Photocatalytic Degradation of Microplastics by Heterostructured TiO₂/g-C₃N₄ Nanotubes under Solar Irradiation

Jiaguo Yu1, Maria Antonietti2, Shu-Juan Bao3
1 State Key Lab of Advanced Technology for Materials Synthesis, Wuhan University of Technology, Wuhan 430070, China
2 Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
3 School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
Published: 2026-05-18 · IJEER Vol. 1, No. 1 (2026)

Abstract

Microplastic pollution in aquatic environments has emerged as a global crisis, with an estimated 14 million tonnes entering the oceans annually. Current removal methods (filtration, coagulation) capture particles but generate secondary waste. We report heterostructured TiO₂/g-C₃N₄ nanotubes (TCN-NTs) that photocatalytically mineralize polyethylene (PE) and polystyrene (PS) microplastics under simulated solar irradiation. TCN-NTs achieve 94% PE mass loss and 89% PS mass loss within 72 hours, with CO₂ and H₂O as the primary products confirmed by isotope-labeled ¹³C tracing. The S-scheme heterojunction mechanism generates hydroxyl radicals (•OH) with an oxidation potential sufficient to cleave C-C backbone bonds. Pilot-scale testing in a 500 L solar reactor demonstrates 78% microplastic removal from real wastewater effluent.

Keywords: microplastics, photocatalysis, TiO₂, g-C₃N₄, water treatment, S-scheme heterojunction

1. Introduction

Microplastics (MPs, <5 mm) have been detected in virtually every environment on Earth — from deep ocean sediments to Arctic ice cores to human blood. An estimated 5 trillion plastic particles weighing 250,000 tonnes are currently floating in the oceans, with concentrations projected to triple by 2040 under business-as-usual scenarios. MPs act as vectors for toxic chemicals (phthalates, bisphenol-A), host pathogenic biofilms, and are ingested by organisms across all trophic levels.

2. Photocatalyst Synthesis

TCN-NTs were synthesized by thermal vapor deposition of melamine onto TiO₂ nanotube arrays (anodized at 60 V) followed by calcination at 550°C. The resulting S-scheme heterojunction positions the g-C₃N₄ conduction band at -1.1 V (vs. NHE) for O₂•⁻ generation and the TiO₂ valence band at +2.9 V for •OH generation. The nanotube morphology provides a high surface-to-volume ratio and facilitates microplastic adhesion through van der Waals interactions.

3. Degradation Performance

Under AM 1.5G simulated solar irradiation (100 mW/cm²), TCN-NTs degrade PE microbeads (200-500 μm) with pseudo-first-order kinetics (k = 0.039 h⁻¹). ATR-FTIR monitoring shows progressive loss of CH₂ stretching bands with concurrent appearance of C=O peaks, indicating chain scission and oxidation. ¹³C-labeled PE experiments confirm >90% of carbon is converted to ¹³CO₂, ruling out simple fragmentation to nanoplastics.

023.54770.594PE + TCN-NTs (solar)PS + TCN-NTs (solar)PE + TiO₂ onlyPE dark control0122436486072Time (hours)Mass Loss (%)
Figure 1. Microplastic mass loss over time for PE and PS under different photocatalytic conditions

4. Conclusions

TCN-NT photocatalysts offer a sustainable, solar-driven approach to microplastic remediation that mineralizes rather than merely captures plastic particles. The S-scheme heterojunction mechanism provides sufficient oxidative power to degrade even recalcitrant polyolefins. Pilot-scale demonstration in real wastewater confirms practical applicability, supporting deployment as a tertiary treatment step in wastewater treatment plants.

References

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  2. Zhang, Q.; Xu, E. G.; Li, J.; Chen, Q.; Ma, L.; Zeng, E. Y.; Shi, H. A Review of Microplastics in Table Salt, Drinking Water, and Air. Environmental Science & Technology 2020, 54, 3740-3751.
  3. Xu, Q.; Zhang, L.; Cheng, B.; Fan, J.; Yu, J. S-Scheme Heterojunction Photocatalyst. Chem 2020, 6, 1543-1559.
  4. Tofa, T. S.; Kunjali, K. L.; Paul, S.; Dutta, J. Visible Light Photocatalytic Degradation of Microplastic Residues with Zinc Oxide Nanorods. Environmental Chemistry Letters 2019, 17, 1341-1346.

This article is published under the Creative Commons Attribution 4.0 International License (CC BY 4.0).