Thermal Evolution of C-Fe-Bi Nanocomposite System: From Nanoparticle Formation to Heterogeneous Graphitization Stage

Carbon xerogel nanocomposites with integrated Bi and Fe particles (C-Bi-Fe) represent an interesting model of carbon nanostructures decorated with multifunctional nanoparticles (NPs) with applicability for electrochemical sensors and catalysts. The present study addresses the fundamental aspects of the catalyzed growth of nano-graphites in C-Bi-Fe systems, relevant in charge transport and thermo-chemical processes. The thermal evolution of a C-Bi-Fe xerogel is investigated using different pyrolysis treatments. At lower temperatures (similar to 750 degrees C), hybrid bismuth iron oxide (BFO) NPs are frequently observed, while graphitization manifests under more specific conditions such as higher temperatures (similar to 1,050 degrees C) and reduction yields. An in situ heating TEM experiment reveals graphitization activity between 800 and 900 degrees C. NP motion is directly correlated with textural changes of the carbon support due to the catalyzed growth of graphitic nano shells and nanofibers as confirmed by HR-TEM and electron tomography (ET) for the graphitized sample. An exponential growth model for the catalyst dynamics enables the approximation of activation energies as 0.68 and 0.29-0.34 eV during reduction and graphitization stages. The results suggest some similarities with the tip growth mechanism, while oxygen interference and the limited catalyst-feed gas interactions are considered as the main constraints to enhanced growth.

Automated summary

Carbon xerogel nanocomposites with integrated Bi and Fe particles (C-Bi-Fe) are investigated for their potential applications as electrochemical sensors and catalysts. The catalyzed growth of nano-graphites in C-Bi-Fe systems is studied, revealing the mechanisms and constraints of this process.