Degradation of gaseous unsymmetrical dimethylhydrazine by vacuum ultraviolet coupled with MnO2

Abstract

In this study, α-, β-, and δ-MnO₂ were prepared by a uniform hydrothermal method and then coupled with vacuum ultraviolet (VUV) for the degradation of gaseous unsymmetrical dimethylhydrazine (UDMH). The performance in the removal of UDMH, by-product distribution and mechanism were systematically investigated. The catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption/desorption, Field Emission Scanning Electron Microscopy (FE-SEM), Raman, thermogravimetry (TG), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) to investigate the factors affecting the catalytic activity. The results showed that O₂ and H₂O were essential for the removal of UDMH. Photooxidation and ozone catalytic oxidation contribute to the removal and mineralization of UDMH. The integrated process considerably improved the removal and mineralization of UDMH by ozone catalytic oxidation. More reactive oxygen species were generated in the integrated process. The catalytic activity of the prepared catalysts follows the order: δ-MnO₂ > α-MnO₂ > β-MnO₂. δ-MnO₂ displayed the highest removal rate of 100% and a CO₂ concentration of 42 ppmv. The good performance of δ-MnO₂ was mainly attributed to the large number of surface oxygen vacancies.