Abstract
The reduction of graphene oxide (GO) thin films deposited on substrates is crucial to achieve a technologically useful supported graphene material. However, the well-known thermal reduction process cannot be used with thermally unstable substrates (e.g., plastics and paper), in addition photo-reduction methods are expensive and only capable of reducing the external surface. Therefore, solid-state chemical reduction techniques could become a convenient approach for the full thickness reduction of the GO layers supported on thermally unstable substrates. Here, a novel experimental procedure for quantitative reduction of GO films on paper by a green and low-cost chemical reductant (L-ascorbic acid, L-aa) is proposed. The possibility to have an effective mass transport of the reductant inside the swelled GO solid (gel-phase) deposit was ensured by spraying a reductant solution on the GO film and allowing it to reflux in a closed microenvironment at 50 °C. The GO conversion degree to reduced graphene oxide (r-GO) was evaluated by Fourier transform infrared spectroscopy (FT-IR) in attenuated total reflectance (ATR) mode and X-ray Diffraction (XRD). In addition, morphology and wettability of GO deposits, before and after reduction, were confirmed by digital USB microscopy, scanning electron microscopy (SEM), and contact angle measurements. According to these structural characterizations, the proposed method allows a bulky reduction of the coating but leaves to a GO layer at the interface, that is essential for a good coating-substrate adhesion and this special characteristic is useful for industrial exploitation of the material.
Highlights
In recent decades, graphene and its derivatives have attracted great interest because of their excellent mechanical, electrical, thermal, and optical properties [1,2,3,4,5]
graphene oxide (GO) was synthesized by a modified Hummers’ method [11,27], that was based on the oxidation of graphite nanoplatelets (GNP) by KMnO4 (≥99%) and KNO3 (≥99%) solution in absolute H2 SO4 and after ca. 1 h the reaction was stopped by adding H2 O2 (30%)
According to the scanning electron microscopy (SEM) investigation, of coating surface follows to the chemical reduction treatment, mainly consisting in an increase of the a structural modification of coating surface follows to the chemical reduction treatment, mainly coating flatness
Summary
Graphene and its derivatives have attracted great interest because of their excellent mechanical, electrical, thermal, and optical properties [1,2,3,4,5]. The GO conversion to r-GO usually requires some reducing agents or a high temperature [13,14,15,16,17,18] Among these reduction strategies, the chemical approach is very promising for bulk production of r-GO at low cost. The solid GO deposit, in a water swelled form, has been reduced by L-aa, taking advantage of a diffusion-based mass-transport mechanism that is possible for the L-aa molecules, in a closed water-refluxing environment. This ecofriendly technique has shown to be very adequate to produce a bulky, uniform and highly reduced GO layer, preserving the paper substrate. USB-microscopy and scanning electron microscopy (SEM), and changes in the GO deposit surface wettability with the reduction treatment was determined by contact angle measurements
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