| With the accelerated development of economy and industry,wastewater containing environmental estrogens is increasingly discharged into the water environment,resulting in causing great harm to humans and organisms.Therefore,it is necessary to select the appropriate process to effectively remove the environmental estrogens in water.Recently,a variety of methods have been used to removal environmental estrogens from water such as adsorption,catalytic degradation,photo-catalytic degradation,biodegradation,and advanced oxidation.Among these method,Adsorption is considered as a low cost,simple and high efficiency method.It has high application potential in the field of removing environmental estrogen pollutants in water.In recent years,graphene oxidation has caused the widespread attention.It is a kind of honeycomb lattice arrays of two-dimensional plane single carbon materials.It has a layered structure,large specific surface area and more active functional groups which make it has great advantage in adsorptive remove pollutants.In this paper,17?-estradiol was selected as the representative environmental estrogens.The adsorption ability of 17?-estradiol onto graphene oxide was studied,and its main adsorption mechanism was also revealed.Adsorption process tended to be affected by the surface structures of adsorbents and the external environment condition.Therefore,this work focused on investigating the graphene oxide surface structure,natural organic matter and inorganic nanoparticles on the adsorption of 17?-estradiol.In addition,graphene oxide is difficult to solid-liquid separation due to its high hydrophilic.So magnetic graphene oxide material was prepared,and further modified by?-cyclodextrin/poly-L-glutamic acid compound to increase its adsorption performance.The specific research work and achievements of this paper can be summarized into the following five aspects:In the first part,the adsorption performance and related mechanism of 17?-estradiol in water were studied.Through scanning electron microscope?SEM?,transmission electron microscope?TEM?,atomic force microscope?AFM?,X-ray diffraction?XRD?,Raman spectra,surface automatic analyzer,Fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?,the morphology,structure and compositions of graphene oxide were investigated.The influences of initial solution pH,contact time,initial concentration of pollutant,temperature,ionic strength and background electrolyte onto graphene oxide were also studied.Besides,adsorption kinetics and isotherm models were applied to analyze the mechanism of graphene oxide adsorption.The results showed that initial pH,contact time,initial concentration of 17?-estradiol,temperature and background electrolyte have significant influence on the adsorption process.Pseudo-second-order dynamic model could better simulate the adsorption kinetic data and Langmuir model better describe the isothermal adsorption data.This indicted that graphene oxide surface was monolayer adsorption and chemical adsorption forces such as?-?interaction and hydrogen bond were the main mechanism of adsorption.The maximum adsorption capacity of 17?-estradiol was 149.4 mg/g at 298 K,indicating that graphene oxide had a great potential for adsorption application.The second part is to study the effect of natural organic matter on the adsorpti on of 17?-estradiol onto graphene oxide.The effect of natural organic matter onto graphene oxide structure characteristics was investigated by using elemental analysis,zeta potential analyzer and automatic surface.The isothermal adsorption experiment was conducted to investigate the natural organic matter on graphene oxide adsorption mechanism with different surface characteristics.Besides,this part comprehensive compared the absorption ability of 17?-estradiol in the presence of natural organic matter between graphene oxide and activated carbon,carbon nanotubes and biochar,and further evaluated the practical application potential of graphene oxide.The results showed that natural organic matter could occupy part of graphene oxide adsorption sites,reduced the specific surface area and pore volume and increased the polar functional groups on surface,resulting in reducing graphene oxide adsorption ability.Compared to other carbon adsorption materials,the effect of natural organic matter on graphene oxide adsorption was less than activated carbon,carbon nanotubes and biochar.Graphene oxide exhibited comparable adsorption performance with activated carbon and carbon nanotubes,but was higher than that of biochar.This indicated that graphene oxide has a great application prospect.The third part is to study the effect of inorganic nanoparticles on the adsorption of 17?-estradiol onto graphene oxide.The influences of two common inorganic nanoparticles,namely SiO2 and Al2O3,on the adsorption of 17?-estradiol onto graphene oxide were examined by using batch adsorption experiments in combination with microscopic,spectroscopic,and computational methods.Results exhibited that the presence of inorganic nanoparticles significantly inhibited the adsorption and increased the time to reach adsorption equilibrium for the adsorption of 17?-estradiol onto graphene oxide.Besides,the impact of Al2O3 was greater than that of SiO2 due to the enhanced electrostatic attraction between positively charged Al2O3 and negatively charged graphene oxide.Derjaguin-Landau-Verwey-Overbeek calculation revealed that graphene oxide tended to first homoaggregate and then heteroaggregate with SiO2.However,oppositely charged Al2O3 and graphene oxide were likely to heteroaggregation rather than homoaggregation.This was also demonstrated by the zeta potential measurement,and scanning electron microscope.These observations highlighted the significant influence of inorganic nanoparticles on the adsorption of contaminants onto graphene oxide,and also provided new insights into the fate and transport of graphene oxide and pollutants in natural water environments.The fourth part is to study the effect of the surface structure of graphene oxide on the adsorption of 17?-estradiol.The reagent hydrazine was used to adjust the surface structure,and the different reduction degree of graphene oxide was prepared.Raman spectra,XRD,XPS,TEM,automatic surface analyzer were used to analyze the surface structure characteristics such as the element analysis,the specific surface area,pore size distribution,oxygen content,the size of unoxidized graphitic zone and oxidized zone.In addition,the adsorption isotherms of 17?-estradiol onto graphene oxide with different reduction degrees,and the influence mechanism of the surface structure was explored,and the quantitative model was used for quantitative analysis.The results showed that the surface structure of graphene oxide was different in different reduction degrees,and the increase of reduction would cause the surface to accumulate and reduce the specific surface area and pore volume.Besides,with the increase of reduction degree,the size of its unoxidized graphitic zone and sp2 aromatic clusters increased gradually,and the sp3 zone gradually decreased.The adsorption capacity of graphene oxide to 17?-estradiol also increased with the increase of reduction degree,and it was found that the?-?interaction and hydrophobic effect were dominant in the adsorption process.The contribution coefficient of the 17?-estradiol adsorption was different in different zones of graphene oxide.In order to improve the solid-liquid separation properties of graphene oxide,in the fifth part magnetic graphene oxide was prepared.In order to improve its adsorption performance,its surface was modified by?-cyclodextrin?CGMG?.The characteristics of CGMG were investigated via using FTIR,XPS,Raman spectra,XRD,vibrating sample magnetometer and Brunauer-Emmett-Teller surface area,respectively.Results indicated that CGMG was successfully prepared and the saturated magnetization could reach up to 0.09043 emu/mg.Meanwhile,investigation of adsorption behavior illustrated that the adsorption process could be better fitted by the pseudo-second-order and Langmuir models.Analysis of intraparticle diffusion model demonstrated that intraparticle diffusion was not the only rate-limiting step;however,both film diffusion and intraparticle diffusion were involved in the diffusion process.Thermodynamic study indicated that adsorption of 17?-estradiol onto CGMG was spontaneous and endothermic.The high pH value and humic acid were not beneficial to the 17?-estradiol adsorption.Moreover,the regeneration experiments illustrated that CGMG could be recovered,and it showed good recycling ability with ca.88.7%of the initial sorption capacity after being used for sixth cycles. |
PDF Full Text Request