| Glyphosate is a non-selective,residue-free herbicide that could cause certain pollution to soil and water sources due to its large amount of use and long-term accumulation.Therefore,it is urgent to research a high-efficiency load and controlled release glyphosate sustained-release.In this study,corn microporous starch was selected as a drug carrier to study the adsorption thermodynamics,adsorption kinetics and release process of drug-loaded microspheres of glyphosate on microporous starch,it provided a theoretical basis for the development of glyphosate sustained-release preparation.1?Corn microporous starch was prepared by double enzyme hydrolysis method and its performance was evaluated.The results showed that the pores of the microporous starch were uniformly distributed with small pores and deep,the pore diameter was about 1.1?m,and the water absorption rate was 131.05%.2?The adsorption equilibriums of glyphosate on corn native starch,microporous starch and microporous starch with 0.02%xanthan gum were studied.The results demonstrated that the adsorption processes of glyphosate on the three starches were stable at around 80 min.3?The adsorption thermodynamics of glyphosate on corn raw starch,microporous starch and microporous starch with 0.02%xanthan gum were investigated.The results indicated that the adsorptions of glyphosate on the three starches basically were in agreement with the Langmuir isotherm adsorption equation,and the adsorption amount was the highest on 0.02%xanthan gum microporous starch and reached 138.89 mg·g-1.By analysis of thermodynamic parameters,the adsorption processes of glyphosate on all three starches were a self-heating process controlled by enthalpy,which interacts with van der Waals forces and hydrogen bonds.4?The adsorption kinetics of glyphosate on corn native starch,microporous starch and microporous starch with 0.02%xanthan gum were assessed.The results revealed that the adsorptions of glyphosate on the three starches were in accordance with the quasi-secondary adsorption kinetics model,which there was no energy barrier in the adsorption processes of glyphosate on the three starches from the results of adsorption activation energy.5?The drug-loading and its releaseprocesses of glyphosate on corn microporous starch and0.02%xanthan gum microporous starch were discussed.The results indicated that the addition of 0.02%xanthan gum slowed the release of glyphosate on corn microporous starch,and the cumulative release rate reached 61%at 48 h.The release kinetics curves of the two drug-loaded microspheres were more consistent with the Ritger-Peppa release model,and the characteristic parameter n values were all less than 0.5,indicating that the glyphosate drug-loaded microspheres release process accords with the Fick diffusion mechanism.Taken together,the above results indicated that corn microporous starch with 0.02%xanthan gum is a good glyphosate controlled release carrier. |
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