N-Alkylation of amines by photocatalytic reaction in a microreaction system

A photocatalytic microreaction system was developed and photocatalytic N-alkylation process of benzylamine, aniline, and piperidine was examined. The reaction proceeded quite rapidly in the microreactors with immobilized Pt-free TiO₂ as well as Pt-loaded TiO₂, while it has been reported that the N-alkylation did not occur by the irradiation of Pt-free TiO₂ in conventional batch reactors. It was revealed that by using the unique features of the continuous-flow microreactor, for instance spatial illumination homogeneity and precise control of flow and irradiation conditions, one can control the selectivity of N-alkylation and N,N-dialkylation processes. These results suggest the possibilities of a photocatalytic microreaction system on organic synthetic reactions.     

Heterogeneous photocatalytic degradation of ethylene glycol and propylene glycol

The photocatalytic decomposition of ethylene glycol and propylene glycol was investigated by using UV-illuminated TiO₂ and metal-loaded TiO₂ catalysts. The effects of pH, initial concentration, and wavelength of light on the decomposition rate of the glycols were explored. Platinum-and palladium-loaded TiO₂ catalysts enhanced the rates of photodecomposition compared to unloaded TiO₂. The glycols were oxidized primarily to carbon dioxide and water. Formaldehyde was found to be an important reaction intermediate. A detailed chemical reaction mechanism for the destruction of ethylene glycol and propylene glycol in water via free radical pathway and trapped hole reactions at the particle surface is proposed.     

Effect of poly(ethylene glycol) additives on the photocatalytic activity of TiO2 films prepared by sol–gel processing and low temperature treatments

Photocatalytic activity of titania with poly(ethylene glycol) (PEG) in the sample films made under different operating conditions was investigated by kinetic analysis of photodegradation tests. The sample films, composed of PEG and nano-TiO₂ particles, were prepared by sol–gel processing and then treated thermally under an atmosphere of wet and dry air at different temperatures. After the thermal treatment, photocatalytic activities of the films were evaluated by a UV-exposure test. Results showed that the photoactivity was enhanced by processing in an atmosphere of wet air at 100 °C. Moreover, the presence of poly(ethylene glycol), and the change in surface morphology in the sample films were verified to be the most influential and significant factors to affect the photoactivitic activity.     

Low temperature preparation and characterization of nanospherical anatase TiO2 and its photocatalytic activity on Congo red degradation under sunlight

Nanospherical titanium oxide with anatase structure was obtained at low temperature and normal pressure using a simple method of preparation. The dilute titanium (III) chloride solution was stirred at room temperature for several hours, and then ammonium hydroxide with hydrogen peroxide was added. A yellow gel TiO₂·xH₂O was obtained with nanodot shape and amorphous structure. Heated at 300 °C, it crystallized to pure anatase structure with nanospherical shape. The anatase particles prepared show good adsorption and photodegradation of Congo red solution under the sunlight. Materials were characterized by powder X-ray diffraction, thermal analysis, transmission electron microscope and UV spectroscopy.     

Single-crystalline heterostructure of ZnO nanowire arrays on large Ag microplates and its photocatalytic activity

This paper presents experimentally a photocatalytic heterogeneous structure of high-density ZnO nanowire (NW) arrays grown on large Ag microplates. First, the dense single-crystalline ZnO NW fabricated using an economical hydrothermal method possess a great reactive surface area because of their high surface-to-volume ratio. In addition, the large Ag microplates synthesized using a simple and competitive growth method serve as an electron reservoir. The heterojunction between ZnO NW and Ag microplates forms a Schottky contact to separate the electrons from the photogenerated excitons in ZnO NW, prolonging the lifetime of excitons and enhancing their photocatalytic capability. The photodegradation experiment employs the methylene blue aqueous solution to reveal a kinetic rate constant of up to 6.60 × 10^?3 min^?1 at a low concentration of the ZnO/Ag heterogeneous structure on the ppm scale, and indicates an outstanding figure of merit of 1.02 × 10^?2 compared with previously reported ZnO/Ag heterogeneous structures.     

Hierarchical CuO/ZnO “corn-like” architecture for photocatalytic hydrogen generation

Novel high efficient photocatalyst is the key for photocatalytic hydrogen generation from water splitting. In this study, a novel hierarchical CuO/ZnO “corn-like” architecture was designed and synthesized via a combination of hydrothermal and photodeposition method. The as-prepared nanostructured materials was shown to effectively generate hydrogen in the mixture of methanol and water (v/v = 1:10). This is because the hierarchical CuO/ZnO “corn-like” architecture: 1) greatly enhances the light utilization rate due to its special architecture, 2) enlarges the specific surface area, providing more reaction sites and promoting mass transfer, 3) promotes the photogenerated electrons transfer from ZnO to CuO, achieving the anti-recombination effect of electrons and holes, and 4) avoids the photocorrosion of ZnO to improve the stability of ZnO as a catalyst during water splitting. Moreover, the novel hierarchical CuO/ZnO “corn-like” architecture is easily recovered for reuse.     

Facile ion-exchanged synthesis of Sn incorporated potassium titanate nanoribbons and their visible-light-responded photocatalytic activity

Sn²⁺-incorporated potassium titanate (K₂Ti₆O₁₃) nanoribbons were prepared by a facile acid-free ion-exchanged method in a dehydrated methanol solution at room temperature. XRD patterns suggested that K₂Ti₆O₁₃ (KTO) and Sn²⁺-incorporated KTO (SKTO) are well crystallized with monoclinic phase structures. The mole ratio of incorporated Sn²⁺ to K⁺ in SKTO was estimated to be 2. X-ray photoelectron spectrum showed that the Sn species of SKTO consisted of 90% of Sn²⁺ and 10% of Sn⁴⁺, suggesting that part of Sn²⁺ was oxidized to Sn⁴⁺ in the incorporation process. The band gap of SKTO was 0.7 eV narrower than that of KTO, which was derived from lift of the top of the valence band due to the hybridization of Sn5s and O2p orbitals. The SKTO nanoribbons showed remarkable photocatalytic activities for H₂ evolution and rhodamine B degradation under visible light irradiation (λ ≥ 420 nm). The photocatalytic mechanism and durability were studied in detail. The advantage of this acid-free ion-exchange method is ease of ion-exchange of K⁺ with H⁺ and maintenance of the integrity of the 1D nanoribbon structures. This method can be applied to preparation of other Sn²⁺-incorporated compounds with special nanostructures.     

Effects of the preparation order of the ternary P25/GO/Pt hybrid photocatalysts on hydrogen production

In this study, ternary P25/GO/Pt hybrid photocatalysts are prepared in different orders, using Degussa's TiO₂ (P25), graphene oxide (GO), chloroplatinic acid as precursor. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). This work is first time to compare the hydrogen production of the ternary P25/GO/Pt hybrid photocatalysts prepared in different orders. We focus on studying the introduction of GO and find that the quantity of introduced GO and electronic transfer path play an important role in photocatalytic activity on ternary P25/GO/Pt hybrid catalysts. When the proper Pt particle loaded on the flat surface of GO which was 0.5wt% of P25, the highest H₂ evolution was obtained.     

Photocatalysis of TiO2 nanoparticles supported on natural zeolite

Abstract

In order to achieve rapid and efficient decomposition of organic pollutants and put it to wastewater treatment, the composite materials of nanoTiO₂ powder immobilised on zeolite were synthesised. Moreover, the effects of technology parameters, such as TiO₂ loading content, calcining temperature and ultrasonic treatment, on photocatalytic reactivity were examined. The proposed research investigates the following aspects, which are important in understanding the preparation and application of TiO₂/zeolite composite photocatalysts: nanosize TiO₂ particles were supported on natural zeolite by a simple sol–gel method in order to maximise the photocatalytic performance of the nanosize TiO₂ as well as reduce the preparation cost; and the effects of TiO₂ loading content, calcining temperature and ultrasonic treatment on photocatalytic reactivity were researched. The novel aspect of the proposed photocatalysts is the combination of nanosize TiO₂ particles and natural zeolite by a simple sol–gel method. The product of the research can be used in wastewater treatment resolving the difficulties of TiO₂ recovery and surface contact based photocatalytic reaction.     

Preparation and characterization of perovskite-type Titania-bearing blast furnace slag photocatalyst

Perovskite-type titania-bearing blast furnace slag (TBBFS) photocatalysts were prepared by the high-energy ball milling method at different calcination temperatures. The particle size and ultraviolet light-absorption capacity of titania-bearing blast furnace slag powders increased with increase in the calcination temperature. Its photocatalytic activity was checked through the photocatalytic reduction of Cr(VI) as a model compound under ultraviolet–visible light irradiation. Titania-bearing blast furnace slag powders calcined at 700 °C showed a higher catalytic activity compared to other titania-bearing blast furnace slag catalysts, indicating that the increase in calcination temperature could improve their photocatalytic activities.