Chemical modification of niobium layered oxide by tetraalkylammonium intercalation

Article abstract of DOI:10.1590/S0103-50532010000700024

Chemical modification of the layered K₄Nb₆O ₁₇ material was systematically investigated through the reaction of its proton-exchanged form (H₂K₂Nb₆O ₁₇) in alkaline solutions containing tetramethylammonium (tma ⁺), tetraethylammonium (tea⁺) or tetrapropylammonium (tpa⁺) cations. The intercalated amount reaches 50percent (for tma ⁺), 25percent (for tea⁺) and 15percent (for tpa⁺) of the H₂K₂Nb₆O₁₇ negative charge (concerning the exchange at interlayer I) due to the steric hindrance of larger cations. Hexaniobate samples present (020) basal reflections equal to 23.0, 26.3 and 26.5 A? once intercalated respectively with tma⁺, tea ⁺ and tpa⁺. When samples are heated above 200-250 °C, CO₂ evolution is observed; Hofmann elimination reaction is also detected for hexaniobate-tpa⁺ samples. Scanning electron microscopy images show the predominance of plate-like particles; stick-like particles are also observed for samples containing bulky ions. The intercalation reaction is promoted in the order tma⁺ > tea⁺ > tpa⁺, while the formation of a dispersion of colloidal particles is facilitated in the inverse order.