Polyamine-functionalized carbon dots as active catalyst for Knoevenagel condensation reactions

In this study, carbon dots coated with diluted polyethylene imine was prepared from the carbonization of citric acid (CA) with branched polyethylene imine (BPEI) at temperature (200 degrees C), designated as BPEI-CDs. The solid catalyst was characterized by various techniques including X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM). The obtained BPEI-CDs are spherical graphite nanocrystals (averaging 5-10 nm). It was found that it could be used as heterogeneous catalyst for Knoevenagel condensation of aromatic aldehydes with malononitrile at 60 degrees C in ethanol. The Knoevenagel aromatic products were obtained with a moderate to excellent conversion within 2 h. The BPEI-CDs as catalyst was easily isolated from the reaction mixtures by simple filtration and reused for three times without significant loss of catalytic activity. There was also no contribution from the leached active species and conversion was only being possible in the presence of the prepared modified carbon dots.