The application of nanotechnology in pesticide delivery is relatively new and in the early stages of development. This technology aims to reduce the indiscriminate use of conventional pesticides and ensure their safe application. This critical review investigated the potential of nanotechnology, especially the nanoencapsulation process for pesticide delivery. In-depth investigation of various nanoencapsulation materials and techniques, efficacy of application, and current research trends are also presented. The focus of ongoing research was on the development of a nanoencapsulated pesticide formulation that has slow releasing properties with enhanced solubility, permeability, and stability. These properties are mainly achieved through either protecting the encapsulated active ingredients from premature degradation or increasing their pest control efficacy for a longer period. Nanoencapsulated pesticide formulation is able to reduce the dosage of pesticides and human exposure to them, which is environmentally friendly for crop protection. However, lack of knowledge of the mechanism of synthesis and lack of a cost-benefit analysis of nanoencapsulation materials hindered their application in pesticide delivery. Further investigation of these materials' behavior and their ultimate fate in the environment will help the establishment of a regulatory framework for their commercialization. The review provides fundamental and critical information for researchers and engineers in the field of nanotechnology and especially the use of nanoencapsulation techniques to deliver pesticides.

Hollow porous silica nanospheres (HSNs) have unveiled as a potential carrier for pesticide delivery. However, HSNs mostly suffer from postsynthesis loading process of pesticides because of the tiny mesopores onto shell. To eradicate this disadvantage, it was hypothesized that developing a large through hole or pore opening on shells (>10 nm) could be effective for the postsynthesis loading of active molecules onto HSNs using a simple immersion method. We synthesized HSNs with a single large through hole or pore opening on shells (15.95 nm) in an earlier study, which was subsequently termed bowl-structured hollow porous silica nanospheres (BHSNs). In this study, the postsynthesis loading of a model pesticide, namely imidacloprid, onto BHSNs was evaluated via the simple immersion method. It was observed that the presence of a single large pore-opening on the shells of BHSNs facilitated loading of imidacloprid to the inner core or void space of BHSNs. Thermogravimetric analysis (TGA) showed that around 16% imidacloprid molecules were loaded to the BHSNs when acetone was used as a dispersing medium. It was evidenced by differences between weight losses patterns of imidacloprid loaded to BHSNs (imi@BHSNs) from pure imidacloprid. Both adsorption and entrapment mechanisms were effective during loading. FTIR analysis showed that pesticide molecules were adsorbed on BHSNs via hydrogen bonding interaction. The controlled releasing profile of imidacloprid from BHSNs was observed in distilled water at room temperature, except an initial burst release of a small amount (<5%). The controlled release composed of a faster sustained release followed by a slower conditional release due to the deposited and adsorbed imidacloprid. The non-Fickian case II transport mechanism prevailed during transportation of imidacloprid to the release media from BHSNs. We anticipate that this study could provide an important avenue for advancing practical applications of BHSNs in pesticide delivery systems.

No abstract

Hollow porous silica nanospheres (HSNs) are emerging classes of cutting-edge nanostructured materials. They have elicited much interest as carriers of active molecules delivery due to their amorphous chemical structure, non-toxic nature and biocompatibility. Structural development with hierarchical morphology is mostly required for obtaining the desired performance. In this context, large through-holes or pore openings on shells are desired so that the post-synthesis loading of active molecules HSNs via a simple immersion method can be facilitated. This study reports the synthesis of HSNs with large through-holes or pore openings on shells, which are subsequently termed bowl-structured hollow porous silica nanospheres (BHSNs). The synthesis of BHSNs was mediated by the core-shell interfaces of the core-shell-corona structured micelles obtained from a commercially available ABC triblock copolymer (polystyrene-b-poly(2-vinyl pyridine)-b-poly(ethylene oxide) (PS-P2VP-PEO)). In this synthesis process, polymer@SiO2 composite structure was formed because of the deposition of silica (SiO2) on the micelles' core. The P2VP block played the significant role in: firstly, hydrolysis and condensation of the silica precursor i.e. tetraethylorthosilicate (TEOS); and secondly, maintaining the shell's growth. The 4 PS core of the micelles built the void spaces. Transmission electron microscopy (TEM) images revealed a spherical hollow structure with an average particle size of 41.87 ± 3.28 nm. The average diameter of void spaces was 21.71 ± 1.22 nm and shell thickness was 10.17 ± 1.68 nm. According to the TEM image analysis the average large pore was determined as 15.95 nm. Scanning electron microscopy (SEM) images further confirmed the presence of large single pores or openings in shells. These were formed due to the accumulated ethanol on PS core acting to prevent the growth of silica.

Higher soil pH and electrical conductivity (EC) were suspected to result in higher extractability and bioavailability of benzo[a]pyrene (B[a]P) in soils. In this study, we investigated the influence of pH, EC and ageing on the extractability of B[a]P in two contracting soils (varied largely in soil texture, clay mineralogy and organic carbon content) over 4 months. Dilute sodium hydroxide (0.2 mol L-1) and sodium chloride (0.1 mol L-1) solutions were used to adjust soil pH and EC either separately or simultaneously. Extractability of B[a]P in these soils was monitored using a mild solvent extraction using butanol (BuOH, end-over-end shake over 24 hours), and an exhaustive mix-solvent extraction using dichloromethane/acetone (DCM/Ace, v:v = 1:1) facilitated by sonication and a subsequent NaOH saponification method following the DCM/Ace extraction. Results showed that increased pH and/or EC significantly increased the B[a]P extractability in the sandy soil (GIA). Variance analysis of contribution of pH and/or EC modification and ageing time on changes in B[a]P extractability indicated that in GIA more than 55% and over 25% of the changes in B[a]P extractability was attributed to increased pH&EC and pH only respectively. While ageing resulted in more than 85% of the change in B[a]P extractability in the clayey soil (BDA), following by increased pH&EC (contribution less than 15%). Large amount of non-extractable residue (NER) were formed over the ageing period, up to 94.6% and 78.8% in GIA/BDA and its modified soils, respectively. Significant correlations were observed between B[a]P BuOH extractability and the exhaustive sequential extraction using DCM/Ace followed by NaOH saponification for all soils (p < 0.001). With slopes of the correlations close to 1, our results indicated that the simple mild solvent BuOH 3 extraction was equivalent to the complex sequential DCM/Ace and NaOH saponification extraction in these soils.