Surface Silanization Of Sulfuric Acid Activated Halloysite For Removing Methlene Blue From Aqueous Solution

Halloysite is a kind of clay mineral ubiquitous in nature.Due to the limited application of natural halloysite,most researchers modify it to expand its application fields.However,most researchers currently only discuss the application effects of modified halloysite,and seldom discuss the modification process from the perspective of modification mechanism.This paper innovatively combines activation modification with organosilane modification,and uses the modified sample to remove the organic dye methylene blue（MB）.Therefore,this article chooses Hubei halloysite with transparent and straight lumen,using XRD,TEM,SEM,FTIR,DRIFT,TG,NMR and many other characterization methods,to explore the effect and mechanism of H₂SO₄ on its activation modification.Use APTES to graft and modify natural halloysite and H₂SO₄ activated samples in different media,explore the graft modification mechanism and the influence of different media on the graft modification.Finally,natural halloysite,acid-activated samples and grafted modified samples in different media were used to remove MB to explore the effect of modified halloysite on methylene blue solution（MB）removal.Furthermore,it can realize the controllable modification of halloysite,and accumulate abundant data for subsequent experiments on the modification of halloysite.The following are the research results of this study:（1）From the XRD spectra before and after sulfuric acid activation,there is no change in the d₀₀₁ value.Observe the diameter of the HNTs in the TEM and find H₂SO₄ selectively dissolves alumina.As a result,the inner diameter of the halloysite tube gradually increases,without any change in the outer diameter of the tube,until the halloysite tubular structure is damaged and unfolded.It shows that the H₂SO₄ did not enter the interlayer spacing of halloysite during the activation of 2mol/L H₂SO₄.It was also found that the erosion process first started from the inner wall of the halloysite and the samples whose activation time was less than 5 days could still retain a large number of intact tubular morphologies.At the same time,according to SEM,it is found that H₂SO₄ activation helps to improve the agglomeration of halloysite.In addition,using FTIR and proton nuclear magnetic resonance spectroscopy to analyze the changes in the surface hydroxyl groups of HNTs,it was found that the internal hydroxyl groups and aluminum hydroxyl groups on the internal surface decreased with the increase of activation time,indicating that sulfuric acid activation can directionally regulate the distribution of halloysite hydroxyl groups.（2）In anhydrous toluene and different ratios of ethanol-water systems,natural halloysite and samples with an activation time of less than 5 days were modified by APTES grafting.Using infrared and proton nuclear magnetic resonance spectroscopy,it is found that because APTES is a macromolecular substance,it is difficult to enter the interlayer spacing of halloysite.Therefore,APTES only reacts with the aluminum hydroxyl on the inner surface of the tube,the hydroxyl on the end face of the tube,and the silanol on the outer surface of the tube.The graft modification mechanism is not only the direct condensation reaction between APTES and hydroxyl,but also the hydrolyzed APTES between each other.Oligomerization occurred.At the same time,it was further found that the sample with H₂SO₄ activated for 3 days had the most silane loading（2.2724%）in the non-polar solvent（anhydrous toluene）.This is mainly because the dipole contained in the polar solvent-absolute ethanol will make it easier for polar molecules to form a surface layer on the surface of halloysite,thereby shielding a part of the hydroxyl groups,making it difficult for APTES to contact this part of the hydroxyl group to undergo condensation reaction,and its A higher dielectric constant（24.6）makes it easier for ethanol molecules to produce hydrogen bonds with organosilanes,making it difficult for APTES to migrate and react with hydroxyl groups.Further comparison of different ethanol-water ratio systems found that the water content of the solvent will also affect the grafting effect,and the grafting effect is best when the ethanol/water ratio is 5/5.This is mainly because the presence of water promotes the hydrolysis of APTES,which increases the amount of silanol hydrolyzed by APTES in the system,which connects to the silanized halloysite surface through covalent bonds or hydrogen bonds,increasing the load.（3）Four representative adsorbents（Raw HNTs,HNTs-3,HNTs-3-M,HNTs-3-M100/0）were selected to adsorb MB.Found that HNTs-3-M has the highest removal rate.At the same time,it is found that p H is proportional to degradation rate.The process of MB adsorption is self-discharging heat.At the same time,it is further found that the ionic strength has a greater influence on the adsorption effect.The modified material has good reusability performance,and its removal effect can still be close to 80%after being reused for 5 times,indicating that it has strong economic and practicality.This is mainly because the halloysite and MB molecules are mainly connected by electrostatic attraction.