The new material is six times more efficient than conventional biochar at converting cadmium, lead, copper and zinc into safe forms and thereby preventing them from entering plants and groundwater from the soil. The technology will help make the restoration of polluted lands in industrial regions of Russia more efficient and affordable, preventing the ingress of toxic elements into living organisms.

Heavy metals such as lead, cadmium, copper, zinc and others enter the soil near factories, power plants, mining and metallurgical enterprises. They do not decompose in nature, and therefore remain in the soil for decades, enter plants and are transported with groundwater to rivers and lakes. As a result, heavy metals enter the animal and human bodies through food chains, accumulating in organs and tissues. In large quantities, these elements lead to damage to the nervous tissue, kidneys, heart and other organs, so it is important to control their content in the environment and, if necessary, clean the soil from them.

One of the cheap and easy ways to clean is using biochar. This porous carbonaceous material, which is obtained from plant waste (straw, husks, husks, and others), is resistant to decomposition and can persist in the soil for hundreds to thousands of years. It absorbs and fixes heavy metals well, and therefore does not allow them to enter groundwater, plants and other living organisms. However, for heavily polluted lands, its capabilities are often insufficient due to the small surface area, which leads to high material consumption and reduces the efficiency of cleaning.

Scientists from the Southern Federal University and colleagues from the Institute of Genetics and Experimental Plant Biology of the Academy of Sciences of the Republic of Uzbekistan (Uzbekistan) have improved the ability of biochar to absorb pollutants by coating its surface with nanoparticles of an iron-containing metal-organic framework.

The authors obtained biochar from wheat straw by heating it without oxygen to 700 °C for 45 minutes. Then the biochar was mixed with iron powder and organic acid, heated for 20 hours at 120 ° C, as a result of which nanoparticles of metal-organic polymer formed on its surface. The researchers studied the structure of the resulting material and found that due to the nanoparticles, the surface area of biochar increased sixfold. This means that the composite has much more "working areas" for binding heavy metals.

The scientists tested the resulting sorbent in an experiment with chernozems contaminated with heavy metals. Six months after applying the sorbents, the researchers estimated how many mobile forms of metals remained in the soils — dangerous, easily entering groundwater and plants — and how many had transformed into tightly bound, safe and practically non-migrating forms. It turned out that the "improved" biochar reduced the number of mobile forms of cadmium by 24-32%, lead by 8-12%, and copper and zinc by 7-11%. This is because when metals entered the pores of the absorber, they were firmly bound to them and could no longer escape. For comparison, pure biochar absorbed about half as many pollutants.

"The proposed material is effective even at low dosages — it is enough to apply it in an amount of 1-2% of the soil mass. This makes the technology economically more profitable than the expensive removal and removal of soil to landfills. The development will make it possible to effectively restore the soils of industrial zones, urban areas and agricultural lands. In the future, we will work to adapt the technology to different types of soils, from chernozems to sandy soils, as well as to different climatic conditions," says Tatiana Bauer, PhD, Senior Researcher at the SFedU laboratory of Agrobiotechnology for Improving Soil Fertility and Agricultural Product Quality.".

The results of the study, supported by a grant from the Russian Science Foundation (RSF), are published in the journal Environmental Nanotechnology, Monitoring & Management.