But the energy would have been dissipated in the brakes and heat is used to charge the batteries.
The study claims that the "pollutants" are particulates from tire wear (rubber) and brake wear (asbestos, among other things).
Yes, you are correct: the energy dissipated by the brakes is instead used to recharge the batteries. So, the particulates from brakes should actually be REDUCED.
Are you claiming direct heat to electric conversion? Figure out the direct kinetic to electric equivalent required to recover a significant percentage. Battery won’t accept the needed charge rate for a 1:1 conversion.
Actually super-caps can respond to very fast charge requirements, but total energy density is far lower than a battery of equivalent weight.