Etching and Precursor Effects on Plasma-Modified Waste Polyethylene Terephthalate (PET) to Laccase Immobilization Applied in Catechol Biodegradation for Water Treatment

Polyethylene terephthalate (PET) is a polyester used in the beverage bottling industry that generates a serious pollution problem. Films were obtained to reuse discarded PET bottles, and their surface was modified to determine their effectiveness in supporting the immobilization of the laccase enzyme applied to a catechol biodegradation assay. Radiofrequency (RF) plasma was used to modify the PET surface using different precursors: (a) with the use of air as precursor, the effect of the etching caused by the air on the greater or lesser immobilization was observed; (b) with the use of ethylenediamine, a mixture of N2/H2, or aniline as precursors, it was observed which of these three precursors presented the greater or lesser number of amino groups deposited on the PET surface. After plasma modification, the films were cross-linked with glutaraldehyde to immobilize the laccase enzyme. Finally, the catechol test was performed. It was found that the best etching time using air as a precursor was 90 min, and the precursor that caused a higher insertion of amino groups on the surface was ethylenediamine, which reached a density of amino groups of 3.98 ± 0.10 g·mm−2. The highest percentage of laccase immobilization achieved on the surface of ethylenediamine-modified PET was 97.30%. In the catechol assay, the highest retention was 86.11%. This research reveals how the effect of plasma increases the surface area on a PET surface and, in conjunction with ethylenediamine as the best precursor of the three precursors evaluated, can immobilize a greater amount of enzyme and oxidize more catechol. There is no scientific evidence from previous studies that used air plasma technology to erode and then used three different precursors to modify a surface to immobilize the laccase enzyme and remove a water contaminant.