| As a kind of natural clay mineral nanotubes,halloysite(HNTs)has been paid more and more attention in recent years.However,a variety of phenomenon,such as size,surface electron and hydrogen bond,often exist in the halloysite nanotubes,which lead to aggregation and affect their properties and application range.Surface modification by organosilane has been proposed as an efficient strategy to avoid such phenomena.At present,the surface modification methods are various,which can be roughly divided into the following categories: coating,intercalation,coupling agent modification,hydroxyl group modification and surfactant modification.After modification,HNTs can overcome the defects or amplify the advantages of the original materials,playing an important role in various field such as environmental area,medical area and nanocomposite materials research.This study based on different regions(ordos,hebei,shanxi,sichuan,hubei)natural halloysite nanotubes,through the used of organic silane on the modification,preparat the desired samples,and further characterizing by X-ray fluorescence spectrometry(XRF),X-ray diffraction analysis(XRD),transmission electron microscopy analysis(TEM),nitrogen stripping analysis,infrared absorption spectroscopy(FTIR),thermogravimetric analysis and hydrogen nuclear magnetic spectra analysis(NMR).The main research results of this paper were as follows:(1)The HNTs in the 5 regions were not very different in structure and morphology,and could be divided into the following three categories according to the overall characteristics: the first is hubei sample(Hub).The Hub halloysite(7 ?-type),with the most complete tubular morphology,abundant pores and the widest intermediate mesoporous cavity,was the best material for surface modification in theory.Second,the samples from ordos(Eeds),hebei(Heb)and sichuan(Sic)were analyzed.The differences between the three samples(Eeds,Heb,Sic)were very small,mainly concentrating in the composition and porosity.The three type samples were mixed with 10 ?-HNTs and 7 ?-HNTs,and also contained impurities such as gibbsite,alunite,and quartz.They were almost the same in terms of pore diameter distribution,specific surface area and pore volume.The third is shanxi sample(Shx).The difference between Shx and other 4 HNTs was the largest.The Shx halloysite had the highest proportion of impurities,that was,its HNTs content ratio is the lowest in the 5 places.(2)APTES was successfully grafted onto HNTs in toluene,and the results were proved by means of characterization.However,the amount of APTES grafted in ethanol and ethanol-water solvent is significantly lower.According to the TG result,the HNTs samples showed the consistent trend about the mass loss.After grafting reaction,the sample(Eeds,Heb,Shx,Sic,Hub)showed difference.The TG curve of Hub is basically unchanged.Eeds,Heb,Sic,Shx TG curve of the more mass loss before 250℃,indicated that by way of absorption,hydrogen bond exists in APTES removal in the samples;there was no significant difference in the main stages of mass loss.In the infrared spectrum,the HNTs of 5 regions showed similar performance,with peak intensity decreasing and new infrared peaks of APTES appearing,indicated that APTES has grafted into the surface of partial samples successfully.The results of NMR hydrogen spectrum more directly showed that the hydroxyl peak strength changed greatly before and after grafting reaction.Moreover,the grafting site was identified as HNTs surface hydroxyl based on the position of the hydroxyl group,which directly proved that the hydroxyl group was consumed in the grafting reaction and the grafting was successful.(3)The grafting reaction of HNTs in 5 fields in different grafting solvent was compared,and it was found that the grafting effect was not significantly different in the anhydrous solvent,only the APTES content of the residual in oligomerization and adsorption was changed,showing the same grafting rule on the whole.But in the different water content ethanol solvent the difference was obvious,the high water content solvent is suitable for the grafting reaction to carry on.The natural samples from Shanxi Province were the least suitable for the grafting modification of organosilane. |
