High surface area mesoporous nanocast LaMO3 (M = Mn, Fe) perovskites for efficient catalytic ozonation and an insight into probable catalytic mechanism

Abstract

Mesoporous nanocast perovskites (NC-LaMnO3and NC-LaFeO3) were synthesized by nanocasting technique using SBA-15 as a template and for the first time they were used in catalytic ozonation of 2-chlorophenol. For the purpose of comparison, uncast counterpart perovskites (CA-LaMnO3and CA-LaFeO3) as well as Mn3O4and Fe2O3were also prepared by conventional citric acid assisted route. Nanocast perovskites possessed high specific surface area and large pore dimensions than uncast perovskites. Catalytic activity in terms of TOC removal followed the order of NC-LaMnO3 > NC-LaFeO3 > CA-LaMnO3 > CA-LaFeO3 > Mn3O4 > Fe2O3 > O3with 80, 68, 50, 43, 39, 33% and 25% respectively. A detailed study is conducted to discuss the mechanism of catalytic ozonation of selected NC-LaMnO3perovskite by using organic and inorganic hydroxyl radical's quenchers, FTIR, florescence spectroscopy, EPR, ATR-FTIR, XPS, LSV, H2O2detection, Raman spectroscopy, TPR-H2, Rctvalue calculation, ozone utilization efficiency and ozone decomposition. It was found that hydroxyl radicals rather than surface peroxide, surface atomic oxygen, superoxide and singlet oxygen were the reactive oxygen species contributed to high catalytic activity. Moreover, high surface area as well as open porous structure of nanocast perovskites were believed to enhance the catalytic activity by surface reaction and easy access of reactants to the active sites.