The Colloidal Stability And Toxicity Of Water-soluble Quantum Dot Modified Wath 3-mercaptopropionic Acid

With extensive use of quantum dots in the electronics,biomedical testing,solar cells and other industrial field,its products and production is increasing by years.These engineering nanoparticles will inevitably enter the environment with the production,use,treatment and disposal of discarded products of quantum dots and related products.Environmental water is one of the important environmental media affected by it.Their aggregation and sedimentation behavior and toxic effects to aquatic organisms in the environmental water are worthy of attention and in-depth study.In this study,the water-soluble single-core MPA-CdTe and core-shell MPA-CdSe/CdS quantum dots modified by 3-mercaptopropionic acid were used as research objects.First,the preparation and characterization of quantum dots were carried out.The effects of pH,ionic species,ionic strength and natural organic concentration on the aggregation and sedimentation of quantum dots were analyzed.The colloidal stability in tap water,lake water and seawater was also investigated.Then the coagulation removal effect of ferric chloride and aluminum sulfate as flocculant on these two quantum dots and the fluorescence characteristics of floc were discussed.The effects of MPA-CdTe on the growth,photosynthesis and oxidative stress were investigated by using Chlorella vulgaris as a test object.The main results are as follows:(1)Particle sizes of MPA-CdSe/CdS and MPA-CdTe were 6-8 nm and 4-6 nm,respectively.The crystal structures were sphalerite cubic and CdTe cubic,respectively.And the fluorescence emission peaks were at 629 nm and 609 nm,respectively.(2)The Zeta potential of MPA-CdSe/CdS and MPA-CdTe solution is affected by pH condition.The absolute value of Zeta potential increases with the increasing pH value,and the stability of quantum dot particles increases.The presence of K+or Ca2+ can increase the hydrodynamic radius of the two quantum dots.The effect of Ca2+ complexing on the surface of the quantum dots causing quantum dots to sink is stronger than that of K+compressing the electric double layers(EDLs).(3)The presence of water-soluble humic acid SRHA increases the colloidal stability of two water-soluble quantum dots,1 mg/L SRHA in the solution MPA-CdSe/CdS and MPA-CdTe,their hydrodynamic diameter was reduced by an average of about 28%and about 9%.The larger concentration of SRHA,the smaller hydrodynamic diameter of the quantum dots in solution,owing to its effect from the negative Zeta potential and the steric hindrance to suppress the precipitation tendency of the nanoparticles.(4)In the coexistence of SRHA and K+,1 mg/L SRHA significantly inhibited the increase in hydrodynamic radius of MPA-CdSe/CdS in 100 mM K+solution,but 10 mg/L SRHA did not inhibit the increase in hydrodynamic radius caused by 2 mM Ca2+.(5)The removal of two water-soluble quantum dots in tap water by iron trichloride and aluminum sulfate is better than that in ultrapure water.In the tap water,0.6 mM Fe3+or 1.8 mM Al3+can remove more than 90%of the MPA-CdTe quantum dots,0.6 mM Fe3+or Al3+ can remove more than 90%of the MPA-CdSe/CdS.And in ultrapure water,1.8 mM Fe3+or 4.2 mM Al3+ can remove more than 90%of MPA-CdTe quantum dots,4.2 mM Fe3+or 7.2 mM Al3+can remove more than 90%of MPA-CdSe/CdS.(6)MPA-CdTe inhibited the growth of Chlorella vulgaris cell density in 96 h,and the inhibitory effect was increased with the increasing of quantum dot concentration.At the initial 24 h of the experiment,the inhibition rate to Chlorella vulgaris was the highest,then the inhibition rate was decreased.(7)The photosynthetic pigment content of Chlorella vulgaris was significantly decreased,and the changes of chlorophyll a were most obviously.Compared with the control group,the chlorophyll a content in treated groups decreased by 33.83%一 70.24%with the in crease concentration of MPA-CdTe.(8)MPA-CdTe resulted in the changes of H2O2 and MDA contents and CAT and SOD activities in the cells of Chlorella vulgaris.The increase of H2O2 content was not obvious,MDA content increased obvious,CAT activity increased gradually,and SOD activity increased first but then decreased.This indicates that MPA-CdTe quantum dots induce the production of reactive oxygen free radicals,which accumulate in Chlorella vulgaris cells and cause oxidative stress to them.The research of this paper will provide basic information and technical support for environment-friendly design,environmental pollution assessment and control of future quantum dots engineering nanoparticles.