Recycled PET conversion to high efficiency catalyst for 4-NP reduction with extended reusability: Insights into reduction products and kinetics

The natural degradation of polyethylene terephthalate (PET) can take hundreds of years making them persistent solid waste in the environment. This study explored a new recycling path for this waste by utilizing it to fabricate nanocomposite catalysts (NCC) with silver nanoparticles (Ag NPs). The latter is an effective catalyst for reducing hazardous compounds such as 4-nitrophenol (4-NP), however using it freely is expensive and poses health and environmental risks. To mitigate the risk of Ag NPs leachability, we applied innovative mild heat treatment which was found to improve Ag NPs exposure while maintaining a strong adhesion. The optimum NCC dosage (5 mg with 5 % Ag) as indicated by response surface methodology (RSM) maintained ≥ 90 % reduction of 4-NP (0.176 mM) over 11 out of 12 consecutive cycles tested. The reduction kinetics concurred with the Langmuir-Hinshelwood model producing a rate constant of 0.0018 (mol/m².s) which increased with increasing NCC dose. The reduction products detected by LC-MS/MS suggest a pathway of conversion to 4-aminophenol (4AP) which eventually produced benzoquinone and hydroquinone. Dehydrobenzoquinone was also detected in the solution which is safer than the parent compounds from which the reduction began.