Kinetic and thermodynamic investigations of AgNPs–Ni/Al–LDH nanohybrids prepared by direct and indirect ion exchange methods

This study presents the synthesis and characterization of silver nanoparticle–intercalated nickel/aluminum–layered double hydroxide (AgNPs–Ni/Al–LDH) nanohybrids prepared through direct and indirect ion-exchange strategies. The synthesized nanomaterial was characterized by XRD, SEM, and UV–visible spectrophotometry. XRD results showed crystalline sizes of 22, 18.7, 8.2, and 8.3 nm, while the average particles obtained from SEM were 30.8, 23.6, 44.99, and 59.68 nm for AgNPs, Ni/Al–LDH, and Ni/Al–AgNPs–LDH by direct and indirect ion exchange method, respectively. The UV–vis spectrum of AgNPs shows a strong absorption at 450 nm. The kinetically controlled release of AgNPs from Ni/Al layered double hydroxides (LDHs) synthesized via direct and indirect ion-exchange methods was systematically evaluated under different acidic and alkaline conditions (pH = 2.5, 5.5, 8.5, and 12.5). The release percentage of AgNPs increased markedly with increasing pH, following the order: 12.5 > 8.5 > 5.5 > 2.5. Moreover, AgNPs released from Ni/Al–LDHs prepared by the direct ion-exchange method exhibited consistently higher release values compared to those synthesized via the indirect method. The increased release percentage can be attributed to enhanced ionization and the progressive weakening of electrostatic interactions between the silver nanoparticles and the LDH host matrix under strongly alkaline conditions.