A German research team has come up with an ingenious way to clean polluted water: tiny self-propelled ‘micromotors’. These structures – nano-sized cores of platinum surround by iron – could be used to clean organic pollutants from industrial wastewaters that are resistant to conventional biological or chemical treatments, as well as from pipes and other hard to reach places.
The team carried out their research at the Institute for Integrative Nanosciences in Dresden. They found that when the micromotors were released into polluted water containing hydrogen peroxide, the platinum inside them converted the hydrogen peroxide into oxygen bubbles. This acts as a propulsion system, while the iron within the device creates hydroxyl radicals that oxidize pollutants in the water, in effect cleaning it.
The self-propelling nature of the micromotors suggests they could also be used to clean larger bodies of water than previous solutions. They leave behind a concentration of iron that is three times lower than that left by the traditional ‘Fenton’ process for cleaning pollutants from wastewater – no small advantage, given that this iron must be removed in order to meet drinking water regulations.
There are drawbacks to the solution, however, as team member Samuel Sanchez from Stuttgart’s Max Planck Institute explains: “The lifetime of the micromotors is limited by the amount of the external iron layer remaining and the amount of hydrogen peroxide in the solution. Also, there could be poisoning of the platinum layer due to the presence of compounds in the wastewater that can bond chemically to the active surface of the catalyst. Or a high viscosity of the treated wastewater could hamper the motion of the micromotors.”
This isn’t the only water pollutant cleansing solution to emerge recently. Last autumn, for example, there were reports that a scientist from the National Taiwan University had developed a technique that used zinc oxide from old CD cases. But the micromotors solution could be more versatile.
Dr David Robbins, an Independent Consultant in Water and Sanitation, belives it has plenty of potential: “They probably wouldn’t be used for municipal sewage treatment”, he says, “but I can certainly see some specific commercial and industrial applications.”
It seems they could even be engineered to address some pre-treatment issues – i.e. targeting a specific chemical in the water. “As the technology develops it will be interesting to see how it is used”, Dr Robbins concludes. – Will Simpson
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