Modification of the properties of carbon nanocoils by different treatments in liquid phase

Carbon nanocoils (CNCs) were synthesized using resorcinol–formaldehyde gel as carbon precursor and a mixture of cobalt and nickel salts as the graphitization catalysts. The last step of the synthesis process involves the elimination of the metals using an oxidative treatment, commonly HNO3 treatment. However, during this treatment not only the metals are eliminated, but also the amorphous and graphitic carbon. On the other hand, this treatment can create surface oxygen groups, modifying the surface chemistry of CNCs. The aim of this work is to study the effect of different oxidative treatments on the final properties of carbon nanocoils in order to obtain materials with high graphitic character. The effect of liquid phase oxidation treatments on the texture, surface chemistry and structure of carbon nanocoils was studied by means of different analytical techniques as N2-physisorption, X-ray diffraction (XRD), temperature programmed oxidation (TPO) and temperature programmed desorption (TPD). During these treatments, surface oxygen groups were created and their number was function of the concentration of the oxidizing agent used and the treatment time.

Graphical abstractThe Raman spectra of the samples were obtained. The first-order (1200-1700 cm−1) and second-order (2500-2900 cm−1) Raman spectra are shown in the figure. The first-order Raman spectrum shows two bands associated with the presence of different types of structural defects: the graphite band (G) at ∼1565-1580cm−1 and the D band at ∼1342-1353 cm−1. On the other hand, the second-order Raman spectrum shows the G′ band which is characteristic of tridimensional ordered materials. All samples had an ordered structure and their graphitization degree depended on the treatment used for the removal of metals. The treatments with H2SO4-H2O2 mixtures eliminate the amorphous carbon preferentially, thus obtaining low specific surface area materials, characteristics of graphitic materials.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Different oxidation treatments were tested to remove the metals. ► The graphitization degree depended on the treatment used for the removal of metals. ► It had an important effect on the textural properties of the carbon materials. ► Surface oxygen groups were created during these treatments.