From powder to cloth: Facile fabrication of dense MOF-76(Tb) coating onto natural silk fiber for feasible detection of copper ions

The deposition of powdered MOFs material onto other substrates is essential to avoid inconvenience during its practical applications. In this work, domestic silk fiber was utilized as the skeleton, for successful coating of dense luminescent MOF-76(Tb). Its surface functionality which consist of abundance of intrinsic carboxylic groups, smooth surface structure, and 80% of tensile strength were maintained after being immersed in different thermal solvents (water, ethanol, DMF @ 80 degrees C) for 24 h, revealing good solvent and thermal resistance. By using hydrothermal, microwave assisted, and layer-by-layer methods, different crystal morphologies (pillar-like, sedimentary-rock-like, and needle-like morphology) and varying degrees of surface coverage rate were obtained, as a result of different levels of anchoring promotion and crystal controlling effect. The MOFs coating can be confirmed by its XRD pattern and fluorescent property. More importantly, the quenching effect of the composite in a condition of Cu2+ was first reported with high selectivity, sensitivity (i.e. a linear detection concentration range of 10(-3)-10(-5)M with a low detection limit up to 0.5 mg/L, KSV of 1192 M-1 at 293 K), and rapid response time (5 min), making the composite a good candidate for colorimetric and fluorescent detection of aquatic Cu2+. The quenching mechanism is proposed to associate with the interaction between Cu2+ and benzene-tricarboxylate (BTC) ligand, which resulted in the decrease of energy transfer efficiency. The selectivity over other common cations depends on the unsaturated electron configuration and the smaller ionic radius of Cu2+.