Monoatomic catalysts help remove organic contaminants. In the course of the new study, scientists learned more about their work and how to create them cheaper and easier.

Researchers from Tokyo Metropolitan University have studied the operation of single-atom catalysts based on iron-pyridine sites in a carbon matrix. First, they developed a new, simple method for synthesizing a catalyst that activates peroxymonosulfate. It is a highly effective compound that helps in breaking down contaminants that are not biodegradable.

In the course of the study, the scientists found that the regions of iron in the high-spin state are strongly correlated with the characteristics of the catalyst due to two different chemical pathways.

The world is full of useful synthetic chemicals, some of them useful and others dangerous. Of particular concern to experts is a class of pollutants known as refractory organics. They are not biodegradable and persist in the environment for a long time. This is why effective disposal or decomposition strategies in wastewater streams are very important.

Scientists have tried to develop efficient catalysts that help break down harmful refractory pollutants. A single-atom catalyst is considered to be promising, in which metal atoms are uniformly dispersed in the carbon matrix. The inclusion of iron would make the technology cheap and non-toxic. However, despite demonstrations in the lab, such a catalyst is still difficult to produce, and their mechanism of operation remains unclear.

Now Japanese scientists have developed a simple method for producing single-atom catalysts with iron-pyridine sites (that’s iron surrounded by four nitrogen atoms) that are “embedded” in carbon sheets.

Based on pyrolysis, the decomposition and recombination of chemicals using heat, the chemists crushed metal oxide frameworks along with melamine and heated the mixture in an inert atmosphere at temperatures above 500 °C. It turned out that when activated with peroxymonosulfate, a common oxidizing agent, the substance effectively removes pollutants, such as bisphenol A (BPA).

The scientists also found that catalysts that were made in different ways had different efficiencies. Using the experimental method of Mössbauer spectroscopy, they studied the state of the iron pyridine sites in different batches. The scientists found a strong correlation between the high-spin states of Fe(ll) and Fe(lll) and catalyst efficiency. It turned out that the high-spin states of iron pyridine are activated by two different mechanisms: either due to the formation of hydroxyl radicals due to peroxymonosulfate, or due to the formation of the Fe(V)-O complex.

The scientists hope that this new technology, and a simple method for making a single-atom catalyst, will be more widely used in real wastewater treatment systems and in environmental cleanup work.