Unified Theory for Characterizing the Effects of Metallic Nanoparticles on the Performance of Microbial Fuel Cell and Cementitious Materials
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This study used fiber shaped metallic nanoparticles (Fe, Ni, and Fe/Ni) as additives to microbial fuel cell (MFC) and smart oil well cement (OWC) because of the rapid growth in the applications of new technologies in these two areas. The purpose in this study was to investigate the effects of nanoparticles on the performance of MFC (fluid system) and the properties of OWC (fluid to solid system), and to develop a new unified theory to better characterize the effects of nanoparticles. A unified theory was developed to represent the two probe method of characterization of changes in a complex system. Anode and cathode in the MFC was similar to the two wires buried in the cement to investigate the bulk property changes. With electrochemical impedance spectroscopy, it was determined that the MFC and cement composite behaviors were controlled by the bulk resistivity of the two systems. Also each probe was represented as a capacitor-resistor system and was quantified. Using the unified theory, it was possible to better characterize the effects of nanoparticles on the MFC electrode system and the smart cement bulk behavior. The effects of various types of nanoparticles on the cathode electrode, power production, and biosurfactant production were investigated. Of the nanoparticles studied, Fe nanoparticles had the highest improvement in the MFC. The addition of Fe nanoparticles to the cathode surface enhanced the power production by over 500% to 66.4 mW/m3 and enhanced the biosurfactant production in the anode solution by about 32% to 3.1 g/L, reduced the cathode charge transfer resistance by about 86% and reduced the bulk resistance of MFC by about 7%. The addition of various types of nanoparticles enhanced the sensing and mechanical properties of smart oil well cement. Of the nanoparticles studied, Fe nanoparticles had the highest improvement in compressive strength of the cement after three days curing by over 39%. Ni nanoparticles had the highest improvement in piezoresistivity of the cement by over 310%. The addition of Fe/Ni nanoparticles reduced the contact resistance by about 80% and the bulk resistivity by 77% after six months of cement curing. Also the effect of nanoparticles on higher temperature application was investigated. The addition of UH-biosurfactant with-and-without nanoparticles influenced the hydration of the smart cement by reducing the peak temperature of hydration by about 18 °F without significantly affecting the time to reach the peak temperature. Also the UH-biosurfactant affected the piezoresistive behavior of the smart cement. Using the unified theory, it was able to characterize the effects of nanoparticles in MFC (1.5 mg/cm2) and cement (0.075% by weight of smart cement). Fe, Ni, and Fe/Ni metallic nanoparticles used in this study enhanced the performances of both MFC and the smart OWC.