Combined adsorption process and photocatalytic degradation of some commercial herbicides over N-doped TiO2 particles supported on recyclable magnetic hexagonal mesoporous silica

Magnetic hexagonal mesoporous silica (magnetic HMS) containing N-doped TiO₂ was prepared by hydrothermal method and used for the removal of trifluralin, 2,4-dichlorophenoxyacetic acid, and glyphosate herbicides at the presence and absence of UV/visible lights. The prepared samples were found as efficient for the removal of the herbicides and easily recyclable after treatment by UV irradiation. A red shift effect by nitrogen doping was also observed in the prepared samples resulting photocatalytic activity at the presence of visible light. Kinetic studies indicated that the photodegradation followed as the first order and k_UV ≈ 10k_vis. The results also showed synergetic effects between the adsorption of herbicides on the surface of magnetic HMS and photoreactions over N-doped TiO₂ species.     

Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors

Zr/N co-doped TiO₂ nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO₂ nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO₂ nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO₂ were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.     

Visible light photocatalytic activity of TiO2/heat‐treated PVC film

BACKGROUND: Semiconductor TiO₂ has been investigated extensively due to its chemical stability, nontoxicity and inexpensiveness. However, the wide band gap of anatase TiO₂ (about 3.2 eV) only allows it to absorb UV light. TiO₂ nanoparticles modified by conditional conjugated polymers show excellent photocatalytic activity under visible light. However, these conjugated polymers are not only expensive, but also difficult to process. Polyvinyl chloride (PVC) was heat‐treated at high temperature to remove HCl and a C?C conjugated chain structure was obtained. When TiO₂ nanoparticles were dispersed into the conjugated polymer film derived from PVC, this composites film exhibited high visible light photocatalytic activity. RESULTS: The photocatalytic activity of TiO₂/heat‐treated PVC (HTPVC) film was investigated by degrading Rhodamine B (RhB) under visible light irradiation. The photodegradation of RhB follows apparent first‐order kinetics. The rate constants of RhB photodegradation in the presence of the TiO₂/HTPVC films with different mass content of TiO₂ are 16–56 and 4–14 times that obtained in the presence of the pure HTPVC and TiO₂/polymethyl methacrylate (PMMA) composite film, respectively. The TiO₂/HTPVC film showed excellent photocatalytic activity and stability after 10 cycles under visible light irradiation. CONCLUSION: TiO₂/HTPVC film exhibits high visible light photocatalytic activity and stability. Copyright © 2012 Society of Chemical Industry     

Simple fabrication of N-doped mesoporous TiO2 nanorods with the enhanced visible light photocatalytic activity

N-doped mesoporous TiO₂ nanorods were fabricated by a modified and facile sol–gel approach without any templates. Ammonium nitrate was used as a raw source of N dopants, which could produce a lot of gasses such as N₂, NO₂, and H₂O in the process of heating samples. These gasses were proved to be vitally important to form the special mesoporous structure. The samples were characterized by the powder X-ray diffraction, X-ray photoelectron spectrometer, nitrogen adsorption isotherms, scanning electron microscopy, transmission electron microscopy, and UV-visible absorption spectra. The average length and the cross section diameter of the as-prepared samples were ca. 1.5 μm and ca. 80 nm, respectively. The photocatalytic activity was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The N-doped mesoporous TiO₂ nanorods showed an excellent photocatalytic activity, which may be attributed to the enlarged surface area (106.4 m² g^-1) and the narrowed band gap (2.05 eV). Besides, the rod-like photocatalyst was found to be easy to recycle.     

One-step fabrication of N-doped TiO2 inverse opal films with visible light photocatalytic activity

N-doped TiO₂ inverse opal films were fabricated by a novel method through one-step coassembly of polymer colloidal spheres and titania precursor. This coassembly approach removed the need of preassembled colloidal crystal for precursor solution infiltration and respective chemicals for titania formation and nitrogen doping. Less crack films with well ordered inverse opal structure could be produced by adding appropriate amount of TiBALDH (titanium(IV)-bis-lactato-bis-ammonium dihydroxide) into the precursor solution. The films prepared at the optimized condition showed enhanced visible light photocatalytic activity, which could be attributed to both the N doping effect and their unique inverse opal structure.     

Low Temperature Preparation and Characterization of N-doped and N-S-codoped TiO2 by Sol–gel Route

This paper reports a new method to prepare the N-doped and N-S-codoped anatase TiO₂ photocatalysts at 100 °C. The as-prepared photocatalysts were characterized by means of XRD, Raman spectra, TEM, BET, UV–Vis diffuse reflectance spectra (DRS) and XPS. The results showed that the N-doping and N-S-codoping extended the absorbance spectra of TiO₂ into visible region with different extent. The BET surface area of the N-S-codoped TiO₂ photocatalysts was high up to 245 m²g⁻¹. The results of degradation of methyl orange (MO) solution showed that the N-doped and N-S-codoped TiO₂ photocatalysts exhibited higher photocatalytic activity than that of Degussa P-25 and the as-prepared pure TiO₂ under visible irradiation. This property can be attributed to the results of synergetic effects of absorption in the visible light region, red shift in adsorption edge, good crystallization and large surface area of the as-prepared N-doped or N-S-codoped TiO₂.     

Fabrication of nitrogen-doped TiO2 monolith with well-defined macroporous and bicrystalline framework and its photocatalytic performance under visible light

In this study, hierarchically porous bicrystalline nitrogen-doped titania (N-doped TiO₂) monolithic material was fabricated by a simple two-step approach: (i) preparation of TiO₂ porous monolith by a sol–gel process of titanium alkoxide in a mild condition utilizing a chelating agent and mineral salt and (ii) annealing of TiO₂ porous monolith obtained under a modest flow of ammonia gas at 700 °C for 2 h. The phase composition, crystal structure, morphology, pore structure, and porous properties of the final product were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, and nitrogen physisorption measurement, respectively. The resultant N-doped TiO₂ porous monolith possesses a bicrystalline (anatase and rutile) framework with a well-defined macroporosity. The results from X-ray photoelectron spectroscopy (XPS) confirm the formation of OTiN bonds in the N-doped TiO₂ porous monolith. The photocatalytic activity of N-doped TiO₂ porous monolith was evaluated by the photodegradation of Rhodamine B over the samples under visible light. Nearly 50% of Rhodamine B in aqueous solution was efficiently degraded by N-doped TiO₂ porous monolith with the mixed-phase of anatase and rutile under visible light within 120 min.     

A Visible Light Photocatalyst of Carbonate‐Like Species Doped TiO2

Carbon‐doped TiO₂ nanomaterials have been successfully synthesized via an effective two‐step procedure involving hydrothermal method and followed by a low‐temperature calcination treatment process, through which a controllable amount of carbonate‐like species could be incorporated into TiO₂. First‐principles calculations suggest the TiO₂ doped with carbon in form of carbonate‐like species can effectively extend the adsorption of the material from ultraviolet region to visible light. And it is experimentally found that carbon‐doped TiO₂ nanomaterials exhibit much higher photocatalytic activity than reference P25 and TiO_2?xN_x catalysts toward the liquid‐phase degradation of organic pollutants under visible light (420 nm < λ < 800 nm) irradiation. The presence of synergic effect between carbonate‐like doping and anatase TiO₂ is believed to play an essential role in affecting the photocatalytic reactivity, and the response to the visible light is ascribed to the narrowed band gap energy controlled by carbon doping. Moreover, the roles of active species in the photocatalytic process are compared using different types of active species scavengers. Meanwhile, the degradation mechanism of the photocatalysis is proposed. It is hoped that our work could provide valuable information on the design of carbonate‐like doped semiconductor with more excellent properties and set the foundation for the further industrial application.     

Preparation of transparent PVA/TiO2 nanocomposite films with enhanced visible-light photocatalytic activity

Polymer/semiconductor oxide nanocomposite films have been intensively investigated for various applications. In this work, we reported a simple hydrothermal method to fabricate highly transparent poly(vinyl alcohol)/titanium dioxide (PVA/TiO₂) nanocomposite films with enhanced visible-light photocatalytic activity. The as-prepared PVA/TiO₂ nanocomposite films showed high optical transparency in the visible region even at a high TiO₂ content (up to 40 wt.%). The determination of photocatalytic activity by photodegradation of methyl orange (MO) and colorless phenol showed that PVA/TiO₂ nanocomposite films exhibited enhanced visible-light photocatalytic activity and excellent recycle stability. This work provided new insights into fabrication of polymer/TiO₂ nanocomposites as high performance photocatalysts in waste water treatment.     

Simple fabrication of thermally stable apertured N-doped TiO2 microtubes as a highly efficient photocatalyst under visible light irradiation

Apertured N-doped TiO₂ microtubes have been fabricated by simple hydrolysis of titania tetrachloride using ammonia without any external templates. The morphology and microstucture characteristics of apertured N-doped TiO₂ microtubes were characterized by means of the specific surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of microtubes and mesoporous microstructure were maintained after a heat treatment at 723 K for 3 h, exhibiting significantly thermal stability. The catalysts exhibited high ultraviolet and visible light photocatalytic activity in degrading phenol and methyl orange.     

Graphene modified Nd/TiO2 photocatalyst for methyl orange degradation under visible light irradiation

A novel nanoscale GR–Nd/TiO₂ composite photocatalyst was synthesized by the hydrothermal method. Its crystal structure, surface morphology, chemical composition and optical properties were studied using XRD, TEM, and XPS, DRS and PL spectroscopy. It was found that graphene and neodymium modification shifts the absorption edge of TiO₂ to visible-light region. The results of photoluminescence (PL) emission spectra show that GR–Nd/TiO₂ composites possess better charge separation capability than do Nd/TiO₂ and pure TiO₂. The photocatalytic activity of prepared samples was investigated by degradation of methyl orange (MO) dye under visible light irradiation. The results show that the GR–Nd/TiO₂ composite can effectively photodegrade MO, showing an impressive photocatalytic activity enhancement over that of pure TiO₂. The enhanced photocatalytic activity of the composite catalyst might be attributed to the large adsorptivity of dyes, extended light absorption range and efficient charge separation due to Nd doping and graphene incorporation.     

N-doped TiO2 nanoparticles obtained by a facile coprecipitation method at low temperature

N-doped TiO₂ nanoparticles (NPs) were synthesized using a facile synthesis route by coprecipitation method. The effect of the HNO₃ volume and calcination temperature on the structural, morphological, optical and surface properties of the N-doped TiO₂ NPs was studied. X-ray diffraction analysis showed particles of nanometric size (< 16 nm), which are consistent with HR-TEM micrographs. A slight shift of the absorption edge to higher wavelengths is observed as the HNO₃ volume and calcination temperature increases. Both X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) show the presence and stability of nitrogen in the N-doped TiO₂ structure. The photocatalytic activity of the N-doped TiO₂ NPs was assessed by testing the degradation of rhodamine B (RhB) under ultraviolet (UV) and visible light.     

Fabrication of CdO–graphene embedded mesoporous TiO2 composite for the visible-light response and its organic dye remediation

ABSTRACT

In this study, mesoporous CdO–graphene and mesoporous TiO₂ were successfully synthesized using a facile method. The results indicated that photocatalytic activity can be enhanced with the combination of mesoporous CdO–graphene and mesoporous TiO₂. The photocatalytic performance of the mesoporous CdO–graphene–TiO₂ photocatalyst presents significantly improved photocatalytic activity of safranine O, reactive black B, and GA due to the improvement of the surface area and the small average pore size distribution of the as-prepared mesoporous CdO–graphene–TiO₂. The photodegradation rate was optimized by safranine O at a pH solution of 11 and by GA at the dosage amount of 0.07 g photocatalyst.     

Optimization of N-doped TiO2 multifunctional thin layers by low frequency PECVD process

A one-step low-frequency Plasma Enhanced Chemical Vapor Deposition (PECVD) process, operating at temperature as low as 350 °C, has been implemented to prepare single-oriented pure and N-doped anatase films. The layers have been synthesized using titanium isopropoxide as a precursor, and NH₃ as a doping agent. Optimized PECVD conditions have enabled to obtain homogeneous micro-columnar porous thin films with thicknesses close to 500 nm. Depth profiling XPS analyses have proved the nitrogen incorporation into TiO₂ lattice after ammonia introduction in the deposition chamber. As another proof of N-doping, Raman and XRD peaks shifting have been observed. Such thin films have been demonstrated as efficient photocatalytic materials which activity region can be tailored from UV to visible region by adjusting the proportion of doping agent in the plasma phase. Due to their microstructural and photocatalytic properties, the prepared thin layers should have an interest as anode materials in solar water splitting cells.     

Synthesis and characterization of carbon-doped titania as a visible-light-sensitive photocatalyst

The synthesis and use of carbon-doped TiO₂ particles in photocatalysis under visible light are demonstrated. The carbon-doped titania with its mesoporous structure was prepared by chemical modification and characterized by several techniques including X-ray diffraction, transmission electron spectroscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectra (EPR), and diffuse reflectance UV-Vis. absorption spectra, with emphasis on the effect of carbon as a doping compound to the titania. Based on EPR data, the photocatalytic activity by visible light can be ascribed to the trapping of electrons at interior sites of the carbon-doped titania between the valence and conduction bands in the titania band structure, and is able to activated by visible light of a wavelength of up to 550 nm. The photocatalytic activity of the carbon-doped TiO₂ nanoparticles was evaluated by examining the decomposition of phenol by irradiation with artificial solar light (>420 nm) and the results were compared with those using Degussa P25, a commercially available titania nanomaterial.     

Size Effect in Hybrid TiO2:Au Nanostars for Photocatalytic Water Remediation Applications

TiO₂:Au-based photocatalysis represents a promising alternative to remove contaminants of emerging concern (CECs) from wastewater under sunlight irradiation. However, spherical Au nanoparticles, generally used to sensitize TiO₂, still limit the photocatalytic spectral band to the 520 nm region, neglecting a high part of sun radiation. Here, a ligand-free synthesis of TiO₂:Au nanostars is reported, substantially expanding the light absorption spectral region. TiO₂:Au nanostars with different Au component sizes and branching were generated and tested in the degradation of the antibiotic ciprofloxacin. Interestingly, nanoparticles with the smallest branching showed the highest photocatalytic degradation, 83% and 89% under UV and visible radiation, together with a threshold in photocatalytic activity in the red region. The applicability of these multicomponent nanoparticles was further explored with their incorporation into a porous matrix based on PVDF-HFP to open the way for a reusable energy cost-effective system in the photodegradation of polluted waters containing CECs.     

One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

Photocatalytic Degradation of Organic Pollutants Under Visible Light Irradiation

Several TiO₂-based photocatalytic systems that have considerable visible light response have been developed, such as the photodegradation of organic pollutants on sensitized TiO₂ by visible light, construction of visible-light-active novel TiO₂ photocatalysts by matrix or surface modification. In this paper, we review briefly our recent progress in the TiO₂ photocatalytic degradation of organic pollutants by visible light, some related work by other groups is also involved.     

Facile preparation of flake-like blue TiO2 nanorod arrays for efficient visible light photocatalyst

Different kinds of oriented TiO₂ nanorod arrays have been actively pursuing in recent years, however, these fabrications relied on the substrates, such as fluorine-doped tin oxide glass (FTO), silicon wafer or other semiconductor precursor layer. Herein, a stable Ti³⁺ and oxygen vacancies doped blue TiO₂ flakes composed of oriented nanorod arrays were synthesized using a facile hydrothermal treatment in diluted hydrochloric acid solution. Such centimeter-scale flake-like TiO₂ product was obtained without any substrate. Since Ti³⁺ self-doped and/or oxygen vacancies TiO₂ could extend the absorption range of TiO₂ to visible light region, the blue TiO₂ sample exhibited excellent photocatalytic activity under visible light irradiation (photocatalytic degradation efficiency can nearly reach up to 100% within 60?min).     

Visible photocatalytic activity and photoelectrochemical behavior of TiO2 nanoparticles modified with metal porphyrins containing hydroxyl group

TiO₂ nanoparticles modified with 5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin (HTPP), 5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin zinc (ZnHTPP) and trans-dichloro-5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin tin (SnHTPP) were prepared in order to improve the visible photocatalytic activity of TiO₂ nanoparticles. The photocatalytic activity of the modified TiO₂ nanoparticles was investigated by carrying out the photodegradation of methyl orange in aqueous solution under visible light irradiation. The TiO₂ nanoparticles modified with SnHTPP show the highest visible photocatalytic activity with a degradation ratio of 86% of methyl orange after 180 min irradiation among three catalysts. This result indicates that the central metal ions in porphyrins can significantly influence the sensitization efficiency of porphyrins. In addition, the photoelectrochemical behavior of the modified TiO₂ nanoparticles was examined and related to their photocatalytic activity. Finally, the photocatalytic mechanism was discussed preliminarily.