Effect Of Modified Sodium Alginate On Adsorption Of Pesticides On Banana Leaves And Soil

Amphiphilic alginic acid derivatives and alkyl glycosides(APG)are widely used in medicine,food and other fields as green environmentally friendly raw materials.In this paper,the natural macromolecular sodium alginate was hydrophobically modified by high-efficiency and mild Ugi four-component condensation reaction to obtain amphiphilic alginic acid derivatives with different molecular weights,and the effects of modified sodium alginate(Ugi-alginate)on the adsorption properties of acetamiprid on banana leaves and soil surface were also investigated.Through the use of a fully automatic surface tension meter,an optical contact angle measuring instrument and an electronic balance,the surface tension of different systems containing pesticides(APG solution,Ugi-alginate solution,APG combined with Ugi-alginate solution),the dynamic and static contact angles,the retention amount,and the drug adsorption amount of the liquid on the banana leaves were measured.(i)Gparaxiai>G abaxial the paraxial surface with larger surface free energy is easily wetted;(ii)when CAPG<0.2 g/L,banana leaves have burrs and bulges(pinning effect),which will prevent the wetting and spreading of liquid droplets on the surface of the leaves;at CAPG>0.2 g/L,due to the micellization,the surface tension of the liquid solution is reduced,resulting in a decrease in the contact angle,from the initial non-wetting state to the wet state.When saturated adsorption is reached,the contact angle no longer changes.Therefore,the addition of APG to the solution can transform the leaves from hydrophobic to hydrophilic;(iii)the addition of Ugi-alginate will slow the wetting and spreading of the liquid on the suface of the blade;(iv)the 0.2g/LAPG synergistic 0.6g/L Ugi-alginate solution system has the largest retention on the leaves compared to the two separate systems.Therefore,the addition of Ugi-alginate can improve the retention and adhesion of the liquid on the leaves.This may be because APG and Ugi-alginate can form a mixed micelle solution to encapsulate acetamiprid,which improves the wetting and adhesion ability of the liquid on the surface of the leaf.In order to reduce the pollution caused by pesticide droplets falling from the banana leaves to the soil-water environment,the experiment further explored the effect of different molecular weight Ugi-alginate on the adsorption of pesticides on the soil.Experimental results show that high molecular weight modified sodium alginate(Ugi-alginate-H)is more conducive to the adsorption of pesticides on the soil.Both the Langmuir and Freundlich models are suitable for simulating the adsorption isotherms of acetamiprid on the soil,and as the molecular weight of Ugi-alginate increases,the Kd value increases and the adsorption capacity of pesticides on the soil increases.This is because the modified sodium alginate not only forms hydrogen bonds with the pesticide molecules but also has hydrophobic interactions,and may also increase the adsorption amount of the pesticides on the soil by bridging with calcium ions.Finally,in order to further explore the interaction between Ugi-alginate and soil colloid in the presence of calcium ions,soil colloids were prepared by simple ultrasonic-centrifugation method,and the properties of soil colloids were characterized by FTIR,XRD and DLS.The morphology of the adsorption was observed by TEM.The results show that Ca2+ can not only inhibit the electric double layer charge on the surface of the soil colloid,but also affect the particle surface zeta potential by bridging with Ugi-alginate in the Ugi-alginate/CaCl2 system.It leads to a more uniform distribution of soil colloids and promotes the firmness and stability of the soil aggregate structure.According to the adsorption experiment,both Langmuir and Freundlich models can be used to fit the adsorption data.The increase of calcium ion concentration can effectively change the maximum adsorption capacity(Qm)of acetamiprid on soil colloid,which is the result of Ca2+ and Ugi-alginate network connection induced soil colloid aggregation.