Synthesis of porous Al pillared montmorillonite after pre-intercalation with dodecylamine: textural and thermal properties

Al pillared montmorillonites (Al-PILM) were synthesized by the reaction of Na⁺-montmorillonite (Na⁺-Mt) and hydroxy-Al cation after pre-intercalation with dodecylamine (DA) under different drying methods and calcination temperatures. The results showed that Al-PILM dried at room temperature was more crystalline and had larger c-axis spacing, d₍₀₀₁₎, BET specific surface area (S_BET) and microporous volume, compared to those by common air-blast drying or vacuum drying and the superiority in the above properties of the drying methods is as follows: air drying > air-blast drying > vacuum drying. This suggests that natural air drying at room temperature favored the formation of more ordered pillar formation. It was also found that the pre-intercalation of DA had important influence on the physicochemical properties of Al-PILM. When the amount of pre-intercalated DA was 1/2 CEC of Na⁺-Mt, c-axis spacing, d₍₀₀₁₎, S_BET and microporous volume of Al-PILM were increased and larger than those prepared without pre-intercalation of DA and the former sample had a more regularly ordered pillar distribution due probably to the reduced pillar density in the montmorillonite interlayers. The DA pre-intercalated PILMs were stable at a larger range of temperatures. With the increase of calcination temperature, the interlayer spacing d₍₀₀₁₎ value decreased, and the S_BET and microporous volume increased firstly and then decreased. During calcination, the pre-intercalated DA was removed and the hydroxyl-Al cation was converted into the rigid Al₂O₃ pillars, which resulted in decreased pillar size between Mt layers followed by porosity improvement of Al-PILM.