It is probably quite difficult to remove. I would try washes with acidic water (HCl, pH = 2) in order to have the protonated form of PAA, followed by washes with acetic acid or DMSO. Collection by centrifugation or ultracentrifugation. Dry in MeOH. Normally, the adsorption of PAA and most other polymers on surfaces is quite irreversible.

Jerome or anyone...do you think that the capping agent is infact blocking hydrogen access to the collected particles that I have collected?

CAN you using calcination? if particle size was not important for you.

yes. capping agent can prohibite catalytic activity. see paper Gabor A. Somorjai

The Role of Organic Capping Layers of Platinum Nanoparticles

in Catalytic Activity of CO Oxidation

I have read some articles about end capping of surface silanol groups. The autors washed with THF and acetonitrile to remove excess and after they used a Soxhlet extraction methanol/acetic acid (9:1)

Probably, you are right that the polymer blocks access to the active catalytic sites. However, it is almoste impossible to remove ligands quantitatively from colloidal nanoparticles without affecting particle size (and stability).

Alternatively, ligand-free metal nanoparticle sythesis could provide highly active colloids with unblocked surface, see realtime process video: ==> http://youtu.be/J0vZgQFDyjo

Those nanoparticles may then easily be adsorbed onto catalyst supports (just by mixing of the microparticle support with the colloid) within seconds.

(Method see: [Wagener, P. ; Schwenke, A. ; Barcikowski, S.: How Citrate Ligands Affect Nanoparticle Adsorption to Microparticle Supports. In: Langmuir 28 (2012), S. 6132–614])

http://youtu.be/J0vZgQFDyjo