Silylation of layered double hydroxidesvia an induced hydrolysis method

Abstract

A series of layered double hydroxides (LDHs) based composites were synthesized by using an induced hydrolysis silylation (IHS) method, surfactant precursor method, in situcoprecipitation method, and direct silylation method. Their structures, morphologies, bonding modes and thermal stabilities can be readily adjusted by changing the parameters during preparation and drying processing of the LDHs. The characterization results show that the direct silylation reaction cannot occur between the dried LDHs and 3-aminopropyltriethoxysilane (APS) in an ethanol medium. However, the condensation reaction can proceed with a heating process between the adsorbed APS and LDHs plates. While using wet state substrates with and without surfactant and ethanol as the solvent, the silylation process can be induced by the hydrolysis of APS on the surface of the LDHs plates. Surfactants improve the hydrophobicity of the LDHs during the process of nucleation and crystallization, resulting in fluffy shaped crystals; meanwhile, they occupy the surface –OH positions and leave less “free –OH” available for the silylation reaction, favoring the formation of silylated products with a higher population in the hydrolyzed bidentate (T²) and tridentate (T³) bonding forms. These bonding characteristics lead to spherical aggregates and tightly bonded particles. All silylated products show higher thermal stability than those of pristine LDHs.