New hybrid polymer-ZnO nanostructures THROUGH ALD synthesis

The development of the nanotechnologies has brought concrete benefits on our daily life, finding application in several fields. In particular, a recent strategy in the water treatment consists in the development of photocatalytic hybrid nanocomposites (HyNC), in which the inorganic photoactive material is immobilized into a polymeric matrix to prevent their dispersion in the aqueous medium . The synthesis of HyNC, in which an inorganic layer grows on a polymeric surface via covalent bonds, persists to be a challenging goal for many applications such as catalysis, sensing, and optoelectronics. Herein, we report the growth of ZnO nanostructures by Atomic Layer Deposition (ALD) technique on modified polyetherimide (PEI-ULTEM® 1000) substrates. The high quality of the ALD materials originate from the peculiar growth mechanism based on selective and self-limiting reactions between the ALD gaseous precursors and the reactive groups exposed at surface of the substrate. The growth of the material on the substrate is controlled at the atomic scale, uniformly and conformably on large areas. A photo-oxidative process of the polymer surface has been properly performed to promote the production of reactive surface-sites suitable for ALD mechanism. The chemical anchoring of the metal species from the gas-phase is demonstrated by spectroscopy, MALDI-TOF mass spectrometry as well as AFM. In the operative ALD conditions used, the chemical grafting exclusively occurred on the pre-oxidized films, whilst the ZnO does not covalently reacted on the untreated ULTEM® 1000 films. Notably, we demonstrate that two different regimes of growth take place in the oxidized polymer as a function of the photo-exposure time. In particular, the formation of a nanostructured coating of ZnO on the polyetherimide surface is found in the case of short-time photo-exposed polyetherimide (ALD-like regime), whilst an intermixed organic/polymer layer is found on the long-time oxidized films (Vapor Phase Infiltration, VPI-like regime). The photocatalytic activity of the synthesized materials has been tested through the degradation of methylene blue dye in aqueous solution under UV light irradiation, so to give a proof of concept of a possible application of the nano-composites.