Dear Henry Ra, I think both are used, AgNPs are historically more investigated. In addition, AgNPs have some features such as the antibacterial activity compared to graphene and its derivatives. Please check the following links. My Regards

https://www.researchgate.net/post/Which_of_the_filler-Silver_nanoparticles_Carbon_Black_Graphene_or_CNTs_would_increase_the_youngs_modulus_of_polymer_composites

https://doi.org/10.1080/03602559.2017.1326135

https://link.springer.com/article/10.1007/s10443-016-9557-5

Dear Henry Ra

Silver Colloidal solution has been used since ancient time. First-time silver colloidal silver used in 1891, due to its antibacterial properties. According to the applications of your materials, you want to decide on the AgNPs or graphene.

Hi dear Henry, i think It could be due to the high price of graphene.

another hand AgNPs has some more properties like being antibacterial and has been used for long time. It's more known and studied as biocompatible material.

Hi;

Silver has been used for centuries in the treatment of wounds and burns and is capable of killing about 650 types of germs. Silver nanoparticles (AgNPs) are produced in large quantities and already find a large number of industrial applications. By contrast, graphene is an emerging material and its industrial production is not yet based on reliable methods for obtaining large quantities. "There is still work to be done". The past has shown that it can take thirty to forty years before a new material is fully adopted. But graphene only really took off in 2004. So it still has time to make its mark. However, very recent work has shown the high toxicity of graphene and its derivatives towards bacteria, suggesting their use as antibacterials.

With my best regards

see the following link for more information

https://www.sciencedirect.com/science/article/abs/pii/S1359835X19301691