Synthesis of poly(methacrylic acid)–manganese oxide dihydroxide/silica core–shell and the corresponding hollow microspheres

Abstract

Poly(methacrylic acid)–MnO(OH)2/SiO2 core–shell microspheres were prepared by sol–gel hydrolysis of tetraethylorthosilicate (TEOS) in the presence of poly(methacrylic acid)–Mn(II) (PMAA–Mn2+) as template with ammonium hydroxide anion as catalyst and n-octadecyltrimethoxysilane (C18TMS) as pore-directing reagent. The PMAA–Mn2+ core was prepared by incubation of Mn2+ cations with PMAA microspheres via the coordination between carboxylate anion group on PMAA microsphere and Mn2+ cations. During this process, the Mn(II) species were formed as white Mn(OH)2 precipitates at first, which were subsequently oxidized into brown MnO(OH)2 in air. The Mn2O3/mesoporous silica (Mn2O3/m-SiO2) double-shelled hollow microspheres (DSHMs) were prepared through calcination of the PMAA–MnO(OH)2/SiO2 core–shell microspheres at 600°C for the selective removal of PMAA template and pore-directing organic component from C18TMS, during which the crystalline structure of DSHM was developed into Braunite-1Q via the reaction between Mn2O3 inner-shell and silica outer-shell by annealing the DSHMs under higher temperatures of 800 and 900°C. The Mn2O3 hollow microspheres (HMs) were prepared through the selective removal of the silica layer from the DSHMs by sodium hydroxide aqueous solution, which exhibited structure integrity and good ethanol dispersity due to the presence of mesoporous structure.