Q-graphene-scaffolded covalent organic frameworks as fluorescent probes and sorbents for the fluorimetry and removal of copper ions

Highlights: • Metal-free COFs were polymerized onto the scaffolds of hollow Q-Graphene (QG). • QG-scaffolded COFs could present enhanced fluorescence, high aqueous stability, and photostability. • The fluorescence of QG-scaffolded COFs could be quenched by Cu²⁺ ions towards the ultrasensitive copper analysis. • The QG-scaffolded COF could serve as powerful sorbents for the removal of Cu²⁺ ions in wastewater with high efficiency. -- Abstract: Metal-free fluorescent covalent organic frameworks (COFs) were synthesized initially with Q-Graphene (QG) scaffolds by the one-step covalent reactions of melamine-aldehyde and phenol-aldehyde poly-condensations using paraformaldehyde. It was discovered that onion-like hollow QG, which consists of multi-layer graphene and different carbon allotropes having a high proportion of folded edges and surface defects, could endow the scaffolded COFs with enhanced green fluorescence and environmental stability. Unexpectedly, they could exhibit the powerful absorption for Cu²⁺ ions resulting in the specific quenching of fluorescence. A fluorimetric strategy with QG-scaffolded COFs was thereby developed to probe Cu²⁺ ions separately in blood and wastewater with the linear concentration ranges of 0.0010–10.0 μM (limit of detection of 0.50 nM) and 0.0032–32.0 μM (limit of detection of 2.4 nM), respectively, promising the potential applications for the field-applicable monitoring of Cu²⁺ ions in the clinical and environmental analysis fields. In addition, the prepared COFs sorbents were employed to absorb Cu²⁺ ions in wastewater showing high removal efficiency. More importantly, such an one-pot fabrication route with hollow QG scaffolds may be tailorable extensively for the preparation of a variety of metal-free multifunctional COFs with enhanced fluorescence, water solubility, environmental stability, and metal removal capability.