Novel Lu-doped Bi2WO6 nanosheets: Synthesis,growth mechanisms and enhanced photocatalytic activity under UV-light irradiation

Polycrystalline systems of lutetium doped bismuth tungstates Bi₂WO₆: Lu (Lu at% 0, 2, 5 and 8) were synthesized using the coprecipitation method, followed by thermal treatment at 500 °C. The Bi₂WO₆:Lu samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-Ray analysis (EDS) and UV–vis diffuse reflectance spectra (DRS). The XRD and SEM analyses showed that the as-prepared samples crystallized in the same orthorhombic structure and consist of agglomerated nanosheets. To characterize the photocatalytic activities, UV–visible spectrometry was used to analyze the evolution of Rhodamine B photodegradation in presence of the Bi₂WO₆: Lu photocatalysts. The characteristic absorption band of Rhodamine B at 554 nm shifted to lower wavelengths under UV irradiation. The pure Bi₂WO₆ and the 5% Lu doped Bi₂WO₆ photocatalysts presented the lowest and highest efficiencies, respectively. An interpretation of improved photocatalytic efficiencies was proposed.     

片状 Bi／Bi2WO6光催化剂的制备及其可见光响应活性

以硝酸铋、钨酸铵为原料,通过水热法制得片状Bi2 WO6,通过KBH4对Bi2 WO6进行还原,生成Bi单质沉积在表面的Bi／Bi2 WO6光催化剂。采用TEM, XRD和UV－Vis DRS分析了催化剂的组成、形貌和光吸收性能。以罗丹明B为模拟污染物,研究了所得Bi／Bi2 WO6的可见光驱动催化活性。结果表明, Bi沉积可有效提高Bi2 WO6可见光催化降解活性。     

The synthesis of biotemplate-based Bi2WO6/TiO2 composite photocatalyst for degradation of microcystin

Microcystin is a harmful hepatic toxin produced by cyanobacteria, is a serious threat due to its toxicity to water ecosystems, and it is found recently that TiO₂ photocatalyst is effective in degradation of microcystin. In this study, hierarchical porous Bi₂WO₆/ TiO₂ composite photocatalysts were synthesized with a novel hydrothermal method by using rice husk as the biological template. The results showed that the original micro- and nanopores of rice husk were efficiently replicated by the synthesized porous TiO₂ photocatalyst with a specific surface area of 137.09 m²/g, which increased by nearly 100 m²/g over the surface area. SEM, TEM, XRD, and XPS spectra showed that heterogeneous structures were formed by Bi₂WO₆ and TiO₂, with which process the crystal structures of both were not affected. In the meantime, we studied the effect of hierarchical porous TiO₂ photo-catalyst, pure TiO₂ photo-catalyst, Bi₂WO₆ photo-catalyst, Bi₂WO₆/ hierarchical porous TiO₂ photo-catalyst on degradation of 1 mg/L MC-LR, and the results showed that to use the unique silicon-carbon structure of rice husk to prepare hierarchical porous TiO₂ photo-catalyst can have the degradation rate of 53.5%, which is higher than that of commercially available TiO₂ photo-catalyst by 13.8%. Compared with a single photo-catalyst, the photo-catalytic activity of Bi₂WO₆/ hierarchical porous TiO₂ photo-catalyst is significantly improved. The optimal mingling amount of Bi₂WO₆ is 0.2 mol/mol. At this time, the degradation rate of MC-LR is 85.3%, and the main active substances for degradation are h+ and ·OH. In addition, the degradation process of MC-LR fit well with the kinetic model of Quasi Primary Reaction. The insight of green synthesis of Bi₂WO₆/ TiO₂ composite photocatalysts for degradation of microcystins was provided by this study.     

Enhanced Solid‐Phase Photocatalytic Degradation Activity of a Poly(vinyl chloride)‐TiO2 Nanocomposite Film with Bismuth Oxyiodide

A new type of photodegradable poly(vinyl chloride)‐bismuth oxyiodide/TiO₂ (PVC‐BiOI/TiO₂) nanocomposite film was prepared by embedding a nano‐TiO₂ photocatalyst modified by BiOI into the commercial PVC plastic. The solid‐phase photocatalytic degradation behavior of the as‐prepared film was investigated in ambient air at room temperature under UV light irradiation, with the aid of UV‐Vis spectroscopy, weight loss monitoring, scanning electron microscopy, and FT‐IR spectroscopy. Compared to the PVC‐TiO₂ nanocomposite film, the PVC‐BiOI nanocomposite film and the pure PVC film, the PVC‐BiOI/TiO₂ nanocomposite film exhibited a higher photocatalytic degradation activity. The optimal mass ratio of BiOI to TiO₂ was found to be 0.75 %. The weight loss rate of the PVC‐BiOI/TiO₂ nanocomposite film reached 30.8 % after 336 h of irradiation, which is 1.5 times higher than that of the PVC‐TiO₂ nanocomposite film under identical conditions. The solid‐phase photocatalytic degradation mechanism of the nanocomposite films was briefly discussed.     

Fabrication of TiO2 nanofibers assembled by Bi2WO6 nanosheets with enhanced visible light photocatalytic activity

A series of Bi₂WO₆/TiO₂ nanofibers (BT NF) hierarchical photocatalysts were synthesized by a facile two-step strategy consisting of electrospinning technique and subsequent solvothermal method. The results showed that the secondary two-dimensional Bi₂WO₆ nanosheets were uniformly assembled onto the surface of the TiO₂ NF. It was also verified that the density of Bi₂WO₆ nanosheets could be tailed by controlling the precursor concentration during the solvothermal process. Photocatalytic tests demonstrated that BT NF with a low concentration of precursor (S1) possessed a much higher visible light degradation rate for Rhodamine B than TiO₂ NF, Bi₂WO₆ and their mixture. The enhanced photocatalytic activity of S1 was ascribed to the extension of the light absorption region induced by the introduction of narrow band gap Bi₂WO_6, and the formation of heterojunction accelerating the interfacial charge separation. Moreover, BT NF with a high concentration of precursor (S2) manifested a higher photocatalytic activity than S1 due to the higher loading of Bi₂WO₆ nanosheets. S2 could be reused by sedimentation, and the photocatalytic activities of S2 were retained with a slight decline after four cycles, which confirmed its stability. Therefore, BT NF composites will be ideal candidates for highly efficient and recyclable photocatalysts for the treatment of organic pollutants under visible light.     

Influence of TiO2‐Layer Thickness of Spray‐Coated Glass Beads on Their Photocatalytic Performance

TiO₂ is a suitable catalyst for potential photocatalytic processes, e.g., in wastewater treatment. For a technical realization of such processes, the application of immobilized TiO₂ in a continuous process would be desirable. However, since UV radiation has a limited penetration depth into a packed bed of pure TiO₂, supporting it on UV‐transparent glass beads offers the possibility to implement continuous photocatalytic processes in a fixed‐bed reactor. Considering this fact, glass beads were coated with TiO₂ powder in a fluidized‐bed reactor. The coated glass beads with varying TiO₂ layer thickness were tested in the photocatalytic degradation of methylene blue, and the influence of an addition of methyl cellulose during the coating process on the photocatalytic performance was investigated.     

Preparation and Characterization of Bi3+‐TiO2 and its Photocatalytic Activity

Bi³⁺‐TiO₂ photocatalysts were prepared by doping bismuth ion into the TiO₂ structure in a sol‐gel process. The catalyst samples were then characterized by UV‐vis diffuse reflectance spectra (DRS), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Rodamine‐B (RhB) was used in this study as a model chemical with the aim of organic pollutants control. The photocatalytic degradation of RhB demonstrated that an optimal loading of bismuth 0.7 at. % achieved the highest photodegradation rate, with the rate constant increasing by a factor of 3.89 over neat TiO₂ (P25) under UV illumination (λ ≥ 320 nm). The degradation of p‐nitrobenzonic acid (pNBA) was also examined to prevent/preclude/exclude/ the photosensitization pathway. GC‐MS results show that pNBA can be effectively degraded and minerized to small molecules, such as quinone, acetic acid and formic acid.     

Flexible Porous SiO2–Bi2WO6 Nanofibers Film for Visible‐Light Photocatalytic Water Purification

Advancement of the synthetic performance of photocatalysts in environmental applications has been the most clinging pursue in relevant research fields. In this article, we propose a novel design strategy of an efficient visible‐light photocatalyst with versatile advantages for environmental remediation. Flexible SiO₂ nanofibers were prepared with sol–gel and electrospinning techniques, followed by uniform anchoring of Bi₂WO₆ nanoplatelets on the fibers’ surface, forming unique hierarchical SiO₂–BiWO₆ composite fibers. Benefitting from the combination of the advantages from both the SiO₂ nanofibers and the Bi₂WO₆ nanoplatelets, the film composed of SiO₂–Bi₂WO₆ fibers simultaneously possess high visible‐light photocatalytic reactivity, good flexibility, and excellent thermal stability, affording many potential applications especially in environmental remediation. Water purification performance of the SiO₂–Bi₂WO₆ fibers film was evaluated here as an application example, and the results demonstrated are intriguing.     

Enhanced Visible Light Photocatalytic Activity of Curcumin‐Sensitized Perovskite Bi0.5Na0.5TiO3 for Rhodamine 6G Degradation

Curcumin‐sensitized perovskite Bi_0.5Na_0.5TiO₃ (BNT) was synthesized for visible light photocatalytic decolorization of rhodamine 6G (Rh6G). Cube‐shaped perovskite BNT was synthesized by solid‐state route, and curcumin sensitization was performed using hydrothermal method. The surface sensitization of curcumin was analyzed by UV–Vis absorption spectra and FTIR. The degradation kinetics of Rh6G over Cur‐BNT were investigated and discussed through first‐order Langmuir–Hinshelwood kinetic model. The effect of catalyst dose on photocatalytic decolorization process was investigated. Photocatalysis was performed with different scavengers to investigate the role of active hole and radical species and photocatalytic degradation mechanism of Rh6G.     

Photocatalytic degradation of 3‐nitrobenzenesulfonic acid in aqueous TiO2 suspensions

The photocatalytic degradation of 3‐nitrobenzenesulfonic acid in the presence of solar radiation and artificial UV radiation with suspended TiO₂ was studied in a batch and continuous annular reactor, respectively. The effects of catalyst loading, pH, presence of anions and cations and initial concentration on the rate of photocatalytic degradation were investigated. Concentration–time data were correlated with the rate equation d[C_t=0]/dt = k_rK[C_t=0]/(1 + K[C_t=0]). Studies were carried out to compare the photolytic, photochemical and photocatalytic methods of degradation. Copyright © 2005 Society of Chemical Industry     

Core@dual‐Shell Nanoporous SiO2–TiO2 Composite Fibers with High Flexibility and Its Photocatalytic Activity

Structural design is of great importance to the performance of photocatalysts in environmental remediation. Therefore, micro/nanofibrous morphology and nanoporous local structures have been found to be beneficial to improve the photocatalytic activity. In this investigation, we report the design and fabrication of flexible and thermal stable nanoporous SiO₂–TiO₂ composite fibers as efficient photocatalysts. Combining electrospinning and modified Stöber techniques, core‐shell and mesoporous SiO₂ fibers with high flexibility were fabricated and employed as the scaffold for supporting TiO₂ nanoparticles. A nanoporous shell of TiO₂ nanoparticles was then muffled over the SiO₂ fibers to form core@dual‐shell SiO₂–TiO₂ composite fibers with hierarchically porous structure, which were conveniently patterned into a nonwoven, recyclable film. This nonwoven film exhibits better photocatalytic activity for Rhodamine B degradation under UV irradiation compared with some other TiO₂‐based materials reported in recent years.     

siRNA Modified with 2′‐Deoxy‐2′‐C‐methylpyrimidine Nucleosides

(2′S)‐2′‐Deoxy‐2′‐C‐methyluridine and (2′R)‐2′‐deoxy‐2′‐C‐methyluridine were incorporated in the 3′‐overhang region of the sense and antisense strands and in positions 2 and 5 of the seed region of siRNA duplexes directed against Renilla luciferase, whereas (2′S)‐2′‐deoxy‐2′‐C‐methylcytidine was incorporated in the 6‐position of the seed region of the same constructions. A dual luciferase reporter assay in transfected HeLa cells was used as a model system to measure the IC₅₀ values of 24 different modified duplexes. The best results were obtained by the substitution of one thymidine unit in the antisense 3′‐overhang region by (2′S)‐ or (2′R)‐2′‐deoxy‐2′‐C‐methyluridine, reducing IC₅₀ to half of the value observed for the natural control. The selectivity of the modified siRNA was measured, it being found that modifications in positions 5 and 6 of the seed region had a positive effect on the ON/OFF activity.     

Gasphasensynthese von Kern/Mantel‐Partikeln am Beispiel von TiO2‐Nanopartikeln mit elektrisch leitendem Mantel

An advanced process enables synthesis and coating of individual TiO₂‐core particles with a shell of transparent conducting oxide (TCO) from the gas phase in one reactor. TiO₂ particles were coated with fluorine‐doped tin oxide (SnO₂:F) or antimony‐doped tin oxide (SnO₂:Sb). Specific electrical conductivity of the core/shell particles was up to 8 · 10^–3 S cm^–1. Variation of process parameters allows modifying dopant level and conductivity in an easy way.     

Photocatalytic oxidation of 4‐nitrophenol in aqueous TiO2 slurries: an experimental validation of literature kinetic models

The photocatalytic oxidation of 4‐nitrophenol in the presence of solid TiO₂ has been studied in an annular reactor. The experiments have been performed in both acidic and basic solutions (pH = 3 and 8.5) at different catalyst loads and temperatures. The concentration–time data have been correlated with the rate equation: −d[R]/dt = k₀k₂[R]/(1 + k₂[R]) in order to evaluate the unknown parameters. The laws of dependence of the parameters k₀ and k₂ on catalyst load and temperature have been interpreted in the terms of detailed kinetic models proposed in the literature. The results throw some light on the different reaction mechanisms occurring on varying the operating conditions. © 2000 Society of Chemical Industry     

Effect of Carbon Nanotubes and Carbon Nanotubes/Gold Nanoparticles Composite on the Photocatalytic Activity of TiO2 and TiO2‐SiO2

A carbon nanotube (CNT)/gold nanoparticle (NP) nanocomposite was synthesized by simultaneously reducing the Au ions and depositing Au NPs on the surface of a CNT. The functional groups were investigated with Fourier transform infrared spectra. From the Raman spectra, the D‐band and G‐band of the CNT were identified. The deposition of nanometer‐sized Au NPs on the CNT sites was observed by transmission electron microscopy. The photodegradation of methylene blue (MB) in aqueous solutions was studied using various photocatalysts, including TiO₂, TiO₂‐SiO₂, CNT/TiO₂, CNT/TiO₂‐SiO₂, Au/TiO₂, CNT‐Au/TiO₂, and CNT‐Au/TiO₂‐SiO₂ composites. CNT addition leads to a synergic effect, improving the photoactivity of the catalysts. A possible physically based mechanism was proposed involving the reduction of electron‐hole recombination and fast electron‐transfer possibility.