Solid-state electrochemiluminescence sensor based on functional covalent organic frameworks for detecting Co²⁺ ions

The application of covalent organic frameworks (COFs) in electrochemiluminescence (ECL)-based detection of environmental pollutants remains relatively underexplored, particularly with respect to achieving high recognition efficiency. In this work, a series of imine-linked functional COFs were constructed using tetrakis(4-aminophenyl)ethene as the C4 building block, with precisely regulated molar ratios of 2,2'-bipyridine-5,5'-dicarbaldehyde (BPYDAH, recognition unit) and 2,2'-bithiophene-5,5'-dicarbaldehyde (BTA, luminescence unit) as co-monomers. All as-prepared COFs exhibited stable solid-state ECL emission in the presence of tri-n-propylamine as a co-reactant, and their ECL intensity showed a positive correlation with the proportion of BTA units in the framework. Among the series, COF1-3 with optimized monomer ratio simultaneously maintained satisfactory ECL emission and specific Co²⁺ recognition capability, thus was selected as an ECL probe to fabricate a solid-state COF1-3/GCE ECL sensor. The constructed sensor achieved linear detection of Co²⁺ in the range of 4.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.8 × 10⁻⁷ mol L⁻¹, and was successfully applied to Co²⁺ detection in real environmental water samples with satisfactory recoveries.