Photodegradation of low- and high-density polyethylene using photoactive ZnO–Fe3O4 hybrid nanocomposites

Abstract

Plastic pollution is one of the key issues in modern environmental science owing to the high stability of synthetic polymers like low-density polyethylene (LDPE) and high-density polyethylene (HDPE), which are used in various fields like packaging materials and agriculture. In the present work, green-synthesized ZnO–Fe 3 O 4 nanocomposites with different composition ratios (1:1, 1:2, and 2:1) were synthesized and explored for photocatalytic degradation of LDPE and HDPE under solar light. Various physicochemical analyses were performed for the nanocomposites. From the XRD analysis, it was confirmed that wurtzite ZnO and spinel Fe 3 O 4 crystalline structures were present in the nanocomposites. From BET analysis, it was confirmed that ZnO–Fe 3 O 4 nanocomposites with a composition ratio of 2:1 possessed the highest surface area of 129.89 m 2 g -1 .Photocatalytic degradation of LDPE and HDPE samples was also conducted over 30 days using natural sunlight. The results showed that LDPE degraded significantly compared to HDPE, and this is due to the low degree of crystallinity and a relatively branched molecular structure of LDPE. The maximum weight loss of LDPE and HDPE samples was recorded when ZnO-Fe 3 O 4 (2:1) nanocomposites were used, and this is 32.68% and 10.15%, respectively, at a pH of 9.23. The results of FTIR spectroscopy showed that carbonyl and hydroxyl groups (C=O and O-H stretching at 1728.97 cm -1 and 3445 cm -1 , respectively) were formed during the degradation of LDPE and HDPE samples. HRSEM results showed that cracking, grooves, and erosion of polymer samples occurred during the degradation process. It is believed that synergistic interactions of ZnO and Fe 3 O 4 in ZnO-Fe 3 O 4 nanocomposites may facilitate enhanced charge separation and possibly lead to the generation of ROS during sunlight irradiation. However, direct detection of the reactive species, for example, by using Electron Paramagnetic Resonance Spectroscopy and conducting a study of a radical scavenger, was not performed in this study and should be a subject of further investigation. This study shows that ZnO-Fe 3 O 4 nanocomposites obtained by a green method can be a promising tool for accelerating polyethylene degradation using natural sunlight.