Preparation Of Carbon Quantum Dots And Its Aquatic Biological Toxicity

Carbon quantum dots(CQDs)as a new class of artificial carbon nanomaterials have attracted the attention of the scientific community due to their unique nanoscale effect,high water dispersibility,high fluorescence stability,and low production cost.With extensive attention,it has become a hot spot in many fields of research such as chemistry,materials science and biology.It has applications in biosensing,in vivo imaging,drug carriers,and photocatalysis.However,because of the wide application prospects of CQDs,it will inevitably enter the environment in the process of production,use,disposal and recycling.At the same time,considering its high water dispersibility,its potential ecological impact on the natural environment,especially the water environment,deserves attention.Aquatic ecology is an ecosystem composed of aquatic organisms and water environment.It plays a very important role in human living environment.Scenedesmus obliquus,Daphnia magna,and zebrafish represent three species of phytoplankton,zooplankton and fish in the aquatic ecosystem.In this paper,citric acid-ethylenediamine carbon quantum dots synthesized by hydrothermal method were used as experimental materials.The above three aquatic organisms were experimental organisms to study the toxic effects of CQDs on aquatic organisms.The results of the study are as follows:1)The experimentally prepared CQDs are uniformly dispersed with an average particle size of 6.47 nm.The surface carries hydroxyl(-OH),amine(-NH),and(CH)groups of aliphatic carbon compounds.The test results show that the CQDs have excellent fluorescence properties.It can be successfully applied to the in vivo imaging of large cockroaches.In addition,the morphology,size,dispersion,and optical properties of CQDs in different test waters were not significantly different.However,the surface properties of CQDs in excreta after zebrafish swallowing have changed to some extent.2)In the aquatic toxicity test of CQDs,the EC50 values for S.obliquus at 48 h and 96 h were 142.6 mg/L and 74.8 mg/L,respectively,with certain sensitivities;24 h,48 h for large pupa.The EC50 and LC50 values were 108.3 mg/L and 190.6 mg/L,97.5 m/L and 160.3 mg/L,respectively,indicating that the carbon quantum dots have no apparent acute toxicity to large ticks;zebrafish were exposed to CQDs(10-200 mg)/L)No deaths and abnormalities within 15 days,no significant effect on swimming and feeding behavior.3)The photosynthesis and nutrient uptake of Scenedesmus obliquus were dose and time dependent,and high-dose CQDs were more toxic to Scenedesmus obliquus.In the investigation of the mechanism of poisoning,the intervention of high-dose CQDs can lead to excessive production of ROS and induce significant oxidative stress and oxidative damage in algal cells.In addition,in the monitoring of living water parameters of algal cells,the decrease in the pH of the water has a positive correlation with the dose of CQDs,confirming that the acidification of the suspension caused negative impacts on the growth and photosynthesis of the algae due to the nature of the CQDs.For this reason,we propose that the biological toxicity of CQDs may not be the result of simple direct exposure,and it may be more likely that CQDs alter the combined effects of both the algae living environment and direct contact.