The Controllable Preparation And Modification Of Hydrothermal Carbonaceous Spheres And Their Application In Anion Exchange Chromatography

As a significant member of chromatographic techniques,ion chromatography(IC)has been broadly employed in the detection of inorganic and organic ions,and become an essential analytical technique for pharmaceuticals,food and chemistry industries.Similar to other types of chromatography,the separation performance of IC primarily relies on its stationary phase.The modern packing materials for IC are mainly aromatic polymers,their preparation process needs special technology and organic solvent,which may have adverse effect on environment protection.On the other hand,the non-ion specific interactions between these aromatic substrates and polarizable anions such as nitrate,iodide,perchlorate,including Vander Waals,anion-π,and π-π interactions,which could cause some unwanted effects including peak tailing and strong retention in IC separation.Therefore,the design of novel green and high-hydrophilic stationary phase for efficient and selective separation is still a crucial goal in modern IC research.This thesis depends on the hydrothermal carbonization of saccharides to synthesize monodisperse carbonaceous nanospheres and microspheres,which are further modified with quaternary ammonium polymers and applied in ion chromatography stationary phase.Chapter one reviews the recent development of ion chromatographic stationary phase,especially anion exchange stationary phase,which is divided into three kinds based on the substrate material:polymer-based,silica-based and other substrates-based anion exchangers.Meanwhile,the research progress and application of biomass-derived hydrothermal carbon spheres are briefly introduced.The synthesis method and surface property are principally discussed,as the basis of applying hydrothermal carbon spheres into ion chromatography packing materials.Chapter two mainly proposes a simple and green modification method for hydrothermal carbon nanospheres(HCNSs),which can introduce controllable layers of quaternary ammonium polyelectrolytes.Based on the hyperbranched polymerization of bis-glycidyl ether and amine,the polyelectrolyte-functionalization could be efficiently achieved in water solvent at 60℃,which is proved by the characterizations of scanning electron microscope(SEM),infrared spectrum(IR),X-ray photoelectron spectroscopy,etc.The modified HCNSs are still monodisperse and have better water dispersibility than raw HCNSs.Furthermore,octadecylamine functionalized HCNSs are facilely prepared through the simple epoxy-imide addition reaction,which demonstrates the potential of polyelectrolyte modification in producing functional carbon materials.Chapter three develops a preparation method of HCNSs-based anion exchange stationary phase,in which quaternary ammonium polyelectrolyte-functionalized HCNSs are stably coated on the surface of polystyrene-divinylbenzene beads.This core-shell structure is proved by SEM images.The baseline separation of common inorganic anions,polarizable anions,small aliphatic and aromatic acids are achieved on prepared phase,the efficiency for fluoride can reach 24900 N/m.The high hydrophilic nature of HCNSs results in excellent peak symmetry of,the asymmetry factor of nitrate and iodide peaks are 1.06 and 1.10,respectively.Moreover,home-made IC column is employed for detecting phosphate in cola drinks.In chapter four,carbon nano spheres(CNSs)with high carbon content and good mechanical property are obtained through the high-temperature carbonization of HCNSs,and employed as latexes in anion exchange stationary phase.The morphology,nitrogen content,column capacity and separation performance for inorganic anions and small organic acids of prepared phase are detailedly investigated,and obtained IC column is further used for the analysis of citric acid in sprite drinks.The stiffness of CNSs improves the permeability of prepared stationary phase,which resulted in lower column pressure than HCNSs-based agglomerated phase.Chapter five designs a high-efficient and controllable synthesis approach of monodisperse carbonaceous microspheres(CMSs)with micron size,based on sodium polyacrylate-assisted hydrothermal carbonization of sucrose.The diameter of CMSs can be easily tuned in the range of 1-5 μm through hydrothermal conditions,including sucrose concentration,reaction time and temperature.The results of various characterizations such as SEM and IR indicate that the addition of sodium polyacrylate do not change the chemical property of CMSs.This synthesis route can still work in scale-up experiment and at high sucrose concentration.Meanwhile,maintaining the morphology and monodispersity,nonporous CMSs can be facilely transformed into porous CMSs through high-temperature carbonization under air atmosphere.These facts open the way for industrial preparation of nonporous or porous large-sized CMSs.In chapter six,the hydrothermal CMSs with the average size of 3.4 μm are modified with quaternary ammonium polymers,and used as grafting stationary phase for IC.The anion-exchange capacities of prepared phases range from 26 μmol to 92 μmol according to the grafted polymer layers on CMS surface.Additional two-week flushing test shows that the chromatographic performance of obtained phases have good stability and repeatability.The stationary phase with different capacities can not only efficiently separate various anions,including common inorganic anions,polarizable anions and monocarboxylic acid,but also achieve the baseline separation of four saccharides,all chromatographic peaks are symmetrical without obvious tailing phenomenon.The high-capacity stationary phase is further applied in analyzing the fluoride content of tea samples.