A similar question has been discussed, (link given below): https://www.researchgate.net/post/Which_nano_particles_are_compactable_with_natural_fibers_or_PLA_to_increase_thermal_properties_of_PLA_composite?
You can use any nano particle of interest. In this green composite i would like to recommend to use natural fillers as nano particles. Even u can go for nano clay since clay is a natural product so it never affects the green pattern.
More over you can try any novel bio nano materials which will be more suitable in this regard.
See my article i have attached below. We used sea urchin spike paerticles as filler in epoxy.