Polyolefin-derived carbon nanotubes as magnetic catalysts for wet peroxide oxidation of paracetamol in aqueous solutions

This work deals with developing feasible valorization technologies to prepare carbon nanotubes (CNTs) from plastic solid waste and demonstrate their application in catalytic wet peroxide oxidation (CWPO). CNTs were synthesized by catalytic chemical vapor deposition (CCVD) at 850 ºC, considering low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) as carbon precursors representative of urban plastic solid waste. Iron oxide nanoparticles supported in alumina, previously synthesized by sol-gel, were used as catalysts in the CCVD process. TEM micrographs allow us to determine 41 nm as the average outer diameter of the CNTs and to visualize magnetic iron nanoparticles (ca. 10 nm) embedded inside the CNTs (ca. 6.4 % of content measured as ashes). These magnetic nanoparticles were kept in the CNT structure even after the purification of the CNTs with sulphuric acid, allowing to obtain magnetic CNTs. All purified and non-purified CNTs prepared from the polyolefins were assessed as catalysts in CWPO of paracetamol (PCM), used as a model pharmaceutical contaminant in water at CPCM,0 = 100 μg mL−1 (CH2O2,0 = 472 μg mL−1, CCNT = 2.5 g L−1, pH0 = 3.5 and T = 80 °C). The concentrations of PCM, H2O2, aromatic and total phenolic compounds were monitored for 24 h. All CNTs showed catalytic activity, allowing the complete degradation of PCM at 6 h of reaction time. The stability and reusability of materials are tested and proved in CWPO.