Converting environmental challenge into chemical resource: New catalyst for nitrite-to-ammonia conversion

Water-soluble nitrite (NO₂⁻) pollution from agricultural runoff and industrial discharge poses serious risks to ecosystems and human health. Excessive nitrite in drinking water can cause severe health problems including thyroid disorders and methemoglobinemia (a dangerous blood condition that impairs oxygen transport). While current nitrite removal technologies like adsorption and biological treatment are available, they face challenges related to complex operation and high costs. The growing accumulation of nitrite in aquatic environments has created an urgent need for more effective and economical remediation strategies.

Researchers from Chengdu University of Technology, Sichuan University, and Shandong Normal University have developed an innovative solution that not only removes harmful nitrite from water but also transforms it into valuable ammonia, offering dual benefits for environmental remediation and resource recovery. This approach offers a promising alternative to conventional wastewater treatment methods, with potential advantages in both environmental impact and resource utilization.

"We've developed a highly selective electrocatalyst by decorating cobalt-iron layered double hydroxides (CoFe-LDH) on a three-dimensional titanium dioxide array," the authors explain. "This novel catalyst structure significantly enhances the conversion of nitrite to ammonia while minimizing unwanted hydrogen production."

The key innovation lies in the catalyst's ability to provide superior hydrogen species supply and hydroprocessing capability. During electrochemical reduction, the CoFe-LDH component efficiently breaks down water molecules to generate hydrogen species, which then combine with nitrite ions to form ammonia. The 3D TiO2 array provides an ideal support structure with high surface area and chemical stability, while the CoFe-LDH provides abundant active sites for the electrochemical reaction. This synergistic effect between the components is crucial for achieving high conversion rates.

Under alkaline conditions, the catalyst (named TiO₂@CoFe-LDH/TP) achieved an impressive ammonia yield of 1056.4 μmol h⁻¹ cm⁻² with a Faradaic efficiency of 97.4% at −0.6 V, significantly outperforming traditional TiO₂ and CoFe-LDH catalysts. Even more remarkably, the catalyst maintained Faradaic efficiency above 87% across a range of applied potentials, demonstrating its robust performance. The high efficiency indicates minimal energy waste during the conversion process, making it more environmentally and economically favorable.

"The most exciting aspect of our work is the catalyst's practical application potential," the researchers note. "In a 60-hour simulated wastewater treatment experiment, our catalyst reduced nitrite concentrations from several hundred mg L⁻¹ to below 15 mg L⁻¹ while enabling efficient recovery of solid ammonium chloride." This substantial reduction in nitrite levels, coupled with the simultaneous recovery of a valuable product, illustrates the promising application potential of this technology for treating nitrite-contaminated wastewater.

The hierarchical structure of the catalyst plays a vital role in its performance. The 3D nanobelt array architecture maximizes the contact area between the catalyst and nitrite ions in solution, while the uniform coverage of CoFe-LDH nanosheets ensures a high density of active sites. Electrochemical analyses revealed that the catalyst exhibits lower electron transfer resistance and faster charge transfer rates compared to other materials, contributing to its superior performance.

This report offers a sustainable approach to wastewater treatment that aligns with circular economy principles by converting a pollutant into a valuable chemical resource. Ammonia is a critical compound used extensively in fertilizer production, refrigeration systems, and various industrial processes. By regenerating ammonia from nitrite waste, this technology helps reduce dependence on energy-intensive ammonia synthesis methods like the Haber-Bosch process.

The team emphasizes, "Unlike noble metal-based catalysts that face limitations due to high cost and scarcity, our catalyst uses earth-abundant elements like cobalt, iron, and titanium. This makes our approach more economically viable for large-scale applications in industrial wastewater treatment and ammonia production." The use of low-cost materials addresses a major barrier to the widespread adoption of advanced water treatment technologies.

The researchers plan to further optimize the catalyst structure and explore its application in treating real industrial and agricultural wastewater streams. Future work will focus on enhancing catalyst stability for long-term operation and adapting the system for varying nitrite concentration levels typically found in different wastewater sources.

Other contributors to this research include Yi Liang, Xun He, Dongdong Zheng, Shengjun Sun, and Yongsong Luo.

This work was supported by the Sichuan Province Youth Fund Project (2025ZNSFSC0897).

About the Authors

Dr. Xuping Sun is a full professor at Sichuan University and Shandong Normal University, China. He is a Fellow of the Royal Society of Chemistry and a globally highly cited scientist in chemistry and materials science. His research interests focus on nanomaterials design and synthesis, including heteroatom-doped carbon dots, transition metal phosphide nanostructures, electrochemical sensing devices, and catalytic systems for electrochemical ammonia synthesis. Professor Sun serves as Associate Editor of Nano Research Energy and Academic Editor of iScience. He has published over 700 research papers in prestigious journals such as Nat. Synt., Nat. Commun., J. Am. Chem. Soc., Angew. Chem., Adv. Mater., Adv. Energy Mater., Nano Lett., Nucleic Acids Res., Anal. Chem., etc., with over 80,000 citations and an H-index of 151.

Dr. Xiaoya Fan is a master's supervisor at Chengdu University of Technology. She received her Doctorate in Engineering from the University of Electronic Science and Technology of China in June 2024. Her main research focuses on the design of nano-functional material interfaces and their performance and promotion mechanisms in electrochemical ammonia synthesis and C-coupled electrocatalytic synthesis of small molecules. She has published over 40 SCI papers to date, including 9 papers as first author or corresponding author in internationally renowned journals such as Adv. Mater., Small, Anal. Chem., and Nano Res.

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.