Fabrication of pH-responsive nanocomposites of gold nanoparticles/poly(4-vinylpyridine)

Novel nanocomposites of gold nanoparticle and poly(4-vinylpyridine) (Au@PVP) were fabricated through surface-initiated atom-transfer radical polymerization (SI-ATRP) at ambient conditions. The citratestabilized gold nanoparticles were first modified by a disulfide initiator for ATRP initiation, and the following polymerization of 4-vinylpyridine (4VP) occurred on the surface of gold particles. The assembled Au@PVP nanocomposites are pH-responsive because of the pyridyl groups, which are facially protonated and positively charged. At low pH (< 3.2), the polymer chains attached on gold nanoparticles are expanded by electrostatic forces, and the polymer layer is loosely swelled; hence, the Au@PVP composite particle displays a comatulid-like nanostructure in 3-D AFM images. However, at a relatively high pH (> 3.2), the polymer chains shrink and wrap around the gold particle surface, which results in the aggregation of gold nanoparticles with a thin shrunken polymer layer under TEM observation. Such assembled Au@PVP nanocomposites as a smart supporter can entrap transition metal ions by their efficient coordinating segments, and subsequently, the metal ions can be reduced in situ to construct novel bimetallic nanocomposites, which are regarded as intelligent catalysts with environmental stimuli activity.