Luminescent Cd(ii)–organic frameworks with chelating NH2 sites for selective detection of Fe(iii) and antibiotics

Abstract

Excess and deficiency of iron(III) and antibiotics from normal permissible limits will induce serious disorders, so their detection is important but challenging. In this work, by introducing a new amino triazole ligand N¹-(4-(1H-1,2,4-triazole-1-yl)benzyl)-N¹-(2-aminoethyl)ethane-1,2-diamine (L), a series of Cd(II)-based metal–organic frameworks (MOFs) [Cd₃(BDC)₃(DMF)₂] (1), [Cd(L)(BDC)]₂·2DMF·H₂O (2), [NaCd₂(L)(BDC)_2.5]·9H₂O (3), [Cd₂(L)(2,6-NDC)₂]·DMF·5H₂O (4) and [Cd₂(L)(BPDC)₂]·DMF·9H₂O (5) were synthesized. MOFs 1, 2 and 3 obtained under the same conditions with the same auxiliary ligand (H₂BDC) but different amounts of alkali (NaOH) show distinct 3D, 1D and 3D framework structures, respectively, in which L and BDC²⁻ exhibit varied coordination modes. 4 and 5 with 3D structures were isolated by using longer auxiliary ligands of 2,6-H₂NDC and H₂BPDC. The porosity and excellent fluorescence performance of 3, 4 and 5 make them potential luminescent sensors for Fe(III) and antibiotics. The results show that 3, 4 and 5 represent high sensitivity for the detection of Fe(III) ions with detection limits of 155 ppb for 3, 209 ppb for 4 and 297 ppb for 5 due to the existence of open channels and chelating NH₂ sites. In addition, the strong emissions of 3, 4 and 5 can be quenched efficiently by trace amounts of NFs (nitrofurazone, NZF; nitrofurantoin, NFT; furazolidone, FZD) antibiotics even in the presence of other competing antibiotics such as β-lactams (penicillin, PCL). They are responsive to NZF with detection limits of 162 ppb for 3, 75 ppb for 4 and 60 ppb for 5.