Iron oxides are widespread in nature and are linked to many natural biogeochemical processes. These minerals play an important role in sorption of metal(loid)s, acceptance of electrons from microbial respiration, photochemical reduction, and heterogeneous catalysis; further, they are used as engineered solutions to aqueous contamination problems. The thermodynamic and kinetic changes of small and large nanoscale hematite particles were investigated under long-term aging, relevant pHs, and ionic strength conditions. Crystallinity, particle size, surface area, pore size volume, and phase purity were analyzed by various techniques including XRD, BET, and TEM. The results indicated that thermodynamic and kinetic changes vary with age for each of the average particle sizes, which were 15-25nm and 40-50nm. Under the same conditions, crystal growth rates were higher for smaller particle sizes. Recrystallization occurred through the Ostwald ripening mechanism. Thermodynamic modeling demonstrated that the solubility product of the hematite nanoparticles was size and age dependent. The results showed that the solubility product decreased over time as particle hydrodynamic diameter increased. The novelty of this approach lies in the relationship of time-resolved changes in thermodynamic quantities of hematite nanoparticles. In addition, the time span of more than five years explores true long-term aging for hematite nanoparticles making this research unique. This study could have important implications for engineered treatment procedures and interpretations of naturally occurring processes which are thus far not well understood.
Civil and Environmental Engineering
Chemical Engineering, Civil Engineering, Materials Science
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Badakhshaneian, Laelsadat, "Size Dependent Hematite Nanoparticle Physiochemical Behavior Under Long-Term Aging" (2020). Civil and Environmental Engineering Theses and Dissertations. 23.
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