Enhanced photocatalytic degradation of gaseous toluene and liquidus tetracycline by anatase/rutile titanium dioxide with heterophase junction derived from materials of Institut Lavoisier-125(Ti): Degradation pathway and mechanism studies

Abstract

Anatase/rutile titanium dioxide (TiO2) with heterophase junction and large Brunauer-Emmett-Teller (BET) specific surface area (50.1 m2 g−1) is successfully synthesized by calcinating Materials of Institut Lavoisier-125(Ti) (MIL-125(Ti)) with 30% O2/Ar at the temperature of 600 °C (M−O−600). Several techniques are used to examine the physicochemical, photoelectrochemical and optical properties of samples, and their photocatalytic performances are evaluated by photodegradation of gaseous toluene and liquidus tetracycline (TC) under visible light illumination. It is found that the calcination temperature has significant influence on the crystal structure and physicochemical parameters of TiO2. The weight fractions of rutile and anatase TiO2 of M−O−600 are approximately 0.7 and 0.3, which displays outstanding photocatalytic activity. Through the construction of heterophase junction, M−O−600 has better oxygen adsorption and higher density of localized states, which effectively promotes the generation of superoxide radical (·O2–) and hydroxyl radical (·OH) species. In-situ infrared spectra indicate that toluene is oxidized to benzyl alcohol, benzaldehyde and benzoic acid in turn and then oxidized to formic acid and acetic acid before eventually degraded into H2O and CO2. Gas chromatography-mass spectrometry (GC–MS) is also used to further investigate the degradation pathway of toluene. Degradation pathway and mechanism of TC are studied by liquid chromatography-tandem mass spectrometry (LC-MS). Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and total organic carbon (TOC) show that TC can be effectively mineralized through a series of reactions by M−O−600 during photocatalysis.