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 and characterization of the Pd/InVO4-TiO2 co-doped thin films with visible light photocatalytic activities

Novel Pd/InVO₄-TiO₂ thin films with visible light photocatalytic activity were synthesized from the Pd and InVO₂ co-doped TiO₂ sol via sol-gel method. The photocatalytic activities of Pd/InVO₄-TiO₂ thin films were investigated based on the oxidative decomposition of methyl orange in aqueous solution. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy (UV-vis). The results indicate that the Pd/InVO₄-TiO₂ thin films are compact, uniform and consist of sphere nanoparticles with diameters about 80-100 nm. The UV-vis spectra show that the Pd/InVO₄-TiO₂ thin films extend the light absorption spectrum toward the visible region. XPS results reveal that doped Pd exist in the form of metallic palladium. The photocatalytic experiments demonstrate that Pd doping can effectively enhance the photocatalytic activities of InVO₄-TiO₂ thin films in decomposition of aqueous methyl orange under visible light irradiation. It has been confirmed that Pd/InVO₄-TiO₂ thin films could be excited by visible light (E < 3.2 eV) due to the existence of the Pd and InVO₄ doped in the films.     

Fabrication of Fe-doped TiO2 nanoparticles and investigation of photocatalytic decolorization of reactive red 198 under visible light irradiation

In this research, Fe-doped TiO₂ nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10 wt%) were prepared by a sol–gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1 eV. Photocatalytic results indicated that TiO₂ had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO₂ nanoparticles. Among the samples, Fe-1 wt% doped TiO₂ nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.     

Synthesis and characteristics of natural zeolite supported Fe-TiO2 photocatalysts

Natural zeolite supported Fe³⁺-TiO₂ photocatalysts were synthesized for the sake of improving the recovery and photocatalytic efficiency of TiO₂. The as-prepared materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Methyl orange was used to estimate the photocatalytic activity of the samples. The results showed that zeolite inhibited the growth of TiO₂ crystallite sizes. The Fe³⁺ concentration played an important role on the microstructure and photocatalytic activity of the samples. The iron ions could diffuse into TiO₂ lattice to the form Fe-O-Ti bond and gave TiO₂ the capacity to absorb light at lower energy levels. The photocatalytic activity of the samples could be enhanced as appropriate dosages of Fe³⁺ were doped.     

Preparation and visible light photocatalytic activity of mesoporous N, S-codoped TiO2(B) nanobelts

The mesoporous N, S-codoped TiO₂(B) nanobelts are synthesized via hydrothermal synthesis and post-treatment, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption measurements (BET), X-ray photoelectron spectra (XPS), and UV-vis diffuse reflectance spectra (DRS). The results show that the prepared samples are mesoporous structured and exhibit stronger absorption in the visible light region with red shift in the absorption edge. The photocatalytic activity of N, S-codoped mesoporous TiO₂(B) nanobelts is evaluated by the photocatalytic photodegradation of potassium ethyl xanthate (KEX) under visible light irradiation. It is found that the photocatalytic activity of the prepared samples increases with increasing the molar ratio of thiourea to Ti (R). At R = 3, the photocatalytic activity of the N, S-codoped TiO₂(B) sample TBLTS-3 reaches a maximum value. With further increasing R, the photocatalytic activity of the sample decreases. The high photocatalytic activity of N, S-codoped TiO₂(B) nanobelts can be attributed to the balance between strong absorption in visible light region and low recombination rate of electron/hole pairs.     

Preparation of visible light responsive N doped TiO2 via a reduction-nitridation procedure by nonthermal plasma treatment

A visible light responsive N-doped TiO₂ was prepared via a reduction-nitridation procedure by nonthermal plasma treatment. X-ray diffraction, N₂ adsorption, UV-vis spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy were used to characterize the prepared TiO₂ samples. The plasma treatment did not change the phase composition and particle sizes of TiO₂ samples, but extended its absorption edges to the visible light region. The photocatalytic activities were tested in the degradation of an aqueous solution of a reactive dyestuff, methylene blue, under visible light. The photocatalytic activities of TiO₂ prepared by reduction-nitridation procedure were much higher than that of samples prepared by simple nitridation treatment. The enhanced activity was ascribed to the substitutional N-doping and appropriate concentration of oxygen vacancies. TOHN10 prepared by reduction-nitridation procedure exhibited excellent photocatalytic stability. A possible mechanism for the photocatalysis was proposed.     

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.     

Sol-gel derived S,I-codoped mesoporous TiO2 photocatalyst with high visible-light photocatalytic activity

A mesoporous S,I-codoped TiO₂ photocatalyst with high visible light photocatalytic activity was synthesized through the hydrolysis and condensation of titanium isopropoxide with thiourea and iodic acid as the precursors. The as-prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-vis diffuse reflectance (DRS), X-ray photoelectron spectroscopy (XPS), Fourier translation infrared spectroscopy (FT-IR), and N₂ adsorption. The results showed that the cations of S⁶⁺ and I⁵⁺ could substitute for some of the lattice titanium (Ti⁴⁺). The S,I-codoping forms the new bands above the valence band and narrows the band-gap of the TiO₂, then shifts the absorption edge from UV light region to visible light range. The activity of the catalyst was examined by photodegradation of methylene blue in an aqueous solution under visible light irradiation. The activity of the S,I-codoped catalyst is far superior to that of single S or I-doped TiO₂ counterpart. The high visible light photocatalytic activity could be attributed to the strong absorption of light, well-crystalline anatase phase, and mesoporous microstructure.     

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.     

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.     

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.     

Enhanced photocatalytic degradation of Safranin-O by heterogeneous nanoparticles for environmental applications

Nanostructure titanium dioxide (TiO₂) has been synthesized by hydrolysis of titanium tetrachloride in aqueous solution and Ag-TiO₂ nanoparticles were synthesized by photoreduction method. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) and UV-vis absorption spectroscopy. The experimental results showed that the sizes of the synthesized TiO₂ and Ag-TiO₂ particles are in the range of 1.9-3.2 nm and 2-10 nm, respectively. Moreover, Ag-TiO₂ nanoparticles exhibit enhanced photocatalytic activity on photodegradation of Safranin-O (SO) dye as compared to pure TiO₂. The positive effect of silver on the photocatalytic activity of TiO₂ may be explained by its ability to trap electrons. This process reduces the recombination of light generated electron-hole pairs at TiO₂ surface and therefore enhances the photocatalytic activity of the synthesized TiO₂ nanoparticles. The effects of initial dye and nanoparticle concentrations on the photocatalytic activity have been studied and the results demonstrate that the dye photodegradation follows pseudo-first-order kinetics. The observed maximum degradation efficiency of SO is about 60% for TiO₂ and 96% for Ag-TiO₂.     

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.     

Photocatalytic properties of porous C-doped TiO2 and Ag/C-doped TiO2 nanomaterials by eggshell membrane templating

Porous organic carbon-doped titania (C-TiO₂) nanomaterials and their composites with Ag nanoparticles (Ag/C-TiO₂) were synthesized by an eggshell membrane templating method, and their structural and photocatalytic properties were systematically characterized. These nanomaterials, exhibiting a macroscopic morphology of a thin film, are composed of interwoven tubes, and the tube wall consists of nanocrystals. The doped organic carbon was composed of the active carbon and carbonate species, which could form a layer around the surface of TiO₂ nanoparticles, while the silver was incorporated into Ag/C-TiO₂ composites as separated Ag nanoparticles. The degradation of methylene blue under visible light irradiation was employed to evaluate the photocatalytic activity of these as-prepared TiO₂-based materials. Both C-TiO₂ and Ag/C-TiO₂ nanomaterials showed higher photocatalytic activity than pure TiO₂ material–commercial Degussa P25. These results can be accounted for the coupling effect of the incorporation of carbon species and Ag nanoparticles.     

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.     

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.     

Scanning transmission X-ray microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry study on the enhanced visible photocatalytic mechanism of carbon-TiO2 nanohybrids

Carbon-TiO₂ nanohybrids (CTs, 5-10 nm TiO₂ nanocrystals evenly dispersed on carbon film) have been successfully prepared via a mild, one-step hydrothermal approach. The interactions and electronic structures of carbon and TiO₂ nanoparticles and the enhanced visible photocatalytic mechanism were investigated by scanning transmission X-ray microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry in detail. Meanwhile, it was demonstrated that the as-obtained CTs had a large BET specific surface area of 304.6 m²/g and showed excellent photocatalytic abilities towards organic (Rhodamine B, benzene) and inorganic pollutant (K₂Cr₂O₇) degradation in visible light. This work provided a new approach for the high performance catalyst design towards new energy sources and environmental issues.     

Nitrogen doped TiO2 nanoparticles decorated on graphene sheets for photocatalysis applications

Nitrogen doped TiO₂ nanoparticles decorated on graphene sheets are successfully synthesized by a low-temperature hydrothermal method. The resulting GR-N/TiO₂ composites are characterized by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-Ray photoelectron spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The optical properties are studied using UV–visible diffuse reflectance spectroscopy (DRS), which confirms that the spectral responses of the composite catalysts are extended to the visible-light region and show a significant reduction in band gap energy from 3.18 to 2.64 eV. Photoluminescence emission spectra verify that GR-N/TiO₂ composites possess better charge separation capability than pure TiO₂. The photocatalytic activity is tested by degradation of methyl orange (MO) dye under visible light irradiation. The results demonstrate that GR-N/TiO₂ composites can effectively photodegrade MO, showing an impressive photocatalytic enhancement over pure TiO₂. The dramatically enhanced activity of composite photocatalysts can be attributed to great adsorption of dyes, enhanced visible light absorption and efficient charge separation and transfer processes. This work may provide new insights into the design of novel composite photocatalysts system with efficient visible light activity.     

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.