Intercalation compounds of a synthetic alkylammonium-smectite with alkanolamines and their unique humidity response properties

• Alkanolamine was successfully intercalated into the interlayer space of a hybrid.
• An alkylammonium group was anchored to a smectite-analogue moiety in the host hybrid.
• Coexistence of an alkylammonium group and alkanolamines was achieved.
• The prepared intercalation compounds exhibited a unique humidity response.

Triethanolamine (TEA) and diethylethanolamine (DEEA) were introduced into the interlayer space of a synthetic alkylammonium smectite (Synth A-Sm) in order to prepare novel intercalation compounds. The inorganic and organic moieties bond covalently with each other in Synth A-Sm. The intercalation compounds prepared (Synth A-Sm TEA and DEEA) showed unique humidity response. A wide range of preparation conditions was tested for the intercalation of the alkanolamines. Then it was revealed that the intercalation was achieved with alkanolamines/Synth A-Sm ratios x of 20–375 mmol/g from room temperature (RT) to 180 °C. X-ray diffraction (XRD) analysis showed that the basal spacing increased by the intercalation of TEA or DEEA in the interlayer space of the Synth A-Sm. The basal spacing was independent of x, indicating that TEA was intercalated less than or equal to the saturation value. The interlayer space of Synth A-Sm did not infinitely swell with the introduction of TEA. The basal spacing did not change under dry nitrogen flow in the case of the Synth A-Sm TEA compounds. On the other hand, the basal spacing decreased under dry nitrogen flow in the case of Synth A-Sm DEEA compounds. DEEA easily deintercalated under nitrogen flow at RT. Fourier transform infrared (FT-IR) spectra of the prepared intercalation compounds were simple superimpositions of the spectra of Synth A-Sm and the guest alkanolamines (TEA or DEEA).The Synth A-Sm TEA compounds prepared were characterized under controlled relative humidity. The XRD measurements indicated that the basal spacing was independent of the relative humidity. However, as relative humidity increased, the X-ray reflections from the Synth A-Sm TEA compounds drastically weakened. The XRD analysis was performed under repeated humidification-drying cycles. The XRD results revealed that the unique humidity response is reversible.

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