Solar Photocatalytic and Biodegradation of Polymer–Semiconductor Composite Film in Series: Characterization and Kinetic Modelling

Abstract

Once hailed as a ‘wonder material'’ for its low cost, durability, lightweight, flexibility, and water resistance, plastics have now become one of the potent threats to human civilization. Imperatively, light and microbes could play significant roles in plastic degradation. Plastic–semiconductor composites enhance photodegradation, whereas the presence of biodegradable compound in composites may facilitate their degradation by soil microbes. In this work, composite films of polyvinyl chloride (PVC) and zinc oxide semiconductor (ZnO) are synthesized in various combinations and subjected to sequential photo- and biodegradation. The photodegradation was exclusively solar, whereas polycaprolactone (PCL) was apprehensively added to the composite for enhancing the biodegradability. The process sequence was also altered to investigate the possible effects. Sequential photocatalytic degradation under sunlight and biodegradation by bacteria isolated from soil could decrease the original weight of a photo-bio degradable polymer composite film comprising of PVC, PCL and ZnO in less than a month. The isolated microbe was later identified as Bacillus altitudinis by 16S rRNA gene sequencing. Identification and isolation of enzymes involved in PVC degradation by the isolated strain may be included in future work. Maximum 26.8 w% degradation was observed within 25 days in case of PVC–ZnO composite. The role of PCL was found to be insignificant in biodegradation especially in presence of ZnO. The solar photodegradation was modelled based on a proposed mechanism that finally led to two parallel reaction pathways following first- and zero-order kinetics, respectively. Biodegradation, on the other hand, was noted to be fairly consistent with the Michaelis–Menten kinetics.