[2] Different stimuli, both external (light,[3] magnetism[4]) and internal (fuel concentration, material composition,[5] particle asymmetry[6]) can be used to control the behavior of these micromotors.
The catalytic difference between each pole of the Janus motor can be characteristic of the material[10] such as metals which catalyze at different rates, or induced by external stimuli like UV light[7] which can be absorbed by semi-conductor materials like titanium dioxide to excite electrons for the redox reaction.
Catalytic activity is not the only way to generate motion using Janus materials; self-propelled Janus droplets can be made using a complex emulsion of two different surfactant oils[11] which move forward spontaneously due to the difference in surface tension as the two oils solubilize.
[17] Since these gold nanoparticles are layered on top of the inner core (usually a reducing agent, such as magnesium), there is enhanced macrogalvanic corrosion observed.
For example, in a TiO2/Au/Mg micromotor in a seawater environment, the magnesium inner core would experience corrosion and reduce water to begin a chain of reactions that results in hydrogen gas as a fuel source.
[21][22] Specifically, micromotors with a titanium dioxide/gold nanoparticle outer layer and magnesium inner core are currently being examined and studied for their degradation efficacy against chemical and biological warfare agents (CBWA).
These new micromotors are composed of a photoactive photocatalyst outer/surface layer that often has active metal nanoparticles (platinum, gold, silver, etc.)
Also, the active metal nanoparticles effectively shift the Fermi level of the photocatalyst, enhancing the distribution of the electron charge.
Therefore, the lifetime of the radicals and anions is extended, so the implementation of the active metal nanoparticles has greatly improved photocatalytic efficiency.
Metal–organic frameworks (MOFs) are a class of compounds that are composed of a metal ion cluster coordinated to an organic linker.
They possess a porous morphology which can be tuned in terms of shape and size depending on the metal ion and organic linker used to form the MOF.
The major limitation of MOFs is that they tend to settle at the bottom of the solution, reducing their effectiveness since they are not coming into contact with the contaminant.