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New Instrumentation for the Characterization of Emerging Photocatalytic Materials

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: Design and build new instrumentation (hardware and software components) for the comprehensive assessment of self-cleaning coatings and construction materials. Instrumentation shall have the capability to simultaneously assess self-cleaning, antimicrobial, and photocatalytic properties of emerging materials and coatings under environmentally relevant conditions. The overarching goal is to develop new analytical methods which will produce a composite merit score which reflects the intrinsic “value” of emerging materials, which may be used as a point of comparison among different suppliers, composite materials and coatings. This system will be useful in identifying new materials and coatings capable of increasing force protection through the retrofitting of existing structures or in the design of new portable or permanent infrastructure. 

DESCRIPTION: This system is needed in support of Department of Defense’s (DoD) force projection and protection strategic focus areas, where the identification and qualification of advanced materials will lead to improved warfighter protection. A key advancement in the field of sustainable construction has been the implementation of photocatalytic products, due to their ability to abate organic and inorganic surface contaminants, as well as keep surfaces clean. Consequently, a variety of paint, mortar, and concrete infrastructure materials are now available with photocatalytic additives. In a brief description of the photocatalytic process, light of the appropriate wavelength activates the photocatalyst surface, thereby generating reactive oxygen species which degrade adsorbed contaminants (photocatalytic) and promotes the reorganization of surface hydrogen bonding groups creating a highly water-wetting surface (self-cleaning). Published studies probing these individual phenomena are typically limited in focus and therefore, inadequate to use in developing a comprehensive assessment tool[3-6]. New instrumentation must be capable of simultaneously evaluating surface photocatalytic activity, changes in water wetting characteristics, and antibacterial activity, and allow for dynamic “real-world” conditions where varying aerodynamic shear stresses, spectral distribution and intensity of solar radiation exists. Self-cleaning and photocatalytic coatings and construction materials continue to surge in their global applications, e.g. the Cowboys Stadium, in Dallas TX; Belgian Road Research Center; “Dives in Misericordia”, Rome and the Milan Marunouchi building, Japan. Remarkable self-cleaning structures have been prepared from high performance concrete containing a TiO2 photocatalyst, where mechanical strength was also enhanced [2]. Emergence of new infrastructure construction materials and coatings has occurred without the synergistic development of assessment tools to evaluate them. Currently we lack a comprehensive understanding and the ability to experimentally and computationally describe competing processes that occur at the surface of photocatalytic construction materials under environmentally relevant (real-world) conditions. New instrumentation and a well-designed set of “real-world” experiments may enable the creation of a comprehensive model where a holistic assessment and performance prediction for globally emerging photocatalytic construction materials becomes possible. Standard laboratory-based analysis of photochemical materials is conducted through a series of seemingly unrelated and isolated experiments. For example, ISO 22197.1-5 provides procedures to qualify airborne removal of nitric oxide, acetaldehyde, toluene, formaldehyde, and methyl mercaptan. Each of these tests is conducted under a set of precise conditions and discloses that each “method is not suitable for the determination of other performance attributes.” Consequently, to determine a materials activity, efficiency, and cycle-life for several parameters is prohibitively time and labor intensive. A secondary goal lies in leveraging computational algorithms to short-cut the time to a successful predictive tool by filling the free-space within a limited experimental data set to visualize the multi-dimensional terrain of the reaction profile, under dynamic “real-world” environmental conditions. This capability is not currently available and will contribute to the growing needs of security and threat resiliency. 

PHASE I: The initial phase will consist of identifying innovative technology, conducting a feasibility investigation, and preparing a preliminary hardware/software design solution. A thorough literature review of the current state of photocatalytic/self-cleaning material characterization tools, as they apply to infrastructure, is required along with a detailed rationale supporting the proposed solution. New instrumentation (hardware and software) must be capable of simultaneously evaluating surface photocatalytic activity, changes in water wetting characteristics, and antibacterial activity, while under dynamic “real-world” conditions where varying aerodynamic shear stresses, spectral distribution and intensity of solar radiation exists. Common organic compounds, bacteria or spores, for which there is literature precedence, may be used to develop and validate the instrumentation and methods. 

PHASE II: Phase II involves the construction of an environmental test chamber, which is suitable for simultaneously performing the tests selected for the data matrix: self-cleaning, antimicrobial, and photocatalytic. The evaluation of at least three commercially available photocatalytic construction materials incorporating a photocatalyst and described as self-cleaning is desired. Additional characterization of the materials according to physical characteristics (surface roughness, porosity) and chemical composition (type and concentration of photocatalytic additive) may be required. Delivery of a prototype and demonstration of capabilities is expected at the close of Phase II. The proposer may leverage the literature available on the photocatalytic degradation of common pollutants and screen a model organic and biologic, while simultaneously monitoring the self-cleaning properties of the material surface using water-contact angle. Typical laboratory studies are performed under sanitized environments, and a fundamental question has evolved among these performance criteria, i.e. what are the environmental correlations among photocatalysis, antimicrobial, and self-cleaning properties. For example, perhaps surface A’s self-cleaning property is not proportional to its photocatalytic activity under increasing relative humidity or contaminant concentration. Any appropriate method, such as Langmuir-Hinshelwood kinetic models may be used to determine initial degradation rates and equilibrium constants in data collection. The matrix of environmental conditions (RH, spectral intensity from a solar simulator, air flow) should be used to determine if a theoretical model can be derived to predict the outcomes of experimental validation experiments, which were not part of the initial data set. 

PHASE III: A final prototype version of the measurement system will be fabricated based upon extensive testing and evaluation (T&E) by the ERDC-CMB. All software, including source code, will be delivered to ERDC-CMB for potential integration with existing DoD infrastructure. It is anticipated that the new technology will provide the DoD with a greatly enhanced measurement tool capable of rapidly and reliably assessing the performance of photocatalytic materials producing a composite merit score which reflects the intrinsic “value” of emerging materials, specifically concerning their photocatalytic, self-cleaning, and antimicrobial attributes. This new merit score may be used as a point of comparison among different suppliers, composite materials and coatings for the identification of materials and coatings capable of increasing force protection through the retrofitting of existing structures or in the design of new portable or permanent infrastructure. The photocatalytic research community and commercial suppliers are positioned to immediately benefit from the successful implementation and fielding of this equipment. There are often large variations in photocatalytic activity observed in those materials described as self-cleaning. Based upon the obvious broader use and potential for commercial quality assessment, a strong commercial potential is anticipated. 

REFERENCES: 

1: Maury-Ramirez, A., K. Demeestere, and N. De Belie, Photocatalytic activity of titanium dioxide nanoparticle coatings applied on autoclaved aerated concrete: Effect of weathering on coating physical characteristics and gaseous toluene removal. Journal of Hazardous Materials, 2012. 211–212: p. 218-225. 2. Cassar, L

2:  Cassar, L., et al., White cement for architectural concrete, possessing photocatalytic properties. 11th Int. Congr. on the Chemistry of Cement, Durban, South Africa, 2003: p. 2012-2021.

3:  Jo, W.-K. and C.-H. Yang, Visible-light-induced photocatalysis of low-level methyl-tertiary butyl ether (MTBE) and trichloroethylene (TCE) using element-doped titanium dioxide. Building and Environment, 2010. 45(4): p. 819-824.

4:  Liang, W., J. Li, and Y. Jin, Photo-catalytic degradation of gaseous formaldehyde by TiO2/UV, Ag/TiO2/UV and Ce/TiO2/UV. Building and Environment, 2012. 51: p. 345-350.

5:  O'Keeffe, C., et al., Air purification by heterogeneous photocatalytic oxidation with multi-doped thin film titanium dioxide. Thin Solid Films, 2013. 537: p. 131-136.

6:  Sarantopoulos, C., A.N. Gleizes, and F. Maury, Chemical vapor deposition and characterization of nitrogen doped TiO2 thin films on glass substrates. Thin Solid Films, 2009. 518(4): p. 1299-1303.

KEYWORDS: Self-cleaning, Coatings, Infrastructure, Materials, Concrete 

CONTACT(S): 

Janice Buchanan 

(601) 467-8683 

janice.p.buchanan2.civ@mail.mil 

Dr. Charles Weiss 

(601) 634-3928 

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