Visible-light-driven titania photocatalyst co-doped with nitrogen and ferrum

Nitrogen and ferrum co-doped titania photocatalyst was prepared by the sol-gel route. The prepared photocatalyst was characterized by various techniques including X-ray diffraction (XRD), UV-vis diffusive reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption-desorption isotherm. The photocatalytic activity of the co-doped titania photocatalyst was evaluated by the degradation of methyl orange (MO) from aqueous solution under visible light irradiation and was compared with that of the commercial TiO₂ photocatalyst (Degussa P25). The results revealed that the nitrogen doping could lead to the response to visible light and that the ferrum doping could improve the photocatalytic performance. The effects of the component and the annealing temperature of the co-doped titania photocatalyst on the photocatalytic activity were investigated.     

First-principles study on anatase TiO2 codoped with nitrogen and praseodymium

The crystal structures, electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO₂ were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory. Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO₂ nanocrystal photocatalyst were synthesized by a microwave chemical method. The calculated results show that the photocatalytic activity of TiO₂ can be enhanced by N doping or Pr doping, and can be further enhanced by N+Pr codoping. The band gap change of the codoping TiO₂ is more obvious than that of the single ion doping, which results in the red shift of the optical absorption edges. The results are of great significance for the understanding and further development of visible-light response high activity modified TiO₂ photocatalyst. The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light. The experimental results show that the codoping TiO₂ photocatalytic activity is obviously higher than that of the single ion doping. The experimental results accord with the calculated results.     

Photocatalytic and superhydrophilicity properties of N-doped TiO2 nanothin films

Pure TiO₂ and nitrogen doped titanium dioxide (N-TiO₂) thin films were prepared by sol-gel method through spin coating on soda lime glass substrates. TiCl₄ and urea were used as Ti and N sources in the sol. XRD results showed nitrogen doping has retarded anatase to rutile phase transformation. The doping also leads to a decrease in roughness of the samples from 4 nm (TiO₂) to 1 nm (N-TiO₂). However, surface analysis by statistical methods reveals that both surfaces have self-affine structure. Optical band gap of thin films was shifted from 3.65 eV (TiO₂) to 3.47 eV (N-TiO₂). Hydrophilic conversion and photocatalytic degradation properties of thin films were investigated and exhibited that N-TiO₂ thin film has more preferable hydrophilicity and photocatalytic properties under UV illumination.     

Visible-light-driven titania/silica photocatalyst co-doped with boron and ferrum

The sol-gel route was employed to prepare a titania/silica photocatalyst co-doped with boron and ferrum. The microstructure and the optical property of the photocatalyst were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffusive reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR), and N₂ adsorption-desorption isotherm. The decomposition of phenol under visible light irradiation was used as probe reaction to evaluate the photocatalytic activity. The results revealed that the dopants could inhibit phase transformation of TiO₂, and that there were intimate molecule-level interactions between titania and silica. The doping boron led to the response to visible light. The doping ferrum, which existed in the form of Fe₂O₃ and dispersed on the surface of TiO₂, increased photoquantum efficiency and resulted in the enhancement of catalytic performance. The photocatalytic activity related to the annealing temperature and component. The synergistic effects of co-doping and intimate interaction between titania and silica were responsible for the increase of photoactivity.     

Boron and nitrogen co-doped titania with enhanced visible-light photocatalytic activity for hydrogen evolution

A visible-light boron and nitrogen co-doped titania (B-N-TiO₂) photocatalyst was prepared by sol-gel method with titanium tetra-n-butyl oxide, urea and boric acid as precursors. The photocatalyst was characterized by Fourier Transform Infrared (FT-IR), UV-vis diffusive reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), BET and electrochemistry method. Photocatalytic activity for hydrogen production over platinized B-N-TiO₂ under visible-light (λ ≥ 420 nm) irradiation was investigated. In nitrogen doped titania (N-TiO₂) NTiO bond is formed, which extends the absorption edge to the visible-light region. A part of doping boron enters into titania lattice and most of the boron exists at the surface of the catalyst. The crystallite size of B-N-TiO₂ decreases compared to N-TiO₂, while its photocurrent and the surface hydroxyl group increase. Furthermore, doping boron could act as shallow traps for photoinduced electrons to prolong the life of the electrons and holes. Therefore, the visible-light activity of B-N-iO₂ increases greatly compared with that of N-TiO₂.     

硫和银共掺杂介孔TiO2的制备、表征及其对染料的光催化降解活性

以P123为模板,以钛酸四正丁酯、硝酸银和硫脲为原料采用模板法制备了一系列硫和银共掺杂介孔TiO₂光催化材料．利用SEM、XRD、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．以甲基橙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,用模板法制备的共掺杂介孔TiO₂光催化材料在紫外和可见光条件下较纯介孔TiO₂和单掺杂介孔TiO₂对甲基橙溶液具有更好的光催化降解效果, 且硫和银的掺杂量及样品焙烧温度显著影响该材料的催化性能．当硫掺杂量为2mol%和银掺杂量为1mol%,在500 oC 焙烧2 h所得光催化材料的催化性能最佳,4 h即可使甲基橙的降解率达98.8%,重复使用4次仍可使甲基橙的降解率保持在87.5%以上     

Visible-light photocatalysis of nitrogen-doped TiO2 nanoparticulate films prepared by low-energy ion implantation

Nitrogen-doped TiO₂ (N-TiO₂) films were prepared by low-energy implantation of nitrogen ions into pulsed laser deposited anatase TiO₂ films. The anatase phase of the films was not changed by the implantation with very low energy of 200 eV. XPS measurements revealed that the implanted nitrogen species were mainly interstitial ones. The nitrogen concentration was increased with increasing ion flux which could be controlled by adjusting the gas flow rate of the ion source. All the produced N-TiO₂ films exhibited visible-light photocatalytic activities in degradation of methylene blue in aqueous solutions, indicating that interstitial nitrogen could also be responsible for the photocatalysis in visible region. Higher visible-light photocatalytic efficiency was achieved with higher implanted nitrogen concentration.     

Visible-light-induced degradation of formaldehyde over titania photocatalyst co-doped with nitrogen and nickel

Titanium isopropoxide, ammonium carbonate and nickelous nitrate were used as the sources of titanium, nitrogen, and nickel to prepare titania photocatalyst co-doped with nitrogen and nickel by means of the modified sol-gel method. The photocatalyst was characterized by X-ray diffraction (XRD), UV-vis diffusive reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The prepared N-Ni co-doped photocatalyst showed optical absorption in the visible light area and exhibited excellent photocatalytic ability for the degradation of formaldehyde under visible light irradiation. The effects of annealing temperature and component on the phase composition and photocatalytic activity were investigated. The results demonstrated that nitrogen atoms was weaved into the structure of titania and led to the response to visible light. However, nickel atoms existed in the form of Ni₂O₃, dispersed on the surface of TiO₂, suppressed the recombination of photo-induced electron-hole pairs, raised the photo quantum efficiency, and led to the enhancement of photocatalytic performance. The increase of photoactivity was attributed to the synergistic effects of co-doping.     

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.     

Photocatalytic activity of multielement doped TiO2 in the degradation of congo red

TiO₂ although considered a promising photocatalyst for the degradation of aqueous pollutants, it suffers from poor absorption in the visible region and hence requires ultraviolet (UV) light for activation. To make TiO₂ a visible active photocatalyst, multielement (C, N, B, and F) doping has been done. The synthesised CNBF/TiO₂ catalysts were calcined at different temperatures and characterized by XRD, BET surface area, UV DRS, XPS, HRSEM-EDAX, and TEM techniques. These catalysts found to show less band gap values when compared to bare TiO₂. These catalysts were tested for their catalytic activity towards the degradation of a textile dye - congo red (CR) under different reaction conditions. It was found that the photocatalytic activity was dependent on both doping of multielement and the calcination temperature of CNBF/TiO₂. The co-doped catalysts which were calcined at 400 °C and 600 °C (100% intensity in anatase phase) were found to be the best catalysts (100% decolourisation of CR in 21/2 h and 2 h respectively). TOC analysis carried out for the samples at the reaction time of 5 h showed very high percentage (83%) degradation of CR over CNBF/TiO₂ catalysts calcined at 600 °C when compared to the other catalysts calcined at different temperatures. CNBF/TiO₂ (1000 °C) showed very less photocatalytic activity due to the formation of rutile phase.     

Gallium- and iodine-co-doped titanium dioxide for photocatalytic degradation of 2-chlorophenol in aqueous solution: Role of gallium

Visible-light-driven TiO₂-based catalysts for the degradation of pollutants have become the focus of attention. In the present work, iodine-doped titania photocatalysts (I-TiO₂) were improved by doping with gallium (Ga,I-TiO₂) and the resulting physicochemical properties and photocatalytic activity were investigated. The structural properties of the catalysts were determined by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis and transmission electron microscopy. We found that Ga probably enters the TiO₂ framework for doping levels <0.5 mol%. A further increase in Ga content probably leads to dispersal of excess Ga on the TiO₂ surface. The photocatalytic activity of Ga,I-TiO₂ catalysts was evaluated using 2-chlorophenol (2-CP) as a model compound under visible and UV-vis light irradiation. The results indicate that 0.5 mol% Ga loading and calcination at 400 °C represent optimal conditions in the calcining temperature range 400-600 °C and with doping levels from 0.1% to 1 mol%. The effective enhancement of 2-CP degradation might be attributed to the formation of oxygen vacancies by Ga doping, which could decrease the recombination of electron-hole pairs.     

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.     

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.     

Photocatalytic thin films containing TiO2:N nanopowders obtained by the layer-by-layer self-assembling method

In this work, TiO₂-N powders were synthesized by high-energy ball milling, using commercial titanium dioxide (TiO₂) in the anatase phase and urea to introduce nitrogen into TiO₂ in order to enhance their photocatalytic properties in the visible spectral region. Several samples were prepared by milling a mixture of TiO₂-urea during 2, 4, 8, 12 and 24 h and characterized by spectroscopic and analytical techniques. X-ray diffraction (XRD) results showed the coexistence of anatase and high-pressure srilankite TiO₂ crystalline phases in the samples. Scanning electron microscopy (SEM) revealed that the grain size of the powder samples decreases to 200 nm at 24 h milling time. UV-Vis diffuse reflectance spectroscopic data showed a clear red-shift in the onset of light absorption from 387 to 469 nm as consequence of nitrogen doping in the samples. The photocatalytic activity of the TiO₂-N samples was evaluated by methylene blue degradation under visible light irradiation. It was found that TiO₂-N samples had higher photocatalytic activity than undoped TiO₂ samples, which could be assigned to the effect of introducing N atoms and XPS results confirm it. Using polyethylenimine (PEI), transparent thin films of TiO₂-N nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO₂ and PEI after each dip cycle. The adsorption of both TiO₂ and PEI showed a saturation dip time of 15 min.     

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.     

Efficient visible-light-induced photocatalytic degradation of MO on the Cr-nanocrystalline titania-S

In order to improve visible light photocatalytic activities of the nanometer TiO₂, a novel and efficient Cr,S-codoped TiO₂ (Cr-TiO₂-S) photocatalyst was prepared by precipitation-doping method. The crystalline structure, morphology, particle size, and chemical structure of Cr-TiO₂-S were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) techniques, respectively. Results indicate that the doping of Cr and S, cause absorption edge shifts to the visible light region (λ > 420 nm) compare to the pure TiO₂, reduces average size of the TiO₂ crystallites, enhances desired lattice distortion of Ti, promotes separation of photo-induced electron and hole pair, and thus improves pollutant decomposition under visible light irradiation. The photocatalytic activities of Cr-TiO₂-S nanoparticles were evaluated using the photodegradation of methyl orange (MO) as probe reaction under the irradiation of UV and visible light and it was observed that the Cr-TiO₂-S photocatalyst shows higher visible photocatalytic activity than the pure TiO₂. The optimal Cr-TiO₂-S concentration to obtain the highest photocatalytic activity was 5 mol% for both of Cr and S.     

A novel Ce, C-codoped TiO2 nanoparticles and its photocatalytic activity under visible light

A novel photocatalyst (Ce, C-codoped titania) was synthesized through a modified sol-gel method under mild condition. The as-prepared sample was investigated by XRD, SEM, DRS and XPS. It was found that the as-prepared photocatalyst was composed of spheroidal particles, which were smaller than undoped ones. The absorbance spectrum of Ce, C-codoped TiO₂ exhibited significant red-shift to visible region. It can be ascribed to appearance of a new electronic state in the middle of the TiO₂ band-gap. Furthermore, cerium doping could slow the radiative recombination process of photogenerated electrons and holes in TiO₂. Accordingly, for degradation of dye Reactive Brillint Red X-3B (C.I. reactive red 2) under visible light, the photocatalytic activity of Ce, C-codoped TiO₂ improved much compared to other samples (C-doped TiO₂, undoped TiO₂ and P25).     

Synthesis and photochemical properties of HTaWO6/ (Pt,TiO2) nanocomposite under visible light irradiation

A new layered nanocomposite, HTaWO₆/(Pt, TiO₂) was synthesized using n-type semi-conductor HTaWO₆ as a host material. HTaWO₆ and HTaWO₆/TiO₂were white, while both HTaWO₆/Pt and HTaWO₆/(Pt, TiO₂) were yellow. The yellow color might be attributed to H_1-xTaWO_6-x/2 formed by the photo-induced phase transformation promoted by Pt. Although HTaWO₆/Pt showed absorption in visible light region (λ > 400 nm), the hydrogen evolution activity was negligibly small. On the other hand HTaWO₆/(Pt, TiO₂) showed excellent photocatalytic activities even under visible light irradiation. The sample containing rutile type titania such as TiO₂(P-25) also showed hydrogen evolution activity, but the activity was smaller than that of HTaWO₆/(Pt, TiO₂). These results suggested that rutile type titania, which can be excited by visible light of wavelength less than 413 nm, played an important role in the visible light-induced photocatalytic activity. The improvement of the hydrogen evolution activity of rutile type titania by intercalating into HTaWO₆/Pt may be due to the depression of the recombination of photoinduced electrons and holes by the heterogeneous electron transfer from rutile type TiO₂ to HTaWO₆/Pt.     

TiO2–carbon nanotube composites for visible photocatalysts – Influence of TiO2 crystal structure

We investigated the influence of the crystal structure of TiO₂ and the use of different TiO₂ precursors on the properties and photocatalytic activity of carbon nanotube (CNTs)–titania composites. We found that the crystal structure and properties of starting TiO₂ nanomaterial significantly affected the effect of CNTs incorporation on the photocatalytic activity under simulated solar and visible light illumination (simulated solar illumination with UV-blocking filter). In case of significant photocatalytic activity under visible light illumination (anatase TiO₂), likely due to the presence of native defects, composites exhibited lower activity under visible illumination only, but higher activity under simulated solar illumination. The opposite trends were observed for P25 (anatase + rutile) and rutile TiO₂, where incorporation of CNTs resulted in a significant increase of photocatalytic activity under visible illumination. Thus, control over crystal structure and native defects is essential for the development of efficient visible light activated photocatalysts.     

Influence of MoS2 deposition time on the photocatalytic activity of MoS2/ V,N co-doped TiO2 heterostructure thin film in the visible light region

Electron-hole separation and a narrow band-gap are essential steps to obtain efficient photocatalysis, towards which the use of co-catalysts or co-doped-TiO₂ photocatalysts has become a widely used strategy. In this article, the combination of MoS₂ and co-doping of V, N is the goal to achieve high performance photocatalysts. We synthesized MoS₂/V, N co-doped TiO₂ heterostructure thin film by sol-gel and chemical bath deposition methods. Herein, we investigated the influence of deposition time of MoS₂ layer on visible-photocatalytic activity of the obtained samples. The thin films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–vis spectroscopy techniques. Visible-photocatalytic activity of these samples were evaluated on the removal of methylene blue (MB) under visible light irradiation. The results show that the aforementioned heterostructure thin films have better photocatalytic activities than those of TiO₂, MoS₂ and V, N co-doped TiO₂ counterparts in visible light region. The mechanism for increasing visible-photocatalytic property of the heterostructure thin films is discussed in detail. We find that MoS₂/V, N co-doped TiO₂ heterostructure thin film at MoS₂ deposition time of 45-min shows the highest photocatalytic performance in the visible light region with MB photodegradation rate about 99% for 150 min and the degradation rate constant is 2.06 times higher than that of V and N co-doped TiO₂ counterpart.