Surface functionalization of ZnO nanostructures: designing material properties at nanoscale

The various functional properties of ZnO are very well known and for this reason ZnO is studied for applications in different fields, such as optoelectronics, transparent electronics, piezoelectric devices, sensing and catalysis. In particular, when ZnO is obtained in form of nanostructures, most of these properties become strongly surface and/or size dependent. Authors here present both their results in the optimized growth of ZnO nanostructures with selected morphologies and an overview on different kinds of surface functionalizations that has been used to add further and new functional properties to them. Inorganic and organic semiconductor, superparamagnetic iron oxide nanoparticles and noble metals have been coupled with ZnO nanostructures by means of different physical or chemical techniques that have been developed in order to optimize the coupling between the different materials (Fig. 1). Clear enhancements or modifications in their surface reactivity, light absorption, magnetic or other peculiar properties are reported and a few examples for gas sensing application, photocatalytic degradation of water pollutants and some new ideas for complex geometries in hybrid photovoltaic applications are presented as case studies. Further perspectives for other feasible applications of these multifunctional composite nanostructures are finally discussed.