Comparative study of cross-linked and linear thermo-responsive carriers supported palladium nanoparticles in the reduction of 4-nitrophenol: Structure, catalytic activity and responsive catalysis property

摘要

In this paper, studies on the structure, catalytic activity and responsive catalysis property of palladium nanoparticles (PdNPs) loaded on cross-linked and linear thermo-responsive polymer were presented. The reduction of palladium acetate immobilized in both systems yielded the corresponding PdNPs. The PdNPs were relatively uniform with a certain degree of aggregation and the diameter is about 6-10 nm in the cross-linked carrier (microgel), and had good monodispersity in size with an average particle size of about 3.2 nm in the linear carrier (single-chain copolymer). The catalytic reduction of 4-nitrophenol (4-NP) by sodium borohydride was adopted as a model reaction to study the catalytic activity of PdNPs embedded in different thermo-responsive carriers. The analysis of the kinetic data obtained showed that the catalytic activity of the PdNPs significantly depend on the type of carrier used. The single-chain thermo-responsive polymeric carrier supported PdNPs exhibited remarkable high catalytic activity compared to microgels supported ones. In addition, both systems presented thermo-responsive catalysis property by displaying different catalytic activities at different temperatures. The thermo-responsive effects were due to the limitation of diffusion of substrate into catalytic active sites for the microgels supported system, and the micelles aggregation and precipitation from reaction mixture for the single-chain copolymer supported system. The present study offers clear indications on what carrier for metallic nanoparticles should be designed to achieve higher catalytic activity, and to realize the control of their catalytic activity by temperature for exothermic catalytic reactions.