Preparation of Ag@AgCl-doped TiO2/sepiolite and its photocatalytic mechanism under visible light

A cube-like Ag@Ag Cl-doped TiO_2/sepiolite(denoted Ag@Ag Cl–TiO_2/sepiolite) was successfully synthesized via a novel method. X-ray diffraction, scanning electron microscopy, energy dispersion X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and diffuse reflectance ultraviolet–visible spectroscopy were performed to determine the structure and physicochemical properties of Ag@Ag Cl–TiO_2/sepiolite. SEM micrographs revealed that Ag@Ag Cl nanoparticles and TiO_2 film are well deposited on the surface of tube-like sepiolite. As a result, Ag@Ag Cl–TiO_2/sepiolite exhibits a red shift relative to TiO_2/sepiolite. Photocatalytic experiments demonstrated that the dosage of catalysts plays an important role during photocatalysis. The photoelectrochemical activities of Ag@Ag Cl–TiO_2/sepiolite and TiO_2/sepiolite were also investigated. Photocurrent responses confirmed that the ability of Ag@Ag Cl–TiO_2/sepiolite to separate photo-generated electron–hole pairs is stronger than that of TiO_2/sepiolite. Methylene Blue degradation is also improved under alkaline conditions and visible light irradiation because more UOH is produced by visible light excitation.This excellent catalytic ability is mainly attributed to the formed Ag nanoparticles and the Schottky barrier at the Ag/TiO_2 interface. Active species analysis indicated that UO2-and h+are implicated as active species in photocatalysis. Therefore, catalysts are excited to produce abundant electron–hole pairs after they absorb photons in photocatalysis.     

Photoelectrochemical performance of birnessite films and photoelectrocatalytic activity toward oxidation of phenol

Birnessite films on fluorine-doped tin oxide(FTO) coated glass were prepared by cathodic reduction of aqueous KMnO_4. The deposited birnessite films were characterized with X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy.The photoelectrochemical activity of birnessite films was investigated and a remarkable photocurrent in response to visible light was observed in the presence of phenol, resulting from localized manganese d–d transitions. Based on this result, the photoelectrocatalytic oxidation of phenol was investigated. Compared with phenol degradation by the electrochemical oxidation process or photocatalysis separately, a synergetic photoelectrocatalytic degradation effect was observed in the presence of the birnessite film coated FTO electrode.Photoelectrocatalytic degradation ratios were influenced by film thickness and initial phenol concentrations. Phenol degradation with the thinnest birnessite film and initial phenol concentration of 10 mg/L showed the highest efficiency of 91.4% after 8 hr. Meanwhile, the kinetics of phenol removal was fit well by the pseudofirst-order kinetic model.