Grantee Research Project Results
Final Report: Design of a Solar Powered Water Purification System Utilizing Biomimetic Photocatalytic Nanocomposite Materials
EPA Grant Number: SU835996Title: Design of a Solar Powered Water Purification System Utilizing Biomimetic Photocatalytic Nanocomposite Materials
Investigators: Keleher, Jason
Institution: Lewis University
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $13,685
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
The lack of access to clean water is a major crisis that primarily resides in developing nations, in places like Africa, India, and Southeast Asia. These developing nations do not have the capital to implement a large cost solution, so the development of an inexpensive and efficient water purification system is of paramount importance. The basis of this project includes the development of a solar capture photovoltaic nanocomposite (PV) to power a pump coupled with a solar activated water purification nanocomposite (WP). The project is unique in that it uses solar energy to power a self-sufficient water purification system. The solar capture photovoltaic cell is composed of an inexpensive, biodegradable polymer in which semiconducting nanoparticles are embedded. This composition creates a conductive nanocomposite that uses solar energy to create enough charge and voltage to power a small pump. This pump is used to transport the contaminated water through the WP filter. The WP filter is composed of biomimetic building blocks (such as cellulose) coupled with photo-catalytic antimicrobial nanoparticles to aid in pollutant degradation and effective elimination of harmful bacterial species in water. The innovative component to the WP filter is twofold. First, the filter is powered solely by solar energy, resulting in no outside source of electricity being needed. The second innovative component is the method of purification. Many conventional filters simply capture the pollutant, but the design proposed chemically degrades the pollutants to carbon dioxide, water, and mineral acids. The specific goal of this project is to develop a working prototype of the solar activated water purification system. The proposed project will design a solution for the lack of access to clean water and help create a sustainable water supply to improve the overall quality of life in developing nations across the world. The proposed water purification system will be able to improve the water quality through natural means that ultimately will educate and improve the life of the people in these nations. This project will also have a profound impact on the university level. Most undergraduate programs focus on teaching the rudiments of their discipline, but never incorporate how their skills can serve humanity.
Summary/Accomplishments (Outputs/Outcomes):
The goal of the project from the Keleher Research Group at Lewis University is to design a solar powered water purification system for underdeveloped nations that contains a solar capture/energy generation (PV) and water purification (WP) nanocomposite materials. For the water purification component, a series of functionalized nanoparticles where synthesized and the chemical degradation potential was tested using both ultraviolet and visible light. The degradation of various pollutants can occur when a semiconducting nanoparticle, such as TiO2, is illuminated with light of energy greater than or equal to its band gap. Electrons excited from the valence band to the conduction band can be transferred to the organic compound, causing it to be reduced. The particle works very well in UV light, but the visible light does not have enough energy to excite an electron in the nanoparticle. One such functionalization pathway to fix this issue is dye sensitization, which involves binding of a dye molecule to the surface of the particle. By adding a dye molecule, visible light, associated with the dye’s color can be used to excite electrons, creating sites for redox reactions. In ultraviolet light, the un-functionalized nanoparticle exhibited excellent chemical degradation, but the rate fell below 10% in visible light. After a series of functionalization, the particle showed results greater than 75% chemical degradation of a pollutant.
After the initial tests showed a clear shift in the ability of the particle to degrade a pollutant, the particle was added to a cellulose biopolymer. The resulting nanocomposite underwent testing in various forms. It was found that the form played a major role in the activity of the filter, with greater surface area being correlated to greater purification. However, when doing tests with a nanocomposite, there are two potential pathways for purification. The first pathway involves a physical phenomenon, where the pollutant is absorbed into the filter membrane, hence removing it from the source, but no chemistry occurs. This pathway is the typical pathway of the majority of filters. The second pathway involves a chemical (redox) reaction between the particle and the pollutant, resulting in the chemical destruction of the pollutant. This is the preferred pathway as the pollutant is totally removed from the environment, but tests revealed that the physical absorption pathway was the driving pathway in remediation.
Conclusions:
In addition to chemically degrading organic pollutant, the goal of this project was to create a multifunctional filter, which also can remediate water sources with metal ions in solution and microbial species. By adding a indicator for complexiometric titrations to the particle, the particle exhibited a dual functionality. Firstly, the particle has an increased chemical degradation capacity, similar to the aforementioned dye sensitization process. Secondly, the particle can now form a complex with many metal ions, such as Zn2+, Pb2+, Ca2+, Mg2+, Sr2+, Mn2+, Cu2+, for example. These complexes serve as a way to removal metal ions from a contaminated water source, which is very advantageous for a water filter. Finally, solid silver (Ag) also was added to the nanoparticle. The addition of Ag to the nanocomposite is important because Ag serves as an antimicrobial agent to aid in destruction of harmful waterborne bacteria. To test the films’ ability to inhibit bacteria growth, a method to evaluate the antimicrobial efficiency (AME) was used. The Ag-functionalized nanocomposite film showed inhibition of Escherichia coli and Staphylococcus aureus during this form of testing. The final step in the water filter aspect is to explore the best method implement the nanocomposite into the overall water purification system.
All of the testing of the nanocomposites has been completed in a batch reactor type setup, where the filter beads and polluted water are all mixed in a container for a certain amount of time. While this serves as a good laboratory method to see how various changes in the nanocomposite effect the rate of remediation, this is not the end goal. Therefore, various different types of reactor setups were explored. The most efficient method was a packed bed reactor, which consists of a column packed with the nanocomposite beads. As shown in Figure 6, the packed bed reactor showed higher average values for both total removal and chemical degradation; however, this is a system which only contained the optimal particle. As explained previously, there also are additional nanocomposite forms that have advantageous properties, such as antimicrobial properties and metal ion removal capabilities. A mosaic system, containing a variety of functionalized nanocomposites, showed similar results to the previous reactors which the addition of the added aforementioned benefits.
The second component of the water purification system is a film that can use sunlight to power a pump. The base of the film involves a cellulose nanofibers that is coupled with a conductive polymer, polyanaline. The polyanaline acts as the means for electron transport, but electrons need to be injected into the polyanaline matrix. There needs to be a photon acceptor in the system to provide the aforementioned electrons. For this current model, the photon acceptor is a Cadmium Sulfide Quantum Dot (CdS QD). The incorporation of the QDs successfully allows for voltage generation. However, this did not translate well into the power outputs of the film. This was attributed to poor electron transport between layers of the nanocomposite. In an attempt to rectify this situation, CNF/PANI coatings were modified with various ligands to better bind the nanoparticles. In efforts to allow optimal interaction between CNF/PANI films and photon acceptors as well as increase the structural rigidity of the films, poly(ethylene glycol) diacrylate (PEG-DA) was added to the nanocomposites. Compression analysis and tensile strength testing revealed that the films were structurally enhanced by the addition of increasing concentrations of PEG-DA. The final step in the flexible photovoltaic development was to improve the overall packing density of the films for improved incorporation of the photon acceptor. This was studied by the effect of sintering temperature on the films post-dehydration. By measuring the resistance, it was found that the overall resistivity increases with increasing temperature, with a major transition state occurring around 250oC. This may be indicative of the oxidation of Polyaniline Emeraldine Salt (ES) into the less conductive Pernigraniline Salt (PNS).
Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
Water purification, solar activated, biodegradable, conducting polymerThe 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.