Grantee Research Project Results
2002 Progress Report: Simultaneous Environmental Monitoring and Purification Through Smart Particles
EPA Grant Number: R829602Title: Simultaneous Environmental Monitoring and Purification Through Smart Particles
Investigators: Sigmund, Wolfgang M. , Wu, Chang-Yu , Mazyck, David
Institution: University of Florida
EPA Project Officer: Aja, Hayley
Project Period: February 10, 2002 through February 9, 2005
Project Period Covered by this Report: February 10, 2002 through February 9, 2003
Project Amount: $390,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The objectives of this research project are to enable the atomic and molecular control of material building blocks and develop engineering tools to provide the means to assemble and utilize these tailored building blocks for developing novel smart particles for environmental applications as purifiers and sensors, which are environmentally benign.
We are pursuing a multidisciplinary synthesis of technologies including self-organized structural control, and smart materials with a focus on environmental purification and monitoring to create intelligent surfaces and structures that not only sense and interact with their environment, but that can fundamentally alter their own behavior and deactivate themselves as preprogrammed or as desired.
Progress Summary:
Synthesis of Composite Particles and Characterization. The synthesis of novel composite particles has been conducted in Year 1 of the project. Three different types of composite particles (i.e., 300-600 µm BaFe12O19-TiO2, ballmilled BaFe12O19-TiO2, and carbon nanotube (CNT)-TiO2), have been synthesized (see Figure 1). Anatase TiO2 nanoparticles, whose sizes are in the range of 2-50 nm, have been formed on BaFe12O19 or CNTs by controlled hydrolysis and condensation of the titania precursor titanium(IV) bis(ammonium lactato)-dihydroxide (TALH) or titanium isopropoxide. The photocatalytic performance, as well as optical and physical properties of novel composite particles, currently is under investigation.
Transmission Electron Microscope (TEM) photos of TiO2 nanoparticles from two different TiO2 precursors (i.e., titanium isopropoxide and TALH, are shown in Figure 2). The peaks from anatase phase of TiO2 nanoparticles were present in the x-ray diffraction (XRD) pattern.
CNT-TiO2 composite particles synthesized by the similar solution technique as BaFe12O19-TiO2 particles have been produced. TALH has been utilized as a TiO2 precursor. CNTs electrosterically dispersed in water were mixed with TALH solution. This mixture then went through a refluxing process forming anatase TiO2 nanoparticles on the surface of CNTs (see Figure 3).
Figure 1. Scanning Electron Microscope (SEM) Micrographs of BaFe12O19-TiO2 Composite Particles. (a), (b) TALH has been used as a TiO2 precursor, which has formed a relatively smooth layer of TiO2. (c) Titanium isopropoxide was used as the TiO2 precursor. A rougher layer of TiO2 has been formed.
Figure 2. TEM Micrographs of TiO2 Nano-Particles. (a) TiO2 Particles from titanium isopropoxide. The diameter of particles is in the range of 30-50 nm. (b) TiO2 particles from TALH. The size of particle is less than 10 nm.
Figure 3. TEM Micrographs of Multiwalled CNTs (MWCNTs) and TiO2 Nanoparticles Formed on the Surface of MWCNTs. (a), (b) Low magnification TEM micrographs. (c) A High Resolution Transmission Electron Microscopy (HRTEM) micrograph of the interface region between MWCNT and TiO2 nanoparticles. The crystal lattice of TiO2 nanoparticles, as well as the fringes of MWCNT, is resolved. Furthermore, the interface between CNT and TiO2 is clearly seen, indicating that TiO2 nanoparticles, whose sizes are less than 5 nm, are well attached on the outermost shell of MWCNT.
A 300-500 µm diameter BaFe12O19 has been ballmilled, producing 1 µm BaFe12O19 to make smaller magnetic core particles. A ballmilled BaFe12O19 dispersion containing TALH solution was sonicated by an ultrasonic horn, keeping the temperature of dispersion under 100°C. Ballmilled BaFe12O19-TiO2 composite particles are presented in Figure 4.
Figure 4. TEM Micrographs of Ballmilled BaFe12O19-TiO2 Composite Particles. The core of the ballmilled BaFe12O19 particles has been coated with the shell of TiO2 nanoparticles.
Air Reactor. Additionally, a smart composite material consisting of SiO2 and TiO2 for removing elemental mercury vapor from air has been developed and evaluated. The composite, with a high surface area, was synthesized by a sol-gel method. Experiments were conducted in a fixed-bed reactor to test both adsorption and photocatalytic oxidation functionalities. Excellent removal efficiency (> 99 percent) was achieved and maintained when the material was illuminated with ultraviolet light (UV). The composite changed its color, which is an indicator of the material’s status, from white in the beginning to yellow to dark brown over time. The material’s capacity was found to be greater than activated carbons reported in the literature. Interestingly, the adsorption capacity (absent of UV illumination) improved after each photocatalytic oxidation step, suggesting the activation of the composite by photocatalysis. A photograph of the fresh composite is shown in Figure 5(a). Figure 5(b) shows a photograph of the composite in the reactor after being tested for 200 hours. Interestingly, however, the adsorption capacity improved after each photocatalytic oxidation step, suggesting that the activation of the composite is done by photocatalysis. Figure 6 shows such a phenomenon. Studies currently are underway to understand the mechanisms that result in such an interesting and unique property.
Development of a Magnetically Agitated Photocatalytic Reactor (MAPR) for Water Purification. Magnetic agitation of magnetic particles was achieved after applying magnetic agitation principles and theory. A prototype reactor has been fabricated and preliminary reactor performance has been investigated. The reactor uses a variable frequency alternating current magnetic field and three ultraviolet light tubes to provide agitation and energy for photocatalytic reactions. BaFe12O19-TiO2 (300-600 µm) shows moderate adsorptive capability. Photocatalytic ability of the titania coating has been demonstrated; however, in water, some coating detachment was observed. Currently, methods are being investigated to retain titania on the BaFe12O19 surface in water under strong abrasive conditions.
Figure 5. Photos of the Novel SiO2-TiO2 Composite for Hg Removal: (a) Freshly Produced Material; (b) After Tested for 200 Hours
Figure 6. Normalized Hg Concentration at the Reactor Outlet as a Function of Time Over 6 Adsorption (UV off for 15 Minutes)/Photocatalytic Oxidation (UV on for 6 Minutes) Cycles
The magnetic particles consist of barium ferrite coated with titanium dioxide (size ~ 300-600 µm) and have a magnetic moment that has been measured (see Figure 7). Figure 7 also shows the magnetization of uncoated barium ferrite to demonstrate that the titanium dioxide coating has little effect on the magnetic properties of barium ferrite.
A solenoid (see Figure 9) is used as the magnetic field generator, and is modeled using the Biot-Savart law:
For a single circular planar loop of wire, Equation 1 can be simplified to its on-axis form as follows:
Figure 7. Magnetization Measurements of Plain and Coated Particles
Equation 2 is used to calculate the field produced by each loop of wire at a point along the z axis. This gives the magnetic field strength (B) in gauss over current (I) in amperes (see Figure 8). Multiplying points on the curve by the applied current will give the magnetic field strength at each point along the z axis. Taking the derivative of the curve with respect to z yields the magnetic field gradient, (B/I)/z (Gauss/Amp/cm), along the z axis (see Figure 8).
Figure 8. The Modeled Magnetic Field Profile and Gradient Field of the Prototype Coil
Design of Solenoid:
1,000 ft. 18 AWG copper wire
60 turns, 16.5 layers
Length: 12 cm
Radius: 6.3 cm
Resistance: 6.4 ohm
Maximum current capacity: 15 A.
Figure 9. Solenoid Dimensions and Specifications
A simple model can be used to calculate the resonant frequency as a function of particle magnetization and magnetic field gradient. The magnetic dipoles of the particles are assumed to instantaneously align with the AC magnetic field. The force can be described as:
where F = force, m = dipole moment, B = magnetic field.
The AC magnetic field can be written as:
where Bs = maximum static value of the magnetic field.
The total forces are combined and result in an equation that also describes damped harmonic motion. The generic form of this equation is:
Assuming negligible damping (ß = 0), the damping term, 2ßz, goes to zero. In addition, we can assume a linear spatial dependence of the gradient of the magnetic field over the distance of movement of the particle, meaning that we can write gradBs ~ dBs/dx x/x. The solution of the simple harmonic motion form then is:
where the resonant frequency may be written as:
In these equations, M is the magnetic moment per unit mass, and is the same quantity plotted in Figure 7. The magnetization of the particle along with the magnetic field gradient of the applied field correlate to the resonant frequency needed for optimal particle movement, which is calculated to be between 10 and 100 Hz from initial measured parameter values.
Particle and Reactor Performance Testing. After fabrication of the MAPR (see Figure 10), preliminary tests were performed to test the initial performance of the reactor. A reactive red dye (R.R.) solution was used for the initial tests for ease of measurement and quantification. (Organic chemicals will be used in future tests).
The tests were performed in a recirculating batch system at a flow rate of 5 mL/min. Three 8-watt UV bulbs with an average wavelength of 365 nm were used.
The unused reactor was first tested with no UV and no magnetic field to test if the frit had any adsorption effects. The frit initially showed about 8 percent removal, but after 30 minutes, removal had ceased (see Figure 11). Therefore, for future experiments, removal can be attributed to other phenomena besides adsorption to the porous frit.
Figure 12 shows the results of the reactor tested with and without UV and magnetic field. The UV and magnetic field have negligible effect on the removal of R.R.
Figure 10. Assembly of the MAPR
Subsequent to the initial studies above, the reactor was tested with 3.9 g of synthesized Particle 3 (arbitrary nomenclature) and 3.5 g of synthesized Particle 4. All particles used were coated with a sol-gel technique. Particle 3 was tested with UV and a magnetic field powered by a variable transformer at 60 Hz. Particle 4 was tested with UV and a magnetic field powered by an audio amplifier at 45 Hz. Particle 4 was tested again after rinsing with DI. Results are shown in Figures 13 and 14.
Figure 11. Clean Frit Adsorbance Test
Figure 12. Test for Effects From Photolysis and Magnetic Field
Particle 3 showed removal of 57 percent after 10 minutes and then decreased to about 30 percent removal after 1.5 to 3.5 hours. Particle 4 showed the same trend of high initial removal that decreased overtime and had the same results after reuse. The used particles had a red tint to them, indicating that the titania surface was adsorbing the dye.
The next step was to test the particle's adsorption ability. Two grams of synthesized Particle 5 were used with a 5 mg/L R.R. solution. No UV and a magnetic field powered by a variable transformer at 60 Hz were applied for the first 3.5 hours. The same trend of high initial removal appears as with the particles with UV and magnetic field on (see Figure 15). The UV was then turned on after 3.5 hours and no additional removal was seen up to 6.5 hours.
Figure 13. Removal of 10 mg/L R.R. Solution With Particle 3
Figure 14. Removal of 10 mg/L R.R. Solution With Particle 4. The particles were DI rinsed before reuse.
It can be concluded that the primary removal mechanism is adsorption to the titania surface. The dye adsorbed to the surface may be blocking the titania from absorbing UV light and creating hydroxyl radicals. It also must be mentioned that the coated particles were not heat-treated before use; therefore, most of the titania coating was in the amorphous phase. The anatase phase is needed for photocatalytic activity. The amorphous phase has a higher specific surface area than the anatase phase, and therefore, is better for adsorption. The synthesized particles now will be heat treated to yield more anatase phase titania, which will improve the photocatalytic properties.
Figure 15. Particle 5 Adsorbance of a 5 mg/L R.R. Solution
SEM pictures were taken of unused and used samples of Particle 4 to examine whether the titania coating still is present after use in the MAPR. Figures 16 and 17 show the before and after images, respectively. After use, the titania surface still is present.
Figure 16. SEM Picture of Unused Sample of Particle 4
Figure 17. SEM Picture of Used Sample of Particle 4
The coated particles were heat-treated at 550ºC and 650ºC in air for 1 hour. Immediate titania detachment was visually observed when the testing solution was pumped through the reactor. The polymer binder linking the titania to the barium ferrite surface likely is being oxidized during the high-temperature treatment.
Future Activities:
Synthesis of Composite Particles and Characterization. The photocatalytic performance, as well as optical and physical properties of novel composite particles, currently is under investigation. The feedback from environmental testing will be used to optimize the design and properties that are closely connected to the synthetic strategy. CNT-Ag and Ag-TiO2 composite particles will be synthesized and tested as smart particles with sensors.
Air Reactor. Studies are underway to understand the mechanisms that result in the interesting and unique property of enhanced adsorption after each cycle of photo-oxidation. Experiments will be conducted to test various hypotheses, including modification of functional groups by photocatalysis, photocatalytic oxidation by mercury oxide, and porosimetry. Also, the novel material's performance in a simulated flue gas will be assessed, where multiple pollutants such as SO2, HCl, and NOx may have influences.
Particle and Reactor Performance Testing. Heat treating the particles in an inert atmosphere and different coating methods are being explored to retain the TiO2 coating on the barium ferrite surface. After successful particle coating, the reactor will be characterized and optimized. Destruction of organic contaminants (bisphenol A) then will be tested.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 45 publications | 8 publications in selected types | All 8 journal articles |
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Lee SW, Sigmund WM. Formation of anatase TiO2 nanoparticles on carbon nanotubes. Chemical Communications 2003;(6):780-781. |
R829602 (2002) R829602 (Final) |
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Supplemental Keywords:
air, water, adsorption, heavy metals, innovative technology, remediation, engineering, industry, drinking water, chemicals, bisphenol A, mercury, environmental chemistry, physics, materials, mano-engineering, templates, carbon nanotubes, magnetic materials, fluidized bed., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, Sustainable Environment, Environmental Chemistry, Technology for Sustainable Environment, Monitoring/Modeling, New/Innovative technologies, Environmental Engineering, nanosensors, environmental monitoring, monitoring, chemical sensors, nanotechnology, environmental sustainability, environmentally applicable nanoparticles, biomonitoring, analytical chemistry, nanoscale sensors, remediation, sustainability, nano engineering, smart particles, innovative technologiesProgress 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.