- Title
- Controlled release formulations of herbicide: role of nanocarriers in loading and releasing behavior of active ingredients
- Creator
- Paul, Santosh Kumar
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Weeds are considered as the most harmful pest in terms of creating losses in quality and yield. Compared with other pests including animals, birds, insects and pathogens, weeds exert severe detrimental effects on agricultural crops due to their dynamic and resilient nature. Generally, weeds compete with crops for light, water, nutrients, and space because of their existence at the same trophic level of the food chain like crop plants. Consequently, a significant amount of yield loss occurs which has major implications for food security as the world’s population continues to grow unchecked. Moreover, weeds play a vital role as the host of many pests and pathogens that harm crop plants. Various common weeds such as Ragweed, Rye Grass, Parthenium and Privet cause respiratory problems and asthma especially for children. Other weeds cause skin irritation and sometimes poisoning to animals and interferes with livestock grazing. For these reasons, weed management is one of the most important issues for more efficient crop production to feed the world’s people, a process that began in ancient civilizations when agriculture was the main economic activity. Of the various weed management/eradication approaches including preventive, physical, cultural, mechanical, chemical, and biological, use of chemicals (herbicides) has been the dominant tool due to selective weed control properties as well as cost-effective, quick, and easy application. Although herbicides are highly effective on most weeds, they are not a complete solution because of the genetic diversity and evolving flexibility or resistance of weed communities. Over-reliance and indiscriminate use of herbicides for weed control have triggered the generation of herbicide-resistant weed species. More than 90% of applied pesticides (including herbicides, insecticides, and fungicides) cannot reach the target pest and they contaminate the surrounding environment (water, soil, air, and food) through water movement. This occurs by leaching and runoff and has now become a major threat for this planet’s life forms in all environments. To minimize the adverse effects of herbicides, improvement of available herbicide formulations has now garnered much research attention. Utilizing the benefit of nanotechnology, preparation of controlled release formulations (CRFs) of herbicides can be considered an effective way to resolve ongoing issues. To this end, a model herbicide 2,4-D and two organoclays along with pristine montmorillonite were used to investigate their potentiality as eco-friendly carrier materials for CRFs of anionic herbicide. The organoclays used in the experiments were ODA and ODA-APTES modified montmorillonite and denoted as MMT1 and MMT2 respectively. In addition, 2,4-D loaded clay-polymer-based nanocomposite microbeads were synthesized and their herbicide releasing behaviors in various experimental conditions along with weed control efficacy were well investigated. The physicochemical properties of both organoclays were investigated at various pH values select an optimum pH for maximum adsorption of 2,4-D onto the organoclays. Both carrier materials were adjusted to different pH values and well characterized using different sophisticated instruments. SEM imaging revealed that both organoclays comprised a cluster structure at slightly acidic to neutral conditions, which meant their hydrophobic characteristics around this acidic pH (pH = 3) gradually decreased with increasing system pH (pH = 7). This was due to the addition of OH¯ ions to the clay-water suspension during pH adjustment. Zeta potential values of both organoclays gradually declined with increasing system pH. The surface area of both materials was highest at neutral pH, and gradually diminished both in acidic and alkaline pH. These results suggested more surfactants were released in strongly acidic and alkaline conditions resulting in reducing the interlayer spaces of organoclays, that in turn decreased surface area of the carrier materials. Total organic carbon (TOC) analysis supported this finding as TOC of both organoclays were highest at neutral pH, which gradually decreased towards acidic and alkaline-treated organoclays. Therefore, it can be concluded that system pH has a significant influence on the physicochemical properties of amine-modified organoclays, which may affect the adsorption of herbicides onto these organoclays. Results revealed that pristine montmorillonite has poor adsorption capacity, whereas ODA and ODA-APTES functionalized organoclays have better adsorption capacities at pH 3, which gradually decreased with increasing system pH. The presence of chlorine (Cl) on the 2,4-D loaded organoclays through TEM-EDAX mapping confirmed the adsorption of 2,4-D onto the layer structured organoclays. The FTIR bands at 1733 cm-1 (carbonyl stretching vibration) and 1473 cm-1 (CH2 scissoring band) confirmed the presence of 2,4-D onto the organoclays. The adsorption of 2,4-D onto the experimented organoclays follows the pseudo-second-order kinetic model rather than first-order variant, thus suggesting that chemisorption was the main rate-limiting step of the entire adsorption process. The results also revealed that both organoclays follow Elovich model and suggested energetically heterogeneous surface of the organoclays. The experimental data fitted well to the Freundlich adsorption isotherm model, which in turn revealed the energetically heterogeneous surface of the experimental organoclays, and chemisorption took place during adsorption. 2,4-D loaded organoclays were used to synthesise clay-polymer based microbeads, where sodium alginate was used as a natural polymer. Herbicide desorption behaviour of synthesised microbeads were investigated in lab (at various pHs, temperatures and ionic strengths) and soil conditions (glasshouse pot experiment). The synthesized 2,4-D loaded clay-polymer-based microbeads revealed excellent herbicide releasing behavior at a wide range of pHs (5 to 9), temperatures (25 °C to 45 °C) and ionic strengths in laboratory along with varying soil conditions. The herbicide releasing behavior was faster for MMT1based microbeads than MMT2, although MMT2 oriented microbeads showed a sharply increasing rate as the experiments progressed. Consequently, fast or slow-releasing formulations can be synthesized using the carrier materials MMT1 and MMT2, respectively, whereas release can be controlled using different proportions of 2,4-D loaded MMT1 and MMT2 during microbead synthesis. The herbicide releasing behavior of both microbeads was greatly influenced by ionic strengths and had significant cationic effect. However, both synthesised microbeads revealed long-term herbicide releasing behaviour in soil at glasshouse pot experiment. The microbeads have excellent weed control efficacy (WCE) on three different broad-leaf weed species. The results revealed that >80% WCE of MMT1Beads were achieved at 2000 mg pot-1, 1000 mg pot-1, and 5000 mg pot-1 for Sowthistle (Sonchus oleraceus), Fleabane (Conyza bonariensis) and Pigweed (Chenopodium album) respectively. Whereas, expected WCE (>80%) of MMT2Beads were achieved at 5000 mg pot-1, 1000 mg pot-1, and 5000 mg pot-1 for Sowthistle (Sonchus oleraceus), Fleabane (Conyza bonariensis) and Pigweed (Chenopodium album) respectively. It can be concluded that herbicide releasing speed of MMT1Beads was faster and less amount was required compared to MMT2Beads, despite both microbeads revealed excellent WCE on the target pest.
- Subject
- nanotechnology; controlled release formulation; CRFs; herbicide; weeds
- Identifier
- http://hdl.handle.net/1959.13/1514220
- Identifier
- uon:56825
- Rights
- This thesis is currently under embargo and will be available from 06.12.2024, Copyright 2023 Santosh Kumar Paul
- Language
- eng
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