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

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).