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

Abstract

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/gplastic. 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/gplastic, 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 (∼180 mg/gCNM) adsorption capacity of metal cations such as Fe, Ag, and Ni.