The Role of the Reactive Species Involved in the Photocatalytic Degradation of HDPE Microplastics Using C,N-TiO2 Powders.

Aranza Denisse Vital-Grappin,Juan Francisco Villarreal-Chiu,Valeria Montserrat Luna-Hernández,Maria Camila Ariza-Tarazona,Cristina Siligardi,Erika Iveth Cedillo-González,Juan Manuel Hernández-López

doi:10.3390/polym13070999

Aranza Denisse Vital-Grappin, Juan Francisco Villarreal-Chiu + Show 5 more

Open Access

https://doi.org/10.3390/polym13070999

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Abstract

Microplastics (MPs) are distributed in a wide range of aquatic and terrestrial ecosystems throughout the planet. They are known to adsorb hazardous substances and can transfer them across the trophic web. To eliminate MPs pollution in an environmentally friendly process, we propose using a photocatalytic process that can easily be implemented in wastewater treatment plants (WWTPs). As photocatalysis involves the formation of reactive species such as holes (h+), electrons (e−), hydroxyl (OH●), and superoxide ion (O2●−) radicals, it is imperative to determine the role of those species in the degradation process to design an effective photocatalytic system. However, for MPs, this information is limited in the literature. Therefore, we present such reactive species’ role in the degradation of high-density polyethylene (HDPE) MPs using C,N-TiO2. Tert-butanol, isopropyl alcohol (IPA), Tiron, and Cu(NO3)2 were confirmed as adequate OH●, h+, O2●− and e− scavengers. These results revealed for the first time that the formation of free OH● through the pathways involving the photogenerated e− plays an essential role in the MPs’ degradation. Furthermore, the degradation behaviors observed when h+ and O2●− were removed from the reaction system suggest that these species can also perform the initiating step of degradation.

Highlights

Microplastics (MPs) are defined as plastic particles with a diameter ≤ 5 mm and are categorized as primary or secondary according to their origin [1]
The Fourier-transform infrared spectroscopy (FTIR) analysis carried out on the microbeads (Figure 1b) revealed the characteristic vibrational bands of high-density polyethylene (HDPE), these being the bands at 2911 and 2846 cm−1 that correspond to the asymmetric and symmetric stretching vibrations of the CH2 group and the bands at 1463 and 719 cm−1 that correspond to the scissoring and rocking bending vibrations of the density polyethylene (HDPE), these being the bands at 2911 and 2846 cm−1 th to the asymmetric and symmetric stretching vibrations of the CH2 group and 1463 and 719 cm−1 that correspond to the scissoring and rocking bending vib same group [27]
scanning electron microscopy (SEM) micrographs demonstrated that the surface5 oof f18the blu exhibited a homogeneous roughness, which may be related to their applica ssiavmeeignrofuapc[i2a7l].sScErMubmsic(rFogigrauprhes d1ecm).onFsutrratthedetrhmatothree,susrofamceeofmthienbilmueaml ircoroubgeahdns ess-rel wexahsibpiterdesaehnomt,owgehneicouhs lreouagdhsnetsos, awhsiuchrfmaacyebae rreelaateodfto0.t4he1ir±ap0p.l0ic3atimon2/ags a(bFraigsiuvere 1d)

Summary

Introduction

Microplastics (MPs) are defined as plastic particles with a diameter ≤ 5 mm and are categorized as primary or secondary according to their origin [1]. Primary MPs are manufactured explicitly to that particle size to be used in cosmetic or personal hygienic products [1]. As MPs are frequently consumed by the biota present in aquatic and terrestrial ecosystems, these hazardous compounds can move through the trophic chain up to humans [1,2]. This has been evidenced by the presence of MPs in human stool [4] and even in the placenta [5]. The SARS-CoV-2 pandemic has increased MPs fibers’ presence in the environment due to the inadequate disposal of single-use plastic face masks [6]

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