Construction of a Luminescent Cadmium-Based Metal–Organic Framework for Highly Selective Discrimination of Ferric Ions

Fluorescent metal-organic frameworks (MOFs) are ideal materials for sensors because of their adjustable pore size and functional groups, which provide them with favorable metal ion selective recognition. In this paper, a new cadmium-based MOF was synthesized using Cd(NO₃)₂·4H₂O and 3,3',5,5'-biphenyltetracarboxylic acid by solvothermal method. CdBPTC owned three types of channels with dimensions of approximately 8.4 × 8.3 Å, 6.0 × 5.2 Å, 9.7 × 8.4 Å along a, b, and c axis, respectively. This MOF has high selectivity to ferric ions and shows excellent anti-inference ability toward many other cations. The results indicate that the fluorescence quenching efficiency of CdBPTC is close to 100% when the concentration of Fe³⁺ reaches 1.0 × 10^-3 mol·L^-1. Moreover, the luminescent intensity at 427 nm presents a linear relationship at a concentration range of 2.0 × 10^-4~7.0 × 10^-4 mol·L^-1, which can be quantitatively expressed by the linear Stern-Volmer equation I₀/I = 8489 [Fe³⁺] - 0.1400, which is comparable to the previously reported better-performing materials. Competitive energy absorption and ion exchange may be responsible for the variation in fluorescence intensity of CdBPTC in different Fe³⁺ concentrations.