| The use of agrochemicals has played an extremely important role in promoting crop growth,increasing crop yield and improving agricultural production efficiency.However,due to the low content of active ingredients,poor chemical stability and backward application technology,agrochemicals are facilitated to lost in target,resulting in soil and water pollutions.Stimuli-responsive controlled release technology has the advantages of strong controllability and high selectivity.It can achieve sustained,stable and efficient release of agricultural chemicals and reduce environmental pollution.However,stimuli-responsive carriers,especially redox-responsive carriers,in the field of controlled release of agricultural chemicals have been rarely studied and few results have been obtained.In view of the above problems,a cellulose-based redox-responsive controlled release system for agrochemicals was developed over this dissertation studies,and its application in controlled release and synchronous control of soil pollution caused by heavy metal ions was explored.The specific work is exhibited as follows:(1)Study on preparation and properties of redox-responsive cellulose hydrogel carrier.Carboxymethyl cellulose(CMC)was crosslinked with cysteamine as crosslinker to prepare redox-responsive hydrogel carriers.Two agrochemicals 6-benzylaminopurine(6-BA)and naphthalene acetic acid(NA)were loaded with pre-loading and post-loading method,respectively.The encapsulation efficiency was 94.6%and 24.3%,and the loading capacity was 2.85 and 0.73 mg/g,respectively.Hydrogels have three-dimensional network structure,and the swelling ratio can reach 1500%.The release behavior of controlled-release agrochemicals by dithiothreotol(DTT)conforms to Kopcha model,and the complete release time can be controlled at 125-600 minutes.The adsorption behavior conforms to Langmuir model.The adsorption capacity of Hg2+and Cu2+can reach 38.9 mg/g and 36.7 mg/g,respectively.(2)Preparation and properties of cellulose-based nanogel carriers with pH and redox dual-responsiveness.To prepare pH and redox dual-response nanogel carrier(SA@CNG),hydrophobic branches were grafted with palmitoyl chloride(PC1)on CMC,then crosslinked with 3,3'-dithiobis(propionylhydrazide)(DTP).Salicylic acid(SA)was loaded as a model agrochemical.The nanogel particles were homogeneous microspheres with an average diameter of 116 nm and a swelling ratio of 282%in water.The nanogels could maintain stable morphology in high concentration sucrose solution.The encapsulation rate and loading capability of salicylic acid were 74.5%and 38.5%respectively.Under the control of acid and glutathione(GSH),SA can be released completely within 4-12 hours,and the release kinetics conforms to the diffusion-erosion mechanism.In simulated soil leachate solution,the removal efficiency of Cu2+ by nanogels reached 89%,and the adsorption behavior accorded with the Langmuir model.(3)Study on preparation and properties of spherical carriers with dual-responsiveness of enzyme and redox.A novel redox and enzyme-responsive spherical carrier was prepared by using artificial zeolite as core,carboxymethyl cellulose as shell,and cyclodextrin-ferrocene(CD-Fc)inclusion complex as linkage.SA was loaded as a model agrochemical(SA@CCZ).The average particle size of the carrier was 1.78 um,the specific surface area was 36.4 m2/g,the encapsulation efficiency and loading capacity of S A were 63.8%and 27.7%,respectively.The maximum cumulative release with the stimulitons of hydrogen peroxide and cellulase can reach 85.2%and 80.4%respectively.The release duration can be controlled in 4-12 hours,and the release kinetics conforms to the diffusion-erosion mechanism.In summary,the cellulose-based redox-responsive controlled release system can achieve precise and controllable release of agrochemicals,improve the utilization efficiency,and effectively reduce the concentration of Hg2+ and Cu2+ in soil.The response mechanism of redox-responsive carriers and multiple-responsive carriers and the adsorption mechanism of heavy metal ions on carriers were clarified.Our research is of important theoretical significance to the investigation of redox-responsive materials in the field of controlled release of agrochemicals and pollution control of heavy metal ions. |
PDF Full Text Request