreated MWCNTs during a sol–gel process could effectively form a MWCNT–TiO_2-x N _x composite. The composite showed excellent activity and effectively enhanced the efficiency of N-doped TiO₂ under the visible light region.     

Comparison of photocatalytic performance of anatase TiO2 prepared by low and high temperature route

Anatase TiO₂ was prepared by a facile sol-gel method at low temperature through tailoring the pH of sol-gel without calcination. As a control, anatase TiO₂ was also synthesized by the conventional sol-gel process, in which calcination at 500 °C was required to transform the amorphous oxide into highly crystalline anatase. As-prepared samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). Their photocatalytic activities were evaluated by degradation of methyl orange under UV light irradiation. On the basis of experiment results, it could be concluded that TiO₂ prepared by low temperature route showed more advantages in small particle size, highly dispersion nature, abundance of surface hydroxyl groups, strong PL signal, and high photocatalytic activity over TiO₂ obtained by the conventional sol-gel process. Furthermore, the reason of the former possessing higher photocatalytic activity was discussed.     

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N-THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-vis (UV-vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03 M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07 M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).     

Effect of post heat treatment on microstructure and photocatalytic activities of TiO2 nanoribbons

Low-dimensional TiO₂ nanoribbons were synthesized by a simple one-step hydrothermal method. The TiO₂ nanoribbons were calcined over the temperature range 200-800 °C in order to enhance their photocatalytic properties by altering their crystal phase and increasing crystallization. Effects of hydrothermal temperature, calcinated temperature and calcination time on the formation of nanostructures have been observed and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The (BET) specific surface area of the samples which with different post treatments were determined by N₂ absorption-desorption experiment. In addition, photocatalytic activities of the nanoribbons were evaluated by photodegradation of organic dyes methyl orange under the radiation of UV light. The results reveal that the post-treatments have great effects on the microstructures and the photocatalytic activities of TiO₂ nanoribbons.     

IR and XPS investigation of visible-light photocatalysis—Nitrogen-carbon-doped TiO2 film

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Nitrogen and carbon doping TiO_2−x−yN_xC_y films were obtained by heating the TiO₂ gel in an ionized N₂ gas and then were calcined at 500 °C. The TiO_2−x−yN_xC_y films have revealed an improvement over the TiO₂ films under visible light (wavelength, 500 nm) in optical absorption and photocatalytic activity such as photodegradation of methyl orange. X-ray photoemission spectroscopy, infrared spectrum and UV-visible (UV-vis) spectroscopy were used to find the difference of two kinds of films. Nitrogen and carbon doped into substitutional sites of TiO₂ has been proven to be indispensable for band-gap narrowing and photocatalytic activity.     

二氧化钛纳米晶/石墨烯复合物的制备及其光催化性能 (cited: 1)

以氧化石墨和TiO₂溶胶为前驱物,结合絮凝与水热技术制备了TiO₂纳米晶/石墨烯复合物,表征了产物的结构、形貌、孔隙率、光谱吸收性质. 结果表明：TiO₂纳米晶的存在一定程度上阻止了石墨烯片层的重组,TiO₂纳米晶/石墨烯复合物较单纯TiO₂材料具有更强的吸光性能、对亚甲基蓝分子更强的吸附性能以及更高的电荷分离效率. 在紫外光和太阳光下,TiO₂纳米晶/石墨烯复合物对亚甲基蓝的光催化降解效率均高于P25和纯TiO₂.     

Surface effect of natural zeolite (clinoptilolite) on the photocatalytic activity of TiO2

The surface interaction between TiO₂ and natural zeolite, clinoptilolite, has been investigated by means of transmission electron microscope (TEM), atom force microscope (AFM), X-ray diffractometer (XRD), diffuse reflectance infrared Fourier transform (DRIFT) and far Fourier transform infrared ray (FTIR) spectroscopy. And the photocatalytic degradation (PCD) rate of methyl orange (MO), a model of recalcitrant azo dye, in aqueous system has been measured to compare the photocatalytic activities of different photocatalysts. A model has been carried out to explain the incorporation between TiO₂ particles and natural zeolite. The results show that the TiO₂ particles loaded on zeolite are 50 nm or so, smaller than the pure one, and combine with zeolite via chemical force. Since the reserved adsorption ability and the existence of electron trapper, the TiO₂-zeolite performed more efficient at low initial concentration and in the later period of PCD process, as compared with pure TiO₂ nanopowders.     

Preparation and characterization of TiO2 photocatalysts co-doped with iron (III) and lanthanum for the degradation of organic pollutants

Titanium dioxide photocatalysts co-doped with iron (III) and lanthanum were prepared by a facile sol-gel method. The structure of catalysts was characterized by X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were evaluated by the degradation of methylene blue in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. Doping with Fe³⁺ results in a lower anatase to rutile (A-R) phase transformation temperature for TiO₂ particles, while doping with La³⁺ inhibits the A-R phase transformation, and co-doping samples indicate that Fe³⁺ partly counteracts the effect of La³⁺ on the A-R transformation property of TiO₂. Fe-TiO₂ has a long tail extending up the absorption edges to 600 nm, whereas La-TiO₂ results in a red shift of the absorption. However, Fe and La have synergistic effect in the absorption of TiO₂. Compared with Fe³⁺ and La³⁺ singly doped TiO₂, the co-doped simple exhibits excellent visible light and UV light activity and the synergistic effect of Fe³⁺ and La³⁺ is responsible for improving the photocatalytic activity.