Effect of Functionalization of Reduced Graphene Oxide Coatings with Nitrogen and Sulfur Groups on Their Anti-Corrosion Properties.

Karolina Ollik,Marek Lieder,Jakub Karczewski

doi:10.3390/ma14061410

Abstract

Electrophoretic production of anticorrosion carbonaceous coatings on copper could be successfully performed by anodic oxidation of negatively charged graphene platelets suspended in an aqueous solution. The various platelets were synthesized by Hummer’s method followed by a hydrothermal reduction in the presence of NH4SCN which was expected to substitute some parts of graphene structure with nitrogen and sulfur groups. X-ray photoelectron spectroscopy analysis confirmed that the graphene precursors, as well as the coatings, contained typical nitrogen groups, such as pyridinic and pyrrolic, and sulfur groups, such as thiol, thiophene, or C-SO2. However, due to oxidation during deposition, the qualitative and quantitative composition of the graphene coatings changed relative to the composition of the precursors. In particular, the concentration of nitrogen and sulfur dropped and some thiophene groups were oxidized to C-SO2. Studies showed the functionalized coatings had a uniform, defect-free, hydrophobic, more adhesive surface than nonmodified films. The corrosion measurements demonstrated that these coatings had better protective properties than the ones without these heteroatoms. This behavior can be assigned to the catalytic activity of nitrogen towards oxidation of C-SO2 groups to C-SO3H with oxygen.

Highlights

Graphene and its various oxidized or chemically functionalized forms have been recently studied as monolayers or multicomponent coatings for corrosion protection of metals
We found that the presence of nitrogen groups in the graphene coatings is generally beneficial for corrosion protection, but still, we have tried to figure out how to block the noxious effect of nitrogen catalytic activity
The results show that the coatings obtained from the GO precursor were the most rough, probably due to intensive CO2 release during electrolysis

Summary

Introduction

Graphene and its various oxidized or chemically functionalized forms have been recently studied as monolayers or multicomponent coatings for corrosion protection of metals. Deposition of the impeccable graphene coatings on a metal substrate is a rather challenging task. It can be carried out either from gaseous or aqueous phases, of which the first one, chemical vapor deposition, is essentially dedicated to the formation of (unoxidized) graphene layers [3,4,5]. The aqueous deposition seems to be more versatile, because the various chemically transformed entities of graphene, e.g., oxidized or doped, can be used as precursors, provided they are dispersible in water. It is a peculiarity of EPD that the composition of the coating differs from that of graphene precursor in a solution

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