This EAGER award will use an atmospheric pressure cold plasma (APCP) coating techniques to make a durable TiO2 coating at the surface of paving materials (or other infrastructural materials). The photocatlytic material will be tested for its ability to oxidize VOCs and remove NOx from the atmosphere. This project will improve our fundamental understanding of the physicochemical and micromechanical behavior of engineering materials under different conditions. The process of identifying appropriate plasma gas and precursor agents will help develop a thorough knowledge of the material chemistry (at the molecular level) and understand interaction at interfaces. The project will produce an innovative engineering material surface treatment and processing method for enhanced TiO2 adhesion and durability, which can be transferrable to other engineering materials such as wood, concrete, and steel. The developed atmospheric pressure cold plasma (APCP) coating technique has great potential to be used to enhance bonding at material interfaces for various purposes such as anti-corrosion and anti-abrasion.
The integration of the research plan with an education and outreach program will address broader environmental and social issues. Once the innovative concept of using atmospheric pressure cold plasma to treat the surface of paving materials with TiO2 and improve the air quality of living environment as proposed in this study is shown to be feasible, this will lead to a new area of research which could have significant impact on the engineering profession and the public.
Increased transportation activities result in enhanced air pollution at the street level in urban areas. The nitrogen oxides (NOx) and volatile organic compounds (VOCs) that are emitted from automobiles cause a wide variety of health problems and environmental impacts. Titanium dioxide (TiO2) is a proven photocatalyst that can be used to oxidize and remove VOCs and NOx from the atmosphere (Figure 1). Although TiO2 treated pavement have great potential to improve air quality due to its wide contact areas with the air pollution, current techniques to adhere TiO2 to pavement are either not durable or lack of direct contact between TiO2 and UV light reducing pollution removal efficiency. To solve this technical difficulty, atmospheric pressure cold plasma (APCP) surface treatment technique was used. APCP processing has been proven to be a powerful process (efficient, non-polluting, and economical) to modify surface characteristics and improve adhesion of additives to engineering materials. The objective of this research is to test the concept of using APCP to coat TiO2 to pavement materials to remove VOCs and NOx for improved air quality. To do this an APCP reactor was developed to generate highly active plasma radicals to adhere TiO2 particles to the surface of asphalt pavements through strong chemical bond. The characteristics of the TiO2 coated surface were evaluated for pollution removal efficiency and durability. The reactor uses an electrical discharge with a high voltage power source to produce APCP corona discharges. These discharges are initiated in the high electric field intensity near the tips of an array of needles creating electron avalanches and streamers among a mixture of argon (carrier gas) and acetylene (precursor gas). Downstream of the acetylene/argon plasma a plasma-polymerized film quickly forms on surfaces. This organic film can be used to bind fine TiO2 particles to asphalt. Evidence of immobilization of TiO2 particles were obtained in the Field Emission Scanning Electron Microscope (FE SEM) images, both before (Figure 2) and after washing and scrubbing (Figure 3), indicating a strong bond between the TiO2 particles and the substrate asphalt sample. Based on the environmental chamber analysis, the TiO2 coated asphalt sample using APCP showed clear NOx reduction before washing and scrubbing. Such effect became limited after washing and scrubbing. It is hypothesized that either very few TiO2 particles were immobilized on the asphalt surface by APCP or the APCP generated TiO2 coating on the asphalt surface is not effective for photocatalytic reaction (perhaps due to excessive organic film thickness presenting a barrier that prevented intimate contact between reactants and catalyst in the presence of a flux of UV lights). Although the FE SEM images confirmed the presence of immobilized TiO2 at asphalt surface, the findings from this study are inconclusive and future research is needed to investigate the reasons of limited NOx reduction effect in the environmental chamber. Further research is also recommended to optimize the APCP reactor and improve the effectiveness of the APCP TiO2 coating. As a highly exploratory and promising research, this study is leading towards a new function of engineering materials as air purifying facilities, and will ultimately result in greater sustainability of the nation’s infrastructure. TiO2 treated engineering materials are becoming popular around the world for their distinguished benefits especially in air quality improvement. This research demonstrates that the APCP technique is an innovative and technically viable method for incorporating TiO2 onto engineering materials. It creates cost-effective, environmental friendly and potentially more durable surface coating to engineering materials, and can improve the material properties such as surface characteristics, bonding characteristics and anti-corrosion properties. As a multidisciplinary study involving chemistry, materials science, civil engineering, electrical engineering, and environmental engineering, this research also contributes significantly to other fields such as electrical engineering and environmental engineering by initiating potential research ideas and offering solutions to environmental concerns from transportation discipline. By integrating the research findings into outreach plan to offer hands-on workshops to MESA (Mathematics Engineering Science Achievement) underrepresented middle school students at the MESA Annual Conference, this research addressed broader environmental and social issues. Students not only received training on hands-on working skills, cooperation skills, and critical thinking skills, but also became aware of the significance of interdisciplinary research for future technology innovation and progress. The engineering outreach activities conducted in this research created a successful model that can be used for future research. A variety of education tools and concepts such as dynamic teaching and learning strategies, hands-on experience, authentic but fun research involvement, and multi-discipline innovations are integrated into the outreach to improve young students’ learning experience. Through the outreach model, more students can be exposed and attracted into engineering disciplines at a much earlier age than college. Positive information about engineering can be disseminated to the students to help them understand the importance of engineering and to enhance their career self-confidence.
