Preparation Of Organic Aerogels And Their Selective Adsorption Mechanism For Noble Metal

Based on the designability of aerogels and the performance of graft groups,a new melamine/thiourea/formaldehyde(MTF)aerogel was designed and prepared,and its adsorption and selective adsorption for Au3+ and Ag+ were studied,and the adsorption performance and adsorption mechanism were studied too.Finally,melamine/thiourea/forma--ldehyde(MTF)composite aerogels were prepared by introducing a certain amount of starch,cellulose and chitosan to improve the MTF aerogels'mechanical properties and guaranteed the adsorption capacity of Au3+.First,a new melamine/thiourea/formaldehyde(MTF)aerogel for adsorption and selective adsorption of noble metal ions was prepared by introducing thiourea into melamine formaldehyde(MF)system.To combine thiourea better with melamine formaldehyde,the experimental conditions were optimized.When the temperature of the reaction system was 95?,the reactant ratio was 5%,the reactant concentration was 10%and the pH value of the reaction system was 1.0,the gelation time of the wet gel was the shortest,and the particle size of the gel was obtained by laser particle size analyzer during the gelation process.The final prepared melamine/thiourea/formaldehyde(MTF)aerogel possesses a typical three-dimensional network structure with a specific surface area of 439.3 m2·g-1 and an average pore size of 1.8 nm.The preparation process is simple,the gelation time is short,and the cost is low,which is conducive to the development of aerogels for practical applications.The adsorption properties of melamine/thiourea/formaldehyde(MTF)aerogels on Au3+and Ag+ were studied through static adsorption.In order to make the best adsorption effect of melamine/thiourea/formaldehyde(MTF)aerogels,the experimental parameters were optimized.The results showed that when the reaction temperature was 60?,the adsorption time was 10 h,the pH value of the counter solution was 3.0,and the initial concentration of the noble metal ions was 3.0mg·ml-1,the adsorption capacity of Au3+ and Ag+ is 409.69 mg·g-1 and 87.99 mg·g-1,respectively.Finally,the selective adsorption ability of melamine/thiourea/formaldehyde(MTF)aerogels to Ag+ was verified,and the adsorption capacity and selective adsorption capacity were compared with those of MTF resins.The adsorption capacity of MTF aerogels to Ag+increased by 39%compared with that of MTF resin,and the selectivity of adsorption was higher than that of MTF resinsBy processing of the melamine/thiourea/formaldehyde(MTF)adsorption data,the adsorption thermodynamics and adsorption kinetics were studied.The isothermal model of Langmuir and Freundlich was linear fitted,and the reaction mechanism between MTF aerogels and noble metal ions was analyzed by combining SEM and FT-IR characterization.The adsorption process of MTF aerogels for Au3+ and Ag+ conforms to the G.E.Boyd liquid membrane diffusion equation and Langmuir isothermal model.?H>0,?G<0,?S>0 were obtained by thermodynamic formula calculation,the results show that the adsorption process is spontaneous endothermic process and the degree of confusion in the system is increased before and after adsorption.Infrared spectrum shows that the S,N and O atoms may have coordination reaction in the adsorption process,which provides electrons for Au3+and Ag+.The low strength and poor toughness of MTF aerogels were prepared in the previous experiments,and it bring a lot of inconvenience to the practical application in the later stage.Therefore,in order to improve the mechanical properties of MTF aerogels,MTF composite aerogels were prepared from three kinds of macromolecules,starch,cellulose and chitosan,and three kinds of substances were optimized.When the amount of starch,cellulose and chitosan was 0.6 g,0.17 g and 0.3 g respectively,the shrinkage rate of MTF aerogels was the lowest.The prepared MTF composite aerogels had better formability than MTF aerogels,of which MTF/S-0.6 composite aerogels could withstand 200 g pressure and had a certain degree of flexibility.Finally,the adsorption capacity of three kinds of composite aerogels to Au3+ was verified.The results showed that the adsorption performance of MTF/S-0.6 composite aerogels was higher.