Engineering Branched Silver Particles: pH-Mediated Morphology Control for Modulated Optical and Photothermal Conversion Properties

The controlled synthesis of branched Ag particles with modulated branch length and core size is crucial for optimizing their localized surface plasmon resonance (LSPR) and photothermal properties. Here, we reported a pH-mediated synthesis strategy to achieve systematic control over these structural parameters. By adjusting the pH of AgNO3 solutions, we prepared silver precursor solutions containing varying amounts of Ag2O particles and free silver ions. Upon introducing hydroxylamine as a reducing agent, the Ag2O intermediates underwent pseudomorphic transformation to form cores of branched Ag particles, while the remaining free silver ions were reduced to form branches through preferential growth of Ag (200) planes. These branches fused through oriented attachment and randomly attached to the cores, enabling the formation of branched particles. Adjusting the pH from 11.9 to 10.2 allowed controllable morphological evolution from cubic to branched structures, with the ratio of branch length to core size modulated from 0:1 to 1.6:1. This morphological control enabled a large red-shift of LSPR peaks from the visible range to the near-infrared II (NIR-II) window. Specifically, branched Ag particles prepared at pH 10.5, with an LSPR peak at 1025 nm, exhibited a photothermal conversion efficiency of up to 43.1% under 1064 nm irradiation. This work provides a robust platform for designing branched Ag particles with systematically controlled optical and photothermal conversion properties, paving the way for their advanced optical and biomedical applications.