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Nitrate pollution in water threatens ecosystems and human health, yet removing it efficiently without producing harmful byproducts remains a challenge. A new study reports a dual single-atomic catalyst engineered on double-shelled mesoporous carbon spheres that achieves both high activity and selectivity.

Excessive nitrate levels in groundwater and wastewater often originate from agriculture, sewage, and industrial effluents, causing eutrophication, ecological imbalance, and health risks such as methemoglobinemia. Traditional treatment methods, including biological denitrification, membrane separation, and adsorption, suffer from high costs, energy demands, or secondary pollution.

Electrocatalytic denitrification has emerged as an attractive alternative, directly converting nitrate into either ammonia or nitrogen gas. However, most catalysts favor ammonia formation due to easier hydrogenation pathways, raising issues of toxicity and recovery costs. Based on these challenges, there is an urgent need to design catalysts that selectively convert nitrate to harmless nitrogen gas, ensuring sustainable water treatment.

Researchers from Jiangnan University have developed a novel dual single-atomic catalyst that selectively converts nitrate into nitrogen gas with exceptional efficiency. The study, in Eco-Environment & Health, demonstrates how double-shelled mesoporous carbon spheres hosting iron and magnesium atomic sites enable nearly complete nitrate removal while avoiding harmful ammonia production. With 92.8% nitrate conversion and 95.2% nitrogen selectivity, the catalyst showed remarkable stability in long-term flow cell operation, highlighting its potential for advancing sustainable wastewater treatment technologies.

The team designed the FeNC@MgNC-DMCS catalyst using a sequential modular assembly and pyrolysis strategy, producing double-shelled mesoporous carbon spheres with spatially separated atomic sites. The inner shell contains Fe–N₄ sites that accelerate nitrogen–nitrogen coupling, while the outer Mg–N₄ shell creates moderate basicity, acting as a "proton fence" to regulate hydrogen distribution. This architecture minimizes competing hydrogenation that would otherwise yield ammonia.

Laboratory tests revealed that the optimized catalyst achieved 92.8% nitrate removal with 95.2% nitrogen selectivity, far outperforming single-shelled or single-metal controls. Mechanistic studies using in situ mass spectrometry and infrared spectroscopy confirmed that the reaction pathway favored N–N coupling rather than N–H hydrogenation.

The catalyst also demonstrated resilience across a wide pH range and varying nitrate concentrations, while maintaining high selectivity in the presence of interfering ions. In continuous flow cell experiments with simulated wastewater, the catalyst preserved >90% removal and >93% nitrogen selectivity over 250 hours. Importantly, leaching of Fe and Mg was minimal and well below World Health Organization drinking water standards, underscoring its structural stability and environmental safety.

"This work illustrates how careful atomic engineering can fundamentally shift reaction pathways in electrocatalysis," said Professor Hua Zou, co-corresponding author of the study. "By introducing a magnesium-based proton fence around iron catalytic centers, we effectively prevented the side reactions leading to ammonia formation. The result is a catalyst that not only achieves high activity but also unprecedented nitrogen selectivity. Such advances pave the way toward practical, scalable solutions for nitrate pollution, which is a pressing issue for global water sustainability."

The development of FeNC@MgNC-DMCS catalysts opens new possibilities for clean water technologies. With its high nitrate removal efficiency, excellent nitrogen selectivity, and long-term durability, the system is particularly suited for wastewater treatment in agricultural and industrial settings where nitrate contamination is severe.

Beyond water purification, the design strategy—combining dual single-atomic sites within a hierarchical carbon framework—provides a blueprint for tailoring other catalytic processes that require balancing competing reaction pathways. By addressing both environmental safety and operational feasibility, this work contributes to global efforts aimed at mitigating nitrate pollution and advancing sustainable resource management.