Distinct features of organosilyl-grafted pendant groups attached in the RUB-18 interlayer space

Abstract

Two distinct methods to graft the silylating agent 3-cyanopropyltriclorosilane (CN) in the interlayer space of the layered silicate Na-RUB-18, with composition Na₂Si₈O₁₇·nH₂O, are described. The organosilylation was carried out by reflux and solvent evaporation methodologies, using the intercalated surfactant cetyltrimethylammonium after sodium exchange as one intermediate (CTA-RUB-18) and the acidic form (H-RUB-18) as the other intermediate. The resulting silylated derivatives obtained by both methods possessed basal spacings of 1.19 and 1.54 nm, and 1.26 and 1.16 nm, starting from CTA-RUB-18 and H-RUB-18, with the reflux and solvent evaporation methods, respectively. A favourable condition for this immobilization methodology is the use of small amounts of the silylating agent, with six times less than the previous procedure. The maximum amount of the silane attached to the RUB-18 surface, based on analytical results considering the nitrogen content, gave the values 5.64, 4.16, 4.37 and 4.05 mmol g⁻¹, respectively. All preparation processes were followed by elemental analyses and X-ray diffraction and the organofunctionalizations were confirmed through chemical and thermogravimetric data. The presence of pendant chains covalently bonded to the inorganic RUB-18 layers was confirmed by ¹³C and ²⁹Si NMR spectroscopy. The inorganic-organic hybrids have the ability for divalent cation removal from aqueous solutions at the solid/liquid interface. The series of adsorption isotherms were favourably adjusted to the Freundlich equation, demonstrating the applicability of these synthesized chemically modified layered materials.