Self-propelling nanomotors, just 200 nanometre in size, could be used for wastewater management in chemical industries. Developed by researchers from Indian Institute of Science Education and Research, Kolkata, and The Institute of Mathematical Sciences, Chennai, the nanomotor can be used for transporting catalysts needed in harsh chemical environments and removing unwanted chemicals in water.
Nanorods (rod shaped nanomotors) are made using ammonium heptamolybdate tetrahydrate and dispersed in the solution to be treated. When hydrazine sulphate is added to water, it reacts with the nanorods producing nitrogen gas. This leads to an osmotic stress in the fluid and causes the nanorods to move along the direction of the gas evolved.
The paper published in Frontiers in Chemistry says that this nanomotor is amongst the fastest reported active nanoparticles.
“Molybdenum based soft-oxometalates are non-toxic and easy to synthesize. The complementary charge interactions on the surface trigger their motion. The speed can be increased by increasing the concentration of the fuel hydrazine on the surface of the nanorods and they were found to remain in their motile state for about three days,” says Prof Soumyajit Roy from the Department of Chemical Sciences, IISER Kolkata and one of the corresponding authors of the paper.
Structure matters
The anterior end of these structures is capped like a pencil while the posterior end consists of a series of rod like protrusions. “We believe that these exposed ends of the rods provide a more accessible reaction surface than the capped end.
Therefore, the fuel hydrazine preferentially reacts at the posterior open end and generates gaseous nitrogen which triggers motion and the propulsion speed reaches up to a maximum of 600 metres per hour.” says Prof. R. Adhikari from Department of Physics at IMSc, Chennai who is one of the corresponding authors of the paper, in an email to The Hindu.
In a paper to be published in the journal Nanoscale, the researchers have shown that another type of nanomotor in the form of a sphere (using titanium dioxide, heptamolybdate and gold) can also be used for delivering a catalyst to a particular area of interest by using visible light. The nanospheres were found to move away from visible light. “The catalyst triggers a reaction and the pollutants get adsorbed on the nanospheres leading to quickly removal of organic pollutants from water. The solution can then be filtered, dried and the nanosphere can be retrieved,” says Apabrita Mallick, an Integrated PhD student at IISER Kolkata and one of the first authors of the paper.
