Tuning Properties of Partially Reduced Graphene Oxide Fibers upon Calcium Doping.

Krzysztof Tadyszak,Emerson Coy,Raanan Carmieli,Karol Załęski,Łukasz Majchrzycki,Jacek K Wychowaniec

doi:10.3390/nano10050957

Abstract

The arrangement of two-dimensional graphene oxide sheets has been shown to influence physico-chemical properties of the final bulk structures. In particular, various graphene oxide microfibers remain of high interest in electronic applications due to their wire-like thin shapes and the ease of hydrothermal fabrication. In this research, we induced the internal ordering of graphene oxide flakes during typical hydrothermal fabrication via doping with Calcium ions (~6 wt.%) from the capillaries. The Ca2+ ions allowed for better graphene oxide flake connections formation during the hydrogelation and further modified the magnetic and electric properties of structures compared to previously studied aerogels. Moreover, we observed the unique pseudo-porous fiber structure and flakes connections perpendicular to the long fiber axis. Pulsed electron paramagnetic resonance (EPR) and conductivity measurements confirmed the denser flake ordering compared to previously studied aerogels. These studies ultimately suggest that doping graphene oxide with Ca2+ (or other) ions during hydrothermal methods could be used to better control the internal architecture and thus tune the properties of the formed structures.

Highlights

Graphene oxide (GO) is a form of graphene having a unique collection of oxygen rich groups on its surface (-COOH, -OH, =O, -O-) [1,2]
We were interested in the change of magnetic, mechanical, and electric properties of graphene oxide fibers prepared via the hydrothermal method with additional doping by divalent Ca2+ ions
We injected a solution of 4 mg/mL graphene oxide flakes inside capillaries containing calcium ions (Figure 1a)

Summary

Introduction

Graphene oxide (GO) is a form of graphene having a unique collection of oxygen rich groups on its surface (-COOH, -OH, =O, -O-) [1,2]. A stronger connection between flakes changes the flake arrangement and alters the above-mentioned properties in comparison to previously studied graphene oxide structures formed by hydrothermal methods [2,13]. Their electrical conductivity strongly depends on the quality of the reduction process and flake ordering and can be described by variable range hopping models [14,15]. The addition of Ca2+ in a coagulation bath while fibers are formed during a wet spinning method results in increased flakes tendency for the formation of a denser network with Calcium ions acting as bridges between the individual flakes [16]. Most of the aforementioned centers are present in different samples, due to preparation processes, making the synthesis method and ion doping a crucial aspect to evaluate

Methods

Results

Conclusion