Palladium (Pd) nanoparticles have a wide variety of catalytic applications, such as carbon-carbon bond forming reactions, selective alkanes oxidation, oxidation of primary alcohols in alkaline media, and cross-coupling reactions of organoboron compounds. However, the main challenge in the application of Pd nanoparticles as catalysts is the nanoparticle aggregation which leads to a significant loss in the catalytic performances. One way of overcoming this difficulty is to immobilize Pd nanoparticles on a suitable support. Moreover, immobilization of Pd nanoparticles on a support also makes the separation of the catalysts from the reaction medium and the recovery easier. Hydroxyapatite (Ca10(OH)2(PO4)6, HA) has been demonstrated as a promising catalyst support material for metal nanoparticles by a few studies because of its high adsorption capacity, ion-exchange ability, and adjustable acid-base properties which can prohibit side reactions. However, the synthesis procedures in these studies were usually time-consuming and had no control over the size and loading of the metal nanoparticles. A double-voltage method was proposed to electrochemically deposit Pd nanoparticles on HA nanocrystals grown on a Ti substrate. A higher voltage was first applied to the electrodes for a short time. It is believed that most of the electrons were consumed by the nucleation of Pd nanoparticles in this step. Then a lower voltage was applied for a longer time to promote the growth of the nanoparticles. The obtained Pd nanoparticles showed small size and uniform distribution on the HA coating. Moreover, the size and distribution of the Pd nanoparticles were controlled by adjusting the duration of the first voltage step and the second voltage step. The obtained HA supported Pd nanoparticles demonstrated significantly higher catalytic activity than commercial Pd nanoparticles in the degradation of methyl orange by NaBH4. XPS analysis indicated that the oxidation states of the prepared Pd nanoparticles were complex, which could be a result of the interaction between the nanoparticles and the HA support. The high dispersity and the special oxidation states of the synthesized Pd nanoparticles are believed to account for the enhanced catalytic activity.

Feasible synthesis of hydroxyapatite-supported palladium nanoparticles with controllable size and distribution and their enhanced catalytic activity

255th National Meeting (2018)

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