The pH definitely affects the size of nanoparticles. The main reason is charge on the surface of a nanoparticle present in a base fluid. This can be explained with zetapotential of a nanofluid. If zetapotential of a nanofluid is less than absolute value of 20 mV, the nanoparticle will have a greater size because of lower stability. If the absolute value of zetapotential is greater than 35, the size of nanoparticles tend to be smaller.