Capping action of ionic surfactants on the nucleation of lawsone-Ag+ redox system

Abstract

Cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used a stabilizing agent to determine the rate of nucleation and growth process for the reduction of Ag+ ions by lawsone. Critical micellar concentration (CMC) were calculated by using surface tension method and found to be 6.3 × 10−3 and 9.2 × 10−4 mol dm−3 for SDS and CTAB, respectively in presence of Ag+ ions. Reaction rates increases with increasing the surfactant concentrations. SDS aggregates formed complex with Ag+ ions due to electrostatic interaction with negative head group as well as solubilized the lawsone into the aqueous micellar phase through hydrophobically. CTAB effect might be due to the solubilization of lawsone into the Stern layer. The rate constants were found to be 3.2 × 10−4 and 8.1 × 10−5 s−1 for CTAB and SDS, respectively. SDS exhibited inhibition effect at post-micellar concentrations. Menger-portnoy model modified by Bunton and his coworkers was used to determine the micelles assisted parameters. For CTAB micellized reaction, binding constant (Ks = 42 mol−1 dm3 and KL = 86 mol−1 dm3), micellar phase rate constant (km = 3.5 × 10−3 s−1) were calculated with pseudo-phase kinetic model. Morphology of AgNPs strongly depends on nature of surfactant head group.