Chinese and American scientists have developed a cheap nanocatalyst based on carbon nanotubes that can purify water from nitrates with the same effectiveness as expensive metal catalysts.
According to an article published in the scientific journal Nature Water, nitrate pollution of water poses a threat to nature and human health. Current methods for purifying water from these substances using microbes or metal catalysts are either slow to operate or expensive. Therefore, an electrocatalytic system was developed that purifies water from nitrates with the same effectiveness as metal catalysts.
Developed by a team of American and Chinese chemists, the system is a membrane containing a large number of carbon nanotubes. Scientists have previously tried to use two-dimensional carbon structures to speed up reactions involving nitrogen atoms, but the efficiency of such catalysts has remained low.
The researchers found that their efficiency could be increased by about four times, from 20% to 80%, by forcing the nitrate molecules to interact with the carbon nanostructures for longer. To do this, the scientists treated the nanotubes with small amounts of polyvinyl alcohol, then placed them inside special ceramic membranes whose permeability could be controlled using an electric current.
During subsequent experiments, the scientists were able to choose the membrane structure and current strength that would cause the nitrate molecules to collide more with the nanotubes, interact with them and turn into pure nitrogen molecules. This was a characteristic of both concentrated nitrate solutions and drinking water samples contaminated with relatively low concentrations of nitric acid salts.
The researchers’ current estimates are that their system consumes about 430 watts of power to remove one gram of nitrate from drinking water, and at the same time remains stable for hours, making the purification process relatively cheap. The researchers hope that their development will eventually eliminate the need for expensive catalysts based on palladium, iridium, ruthenium and other rare and precious metals.