Insights on Gemini cationic surfactants influence AgNPs synthesis: Controlling catalytic and antimicrobial activity

Abstract

We engineered various surfactants by altering their hydrophobic properties, adjusting tail length. These changes significantly impacted their surface and thermodynamic characteristics in solution. Higher hydrophobicity led to a lowered critical micelle concentration (CMC), indicating increased surface adsorption. Among the gemini amphiphiles we synthesized, the one with the longest hydrophobic tail exhibited the lowest CMC of 0.58 mM and the highest ΔG°ads of −65.91 kJ.mol−1 at 20 °C. Elevated temperatures decreased CMC, enhancing both micellization and adsorption affinity. The surfactants, acting as capping agents during AgNPs preparation, influenced uniformity, stability, and size of the resulting AgNPs based on their hydrophobicity. Particularly, those with higher hydrophobicity resulted in smaller, stable AgNPs (10.1 ± 3.4 nm) compared to those with lower hydrophobicity. A clear link between surfactant hydrophobicity and the catalytic activity of AgNPs was evident. AgNPs derived from highly hydrophobic surfactants exhibited superior catalytic performance compared to those from less hydrophobic surfactants, showing efficient activity in converting methylene blue at −0.15 min-1 with a 20 μL dose. Moreover, the integration of AgNPs into surfactants displayed improved antibiotic activity against tested microbes, demonstrating exceptional efficacy, even surpassing common commercial antimicrobial agents.