Calcium incorporation in graphene oxide particles: A morphological, chemical, electrical, and thermal study

• Graphene oxide has been chemically modified with Ca ions by immersion in a CaCO3 solution.
• GO–Ca has morphology similar to an ultra-thin membrane composed of overlapping sheets.
• CaCO3 residue was completely removed by acid washes, leaving only ionic calcium.
• EDS maps show that Ca incorporation is spatially homogeneous in GO structure.
• Thermal analyses show a remarkable increase in GO stability after Ca incorporation.

Surface chemical modification and functionalization are common strategies used to provide new properties or functionalities to a material or to enhance existing ones. In this work, graphene oxide prepared using Hummers' method has been chemically modified with calcium ions by immersion in a calcium carbonate solution. Transmission electron microscopy analyses showed that graphene oxide (GO) and calcium incorporated graphene oxide have a morphology similar to an ultra-thin membrane composed of overlapping sheets. X-ray diffraction and Fourier-infrared spectroscopy show that calcium carbonate residue was completely removed by hydrochloric acid washes. Energy dispersive X-ray spectroscopy mapping showed spatially homogeneous calcium in Ca-incorporated graphene oxide sample after HCl washing. This Ca is mainly ionic according to X-ray photoelectron spectroscopy, and its incorporation promoted a small reduction in the graphene oxide structure, corroborated also by four-point probe measurements. A thermal study shows a remarkable increase in the GO stability with the presence of Ca2 + ions.