Grantee Research Project Results
Final Report: Dendritic Nanoscale Chelating Agents: Synthesis, Characterization, Molecular Modeling and Environmental Applications
EPA Grant Number: R829626Title: Dendritic Nanoscale Chelating Agents: Synthesis, Characterization, Molecular Modeling and Environmental Applications
Investigators: Diallo, Mamadou S. , Goddard, William A. , Johnson, James H. , Balogh, Lajos
Institution: California Institute of Technology , University of Michigan , Howard University
Current Institution: California Institute of Technology , Howard University , University of Michigan
EPA Project Officer: Hahn, Intaek
Project Period: May 1, 2002 through April 30, 2005
Project Amount: $400,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Nanotechnology , Safer Chemicals
Objective:
Metal ion complexation is an acid-base reaction that depends on several parameters—including metal ion size, acidity, ligand basicity, and molecular architecture—and solution physical-chemical conditions. Three milestones in coordination chemistry were the discoveries of the Hard and Soft Acids and Bases (HSAB) principle, the chelate effect, and the macrocyclic effect. The invention of dendrimers is another milestone in coordination chemistry. Dendrimers are highly branched nanostructures with controlled composition and architecture. Poly(amido)amine (PAMAM) dendrimers possess functional nitrogen and amide groups arranged in regular “branched upon branched” patterns. This high density of nitrogen ligands enclosed within a nanoscale container makes PAMAM dendrimers particularly attractive as high capacity chelating agents for metal ions. The objectives of this research project were to explore the fundamental science of metal ion uptake by PAMAM dendrimers in aqueous solutions and assess the extent to which this fundamental knowledge could be used to develop high capacity and reusable chelating agents for industrial and environmental separations and to develop FeS-laden nanoparticles with enhanced reactivity, selectivity, and longevity for reductive and detoxification of tetrachloroethylene (PCE) in aqueous solutions.
Summary/Accomplishments (Outputs/Outcomes):
The research activities were structured around the following tasks:
- Dendrimer Synthesis and Characterization
- Measurements of Proton and Metal Ion Binding to PAMAM Dendrimers in Aqueous Solutions
- Thermodynamic Modeling of Metal Ion Binding to PAMAM Dendrimers in Aqueous Solutions
- Environmental Application 1: Recovery of Metal Ions from Aqueous Solutions by Dendrimer Enhanced Filtration
- Environmental Application 2: Synthesis and Characterization of Dendrimer Encapsulated FeS Nanoparticles.
A summary of the research activities and findings for each task is given below.
Task 1: Dendrimer Synthesis and Characterization (University of Michigan)
PAMAM dendrimers with ethylene diamine (EDA) cores were evaluated in this study. G3-NH2, G4-NH2, and G5-NH2 PAMAM dendrimers with EDA cores were purchased from Dendritech (Midland, MI) and used as received. G4 EDA-core PAMAM dendrimers with succinamic acid (NHCOCH2CH2COOH) terminal groups (G4-Sac), glycidyol (NHCH2CH(OH)CH2OH) terminal groups (G4-Gly), and acetamide (NHCOCH3) terminal groups (G4-Ac) were synthesized. All the dendrimers evaluated in this study were characterized by 1H/13C nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, polyacrylamide gel electrophoresis, capillary electrophoresis, size exclusion chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. We found that all the dendrimers evaluated in this study have chemical purity greater than 95 percent and exhibit molar mass within 94-100 percent of the theoretically estimated molecular weight of the corresponding pure and monodisperse dendrimers.
Task 2: Measurements of Proton and Metal Ion Binding to PAMAM Dendrimers in Aqueous Solutions (Howard University and Caltech)
In the first phase of this project, we used Cu(II) as model cations to probe the binding of metal ions with affinity toward the amine groups of PAMAM dendrimers. We used bench-scale measurements of proton and metal ion binding to assess the effects of: (1) metal-ion dendrimer loading; (2) dendrimer generation/terminal group chemistry; and (3) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA-core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ Extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH2 EDA-core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA-core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. The extents of protonation of these groups, however, control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH2 EDA-core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to two to four dendrimer tertiary amine groups located in the equatorial plane and two axial water molecules. We also carried out measurements of the binding of Co(II), Ni(II), Ag(I), and Fe(III) to EDA-core PAMAM dendrimers in aqueous solutions. The overall results of these studies show that PAMAM dendrimers can be used as high capacity and reusable chelating agents for industrial and environmental separations.
Task 3: Thermodynamic Modeling of Metal Ion Binding to PAMAM Dendrimers in Aqueous Solutions (Caltech and Howard University)
Conventional thermodynamic models of complexation typically have described metal ion chelation in aqueous solutions as a set of successive reactions between a central metal ion M, a ligand L, and the proton (H+) or hydroxide ion (OH-). The stability constants of a given metal ion can be determined by fitting experimental data to the corresponding chemical equilibrium and mass balance equations. Although this approach has worked well for a traditional chelating agent with a limited number of Lewis base donors (e.g., a polydendate ligand or a macrocycle), it is not feasible for nanoscale ligands with a large number of metal ion binding sites such as proteins and dendrimers. As a first step toward the development of a multiscale model of metal ion binding to dendrimers in aqueous solutions, we formulated and tested a two-site thermodynamic model of Cu(II) binding to Gx-NH2 PAMAM dendrimers in aqueous solutions. This model expresses the extent of binding (EOB) of Cu(II) in aqueous solutions (at neutral pH) of Gx-NH2 PAMAM dendrimers as function of metal ion-dendrimer loading, number of dendrimer tertiary amine group, number of water molecules bound to the dendrimers, metal ion amine group/bound water coordination numbers, and the intrinsic association constants of Cu(II) to the dendrimer tertiary amine groups and bound water molecules. At low metal ion-dendrimer loadings, the model provides a good fit of the measured EOB of Cu(II) in aqueous solutions of PAMAM dendrimers with terminal NH2 groups.
Task 4: Environmental Application 1—Recovery of Metal Ions from Aqueous Solutions by Dendrimer Enhanced Filtration (Howard University and Caltech)
The Principal Investigator (PI) of this project (Mamadou Diallo) leveraged U.S. Environmental Protection Agency (EPA) funding with funding the National Science Foundation, the Department of Energy, and the National Water Research Institute (http://www.nwri-usa.org Exit ) to develop and evaluate a dendrimer-enhanced filtration (DEF) process for recovering metal ions from aqueous solutions. DEF is a patented process that exploits the unique properties of dendritic polymers (e.g., dendrimers, dendrigraft polymers, and hyperbranched polymers) as high capacity and recyclable chelating agents. It is structured around two unit operations: a clean water recovery unit and a dendrimer recovery unit. In the clean water recovery unit, contaminated water is mixed with a solution of functionalized dendritic polymers (e.g., dendrimers, dendrigraft polymers, hyperbranched polymers, core-shell tecto(dendrimers), etc.) to carry out the specific reactions of interest (metal ion chelation in this case). Following completion of the reaction, the resulting solution is filtered to recover the clean water. The contaminant-laden dendrimer solutions subsequently are sent to a second filtration unit to recover and recycle the functionalized dendritic polymers. The key novel feature of the proposed DEF process is the combination of dendritic polymers with multiple chemical functionalities with the well-established technology of ultrafiltration and microfiltration. This allows the development of a new generation of water treatment processes that are flexible, reconfigurable and scalable. Additional experiments are underway to commercialize DEF as a cost effective and environmentally acceptable process for recovering metal ions from industrial wastewater solutions.
Task 5: Environmental Application 2—Reductive Dehalogenation of Tetrachloroethylene by FeS Dendrimer Encapsulated Nanoparticles (University of Michigan and Howard University)
Co-PI Lajos Balogh and his group at the University of Michigan carried out the synthesis and characterization of iron sulfide (FeS) dendrimer nanocomposites in solutions, thin films, and mesoporous silica gels. The FeS nanoparticles were prepared by reactive encapsulation of Fe(II)-dendrimer complexes using G4 PAMAM dendrimers with amine, hydroxyl, and succinamic acid terminal groups as templates and sodium sulfide as reducing agent. The ability of the FeS dendrimer nanocomposites (25 ppm of FeS) to reduce tetrachloroethylene (5 ppm) in aqueous solutions was evaluated by PI Mamadou Diallo and his group at Howard University using gas chromatography (GC) with electron capture detector (ECD) and flame ionization detector (FID). We found significant reduction of PCE (40-50% after 3 hours) with no production of tricholoroethylene in all cases of reaction byproducts such as tricholoroethylene and vinyl chloride.
Conclusions:
PAMAM dendrimers (the focus of this research) possess functional nitrogen and amide groups arranged in regular “branched upon branched” patterns that are displayed in geometrically progressive numbers as a function of generation level. This high density of nitrogen ligands along with the possibility of functionalizing PAMAM dendrimers with various terminal groups such as primary amines, carboxylates, hydroxymates, etc. make them particularly attractive as chelating agents for metal ions. The objectives of this EPA Nanotechnology Science To Achieve Results (STAR) grant were to: (1) characterize the fundamental science of metal ion uptake by PAMAM dendrimers in aqueous solutions; and (2) assess the extent to which this fundamental knowledge could be used to develop novel nanostructured materials and processes for treating water contaminated by metal ions and organic solutes.
The overall results of this research suggest that PAMAM dendrimers can be used as high capacity and recyclable chelating agents. A major accomplishment of this project was the invention of the novel process of “Water Treatment by Dendrimer Enhanced Filtration” (Diallo, U.S. Patent Pending). This process can be used to remove and recover metal ions from aqueous solutions. We also exploited the unique properties of EDA-core PAMAM dendrimers as nanoscale containers for transition metal ions such as Fe(II) to synthesize dendrimer-encapsulated FeS nanoparticles. The ability of the FeS dendrimer nanocomposites (25 ppm of FeS) to reduce PCE (5 ppm) in aqueous solutions was evaluated by GC with ECD and FID. We found significant reduction of PCE (40-50% after 3 hours) with no production of tricholoroethylene in all cases.
Journal Articles on this Report : 7 Displayed | Download in RIS Format
Other project views: | All 41 publications | 10 publications in selected types | All 7 journal articles |
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Type | Citation | ||
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Diallo MS, Christie S, Swaminathan P, Johnson Jr. JH, Goddard III WA. Dendrimer enhanced ultrafiltration. 1. Recovery of Cu(II) from aqueous solutions using PAMAM dendrimers with ethylene diamine core and terminal NH2 groups. Environmental Science & Technology 2005;39(5):1366-1377. |
R829626 (2002) R829626 (2003) R829626 (Final) |
not available |
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Diallo MS, Christie S, Swaminathan P, Balogh L, Shi X, Um W, Papelis C, Goddard III WA, Johnson Jr. JH. Dendritic chelating agents. 1. Cu(II) binding to ethylene diamine core poly(amidoamine) dendrimers in aqueous solutions. Langmuir 2004;20(7):2640-2651. |
R829626 (2002) R829626 (2003) R829626 (Final) |
Exit |
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Diallo MS, Savage N. Nanoparticles and water quality. Journal of Nanoparticle Research 2005;7(4-5):325-330. |
R829626 (Final) |
not available |
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Savage N, Diallo MS. Nanomaterials and water purification: opportunities and challenges. Journal of Nanoparticle Research 2005;7(4-5):331-342. |
R829626 (Final) |
not available |
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Shi XY, Patri AK, Lesniak W, Islam MT, Zhang CX, Baker JR, Balogh LP. Analysis of poly(amidoamine)-succinamic acid dendrimers by slab-gel electrophoresis and capillary zone electrophoresis. Electrophoresis 2005;26(15):2960-2967 |
R829626 (Final) |
not available |
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Shi XY, Banyai I, Lesniak WG, Islam MT, Orszagh I, Balogh P, Baker JR, Balogh LP. Capillary electrophoresis of polycationic poly(amidoamine) dendrimers. Electrophoresis 2005;26(15):2949-2959 |
R829626 (Final) |
not available |
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Shi XY, Lesniak W, Islam MT, Muniz MC, Balogh LP, Baker JR. Comprehensive characterization of surface-functionalized poly (amidoamine) dendrimers with acetamide, hydroxyl, and carboxyl groups. Colloids and Surfaces A-Physicochemical and Engineering Aspects 2006;272(1-2):139-150 |
R829626 (Final) |
not available |
Supplemental Keywords:
polymer chemistry, materials chemistry, physical/theoretic chemistry, computational chemistry, molecular modeling, environmental chemistry, environmental engineering, chemical engineering, process engineering, environmental detoxification, groundwater remediation, pollution prevention, hazardous organics, industrial wastewater, membrane technology, polymer enhanced ultrafiltration, metal removal, nanocatalysts,, RFA, Scientific Discipline, Water, Sustainable Industry/Business, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Civil/Environmental Engineering, Biochemistry, New/Innovative technologies, Chemistry and Materials Science, Ecological Risk Assessment, Engineering, Chemistry, & Physics, Environmental Engineering, nanoscale chelating agents, detoxification, industrial wastewater, dendrimers, nanotechnology, environmental sustainability, membrane filtration, membranes, membrane-based, ultrafiltration system, environmentally applicable nanoparticles, sustainability, innovative technology, PCE, innovative technologies, reductive detoxification, membrane technologyProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.