Microwave-Mediated Synthesis and Characterization of Ca(OH)2 Nanoparticles Destined for Geraniol Encapsulation

Nanotechnology presents promising opportunities for enhancing pest management strategies, particularly in protecting active ingredients to prolong their shelf life and effectiveness. Among different approaches, the combination of inorganic nanoparticles with active ingredients such as the main constituents of natural essential oils in one nanoarchitecture is challenging. In this study, hydrophobic calcium hydroxide nanoparticles coated with oleylamime [Ca(OH)2@OAm NPs] were synthesized using microwave-assisted synthesis. These primary NPs were physicochemically characterized and subsequently utilized to prepare nanocapsules (NCs) either alone (Ca NCs) and/or in combination with geraniol at different ratios of Ca(OH)2@OAm NPs and geraniol, i.e. 1:1 (CaGer1 NCs), 1:2 (CaGer2 NCs), and 1:3 (CaGer3 NCs), respectively. Among the formulations, the CaGer2 NCs demonstrated higher encapsulation efficiency (EE) and loading capacity (LC) of 95% and 20%, correspondingly. They exhibited a hydrodynamic size of 306 nm, a ζ-potential of −35 mV, and a monodisperse distribution. Release kinetics of geraniol from CaGer2 NCs indicated a pH-dependent slow release over 96 h at both 25 °C and 35 °C. In vitro antifungal assay against B. cinerea revealed a concentration-dependent activity, and the EC50 values for Ca(OH)2@OAm NPs, Ca NCs, and CaGer2 NCs were estimated to be 654 µg/mL, 395 µg/mL, and 507 µg/mL, respectively. These results underscore the potential of Ca-based nanoformulations to control plant pathogens, suggesting that while Ca NCs showcase potent antifungal attributes, the different architectures/structures play a critical role in the antifungal effectiveness of the nanoformulations that have to be explored further.