Different degradation mechanisms of low-concentration ozone for MIL-100(Fe) and MIL-100(Mn) over wide humidity fluctuation.

The synergistic control of ozone and fine particulate matter is a research hotspot in the current environmental fields. Among the ozone removal, wide humidity fluctuation and low concentration dynamic adsorption are two thorny problems. In this work, MIL-100(Fe) and MIL-100(Mn), synthesized by hydrothermal and solvothermal methods respectively, were selected to investigate the degradation of flowing ozone pollutants. The samples showed different ozone degradation mechanisms, namely photocatalytic degradation and normal temperature degradation. Notably, MIL-100(Fe) exhibited more outstanding photocatalytic activity than MIL-100(Mn), while the normal temperature catalytic efficiency of MIL-100(Mn) was much superior to MIL-100(Fe). For different humidity conditions, MIL-100(Fe) has the optimal photocatalytic performance at 10% humidity, which is 38%, while MIL-100(Mn) has basically no change in normal temperature catalytic degradation efficiency at different humidity levels of 10-90%. Furthermore, the degradation mechanism was proposed by in-situ DRIFTS and ESR, which was significantly correlated with oxygen vacancy and photogenerated electron efficiency. By the aid of Temperature Programmed Desorption (TPD), a large quantity of Lewis acid sites was detected in MIL-100(Mn), which was the critical factor that the selected materials could maintain excellent normal temperature degradation performance under high humidity. This work will expand the practical application of ozone removal and improve the degradation efficiency.