A new chemical strategy offers precision control in water treatment by producing hydroxyl radicals (•OH) only within a specific pH range. In this newly developed system, hydroxylamine and EDTA are used to finely tune iron-based redox reactions in a modified Fenton process. The system intelligently halts radical production when pH falls outside the optimal window of 7.0 to 10.0—automatically preventing side reactions, corrosion, and treatment inefficiencies in fluctuating water environments. This "pause-then-adjust" mechanism ensures both immediate responsiveness and spatially coordinated pollutant removal, addressing a longstanding hurdle in smart water management. The technology marks a step forward in developing intelligent, adaptive oxidation processes tailored for complex and hazardous wastewater streams.
Despite advances in real-time monitoring, smart water systems still struggle with delayed feedback and uneven chemical distribution. In large-scale or decentralized operations, these issues can reduce the effectiveness of treatment or, worse, lead to dangerous byproducts such as cyanide volatilization. The Fenton reaction—renowned for generating potent oxidants—remains sensitive to pH changes, limiting its applicability in variable environments. Traditional solutions attempt to broaden the pH range through chemical adjustments, but often at the expense of safety or sensitivity. These challenges highlight the urgent need for self-regulating chemical systems that can autonomously respond to environmental signals, especially pH fluctuations.
In response to these challenges, scientists from Xiamen University and partnering institutions have unveiled a pH-responsive Fenton system that activates only under optimal alkaline conditions. Published (DOI: 10.1016/j.ese.2025.100566) on May 13, 2025, in Environmental Science and Ecotechnology , the study demonstrates how specific iron–ligand complexes enable a self-limiting oxidation process precisely tuned to real-time pH levels. By doing so, the researchers have introduced a "smart Fenton" platform that improves safety, reactivity, and adaptability in water purification—particularly in scenarios involving hazardous or pH-sensitive waste.
At the core of this innovation is a modified Fenton reaction incorporating hydroxylamine (HA) and EDTA. Unlike conventional acidic systems, this configuration generates hydroxyl radicals only when the solution pH is between 7.0 and 10.0. Using benzoic acid as a probe and electron spin resonance (ESR) for detection, the team confirmed up to 69% degradation at pH 9.0. Further computational modeling revealed that changes in pH influence the structure—and thus the reactivity—of iron–EDTA complexes. Specifically, [Fe²⁺–EDTA]2− is most effective in activating hydrogen peroxide, while [Fe³⁺–OH–EDTA]2− is more easily reduced by HA. These complementary species coexist only within the defined pH range, enabling controlled radical production. Importantly, once the pH drifts out of range, the reaction self-terminates—offering a built-in safety mechanism that avoids harmful byproducts or equipment wear. A multiple-dosing strategy for HA further improves radical stability and extends •OH half-life, enhancing overall system performance in dynamic water environments.
This pH-responsive Fenton system introduces a paradigm shift in oxidation-based water treatment, said Dr. Huabin Zeng, corresponding author of the study. Rather than simply expanding the effective pH range, we've designed a process that senses and adapts in real time. It offers built-in safeguards for delicate applications, such as cyanide-containing wastewater, and brings us closer to truly intelligent chemistry in environmental engineering.
The implications of this work are far-reaching for next-generation water management. The system's automatic shutdown in acidic conditions prevents accidental cyanide volatilization, a major risk in industrial wastewater treatment. It also minimizes chemical overuse and reduces reliance on energy-intensive mixing or pH correction methods. With its intelligent control, environmental safety, and operational efficiency, the technology paves the way for a new class of self-regulating chemical processes designed for complex, real-world challenges in sustainable water infrastructure.
