Study On The Characteristics Of Layered Minerals/water Interface Based On Atomic Force Microscope Technique

With the progress of science and technology and the development of economy,the application fields of mineral materials are expanding,and the application efficiency is increasing.Among them,many interfacial properties of layered minerals,such as adsorption,oxidation and defect properties,have a decisive impact on its application.Therefore,the detailed researches on the surface characteristics of different layered minerals have important significance for broaden the cognitive characteristics of mineral surface layer,the development of layered mineral nano materials and its complex potential application space,as well as the guidance the preparation and application of nano layered mineral materials Atomic force microscopy?AFM?can reach the scanning resolution of the atomic level.It is a very effective research method to explore the characteristics of the surface/interface of layered minerals.Therefore,the adsorption,wettability,defect information and oxidation characteristics of different layered mineral surfaces are studied by AFM in this paper,and the main contents and conclusions are as follows:?1?The adsorption of Hg²⁺on the surface of natural molybdenite was studied by AFM,and the effect of the hydration layer caused by the oxidation of the molybdenite on the adsorption of Hg²⁺was also investigated.It was found that the surface of Molybdenite could better adsorb Hg²⁺,but the hydration layer impeded the adsorption of Hg²⁺.Moreover,the Hg²⁺adsorption on molybdenum disulfide surfaces appeared in the form of a multilayer.The first adsorbed Hg²⁺layer was probably caused by the complexation of Hg²⁺with the S atoms on the surfaces,while the second one might be due to the electrostatic interaction between negatively charged molybdenum disulfide and the cation Hg²⁺.?2?This work applied AFM technique to study the wettability characteristics on hydrophilic mica and hydrophobic graphite that both modified with the surfactant DTAB.Contact angle measurements were made on DTAB-modified surfaces,and results verified that surface coverage?determined by AFM?was correlating with the wettability.For hydrophilic mica,the increased DTAB aggregates coverage on mica led to a strong hydrophobicity on the surfaces at concentration of 10^-6-10^-4 mol/L.At concentration of 10^-3 mol/L,the occurrence of large aggregates caused by bilayer adsorption was adverse to hydrophobicity as the adsorption time extended.In the case of hydrophobic graphite,DTAB aggregates mainly formed as stripes covering on the surfaces,leading to the reduction of hydrophobicity.This reduction became stronger as more DTAB aggregates covered on graphite surfaces.?3?We proposed a new method to study the isomorphism defect of mica and graphene surface defects by AFM,namely,observing the absorption of organic ion?BS,BTMA⁺?on layered mineral surface in the nanometer scale.Then,the adsorption regions of AFM image could be marked by image processing software,furthermore,the defect area could be measured and defect rate could be calculated.?4?In-situ observation of molybdenum disulfide?MoS₂?sheet exposed in water was investigated using AFM in order to obtain more understandings for the preparation and application of two-dimension molybdenum disulfide.It has been found that chemical reactions really happened to MoS₂ sheet in water,leading to the partial etching of surface layer and the formation of needle-like humps on the surfaces.Results showed that the observation might be originated from the oxidation of MoS₂into Mo?VI?and SO₄^2-.The oxidative product Mo?VI?presented either in the form of MoO₃·H₂O crystalline on the MoS₂ surfaces or molybdate ions in aqueous solution,while SO₄^2-presented in the solution,resulting in the etching of surface layer and the formation of needle-like humps.