SDC/OS-LDH composite for highly sensitive fluorescence detection of Fe³⁺ at a much lower concentration

In this work, we demonstrate the tunable luminescence of newly synthesized SDC/OS Mg/Al-LDH composites (SDC is 4,4'-stilbenedicarboxylic acid; OS is 1-octanesulfonic acid sodium; LDH is layered double hydroxide) and their application in fluorescence sensing to detect Fe(iii) ions. Through an ion-exchange method, the SDC^2- and OS^- anions with changed molar ratios are intercalated into the LDH interlayers to obtain composites of SDC_xOS_1-x-LDH (x = 0.02, 0.05, and 0.10). In the solid state, the optimized SDC_0.05OS_0.95-LDH exhibits a blue emission (441 nm) with a 54 nm blue-shift compared with SDC-Na solid salt (495 nm). In a delaminated state, the colloidal suspension of SDC_0.05OS_0.95-LDH in formamide (FM) also gives a blue emission at 444 nm in comparison to the 451/468 nm emissions of the FM solution of free SDC^2- anions, and the luminescence intensity of the exfoliated composite is ∼28 times higher than that of the SDC^2- anions. The SDC_0.05OS_0.95-LDH composite could be utilized in chemical fluorescence sensing for detecting Fe³⁺ ions. In aqueous solutions with extremely low Fe³⁺ concentrations of 0.18-1.78 μM (0.01-0.1 ppm), the composite gives a large quenching constant of 2.34 × 10⁵ M^-1, and an ultralow detection limit of 6.12 × 10^-8 M. This work may provide a highly effective while simple method for the detection of Fe³⁺ in a small concentration range.