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.     

Properties of carbon and iron modified TiO2 photocatalyst synthesized at low temperature and photodegradation of acid orange 7 under visible light

The nanoparticles of TiO₂ modified with carbon and iron were synthesized by sol-gel followed solvothermal method at low temperature. Its chemical composition and optical absorption were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence emission spectroscopy (PL), UV-vis absorption spectroscopy, and electron paramagnetic resonance (EPR). It was found that carbon and iron modification causes the absorption edge of TiO₂ to shift the visible light region. Fe(III) cation could be doped into the matrix of TiO₂, by which could hinder the recombination rate of excited electrons/holes. Superior photocatalytic activity of TiO₂ modified with carbon and iron was observed for the decomposition of acid orange 7 (AO7) under visible light irradiation. The synergistic effects of carbon and iron in modified TiO₂ nanoparticles were responsible for improving visible light photocatalytic activity.     

A facile method to synthesize nitrogen and fluorine co-doped TiO2 nanoparticles by pyrolysis of (NH4)2TiF6

The nitrogen and fluorine co-doped TiO₂ (N-F-TiO₂) nanoparticles of anatase crystalline structure were prepared by a facile method of (NH₄)₂TiF₆ pyrolysis, and characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet visible (UV-Vis) spectroscopy etc. With the increase of calcination temperature, (NH₄)₂TiF₆ decomposed into TiOF₂ and NH₄TiOF₃ at first, and then formed anatase-type TiO₂ with thin sheet morphology. H₃BO₃ as oxygen source can promote the formation of anatase TiO₂, but decrease the F content in the N-F-TiO₂ materials due to the formation of volatile BF₃ during the precursor decomposition. The photocatalytic activity of the obtained N-F-TiO₂ samples was evaluated by the methylene blue degradation under visible light, and all the samples exhibited much higher photocatalytic activity than P25. Moreover, the merits and disadvantages of this proposed method to prepare doped TiO₂ are discussed.     

Synthesis, characterization and effect of calcination temperature on phase transformation and photocatalytic activity of Cu,S-codoped TiO2 nanoparticles

A novel copper and sulfur codoped TiO₂ photocatalyst was synthesized by modified sol-gel method using titanium(IV) isopropoxide, CuCl₂·2H₂O and thiourea as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy equipped with energy dispersive X-ray micro-analysis (SEM-EDX), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) analysis. The XRD results showed undoped and Cu,S-codoped TiO₂ nanoparticles only include anatase phase. Effect of calcination temperature showed rutile phase appears in 650 and 700 °C for undoped and 0.1% Cu,S-codoped TiO₂, respectively. The SEM analysis revealed the doping of Cu and S does not leave any change in morphology of the catalyst surface. The increase of copper doping enhanced “red-shift” in the UV-vis absorption spectra. The TEM images confirmed the dopants suppressed the growth of TiO₂ grains. The photocatalytic activity of samples was tested for degradation of methyl orange (MO) solutions. The results showed photocatalytic activity of the catalysts with 0.05% Cu,0.05% S and 0.1% Cu,0.05% S were higher than that of other catalysts under ultraviolet (UV) and visible irradiation, respectively. Because of synergetic effect of S and Cu, the Cu,S-codoped TiO₂ catalyst has higher activity than undoped and Cu or S doped TiO₂ catalysts.     

Structural, photochemical and photocatalytic properties of zirconium oxide doped TiO2 nanocrystallites

Composite photocatalysts composed of TiO₂ and ZrO₂ have been prepared via the sol-gel method. The as-prepared nanocomposites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis spectrometry and fluorescence emission spectra. The results shows that TiO₂/ZrO₂ nanocomposites are composed of mainly anatase titania and tetragonal ZrO₂. Incorporating TiO₂ particles with ZrO₂ plays an important role in promoting the formation of nanoparticles with an anatase structure and leads to decreased fluorescence emission intensity. Most of the TiO₂/ZrO₂ nanocomposites exhibited comparable photocatalytic activity compared with commercial TiO₂ for the degradation aqueous methyl orange (MO) under ultraviolet irradiation, while the composite with Zr/Ti mass ratio of 15.2% shows the highest photocatalytic performances. Furthermore, the as-prepared nanocomposites can be reused with little photocatalytic activity loss. Without any further treatment besides rinsing, the photocatalytic activity of TiO₂/ZrO₂ (15.2%) composites is still higher than after five-cycle utilization.     

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.     

Low-temperature preparation of F-doped TiO2 film and its photocatalytic activity under solar light

A novel and simple method for preparing F-doped anatase TiO₂ (defined as FTO) film with high photocatalytic activity was developed using titanium-n-butoxide and NH₄F as TiO₂ and fluorine precursors under mild condition, i.e. low temperature (lower than 373 K) and ambient pressure. The prepared samples were characterized by XRD, SEM, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectrum (DRS), photoluminescence spectrum (PL) and TG-DSC analysis. The photocatalytic activity was evaluated by decomposing X-3B under artificial solar light. The results showed that the crystallinity of TiO₂ was improved by F-doping. F⁻ ions can prevent the grain growth, and the transformation of anatase to rutile phase was also inhibited. The doped fluorine atoms existed in two chemical forms, and the ones incorporated into TiO₂ lattice might take a positive role in photocatalysis. Compared with surface fluorination samples, FTO film exhibited better photocatalytic activity. The high photocatalytic activity of FTO may due to extrinsic absorption through the creation of oxygen vacancies rather than the excitation of the intrinsic absorption band of bulk TiO₂. Furthermore, the FTO can be recycled with little photocatalytic activity depression. Without any further treatment besides rinsing, after 6 recycle utilization, the photocatalytic activity of FTO film was still higher than 79%.     

Low temperature synthesis of iodine-doped TiO2 nanocrystallites with enhanced visible-induced photocatalytic activity

Iodine-doped TiO₂ nanocrystallites (denoted as I-TNCs) were prepared via a newly developed triblock copolymer-mediated sol-gel method at a temperature of 393 K. I-doping, crystallization and the formation of porous structure have been simultaneously achieved. The obtained particles were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV-vis spectrophotometer. The results indicated that the as-prepared I-TNCs possessed a diameter of ca. 5 nm with anatase crystalline structure and a specific surface area of over 200 m² g⁻¹. The presence of iodine expanded the photoresponse in visible light range, and led to enrich in surface hydroxyl group on the TiO₂ surface. Compared with the commercial photocatalyst P25, the I-TNCs significantly enhanced the photocatalytic efficiency in the degradation of rhodamine B and 2,4-dichlorophenol, and the I-TNCs with 2.5 mol% doping ratio exhibited the best photocatalytic activity.     

Enhanced photocatalytic activity and stability of nano-scaled TiO2 co-doped with N and Fe

Titanium dioxide (TiO₂) nanoparticles co-doped with N and Fe were prepared via modified sol-gel process. The products were characterized by transmission electron microscopy (TEM), N₂ adsorption, X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). It is shown that the prepared TiO₂ particles were less than 10 nm with narrow particle size distribution. The addition of MCM-41 caused the formation of Ti-O-Si bond which fixed the TiO₂ on MCM-41 surface, thus restricted the agglomeration and growth of TiO₂ particles. The photocatalytic performance in the degradation of methylene blue showed that N, Fe co-doped TiO₂ exhibited much higher photocatalytic activity than doped sample with nitrogen or Fe³⁺ alone under both UV and visible light. N, Fe co-doping decreased the loss of doping N during the degradation reaction, thus increased the photocatalytic stability. It was also found that the nitridation time had significant influence on the photocatalytic activity of prepared TiO₂ catalysts.     

Synthesis of fluorinated TiO2 hollow microspheres and their photocatalytic activity under visible light

Fluorinated TiO₂ hollow microspheres with three-dimensional hierarchical architecture were prepared by solvothermally treatment using solid microspheres as precursor. The obtained solid and hollow TiO₂ microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectrum (DRS) and photoluminescence (PL) spectra. The photocatalytic activity of as-prepared solid and hollow TiO₂ microspheres was determined by degradation of methyl orange (MO) under visible light irradiation. The results showed that the surface fluorination, the existence of accessible mesopores channels, and the increased light harvesting abilities could remarkably improve the photocatalytic activity of TiO₂ hollow microspheres.     

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.     

The effects of activated carbon supports on the structure and properties of TiO2 nanoparticles prepared by a sol-gel method

TiO₂-coated activated carbon (TiO₂/AC) composites and pure TiO₂ powders were prepared by a sol-gel method using tetrabutylorthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), X-ray photoelectron spectrum (XPS) and nitrogen absorption. The photoactivity of samples was evaluated by methylene blue (MB) degradation. The analysis results show that compared with pure TiO₂ powders, the spherical-shaped TiO₂ particles are well-dispersed in the AC matrix and the size of the resulting TiO₂ crystallites decreases to below 40 nm with increasing phase transformation temperature. The AC matrix creates anti-calcination effects and shows interfacial energy effects that control the growth of the TiO₂ particles, baffle the anatase to rutile phase transition, and cumber the TiO₂ particles to agglomerate. Compared with the surface areas of TiO₂ powders, the combination of TiO₂ and AC forms composites with high surface areas which are slightly affected by calcination temperature. By AC support, the photoactivity of TiO₂ is increased in MB photocatalytic course, possible because active carbon increases photocatalytic activity of TiO₂ particles by producing high concentration of organic compound near TiO₂, and small-size TiO₂ particles are well-dispersed on the surface of AC.     

Study of effect annealing temperature on the structure, morphology and photocatalytic activity of Si doped TiO2 thin films deposited by electron beam evaporation

Transparent Si-doped TiO₂ thin films (Si-TiO₂) were deposited on quartz glasses using electron beam evaporation (EBE) and annealed at different temperature in an air atmosphere. The structure and morphology of these films were analyzed by X-ray diffraction (XRD), Raman microscopy (Raman), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Meanwhile the photocatalytic activity of the films has also been evaluated on the basis of the degradation degree of rhodamine B in aqueous solution. Our experimental results suggest that the annealing temperature impact a strong effect on the structure, morphology and photocatalytic activity of Si-TiO₂ thin films. Furthermore the enhanced thermal stability of Si-TiO₂ films enabled them to elevate the phase transformation temperature of TiO₂ from anatase to rutile and enhanced the photocatalytic efficiency.     

Preparation, characterization of Au (or Pt)-loaded titania nanotubes and their photocatalytic activities for degradation of methyl orange

TiO₂ nanotubes were prepared by hydrothermal method and Au (or Pt) was loaded on TiO₂ nanotubes by photodeposition method. The photocatalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption technique, respectively. The photocatalytic properties of the samples were also investigated. The results show that TiO₂ nanotubes with uniform diameter were prepared, and they have specific surface areas over 400 m²/g. The specific surface areas of TiO₂ nanotubes decrease with the increasing of calcining temperature, and crystalline phase of TiO₂ in the wall of nanotubes was transformed from anatase into rutile phase in calcination process. The photocatalytic activities of TiO₂ nanotubes are higher than that of nanosized TiO₂, and the photocatalytic activities of TiO₂ nanotubes were enhanced after loading Au (or Pt). After irradiation for 40 min under a 300 W of middle-pressure mercury lamp (MPML), the degradation rate of methyl orange solution using the Au/TiNT-500 (or Pt/TiNT-500) as a catalyst can reach 96.1% (or 95.1%). On the other hand, Au-loaded sample has evident adsorption peak in visible range, indicating that Au-loaded TiO₂ nanotubes are hopeful to become visible light photocatalyst.     

Preparation of nanosized crystalline TiO2 particles at low temperature for photocatalysis

Nanocrystalline titanium dioxide (TiO₂) particles were prepared by a modified alkoxide method under acidic conditions at temperatures ranging from 60°C to 90°C. The reaction temperature was used to control the crystalline phase of the TiO₂ particles. At 60°C and 75°C rutile was formed whilst at 90°C anatase and brookite were formed.The photocatalytic activity of the prepared particles was tested for the degradation of sucrose. The photocatalytic activities of the prepared nanosized TiO₂ were compared to those obtained from Degussa P-25 TiO₂ as well as TiO₂ crystalline samples prepared using the conventional sol–gel/heat treatment method. At low organic concentrations, Degussa P-25 exhibited higher photocatalytic behaviour than all the prepared particles while, at high organic concentrations, the nanosized TiO₂ particles prepared at low temperature displayed an activity comparable to Degussa P-25 but much higher than the heat treated sample. The formation of excess intermediates during the degradation of higher sucrose loadings is believed to hinder the photoactivity of Degussa P-25, while the prepared TiO₂ particles are able to maintain their activity for the degradation of the intermediates of sucrose.     

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.     

Preparation of bimetal incorporated TiO2 photocatalytic nano-powders by flame method and their photocatalytic reactivity for the degradation of diluted 2-propanol

Bimetal incorporated TiO₂ photocatalysts (FeZn–TiO₂) prepared by a flame method showed high photocatalytic activity for the degradation of 2-propanol dissolved in water as compared with mono-metal incorporated or unincorporated TiO₂. By using this flame method, parameters such as uniform particle size, crystallinity as well as the anatase and rutile phase ratio (anatase/rutile) could be controlled without calcination of the catalysts at high temperatures, the parameters being important to achieve a high photocatalytic activity. The presence of a small amount of bimetals such as Fe and Zn plays a vital role as a catalyst in the formation of highly crystalline, small and uniform size particles with defined anatase/rutile phase ratio of around 60/40, this being similar to that of P-25 which is well known as a highly active photocatalyst.     

Preparation and characterization of Fe-doped TiO2 on fly ash cenospheres for photocatalytic application

Fe³⁺-doped TiO₂ film deposited on fly ash cenosphere (Fe-TiO₂/FAC) was successfully synthesized by the sol-gel method. These fresh photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). The XRD results showed that Fe element can maintain metastable anatase phase of TiO₂, and effect of temperature showed rutile phase appears in 650 °C for 0.01% Fe-TiO₂/FAC. The SEM analysis revealed the Fe-TiO₂ films on the surface of a fly ash cenosphere with a thickness of 2 μm. The absorption threshold of Fe-TiO₂/FACs shifted to a longer wavelength compared to the photocatalyst without Fe³⁺-doping in the UV-vis absorption spectra. The photocatalytic activity and kinetics of Fe-TiO₂/FAC with varying the iron content and the calcination temperatures were investigated by measuring the photodegradation of methyl blue (MB) during visible light irradiation. Compared with TiO₂/FAC and Fe³⁺-doped TiO₂ powder (Fe-TiO₂), the degradation ratio using Fe-TiO₂/FAC increased by 33% and 30%, respectively, and the best calcined temperature was 450 °C and the optimum doping of Fe/Ti molar ratio was 0.01%. The Fe-TiO₂/FAC particles can float in water due to the low density of FAC in favor of phase separation to recover these photocatalyst after the reaction, and the recovery test shows that calcination contributes to regaining photocatalytic activity of Fe-TiO₂/FAC photocatalyst.     

Investigation on mechanism of photocatalytic activity enhancement of nanometer cerium-doped titania

A series of Ce-TiO₂ are prepared by the sol-gel process with ammonium cerium(IV) nitrate and tetra-n-butyl titanium as raw materials and characterized with XRD, TEM, DRS, and XPS. The aberrance (0.355) of anatase(1 0 1) plane of 0.1% Ce/TiO₂ increases compared to that of TiO₂. Cerium is found to be present as a mixture of Ce^3+/4+ oxidation states, that is, the oxidation state of some cerium in Ce-TiO₂ has changed after calcination. Ce/TiO₂ yields a large red shift compared to TiO₂. Moreover, the reflectance decreases in the visible region after cerium doped on TiO₂, and the lower the reflectance the higher the activity. Cerium appears to enhance the photocatalytic activity of Ce/TiO₂ by suppressing electron-hole recombination with electron trapping at Ce⁴⁺. 0.1% Ce/TiO₂ shows highest activity for the degradation of aqueous suspension of formaldehyde.     

Surface modification of nanocrystalline anatase with CTAB in the acidic condition and its effects on photocatalytic activity and preferential growth of TiO2

The nanocrystalline anatase TiO₂, which was synthesized by a sol-hydrothermal process in advance, has successfully modified with cetyltrimethylammonium bromide (CTAB) in the acidic condition as well as in the basic condition. On the basis of the measurements of infrared spectrum and X-ray photoelectron spectroscopy of the resulting TiO₂, together with the phase-transfer experiments, it is suggested that the modification mechanism in the acidic condition is closely related to Br⁻. Interestingly, compared with un-modified TiO₂, the modified TiO₂ exhibits high photocatalytic activity for degrading Rhodamine B (RhB) solution, especially for that modified in the acid. The enhanced photocatalytic activity of modified TiO₂ in the acid is attributed to the role that the Br⁻ can easily capture photo-induced holes and then form active Br, consequently effectively inducing photocatalytic oxidation reactions, based on the surface photovoltage responses of the resulting TiO₂. After that, a one-pot sol-hydrothermal route at the temperature as low as 80 °C is developed to directly synthesize CTAB-modified nanocrystalline TiO₂ with a little preferred growth along 〈0 0 1〉 direction, which can be easily dispersed in the organic system and possess good photocatalytic performance. This work provides a feasible strategy to further improve the photocatalytic performance of nanocrystalline anatase and to synthesize TiO₂ nanocrystals with preferential growth.