Researchers at IIT- Bombay have successfully removed heavy metals such as arsenic, chromium, cadmium and mercury from waste water with very high efficiency.
The carbon-based nanostructure that the team fabricated shows 80-90% adsorption efficiency for all the four heavy metals studied.
No electricity is required for the nanostructure to remove heavy metals from water as it allows for gravity-driven purification of the water.
The nanostructures can be recycled and reused multiple times. While there is an initial drop of about 8% after the first cycle, the efficiency remains constant at 75-85% in the subsequent cycles.
The carbon nanostructure is able to adsorb the heavy metals in the wide range of pH conditions, pH 2 to 13.
The nanostructure is obtained through a single-step process of chemical vapour deposition followed by removing the silica template.
The reason it shows very high adsorption efficiency is its hydrophilic [water-loving nature] nature that allows for extensive and rapid interaction between the heavy metal-containing water and the carbon nanostructure.
For the four heavy metals to get adsorbed on the nanostructure the water has to be in contact with the nanostructure for at least 32 seconds.
Since the heavy metals chemically react and bind to the surface of the nanostructure, they do not leach back into the water. They can be recovered by treating the nanostructure with mild acid.
The team tested the ability of the structure to adsorb heavy metals in industrial effluent over a range of pH conditions (pH 2-13). The industrial effluent was simulated by mixing 100 ppm of each metal.