Sonophotocatalytic degradation of dinitrotoluenes and trinitrotoluene in industrial wastewater

Oxidative degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using ultrasonic irradiation combined with UV/TiO2, wherein a synergistic effect is observed. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonophotocatalytic behavior, including ultrasonic power intensity, TiO2 dosage, reaction temperature and oxygen dosage. It is remarkable that the nitrotoluene contaminants could be almost completely eliminated by virtue of sonophotocatalysis, wherein TiO2 serves as both photocatalysts and nuclei, leading to enhancement of cavitation bubble numbers. Based on the result given by pyrolysis/gas chromatograph–mass spectrometer (Pyrolysis/GC–MS), it is postulated that DNTs adsorbed on TiO2 preliminarily undergo denitration pathway into o-mononitrotoluene (MNT) or oxidation pathway into 1,3-dinitrobenzene (DNB), respectively. Further, according to the spectra obtained from GC–MS, it is proposed that DNTs existed in wastewater proceed with similar reaction pathways as those adsorbed on TiO2. Besides, sonophotocatalytic degradation of 2,4,6-TNT results in the formation of 1,3,5-trinitrobenzene (TNB). Transparently, the sonophotocatalytic technique is promising for direct treatment of wastewater from TNT manufacturing process.

► US/UV/TiO2 is more efficient than US and UV/TiO2 on the elimination of nitrotoluenes.
► There are dual functions played by TiO2, i.e. photocatalysts and cavitation nuclei.
► DNTs adsorbed on TiO2 undergo denitration or oxidation pathway into o-MNT and 1,3-DNB.
► Sonophotocatalytic degradation of 2,4,6-TNT results in the formation of 1,3,5-TNB.