Dendrimer-mediated synthesis of supported rhodium nanoparticles with controlled size: Effect of pH and dialysis

Rh–dendrimer nanocomposites were synthesized in solution under different conditions and were subsequently used as precursors for the preparation of ZrO2-supported Rh nanoparticles. Elemental analysis, UV–vis, XPS, and STEM measurements were used to estimate the extent of the Rh–dendrimer interactions and to illustrate how the solution pH and dialysis affect the number of Rh atoms complexed with each dendrimer molecule, as well as the final size of the ZrO2-supported Rh particles. When the solution acidity was not controlled and the solution was not purified by dialysis, Rh particles with sizes in the 1–6 nm range were formed on the ZrO2 support. In contrast, the formation of nearly uniform Rh particles was observed when the synthesis was performed under controlled pH and dialysis conditions. Furthermore, the size of these Rh particles can be regulated by controlling the Rh/dendrimer ratio in the original solution.

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► Non-protonated tertiary amines are the preferred sites for Rh complexation with PAMAM dendrimers.
► The solution acidity affects significantly the Rh/dendrimer ratio in the nanocomposites formed.
► Dialysis can be effectively used to remove free Rh cations from the solution.
► Combination of pH control and dialysis yields nearly uniform Rh nanoparticles on ZrO2.