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.     

A precursor route to prepare tantalum (V) nitride nanoparticles with enhanced photocatalytic activity for hydrogen evolution under visible light

Nanoparticulate Ta₃N₅ was prepared by nitridation of nanoparticulate Ta₂O₅ precursor in an attempt to improve the photocatalytic activity for H₂ evolution from aqueous methanol solution under visible light (λ > 420 nm). When platinum (Pt) was deposited in situ as a H₂ evolution cocatalyst, the as-prepared Ta₃N₅ with a primary particle size of 30–50 nm exhibited enhanced activity, three times higher than that of bulk Ta₃N₅ particles 300–500 nm in size. The improvement in activity arises from a lower density of defect sites, which is favorable for electron migration from the Ta₃N₅ bulk to the surface and/or for electron transfer from the conduction band of Ta₃N₅ to the loaded Pt.     

Onion-like carbon modified porous graphitic carbon nitride with excellent photocatalytic activities under visible light

A series of onion-like carbon modified porous g-C₃N₄ (OLC/pg-C₃N₄) composites have been fabricated by a simple ultrasonic adsorption approach. The resultant OLC/pg-C₃N₄ composites exhibit excellent photocatalytic activity and stability towards the degradation of the dyes and phenol in aqueous solution under visible-light irradiation. The composite with 2.0 wt% OLC content shows the optimal photocatalytic activity for degrading rhodamine B (RhB), its rate constant is about three times that of pure pg-C₃N₄. The improved photocatalytic activity is mainly attributed to the synergetic effect of pg-C₃N₄ and OLC, including larger surface area, stronger visible light adsorption and efficient separation of photogenerated electrons and holes. Moreover, a possible mechanism of photocatalytic reaction over OLC/pg-C₃N₄ composite is proposed.     

The synthesis of Ag/AgCl/BiFeO3 photocatalyst with enhanced visible photocatalytic activity

A novel AgCl/Ag/BiFeO₃ photocatalyst was synthesized via an ultrasonic-assisted precipitation-photoreduction method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence emission spectra (PL) analysis were implemented to characterize the composition, morphology, structure, and optical property of the as-synthesized photocatalyst. For the decomposition of methyl orange (MO) and other organic dyes, AgCl/Ag/BiFeO₃ photocatalyst manifested much superior visible-light catalytic activity than pure BiFeO₃ and AgCl/Ag. Based on the trapping experiments and band structure analysis, a probable Z-scheme light catalytic mechanism was proposed.     

Selective photocatalytic degradation of azodyes in NiO/Ag3VO4 suspension

BACKGROUND: This work deals with the development of an active heterogeneous catalyst for selective organic synthesis under both visible light and UV irradiation to utilize efficiently solar light. Very few studies have been reported on the selective photooxidation performance of multimetal oxide materials under visible light irradiation. The photocatalytic degradation of azodyes was investigated systematically in aqueous NiO/Ag₃VO₄ dispersion under visible light irradiation. RESULTS: The catalyst NiO/Ag₃VO₄ showed high activity and selectivity for the photodegradation of the nonbiodegradable azodyes acid red B, reactive brilliant red X‐3B, and acid orange 7. From total organic carbon (TOC), Fourier transform infrared spectroscopy (FTIR), and gas chromatography/mass spectroscopy analyses, the tested azodyes were selectively oxidized into aromatic and aliphatic acids without any decrease of TOC. The high photooxidation selectivity also applied to UV light irradiation. Electron spin resonance and radical scavenger studies suggest that the anionic superoxide radical O₂^?? was the predominant active species in the photocatalytic reaction. CONCLUSION: The selectivity of NiO/Ag₃VO₄ for the oxidation of azodyes was not affected by the energy of light (UV and visible light). This approach allows effective controlled oxidation but avoids undesirable mineralization into CO₂ and H₂O. Copyright © 2010 Society of Chemical Industry     

Photocatalytic reduction of water by TaON under visible light irradiation

Some noble metals have been studied as H₂ evolution promoters for TaON, a visible light driven oxynitride photocatalyst. H₂ evolution on TaON photocatalyst under visible light irradiation (420 nm≤λ≤500 nm) in an aqueous methanol solution was found to be remarkably enhanced by adding Ru as a noble metal co-catalyst.     

Hydrothermal synthesis, characterization, and photocatalytic performances of Cr incorporated, and Cr and Ti co-incorporated MCM-41 as visible light photocatalysts for water splitting

A series of Cr incorporated, and Cr and Ti co-incorporated MCM-41 photocatalysts were synthesized by hydrothermal method. X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence analysis (XRF), N₂ adsorption–desorption isotherms and Raman spectra were used to investigate the effects of the incorporated elements on the structure of MCM-41. The experimental results for photocatalytic water splitting under visible light irradiation (λ > 430 nm) demonstrated that the photocatalytic activities of Cr-MCM-41 and Cr-Ti-MCM-41 catalysts for hydrogen production decreased with an increase in the amount of Cr incorporated. Compared with the Cr-MCM-41 which had the same amount of incorporated Cr, the Cr-Ti-MCM-41 exhibited much higher hydrogen evolution activities.     

Fabrication of CdS and CuWO4 modified TiO2 nanoparticles and its photocatalytic activity under visible light irradiation

CdS and CuWO₄ modified TiO₂ nanoparticles (CdS–CuWO₄-TiO₂) were prepared by the chemical impregnation method. The as-prepared nanoparticles were characterized using UV–visible-diffuse reflectance spectroscopy (UV–vis-DRS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and B.E.T. surface area analysis techniques. The photocatalytic activity was evaluated based on the degradation of a dye (eosin-Y) and inactivation of a bacterium (Pseudomonas aeruginosa). The results revealed that CdS–CuWO₄-TiO₂ showed high photocatalytic activity over CdS-TiO₂, CuWO₄-TiO₂ and TiO₂. Moreover the reusability and stability of the photocatalyst for the degradation of eosin-Y was also studied.     

Fullerene modification CdSe/TiO2 and modification of photocatalytic activity under visible light

CdSe, CdSe-TiO₂, and CdSe-C₆₀/TiO₂ composites were prepared using sol–gel method, and their photocatalytic activity was evaluated by measuring the degradation of rhodamine B solutions under visible light. The surface area, surface structure, crystal phase, and elemental identification of these composites were characterized by nitrogen adsorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and UV-visible (vis) absorption spectrophotometry. XRD showed that the CdSe-C₆₀/TiO₂ composite contained a typical single and clear anatase phase. SEM of the CdSe-C₆₀/TiO₂ composites revealed a homogenous composition in the particles. EDX revealed the presence of C and Ti with strong Cd and Se peaks in the CdSe-C₆₀/TiO₂ composite. The degradation of dye was determined by UV–vis spectrophotometry. An increase in photocatalytic activity was observed and attributed to an increase in the photoabsorption effect by fullerene and the cooperative effect of the CdSe. The repeatability of photocatalytic activity was also tested in order to investigate the stability of C₆₀ and CdS-C₆₀/TiO₂ composites.     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

Novel spindle-shaped nanoporous TiO2 coupled graphitic g-C3N4 nanosheets with enhanced visible-light photocatalytic activity

Highly efficient visible-light-driven heterojunction photocatalysts, spindle-shaped nanoporous TiO₂ coupled with graphitic g-C₃N₄ nanosheets have been synthesized by a facile one-step solvothermal method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption analysis and UV–vis diffuse reflectance spectrometry (DRS), proving a successful modification of TiO₂ with g-C₃N₄. The results showed spindle-shaped nanoporous TiO₂ microspheres with a uniform diameter of about 200 nm dispersed uniformly on the surface of graphitic g-C₃N₄ nanosheets. The g-C₃N₄/TiO₂ hybrid materials exhibited higher photocatalytic activity than either pure g-C₃N₄ or nanoporous TiO₂ towards degradation of typical rhodamine B (RhB), methyl blue (MB) and methyl orange (MO) dyes under visible light (>420 nm), which can be largely ascribed to the increased light absorption, larger BET surface area and higher efficient separation of photogenerated electron–hole pairs due to the formation of heterostructure. In addition, the possible transferred and separated behavior of electron–hole pairs and photocatalytic mechanisms on basis of the experimental results are also proposed in detail.     

Synthesis of cube-like Ag/AgCl plasmonic photocatalyst with enhanced visible light photocatalytic activity

Cube-like Ag/AgCl plasmonic photocatalyst was successfully synthesized through a one-pot precipitation method by simply adding an aqueous solution of AgNO₃ into the natural hot spring, wherein the hot spring acted as the chlorine source. The cube-like Ag/AgCl with a size of 0.5–0.9 μm exhibited enhanced visible light photocatalytic performance for the degradation of organic MO dye due to the localized surface plasmon resonance (LSPR) of the photoexcited Ag species. The trapping experiments confirmed that O₂⁻ and h⁺ were the main active species during the photocatalytic process.     

The visible light induced photocatalytic activity of tungsten trioxide powders

The preparation, characterization and photoreactivity of tungsten trioxide powders are presented. Tungsten trioxide powders were prepared by air annealing of various W precursors. The effects of W precursor type and pretreatment conditions on the physical properties, and photocatalytic performance of the obtained WO₃ powders were examined. The photooxidation of water to oxygen and protons in the presence of reducible additives Ce⁴⁺, using the luminous and near IR illumination was used as a test reaction to evaluate the activity of the powders. Increasing annealing temperatures gave materials with a high degree of crystallinity and red-shifted the onset of light absorption. The light absorption of the obtained powders in the long wavelength region versus the type of the W precursor increased in the order: H₂WO₄<(NH₄)₆W₁₂O₃₉<(NH₄)₁₀W₁₂O₄₁. The level of crystallinity of the obtained powders increased in the order: (NH₄)₁₀W₁₂O₄₁≈(NH₄)₆W₁₂O₃₉2WO₄. The activity of the WO₃ powders depended on the type of W precursor used, annealing conditions, and the physico-chemical characteristics of the resulting powders. The activity according to the types of the W precursor increased in the order: (NH₄)₁₀W₁₂O₄₁<(NH₄)₆W₁₂O₃₉2WO₄. The activity as a function of annealing temperature and duration of W precursors goes through a maximum at 700–800°C and 4–8 h, respectively. Increasing the specific surface area of WO₃ powders, did not alter the activity significantly. Addition of 0.1–1% Pt and RuO₂ as co-catalysts improved the initial rates and long-term activity by about 1.3–1.5 times. Small amounts of hydrogen were also produced from photochemical reactions involving the photoexcitation of Ce³⁺.     

Hydrothermal synthesis of Ag2CO3-TiO2 loaded reduced graphene oxide nanocomposites with highly efficient photocatalytic activity

Abstract

In this work, a growth of Ag₂CO₃-TiO₂ NPs over GO sheets and reduction of GO were simultaneously achieved by the hydrothermal process at 130 °C for 4?h. The photocatalytic activity of the as-prepared Ag₂CO₃-TiO₂ NPs decorated reduced graphene oxide (Ag₂CO₃-TiO₂/rGO) composite was studied by the degradation of methylene blue (MB) solution under visible light irradiation. A remarkable enhancement in the photocatalytic activity of the TiO₂ was achieved after sensitizing with Ag₂CO₃ and loading in rGO sheets which is attributed to the reduced charge recombination, enhanced dye adsorption, and the improvement in the light harvesting capacity of the composite.     

Preparation of hollow porous Cu2O microspheres and photocatalytic activity under visible light irradiation

Cu₂O p-type semiconductor hollow porous microspheres have been prepared by using a simple soft-template method at room temperature. The morphology of as-synthesized samples is hollow spherical structures with the diameter ranging from 200 to 500 nm, and the surfaces of the spheres are rough, porous and with lots of channels and folds. The photocatalytic activity of degradation of methyl orange (MO) under visible light irradiation was investigated by UV-visible spectroscopy. The results show that the hollow porous Cu₂O particles were uniform in diameters and have an excellent ability in visible light-induced degradation of MO. Meanwhile, the growth mechanism of the prepared Cu₂O was also analyzed. We find that sodium dodecyl sulfate acted the role of soft templates in the synthesis process. The hollow porous structure was not only sensitive to the soft template but also to the amount of reagents.     

Preparation of Cu2O/exfoliated graphite composites with high visible light photocatalytic performance and stability

Cu₂O/exfoliated graphite composites (Cu₂O/EG (1 wt%), Cu₂O/EG (4 wt%), Cu₂O/EG (7 wt%), Cu₂O/EG (10 wt%), and Cu₂O/EG (15 wt%)) were prepared by the precipitation method. The photocatalytic activity of the material was evaluated using the decolorization of methyl orange (MO) solution as model reaction. Results showed that Cu₂O deposited on the worm-like flakes of EG in the form of nanocrystals. The EG provided a three-dimensional environment for photocatalytic reaction and endowed a high adsorption capacity for the sample. Under optimal conditions, the decolorization efficiencies of MO for 60 min reached 96.7%. Recycling of the catalyst showed Cu₂O/EG composites (10 wt%) to possess high photocatalytic efficiency even when repeatedly used for five times.     

Photocatalytic effect of carbon-modified n-TiO2 nanoparticles under visible light illumination

The present research focused on wet process synthesis of visible light active carbon-modified (CM)-n-TiO₂ nanoparticles and their photocatalytic activity. The CM-n-TiO₂ was synthesized by hydrolysis of TiCl₄ in the presence of tetrabutylammonium hydroxide and also in the presence of glucose and sodium hydroxide. UV–vis spectra, X-ray diffraction (XRD), and FT-IR were used to characterize these photocatalysts. It was found that the CM-n-TiO₂ nanoparticles synthesized by hydrolysis with tetrabutylammonium hydroxide or with sodium hydroxide and glucose when subjected to extended aging and subsequent calcinations absorb well into the visible to near infrared region up to 800 nm and exhibit enhanced visible light photocatalytic activity on degradation of 4-chlorophenol. CM-n-TiO₂ synthesized using glucose as the carbon source generated 13-fold increase in the initial rate of photodegradation of 4-chlorophenol compared to those by regular n-TiO₂, whereas, it increased only eight-fold when tetrabutylammonium hydroxide was used as the carbon source.     

Silver-modified TiO2 nanorods with enhanced photocatalytic activity in visible light region

Silver-modified TiO₂ nanorods (SMTN) have been synthesized via controlled hydrolysis of tetrabutyltitanate (TBOT) in ethanol and immersion method by using AgNO₃ as an Ag source. The physical and chemical properties of SMTN were studied by XRD, SEM, TEM, and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of the as-prepared products was evaluated by photocatalytic decolorization of Rhodamine B (Rh B) aqueous solution at ambient temperature under visible light irradiation. The experimental results reveal that the TiO₂ nanorods, which are well dispersed and uniform, attached large numbers of silver nanoparticles on the surface, and the major crystalline phase of TiO₂ is anatase. The photocatalytic activity research shows that the SMTN exhibit an enhanced photocatalytic activity in visible light region compared with that of pure TiO₂ nanorods and commercial TiO₂ (P25).