Abstract
Arrays of titania nanotubes (TiO2NTs) were developed by electrochemical anodization and doped with silver on their surface by photodeposition to achieve TiO2NTs/Ag. It is found that only anatase TiO2NTs were formed, with the preferential growth direction perpendicular to the titanium substrate, and with the length and diameter of ~2 µm and 90–120 nm, respectively. The presence of Ag on the surface of TiO2NTs was also confirmed. The TiO2NTs and TiO2NTs/Ag were used as photocatalysts to decolorize the methylene blue (MB) aqueous solution. The photodegradation efficiency (PDE) is as high as 83% for TiO2NTs and 98% for TiO2NTs/Ag photocatalysts. This work focused on the investigation of the stability and recyclability of these photocatalysts in terms of efficiency and its physical origin by surface analysis using X-ray photoelectron spectroscopy (XPS). It is found that PDE diminishes from 83% to 76% in TiO2NTs upon eight recycling runs and from 98% to 80% in TiO2NTs/Ag upon six recycling runs. The XPS analysis revealed that the physical origin of diminishing efficiency is the carbon contamination on the surface of recycled TiO2NTs and a combination of carbon contamination and Ag leaching in recycled TiO2NTs/Ag.
Highlights
Titania nanotubes (TiO2 NTs) continue to attract attention from researchers interested in photocatalytic degradation of organic pollutants in water
We present a study primarily focused on an exploration of the physical origin of diminishing photocatalytic efficiency of TiO2 NTs and TiO2 NTs/Ag after repeated recycling runs
The electrochemically anodizedTiO2 NTs and TiO2 NTs loaded with varying amounts of Ag (TiO2 NTs/Ag) were used as UV-driven photocatalysts for the degradation of an organic pollutant (MB) in aqueous solution
Summary
Titania nanotubes (TiO2 NTs) continue to attract attention from researchers interested in photocatalytic degradation of organic pollutants in water. The parent material TiO2 is stable and inexpensive and the TiO2 NTs have several physical properties ideal for photodegradation: their ordered porous architecture, with a unidirectional electrical channel, large surface area, and long charge carrier lifetime [1–7]. Two well-known drawbacks of using TiO2 in solar photocatalysis applications are: (i) its wide band gap, which requires UV frequencies to initiate the charge transfer mechanism and (ii) the rapid electron hole recombination rate of photogenerated carriers [8–12]. Isolated impurities can provide absorbing defect states that may improve the problem (i). These localized states can relieve problem (ii) by trapping one carrier while the other escapes. There is an enormous literature describing the effects of metallic, and nonmetallic, dopants on the optical and electrical properties of composite TiO2 [17–20]
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