Dị tụ vật liệu nano, hematit trong môi trường nước - Luận án Khanh An Huynh

HETEROAGGREGATION BETWEEN ENGINEERED NANOMATERIALS AND HEMATITE NANOPARTICLES IN AQUATIC ENVIRONMENTS by Khanh An Huynh A dissertation submitted to Johns Hopkins University in conformity with the requirements for the degree of Doctor of Philosophy Baltimore, MD February 2014 © 2014 Khanh An Huynh All Rights Reserved ABSTRACT The rapid growth in the utilization of engineered nanomaterials for industrial and research applications, as well as in consumer products, will inevitably result in the release of these nanomaterials into the environment. In natural and subsurface waters, engineered nanomaterials can undergo aggregation with each other (homoaggregation) or with other types of nanoparticles (heteroaggregation), such as naturally occurring colloids (NOCs). Since the concentration of engineered nanomaterials is likely to be much lower than that of NOCs in natural aquatic systems, heteroaggregation is expected to play a more important role than homoaggregation in determining the environmental fate and transport of engineered nanomaterials. While homoaggregation of engineered nanomaterials has been extensively investigated, the heteroaggregation behavior of these nanomaterials has rarely been studied and therefore is not well understood.

The objectives of this dissertation work are to investigate the heteroaggregation of engineered nanomaterials with hematite nanoparticles (HemNPs), a model NOC, and the effects of heteroaggregation on the antimicrobial activity of engineered nanomaterials. The engineered nanomaterials of focus in this dissertation work are carbon nanotubes (CNTs) and silver nanoparticles (AgNPs). In the first part of the dissertation, aggregation studies demonstrate that the heteroaggregation rate between CNTs and HemNPs depends on the concentration ratio between CNTs and HemNPs. The heteroaggregation rate increases with an initial increase in the CNT/HemNP concentration ratio, reaches the maximum value at an optimal concentration ratio, and then decreases with further increase in the concentration ratio.

In the presence of humic acid, the maximum heteroaggregation rate decreases when the humic acid concentration is increased. As the i CNT–HemNP heteroaggregates are exposed to solution chemistries that lead to electrostatic and electrosteric repulsion between these nanoparticles, the strength of the heteroaggregates is weakened and hence the heteroaggregates becomes more susceptible to disaggregation. The heteroaggregation behavior of two other carbon-based nanomaterials, namely, graphene oxide nanosheets and fullerene (C60) nanoparticles, with HemNPs is also investigated and compared with that of CNTs with HemNPs. In the second part of the dissertation, the homoaggregation behavior of citrate- coated AgNPs in NaCl solution is shown to be in excellent agreement with the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory.

Polyvinylpyrrolidone (PVP) is shown to be a more effective stabilizer than citrate in both monovalent (NaCl) and divalent (CaCl2 and MgCl2) electrolyte solutions. The adsorption of humic acid on citrate- and PVP-coated AgNPs increases the colloidal stability of these nanoparticles in NaCl solutions and also at low CaCl2 concentrations. Conversely, humic acid enhances the homoaggregation kinetics of both AgNPs at high CaCl2 concentrations. In addition, the heteroaggregation between citrate-coated AgNPs and HemNPs is shown for the first time to reduce the antimicrobial activity of AgNPs toward Escherichia coli bacteria Advisor: Kai Loon Chen Committee members: Edward J.

Howard Fairbrother ii ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Professor Kai Loon Chen, who has been the most important person that helped me to persevere and succeed in my Ph. I am so fortunate and grateful to have Kai Loon as my mentor. He has been always kind, patient, understanding, and supportive whenever I needed his help and advice. I believe that the skills and knowledge that I acquired with the help of Kai Loon are sufficient for me to build my own future successful career.

I would like to thank the members of my dissertation committee: Professors Edward Bouwer, Bill Ball, and Howard Fairbrother for spending their time reading this dissertation and providing me with valuable feedback throughout my Ph. In addition, I would like to acknowledge Professors Haiou Huang and Joelle Frechette for serving on my Graduate Board Oral Examination, as well as Professors Alan Stone and Markus Hilpert for being the members of my Department Qualifying Examination. They have not only challenged me to improve my knowledge, but also have given me valuable suggestions to increase the quality of my work. research could not be completed without the help from Dr.

Michael McCaffery from the Integrated Imaging Center at JHU. Michael has been always an extremely helpful and patient collaborator, who agreed to spend a lot of his time capturing beautiful cryogenic transmission electron micrographs for my research projects. I would like to thank previous members of Fairbrother’s group, Drs. Billy Smith and Kevin Wepasnick, for oxidizing and characterizing the carbon nanotubes used in my dissertation work.

I am extremely grateful to be a part of the Department of Geography and Environmental Engineering (DoGEE) with a very warm and friendly atmosphere that iii made me always feel at home. At DoGEE, I have received a world-class education and made life-long friendships. I had the opportunities to take classes and have stimulating discussions with many inspiring professors such as Professors Edward Bouwer, Alan Stone, Bill Ball, and Lynn Roberts. I would like to specially thank Ed, Alan, and Bill for countlessly helping me on job hunting and giving me inputs and opinions regarding my research and future career plans.

In addition, I would like to acknowledge tremendous help from Keith and other DoGEE staff members, such as Denise, Adena, Christine, Joyce, and Rob, during the time I spent at DoGEE. I would like to thank the past and current members of Chen’s research group, such as Peng, Li, Myunghee, Wenyu, Harry, Xitong, and Yeunook, for their help when we have been working together in the lab. I also would like to thank Jin, Pavlo, Amar, Andrew, Chip, Jessica, Katie, John, Nate, Phillip, Xiaomeng, and other students and postdocs in the wet groups at DoGEE for their support. I would like to thank the Vietnam Education Foundation (VEF) for funding me through the first two years of my Ph.

Because of their support, my dream of getting a Ph. degree from Hopkins has become a reality. Finally, I would like to thank my family members for their unconditional love, support, and encouragement. They have always been on my side whenever I had ups and downs during my Ph.

studies, and helped me to see the light at the end of the long tunnel. iv TABLE OF CONTENTS TABLE OF CONTENTS. v   LIST OF FIGURES. ix   LIST OF TABLES.

  Two Popular Engineered Nanomaterials: Carbon Nanotubes and Silver Nanoparticles.   Fate and Transport of Carbon Nanotubes and Silver Nanoparticles Aquatic Environments.   Toxicity of Carbon Nanotubes and Silver Nanoparticles.   Objectives and Scopes of Dissertation.

  HETEROAGGREGATION OF MULTIWALLED CARBON NANOTUBES AND HEMATITE NANOPARTICLES: RATES AND MECHANISMS.   Materials and Methods.   Preparation of Carbon-Based Nanomaterials and Hematite Nanoparticles.   Characterization of Carbon-Based Nanomaterials and HemNPs.

  Time-Resolved Dynamic Light Scattering.   Determination of Homoaggregation Kinetics.   Determination of Heteroaggregation Rates.   Cryogenic Transmission Electron Microscopy.

  Results and Discussion.   Physicochemical Properties of Carbon-Based Nanomaterials and HemNPs.   Electrokinetic Properties of Carbon-Based Nanomaterials and HemNPs.   Homoaggregation Kinetics of Carbon-Based Nanomaterials and HemNPs.

  CNTs and HemNPs Undergo Exclusive Heteroaggregation at Low NaCl Concentration.   Influence of CNT/HemNP Ratio on Rates of Heteroaggregation.   Cryogenic TEM Imaging of CNT–HemNP Heteroaggregates.   Proposed Heteroaggregation Mechanisms of CNTs and HemNPs.

  Influence of Humic Acid on Heteroaggregation Rates of CNTs and HemNPs. Heteroaggration Behavior of GO Nanosheets and C60 Nanoparticles with HemNPs.   DISAGGREGATION OF HETEROAGGREGATES COMPOSED OF MULTIWALLED CARBON NANOTUBES AND HEMATITE NANOPARTICLES.   Materials and Methods.

  Preparation and characterization of CNTs and HemNPs.   Time-Resolved Dynamic Light Scattering.   Determination of Power Delivered by Ultrasonication Bath.   Determination of Degree of Disaggregation.

  Results and Discussion.   Power of Ultrasonication Bath.   Disaggregation of CNT Homoaggregates at pH 5.   Disaggregation of CNT–HemNP Heteroaggregates at pH 5.

  Disaggregation of CNT–HemNP Heteroaggregates at Elevated pH.   Disaggregation of CNT–HemNP Heteroaggregates in the Presence of Humic Acid.   AGGREGATION KINETICS OF CITRATE AND POLYVINYLPYRROLIDONE COATED SILVER NANOPARTICLES IN MONOVALENT AND DIVALENT ELECTROLYTE SOLUTIONS.   Materials and Methods.

  Silver Nanoparticle Synthesis and Characterization.   Determination of Silver Nanoparticle and Dissolved Silver Concentrations.   Electrophoretic Mobility Measurements.   Time-Resolved Dynamic Light Scattering.

  Determination of Aggregation Kinetics.   Detection of AgNP Dissolution.   Results and Discussion.   Physicochemical Properties of Citrate- and PVP-Coated AgNPs.

  Electrokinetic Properties of Citrate- and PVP-Coated AgNPs.   Dissolution of Citrate- and PVP-Coated AgNPs at High Electrolyte Concentrations.   Aggregation Kinetics of Citrate-Coated AgNPs in Monovalent Electrolyte Solution.   Comparing Citrate-Coated AgNP Aggregation Kinetics with DLVO Theory.

  Aggregation Kinetics of Citrate-Coated AgNPs in Divalent Electrolyte Solutions.   Comparing Aggregation Kinetics of PVP-Coated AgNPs with Citrate-Coated AgNPs.   Influence of Humic Acid on Aggregation Kinetics of Citrate- and PVP-Coated AgNPs.   HETEROAGGREGATION REDUCES ANTIBACTERIAL ACTIVITY OF SILVER NANOPARTICLES: EVIDENCE FOR NANOPARTICLE–CELL PROXIMITY EFFECTS.

  Materials and Methods.   Preparation of Nanoparticles.   Electrophoretic Mobility Measurements.   Heteroaggregation of AgNPs and HemNPs.

  Preparation of Bacteria.   Evaluation of the Effects of Heteroaggregation on Antimicrobial Activity of AgNPs.   Determination of Dissolved Silver Concentrations at the Beginning and End of Incubation in the Absence of Bacteria.   Cryo-TEM Imaging of Heteroaggregates.

  Results and Discussion.   AgNPs Completely Inhibit Bacterial Growth at Sub-Lethal Concentration of Dissolved Silver in Bulk Solution.   Heteroaggregation with HemNPs Reduces Antibacterial Activity of AgNPs.   Heteroaggregation Inhibits Direct Contact or Close Proximity between AgNPs and Bacterial Cells.

  CONCLUSIONS AND KEY CONTRIBUTIONS. 152   viii LIST OF FIGURES Chapter 2 Figure 2. Scattered light intensities from HemNP suspension (0.44 mg/L), CNT suspension (28 µg/L TOC), and 0.1 mM NaCl solution at the same incident laser intensity. Intensities are presented in kilo counts per second (kcps).

Representative TEM images of (a) CNTs, (b) GO nanosheets, (c) C60 nanoparticles, and (d) HemNPs. High-resolution TEM images of (a) a CNT and (b) a HemNP. (a) Length distribution of CNTs with each bar representing a length range of 100 nm. (b) Size distribution of HemNPs with each bar representing a diameter range of 10 nm.

Representative homoaggregation profiles of (a) CNTs at a concentration of 83 µg/L TOC and (b) HemNPs at a concentration of 0.44 mg/L at different NaCl concentrations. Attachment efficiencies of CNTs and HemNPs as functions of NaCl concentration at pH 5. Cryo-TEM image of a CNT homoaggregate after 20 min of aggregation at 500 mM NaCl and pH 5. CNT concentration was 1.

(a) Attachment efficiencies of GO nanosheets at different NaCl concentrations. GO nanosheet concentration was 0. (b) The homoaggregation profiles of C60 nanoparticles at a concentration of 1.52 mg/L TOC in 500 mM NaCl. The pH in (a) and (b) was 5.

Homoaggregation profiles of CNTs and HemNPs, as well as heteroaggregation profile of CNTs and HemNPs at CNT/HemNP ratio of ix 0. All the experiments were conducted at 0.1 mM NaCl and pH 5. (a) Heteroaggregation profiles of CNTs and HemNPs at different CNT/HemNP ratios. (b) Heteroaggregation rate of CNTs and HemNPs as a function of CNT/HemNP ratio.

Error bars represent standard deviations of at least three replicates. The dashed line represents the homoaggregation rate of HemNPs in the diffusion-limited regime. Representative cryo-TEM images of heteroaggregates at (a) low CNT/HemNP ratio (0.003), (b) optimal CNT/HemNP ratio (0.032), and (c) high CNT/HemNP (0. 15 min of heteroaggregation.

(d) Proposed heteroaggregation mechanisms at different CNT/HemNP ratios. The rates in the absence of humic acid are reproduced from Figure 2. The dash line represents the homoaggregation rate of HemNPs in the diffusion- limited regime. (b) Electrophoretic mobilities (EPMs) of CNTs and HemNPs at 0.1 mM NaCl and pH 5.2 in the presence of humic acid.