Construction of bifunctional 2-fold interpenetrated Zn(ii) MOFs exhibiting selective CO2 adsorption and aqueous-phase sensing of 2,4,6-trinitrophenol

Abstract

Two new 3D, Zn(II)–organic frameworks, [{Zn(BINDI)_0.5(bpa)_0.5(H₂O)}·4H₂O]_n (MOF1) and [{Zn(BINDI)_0.5(bpe)}·3H₂O]_n (MOF2) (where H₄BINDI = N,N′-bis(5-isophthalic acid)naphthalenediimide, bpa = 1,2-bis(4-pyridyl)ethane and bpe = 1,2-bis(4-pyridyl)ethylene), have been successfully synthesized by room temperature self-assembly and structurally characterized. Both MOF1 and 2 show 2-fold interpenetrated 3D framework structures with 1D channels of dimensions 4.4 × 9.5 and 4.6 × 2.5 Ų respectively. Gas adsorption studies of the MOFs revealed selective and higher CO₂ uptake properties of MOF1 over 2 owing to the presence of a polar pore surface and an optimum pore size of 1 for CO₂ gas molecules. Furthermore, the high water stability and luminescence properties of MOF1 and 2 were exploited for sensing of nitroaromatic pollutants in water. Consequently, both the MOFs exhibit highly selective aqueous-phase sensing of 2,4,6-trinitrophenol (TNP) through a luminescence quenching mechanism. Furthermore, MOF1 exhibits a relatively higher efficiency of TNP detection (LOD = 0.6 ppm, K_sv = 4.9 × 10⁴ M⁻¹) compared to 2 (LOD = 1.5 ppm, K_sv = 1.29 × 10⁴ M⁻¹) due to higher resonance energy transfer between MOF1 and TNP owing to their better spectral overlap. Herein, the influence of N,N′-donor spacers on the structure, selective gas adsorption and the sensing properties of two new Zn(II) MOFs has been demonstrated.