Ultrathin BPH Nanosheets with Exceptional Water Adsorption Properties

Abstract

The synthesis of ultrathin BPH zeolite nanosheets from an aluminosilicate colloidal suspension using exclusively inorganic structure directing agents under mild conditions is reported. The improved synthesis yields nanosheets of 4–7 nm and a Si/Al ratio of 1.5; combined 3D electron diffraction and DFT calculations reveal the spatial distribution of extra-framework cations throughout the microporous structure. The ultrathin BPH nanosheets exhibit high and regular intersheet mesoporosity, and substantially improved thermal stability. The notable mesoporosity bestows exceptional water adsorption behavior typically unseen for zeolites; the as-prepared material consists of up to 49% adsorbed H₂O by weight and adsorbs up to 32 wt % H₂O at 90% relative humidity. ²H MAS NMR spectroscopy identifies different types of O²H environments ascribed to silanol species exhibiting two motion behaviors. H₂O sorption analysis demonstrates reproducible behavior over multiple cycles and low temperature regeneration, making the ultrathin BPH nanosheets attractive candidates for gas drying and membrane applications.