Phenolic Contaminants Drive Selective Radical Pathways for Antibiotic Degradation

Emerging contaminants such as antibiotics and persistent organic pollutants increasingly threaten global water security and public health. Advanced oxidation processes are widely used to degrade these chemicals by generating highly reactive species, yet their effectiveness often declines in real wastewater because multiple contaminants compete for reactive intermediates. Phenolic compounds-common industrial and environmental pollutants-are usually regarded as problematic matrix components that suppress treatment efficiency. However, isolated observations have hinted that pollutant interactions might sometimes produce unexpected positive effects. Whether such cooperation can be systematically understood and controlled has remained unclear. Based on these challenges, deeper investigation into how coexisting contaminants interact during oxidation processes became necessary.

Researchers from Sichuan University and collaborating institutions reported the findings (DOI: 10.1016/j.ese.2026.100680) in Environmental Science and Ecotechnology (Available online 27 February 2026). The study investigated how phenolic contaminants influence antibiotic removal within a permanganate/chlorite oxidation system. Using sulfamethoxazole as a model antibiotic, the team demonstrated that phenolic compounds fundamentally reshape reaction pathways, generating stable radical intermediates that dramatically accelerate degradation. The work combines experimental chemistry, spectroscopy, and theoretical modeling to reveal a previously unrecognized contaminant-assisted oxidation mechanism that improves treatment performance in complex water systems

The researchers first evaluated how different coexisting pollutants affect antibiotic degradation. Most contaminants inhibited removal, as expected from competitive reactions. Surprisingly, phenolic compounds produced the opposite effect: sulfamethoxazole removal increased from roughly 15% to nearly complete degradation within minutes under optimized conditions.

Mechanistic experiments revealed that the enhancement was not caused by conventional reactive oxygen species. Instead, phenolic molecules underwent proton-coupled electron transfer reactions with permanganate and chlorite, forming long-lived phenoxyl radicals. Unlike short-lived oxidants, these radicals persisted after the initial reaction stage and continued degrading antibiotics independently.

Advanced spectroscopic trapping experiments confirmed the presence of phenoxyl radicals, while inhibition tests showed that removing them halted degradation entirely. Computational modeling further demonstrated that hydrogen-bond-mediated electron transfer drives radical formation, explaining why only certain phenolic structures produce strong acceleration effects.

Importantly, the radicals displayed selective behavior: they preferentially attacked amino-containing antibiotics through electron transfer followed by radical–radical coupling reactions. Their activity correlated with pollutant hydrophobicity, revealing an unusual selectivity mechanism rarely observed in inorganic oxidation systems. Moreover, the radicals remained effective even in real water matrices containing inorganic ions and natural organic matter, highlighting strong resistance to environmental interference.

According to the research team, the study challenges the traditional view that contaminant coexistence is always detrimental to water treatment. By demonstrating that phenolic pollutants can function as reactive mediators, the work introduces a paradigm shift from eliminating interference to engineering beneficial chemical interactions. The researchers emphasize that long-lived phenoxyl radicals combine stability, selectivity, and matrix tolerance-three properties rarely achieved simultaneously in advanced oxidation systems. This insight provides a mechanistic foundation for designing adaptive remediation strategies capable of handling increasingly complex wastewater compositions.

The discovery suggests new opportunities for treating pharmaceutical wastewater, where phenolic byproducts and antibiotics frequently coexist. Instead of removing phenolic compounds beforehand, treatment systems could exploit them to enhance oxidation efficiency through controlled pre-oxidation stages. Such strategies may improve pollutant removal while reducing chemical consumption and operational costs. The findings also support a broader shift toward "self-adaptive" remediation technologies that leverage contaminant networks rather than treating pollutants individually. Future work will focus on pilot-scale testing, process optimization, and intelligent control systems capable of adjusting oxidant dosing under fluctuating wastewater conditions. Ultimately, the study points toward smarter water treatment designs that transform pollution complexity into a functional advantage.