Pd-promoted Ni-P electroless deposition on a hydrogen-bonded molecular surface of a supramolecular fibrous template

A nickel-phosphorus (Ni-P) hollow microfiber was obtained by simply immersing a recyclable hydrogen-bonded supramolecular fibrous template made of amphoteric azopyridine carboxylic acid in an HCl-acidic PdCl₂ aqueous solution and in a Ni-P electroless plating bath, followed by template removal in an alkaline aqueous solution. The Ni-P hollow microfiber had an inner pore diameter of 0.5 μm and a wall thickness of about 50 nm. The mechanism of the Pd-promoted Ni-P electroless deposition on the template surface was revealed by XPS analysis and TEM observation. Coordination of the [PdCl₄] ^2- species and its subsequent hydrolysis and condensation polymerization to a tubular Pd²⁺ nanosheet and formation of the Pd⁰ nanoparticle as plating catalyst were brought about on the molecular surface of successive head-to-tail COOH⋯NC₅H ₄ hydrogen bonds, which comprised the supramolecular fibrous template. The hydrogen-bonded surface ordered at a molecular level leading to the tubular Pd²⁺ nanosheet played an important role in homogeneous Pd-promoted Ni-P electroless deposition and allowed us to fabricate a uniform Ni-P hollow microfiber.