- Title
- Nanoencapsulated pesticide: insights of pesticide loading to enhance the sustainability of nanocarriers
- Creator
- Nuruzzaman, Md
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The application of nanotechnology in pesticide delivery is relatively new but has created many opportunities in reducing the losses of pesticides to the environment and ensuring their safe application. Of the various potential applications of nanotechnology, the nanoencapsulation process for pesticide delivery is one of the promising fields of current research. The focus of ongoing research is on the development of nanoencapsulated pesticide formulations that have 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. So far, various nanoencapsulation materials have demonstrated their potential to achieve these goals such as polymer-based, lipid-based, clay-based as well as inorganic porous nanomaterial. Given the current status of nanoencapsulation technique, this project aims to enhance the sustainability of nanocarriers or nanoencapsulation materials, namely, hollow porous silica nanospheres (HSNs) and organically modified montmorillonite (MMT) nanoclay via facilitating the pesticide loading process and/or enhancing the pesticide loading to the nanocarriers. The most commonly used insecticide – imidacloprid - is used as a model as well as target pesticide because of its efficacy, physico-chemical properties and potential threat to the environment. Homogeneously distributed spherical shaped hollow porous silica nanospheres were synthesized successfully using poly(styrene-b-2vinyl pyridine-b-ethylene oxide) (PS-P2VP-PEO) tri-block copolymer as a soft template having a large pore opening in the shell. The hollow spherical structure (average particle size 41.87 (± 3.28) nm; average diameter of void spaces 21.71 (± 1.22) nm and shell thickness 10.17 (± 1.68) nm) as well as presence of a large pore or opening in the shell was confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images analysis, respectively. Hence, the synthesized HSNs were denoted as bowl-structured hollow porous silica nanospheres (BHSNs). X-ray diffraction (XRD) analysis also indicated the disordered mesoporous structure, i.e. amorphous nature of synthesized BHSNs. Further investigation found that approximately 18 wt% of imidacloprid loading was calculated via thermogravimetric analysis (TGA) using the simple immersion method while BHSNs were dispersed in pesticide containing acetone solution. TEM images confirmed the existence of pesticide in the inner core of BHSNs but loading of imidacloprid to BHSNs was not homogeneous. To increase the loading percentage of imidacloprid to the inner core of nanospheres, it is essential to ensure proper dispersion of BHSNs in highly concentrated pesticide solution. Fourier transform infrared spectroscopy (FTIR) spectrum of imidacloprid loaded BHSNs exhibited a vibration band of Si-OH indicating that to some extent pesticide molecules interacted with BHSNs via hydrogen bonding interaction. This was supported by TGA as well as energy dispersive X-ray spectroscopy (EDAX) elemental analysis. Therefore, both adsorption and entrapment mechanisms in imidacloprid loading to BHSNs were effective. Furthermore, releasing behavior of imidacloprid from BHSNs indicated the potential of BHSNs to serve as a carrier for pesticide delivery. Over 92.5% imidacloprid was released from BHSNs over seven days at three stages where <5% imidacloprid was released in the first six hours, around 83% of imidacloprid was discharged within 60 hours and only ~4.5% pesticide was released over of 4.5 days (108 hours) possibly due to the deposited and loosely adsorbed imidacloprid on the outer surface on BHSNs, the dissolution of deposited imidacloprid present at the hollow sphere of BHSNs and highly adsorbed imidacloprid onto the inner surfaces and within mesopores of the BHSNs, respectively. The release kinetics described the release process of imidacloprid where at the first stage Fickian diffusional release mechanism was observed. Conversely the overall release process followed the non-Fickian case II transport mechanism. This project also investigated the efficacy of commercially available amine (octadecylamine, ODA and 3-amino-propyltriethoxysilane, APTES) functionalized MMT nanoclay as an applicable carrier for imidacloprid by observing the adsorption-desorption behavior of imidacloprid to this nanoclay. The material was well-characterized using SEM, XRD, TGA, zeta potential analyzer as well as FTIR. From the characterization, the aggregated cluster structure was observed in SEM image analysis which implied its hydrophobic nature. It was observed that MMT nanoclay was high in organic carbon (19.2%) but the intercalation of the organic cation was less than the saturation level of total cation exchange capacity (CEC) of pristine MMT. Therefore, significant amounts of metallic elements were detected through EDAX analysis. Expansion of interlayer space revealed that surface functionalizing agents were well intercalated to the interlayer of MMT nanoclay and also directed a bilayer or pseudo-trimolecular arrangement of the intercalated alkyl chain at the interlayer space. Furthermore, zeta potential (ζ) values were positive over a pH range from 3 to 9 and decreased consistently with increasing pH values. The presence of alkylamine was further confirmed by the FTIR spectrum of MMT nanoclay that represented the IR bands related to symmetric and asymmetric stretching of –CH2 group as well as stretching of N-H. Langmuir isotherm revealed that MMT nanoclay possessed high adsorption capacity (84 mg g-1) for imidacloprid. However, the correlation coefficient reflects the best fit of experimental data with the Freundlich model, which indicated the surfaces of MMT nanoclay are energetically heterogeneous where hydrophobic interaction played the vital role in adsorption. Additionally, hydrogen-bonding interaction was predicted from FTIR analysis. Moreover, sorption–desorption of the imidacloprid by the MMT nanoclay showed hysteresis and around 75% of the total adsorbed imidacloprid desorbed after 5 cycles of successive dilution desorption experiment. It was therefore assumed that nanoclays modified with a long hydrocarbon chain and having a functional amine group are the potential materials for high adsorption of pesticides such as imidacloprid. Also, adsorption kinetics of imidacloprid to MMT nanoclay showed a biphasic pattern where initially 80% of the total adsorbed amounts were adsorbed within 1 h of adsorption and 24 h was found to be enough to reach equilibrium. Adsorption kinetics of imidacloprid to MMT nanoclay reflects the high hydrophobic character and consequent low diffusion rates resulting in initial high adsorption on the surface of MMT nanoclay followed by diffusion-controlled low sorption rate at the later stage to the internal binding sites. The system pH also influenced the surface properties of MMT nanoclay where amines’ protonation-deprotonation behavior played the critical role in changing the surface properties from hydrophobic to hydrophilic. Therefore, hydrophobic interaction is predominantly an interaction at lower pH and decreases when the system’s pH increases. The amount of protonated and neutralized ODA acted as the driving force, establishing a pH dependent H-bonding interaction among the amines and neutral imidacloprid. Therefore, the adsorption mechanisms of imidacloprid to MMT nanoclay revealed that along with hydrophobic interaction, the hydrogen bonding interaction between charge neutral amines and imidacloprid also plays the key role in adsorption under optimum pH conditions. It is apparent that the MMT nanoclay retained high adsorption capacity for imidacloprid over broad pH ranges, yet neutral system pH with maximum deprotonated amines makes it possible to achieve the maximum adsorption capacity (around 200 mg g-1). Due to the lack of ionic bonding interaction it can be assumed that MMT nanoclay will be able to release the adsorbed pesticide molecules.
- Subject
- nanoencapsulation; pesticide; nanocarrier; loading
- Identifier
- http://hdl.handle.net/1959.13/1385113
- Identifier
- uon:32171
- Rights
- Copyright 2018 Md Nuruzzaman
- Language
- eng
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