Benzimidazole-based covalent organic polymer nanosheets incorporated in mesoporous organosilica nanoparticles with excitation-dependent fluorescence for sensing of Cu2+

A novel type of small-sized nanosheets (TD-Si) was prepared by chemical exfoliating stacked bulk materials of benzimidazole-based covalent organic polymer (TpDAB). Then TD-Si was used as organosiloxane precursor to incorporate into silica frameworks of mesoporous organosilica nanoparticles (TD-MONs) using CTAB as structural-directing agents. The obtained TD-MONs show a clearly hexagonal mesoporous structure with high surface area. Moreover, the optical properties of TD-MONs were measured with fluorescence and Ultraviolet–visible (UV–vis) spectroscopies. The results showed that TD-MONs possessed excitation wavelength dependent fluorescence and had better fluorescence properties due to the reduction of π-π stacking between nano-layers of TpDAB polymer. The emission peaks of TD-MONs were red-shifted as the excitation wavelength increases and TD-MONs exhibited the optimal fluorescence emission at 525 nm when excited at 400 nm. TD-MONs showed high selectivity, sensitivity and recyclability toward copper ions and could be used for the detection of Cu2+ with a low limit of detection (LOD) as low as 3.77 × 10−7 M. In addition, the coordination interaction between TD-MONs and copper ions was demonstrated by FT-IR spectra and high-resolution X-ray photoelectron spectra, and further proved that the binding sites were carbonyl oxygen atoms and imidazole nitrogen atoms in TD-MONs. Therefore, TD-MONs is expected to be a high-sensitive chemical sensor for detecting Cu2+.