Synthesis And Characterization Of Pesticides/Hydrotalcite-like Compounds Nanohybrids

Nowadays in china,the second biggest country of pesticide producing, preparations forms are mainly powder,oil concentrate and suspension concentrate, which are irrational and large application.Pesticide has brought many ignorant effects such as air pollutions,environmental destroy,food safety and so on,which has baffled agricultural sustainable development.Now the hit research trends of pesticide forms in the world are focused on controlled-release formulations.Hydtrotalcite-like compounds(HTlc),also called Layered double hydroxides (LDHs),consisting of divalent and trivalent metal ions and with the same layered crystal structure as hydrotalcite,are a class of layered materials which has been paid a great of attention in recent years.The interlayer region of HTlc may be considered as a microvessle,some pesticide and drug molecules may be intercalated into the gallery of HTlc to form pesticide/drug-HTlc nanohybrids.The nanohybrids may evidently inhibit the release of moleculars in the interlayer.So pesticide/drug-HTlc nanohybrids are greatly potential controlled-release formulations.HTlc was chosen as host material and some pesticides as guest species, Indole-3-buytric acid(IBA),Avermectin(AVM) and Imidacloprid(IM) have been successfully intercalated into HTlc using different methods to obtain a series of pesticide-HTlc nanohybrids.The synthesis strategy and the properties of nanohybrids,released behavior, released mechanism and the relationship between structures and released behavior of nanohybrids were systematically studied.The main contents of this paper are as follows.1,Synthesis and characterization of IBA-HTlc nanohybrids (1) The adsorption of IBA on HTlc was studied,and some fators were investigated,for example,solid/liquid ratio(HTlc concentration),initial concentrations,temperature and pH.It was found that the adsorption kinetics and isotherms was well fitted by pseudo-second order kinetic equation and Langmiur isotherms equation.And with the increase of HTlc concentration and temperature, the constant(k₂) of pseudo-second order kinetics and the initial adsorption rate both increase;The adsorption amount arrived maxium at pH 6.5-10.5;The adsorption capacity will decrease with the increase of solid/liquid ratio;The activation energy was calculated by Arrhenius equation.(2) IBA-HTlc nanohybrids were synthesized by exchange method and reconstruction method,which were also characterized.The release behavior was studied.The effect of temperature and electrolyte were investigated.According to the dimensions of pesticide structure and the gallery height of nanohybrids,a possible arrangement(vertical-arranging overlapped bilayer) of indole-3-buytric acid in the interlayer of nanohybrids was proposed.IBA-HTlc nanohybrids was a good controlled release pesticide formulation.And the release kinetics was well analyzed by pesudo-second-order kinetic equation.Higher temperature and electrolyte concentration,higher the release rate.According to the different values of k₂ at different temperatures and Arrhenius equation,the activation energy of release process was calculated to be 16 kJ/mol.2,Synthesis and characterization of IM-SDS-Zn₂Al HTlc nanohybrids(1) Non-ionic and water-soluble imidacloprid was chosen as pesticide guest, and Zn₂Al HTlc was the host.IM-SDS-Zn₂Al HTlc nanohybrids were synthesized by Second Assembling Intercalation method,which were also characterized. Firstly,HTlc was modified by SDS,and the basal spacing increased with the intercalation of SDS,then SDS-HTlc nanohybrids were obtained.Secondly, imidacloprid would be intercalated into the gallery of SDS-HTlc to form IM-SDS-Zn₂Al HTlc nanohybrids.The driving force may be the concentration difference.According to the gallery height of SDS-HTlc and SDS molecular structure,the possible arrangement may be vertical-arranging monolayer.It was found that the intercalation of imidacloprid induced the decrease of basal spacing of SDS-HTlc,which may be caused by the interaction of pesticide and SDS.The hydrophobic chain of SDS was distorted.(2) The release behavior was studied,and the effect of pH and electrolyte was also investigated.It was indicated that the synthesized nanohybrids could well control the release of imidacloprid.And pseudo-second order kinetic equation was satisfactory for describing the release behavior.The presence of electrolyte and lower pH would increase the release rate.The release rate will increase with the increase of SDS loading(Asps),which may be caused by the hydrophilic property of imidacloprid.3,Synthesis and characterization of AVM-SDS-Mg₂Al HTlc nanohybrids(1) Non-ionic and poorly water-soluble avermectin(AVM) was chosen as pesticide guest,and Mg₂Al HTlc was the host.AVM-SDS-HTlc nanohybrids were synthesized by Second Assembling Intercaltion method(enhanced intercalation by evaporating solvent).Firstly,SDS-HTlc nanohybrids were synthesized by the intercalation of SDS into the gallery of HTlc,and hydrophobic region was formed. Secondly,SDS-HTlc nanohybrids were dispersed into ethanol solution containing avermectin.Then the solvent(ethanol) was gradually evaporated out,avermetin will be forced to intercalate into the hydrophobic region of HTlc to form AVM-SDS-HTlc nanohybrids.According to the gallery height of SDS-HTlc and SDS molecular structure,the possible arrangement may be vertical-arranging monolayer.The gallery height will slightly decrease with the increase SDS loading (A_SDS).The intercaltion of avermectin slightly induced the increase of gallery height. (2) The release behavior of nanohybrids was studied,and effect of temperature,electrolyte and pH was investigated.It was found that the obtained nanohybrids were a good controlled release pesticide formulation.Its releae kinetics was better fitted by pseudo-first order kinetic equation.The presence of electrolyte,lower pH and higher temperature all increase the relase rate.The release rate will decrease with the increase of SDS loading(A_SDS),which was interpreted that higher A_SDS,stonger hydrophobicity of HTlc gallery,and the interaction between avermectin and SDS will be enhanced.Using the pseudo-first order kinetic constant with different temperatures and Arrhenius equation,the acitivation energy of release process was calculated to be 279 kJ/mol.