SYNTHESIS AND CHARACTERIZATION OF ORDERED MESOPOROUS MCM-41 FROM NATURAL CHLORITE AND ITS APPLICATION IN METHYLENE BLUE ADSORPTION

Mesoporous materials have a wide range of applications in the fields of nanotechnology, biotechnology, information technology, and medicine, but historically, the resource materials used for their synthesis have been expensive. Natural silicate minerals are characterized by their abundance, low cost, and large SiO 2 contents, making them an alternative silicon source for mesoporous silica. The objective of the present study was to determine the utility of natural chlorite as the source of Si for synthesizing hexagonal mesoporous silica materials (MCM-41). The natural chlorite was pretreated by acid leaching and calcination, followed by a hydrothermal reaction with cetyltrimethylammonium bromide (CTAB) as the template, and subsequent calcination to prepare MCM-41. The structures and the porosity of MCM-41 were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 29 Si magic-angle spinning solid-state nuclear magnetic resonance spectroscopy ( 29 Si MAS NMR), and N 2 adsorption–desorption measurements. The mechanism of structural evolution from natural chlorite to MCM-41 was investigated using these techniques. Calcination of chlorite results in amorphization and partial structural breakdown, while subsequent acid leaching dissolves the Mg and Al in the octahedral sheets to leave the Si–O framework as a silicon source. 29 Si MAS NMR results revealed that the ratio of Q 4 /Q 3 increased from 0.91 to 1.21 after hydrothermal synthesis of MCM-41 from leached chlorite, demonstrating more polymerization of the Si–O structure in MCM-41. The final MCM-41 products were amorphous SiO 2 , with a large surface area of 630 m 2 /g, a pore volume of 0.46 mL/g, and a narrow pore-size distribution of 2.8 nm. MCM-41 showed favorable adsorption toward methylene blue (MB) with a monolayer adsorption capacity of up to 302 mg/g, indicating potential for application in adsorption.