Microwave-Assisted Synthesis of Titanate Nanotubes Loaded with Platinum with Enhanced Selectivity for Photocatalytic H2 Evolution from Methanol

Abstract

Titanate nanotubes (TNTs) fabricated through microwave-assisted synthesis were examined for their ability to catalyze hydrogen production from a 20% v/v methanol solution under UV and visible light irradiation. Herein, TiO2 was used not only as the raw material for TNT synthesis but also as a reference support to compare its performance with that of TNTs. The UV–Vis spectral analyses of the TNT composites showed greater shifts toward the visible region after Pt loading than the spectra of Pt/TiO2. Moreover, using the Kubelka–Munk equation and Tauc Plot method, we determined that the direct allowed transition in TNT composites was more probable than the indirect allowed transition. The photocatalytic performances were evaluated by measuring the hydrogen production, and the experimental results showed that Pt/TNTs exhibited higher activity than Pt/TiO2. Furthermore, bare TNTs and Pt/TNTs showed lower CO generation than bare TiO2 and Pt/TiO2. As such, TNT composites enhanced the photocatalytic selectivity for H2 generation from formic acid to a greater extent than Pt/TiO2, because the kinetic diameter of CO (0.38[Formula: see text]nm) is larger than that of CO2 (0.33[Formula: see text]nm). This result may be attributed to the inability of CO to diffuse into the pores of TNTs because of the diameter difference. Also, XPS results showed negative shifts of Pt binding energies and positive shifts of Ti binding energies due to the strong metal-support interaction between Pt and TNTs. Thus, the remarkably high photocatalytic efficiency of TNT composites facilitates their application as promising photocatalysts.