Surface modification of aqueous miscible organic layered double hydroxides (AMO-LDHs)

Abstract

Silane modification of layered double hydroxides (LDHs) plays an important role in controlling the surface hydrophobicity and improving the compatibility of LDHs dispersed in non-polar materials. However, the surface modification of conventional LDHs in hydrous conditions typically results in aggregated particle morphologies, low surface areas and accessible pore volumes. In this study, well dispersed and high surface area silane grafted AMO-Zn₂MgAl-CO₃ LDH were prepared using the silane coupling agents (triethoxyvinylsilane (TEVS), triethoxyoctylsilane (TEOS) and (3-glycidyloxypropyl)trimethoxysilane (TMGPS)) in anhydrous acetone. Solution ¹H NMR spectroscopy was initially used to study the rate and extent of silane reactivity with AMO-Zn₂MgAl-CO₃ LDH. Powder XRD, TEM, N₂ BET specific surface area and total pore volume measurements showed that the structure and morphology of silane-treated AMO-Zn₂MgAl-CO₃ LDHs remained largely unchanged. Solid state ¹³C CP-MAS, ²⁷Al DP-MAS and ²⁹Si CP-MAS NMR spectroscopy indicates that the silanes have been successfully grafted onto the surface of the LDH. In addition to maintaining their structure, morphology, high surface area and total pore volume, these surface-functionalised LDHs are now more hydrophobic, displaying a saturation water vapour uptake (<4 wt%) that is ca. 60% lower than the untreated AMO-LDH.