Preparation And Application Of Mn-potassium Absorbent Material And Research On Molecular Simulation

In this paper,α-MnO₂ ion-sieve was obtained by hydrothermal synthesis method at a certain temperature,hydrothermal time,acid concentration and molar ratio of the materials（KMnO₄ and MnSO₄）.On the basis of hydrothermal method,ultrasonic,microwave and the addition of 1,2-dodecanediol were used respectively to systhesizeα-MnO₂ ion-sieve.All the samples were applied to K⁺adsorption experiments in simulated sea brines and characterized.As meanwhile,the influence of the synthesis conditions on the performance ofα-Mn O₂ ion sieve was investigated.What’s more,molecular simulation of the adsorption process was studied on Material Studio 8.0.The results show:（1）Crystal structure of nanorodα-MnO₂ ion sieve turned out to be more perfect with temperature and crystallization time increasing.Preparation temperature and hydrothermal time can be selected among 100°C—120°C and 12h.With the molar ratio of the material increasing from 3:1 to 1:5,the sample changed fromα-MnO₂ toγ-MnO₂,and the morphology was changed from hollow urchins into nanobar and then raphides clusters.The molar ratio of the material can be selected around 1:3.With the increase of acid concentration from 0 to 3 M,α-MnO₂ nanorods changed to nano particles.So acid concentration can be selected within the range of 0.5-1.5 M.（2）The diameter ofα-MnO₂ under ultrasonic treatment before hydrothermal synthesis（hydrothermal time 4—6 h）proved to be smaller（100—150nm）and the distribution was more uniform.α-MnO₂ under microwave treatment before hydrothermal synthesis（hydrothermal time 6 h）proved to be hollow sphere composed of shorter and thinner nanorods.With the addition of 1,2-dodecanediol as a reactant increasing,α-MnO₂ was converted into nanofiber needle from the nanorod.The 20μm needles were connected with each other through terminal nodes just like a mesh shape.When the addition ratio exceeds 1:4（molar ratio of 1,2-dodecanediol to KMnO₄）,the purity of sample decreased.（3）Crystal form of sample didn’t change after modification and adsorption,and the unit cell size became larger after adsorption.Mn³⁺:Mn⁴⁺in the cell was nearly 1.The influence order of the four synthesis factors on ion-sieve adsorption capacity was reactant ratio>temperature>time>sulfuric acid concentration.The highest saturated adsorption capacity of normal hydrothermal sample to K⁺in pure KCl solution was272.91 mg/g,and the highest saturated adsorption capacity in simulated seawater and was 109.27 mg/g.The highest saturation adsorption of sample of ultrasonic,microwave and 1,2-dodecanediol addition groups to K⁺in pure KCl solution was240.78 mg/g,the highest saturated adsorption capacity in simulated seawater and was91.08 mg/g.In addition,the adsorption kinetics of theα-MnO₂ was best described by pseudo-second-order kinetic equation and the ion exchange process was controlled by liquid film diffusion.The adsorption process of K⁺need 360 min to reach equilibrium.In addition,adsorption capacity of chosen sample decreased from 214.48mg/g to181.75mg/g after five times adsorption and desorption.（4）K⁺adsorptive sites inα-MnO₂ framework were gained by molecular simulation.The maximum theoretical adsorption capacity was 299.62mg/g,indicating that the K⁺adsorption capacity still has room for improvement for experimental sample.After the insertion of K⁺,the undulation of the energy band became larger,the non-local degree of the electron cloud around the selected feature point and the orbital expansion after hybridization were enhanced.The effective mass of the electron cloud group was smaller than that of the crystal without K⁺inserting.The sp orbital interaction between K⁺and Mn^x+is stronger than H⁺and Mn^x+which favors the existence of K⁺in the crystal.The adsorption process is an exothermic reaction so that it’s suitable to desorb at higher temperature and adsorb at lower temperature.As the number of K⁺in the cell increased,ΔH gradually became larger.When other ions present in solution simultaneously,K⁺is preferentially adsorbed.But actually,the adsorption amount of K⁺isn’t as high as it should be due to other ions’competition.