Hybrid materials based on pyrrhotite, troilite, and few-layered graphitic nanostructures: Synthesis, characterization, and cyclic voltammetry studies

Abstract

Hybrid nanomaterials are complex systems containing two or more types of nanostructures that can be joined covalently or via Van der Waals forces to form a hybrid nanomaterial. In this work, we produced hybrid carbon nanomaterials with embedded FeS-based nanoparticles through a facile one-step AACVD method at 850 °C in a two-furnace approach. A nebulized solution containing n-hexane and ferrocene was employed as a carbon and iron source. As nitrogen and sulfur source, thiourea powder was evaporated in the first furnace taking into account its main endothermic process that occurs at ~180 °C and ~220 °C. Therefore, we use three temperatures, close to these values (190 °C and 230 °C), and another temperature above (290 °C). The results show a strong dependence between the evaporation temperature of thiourea and the synthesized structure. At the lower temperature we obtain flower-like carbon fibers with embedded troilite nanoparticles. At the intermediate thinner fibers covered by troilite and pyrrhotite rod nanoparticles were formed, which in turn, are enclosed by few graphitic layers (8GL). At a higher temperature of ~290° C, large FeS nanostructures with hexagonal platelet morphology and few graphite layers prevailed. XRD characterizations revealed graphitic carbon, FeS troilite, and Fe7S8 pyrrhotite phases. Through cyclic voltammetry measurements, the electrochemical processes involved in the synthesized carbon nanohybrids were qualitatively studied. By X-ray photoelectron spectroscopy analysis (XPS) the nitrogen and sulfur co-doping were observed for all samples, as well as the presence of oxygen, nitrogen and sulfur functional groups which vary in their atomic content for each case.