Hydrazine-based synergistic Ti(III)/N doping of surfactant-templated TiO2 thin films for enhanced visible light photocatalysis

Abstract

This study reports the preparation of titanium (Ti3+) and nitrogen co-doped cubic ordered mesoporous TiO2 thin films using N2H4 treatment. The resulting co-doped TiO2 (Ti3+-N-TiO2) thin films show significant enhancements in visible light absorption and photocatalytic activity. Cubic ordered mesoporous TiO2 thin films were prepared via a sol-gel method with Pluronic F127 as the pore template. After brief calcination, the TiO2 films were dipped into hydrazine hydrate which acts both as a nitrogen source and as a reducing agent, followed by heating at low temperature (90 °C). The hydrazine treatment period was varied from 5 to 20 h to obtain different degrees of reduction and nitrogen doping. X-ray photoelectron spectroscopy (XPS) analyses and UV–vis absorbance spectra of Ti3+-N-TiO2 films indicate that the incorporated N atoms and Ti3+ reduce the band gap of TiO2 and thus enhance the absorption of visible light. The corresponding visible light photocatalytic activity of Ti3+-N-TiO2 films was determined from the photocatalytic degradation of methylene blue under visible light illumination (at 455 nm). The Ti3+-N-TiO2 films prepared with 10 h of treatment show the optimum photocatalytic activity, with a pseudo-first order rate coefficient of 0.12 h−1, which is 3 times greater than that of undoped TiO2 films. Calcination temperature and time were varied prior to hydrazine treatment to confirm that a brief calcination at low temperature (10 min at 350 °C) gave the best photochemical activity. In photoelectrochemical water oxidation using a 455 nm LED, the Ti3+-N-TiO2 films prepared with 10 h of N2H4 treatment show about 4 times the photocurrent compared to undoped TiO2 films. The present study suggests that hydrazine induced doping is a promising approach to enable synergistic incorporation of N and Ti3+ into the lattice of surfactant-templated TiO2 films and enhanced visible light photoactivity, but that the benefits are limited by gradual mesostructure deterioration.