Construction Of Multifunctional Water/Drug Controlled-release System And Its Regulation Mechanism And Application

The utilization efficiency and stability of traditional agricultural water and pesticide formulations are so low,which poses a great threat to the environment.Based on slow/controlled release research,it is expected that the response controlled release systems which regulate the release of active ingredients by intelligently responding to external environmental stimuli can achieve the purpose of the effective utilization of water and pesticides,and improve the productivity and sustainability of agriculture.Given the current high application rates and low utilization efficiency of agricultural water and pesticides,and agricultural non-point source pollution caused by the loss of pesticides,multifunctional water/pesticide controlled release systems with different network structures were designed and developed by using the natural biological macromolecule SA,temperature-sensitive material PNIPAm as carriers,and photothermal materials as fillers in this study.The responsive release behavior under different external environmental stimuli and the regulated release mechanism of the responsive controlled release system were investigated,which can provide theoretical guidance and technical reference for the efficient utilization of agricultural water and pesticides.The main research results are described as follows:（1）Photothermal p H-sensitive water absorbent DND@Ca-alginate hydrogel beads composed of matrix SA and photothermal material DND were fabricated by an ion gelation technique,and their application prospects in controlled water release were investigated.The interaction between DND and SA matrix was explored using various characterization methods.UV-vis-NIR diffuse reflectance spectra verified DND can absorb solar energy in the UV,visible,and even near-infrared regions.Under light irradiation,DND dispersed in the hydrogel matrix could absorb sunlight and generate heat,increasing the temperature of the matrix and resulting in the slow release of water from the elastic beads.In addition,the effects of DND content and p H were systematically studied to evaluate their water absorption properties.The swelling kinetics of DND@Ca-alginate hydrogel beads in distilled water fits well with a pseudo-second-order kinetic model.Six consecutive cycles of water release–reswelling indicated regeneration and reusability.The experimental results of the cabbage growth test show that the gel beads could release water on demand to supply plant growth.（2）Photothermal self-hygroscopic Ca-Alg-g-PNIPAm/DND hydrogel was prepared by redox copolymerization and ion crosslinking for atmospheric water absorption and controlled release of absorbed water.Therein,sodium alginate grafted PNIPAm（Alg-g-PNIPAm）was used as a hydrogel matrix,Ca Cl₂ was used as hygroscopic salt,and DND was used as photothermal material.The composite sorbent showed water sorption of 1.85 g/g at 80%relative humidity and 25°C,and the fitting results of the linear driving force model present that the experimental data are in good agreement with the predicted values.Then,the absorbed water could be controlled release under simulated sunlight by the photothermal conversion of DND and the transformation of the PNIPAm side-chain structure,and the hydrogel sorbent showed excellent reusability.Moreover,the outdoor experimental results show that this hydrogel-based atmospheric water absorbent could achieve 1.09 g/g water collection efficiency under natural sunlight,and the collected water can be used for agricultural irrigation,which provides more options for agricultural water supply.（3）Multiple environmental responsive Ca-alginate/PNIPAm@PDA hydrogel microspheres with interpenetrating network structure were prepared by free radical polymerization and ionic crosslinking methods for regulating the release of indolebutyric acid.Therein,SA,PNIPAm,and PDA endowed the microspheres with p H-sensitive,temperature-sensitive,and light-sensitive properties,respectively.The comprehensive performances,including photothermal conversion,water absorbency,and controlled release behaviors,were systematically investigated.The results show that the release amount of the encapsulated indolebutyric acid increased with decreasing p H and increasing temperature.In addition,under light irradiation,the temperature of the microspheres increased through the photothermal conversion effect of PDA,thus causing the increased release of indolebutyric acid.（4）A multifunctional responsive pesticide delivery system（IPKCPD@ASO）with enhanced adhesion was synthesized based on PDA-modified kaolin,SA,PNIPAm,DND,and amino silicone oil for regulating the release of imidacloprid.Therein,the PDA-modified kaolin with high adsorption performance adsorbed imidacloprid through hydrogen bonding and electrostatic action,avoiding drug loss during the system synthesis process.SA was used as the structural matrix,which formed a semi-interpenetrating network structure with PNIPAm to jointly build a drug delivery composite system.The amino silicone oil coating could bind with the hydrophobic rough surface and the waxy layer of crop leaves by the theory of“similarity-intermiscibility”,which enhances the adhesion of the composite on the crop leaves and improves the deposition effect of the drug-carrying system on the target crops.Moreover,by the excellent light-sensitive property of DND and temperature-responsive performance of PNIPAm,the functional systems could regulate the imidacloprid release amounts through light stimulation to adapt to the diurnal feeding habit of pests along with the daylight changes.Besides,the composite displayed outstanding control efficiency,unique p H sensitivity,and good biosafety.（5）A graft copolymer with alginate backbone and thermo-responsive poly（N-isopropyl acrylamide-co-N,N-diethylacrylamide）side chain was constructed through redox copolymerization,and its thermo-induced responsive property was studied.Then,the copolymer used as the matrix of the pesticide controlled release system was mixed with a promising photothermal material semi-coke to form the multifunctional responsive Ca-Alg-g-P（NIPAm-co-NDEAm）/SC hydrogel beads by ion crosslinking.The water absorbency of beads under different stimuli（p H,temperature,and light）presented outstanding responsive performance and the swelling mechanism was explained through mechanics-electrostatics-solute transport coupling theory.Furthermore,the release of glyphosate from beads under environmental stimuli displayed regulatable behaviors.