Effects of CaCO₃/MgO on Fe-Co-Mo catalyst in the reprocessing of recycled polypropylene to carbon nanotubes

In recent times, there has been a global discourse on the menace of plastic waste (PW) materials on the ecosystem and ways for effective management of PW. This has resulted in the utilization of PW in the research arena in the synthesis of smart nanomaterials of high value as a sustainable solution. In this study, the catalytic-pyrolysis procedure was used to develop carbon nanotubes (CNTs) from recycled polypropylene (PP) plastic in a one-step chemical vapour deposition (CVD) reactor. The impacts of CaCO₃ and MgO as supports for Fe-Co-Mo catalysts in the production of CNTs were studied. Kinetic and thermodynamic parameters were determined from the thermal profile of the catalysts to establish the nature of the reaction in CNTs synthesis. Transmission electron microscopy (TEM), energy Dispersive X-ray (EDX), selected area electron diffraction pattern, particle size distribution (PSD), thermogravimetric analysis (TGA), Raman spectroscopy, Fourier transforms infrared (FTIR) and X-ray diffraction (XRD) were employed to characterize the catalysts and CNTs. The results obtained showed the impact of the supports on the yield, quality, and morphology of the synthesized CNTs. The CNTs yield from catalysts supported with CaCO₃ and MgO were 35.12 % and 37.24% respectively. The average outer diameters of CNTs produced over the catalyst with CaCO₃ and MgO supports were 36 and 29 nm respectively. The I_D/I_G ratio for CaCO₃ and MgO supports were 0.6724 and 0.8401 respectively. The change in entropy for all phases were −274.41 and −1032.97 J/mol/K and −213.0, −318.48 and −1022.13 J/mol/K for CaCO₃ and MgO supported catalyst respectively which confirmed non-spontaneous endothermic reaction. It was observed that MgO support showed better catalytic activity toward CNTs growth in terms of yield while those with CaCO₃ support showed higher graphitization.