(534h) Lignin-Silica Hybrid and Silica Nanoparticles from Rice Husk As Smart Biopesticide Delivery Systems

Pesticides play an essential role in protecting crop yields worldwide. Nonetheless, their utilization presents considerable concerns regarding health, economic, and environmental issues. Smart delivery systems for agrochemical delivery may deal with more effective and sustainable processes when using pesticides in agriculture, and nanoparticles (NPs) have widely been utilized for this purpose. These particles in nano-scale size offer several advantages when applying pesticides, including enhanced distribution on both leaves and insect bodies. The use of lignin and silica-based nanoparticles for agrochemical delivery has extensively been investigated. Lignin nanoparticles have been produced from different types of biomasses, but most silica nanoparticles have been synthesized from tetraethyl orthosilicate (TEOS) as the silica precursor. The use of this chemical to produce SNPs may deal with issues as toxicity and safety due to its highly reactive and volatile structure, and its high cost. Moreover, to the best of our knowledge, lignin-silica hybrid nanoparticles from a biowaste as rice husk (RH) have not yet been synthesized for pesticide delivery applications. In this work, bio-based nanoparticles were synthesized from RH to be used as nanocarriers for a model bioinsecticide, Soybean Trypsin Inhibitor (STI). STI is a proteinaceous protease inhibitor derived from soybean. As a bioinsecticide, it acts binding to trypsin in the insect`s gut after its ingestion, triggering the insect death or growth retardation. This work aimed to generate green and low-cost bio-based smart delivery system made of lignin and silica with key features for effective release of the insecticide`s active ingredients under targeted conditions. Lignin-silica hybrid (LSNPs) and silica (SNPs) nanoparticles were produced from RH through a modified Stöber method employing three pH values in the synthesis: 6, 5, and 4. The NPs morphology was typically spherical with sizes smaller than 200 nm. For the nanoinsecticide production, STI was adsorbed onto the NPs surface, obtaining the highest adsorption capacity of 213.2 mg/g and 205.7 mg/g for LSNPs and SNPs synthesized at pH 5, respectively. These NPs were used to evaluate the in-vitro STI release kinetics at pH 8 which is the typical pH of many insect’ guts. Using the experimental data, mathematical modelling of STI release kinetics was performed to obtain insights into the release behavior of the final bio-based nanoinsecticides once in contact with alkaline media. In-vivo STI bioactivity against Helicoverpa armigera larvae was performed to investigate the efficacy of the final nanoinsecticides. Moreover, the adhesion of the nanoformulations (STI@LSNPs and STI@SNPs) onto cotton leaves was evaluated to show the washout resistance of the final products, indicating a stronger adherence of lignin-silica hybrid NPs. It may likely be due to the increase in the hydrophobicity of the nanoformulations with lignin in the structure. This result tackles the issue related to the pesticide leaching under harsh environmental conditions as strong rainfall. In general, this work demonstrates the promising use of RH to produce bio-based nanoparticles for bioinsecticide delivery against insects, highlighting the idea of potential valorization of bioresidues, aligning to the circular economy, and handling a more sustainable and intelligent agriculture.

Keywords: Nanoscale Engineering, Particle Characterization, Sustainable Engineering, Nanomaterials, Environmental Sustainability