| The study of the interaction between dissolved organic matter(DOM)and carbon nanotubes(CNTs)is crucial to clarify the occurrence and fate of the two in the aquatic environment.Therefore,many studies had focused on solving a series of related problems such as the effects of DOM on the toxicity and environmental behavior of CNTs,the adsorption behavior of DOM on CNTs and the effects of CNTs on the properties and environmental behavior of DOM.Currently,the studies of the interaction between CNTs and DOM mainly focused on allochthonous DOM,while the studies of the interaction between CNTs and autochthonous DOM are still relatively few to be reported.Given the toxic effect of CNTs on algal cells,the properties of DOM releasing by algae is inevitably affected by CNTs.The properties of algogenic DOM(ADOM)vary fast and its conversion period is short.The original occurrence state of ADOM is destroyed due to the complex pretreatment process when the properties of ADOM were characterized by chromatography and mass spectrometry.Thus,it is difficult to clarify the process and mechanism of CNTs affecting the properties of ADOM.Studies have shown that the surface oxidation defects of functionalized CNTs could form hydrogen bonds with the surface of algal cells,which could overcome the steric hindrance and electrostatic repulsion between CNTs and the surface of algal cells,thus triggering a strong cell response of algae cells.However,the process and mechanism of functionalized CNTs affecting the properties of ADOM was still unclear.In addition,as the most important component that affected the environmental behavior of polycyclic aromatic hydrocarbons(PAHs),the changes in the DOM properties could result in several orders of magnitude changes in its binding ability with PAHs.Current studies showed that the binding between ADOM and PAHs significantly affected by light,dissolved oxygen and microbial transformation,but there are few studies on the effects of CNTs on the binding between ADOM and PAHs by affecting the release process and properties of ADOM.In order to solve the above issues,unmodified CNTs,functionalized CNTs and Prorocentrum donghaiense(P.donghaiense)were selected in this thesis,and fluorescence excitation-emission matrices with parallel factor analysis(EEM-PARAFAC)and Ultraviolet-visible(UV-vis)absorption were used to carry out related studies,the main studies results were summarized as followings:(1)The process of 0.1-10.0 mg L-1 unmodified CNTs affecting the properties of DOM released by P.donghaiense(P.donghaiense-DOM)were in situ studied by the use of EEM-PARAFAC and UV-vis absorption.The results showed that the changes in the properties of P.donghaiense-DOM were highly dependent on the concentration of unmodified CNTs.The properties of P.donghaiense-DOM in the 0.1 mg L-1 unmodified CNTs treatment showed no obvious differences compared to the control.The intracellular ROS levels of P.donghaiense were significantly enhanced under stress of 0.5-1.0 mg L-1 unmodified CNTs on day 4,which induced the overproduction of extracellular DOM(EDOM).From the reasons presented above,the amounts of protein-like and humic-like componnets of P.donghaiense-DOM in the 0.5-1.0 mg L-1 unmodified CNTs treatments increased by 10.0-14.1%and 14.9-20.2%compared to the control respectively,which significantly increased the aromaticity and molecular weight of P.donghaiense-DOM.Compared to the control,the protein-like componnets of P.donghaiense-DOM increased by 29.9-35.7%in the high levels(5.0-10.0 mg L-1)unmodified CNTs treatment,while the humic-like componnets decreased by 141.8-171.7%.The membrane damage of P.donghaiense in the high levels unmodified CNTs treatment increased by 141.8-171.7%,indicating that the leakage of intracellular DOM(IDOM)induced by high levels unmodified CNTs was main factors affecting the properties of P.donghaiense-DOM.In addition,the high levels unmodified CNTs indcued the growth inhibition of P.donghaiense lasted longer than 0.5-1.0 mg L-1 unmodified CNTs,which resulted in the aromaticity and molecular weight of P.donghaiense-DOM were significantly lower than that of control.In the 0.5-10.0 mg L-1 unmodified CNTs treatments,P.donghaiense got the decline phase on day 18,and the changes in the properties of P.donghaiense-DOM were mainly due to the decreased in the cell densities of P.donghaiense induced by 0.5-10.0 mg L-1 unmodified CNTs.(2)The the effects of 0.1-10.0 mg L-1 functionalized CNTs on the properties and release process of P.donghaiense-DOM were in situ studied during the exponential phase by the use of EEM-PARAFAC and UV-vis absorption.The results showed that the effects of 0.1-10.0 mg L-1 functionalized CNTs on the protein-like componnets of P.donghaiense-DOM(14.0-91.3%)were significantly higher than that of unmodified CNTs(4.1-56.6%),and it was positively correlated with(O+N)/C values of functionalized CNTs.Linear regression analysis showed that the adsorption of P.donghaiense-DOM on functionalized CNTs was the main influencing factor leading to the decrease of protein-like and humic-like components of P.donghaiense-DOM in the early stage of exponential phase(12 h).During the late stage of P.donghaiense exponential phase(96 h),low levels(0.1-0.5 mg L-1)functionalized CNTs induced strong lipid peroxidation reaction for P.donghaiense,resulting in the humic-like components of P.donghaiense-DOM under stress of low levels functionalized CNTs increased by 29.9-35.7%compared to the control,and thus,significantly increased the aromaticity of P.donghaiense-DOM.Besides,the laser scanning confocal microscopy(LSCM)images of P.donghaiense showed that 1.0 mg L-1 hydroxylated CNTs firstly induced significant membrane damage of P.donghaiense with the increase of functionalized CNTs concentrations,which resulted in the protein-like componnets of P.donghaiense-DOM increased by 26.6%compared to the control,and thus,significantly increased the molecular weight of P.donghaiense-DOM.The study revealed that the surface functional groups of CNTs played an important role in the process of CNTs affecting the properties of ADOM.(3)The process of unmodified and functionalized CNTs affecting the properties of P.donghaiense-DOM were in situ studied by the use of UV-vis absorption and EEM-PARAFAC,and the fluorescence quenching method was used to study the changes in the binding between P.donghaiense-DOM and pyrene after P.donghaiense-DOM affected by unmodified and functionalized CNTs.The results showed that the effects of unmodified and functionalized CNTs on the binding between P.donghaiense-DOM and pyrene was dynamically changing,and 0.5-10.0 mg L-1 unmodified CNTs and 0.1-10.0 mg L-1 functionalized CNTs altered the binding between P.donghaiense-DOM and pyrene mainly by affecting the aromaticity of P.donghaiense-DOM.During the exponential phase of P.donghaiense,functionalized CNTs induced more humic-like components released by P.donghaiense compared to unmodified CNTs,resulting in the KDOC values in functionalized CNTs treatments were significantly higher than that of unmodified CNTs treatments.During the stationary and decline phase of P.donghaiense,the inhibitory effect of functionalized CNTs on P.donghaiense growth were greater than unmodified CNTs resulted in the humic-like components of P.donghaiense-DOM increased slowly.Thus,the binding between P.donghaiense-DOM and pyren were reduced in functionalized CNTs treatments.(4)In order to further improve the understanding of the process and mechanism of CNTs affecting the properties of ADOM,and to solve the study on properties and process of CNTs affecting ADOM on micro-zone and micro-interface cannot achieve using the existing analysis methods,the UV confocal microscopic fluorescence spectral system was built relied on national major projects of scientific research instruments development.Aiming at the shortcomings of the current fluorescence spectroscopy and microscopy techniques in characterizing the ADOM properties,the measurement,redesign and processing of the lens group of the scanning module in the incident light path of the confocal microscope,the design and processing of the confocal incident and output light adapter,the combination of fluorescence spectrometer and confocal microscope were conducted.Finally,the construction of UV confocal microscopic fluorescence spectral system was completed.The successful construction of the system provided new research method to clarify the relationship between the behavioral process of CNTs on the micro-zones and micro-interface of algal cell membranes and the changes in the ADOM properties. |
PDF Full Text Request