Conversion of Waste Plastic Packings to Carbon Nanomaterials: Investigation into Catalyst Material, Waste Type, and Product Applications

Waste plastics collected from local food courts were catalytically pyrolyzed and decomposed to produce carbon nanomaterials (CNMs) as well as hydrogen-rich gases as byproducts in this work. A series of bimetallic catalysts: Co-Fe, Co-Ni, and Fe-Ni with MgO as the catalyst support were synthesized and compared for the process. Products including high value-added carbon nanomaterials and gases were characterized to evaluate the activity of each bimetallic catalyst. In addition, products from four types of plastic: LDPE-plastic bags for bagging, PP-plastic bottles for drinking, PS-plastic lids, and PET-mineral water bottles were further comprehensively compared in terms of yield, purity of carbon, and adsorption capacity. Results show that Fe-Ni-Mg prepared by the pH-increase precipitation method exhibited the best performance for plastic conversion, contributing to the maximum CNM yield of 30.25 wt % and hydrogen yield of 31.52 mmol/g(plastic). However, the Co-Ni/MgO synthesized by impregnation gave the least activity. Regarding the different plastic types, plastic waste from LDPE bags produced hydrogen with a relatively high yield of 35.27 mmol/g(plastic), while PS lid plastic resulted in a relatively high CNM yield of 38.26 wt %. It is also found that the PET bottle was not suitable for CNM production accompanied by a high content of CO2 in product gases. The CNMs were further applied as adsorbents for wastewater treatment. The plastic-derived CNMs show strong (similar to 180 mg/gCNM) adsorption capacity of metal cations such as Fe, Ag, and Ni.