Hybrid Hairy Janus Particles Decorated with Metallic Nanoparticles for Catalytic Applications.

We report for the first time on the design of an advanced hairy hybrid Janus-type catalyst, which is comprised of an inorganic silica core covered with two distinct polymeric shells (hydrophilic and hydrophobic) on its opposite sides, while the catalytic species (in our case silver or gold nanoparticles) are immobilized directly into the hydrophilic stimuli-responsive polymer shell. The primary 200 nm large Janus particles with poly(acrylic acid) serving as the hydrophilic and polystyrene as the hydrophobic polymer were synthesized through a Pickering emulsion and a combination of "grafting from"/"grafting to" approaches. The incorporation of silver and gold nanoparticles within the hydrophilic polymer shell was achieved by infiltrating the respective metal ions into the polymer matrix, and nanoparticles were formed upon the addition of a reducing agent (triethylamine). Plasmon absorptions typical for silver and gold nanostructures were observed on the functionalized Janus particles using UV-vis spectroscopy. The respective systems were investigated by TEM and cryo-TEM revealing that the incorporated nanoparticles are selectively localized on the poly(acrylic acid) side of the Janus particles. The efficiency of the catalyst as well as the accessibility of the incorporated nanoparticles was tested on the reduction of Methylene Blue, Eosin Y, and 4-nitrophenol as convenient benchmark systems. Ultimately, the hairy Janus particles with immobilized Ag or Au nanoparticles efficiently catalyzed the respective reactions by applying extremely low amounts of catalyst. Finally, we demonstrated several advantages of the use of JPs with immobilized metallic nanoparticles, which are (i) JPs stabilize the emulsions, (ii) the emulsion can be destabilized by utilizing responsive properties of the JPs, and (iii) JPs can easily be recovered after reaction and reused again.