Surface Silanization Of Acid-Activated Montmorillonite For Removing Orange Ⅱ Dye Pollutant From Aqueous Solution

Montmorillonite（MMT）has rich storage,low price,environment-friendly,natural two-dimensional nano-layered structure and many unique properties,which make its structure and properties easy to control,although natural montmorillonite can adsorb a variety of pollutants through complexation and cation exchange,however,most of the adsorbents are modified products from montmorillonite,at present,most researchers focus more on the application of modified montmorillonite,and less on the mechanism of the modification process.Therefore,this paper combines the modification of organic silane with the activation of acid（4mol/L H₂SO₄）.X-Ray Diffraction（XRD）,Fourier Transform Infrared Spectroscopy（FTIR）,Thermal Analysis（TG-DTG）and Nuclear Magnetic Resonance（NMR）were used to study the modification mechanism,the organic dye Orange Ⅱ（AO7）was removed by modified samples,and the removal efficiency,process and mechanism were investigated,the research results are expected to provide theoretical and experimental support for the development and preparation of MMT and its application in the removal of Orange Ⅱ dye.The main results of this paper are as follows:（1）MMT was activated by 4mol/L sulfuric acid at room temperature.Comparing the XRD patterns before and after activation,it was found that the d₀₀₁value of the acid-activated samples increased,indicating that H⁺entered the interlayer of montmorillonite,and the layered structure of montmorillonite remained after 80days of activation,it shows that montmorillonite has good acid stability.Further characterization by FTIR and NMR showed that Al-OH groups decreased with the increase of activation time,but more Si-OH sites were exposed.（2）After the organic modification,APTES were successfully grafted onMMT,and it was found that the modified mechanism was not only direct grafting,but also oligomerization.Acid activation controls organic modification by stimulating more active hydroxyl sites.After acid activation,the silanol group on the surface of montmorillonite gradually became the main reaction site,and the most silane grafting（7.59%）was found in the modified samples which were activated by sulfuric acid for16 days in toluene solvent.The effects of solvents on graft modification of montmorillonite with organosilane were investigated.The results showed that the grafting reaction was better in non-polar solvent（anhydrous toluene）than in polar solvent（anhydrous ethanol）.The increase of water content in the ethanol-water system can promote the hydrolysis and condensation of APTES,increase the degree of oligomerization of organosilane on the surface of montmorillonite,and then increase the loading of silane.But if the water content is too high,the degree of hydrolysis and condensation between APTES will intensify,so that the silanols in the system will be consumed,which will limit the grafting of silanes.When the ratio of ethanol to water was 70/30,the optimum modification effect was obtained（7.61%）.（3）The modified montmorillonite was used as an adsorbent to remove the Orange Ⅱ anion dye pollutants in water.It was found that the removal effect was influenced by p H value of the system.The optimal p H value was 2.0,the reaction time was 20min and the maximum equilibrium adsorption capacity was270.7475mg/g.The adsorption kinetics followed quasi-secondary kinetic model and the thermodynamic process was more consistent with Langmuir model,the removal of pollutants is mainly chemical adsorption,the calculation results of thermodynamic parameters show that the adsorption is a spontaneous endothermic reaction.The modified samples can be reused many times and have a good practical application prospect.