Researchers have enhanced the performance of graphitic carbon nitride (g-C3N4) through targeted molecular surface modifications, improving hydrogen peroxide (H2O2) production and pollutant degradation under visible light.
This recent study in npj Clean Water represents a breakthrough in photocatalytic material research.
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Photocatalysis and Its Role in Sustainable Chemical Processes
Photocatalysis uses light energy to drive chemical reactions, providing a cleaner alternative to traditional methods that rely on harsh chemicals or energy-intensive procedures.
H2O2, an essential oxidizing agent, is typically produced using the anthraquinone method, a process that consumes huge amounts of energy and creates toxic byproducts.
Harnessing visible light with semiconductors for H2O2 generation represents a more sustainable path by activating oxygen reduction reactions under mild conditions.
However, issues like inefficient electron-hole separation and instability in photocatalysts are preventing this generation method from becoming mainstream.
Using rare metals like platinum is a way around these issues, but their high cost and scarcity are pushing researchers toward more accessible alternatives.
Developing Photocatalysts at the Molecular Level for Enhanced Performance
To improve charge separation and stability in photocatalysts, researchers synthesized ten variants (CN-301 to CN-310) of g-C3N4 via amino-site functionalization using substituted benzaldehydes.
They began by heating urea at 580 °C to form a precursor, followed by a condensation reaction in ethanol with acetic acid. This method achieved high yields with scalable, reproducible results.
Subsequent structural characterization through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning and transmission electron microscopy (SEM and TEM), and X-ray photoelectron spectroscopy (XPS) confirmed successful molecular functionalization and improved crystallinity.
Among the derivatives produced, CN-306, functionalized with a trifluoromethyl group, stood out with its higher surface area (83.56 m2/g), compared to unmodified CN550 (52.07 m2/g). The increased surface area allowed for better mass transfer and more accessible active sites.
Optical studies using UV-Vis diffuse reflectance spectroscopy showed a red shift in light absorption and a narrowed bandgap, decreasing from 2.63 eV (CN550) to 2.45 eV (CN-306) and improving visible light utilization.
Electrochemical analysis, including Mott-Schottky plots and photoluminescence measurements, revealed enhanced charge separation, increased lifetimes and reduced electron-hole recombination rates in the modified samples.
Density functionalised theory (DFT) calculations supported this, showing that the electron-withdrawing substituents and amino modifications effectively separated electron-hole pairs and reduced the HOMO-LUMO gap by 0.5–1.0 eV. These observations matched the improvements to photocatalytic activity.
Enhanced Photocatalytic Performance and Mechanistic Outcomes
Performance tests under visible light demonstrated that CN-306 significantly improved H2O2 production in water-ethanol mixtures, with a peak rate of 5022 μmol g-1 h-1.
CN-306 also achieved a quantum yield of 6.82 % at 450 nm, indicating its efficient light-to-chemical energy conversion.
When paired with potassium peroxymonosulfate (PMS), CN-306 greatly accelerated the degradation of Rhodamine B and Fludioxonil, outperforming unmodified CN550 by as much as 32 times. The ideal PMS concentration was found to be 300 μL per 10 mL solution.
Electron Spin Resonance (ESR) spectroscopy detected multiple reactive oxygen species under visible light, including superoxide (O2⁻), hydroxyl radicals (OH), and singlet oxygen (1O2). Detection of these species confirmed the activity of the photocatalytic pathways of CN-306.
ESR spectroscopy also showed that CN-306's conduction band potential was more negative than the O2/O2-1 redox potential, allowing for efficient one-electron reduction of oxygen to O2-, a crucial step in H2O2 formation.
However, free radical scavenging experiments showed that 1O2 competes with the desired reaction by depleting O2-, slightly hindering H2O2 production.
Amino modifications also improved charge dynamics and hydrophilicity. CN-306 showed a lower water contact angle (~50 ° versus 65 ° for CN550), indicating better interaction with aqueous environments.
Durability tests demonstrated over 95 % retention of catalytic activity after five cycles, with no significant structural degradation.
Potential Impact on Environmental and Optical Technologies
This research highlights the importance of surface modification in controlling internal electron-hole distributions, crucial for enhancing photocatalytic efficiency and stability under visible light.
The optimized g-C3N4 photocatalysts offer a solar-powered, sustainable route for H2O2 production, with the potential to replace energy-intensive industrial processes. They also show promise for broader applications like water purification, environmental cleanup, and solar fuel generation.
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Conclusion and Future Directions in Photocatalytic Material Design
This study presented a practical, molecular-level strategy for enhancing g-C3N4 performance in visible-light photocatalysis. Functionalizing the material with electron-withdrawing organic molecules improved electron-hole separation, extended light absorption, and increased both catalytic activity and stability.
Looking ahead, further research should focus on scaling up the synthesis process, exploring additional functional groups, and integrating these materials into environmental remediation and solar-driven chemical production devices.
Journal Reference
Tu, H., et al. Enhancing photocatalytic efficiency through surface modification to manipulate internal electron-hole distribution. npj Clean Water 8, 48 (2025). DOI: 10.1038/s41545-025-00480-4, https://www.nature.com/articles/s41545-025-00480-4
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