Carbon nanotube production from low-density polyethylene: catalyst design, modeling and purification

In this study, multi-walled carbon nanotubes were synthesized from plastic waste using Fe-Ni/Olivine catalyst via the chemical vapor deposition method. Process parameters were optimized, and the nanotubes were characterized. In the first stage, Fe-Ni/Olivine catalysts with varying Fe:Ni ratios were synthesized using the impregnation method and characterized by XRF, TG/DTA, XRD, BET, and SEM-EDS analyses. The results indicated homogeneous metal distribution and high thermal stability of the catalysts. In the synthesis stage, low-density polyethylene was used as the carbon source, and the synthesis conditions were optimized using central composite design. Response surface methodology was employed to evaluate the effects of temperature, reaction time, carrier gas flow rate, and Fe:Ni ratio on carbon yield. The optimal conditions were determined as 700 °C, 25 minutes, 0.0045 m³/h N₂ flow rate, and a 4:1 Fe:Ni ratio. The nanotubes synthesized under these conditions were characterized by XRD, SEM, TEM, RAMAN, and TG analyses. Purification was performed using HNO₃ and HCl, and the effects of different acid ratios on structural and chemical properties were investigated. The optimal purification condition was found to be a 4:2 HNO₃:HCl ratio at 80 °C for 4 hours. As a result, the Fe-Ni/Olivine catalyst exhibited high catalytic activity and thermal stability, enabling efficient and sustainable multi-walled carbon nanotube production under optimized conditions.