Surface-Engineered Polydopamine Particles as an Efficient Support for Catalytic Applications.

Mussel-inspired polydopamine (PDA) particles with the size of ∼270 nm are used as a support of palladium (Pd) nanoparticles (NPs) for catalyst preparation. The surface morphology of the PDA particle has been modified via corrosion of CF3COOH. Surface chemistry of the obtained PDA particle has been engineered by the formation of a carboxylic acid-terminated alkanethiol monolayer. The obtained self-assembled monolayer-modified PDA (SAM-PDA) particles are used to load Pd NPs by simply adding H2PdCl4 solution to a suspension of SAM-PDA particles at room temperature. Transmission electron microscopy, energy-dispersive X-ray mapping, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis, and Fourier transform infrared are used to characterize the catalyst and to investigate the process. Uniform Pd NPs (2-3 nm) have been well-dispersed on the SAM-PDA particles via controllable surface engineering. Surface charges and interactions with a metal ion are regulated by the monolayer of carboxylic acids. The surface chemistry of PDA particles has been finely engineered for efficient loading of noble metal NPs. The obtained Pd/SAM-PDA catalyst has shown greatly increased activity and good reusability compared with Pd/PDA in the reduction of 4-nitrophenol (4-NP) by sodium borohydride or H2. The kinetic data of 4-NP hydrogenation catalyzed by Pd/SAM-PDA are fitted to a Langmuir-Hinshelwood (L-H) model, and the calculated apparent activation energy of this process is 40.77 kJ mol-1.