TEMA: Analytical approaches to assess degradarion of Micro and Nanoplaplastics over diferent TiO₂/MOF-based photocatalysts

1. Introduction – The presence and accumulation of plastic waste in the environment is a growing concern due to increased global consumption and its resistance to degradation. The presence of microplastics (MPs< 5 mm) and nanoplastics (NPs< 1 μm) in water bodies may have potential adverse effects on human health. Among commonly used plastics, fossil fuel-based polyesters and polyamides are very important classes of condensation polymers. Both types of materials have a variety of applications, such as food packaging, automotive parts, flexible films, and synthetic fabrics. Polyethylene terephthalate (PET) and nylon-6 are common polymers found in aquatic environments and the influents and effluents of wastewater treatment plants. Heterogeneous photocatalysis has been described as a practical treatment technology for removing MPs and NPs from water due to its high efficiency, low cost, and operation facility. The coupling of TiO₂ with other materials as a metal-organic framework (MOF) is a strategy to enhance surface area, reduce the band gap of TiO₂, increase absorption in the visible region, decrease the recombination rate of photogenerated electron-hole pairs, and improve the photocatalytic performance of TiO₂. One of the challenges in the degradation of MPs and NPs is the availability of reliable analytic methods to analyze these solids in the reaction output and relate them to the degree of oxidation of the plastic. This work evaluated the photocatalytic degradation of PET nanoplastics and nylon-6 microplastics in an aqueous solution using TiO₂@MIL-100(Fe) and TiO₂@ HKUST-1 materials.

2. Experimental – TiO₂@MIL-100(Fe) and TiO₂@ HKUST-1 were prepared using the solvothermal method. The photocatalytic efficiency of these materials was then compared with that of pristine TiO₂, synthesized without the addition of MIL-100(Fe) and HKUST-1 under the same experimental conditions. The degradation of PET nanoplastics and nylon-6 microplastics were monitored using a range of advanced analytical techniques, including scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR), total organic carbon (TOC) analysis, thermogravimetric measurement (TGA), X-ray photoelectron spectroscopy (XPS), gel-permeation chromatography (GPC) and gas chromatography with mass spectrometry detection (GC-MS).

3. Results and discussion – The TiO₂@MIL-100(Fe) and TiO₂@HKUST-1, with enhanced visible-light absorption, higher surface area, and decreased electron-hole recombination rate than TiO₂, exhibited improved performance on the PET nanoplastics and nylon-6 microplastics degradation under simulated solar light than TiO₂ as demonstrated by FTIR and XPS analysis, and SEM and TOC measurements. Moreover, the average molecular weight of the polymers decreased after photocatalytic treatment, and the polymers degraded by photocatalytic treatment showed reduced thermal stability that might be attributed to the main chain scission during the photocatalytic process using TiO₂@MIL-100(Fe) and TiO₂@HKUST-1 photocatalysts corroborated by the detected low molecular weight byproducts in the effluent by GC-MS.

4. Conclusions – This comprehensive analytical approach allowed for an accurate correlation of the degradation efficiency with the oxidation of microplastics and nanoplastics through the photocatalytic process. The results strongly suggest that the photocatalytic process using TiO₂@MIL-100(Fe) and TiO₂@ HKUST-1 is a potential approach to degrade PET nanoplastics and nylon microplastics from wastewater effluents, offering a practical solution to the plastic waste problem.

5. Referencias [1] C. A. Rojas-Guerrero, M. Villanueva-Rodríguez, J. L. Guzmán-Mar, A. Hernández-Ramírez, E. I. Cedillo-González, F. L. Rodríguez, L. Hinojosa-Reyes, (J Environ Chem Eng, 11(5), 2023).110415.