Study On Preparation Of Magnetic FeMgAl-LDHs Composite Materials And The Adsorption Behavior Of Plant Growth Regulators

Plant growth regulators regulate plant growth by affecting basic physiological processes such as cell growth and division,seed germination,bud differentiation and leaf senescence.Plant growth regulators have been widely used in agriculture and forestry because of their low cost,high yield and quick effect.However,the overused growth regulators are discharged into the water environment such as rivers and lakes by Rain Water,destroying the ecological environment and causing harm to the human body.Therefore,it is necessary to develop adsorption materials that can effectively adsorb plant growth regulators to remove or quickly detect pollutants in the environment.Layered bimetallic hydroxide（LDHs）is a good adsorption material because of its large specific surface area and adjustable structure.This study added Fe element to the classical magnetic Mg Al-LDH and adjusted the content of Fe element to synthesize magnetic Fe Mg Al-LDHs with different Fe content for the adsorption of plant growth regulators.In-depth study of the effect of Fe on the adsorption effect of LDHs,analyze its adsorption process,and explore the adsorption mechanism between it and plant growth regulators.The main research contents and results are as follows:（1）Magnetic Fe Mg Al-LDH（Fe-MLDH）was synthesized by co-precipitation method with ammonia as alkali source and used to adsorb plant growth regulator 1-naphthylacetic acid（NAA）.The morphology and properties of the materials were characterized by SEM,TEM,zeta potential,XPS and FTIR,and the effects of p H,adsorbent concentration and temperature were investigated.The isotherm fitting and kinetic fitting of the experimental data show that the isotherm fitting of Fe-MLDH adsorption of NAA is more consistent with the Liu isotherm model.The maximum adsorption capacity obtained by Liu model fitting is 288.5 mg/g.The adsorption kinetics of Fe-MLDH on NAA is more consistent with the Avrami model,which indicates that the adsorption mechanism may follow multiple kinetic orders,which may change during the contact between NAA and Fe-MLDH.Compared with magnetic Mg Al-LDH and magnetic Co Mg Al-LDH,the results show that Fe can promote the adsorption of LDHs,and the promoting effect of Fe is stronger than that of Co.（2）By changing the content of Fe in Fe-MLDH,a series of Fe-MLDHs materials were synthesized and applied to the adsorption of NAA.The experimental data of NAA adsorption on Fe-MLDHs materials were fitted by isotherm and kinetic fitting.The experimental results show that the isotherm fitting of all Fe element content Fe-MLDHs adsorption NAA is more consistent with the Liu model,and the adsorption kinetics fitting is more consistent with the Avrami model.It shows that the adsorption energy of Fe-MLDHs adsorbing NAA is constantly changing and the adsorption mechanism may follow several kinetic sequences,which is not affected by the content of Fe elements.In this study,by optimizing the content of Fe element,the role of Fe element in LDHs was analyzed.The results show that the low content of Fe element will lead to the loss of skeleton structure,the decrease of structure specific surface area and the reduction of exposed adsorption sites;the high content of Fe element will lead to the decrease of other main elements with adsorption effect and the total number of adsorption active sites.By comparing the adsorption effect of each Fe-MLDHs material for NAA,it is concluded that the material with the best adsorption effect is Fe_0.5-MLDH,and the maximum adsorption capacity of Fe_0.5-MLDH for NAA is 330.1 mg/g by Liu model fitting.（3）Fe_0.5-MLDH with better adsorption effect was used to adsorb other plant growth regulators,and the removal rate and isotherm of Fe_0.5-MLDH to four plant growth regulators were analyzed.Through the characterization results of SEM,TEM,XRD,FTIR and DFT theoretical calculation and analysis,the adsorption mechanism of Fe_0.5-MLDH to plant growth regulators was explored.The results show that the isotherm fitting of Fe_0.5-MLDH for 2-naphthoxyacetic acid（NOA）,indole-3-acetic acid（IAA）and 3-indole propionic acid（IPA）is more consistent with the Langmuir model,indicating that the adsorption of NOA,IPA and IAA by Fe_0.5-MLDH is monolayer adsorption and does not form or form a small number of clusters.The adsorption isotherm of Fe_0.5-MLDH for3-indolebutyric acid（IBA）is more consistent with the Liu model,indicating that large clusters are formed in the adsorption process,resulting in the continuous change of the adsorption energy,and the adsorption of one IBA molecule will affect the adsorption of the next IBA molecule.Through the analysis of the adsorption mechanism,it is found that the adsorption of plant growth regulators by Fe_0.5-MLDH materials is related to the chain length and functional groups of pollutants.With the increase of pollutant chain length,it is easier to form large clusters around Fe_0.5-MLDH materials,which makes the adsorption effect better,and the cation-πinteraction between plant growth regulators with naphthyl groups and Fe_0.5-MLDH is stronger than that between plant growth regulators with indolyl groups,so the adsorption capacity of Fe_0.5-MLDH to NAA and NOA is stronger than that of IAA.In this study,the effect of Fe element on the adsorption of LDHs was verified.The optimal proportion of Fe element was studied,and the adsorption mechanism was supplemented and enriched by the adsorption of various plant growth regulators.