Zinc titanate nanopowder: an advanced nanotechnology based recyclable heterogeneous catalyst for the one-pot selective synthesis of self-aggregated low-molecular mass acceptor–donor–acceptor–acceptor systems and acceptor–donor–acceptor triads

Abstract

Highly stable, environmentally benign ZnTiO₃ nanopowder has been prepared via a sustainable sol–gel method. The nanopowder (90 nm) has been thoroughly characterized by SEM, XRD, EDS, Laser Raman, photoluminescence, UV and IR. The activity of the catalyst was probed through one-pot four-component reaction of aldehydes, ketones and two equivalent propanedinitriles in water without requiring any additives or anhydrous conditions. The reaction requires two different catalytic functions, i.e., an acidic one which is given by Ti(IV) ions and a basic one, given by the oxide ion incorporated within the ZnTiO₃ metal oxide framework. The advantages of this method lie in its simplicity, cost effectiveness, environmental friendliness, and easier scaling up for large scale synthesis without using high pressure, temperature and toxic chemicals. As water was used as a reaction medium and since we are particularly interested in the isolation of a non-aromatic intermediate, the elimination of poisonous HCN was prevented by the Lewis acid character of Ti⁴⁺ up to a sufficiently high temperature. Thus, this process can be considered as a “green” process. Elimination of HCN at higher temperatures still maintains “green” attributes as HCN can be trapped by the basic catalyst under such conditions. Spontaneous generation of low molecular mass self-aggregated organic materials, their one-dimensional packing, and interesting photophysical properties are reported.