Particulate matter capturing over manganese dioxides with different crystal structures

Particulate matter (PM) is the main contributor to air pollution, and filtration has been reported to be promising for PM capturing. Considering the complexity of polluted air (volatile organic compounds (VOCs) and ozone are likely concomitant with PM particles) and in view of the versatility of MnO 2 for the degradation of VOCs and ozone, the feasibility of MnO 2 materials as PM filtering media was investigated in this study, and the effect of crystal structure on PM filtration was clarified. Compared with the layered δ-MnO 2 , the MnO 2 with tunnel structure (including 1 × 2-, 2 × 2- and 3 × 3-MnO 2 ) exhibited greatly enhanced PM removal efficiencies, and particularly, the 3 × 3-MnO 2 possessed not only significant activity for adsorbing PM particles but also high utilization efficiency of the active surface. Physicochemical properties of the adsorbents were studied by XRD, ATR, isothermal N 2 adsorption, SEM and (HR)TEM. The correlation between pore characteristics and particle elimination activity demonstrates that the most developed mesoporous structure of the 3 × 3-MnO 2 sample played an important role in strengthening the PM adsorption capability. Further comparison of the surface properties of the fresh and spent samples reveals that with respective to the occasion of δ-MnO 2 , the structure of 3 × 3-MnO 2 was robust enough to resist collapse after PM capturing and the great accommodation of the inorganic and organic PM substances in the voluminous pores induced strong affinity between PM particles and 3 × 3-MnO 2 . Thereby, a higher particle filtration ability was retained.