Structural response of organically modified layered niobate K4Nb6O17 to the adsorption of 2,4-dichlorophenol

We investigated structural alteration of organically modified layered hexaniobate K₄Nb₆O₁₇ upon adsorption of 2,4-dichlorophenol. Two adsorbents examined were hexaniobate intercalated with dodecylammonium (C₁₂N) or dioctadecyldimethylammonium (2C₁₈2MeN) ions. The adsorbent modified with the C₁₂N ions was structurally durable for the adsorption of 2,4-dichlorophenol from 0.4 to 10 mmol dm^?3 aqueous solutions. The adsorbate molecules were accommodated among the pre-intercalated C₁₂N moieties. In contrast, the adsorbent intercalated with the 2C₁₈2MeN ions suffered from structural collapse with the uptake of adsorbate molecules from relatively concentrated solutions (10 mmol dm^?3), although this sample adsorbed larger amount of 2,4-dichlorophenol than the niobate modified with C₁₂N ions. X-ray diffraction and IR spectroscopy showed that the 2C₁₈2MeN ions were deintercalated with the adsorption. However, liquid chromatography and total organic carbon analysis indicated that the deintercalated organic moiety stayed on the external surface of niobate to form an effective adsorption site of 2,4-dichlorophenol. The “deintercalative adsorption” was ascribed based on UV spectroscopy to a specific interaction between the adsorbate and 2C₁₈2MeN molecules. Such drastic structural response had not been reported for other organically modified layered adsorbents.