Equipping carbon dots in a defect-containing MOF via self-carbonization for explosive sensing

Abstract

Convenient and controllable methods for preparing carbon dots (CDs) and their composites have attracted great interest. Metal–organic frameworks (MOFs), which consist of metal ions or clusters and organic ligands, are considered as ideal platforms for creating functional nanocarbon materials. Here, by facile thermal treatment, we successfully prepared CDs@MOF composites via MOF self-carbonization. By replacing 1,4-benzenedicarboxylic acid with 1,4-naphthalenedicarboxylic acid and adopting hydrochloric acid or benzoic acid as a modulator, the near defect-free and defect-containing forms of a luminescent UiO-66 type MOF (named UiO-66N) can be obtained through a solvothermal reaction. The synthesized products were characterized by powder X-ray diffraction, transmission electron microscopy and gas/dye sorption, so as to determine the existence of crystal defects. After calcination at different temperatures from 100 to 400 °C, the luminescence of the near defect-free UiO-66N had no significant change, while that of the defect-containing UiO-66N changed from blue to green. Experimental evidence indicated that the change of luminescence can be attributed to the formation of CDs and the existence of defects is favourable for self-carbonization in microporous MOFs under mild conditions. Moreover, the CDs@MOF composites exhibited exceptional luminescence sensing for picric acid with a high quenching constant (K_SV = 4.0 × 10⁵ M⁻¹) and a low limit of detection (LOD: 6.54 × 10⁻⁷ M).