Covalently immobilized ionic liquids on single layer nanosheets for heterogeneous catalysis applications

Ionic liquids (ILs) have attracted significant attention because of their unique chemical and physical properties. Immobilization of ILs on solid materials helps increase their efficiency and facilitate their recycling. In our present work, ILs were immobilized on α-zirconium phosphate (ZrP) single layer nanosheets by a post-grafting method. The immobilized ILs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The characterization results supported that the ILs were covalently grafted onto ZrP nanosheets via the chemical reaction of ethoxyl silane groups in ILs with the surface hydroxyl groups on ZrP nanosheets. A high density of grafting of ILs on individual ZrP nanosheets was achieved. The immobilized ILs on individual ZrP nanosheets can be uniformly dispersed in polar chemicals and are readily accessible. When applied as a heterogeneous catalyst for Knoevenagel condensation under a solvent-free condition, such immobilized ILs exhibited high efficiency and can be easily recycled and reused.