Study On Stability Of Graphene Oxide And Graphene Oxide Quantum Dots And Toxicity To Microcystis Aeruginosa

The wide use of graphene oxide and graphene oxide quantum dots increases their chances of entering the ecological environment,especially the water environment.In order to better understand the environmental risks of GO and GOQD,it is necessary to study their aquatic behavior and adverse effects and possible toxic effects.In this study,GO and GOQD were used as typical tested nanomaterials.First,the differences in physical and chemical properties of their morphology and composition were investigated.Then the effects of pH,electrolyte and humic acid on the stability of GO and GOQD in water were compared.Finally,the microbial bacterium was used as the test organism,and the biological toxicity of GO and GOQD was analyzed.Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy indicated that both GO and GOQD surfaces contained a large number of oxygen-containing functional groups.Compared with GOQD,the total surface oxygen content of GO is higher,and the proportion of hydroxyl groups is larger,while the content of carbonyl and carboxyl groups is less.The effects of pH and Ca²⁺,Mg²⁺,K⁺and Na⁺on the stability of GO and GOQD were investigated by measuring zeta potential and hydrated particle size to predict its migration in water environment.With the increase of pH,the zeta potential decreases.In the range of pH 6-9,the zeta potential changes little and is maintained between-20mV and-25mV.The system is relatively stable due to the surface electrostatic repulsion in this pH range.The effects of four cations on the stability of GO and GOQD were investigated.It was found that the four cations had a certain degree of influence on the stability of GO and GOQD.The hydrated particle size and zeta potential of graphene oxide and graphene oxide quantum dots increased with the increase of electrolyte concentration.The coagulation effect of the four cations on GO and GOQD is Ca²⁺,Mg²⁺,K⁺,Na⁺,from strong to weak.Among them,the divalent cation has a greater coagulation effect on GO and GOQD than the monovalent cation,and the cation with a larger atomic weight in the same valence state promotes coagulation more than the cation with a small atomic weight.The effects of GO and GOQD on the growth of Microcystis aeruginosa cells were studied.The protein and chlorophyll,antioxidant content and antioxidant enzyme activities were determined to investigate the mechanism of GO and GOQD on the production of Microcystis aeruginosa.It was found that GO and GOQD inhibited the growth of microcystis aeruginosa,and the algal density was negatively correlated with the concentration of GO and GOQD.Exposure to GO and GOQD inhibited protein synthesis in Microcystis aeruginosa.Due to the increased ROS content in algae cells,more energy is needed to maintain the expression of protective genes and the normal function of the antioxidant system.Therefore,esterase activity,chlorophyll content and intracellular polysaccharide content are observed to increase.It was observed that the activities of antioxidant enzymes in the cells of Microcystis aeruginosa were generally increased,and the contents of antioxidants and lipid peroxidation products increased.This indicates that the toxic effects of GO and GOQD on Microcystis aeruginosa are closely related to oxidative damage.