Kinetically controlled ammonia vapor diffusion synthesis of a Zn(ii) MOF and its H2O/NH3 adsorption properties†
A unique method for synthesizing a Zn(II) complex Zn(INA)2(H2O)4 (INA = isonicotinate) has been developed by kinetically controlled ammonia (NH3) vapor diffusion at low temperatures without any external energy input. The pH gradient caused by ammonia diffusion from the gas phase to the liquid phase affords an appropriate environment for the rapid, catalytic-like growth of single crystals. This provides a novel method for the synthesis of complex crystal films by an interface reaction. It was found that the three-dimensional MOF Zn(INA)2 obtained by dehydration of Zn(INA)2(H2O)4 could capture ammonia under dry conditions, without any influence on the structure, over several cycles. Interestingly, Zn(INA)2 can co-adsorb H2O and NH3 to form a new material, Zn(INA)2(H2O)2(NH3)2, in moist ammonia. In addition, the amount of NH3 adsorbed by Zn(INA)2 was 6 mmol g−1 whether under dry or moist conditions, and the adsorbent could only be regenerated without performance loss by heating. This particular ammonia adsorption property of Zn(INA)2 has advantages in ammonia capture over other MOFs, which show structural instability.