Abstract:

Characterizations of microwave-induced titanate nanotubes (Na_xH_2−xTi₃O₇, TNTs) were conducted by the determinations of specific surface area (S_BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS), ionic coupled plasma−atomic emission spectrometry (ICP-AES), scanning electron microscopy/energy dispersive X-ray (SEM/EDX), and high-resolution transmission electron microscopy (HR-TEM). The applied level of microwave irradiation during the fabrication process is responsible for both the intercalation intensity of Na atoms into TNTs and the type of crystallization phase within TNTs, which dominate the efficiency of photocatalytic NH₃/NH₄⁺. A pure TNT phase presents no powerful ability toward photocatalytic NH₃/NH₄⁺, while the photocatalytic efficiency can be enhanced with the presence of a rutile phase within TNTs. In addition, the mixture of anatase and rutile phase within P25 TiO₂ prefers forming NO₃⁻, whereas TNTs yield higher NO₂⁻ amount. Regarding the effect of acid-washing treatment on TNTs, the acid-treated TNTs with enhanced ion exchangeability considerably improve the NH₃/NH₄⁺ degradation and NO₂⁻/NO₃⁻ yields. This result is likely ascribed to the easy intercalation of NH₃/NH₄⁺ into the structure of acid-washing TNTs so that the photocatalytic oxidation of intercalated NH₃/NH₄⁺ is not limited to the shielding effect resulting from the overload of TNTs.