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 (SBET) 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), SBET 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 SBET 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.