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Final Report: Biotemplating of Titanium Dioxide Nanoparticles for the Green Production of Photochemically Active Catalysts: Synthesis, Characterization, and Photocatalytic Evaluation
EPA Grant Number: SU831824Title: Biotemplating of Titanium Dioxide Nanoparticles for the Green Production of Photochemically Active Catalysts: Synthesis, Characterization, and Photocatalytic Evaluation
Investigators: Dionysiou, Dionysios D. , Brectz, Dan , Long, Jennifer , Myre, Beth , Yates, Brian
Institution: University of Cincinnati , Miami University - Oxford
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: September 30, 2004 through May 30, 2005
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity, and the Planet (2004)
Research Category: Pollution Prevention/Sustainable Development
Description:
Objective:The purpose of this project was to investigate the potential for biotemplating metal nanostructured materials (NSM) in-vivo using two plants: Alfalfa (ALF) (Medico sativa) and Morning Glory (MG) (Ipomoea lacunose L.). Through the work done on this project, our group attempted to answer four questions: Firstly, do ALF and MG have the capability of uptaking and concentrating certain metals without severe toxicological effects which may inhibit growth; Secondly, is it possible that certain metals can be precipitated in-vivo to produce metal NSM and what are the properties of these particles (i.e. size, size distribution, crystal habit and degree of crystallinity). The final two questions deal with the practical production of these materials on a larger scale, namely, how fast are the metals accumulated/precipitated and in what amounts?
The overall goal of this project was to evaluate the possibility for the recycle of metal waste streams using phytomining techniques to produce NSM metal particles which may have applications to environmental sensing and/or remediation.
Summary/Accomplishments (Outputs/Outcomes):It was found that ALF has the capability of uptaking and concentrating metal ions of cobalt (0.52% of plant dry weight), chromium (0.72% of plant dry weight), and silver (1.1% of plant dry weight) after contact for 14 days with a 40 mg L solution of each metal ion. Thus the absorption kinetics of ALF for these metals is relatively quick and therefore gives promise for phytoremediation of contaminated soils, and7or recycling of metals from waste streams. MG is capable of uptaking and concentrating metal ions of chromium (0.11% of plant dry weight), cobalt (0.14% of plant dry weight) and zinc (0.25% of plant dry weight). Titanium quantification analysis for both plants is still in progress. These values are significantly less than the corresponding values for ALF, suggesting that phytorernediation using MG may not be practical. It was found that silver tended to stunt the growth of MG and result in lower dry weight yields compared to the other metal treatments and control. ALF was not resistant to chromium (in the form of Cr6+) even in small amounts (40 mg/L) and exposure resulted in death.
Both plants did show promise for their ability to biotemplate nano-sized particles of certain metals, however. For ALF and MG, nanoparticles of gold and silver were recovered from the biomass, and for MG only, nanoparticles of elemental titanium were recoverable. The titanium particles could be immobilized on a stainless steel support, although the amount of coverage of the support was small (<1%). There is promise that in some applications (for example nano-computing) this method of nanoparticle formation may be useful, and with further optimization may result in more developed, useful films. More work must be done to determine the feasibility to produce materials for environmental applications by this method (such as films of photocatalytically active titanium dioxide or nano-electrodes of gold and/or silver).
The uptake kinetics was also studied to determine how fast the metals are incorporated into the plant material. For MG, the time required for the concentration of silver within the biomass to remain constant is relatively fast (within 10 days) while the kinetics for gold is much slower (constant concentration not reached after 32 days). This suggests that a regular harvest of MG for the production of silver nanoparticles maybe feasible on a reasonable time scale.
A profile displaying the final dry biomass and final metal concentration (after 7 days) for MG when exposed to differing concentrations (20 ppm — 320 ppm) of silver and gold solution was also obtained. The final dry biomass values reduced slightly for both metals up to 80 ppm and then remained constant to 320 ppm. The concentration of gold within the biomass remained relatively constant for all treatments (0.0-0.5 mg gold per g dry biomass) while that of silver rose steadily up to 160 ppm (0.06-0.38 mg silver per g dry biomass) and then increased significantly at 320 ppm (4.60 mg silver per g dry biomass).
Conclusions:The production of silver, gold and titanium nanoparticles is possible by using phytomining techniques with MG while ALF has the capability of biotemplating nanoparticles of silver and gold. The kinetics for silver uptake are much faster than those of gold and for silver, a reasonable timeframe of a few days to reach saturation is observed, indicating that the optimum harvest time for nanoparticles will be dictated by the amount of particles desired and the total dry biomass of the plant at the time of harvest. For gold, saturation was not observed and the optimum time for nanoparticle harvest will be controlled by the amount of particles desired and the time for uptake by the plant.
Exposure concentration of gold seemed to have little effect on the uptake of gold by MG. This indicates that the uptake of gold by MG is kinetically controlled, possibly by internal metabolic process and translocation process. On the contrary, MG showed a near linear increase in silver concentration in the dry biomass up to 160 ppm exposure and then a large increase at 320 ppm exposure. This indicates that the uptake of silver by MG is thermodynamically controlled, possibly by the number of binding sites available in the roots of MG.
Although biotemplated nanoparticles of gold. silver and titanium were recoverable, more work needs to be done on methods for preparing environmental nano-materials, such as photocatalvtic films, or sensors. From this work, we can conclude that although fixing elemental titanium nanoparticles to a stainless steel support and subsequent calcination to the oxide is possible, the usefulness of such a film in a photocatalytic reactor may be negligible if a more efficient mechanism for fixing titanium nanoparticles to the support and converting them to active titanium dioxide is not elucidated.
ALF showed increased concentration of all metals tested (Ag, Au, Cr, Co, Ti. Zn) over MG indicating that it is a better candidate for phytoremediation and metal recycling (phytornining), especially for cobalt, chromium and silver.
Proposed Phase II Objectives and Strategies:
The demonstration of the ability of certain plants to uptake and reduce metals to nanoparticles has been demonstrated by others. However, we are the first (in Phase 1)10 demonstrate this principle using titanium. We are also the first (in Phase 1) to demonstrate the limited promise of MG as a potential candidate for phytoremediation, although not under the conditions specifically investigated in Phase I. In Phase II, we propose to go beyond understanding the basic mechanisms of binding and precipitation to be the first group to approach the recycling of metal nanoparticles by this method from an engineering standpoint. Phase 11 xviii allow the determination of optimal parameters of environmental interest (such as pH, metal concentration, interfering substances, and ionic strength) and to attempt the first pilot scale operation of the biotemplating technique for the production of a valuable water resource technology: photocatalytic surfaces for water treatment.
Firstly, we propose to repeat demonstration of concept, time profile and concentration profile experiments carried out in Phase I with plants of the same taxonomical family as MG. Given that uptake and precipitation mechanisms are common to certain classes of hyperaccumulating plants, it is hypothesized that plants in the same taxonomical family as MG will behave in similar ways with respect to its interaction with titanium; possibly, some of these plants will be better suited for phytomining of titanium and production of titanium NSM. Table I lists some plants in the same family as MG (Convolvulaceae) which may show these enhanced uptake and precipitation characteristics.
Table 1: Proposed Plants for Phase II
Genus |
Common Name |
Cressa |
Aikalaiweed |
Convolvulus |
Bindweed |
Jacqueniontia |
Ciustervine |
Xenostegia |
Morningvine |
Merremia |
Woodrose |
Full scale trials of the biotemplating technique eventually will have to take place in soils, since hydroponic growth of MG and its relatives is economically unfeasible on a large scale, especially in the developing world (due to the expense incurred by using synthetic nutrients in the hydroponics system and maintenance and capital costs associated with startup of such as system). It is important then, to discern the partitioning kinetics of titanium in common soils and assess their phytoavailability as a function of this partitioning. This kinetics can then be used to optimize the recycle process.
The plant material that is obtained from both the hydroponics and soil trials mentioned above will be analyzed as in Phase I by GFAA and transmission electron microscopy/electron diffraction spectroscopy (TEM/EDS). However, more important than the total metal concentration in the plant biomass is the oxidation state of the titanium and kinetics of precipitation in-vivo. To determine these important parameters, samples of MG and its relatives will be analyzed using X-ray absorption near edge spectroscopy (XANES) and X-ray absorption fine structure (XAFS) to determine the oxidation state, interatomic distance and number of nearest atom neighbors in the different parts of the plant. By constructing a time profile of oxidation state of titanium and the degree of reduction/precipitation we will be able to determine which of the Convolvulaceae family is the most efficient producer of titanium NSM and under which conditions the optimum recovery may be reached.
The final aspect of the Phase II proposal is the development of useful photocatalytic surfaces. We propose a solventless recipe for the production of such materials, in keeping with the 12 Principles of Green Engineering. MG and relatives that demonstrate the highest concentration of titanium NSM in their biomass ill be ground in a mill and dispersed in water. The NSM solution will be deposited on a glass surface and converted to titanium dioxide by way of heat treatment. We propose to attempt this procedure without the use of solvents (except water) if possible, using different heat treatments. Specifically, we attempt to vary three parameters of the heat treatment: heating time, heating temperature and (if absolutely necessary) amount and type of organic fixing agent to be used -- commonly used fixing agents are poly-vinyl acetate and poly-ethylene glycol. The characteristics of these titanium dioxide films will be evaluated by X-ray diffraction, atomic force microscopy, and UVV is spectra.
The titanium dioxide nano-catalyst will be used in the photo-catalytic induced destruction of an aqueous phase priority pollutant (2,4,6-trichiorophenol), a common organic solvent (cyclohexane) and biological toxins (microcystin). From the photo-oxidation experiments, we will be able to assess the extent and limitations of nano-sized photocatalysts produced by this biotemplating technique to degrade important pollutants. Moreover, we will also be able to assess some of the important parameters defining the efficiency of these reactions (such as kinetic modeling, photon efficiency, and thermodynamic limitations) as they relate to the material properties and production mechanism of the catalyst. From the mass balance of the templating procedure, through the evaluation of the biotemplated photocatalysts in photo-oxidation experiments, the green production of nano-materials for use in water disinfection will be evaluated for feasibility in the developing world and economic attractiveness in the developed world for the first time.
Journal Articles:No journal articles submitted with this report: View all 2 publications for this project
Supplemental Keywords:Nanotechnology, phytoremediation, phytomining, hioternpaiing. titanium dioxide, photocatalysis,
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Water, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Engineering, Chemistry, & Physics, Biochemistry, Environmental Engineering, Environmental Chemistry, Chemistry and Materials Science, New/Innovative technologies, nanotechnology, environmentally applicable nanoparticles, environmental sustainability, nanoscale biopolymers, nanocatalysts, biotechnology, contaminated aquifers, aquifer remediation design, bioengineering, decontamination, sustainability, titanium oxide nanoparticles, groundwater contamination, bioremediation, groundwater remediation, water treatment, nanoparticle remediation, innovative technologies
Relevant Websites:
http://www.eng.uc.edu/~ddemetri/ 
http://www.eng.uc.edu/~byates/
Progress and Final Reports:
Original Abstract