Electrostatic Adsorption of Pt onto Carbon Nanotubes and Fibers

Strong Electrostatic Adsorption (SEA) has been demonstrated as a simple, scientific method to prepare well dispersed Pt nanoparticles over typical forms of carbon: activated, black, and graphitic carbons [1]. Many varieties of specialty carbons have been invented in the last few decades including multi-walled nanotubes, nanofibers, graphene nanoplatelets, etc. In this work we explore whether SEA can be applied to these specialty carbons for the synthesis of Pt nanoparticles.

Over a number of oxidized and unoxidized multiwalled nanotubes and nanofibers the point of zero charge (PZC) was measured and the uptake of anionic Pt complexes (Pt hexachloride, [PtCl₆]^2-, and cationic Pt complexes (platinum tetraammine, [Pt(NH₃)₄]²⁺) as functions of final pH were surveyed. Pt nanoparticles on the various supports were synthesized at the optimal pH and were characterized by XRD and STEM.

The specialty carbons displayed volcano-shaped uptake curves typical of electrostatic adsorption for both Pt anions at low pH and Pt cations at high pH. However, the regimes of uptake often did not correspond to the measured PZC. It was seen that the PZC of many of the carbons could be changed with washing, and so was likely affected by residual impurities of the manufacturing process. This renders the measured PZC of these specialty carbons unreliable for predicting anion and cation uptake. On the other hand, the anion and cation uptake curves provide an “effective” PZC and do indicate the optimal pH for the synthesis of ultrasmall nanoparticle synthesis.

Reference

[1] Hao X, Barnes S, Regalbuto J.R, Journal of Catalysis, 2011, 279, 48.