Interlayer spacing in pillared and grafted MCM-22 type silicas: density functional theory analysis versus experiment

Area of Science:

• Materials Science
• Computational Chemistry
• Nanotechnology

Background:

• Synthetic layered crystalline silicates and aluminosilicates are crucial for adsorption and separation.
• Pillaring these materials is a known strategy to improve their performance.
• Understanding pillaring in synthetic materials aids in studying natural clays.

Purpose of the Study:

• To investigate the pillaring of a pure silica polymorph of MCM-22 type molecular sieve using first-principles calculations.
• To determine the effect of different pillaring configurations on interlayer spacing.
• To compare computational findings with experimental data for similar materials.

Main Methods:

• First-principles density functional theory (DFT) calculations were employed.
• A precursor material, MCM-22P, with hydroxylated layers was used.
• A simplified pillaring agent, (EtO)3SiCH3, was utilized to model the reaction with hydroxyl groups.

Main Results:

• Pillaring reduced the interlayer spacing of MCM-22 by 2.66 Å compared to MCM-22P.
• Bridging pillaring agents increased interlayer spacing by 2.52 Å (50% coverage) and 2.46 Å (100% coverage).
• Grafted pillaring agents resulted in a smaller interlayer spacing expansion of 2.17 Å.

Conclusions:

• Computational results for interlayer spacing are consistent with experimental observations.
• Pillaring significantly modifies the interlayer spacing of MCM-22 type materials.
• The study provides insights into the structural changes induced by pillaring in layered silicates.