Plastic waste-derived carbon nanotubes: Influence of growth catalyst and catalytic activity in CWPO

Low-density polyethylene (LDPE) was used in this work to grow carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over catalysts based on Ni, Fe and Al, synthesized either by co-precipitation (C) or wet impregnation (I) methods, with CNT yields in the range of 16–33 %. The morphology of the CNTs was directly influenced by the route used for the CVD catalyst synthesis, with co-precipitation-derived CVD catalysts resulting in CNT samples with curly walls. CNTs were purified with H 2 SO 4 (10–50 wt. %) to remove attached metal particles. All synthesized materials (CVD-catalysts, as-synthesized CNTs, and purified CNTs) were tested as catalysts in the catalytic wet peroxide oxidation (CWPO) of paracetamol (PCM), chosen as a model pharmaceutical compound. Removals of 100 % of PCM in 8 h and 71 % of total organic carbon (TOC) in 24 h were achieved, with an H 2 O 2 consumption efficiency of 76 % in 24 h for purified CNT (CNT@NiFeAl-C-P). The same CVD-catalyst (NiFeAl-C) was used to grow CNTs using real LDPE waste, and it was tested under the same reaction conditions, resulting in a PCM and TOC abatement of 90 % and 65 %, respectively. The synthesis of CNTs using LDPE waste was a good alternative, given the environmental benefits associated with its reintroduction into the economic cycle as a material with higher value than initially (upcycling). • CNTs were synthesized from LDPE considering distinct CVD catalysts. • CNTs were applied as catalysts in the wet peroxide oxidation (CWPO) of paracetamol. • H 2 SO 4 -washed CNTs display slower H 2 O 2 decomposition but higher CWPO efficiencies. • H 2 SO 4 -washing with concentrations over 30 % removes metals and reduces leaching. • CNTs obtained from pure LDPE and LDPE plastic waste behave similarly in CWPO.