Surface-Modified Magnetite Nanoparticles for Advanced Separation and Purification
Creators: Liu, Xuyang
Publisher: name: University of Alberta Library
Year: 2024

<p>When used as selective sorbents, surface-modified magnetic nanoparticles possess numerous advantages, including cost-effectiveness, high adsorption capacities, tunable surface properties, and convenient solid-liquid separation, making them a promising solution for challenging separation problems. In this thesis research, the author studied the potential and significance of utilizing surface-modified magnetite nanoparticles in two specific areas: (1) removal of fine mineral solids from non-aqueous extracted (NAE) bitumen, and (2) extraction and purification of nucleic acids from biomatrix.<br>
In the oil sands industry, relatively high fine mineral solids content in produced bitumen (greater than 300 ppm or 0.03 wt%) is one of the hurdles preventing non-aqueous extraction from being used in commercial operations. In this work, surface-modified magnetite nanoparticles were studied to capture fine solids in cyclohexane-diluted NAE bitumen at a low cyclohexane-to-bitumen ratio of 2. The magnetite nanoparticles, together with the captured fine solids, were removed from bitumen through a magnetic field-assisted sedimentation and filtration process. Stearylamine acetate-functionalized magnetite nanoparticles (SAA-MNPs) were prepared and characterized, and their performance in separating fine solids from NAE bitumen was quantitatively evaluated and compared with un-modified magnetite nanoparticles (MNPs). It was shown that surface modification by SAA significantly improved separation efficiency from 16% to 89%. The increased separation efficiency resulted from the formation of hetero-aggregates between the NAE fine solids and SAA-MNPs in cyclohexane. <br>
Since asphaltenes in solvent-diluted-bitumen have a strong tendency to adsorb on any surfaces upon contact, asphaltene-modified magnetite nanoparticles (Asp-MNPs) were also used in this study. It was found that asphaltene coating of MNPs increased the fine solids separation efficiency from 16% to 84%. Therefore, asphaltene adsorption on the MNPs was not a detriment but an advantage because it did not diminish the capture efficiency of the MNPs. Results illustrated that the re-generated and recycled SAA-MNPs and Asp-MNPs could lower fine solids content from 3600 ppm to 417 ppm (88% removal) and 587 ppm (84% removal), respectively, in a single pass.<br>
The mechanisms of the developed magnetic sorbent separation process were studied using quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM) studies. Modification by SAA increased the adhesion interaction between the MNPs and NAE fine solids through a bridging effect, and the use of an external magnetic field helped form magnetic aggregates of SAA-MNPs and strengthened the hetero-aggregation between SAA-MNPs and the NAE fine solids. Interestingly, asphaltene-modified MNPs (Asp-MNPs) showed a repulsive force towards NAE fine solids due to steric effect because the latter was coated by asphaltene as well; however, the applied external magnetic field caused the formation of magnetic aggregation of Asp-MNPs, and the extended asphaltene polymer brushes of the Asp-MNP magnetic aggregates could capture the NAE fine solids through a sweeping effect by the networked Asp-MNPs. Therefore, this work demonstrated the unique advantage of magnetic sorbents, i.e., even without affinity to the target, the magnetic sorbents could still capture the target under an external magnetic field when coated with polymer “brushes”. A non-magnetic sorbent would not be able to capture the target in this case. <br>
For another advanced separation application, surface-modified SiO2 encapsulated core-shell magnetic sorbents and associated buffers were developed aimed at SARS-CoV-2 viral RNA extraction. A wastewater sample containing SARS-CoV-2 virus collected from a wastewater plant in Alberta was used for the extraction studies. The human coronavirus strain 229E (hCoV-229E) was first spiked into the wastewater sample as a surrogate to study the RNA extraction abilities of the core-shell magnetic beads and optimize the extraction process. Subsequently, the SARS-CoV-2 RNA extraction performances using the developed magnetic beads, buffer system, and protocol were investigated and compared with a commercial nucleic acid extraction kit (magnetic beads-based method) through reverse transcription polymerase chain reaction (RT-PCR) analysis. By using the developed protocol, both Fe3O4@SiO2 and Fe3O4@SiO2-COOH magnetic sorbents demonstrated high hCoV-229E extraction efficiency from hCoV-229E-spiked wastewater samples, with Fe3O4@SiO2-COOH exhibiting superior extraction efficiency compared to the commercial kit. Additionally, following the developed protocol, Fe3O4@SiO2 and Fe3O4@SiO2-COOH showed comparable abilities as the commercial kit in extracting SARS-CoV-2 viral RNA from wastewater, providing a viable alternative to the commercial kit in case of severe shortage of supplies. The amino-functionalized Fe3O4@SiO2-NH2 showed significantly lower efficiency for hCoV-229E or SARS-CoV-2 viral RNA extraction from the same sample.</p>