Rational Design of a Bifunctional, Two‐Fold Interpenetrated Zn^II‐Metal–Organic Framework for Selective Adsorption of CO₂ and Efficient Aqueous Phase Sensing of 2,4,6‐Trinitrophenol

Abstract

A bifunctional, microporous Zn^II metal-organic framework, [Zn₂ (NH₂ BDC)₂ (dpNDI)]_n (MOF1) (where, NH₂ BDC=2-aminoterephthalic acid, dpNDI=N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) has been synthesized solvothermally. MOF1 shows an interesting two-fold interpenetrated, 3D pillar-layered framework structure composed of two types of 1D channels with dimensions of approximately 2.99×3.58 Å and 4.58×5.38 Å decorated with pendent -NH₂ groups. Owing to the presence of a basic functionalized pore surface, MOF1 exhibits selective adsorption of CO₂ with high value of heat of adsorption (Q_st =46.5 kJ mol^-1 ) which is further supported by theoretically calculated binding energy of 48.4 kJ mol^-1 . Interestingly, the value of Q_st observed for MOF1 is about 10 kJ mol^-1 higher than that of analogues MOF with the benzene-1,4-dicarboxylic acid (BDC) ligand, which establishes the critical role of the -NH₂ group for CO₂ capture. Moreover, MOF1 exhibits highly selective and sensitive sensing of the nitroaromatic compound (NAC), 2,4,6-trinitrophenol (TNP) over other competing NACs through a luminescence quenching mechanism. The observed selectivity for TNP over other nitrophenols has been correlated to stronger hydrogen bonding interaction of TNP with the basic -NH₂ group of MOF1, which is revealed from DFT calculations. To the best of our knowledge, MOF1 is the first example of an interpenetrated Zn^II -MOF exhibiting selective adsorption of CO₂ as well as efficient aqueous-phase sensing of TNP; investigated through combined experimental and theoretical studies.