Mid-Infrared monitoring of aromatic hydrocarbons in an aquatic environment based on polyhydroxyalkanoate biopolymers for use in a chalcogenide infrared microsensor

Abstract

In the context of mid-infrared monitoring of chemical pollutants in an aquatic environment, petrosourced polymers are typically used for the functionalization of optical infrared transducers. These polymers serve to extract pollutants from water solutions while minimizing the interference caused by the strong infrared absorption of water in the relevant spectral regions. This work explores the feasibility of replacing petrosourced polymers with their bio-based alternatives. The inspiration behind this study was to find durable and environmentally friendly polymer materials, capable of replacing conventional polymers, which are deposited on a chalcogenide infrared transducer designed for evanescent wave spectroscopy. Regarding the life cycle analysis of the optical infrared transducer, this substitution aims to minimize potential pollution arising from the manufacturing process, as well as its degradation or wear during field use. For this, polymers from the polyhydroxyalkanoate (PHA) family were considered and several commercial PHAs with different molecular structures were chosen for this evaluation. The optical transducers were functionalized by depositing a PHA membrane, which was prepared using a phase inversion procedure. Different solvents were evaluated for this process as well as two casting methods, namely spin-coating and knife-coating. The two least crystalline PHA samples (crystallinity degree of 0% and 19%) were found to be suitable for BTX detection, unlike other tested variants of PHAs. Calibration curves were then established with these two polymers, followed by a regeneration experiment, where the amorphous PHA demonstrated the ability to be regenerated by distilled water under ambient conditions. This paper presents, for the first time, the use of a bio-based polymer for mid-infrared in situ monitoring of aromatic hydrocarbons in aquatic environments. Furthermore, these polymers are compatible with infrared microsensors based on chalcogenide materials. These results open up possibilities for the use of PHAs in a new field, where their application has been previously unexplored and propose an environmentally friendly solution to the problem of water absorption.