Scaffolding molecule pulls glyphosate out of the water

Scaffolding molecule pulls glyphosate out of the water

Glyphosate could be removed from water using a metal-organic framework. © Shaghayegh Naghdi

The herbicide glyphosate is widely used around the world, but is highly controversial due to possible health and environmental effects. Chemists have now developed a special chemical filter that can selectively remove the pesticide from water. Active centers in a metal-organic framework hold the herbicide in place. This opens up new opportunities to remove glyphosate contamination from drinking water and wastewater.

Glyphosate is the world’s most commonly used crop protection product – it accounts for around 60 percent of the total volume of herbicides used worldwide. So it’s no wonder that glyphosate has long been present in soil, water and the food chain. This is precisely why the use of this pesticide is highly controversial. Because there is increasing evidence that organophosphate can cause malformations and nerve damage in various organisms, and it is also suspected of being carcinogenic.

Metallo-organic framework as a glyphosate scavenger

A new technique could now help to remove glyphosate contamination from water – for example when treating drinking water. The core component of the method developed by Shaghayegh Naghdi from the Technical University of Vienna and her colleagues is a metal-organic framework (MOF). These porous solids consist of an organic hydrocarbon framework into which metal ions are attached via complex bonds. Due to their spongy structure, these molecular complexes have a particularly large surface area of ​​up to 7000 square meters per gram.

“This means that there is space for a whole soccer field in one gram of MOF,” explains senior author Dominik Eder from the Vienna University of Technology. “As a result, many molecules can be adsorbed in the pores, which makes MOFs ideal materials for binding molecules such as CO2, inorganic salts and organic pollutants directly from the air or water.” When scaffold molecules are latched, the MOF selectively bind only certain substances and trap them in their pores. “Think of MOFs as a large building made up of individual small blocks,” explains Naghdi. “Each block is made of metal atoms or organic molecules, and you put them together like a puzzle to achieve the desired functions.”

Effective adsorption

This is exactly what Naghdi and her colleagues have now used to construct a selective “filter” for glyphosate. As a starting point, they used the framework compound MIL-125-Ti, which contains titanium ions in the lattice. However, under normal conditions, the pores of this MOF are too narrow for efficient adsorption of the glyphosate. To solve this problem, the chemists have developed a strategy to incorporate additional pores with a diameter of up to ten nanometers into their MOF. To do this, the chemists selectively reduced the number of organic struts in the framework. Not only does this create more space for the glyphosate, it also encourages the creation of additional active binding sites for the herbicide.

The result is a metal-organic framework that can selectively and efficiently remove glyphosate from water. Initial tests showed that the new material can absorb three times as much glyphosate in just 20 percent of the time as the current best adsorbent. “At the same time, the bonds are weak enough to remove glyphosate with a simple sodium chloride saline solution, so these MOFs can be used multiple times,” says Eder. The research group plans to develop other MOFs that can adsorb or convert other pollutants.

Source: Vienna University of Technology, specialist article: Advanced Functional Materials, doi: 10.1002/adfm.202213862)

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