Experimental and computational insights into the mechanism of destabilization of poly(acrylic acid)-capped silver nanoparticles induced by weak conjugate bases

Abstract

Herein we report a systematic study of the effects of H2PO4− and ClO4− on the stability of poly(acrylic acid)-capped silver nanoparticles (PAA-AgNPs). Spectroscopic titration revealed that a smaller amount of ClO4− is required to detach PAA, and a blue-shift in surface plasmon resonance (SPR) was observed relative to H2PO4−, owing to its electron accepting nature which leads to a weaking of the PAA-AgNP donor bond. Experimental observations were supported by DFT calculations, which revealed that complexation of AgNPs with ionized PAA, H2PO4– and ClO4− is mediated by the electron affinity of the AgNP and the conjugated bases. Electron donation by the weak acids leads to the weakening of the PAA-AgNP donor bond, whereby ClO4− contributes more to the destabilization of the PAA capped AgNPs due to its greater electron affinity. Additionally, H2PO4− can form hydrogen bonds with PAA, which promotes the formation of aggregates. Moreover, DFT calculations have shown that the structure of the model Ag14 cluster is significantly distorted in the presence of H2PO4−, more so than in the case of ClO4−. The findings are supported by the experimental quantification of residual PAA by differential scanning calorimetry and solid-state total organic carbon analysis (SSM-TOC), and powder X-ray diffraction (XRD).