Prepration Of Graphene Oxide/Carrageenan Composite Hydrogels And Their Adsorption Properties For Dyes And Heavy Metals In Water

In recent years,excessive use and massive discharge of dyes and heavy metals have caused environmental pollution and endangered human health,which attract people’s great concerns.It is an urgent problem that how to effectively remove dyes and heavy metals from wastewater.Adsorption technology is currently the most effective wastewater treatment method.It is of great significance to design and synthesize adsorbents with high efficiency and adsorption capacity for the remediation of water environment.Hydrogel has a three-dimensional network cross-linked structure with a large number of hydrophilic groups in the main or branch chain.Due to the high water absorbing capacity and size control,it is a potential new adsorption material.However,most of polymer hydrogels are difficult to recycle because of the poor mechanical properties,which greatly limit their application in water purification.Therefore,this thesis aims to construct graphene oxide/carrageenan composite hydrogels(SeCA-GH)as adsorbent with good mechanical properties,high adsorption capacity and recyclability for adsorption of dyes and heavy metals in water.The first chapter briefly introduces the pollution sources and treatment methods of dyes and heavy metals in water,and summarizes the structural properties and application fields of carrageenan,the preparation of composite hydrogels and their application in the environmental field.In the second chapter,the graphene oxide(GO)/carrageenan hydrogels were prepared by a simple heating and stirring method.The composite hydrogels were characterized by Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),thermogravimetric analysis(TGA),X-ray diffraction(XRD)and other methods.The presecnce of GO changes the smooth sheet structure of the carrageenan into a pleated sheet structure.As a new type of adsorbent,the composite hydrogels exhibit excellent adsorption performance for industrial pollutant methylene blue(MB)with a maximum adsorption capacity of 189 mg·g-1,and the adsorption is spontaneous and endothermic process.The adsorption kinetic study showed that the adsorption of MB by the composite hydrogels accorded with the pseudo-second-order kinetic model,and the correlation coefficient R2 was 0.999.The adsorption isotherm study shows that the adsorption process of the composite hydrogels is well fit with Langmuir model,and the correlation coefficient R2 is 0.993～0.995.The MB adsorbed on the surface of the hydrogels could be effectively eluted by alcohol,and the removal efficiency can still reach 80%after 6 times of elution.In addition,the composite hydrogels can also act as a catalyst to accelerate the reduction of MB in water.The catalytic rate constant of the composite hydrogels is 1.161 min-1,which is 3.3 times than that of the pristine carrageenan.The third chapter investigates the adsorption capacity of the composite hydrogels for Hg2+in water.The adsorption efficiency of 50μg L-1 Hg2+ on the surface of the hydrogels can reach 98.2%at 25℃.Langmuir model can well describe the adsorption process of Hg2+.The monolayer saturated adsorption capacity is 344.8 mg·g-1,which is similar to the actual adsorption capacity of 330.6 mg·g-1.Adsorption kinetics studies show that the adsorption process of Hg2+ by hydrogels is well fit with the pseudo-second-order kinetic model,and the correlation coefficient R2 is 0.998.In addition,when the hydrogels are recycled 8 times,the removal efficiency can still reach 75%.The fourth chapter summarizes the research content of this thesis,and prospects the further development and application of the composite hydrogrel materials.