Gemini surfactant with pyrrolidinium head groups and a hydroxyl-substituted spacer: surface properties and assisted one-pot synthesis of dendritic Au nanocrystals

Abstract

Surfactants have proven to be the best shape directing agents for the synthesis of desired nanomaterials. Herein, a series of cationic gemini surfactants with pyrrolidinium head groups and a hydroxyl-substituted spacer (C_n-3OH-_nPB, n = 10, 12, 14 and 16) were synthesized, characterized and investigated by surface tension, electrical conductivity, steady-state fluorescence, dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements for their surface activity and aggregation behaviors in aqueous solution. Their critical micelle concentrations (CMCs) followed the order of C₁₀-3OH-₁₀PB > C₁₂-3OH-₁₂PB > C₁₄-3OH-₁₄PB > C₁₆-3OH-₁₆PB and the aggregation tendency was enhanced as the hydrocarbon chain length increased. Interestingly, C₁₆-3OH-₁₆PB performed particularly prominently with respect to both the surface-active properties and the preparation of dendritic Au nanocrystals (NCs) compared to others with different hydrocarbon chain lengths. Dendritic Au NCs can be facilely prepared by a one-pot method at room temperature with C₁₆-3OH-₁₆PB as the stabilizing agent and structure director. Meanwhile, the other reaction parameters involved including the reaction time and the concentration of the gemini surfactant, AA and HAuCl₄ were also investigated in order to evaluate the optimal conditions for the formation of dendrites. Moreover, the dendritic Au NCs exhibited good surface-enhanced Raman scattering (SERS) sensitivity toward crystal violet (CV), suggesting their potential application in SERS-based detection and analysis. This facile synthetic method for creating dendritic Au NCs based on a gemini surfactant may open viable opportunities and provide inspiration for future studies on the preparation of shape-controlled Au NCs.