Al-MCM-41 synthesized from kaolin via hydrothermal route: structural characterization and use as an efficient adsorbent of methylene blue

The mesoporous material Al-Mobil Composition of Matter No. 41 (Al-MCM-41) was successfully obtained from kaolin, a low cost raw material, by means of hydrothermal route. The process of synthesis of Al-MCM-41 was based on calcination of kaolin, dealumination by acid treatment, hydrothermal synthesis in alkaline medium and surfactant extraction. The characterization of the obtained mesoporous material was carried out by techniques such as: X-ray diffraction, infrared vibrational spectroscopy, ²⁹Si and ²⁷Al solid state nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption. The X-ray diffraction at low angles allowed the determination of the cell parameter, which was 4.02 nm. The analyses of scanning and transmission electron microscopy revealed important morphological properties of the synthesized material. N₂ adsorption/desorption showed a Brunauer-Emmett-Teller (BET) specific surface area of 1,303 m² g^-1, pore volume of 1.23 cm³ g^-1 and average diameter of 2.45 nm. The mesoporous material presented a maximum adsorption capacity of 316 mg g^-1 for the cationic dye methylene blue (MB) in a concentration typical of industrial effluents, which makes it a potential adsorbent for MB removal from wastewaters. (author)