Al-MCM-41 Synthesized from Kaolin via Hydrothermal Route: Structural Characterization and Use as an Efficient Adsorbent of Methylene Blue

Abstract

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, 29 Si and 27 Al solid state nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy and N 2 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. N 2 adsorption/desorption showed a Brunauer-Emmett-Teller (BET) specific surface area of 1,303 m 2 g-1 , pore volume of 1.23 cm 3 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.

Acetylation of Eugenol on Functionalized Mesoporous Aluminosilicates Synthesized from Amazonian Flint Kaolin

“…XRD patterns of AlSiM exhibited four peaks (1 intense and 3 weaks) at low 2θ values that can be indexed as (100), (110), (200) and (210) reflections characteristics of mesoporous materials with hexagonal arrangement of their cylindrical channels [40][41][42]; even after calcination (540 • C) there was no collapse of the structure. The Si/Al molar ratio of AlSiM obtained, which was close to 23, is suitable to form mesoporous silicas with well-defined structures, which have a high silicon content [28,38]. These results according with data found in literature, proving well-ordered formation of the structures with Si/Al molar ratio equal to 13.8 [53], Si/Al of 20 [28], Si/Al of 29.3 [42] and Si/Al of 32.1 [38].…”

“…The Si/Al molar ratio of AlSiM obtained, which was close to 23, is suitable to form mesoporous silicas with well-defined structures, which have a high silicon content [28,38]. These results according with data found in literature, proving well-ordered formation of the structures with Si/Al molar ratio equal to 13.8 [53], Si/Al of 20 [28], Si/Al of 29.3 [42] and Si/Al of 32.1 [38].…”

“…[25,43,44]. Due to the dealuminization process caused by acid leaching of metakaolin flint (MF), in KF there is a mass a Si/Al ratio close to 1, in metakaolin flint leached (MFL) this ratio rises to 13 [28,38], while in the synthesized AlSiM it showed a Si/Al of 23 much higher than its precursor MFL. The data in Table 1 also shows the presence of SO 3 for (3)SO 3 H/AlSiM and (5)SO 3 H/AlSiM, indicating that sulfonic groups are present in the AlSiM structure [28,50]…”

“…However, these silica precursors have some disadvantages such as toxicity and the high cost of producing the material [36,37]. For economic and environmental reasons, the search for a synthesis procedure using alternative sources of silica, such as high purity kaolin, has been intensified aiming to obtain mesoporous material with a well-defined hexagonal arrangement [38][39][40][41][42]. Additionally, the waste from the kaolin processing [28] has proven to be an excellent source of silicon and aluminum for synthesis of highly ordered Al-MCM-41.…”

“…As mentioned above, we have examples of work reporting the use of natural kaolinite as starting materials to synthesize Al-MCM-41. Generally, Al-MCM-41 exhibits a very high Si/Al molar ratio, and tends to show a decrease in the number of acid sites, thus reducing catalytic efficiency in reactions requiring a strong acid catalyst [24,28,38]. However, this problem can be solved by heteropoly acid impregnation [24,45] and anchoring of sulfonic groups [28] on the structure of Al-MCM-41 as an alternative method to obtain a high acid catalyst.…”