Key Takeaways & Executive Findings
- •• • FeCl3 anchoring on g-C3N4 achieves high dispersion, enabling efficient photo-Fenton degradation of oxytetracycline, with performance validated in Water Research (2024) – critical for treating antibiotic-laden wastewater. • • Z-scheme γ-Fe2O3/g-C3N4 in Photo-Fenton reaction degrades oxytetracycline, with mechanism and DFT calculations confirming enhanced charge separation – provides a design blueprint for solar-driven remediation. • • Oxygen vacancy engineering and built-in electric field in Fe-g-C3N4/Bi2MoO6 Z-scheme heterojunction boosts photo-Fenton degradation of tetracycline, achieving superior performance (Small, 2024) – addresses recalcitrant antibiotic residues. • • Nitrogen-doped carbon quantum dots modified dual-vacancy Z-scheme CuFe2O4/g-C3N4 synergizes with Fenton technique for photothermal degradation of antibiotics (Chemical Engineering Journal, 2024) – demonstrates multifunctional integration for enhanced efficiency.
Abstract
Emerging organic pollutants (EOPs) represent a class of toxic and hazardous chemicals characterized by ecotoxicity, environmental persistence, and bio-accumulation. Conventional water treatment processes have proven inadequate in eliminating these EOPs, leading to their accumulation in aquatic ecosystems and posing severe threats to the health and safety of aquatic organisms. Consequently, the development of efficient technologies for the complete elimination of EOPs from water matrix is of great importance. Recently, carbon nitride (CN)-based photocatalytic degradation technologies have been extensively utilized for the efficient treatment of organic pollutants in water environments due to their advantages of being green, efficient, and cost-effective. Furthermore, the catalytic activity of CN-based photocatalytic systems can be significantly improved and energy recovery can be achieved via coupling these systems with other advanced oxidation technologies. This review provides a critical review of the modification strategies for CN photocatalytic materials and their application in photocatalytic coupling systems toward EOPs elimination. Moreover, the opportunities and challenges on the photocatalytic coupling systems have been discussed.
1. Introduction
Emerging organic pollutants (EOPs) such as endocrine disruptors, pharmaceuticals, and perfluorinated compounds persist in aquatic environments due to the inefficacy of conventional treatment processes like activated sludge. Their concentrations in surface waters can reach up to 233 µg·L−1 for PFCs, and in Chinese rivers, over 121 quantifiable EOPs have been identified, including antibiotics and PAHs, at concentrations ranging from 7.07 to 4611.26 ng·L−1. This contamination poses severe risks to aquatic organisms and human health, necessitating advanced oxidation processes (AOPs) capable of complete mineralization.
Graphitic carbon nitride (g-C3N4) photocatalysis offers a green, cost-effective solution, but its practical application is hindered by rapid charge recombination and limited visible-light absorption. Coupling g-C3N4 with other AOPs, such as Fenton or persulfate activation, enhances degradation efficiency and enables energy recovery. This review critically examines modification strategies—including elemental doping, heterojunction construction, and defect engineering—and their integration into coupled systems, providing a roadmap for overcoming current bottlenecks in EOP removal.
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WANG Yingfei, CHEN Ping, LIU Guoguang (2026). Degradation of Emerging Organic Pollutants in Water Matrix over Modified Graphitic Carbon Nitride Based Photocatalytic Coupling Systems. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025030303
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Frequently Asked Questions
What are the main limitations of pristine g-C3N4 in photocatalytic degradation of EOPs, and how do modification strategies address them?
Pristine g-C3N4 suffers from rapid recombination of photogenerated electron-hole pairs and limited visible-light absorption. Modification strategies such as metal doping (e.g., Fe, Mn), construction of Z-scheme heterojunctions (e.g., γ-Fe2O3/g-C3N4), and introduction of oxygen vacancies (e.g., Fe-g-C3N4/Bi2MoO6) enhance charge separation and extend light absorption, thereby improving degradation efficiency.
How does coupling g-C3N4 with Fenton or persulfate-based AOPs improve degradation performance compared to photocatalysis alone?
Coupling introduces additional reactive oxygen species (e.g., hydroxyl radicals, sulfate radicals) and facilitates redox cycles (e.g., Fe2+/Fe3+), leading to synergistic effects. For instance, photo-Fenton systems with Fe-g-C3N4/Bi2MoO6 achieve higher tetracycline degradation rates due to enhanced electron transfer and radical generation.
What are the scalability challenges for these coupled photocatalytic systems in real water treatment?
Scalability issues include catalyst stability over multiple cycles, potential leaching of metal ions, and energy costs for light sources. Research must focus on developing robust, recyclable catalysts and optimizing reactor designs for solar-driven applications to achieve cost parity with conventional treatments.
Can these systems achieve complete mineralization of EOPs, and what metrics are used to assess this?
Complete mineralization is assessed via total organic carbon (TOC) removal and identification of intermediate products. Studies report high TOC removal efficiencies, but residual intermediates may remain. For example, in photo-Fenton systems, oxytetracycline degradation follows pseudo-first-order kinetics with rate constants up to 0.05 min−1, but TOC removal may be lower, indicating partial mineralization.
What is the role of light wavelength and intensity in these coupled systems, and how does it affect energy efficiency?
Visible light (λ > 400 nm) is typically used to activate g-C3N4-based catalysts. Light intensity influences photon absorption and charge carrier generation. Energy efficiency is often quantified by electrical energy per order (EE/O). For instance, in persulfate-assisted systems, the quantum yield can be improved by optimizing catalyst loading and light intensity, but excessive intensity may lead to heat generation and reduced efficiency.
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