Study Of Ion Intercalation Into Graphene-based Materials

Graphene-based materials have attracted extensive attention in recent years due to their excellent optical,mechanical,chemical and electrical properties.The functionalization of graphene-based materials is beneficial to broaden its application fields and become a current research hotspot.Among almost functional-modified methods,ion intercalation is an effective method to improve the physical and chemical properties of materials,such as conductivity,band gap,optical property and superconductivity.The Coulomb interaction between guest ions and π-conjugated electrons in graphene can precisely control the interlayer spacing of graphene layers and improve ion screening efficiency;It can also promote the formation of unconventional crystals and produce physical properties that are very different from the bulk structure;In addition,it can affect the band structure and electrical properties of graphene-based materials.However,the influence of graphene-based materials on the physical properties(such as crystal structure)of guest materials under the spatial confinement mechanism is still not in-depth.Developing more functional materials with excellent performance based on the ion intercalation method and enhancing its application potential still needs further exploration.This thesis focuses on the interaction between guest materials and graphene-based host materials and the reversible phase transition of the guest materials by regulationg the interlayer spacing of graphene oxide(GO)membranes,then studies the effect of ion intercalation on the infrared emissivity of graphene.The specific research content is as follows:1.The stable monoclinic potassium dihydrogen phosphate(KDP)structure is prepared by using GO and unsaturated KDP solution at room temperature(this structure is usually only stable at high temperature above 230℃).By adjusting the humidity level of the sample to change interlayer spacing of GO membranes,the reversible phase transition of KDP between the tetragonal structure and the monoclinic structure is realized.Experimental and theoretical studies such as X-ray diffraction(XRD),Raman spectroscopy(Raman),and first-principles calculations have shown that spatial confinement and cation-π electron interaction lead to disordered arrangement of hydrated K+and H2PO4-clusters,which results in stable formation of monoclinic KDP structure at room temperature.The local structure of the H2PO4-cluster can be changed by regulating the cation-π electron interaction strength and GO interlayer spacing by introducing water molecules.So as to realize the regulation of the crystal structure of KDP.2.By controlling the cations and anions composition of the guest molecules and changing the chemical reaction potential between the guest molecules and graphene,the dynamic regulation performance of the infrared emissivity of graphene is effectively improved.It is found that the emissivity modulator using[EMIm]NTf2 ionic liquid could achieve a modulation depth of about 0.52,which is about 21%higher than the best reported values in the literature,and its lifetime is equivalent to the value reported in the literature by changing the intensity of the external electric field.A series of characterizations of MLG microstructure(XRD,Raman and other methods)show that the smaller size of ions are beneficial to maintain the structural integrity of MLG and obtain a longer lifetime of device.The lower chemical reaction potential makes it easier for charge to be transferred from the anions in the ionic liquid to graphene,thus,increasing the modulation depth of the emissivity.In summary,the influence of graphene-based materials on KDP guest material is fully studied in this thesis,which is favourable for revealing the physical mechanism of the ion intercalation process and provides a new way to regulate the crystal structure of metal salts.In addition,the influence mechanism of different ionic liquids on the infrared emissivity of MLG is studied comprehensively and reveals the key factors that affect the performance of emissivity modulator,therefore,an important basis for device optimization is proposed.