An advanced approach for fabricating a reduced graphene oxide-AZO dye/polyurethane composite with enhanced ultraviolet (UV) shielding properties: Experimental and first-principles QM modeling

Polyurethane (PU) is a ubiquitous organic coating which has been widely used in a variety of industries (e.g., automotive and microelectronics) thanks to its high elasticity, flexibility, and resistance to abrasion, impact and weather. However, obtaining a PU-based coating with long-term durability against UV irradiation is still a serious challenge. This study presents the synthesis of graphene oxide (GO)-AZO dye composite, an advanced UV-resistant nanomaterial with appropriate dispersion and highly effective UV light shielding features. The influence of temperature, time and GO/AZO dye ratio on dye-mediated reduction and functionalization of GO nanosheets was studied. Further, the chemistry of the GO-AZO composite was examined by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD) and UV-visible measurements. Experimental analyses evidenced that upon dye addition the GO sheets were partially reduced and covalently modified, resulting in the creation of GO-AZO composite with suitable UV absorption capability. Furthermore, the electronic structure quantum mechanics (QM) modeling studies applied on different variants of AZO dye/GO complexes (i.e., neutral/protonated dye on uncharged/charged GO) demonstrated that the AZO dye adsorbed onto GO sheets via physisorption (e.g., hydrogen bonding and pi-pi stacking) as well as chemisorption (proton transfer from AZO dye to GO) mechanisms. Subsequently, the synthesized composite at optimum conditions was incorporated into PU matrix. The color changes by gonio-spectrophotometer, surface morphology by atomic force microscopy (AFM), chemical structure by FT-IR and cross-linking density by dynamic mechanical thermal analysis (DMTA) were considered before and after exposure of GO-AZO/PU composites to the QUV chamber condition. The results revealed that the GO-AZO composite inclusion into the PU significantly improved its durability and resistance against degradation when exposed to UV irradiation. (C) 2017 Elsevier B.V. All rights reserved.