A controlled alkaline treatment of Al-SBA-15: a facile route to adjust the chemical composition and synthesize an ordered mesoporous carbon material, CMK-3, possessing strong pressure resistant capability

Abstract

The effect of an alkaline treatment on the mesoporous material Al-SBA-15 was investigated using powder X-ray diffraction (XRD), inductively coupled plasma (ICP) analysis, mid-infrared spectroscopy (IR), N₂ sorption isotherm measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM), solid state ²⁷Al MAS NMR analysis, and structural replicating technology. It was observed that elemental Si could be readily extracted from wall structures, and the Al-rich surface that was consequently exposed protected the uniform hexagonal arrays. The extracted substances rapidly accumulate inside the Al-SBA-15 mesopores and continuously dissolve and migrate into the alkaline solution upon a prolonged treatment time. Therefore, alkaline-treated Al-SBA-15 exhibits a larger pore size and a thinner wall than that before treatment. Due to its Al-rich surface and highly-open mesostructure, alkaline-treated Al-SBA-15 exhibits excellent catalytic performance in a low density polyethylene (LDPE) catalytic degradation reaction. The temperature corresponding to the maximum degradation rate was measured to be ∼10 K lower than that in raw Al-SBA-15. More importantly, the secondary-scale mesopores inside the Al-SBA-15 walls were remarkably expanded, allowing efficient penetration of the carbon precursor. Its structural replica, CMK-3, has a highly ordered mesostructure, which is attributed to the formation of enhanced carbon sticks that connect the primary carbon rods. For the same reason, CMK-3 templated from alkaline-treated Al-SBA-15 exhibits a strong pressure resistant capability. The reduction in the surface area and pore volume after high-pressure treatment were calculated to be as low as 4.5% and 3.0%, respectively.