title: Adsorption of superparamagnetic iron oxide nanoparticles on silica and calcium carbonate sand.
abstract: Superparamagnetic iron oxide (SPIO) nanoparticles have the potential to be used in the characterization of porous rock formations in oil fields as a contrast agent for NMR logging because they are small enough to traverse through nanopores and enhance contrast by shortening NMR T2 relaxation time. However, successful development and application require detailed knowledge of particle stability and mobility in reservoir rocks. Because nanoparticle adsorption to sand (SiO2) and rock (often CaCO3) affects their mobility, we investigated the thermodynamic equilibrium adsorption behavior of citric acid-coated SPIO nanoparticles (CA SPIO NPs) and poly(ethylene glycol)-grafted SPIO nanoparticles (PEG SPIO NPs) on SiO2 (silica) and CaCO3 (calcium carbonate). Adsorption behavior was determined at various pH and salt conditions via chemical analysis and NMR, and the results were compared with molecular theory predictions. Most of the NPs were recovered from silica, whereas far fewer NPs were recovered from calcium carbonate because of differences in the mineral surface properties. NP adsorption increased with increasing salt concentration: this trend was qualitatively explained by molecular theory, as was the role of the PEG grafting in preventing NPs adsorption. Quantitative disagreement between the theoretical predictions and the data was due to NP aggregation, especially at high salt concentration and in the presence of calcium carbonate. Upon aggregation, NP concentrations as determined by NMR T2 were initially overestimated and subsequently corrected using the relaxation rate 1/T2, which is a function of aggregate size and fractal dimension of the aggregate. Our experimental validation of the theoretical predictions of NP adsorption to minerals in the absence of aggregation at various pH and salt conditions demonstrates that molecular theory can be used to determine interactions between NPs and relevant reservoir surfaces. Importantly, this integrated experimental and theoretical approach can be used to gain insight into NP mobility in the reservoir.
authors.affiliation: Department of Biomedical Engineering, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Yoonjee C
authors.initials: YC
authors.lastname: Park
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Paulsen
authors.forename: Rikkert J
authors.initials: RJ
authors.lastname: Nap
authors.forename: Ragnhild D
authors.initials: RD
authors.lastname: Whitaker
authors.forename: Vidhya
authors.initials: V
authors.lastname: Mathiyazhagan
authors.forename: Yi-Qiao
authors.initials: YQ
authors.lastname: Song
authors.forename: Martin
authors.initials: M
authors.lastname: Hürlimann
authors.forename: Igal
authors.initials: I
authors.lastname: Szleifer
authors.forename: Joyce Y
authors.initials: JY
authors.lastname: Wong
mesh_terms: D000327:Adsorption; D002119:Calcium Carbonate / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D012492:Salts / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; D012492:Salts; C000499:ferric oxide; D012822:Silicon Dioxide; D002119:Calcium Carbonate