Iron complex breaks down stubborn pollutant using light-powered reaction

Harmful algal blooms and some groundwater contamination are caused by the same nitrogen compound that has supported agriculture for centuries: nitrate. While essential for plant growth, nitrates are challenging to eliminate due to their stability. University of Michigan scientists have devised a method to convert nitrates into reusable compounds using light-powered reactions.

Nitrogen, a critical element in the nitrogen cycle, is inert in its atmospheric form but can be converted to ammonia or nitrates through lightning or bacterial processes. Overfertilization has led to excessive nitrate runoff, disrupting ecosystems and causing environmental issues.

Researchers led by U-M chemist Nathaniel Szymczak examined how nature binds nitrates using hydrogen bonds in proteins called nitrate transporter proteins. They discovered that positioning hydrogen bonds correctly can influence nitrate's bonding structure, enabling reduction.

The team created an iron complex with hydrogen bonds, which selectively binds nitrates and primes them for reduction. When heated, the iron complex removes oxygen from nitrate, converting it to nitric oxide, which has medical and other applications. Under light, the iron complex removes oxygen entirely, transforming nitrate into ammonia, which can be reused as fertilizer.

This research provides a foundation for developing methods to remove nitrates from the environment, addressing the challenges posed by excess nitrate levels in wastewater treatment plants and other sites. The study advances fundamental understanding of nitrate behavior and reduction, paving the way for innovative solutions to environmental concerns.