Preparation And CO₂ Responsiveness Performances Of Graphene-g-Poly（Dimethylaminoethyl Methacrylate） Copolymer

Graphene Oxide（GO）,an oxygen-containing derivative of graphene,has been widely studied for its large specific surface area,excellent optoelectronic and other properties.However,GO flake layers suffer from severe parallel stacking and are in powder form,which is difficult to recover.Graft modification of GO by polymers can effectively increase the layer spacing of GO lamellae,suppress their parallel stacking,and enhance their flexibility and processability.In addition,Poly（Dimethylaminoethyl Methacrylate）（PDMAEMA）is a multi-stimulus responsive polymer,and PDMAEMA grafting of GO can not only improve the properties of the composites,but also give the composites p H,temperature and CO₂responsive properties.The aim of this paper is to prepare a series of PDMAEMA grafted GO copolymers and their gels and further investigate their dispersion in solvent,swelling and CO₂responsiveness and adsorption properties.This paper consists of four main parts.In Chapter 1,firstly reviews the structure and properties,preparation methods and applications of graphene.Secondly,the research progress on the functionalized modification of graphene through covalent and non-covalent interactions is detailed,and the preparation of graphene/polymer composite gels and their applications in wastewater treatment,sensors,adsorbents and drug loading are further introduced.Finally,the research content and significance of this thesis are described.In Chapter 2,PDMAEMA grafted GO copolymers（GO-g-PDMAEMA,GP_x,where x is the amount of added monomer）were prepared using a radical copolymerization reaction.The GP_xwere characterized by powder X-ray diffraction（PXRD）,Fourier transform infrared spectroscopy（FT-IR）,thermogravimetry（TG）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The effects of the monomer injection on the GO layer spacing,crystallinity,thermal stability and microscopic morphology were investigated.The results showed that changing the amount of monomer addition could affect the crystallinity and layer spacing of GO.The crystallinity of GP₁was higher,which increased the layer spacing while preserving the orderliness of GO,and the PDMAEMA polymer chains were observed to grow on the surface of GP₁and self-assemble to form uniformly distributed 50-100 nm spherical particles,which realized the effective wrapping of polymer nanoparticles by the GO layer.The thermal stability results showed that the thermal stability of GP_xwas improved by 36%compared with that of GO.It was shown that the monomer dosage could effectively regulate the layer spacing of GO,and the covalent grafting of polymer chains between GO layers was the main factor to enhance the thermal stability of GP_x.In Chapter 3,PDMAEMA grafted GO double network gels（GP_xG,where x is the amount of monomer added in the preparation process）were prepared by in situ polymerization using MG suspension as precursor,potassium persulfate（KPS）initiating monomer DMAEMA and crosslinker N,N-Methylene Bisacrylamide（BIS）.The GP_xG was characterized by PXRD,FT-IR,TG,Raman spectroscopy（RAMAN）,SEM and TEM.The effects of the amount of monomer cast on the formation,layer spacing,crystallinity and microscopic morphology of GP_xG gels were investigated.The results showed that when the monomer dosage was 0.8 ml,the hydrogel was formed and the structure was relatively loose and easy to collapse.The flexibility and viscoelasticity of the formed hydrogel gradually increased with the increase of the monomer dosage.Meanwhile,PDMAEMA and GO formed a double network structure with mutual cross-linking,which effectively inhibited the parallel accumulation of GO lamellae.It is shown that changing the monomer dosage can affect the covalent interaction and cross-linking degree between GO and PDMAEMA,which leads to the difference of GP_xG microscopic morphology,and then affects the formation of GP_xG as well as flexibility and viscoelasticity.Meanwhile,the crystal diffraction peaks of PDMAEMA in GP_xG were enhanced significantly with the increase of monomer injection.The thermal stability of GP_xG was significantly enhanced.In Chapter 4,firstly investigated the dispersibility,surface wettability,CO₂responsiveness and cycle reversibility of copolymer GP_xin solvent.The results showed that the dispersibility of GP_xin water was significantly improved compared with that of GO,and good dispersibility was maintained after 24 h of standing in isopropanol,chloroform,hexane and methanol,respectively.In addition,GP_xhas good solubility in acidic solutions.the surface of GP_xwas completely wetted by distilled water in only 4.7 s,which was significantly improved compared with that of GO.GP_xwas added to the mixed system of hexane/water(V _hexane:V _water=2:3),GP_xwas dispersed in the aqueous phase,and after passing CO₂,some GP_xwas transferred from the aqueous phase to the oil phase,and continued to pass N₂,GP_xwas transferred to the aqueous phase again.It is shown that GP_xhas good CO₂responsiveness and shows certain emulsification performance for oil/water mixed system under the action of CO₂and can realize phase transfer.Meanwhile,the mixed system conductivity results indicate that GP_xhas reversible cyclability in the oil/water mixed system under the action of CO₂/N₂cycle.Next,the swelling,p H and temperature responsiveness,CO₂and rhodamine B dye adsorption properties of GP_xG double network gels were investigated.GP_1.4G double network gels showed swelling up to 10.13 g/g in distilled water with p H and temperature responsiveness.Among them,the swellings of GP_0.8G,GP₁G,GP_1.4G and GP₂G were 23.20,23.02,30.52 and27.58 g/g in buffer solution at p H=3.6,respectively,and the swellings of GP_xG decreased significantly in deionized water at 45℃.The adsorption of CO₂by GP_xG was improved by64%compared with pure GO.The kinetic simulation results showed that the adsorption of CO₂by GO,GP₁G and GP₂G was chemical adsorption,and the adsorption of CO₂by GP_1.4G was mainly physical adsorption.the adsorption of rhodamine B at different concentrations by GP₁G decreased compared with GO,and the adsorption of rhodamine B dye by GO was chemical adsorption,while GP₁G was physical adsorption.In this paper,a series of PDMAEMA grafted GO copolymers（GP_x）and their double network gels（GP_xG）were prepared by free radical copolymerization reaction to achieve the growth and layer spacing regulation of PDMAEMA between GO lamellae.At the same time,GP_xexhibits excellent dispersion and thermal stability properties,and has controlled CO₂response and emulsification properties.In addition,GP_xG exhibits excellent swelling properties,p H and temperature response properties,and significantly increased adsorption of CO₂compared to GO.Through the exploration of polymer grafted GO copolymer and gel preparation and properties in this paper,the foundation for further realization of stimuli-responsive composites in specific environments is laid.