Researchers estimate that mercury emissions into 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 Fish species 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 might have found the right material to effectively catch evasive quicksilver — even at low levels — and clean up contaminated waterways.
Of the many methods of removing mercury from water, adsorption – the process of attracting and chemically removing contaminants – is the most promising technology due to its relative simplicity, effectiveness and low cost, according to Dr. Masoud Soroush, PhD, professor at Drexel University 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 capacities,” 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 outstanding properties. The team recently published their findings in the Journal of Harmful Elements.
For the removal of mercury ions, the advantages of MXene titanium carbide, according to Soroush, are its area negatively charged and the tunability and versatility of its surface chemistry, which makes the MXene attractive for heavy metal ion removal. 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 kidney dialysis.
“We knew that 2D materials, such as graphene oxide and molybdenum disulfide, had already been effective in removing heavy metals from wastewater by adsorption due to their chemical functionalities/buildings that attract metal ions,” Soroush said. “MXenes are a similar type of material, but we felt that titanium carbide MXene might have much greater sorptive 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 framework of MXene titanium carbide to further improve the material for one of its toughest jobs.
“Mercury is called mercury for a reason – it is quite elusive once emitted into the atmosphere. environment, whether through burning fossil fuels, mining or incinerating waste,” Soroush said. “It quickly changes chemical form – increasing its toxicity and making it extremely difficult to remove from bodies of water where it inevitably accumulates. So, to attract mercury ions even faster, we needed to change the surface area of the MXene titanium carbide flakes.”
There is a natural attraction between mercury ions and the surface of MXene titanium carbide, because metal ions, such as 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 floor negative charge of MXene flakes, enhancing thus the ability of the flakes to attract and retain mercury ions.
The result was a new absorbent material – MXene carboxylated titanium carbide, which demonstrated faster absorption of mercury ions and greater capacity than any commercially available adsorbent, according to the researchers.
used for mercury ion removal,” Soroush said. “In an instant, it was able to remove 95% mercury ions from a contaminated water sample at a concentration of 50 events per million, which means 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 water sample of 10 milliliters contaminated with mercury ions at concentrations between 1 and 1 000 events per million.
“This indicates that both and are effective adsorbents for removing mercury ions from wastewater due to their particular structural properties and the high density of functional area groups,” the team wrote. “Generally, the metal ion adsorption mechanism follows two steps at first, the ions are rapidly adsorbed on the available active web pages, and the process is rapid. Adsorption proceeds more slowly as the adsorption web sites fill, and the ions must diffuse into the pores and the interlayer.”
The development is important in the fight to contain mercury air pollution, which has become so prevalent that health authorities recommend avoiding eating certain species of fish altogether. Attempts to contain the mercury released by burning fossil fuels have proven as difficult as reducing dependence on the fuels themselves.
While moving away from sources of Energy is the ultimate option to prevent 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.”