Preparation of nanocrystalline Fe-doped TiO<Subscript>2</Subscript> powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO₂ powders were prepared using TiOSO₄, urea, and Fe(NO₃)₃ · 9H₂O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO₂, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m²/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe³⁺ and Fe²⁺ have been detected on the surface of TiO₂ powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO₂ powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO₂ was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO₂ powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.     

A novel approach for the synthesis of visible-light-active nanocrystalline N-doped TiO2 photocatalytic hydrosol

A visible-light-active nitrogen doped nanocrystalline titanium dioxide (N–TiO₂) hydrosol was prepared by precipitation–peptization method and following with hydrothermal crystallization at 110 °C holding for 6 h. XPS results show that nitrogen ions have been doped into the TiO₂ lattice successfully and the UV–Vis absorption spectra indicate that the light absorption edge of the N-doped TiO₂ has been red-shifted into visible light region. The photocatalytic performance of the N-doped TiO₂ thin film prepared from the synthesized hydrosol was evaluated by photodegrading the gaseous formaldehyde (HCHO) under visible light irradiation. The photodegradation ratio of HCHO reached up to 90% within 24 h and the degradation ratio was stable for ten degradation cycles, indicating the prepared hydrosol has good reusable performance in photodegrading gaseous pollutants.     

Visible-light-driven photocatalytic degradation of microcystin-LR by Bi-doped TiO<Subscript>2</Subscript>

Bi-doped nano-crystalline TiO₂ (Bi–TiO₂) has been synthesized by sonocrystallization at low temperature. The Bi–TiO₂ materials have narrower bandgaps than pristine TiO₂, which endow them with significant visible light absorption. Accordingly, these materials had enhanced photocatalytic activity in the degradation of organic dye pollutants and the cyanotoxin microcystin-LR (MC-LR) under visible irradiation. It was found that degradation of MC-LR is rather efficient. After irradiation with visible light for 12 h the original MC-LR was removed completely, and 78% of the organic carbon was mineralized into CO₂ after irradiation for 20 h. The hydroxyl radical (·OH) is the major active species responsible for the degradation reaction. Identified intermediates primarily originate from attack of ·OH radicals on the double bonds between C4 and C5 (C6 and C7) of Adda and the ethylenic bond of Mdha in MC-LR. Some peptide bonds are also broken with longer irradiation time.     

Structural characterization and photocatalytic properties of novel Bi<Subscript>2</Subscript>FeVO<Subscript>7</Subscript>

Bi₂FeVO₇ was prepared by a solid-state reaction technique for the first time and the structural and photocatalytic properties of Bi₂FeVO₇ were studied. The results shows that this compound crystallized in the tetragonal crystal system with space group I4/mmm. Moreover, the band gap of Bi₂FeVO₇ was estimated to be about 2.22(6) eV. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water with Bi₂FeVO₇ as the photocatalyst by ultraviolet light irradiation. Degradation of aqueous methylene blue (MB) dye by photocatalytic way over this compound was further studied under visible light irradiation. Bi₂FeVO₇ shows higher catalytic activity compared to TiO₂ (P-25) for MB photocatalytic degradation under visible light irradiation. Complete removal of aqueous MB was realized after visible light irradiation for 170 min with Bi₂FeVO₇ as the photocatalyst. The reduction of the total organic carbon (TOC) and the formation of inorganic products, SO ₄ ²⁻ and NO ₃ ⁻ revealed the continuous mineralization of aqueous MB during the photocatalytic course.     

Hydrothermal synthesis of (Fe,N) co-doped TiO<Subscript>2</Subscript> powders and their photocatalytic properties under visible light irradiation

(Fe, N) co-doped titanium dioxide powders have been prepared by a quick, low-temperature hydrothermal method using TiOSO₄, CO(NH₂)₂, Fe(NO₃)₃, and CN₃H₅ · HCl as starting materials. The synthesized powders were characterized by XRD, TEM, BET, XPS, and UV–Vis spectroscopy. Experimental results show that the as-synthesized TiO₂ powders are present as the anatase phase and that the N and Fe ions have been doped into the TiO₂ lattice. The specific surface area of the powders is 167.8 m²/g by the BET method and the mean grain size is about 11 nm, calculated by Scherrer’s formula. UV–Vis absorption spectra show that the edge of the photon absorption has been red-shifted up to 605 nm. The doped titanium dioxide powders had excellent photocatalytic activity during the process of photo-degradation of formaldehyde and some TVOC gases under visible light irradiation.     

Sol-gel preparation of Fe-doped mixed crystal TiO<Subscript>2</Subscript> powder and its photocatalytic activity for degradation of azo fuchsine under visible light irradiation

In this work, the Fe-doped mixed crystal TiO₂ photocatalyst which can utilize visible light was prepared by sol-gel and heat-treated methods. During heat-treatment, the phase transformation of Fe-doped TiO₂ powder occurs and the process is characterized by XRD and TG-DTA technologies. Otherwise, the sizes and shapes of Fe-doped and undoped TiO₂ powders were also compared using TEM images. The azo fuchsine in aqueous solutions, as a model compound, was treated under visible light irradiation using Fe-doped mixed crystal TiO₂ powders as photocatalyst. The results showed that, under visible light irradiation, the (0.25%) Fe-doped mixed crystal TiO₂ powder heat-treated at 600°C for 3.0 h behaved very high photocatalytic activities for degradation of azo fuchsine. The remarkable improvement of the photocatalytic activity of TiO₂ powder was elucidated through the cooperative effects of iron doping and phase transformation. The iron doping can restrain the recombination of photogenerated electron-hole pairs and the phase transformation can enhance the absorption of visible light. Furthermore, other influence factors such as azo fuchsine concentration, solution acidity, Fe3+ ion content and irradiation time were also studied. Thus, this method is applicable for the treatment of wastewater.     

Preparation of PANI-TiO2 nanocomposites and their solid-phase photocatalytic degradation

A series of polyaniline-anatase TiO₂ (PANI-TiO₂) nanocomposite powders with different PANI:TiO₂ ratios were prepared by ‘in-situ’ deposition oxidative polymerization of aniline hydrochloride using ammonium persulfate (APS) as oxidant in the presence of ultrafine grade powder of anatase TiO₂ cooled in an ice bath. And the solid-phase photocatalytic degradation of PANI-TiO₂ nanocomposites was investigated under the ambient air in order to assess the feasibility of developing photodegradable polymers. The photodegradation of the composite powders was compared with that of pure PANI powders by performing weight loss monitoring, elemental analysis, FT-IR and UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The PANI-TiO₂ nanocomposite powders showed highly enhanced photodegradation and the photodegradation increased with decreasing ratios of PANI:TiO₂. A weight loss of about 6.8% was found for the PANI-TiO₂ (1:3) nanocomposite; however, the weight loss of the PANI-HCl powder was only 0.3% after being irradiated for 60 h under air. The photocatalytic degradation of the nanocomposite powders accompanied the peak intensity decrease in the FT-IR spectra at 1235 cm⁻¹, attributed to C-N stretching mode for benzenoid unit, and the depigmentation of the powders due to the visible light scattering from growing cavities. The elemental analysis and XPS analysis of the composite showed that the bulk and surface concentrations of N decreased with irradiation. A possible mechanism for the photocatalytical oxidative degradation was also mentioned.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Preparation and characterization of mesoporous N-doped and sulfuric acid treated anatase TiO2 catalysts and their photocatalytic activity under UV and Vis illumination

Nitrogen-doped TiO₂ catalysts were prepared by a precipitation method. The samples were calcined at 400 °C for 4 h in air. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature N₂-adsorption was used for structural characterization and UV-diffuse reflectance (UV-DR) was applied to investigate the optical properties of the as-prepared samples. It was found that microporous N-doped catalysts have solely anatase crystalline structure. Acidic treatment of the calcined samples was performed using sulfuric acid agitation. The crystalline structure remained unchanged due to surface treatment, while the porosity and the surface areas were decreased dramatically. Optical characterization of the doped catalysts showed that they could be excited by visible light photons in the 400–500 nm wavelength range (λ_g,1=390 nm, λ_g,2=510 nm). It was also established that surface treatment enhances the Vis-light absorption of the N-TiO₂ powders. Finally the catalysts were tested in the photocatalytic degradation of phenol in aqueous suspensions. Two different light sources were used; one of them was a UV-rich high pressure Hg-lamp, while the other was a tubular visible light source. We found that using visible light illumination N-doped, acid treated TiO₂ samples were more catalytically active than non-doped TiO₂ catalysts.     

不同形貌Bi4Ti3O12粒子的可控合成及光催化性能

研究了用一步水热法制备的不同形貌的钛酸铋(Bi₄Ti₃O₁₂, BIT)粒子的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. XRD结果表明, 所制备的BIT 样品为层状钙钛矿结构. FESEM结果表明, 通过控制水热过程的反应参数可以得到不同形貌的纳米粒子. 紫外-可见漫反射光谱(UV-Vis DRS)表明BIT 样品的带隙能约为2.88-2.93 eV. 利用可见光(λ>420 nm)照射下的甲基橙(MO)降解实验评价了BIT 样品的光催化性能. 结果表明, BIT 的光催化活性比掺氮TiO₂ (N-TiO₂)高得多. 研究了形貌对BIT 光催化性能的影响. 所制备的BIT纳米带光催化效率最高, 经可见光照射360 min, 甲基橙溶液的降解率可达到95.0%.     

One-step synthesis of nanocrystalline N-doped TiO2 powders and their photocatalytic activity under visible light irradiation

Nanocrystalline N-doped TiO₂ powders were successfully prepared by hydrothermal reaction for 2 h at low temperature (120 °C) and at an applied pressure of 3 MPa. The grain size of the powders (calculated by use of Scherrer’s method) ranged from 8.2 to 10.2 nm. The BET specific surface area ranged from 151.0 to 220.0 m²/g. A significant shift of the light absorption edge toward the visible light zone was observed in the UV–visible spectra. XPS results showed that nitrogen atoms were incorporated into the TiO₂ lattice. The photocatalytic activity of the synthesized N-doped TiO₂ powders was evaluated by measurement of photodegradation of methylene blue (MB) in aqueous solution under visible light irradiation. The amount of MB degraded increased with increasing illumination intensity.     

稀土离子Tm3+掺杂Bi2WO6的可见光催化性能

以Na_2WO_4·2H_2O和Bi(NO_3)_3·5H_2O为主要原料,采用水热法合成了稀土离子Tm~(3+)掺杂的Bi_2WO_6光催化剂。采用XRD、SEM、TEM、Raman、PL、DRS研究了Tm~(3+)掺杂Bi_2WO_6的物相,微观形貌和可见光催化性能。结果表明,Tm~(3+)掺杂有效提高了Bi_2WO_6的光催化性能,当掺杂量为6%时,样品的光催化性能最好,可见光照射30 min后,对罗丹明B的降解效率达到91.27%,而可见光照射5 h后,对焦糖色素的降解效率达45.25%。与未掺杂Bi_2WO_6相比,分别提高了27.78%和35.22%。     

Visible light photocatalytic activity of BiVO4 particles with different morphologies

Bismuth vanadate (BiVO₄) particles with different morphologies were synthesized by a one-step hydrothermal process and their optical and photocatalytic properties were investigated. Their crystal structure and microstructures were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). XRD patterns demonstrate that the as-prepared samples are monoclinic cell. FESEM shows that BiVO₄ crystals can be fabricated in different morphologies by simply manipulating the reaction parameters of hydrothermal process. The UV–visible diffuse reflectance spectra (UV–vis DRS) reveal that the band gaps of BiVO₄ photocatalysts are about 2.07–2.21 eV. The as-prepared BiVO₄ photocatalysts exhibit higher photocatalytic activities in the degradation of rhodamine B (Rh B) under visible light irradiation (λ > 420 nm) compared with traditional N-doped TiO₂ (N-TiO₂). Furthermore, wheat like BiVO₄ sample reveals the highest photocatalytic activity. Up to 100% Rh B is decolorized after visible light irradiation for 180 min. The reason for the difference in the photocatalytic activities for BiVO₄ samples obtained at different conditions were systematically studied based on their shape, size and the variation of local structure.     

Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.     

Visible light-induced N-doped TiO2 nanoparticles for the degradation of microcystin-LR

N-doped nano-crystalline TiO₂ powders have been synthesized by the sol-gel method. The shape and crystal structure of the resulting N-doped TiO₂ were investigated by X-ray Photoelectron Spectroscopy (XPS), X-ray spectroscopy (XRD), Transmission Electron Microscopy (TEM) and UV-vis reflection spectrum. The results showed that doping TiO₂ with nitrogen can lower its band gap and apparently shift its optical response to the visible region. Under the visible light (λ > 420 nm) irradiation, the MC-LR was degraded by the synthesized N-TiO₂ nano-material. The variation of MC-LR amount and its intermediates were detected by high performance liquid chromatography (HPLC) and LC-MS, respectively. The mineralization of MC-LR was determined by total organic carbon (TOC) analysis. Simultaneously, transient oxidative species generated during photocatalysis were tracked by electron spin resonance (ESR) and Peroxidase method. All these results indicated that visible-light excited N-TiO₂ can activate molecular oxygen and thereby achieve degradation of MC-LR completely within 14 h. The removal of 59% of TOC was achieved after 20 h irradiation. The major oxidative species in the system were hydroxyl radical (·OH) and H₂O₂. 13 Kinds of intermediates were primarily identified in the process. Based on these results, a reasonable conclusion was drawn for the degradation of MC-LR wherein its four positions are easy to be attacked by the photo-generated OH radical followed by the hydrolyzation of peptides.     

Synthesis of N-TiO2: Stability and Visible Light Activity for Aqueous Styrene Degradation

Nitrogen-doped TiO₂ (N-TiO₂) were prepared by the impregnation method using urea as a nitrogen source and TiO₂-P25 as precursor. N-TiO₂ was characterized by x-ray diffraction (XRD), UV–vis diffusion reflectance spectra (UV–vis DRS), Fourier transform infrared spectroscopy (FTIR), and x-ray photoelectron spectroscopy (XPS) techniques. XPS analysis indicates the incorporation of nitrogen in TiO₂ lattice as O–Ti–N linkage. DRS spectra reveal the extended absorption to the visible range. Photocatalytic performance of the N-TiO₂ was studied by testing the degradation rate of aqueous styrene under visible light. Also, the degradation kinetics of aqueous styrene and possibility of cyclic usage of N-TiO₂ were investigated.     

Preparation of nanocrystalline TiO<Subscript>2</Subscript> powders for photocatalytic oxidation of phenol

Nanocrystalline TiO₂ powders in the anatase, rutile, and mixed phases prepared by hydrolysis of TiCl₄ solution were of ultrafine size (<7.2 nm) with high specific surface areas in the range 167 to 388 m²/g. In the photocatalytic degradation of phenol as model reaction, the photocatalytic properties of TiO₂ nanoparticles were evaluated by use of UV–vis absorption spectroscopy and total organic carbon (TOC) content. The synthetic mixed-phase TiO₂ powder calcined at 400 °C had higher activity than pure anatase or rutile; it degraded more than 90% phenol to CO₂ (evaluated by TOC) after irradiation with near UV light for 90 min at a catalyst loading of 0.4 g/L. The TOC results indicated that rutile TiO₂ crystallites of particle size 7.2 nm resulted in much better photocatalytic performance than particles of larger size. This result suggested that some intermediates, not determined by UV–vis absorption spectroscopy, existed in the solution after the photocatalytic process over the rutile TiO₂ photocatalysts of larger crystallite size.     

Influence of NH<Subscript>3</Subscript>-treating temperature on visible light photocatalytic activity of N-doped P<Subscript>25</Subscript>-TiO<Subscript>2</Subscript>

The influence of NH₃-treating temperature on the visible light photocatalytic activity of N-doped P₂₅-TiO₂ as well as the relationship between the surface composition structure of TiO₂ and its visible light photocatalytic activity were investigated. The results showed that N-doped P₂₅-TiO₂ treated at 600°C had the highest activity. The structure of P₂₅-TiO₂ was converted from anatase to rutile at 700°C. Moreover, no N-doping was detected at the surface of P₂₅-TiO₂. There was no simply linear relationship between the visible light photocatalytic activity and the concentration of doped nitrogen, and visible light absorption. The visible light photocatalytic activity of N-doped P₂₅-TiO₂ was mainly influenced by the synergistic action of the following factors: (i) the formation of the single-electron-trapped oxygen vacancies (denoted as V_o^·); (ii) the doped nitrogen on the surface of TiO₂; (iii) the anatase TiO₂ structure.     

Pt助剂对N掺杂TiO2可见光光催化性能的影响

考察了Pt促进的N掺杂TiO2(Pt/N-TiO2)催化剂对光催化降解有机污染物性能的影响及其作用本质.采用X射线衍射、透射电镜、X射线光电子能谱、紫外-可见漫反射光谱、光电化学和荧光光谱等手段对催化剂进行了表征,并考察了样品在可见光下光催化降解甲基橙(MO)的反应性能.结果表明,Pt的存在并未明显改变N-TiO2的晶...     

Microwave synthesis and phase transitions in nanoscale BiFeO<Subscript>3</Subscript>

Nanosized multiferroic BiFeO₃ powders were synthesized by a microwave combustion method. The average crystallite sizes of the samples stay at a same level with the ratio of fuel glycine 0.5 ≤ G/N ≤ 1.5 and it increases significantly with G/N = 2.0. An inhomogeneity of amorphous and microcrystallites is observed directly by HRTEM. A ferromagnetic hysteresis loop with a saturation magnetization (M _S) of ~0.09 μ _B /Fe has been observed at room temperature in the sample with a crystallite size of 53 nm, whereas other powders with much smaller crystallite size (~20 nm) will not saturate even at 20 kOe. These magnetic behaviors were ascribed to a combination of the magnetic enhancement effect of a decreased crystallite size and superparamagnetic mechanism.