The microwave-assisted synthesis of silica nanoparticles and their applications in a soy plant culture

Abstract

A rapid and environmentally friendly synthesis of thermodynamically stable silica nanoparticles (SiO₂-NPs) from heating via microwave irradiation (MW) compared to conductive heating is presented, as well as their evaluations in a soy plant culture. The parameters of time and microwave power were evaluated for the optimization of the heating program. Characterization of the produced nanomaterials was obtained from the dynamic light scattering (DLS) and zeta potential analyses, and the morphology of the SiO₂-NPs was obtained by transmission electron microcopy (TEM) images. From the proposed synthesis, stable, monodisperse, and amorphous SiO₂-NPs were obtained. Average sizes reported by DLS and TEM techniques were equal to 11.6 nm and 13.8 nm, respectively. The water-stable suspension of SiO₂-NPs shows a zeta potential of −31.80 mV, and the homogeneously spheroidal morphology observed by TEM corroborates with the low polydispersity values (0.300). Additionally, the TEM with fast Fourier transform (FFT), demonstrates the amorphous characteristic of the nanoparticles. The MW-based synthesis is 30 times faster, utilizes 4-fold less reagents, and is ca. 18-fold cheaper than conventional synthesis through conductive heating. After the synthesis, the SiO₂-NPs were added to the soil used for the cultivation of soybeans, and the homeostasis for Cu, Ni, and Zn was evaluated through the determination of their total contents by inductively coupled plasma mass spectrometry (ICP-MS) in soy leaves and also through bioimages obtained using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Although the results corroborate through both techniques, they also show the influence of these nanoparticles on the elemental distribution of the leaf surface with altered homeostasis of such elements from both transgenic crops compared to the control group.