2003 Progress Report: Advanced Nanosensors for Continuous Monitoring of Heavy MetalsEPA Grant Number: R830906
Title: Advanced Nanosensors for Continuous Monitoring of Heavy Metals
Investigators: Sadik, Omowunmi , Andreescu, Daniel , Deo, Rhandir , Karasinki, Jason , Kowino, Isaac , Mulchandani, Ashok , Wanekaya, Adam , Wang, Joseph
Current Investigators: Sadik, Omowunmi , Mulchandani, Ashok , Wang, Joseph
Institution: The State University of New York at Binghamton , New Mexico State University - Main Campus , University of California - Riverside
EPA Project Officer: Hahn, Intaek
Project Period: May 19, 2003 through April 18, 2006
Project Period Covered by this Report: May 19, 2003 through April 18, 2004
Project Amount: $351,000
RFA: Environmental Futures Research in Nanoscale Science Engineering and Technology (2002) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
The overall objective of this research project is to incorporate novel, colloidal-metal nanoparticles into a bed of electrically conducting polymers and then use this device for the development of nanosensors.
The field of nanomaterials and nanotechnology encompasses research areas that involve the development and application of materials and devices having structures and sizes in the range of 1 to a few nanometers. Tailoring nanomaterials to meet specific environmental or industrial needs is an emerging area of research. A goal of this collaborative research is to meet the needs for innovative, advanced nanomaterials and sensors for continuous detection of priority inorganic pollutants. The specific objectives of this research project are to: (1) prepare, characterize, and optimize the direct incorporation of colloidal metal nanoparticles into conducting polymers using photochemical polymerization; (2) design and test novel nanosensors for the identification, detection, speciation, and quantitation of heavy metals using the nanoparticle-modified conducting polymers; and (3) fabricate disposable nanosensors using the New Mexico State University (NMSU) nanofabrication facility and utilize the sensors for the analysis of metal ions from aqueous effluents.
During the first segment of the project activities, we explored the feasibility of designing advanced conducting polymeric materials for sensing and remediation applications. Specifically, we examined the synthesis of: (1) polyamic acid-silver nanoparticle composite membranes; (2) polyoxy-dianiline films; and (3) electrochemical deposition of gold (Au) nanoparticle films onto functionalized conducting polymer substrates. We developed a one-step, rapid, and simple synthesis of stable Au nanoparticles using polyamic acids both as the reducing and stabilizing agents. These materials were characterized using electrochemical and morphological techniques, including Fourier-transform infrared (FTIR) spectroscopy, cyclic voltammetry, galvanostatic methods, energy-dispersive spectroscopy, and transmission electron microscopy. The polymer conjugates also were studied using structural and chromatographic analysis. The conditions of the synthesis were optimized to generate different shapes and sizes of the nanoparticles while the ability to detect different metals is being explored. Thus far, we have submitted three manuscripts that summarize our efforts to Langmuir (Andreesca, et al., in review, 2004), Advanced Materials (Andreescu, et al., submitted, 2004), and Macromolecules (Andreescu and Sadik, submitted, 2004). Also, these findings have been presented at three national and regional conferences. Our next goal is to explore the use of these polymers for the analysis of different metals and to optimize the product yield. The application of our new, one-step synthetic method to other metals will be explored. These include palladium, cobalt, iron, and titanium. These materials have wide applications in catalysis, ion exchange, sensors, and remediation.
- Three different materials that incorporate nanoparticles of varying sizes have been successfully synthesized and characterized as precursors for environmental sensing and remediation.
- We have discovered a fast and simple synthesis method for stable Au nanoparticles using polyamic acid as a reducing and stabilizing agent.
- A new synthetic approach for nanostructured membranes has been achieved for polyamic acid at a relatively low temperature, and the molecular weight of the solid polyamic material was confirmed using gel permeation chromatography.
- New poly (4,4'-oxydianiline) (poly-ODA) films have been electrochemically deposited onto Au electrodes using cyclic voltammetry.
- A preliminary test for lead, chromium, and uranium detection using carbon substrates has been conducted.
- Carbon nanotube-based transducers have been used for monitoring environmental pollutants.
Fast and Simple Synthesis of Stable Au Nanoparticles Using Polyamic Acid as a Reducing and Stabilizing Agent . Many of the current synthetic approaches for nanoparticles require that the particles be stable and evenly distributed, with precise control of size, geometry, and morphology. The stable dispersion of nanoparticles in water is important to many applications, including environmental sensing and remediation, catalysis, and photonics. Water-based synthesis of nanoparticles, however, is fraught with inherent problems such as ionic interaction, low reactant concentration, and difficulty in removing the residue of stabilizers after synthesis. Particles that are synthesized in organic solvents can be made at relatively high concentration with predefined size and shape and with improved monodispersibility when compared with those that are prepared in aqueous media. Most reports on the synthesis of Au nanoparticles in nonpolar organic solvents have followed the Brust protocol, wherein aqueous chloroaurate ions are transferred into the organic solvent using phase-transfer molecules (tetraalkylammonium salts).
In this project, we have explored different polymers and ligand combinations for the design of novel nanostructured materials. We have discovered a rapid, one-step synthesis of Au nanoparticles via the reduction of AuCl3 by polyamic acid in organic medium in less than 1 hour. The polyamic acid acts as a reducing agent for the metal salt and a stabilizing agent for the resulting Au nanoparticles. The procedure resulted in Au nanoparticles capped with the π-conjugated polyamic acid. Depending on the reactant concentrations and ratios, the polyamic acid-metal hybrid was synthesized either as well-dispersed or aggregated particles. The size of the particles, which can be controlled by varying the polyamic acid: AuCl3 ratios, ranged from 4.0 ± 0.7 nm to 7.8 ± 1.0 nm.
Characterization of Polyamic Acid-Silver Nanoparticle Composite Membranes on Vitreous Carbon Substrates. We have explored an alternative synthetic design using the incorporation of metal nanoparticles with polyamic membranes on vitreous carbon electrodes. We prepared many composites of polyamic acid with metallic silver particles by electrochemical deposition onto carbon vitreous electrodes using organic and aqueous solvents. These composites were achieved using polyamic acid derived from pyromellitic dianhydride and ODA solutions containing soluble silver salts. The polyamic acid-nanocomposite silver films were subsequently dried at 105ºC. Thermal curing of silver (I) polyamic acid at this relatively low temperature was sufficient to eliminate all residual solvents after 2 hours with concomitant reduction of silver (I) into metallic silver. FTIR, scanning electron microscopy (SEM), and nuclear magnetic resonance analysis were used to characterize the metallic composite films. The molecular weight of the solid polyamic acid was estimated to be 10,000 daltons using gel permeation chromatography. Using elemental analysis, we confirmed the presence of metallic silver in the size range of hundreds of nanometers.
Electrochemical and Morphological Characterization of Au-Modified Poly-ODA Film. Another aspect of our material design was focused on the electrochemical synthesis of poly-ODA. We electrochemically deposited new poly-ODA films onto Au electrodes using cyclic voltammetry . These conducting films have morphological properties that are strongly dependent on a number of parameters, including the nature of solvent, supporting electrolytes, and the scanning rates. The progress and mechanism of polymerization, as well as the surface morphology and structural characteristics of these films, were studied using techniques such as cyclic voltammetry, SEM, and FTIR. A possible electropolymerization mechanism involves the diradical-dication coupling of the ODA monomers. Also, we conducted a study of the influence of solvophobic interaction between anions and the hydrocarbon radical cation using a range of solvents having different electron acceptor/donor properties. The SEM results indicated that in acetonitrile, the poly-ODA formed an open, dull, porous structure. In tetrahydrofuran (THF), however, the same film resulted in a compact, shiny sheet deposit. The conductivity of the poly-ODA film using THF was 3.7 x 10-5 S cm-1.
Preliminary Environmental Application of Conducting Polymer Nanocomposite. The electrochemical deposition of metal nanocrystals onto carbon electrodes has generated a significant research interest because of possible applications in electrocatalysis and as model systems for electroplating. The focus of many of these studies is at the early stages of electrochemical deposition to elucidate the nucleation and growth mechanism of the metal phase on the substrate. There are several articles in the literature dealing with the modification of Au electrodes and colloids by spontaneous chemisorption of alkanethiols (X(CH2)nSH).
Because of their wide range of applications in electroanalysis, electrocatalysis, and electrosynthesis, carbon electrode materials have become the focus of several modification schemes. These include the derivatization of existing surface functional groups, irreversible physical adsorption of suitable organic molecules, and coating with a thin polymer film. Our approach consists of the following:
- Electrochemical deposition of Au nanoparticles and/or conducting polymers on glassy carbon electrodes and reticulated vitreous carbon (RVC).
- Self-assembled formation of thiolate monolayers containing NH2 (amino) groups on these particles.
- Reaction of carboxylic acid groups of the ethylenediaminetetraacetic acid with the amino groups of the thiolate monolayers.
- Accumulation/preconcentration of heavy metals by the above-modified electrode (remediation application).
- Stripping of the accumulated heavy metals, including replacement of toxic mercury sensors with “green” bismuth devices (sensor application).
- Adsorptive accumulation of pollutants onto large-area nanotubes.
Eventually, we plan to use this procedure on RVC with a very large surface area to volume ratio. This will not only enable the remediation of very large quantities of heavy metals, but also the analysis of the same in ultra trace quantities. We shall explore both the electrochemical and photochemical approaches.
Research activities are continuing. We will test the different polymers mentioned above for their sensitivity to metal sensing. The best polymer will be selected for optimized metal analysis and packing materials for metal remediation. The polymers will be used as packing for the design of a nanoreactor using a flow cell to be designed in Dr. Wang’s laboratory at NMSU.
We will conduct a simultaneous characterization and optimization of the polymers for metal detection and speciation at the State University of New York and NMSU. The polymers also would be used for the fabrication of disposable nanosensors and analysis of metal ions, and Dr. Mulchandani will collaborate for possible testing of the advanced nanomaterials for metal removal applications.
The NMSU (ASU) fabrication facility has personnel that are experienced in designing relevant microfluidic devices and nanovials for ultra-small volume analysis. The fabrication process will be optimized systematically. We will use the polymers synthesized for fabrication and compare different inks, printing conditions (pressure, curing temperature, or time), and substrates (plastic, ceramics). We also will dope different metals into the polymers at different loading and examine its affect on the metal uptake and response. Finally, we will determine the analytical performance of the nanosensor for continuous and in situ sensing. These will be compared to existing technology.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 39 publications||14 publications in selected types||All 10 journal articles|
||Andreescu D, Wanekaya A, Sadik OA, Wang J. Nanostructured polyamic acid membranes as novel electrode materials. Langmuir 2005;21(15):6891-6899.||