Sustainable carbon–metal oxide composites from waste sources: synthesis, characterization, and mechanical properties

Abstract

Carbon–metal oxide composites are widely utilized as lightweight materials in aerospace, automotive, and sports equipment. Since the discovery of carbon nanotubes (CNTs) in 1991, exploration of CNTs and their incorporation into composites has gained attention; however, large-scale, cost-effective production and property control remain challenges. This study reports the thermocatalytic synthesis of Al2O3–CNT, Al2O3/Fe2O3–CNT, Fe2O3–C, and ZnO–C composites using waste plastic as a carbon source and aluminum cans and scrap iron for metal oxides. Characterization via UV-vis spectroscopy, SEM, TEM, EDX, Raman spectroscopy, XRD, and nanoindentation test confirms the material composition and structure. TEM and Raman spectroscopy reveal successful CNT formation in Al2O3 and Al2O3/Fe2O3 systems, while Fe2O3 and ZnO form CNT-free carbon composites. The Al2O3/Fe2O3–CNT composite shows a better density-normalized elastic modulus value, i.e. 9.66 GPa g−1 cm3, in comparison to other samples. The elastic modulus values of Al2O3–CNT, Fe2O3–C, Al2O3/Fe2O3–CNT, and ZnO–C are found to be in the range 10.19 GPa to 23.31 GPa, whereas hardness is in the range 0.42 GPa to 0.75 GPa, and elastic recovery is in the range 8.1% to 28.9%. The higher I G/I D ratio of the Al2O3/Fe2O3–CNT composite (2.05) compared to other composites (1.5, 1.41, 1.4) reflects a higher quality and responsible parameter for the higher elastic modulus of Al2O3/Fe2O3–CNT. This work highlights a low-cost, waste-derived route to high-performance, lightweight carbon–metal oxide composites.