Study Of Silanization On Acid-Treated Halloysite Nanotubes

As a kind of common clay mineral material in nature,halloysite has sepcial tubular morphology and great application potential in multiple domains.However,a variety of phenomenon,such as surface electron and hydrogen bond,often exist in the nutural halloysite nanotubes,which affect their properties and application range.The surface modification to halloysite has been proposed as an efficient strategy to avoid such phenomena as well as additional performance improvements.Up to now,most research achievements concentrated on the test of the entire performance of modification but less exploration focused on the directional regulation of hallosite modification from perspective of mineralogy.Hence,this study focused on the research of the surface modification of acid-treated Hubei halloysite?by APTES?,combined with TEM,XRD,ICP,FTIR,TG,NMR,nitrogen adsorption and other characterization methods,investigating the effects of acid pretreatment and the influence of diverse reaction solvents on the modification of halloysite.The valid parameters for the motivated regulation of halloysite modification were acquired and the basic data for the practical application of modified halloysite in the correlative territory was gathered in this study.This paper has got several conclusions below:?1?During the acid?4 mol/dm³ HCl solution?activation of halloysite,the inner?concave?surface of halloysite composed by AlO₆ octahedra is firstly attacked by the acid resulting in the release of Al?III?to the solution.Further dissolution predominantly continues on the concave surface leading to the release of Si?IV?,which rapidly reaches a saturated concentration in 6 days and precipitates in the form of amorphous SiO₂ nanoparticles inside the nanotubes.Over a long period of time,the inner diameter of nanotubes and the diameter of SiO₂ nanoparticles increase.Within 10 days of activation,the samples were still maintained in tubular morphology well.?2?In the polar reaction solvents?anhydrous toluene?,the acid-treated halloysite with good tubular structure and the raw sample were modified by APTES.The results proved that the modification mechanism included not only direct grafting but also oligomerization.The acid activation principally regulated the modification by influencing the tubular morphology and the distribution of hydroxyl groups.The6-days acid-treated sample?HNTs-6?was the optimal sample for silanization,which has the highest silane loading of 4.16 mass%.?3?In the nonpolar reaction solvent?anhydrous ethanol?and the diverse proportions of ethanol/water,HNTs-6 was modified by APTES.Through comparative study,it was found that the organosilane load of HNTs-6 was strongly affected by the polarity of solvent and water content in the system from the point of the modification mechanism and the modification extent.Silanized HNTs-6 modified in the nonpolar reaction solvent had higher silane load and oligomerization extent in comparison with the samples modified in the polar solvent.And it has higher silane load and oligomerization extent than silanized raw halloysite in the polarity of the solvent.Besides,a certain percentage of water in the solvent was capable of promoting the hydrolysis and condensation reaction of the organosilane,increasing the loading capacity of organosilane.When the ethanol/water ratio was 8/2,the modification effect was best,but still lower than the loading capacity in hte polar reaction solvent.Nonetheless,excessive water in the solvent would cause the aggregation of HNTs-6,and aggravated the hydrolysis and condensation reaction between organosilane,reducing the content of silanol in the system,resulting in the reduction of the degree of oligomerization and organosilane load.