Cyclobis(paraquat-p-phenylene) – mediated electrosynthesis of new-type nanocomposite of palladium nanoparticles with designated macrocyclic organic compound

Abstract

A new type nanocomposite of palladium nanoparticle (PdNP) with macrocyclic organic compound cyclobis(paraquat-p-phenylene) (CBPQT4+) was obtained by CBPQT4+- mediated electrosynthesis in the MeCN/ 0.05 М Bu4NPF6 and MeCN (50 vol%) – H2O/ 0.05 М Bu4NCl media. The nanocomposite has a pseudorotaxane structure formed due to the donor-acceptor binding of an electron-donor metal particle inside the cavity of an electron-acceptor CBPQT4+. Theoretical calculations have shown that up to 10 Pd atoms can fit into the CBPQT4+ cavity and the energy of such interaction is ∼500 kJ/mol in the gas phase. In addition to the target process, dispersion of the Pd-anode (current efficiency ∼ 170%) to form PdNPs in solution occurs in electrolyses in a diaphragmless cell. The resulting particles combine together with CBPQT4+to form aggregates, the size of which in solution is 80–900 nm. In the absence of stabilizer cetyltrimethylammonium chloride (CTAC), particles with an average size of PdNPs equal to 6.1 ± 1.8 nm and size of Pd crystallites of 4.1 – 8.2 nm are formed. The addition of CTAC leads to increased binding of PdNP with CBPQT4+and a decrease in the size of PdNPs and Pd crystallites (4.9 ± 2.9 nm, 3.0 – 5.9 nm, respectively). Nanocomposites obtained in a diaphragm electrolysis process contain PdNPs and Pd crystallites (3.2 ± 1.3 nm, 2.2 – 3.8 nm) of the smallest size. Binding with CBPQT4+causes slow activation and a decrease in the catalytic properties of PdNPs in the test reaction of p-nitrophenol reduction with sodium borohydride compared to larger PdNPs (5.9 ± 1.4 nm, Pd crystallite size is 2.9 – 5.6) obtained in the MV2+- mediated electrosynthesis under the same conditions.