MXene material can counter mercury contamination

Researchers estimate that mercury emissions to the atmosphere have quadrupled since the industrial revolution. The heavy metal, generated by burning fossil fuels and disposing of industrial and medical waste, has become so persistent in aquatic environments that the United States Food and Drug Administration suggests that about half a dozen species fish are so contaminated with mercury that people should avoid consuming it. their. Researchers have been working for many years to develop systems to remove mercury from water. But a team from Drexel University may have found the right material to effectively catch evasive quicksilver – even at low levels – and clean up contaminated bodies of water.

Of the many methods for removing mercury from water, adsorption – the process of attracting and chemically removing contaminants – is the most promising technology due to its relative simplicity, efficiency and low cost. low cost, according to Dr. Masoud Soroush, PhD, a professor at Drexel College of Engineering, whose lab is developing new adsorption technology.

“Modern adsorbents, such as resins, mesoporous silica, chalcogenides, and mesoporous carbons, have higher efficiencies than traditional adsorbents, such as activated carbon, clays, and zeolites which have low affinity for mercury. and low abilities,” Soroush said. “However, the problem with all of these materials is that their mercury removal efficiency is still low and they are unable to lower the mercury level below 1 part per billion.”

Soroush’s team of researchers from Drexel and Temple University explored the synthesis and use of a surface-modified titanium carbide MXene for mercury removal. MXenes are a family of two-dimensional nanomaterials discovered at Drexel over a decade ago that have demonstrated many unique properties. The team recently published their results in the Hazardous Materials Journal.

For mercury ion removal, the advantages of MXene titanium carbide, according to Soroush, are its negatively charged surface and the tunability and versatility of its surface chemistry, which makes MXene attractive for mercury ion removal. heavy metals. Due to these properties and the layered structure of MXene, MXene titanium carbide materials have shown superior performance in gas separation, salt removal from water, bacteria killing and renal dialysis.

“We knew that 2D materials, such as graphene oxide and molybdenum disulfide, had previously been effective in removing heavy metals from wastewater by adsorption due to their chemical functionalities/structures that attract metal ions,” Soroush said. “MXenes are a similar type of material, but we felt that titanium carbide MXene might have much greater absorption capabilities than these other materials, making it a better sorbent for mercury ions.”

But Soroush’s team needed to make a key adjustment to the chemical structure of MXene titanium carbide to further improve the material for one of its toughest jobs.

“Mercury is called mercury for a reason — it’s pretty elusive once emitted into the environment, whether through fossil fuel burning, mining, or waste incineration,” Soroush said. “It changes chemical form rapidly, which increases its toxicity and makes it extremely difficult to remove from bodies of water where it inevitably accumulates. So to attract mercury ions even faster, we needed to modify the surface of the flakes of MXene titanium carbide.

There is a natural attraction between mercury ions and the surface of MXene titanium carbide, because metal ions, like mercury, are positively charged and the surface of MXene flakes is negatively charged. However, to extract mercury ions more strongly from the water, the team needed to give this attraction a boost. To this end, they treated MXene flakes with chloroacetic acid – a process called carboxylation – which provides MXene with strong, highly mobile carboxylic acid groups and increases the surface negative charge of MXene flakes, enhancing thus the ability of the flakes to attract and retain mercury ions.

The result was a new sorbent material – MXene carboxylated titanium carbide, which demonstrated faster absorption of mercury ions and greater capacity than any commercially available adsorbent, according to the researchers.

“MXene carboxylated titanium carbide has proven to be far superior to currently used absorber material for mercury ion removal,” Soroush said. “In one minute, it was able to remove 95% of the mercury ions from a contaminated water sample at a concentration of 50 parts per million, meaning it could be effective and efficient enough to be used in large-scale wastewater treatment.”

In five minutes, MXene Titanium Carbide and MXene Carboxylated Titanium Carbide removed 98% of mercury ions from a 10 milliliter water sample contaminated with mercury ions at concentrations between 1 and 1,000 parts per million .

“This indicates that both [MXene] and [carboxylated MXene] are effective adsorbents for removing mercury ions from wastewater due to their particular structural properties and high density of surface functional groups,” the team wrote. “Generally, the metal ion adsorption mechanism follows two steps; at first, the ions are rapidly adsorbed on the available active sites, and the process is rapid. Adsorption proceeds more slowly as the adsorption sites fill up and the ions must diffuse into the pores and the interlayer.

The development is important in the fight to contain mercury pollution, which has become so widespread that health authorities recommend avoiding eating certain species of fish altogether. Efforts to contain the mercury released by burning fossil fuels have proven as difficult as reducing dependence on the fuels themselves. While moving away from polluting energy sources is the ultimate solution to preventing the release of heavy metals, like mercury, into the environment, Soroush suggests this breakthrough could open up new possibilities for cleaning up the pollution that has already been created. .

“We are considering the use of carboxylated MXene technology to remove all heavy metal ions,” he said. “Besides using the carboxylated MXene as a sorbent, another way to achieve this is to make filters coated or embedded with the carboxylated MXene.”

Besides Soroush, Ali Pournaghshband Isfahani and Ahmad A. Shamsabadi from Drexel University and Farbod Alimohammadi from Temple University contributed to this research. It was supported by the National Science Foundation. Read the full article here: https://www.sciencedirect.com/science/article/abs/pii/S0304389422005696?via%3Dihub

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