Abstract
Effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the optical sensing of AgNPs toward ferric ions were investigated spectrophotometrically in an aqueous media. Surface Plasmon resonance (SPR) intensity of AgNPs was decreases after addition of ferric ions at room temperature. CTAB and SDS, respectively, catalyzed and inhibited the oxidative dissolution rates of AgNPs. The redox reaction between AgNPs and Fe3+ ions proceeds through the complex formation. The reaction follows first-, and fractional-order kinetics with AgNPs and Fe3+ ions, respectively. CTAB catalytic role was explained with micellar pseudo-phase model, and associated parameters were estimated. The activation parameters (Ea, ΔH#, and ΔS#) were found to be 23.7 kJ/mol, 16.6 kJ/mol, −226 J/K/mol, and 16.5 kJ/mol, 13.5 kJ/mol, −238 J/K/mol for aqueous and CTAB assisted dissolution of AgNPs. SDS coordinated with Fe3+ through electrostatic interactions in pre-, and post-micellar region, which in turn reduces the electron gaining tendency of Fe3+, and overall rates of sensing reaction decreases.
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