Date of Award
Doctor of Philosophy in Environmental Engineering - (Ph.D.)
Civil and Environmental Engineering
Taha F. Marhaba
There is a growing interest in nanobubble (NB) technology because of its diverse applications (e.g., detergent-free cleaning, water aeration, ultra-sound imaging and intracellular drug delivery, and mineral processing). NBs have a higher efficiency of mass transfer compared to bulk scale bubbles due to the high specific surface areas. The high specific surface also facilitates physical adsorption and chemical reactions in the gas liquid interface. Furthermore, the collapse of NBs creates shock waves and the formation of hydroxyl radicals (OH).
However, it remains elusive why or how NBs are stabilized in water and particularly, the states of internal pressures of NBs are difficult to measure. This thesis employs the injection of high-pressure gases through a hydrophobized ceramic membrane to produce different gaseous NBs in water. The results indicate that increasing the injection gas pressure (60–80 psi) and solution temperatures (6–40 oC) both reduce bubble sizes, which are validated by two independent models develop from the Young-Laplace equation and contact mechanics. Both models yield consistent prediction of the internal pressures of various NBs (120 psi-240 psi). The developed methods and model framework are useful to unravel properties of NBs and support engineering applications of NBs.
In addition, Atomic Force Microscopy-Scanning Electrochemical Microscopy (AFM-SECM) has evolved to be a powerful tool for simultaneous topographical-electrochemical measurements at local material surfaces with high spatial resolution. Such measurements are crucial for understanding structure-activity relationships relevant to a wide range of applications in material science, life science and chemical processes. The electrochemical behavior of surface NBs on gold substrate is measured by AFM-SECM, to better understand the chemical properties of NBs.
Moreover, this study investigates the effects of four types of NBs (air, oxygen, nitrogen, and carbon dioxide) on seed germination and plant growth. Nitrogen NBs exhibit considerable effects in the seed germination, whereas air and carbon dioxide NBs do not significantly promote germination. The growth of stem length and diameter, leave numbers, and leave width are promoted by NBs (except air). Furthermore, the promotion effect is primarily ascribed to the generation of exogenous reactive oxygen species (ROS) by NBs and higher efficiency of nutrient fixation or utilization.
Shi, Xiaonan, "Understanding the interfacial processes of reactive nanobubbles toward agricultural applications" (2022). Dissertations. 1609.