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Polymorph-dependent titanium dioxide nanoparticle dissolution in acidic and alkali digestions
Silva, R. G., M. N. Nadagouda, C. L. Patterson, S. Panguluri, T. P. Luxton, E. Sahle-Demessie, AND C. A. Impellitteri. Polymorph-dependent titanium dioxide nanoparticle dissolution in acidic and alkali digestions. Environmental Science: Nano. RSC Publishing, Cambridge, Uk, 1(3):284-292, (2014).
The study compared techniques for polymorph-dependent titanium dioxide nanoparticle dissolution in acidic and alkali digestions to determine the accuracy and applicability of digestion methods for detecting, quantifying and characterizing nanomaterials.
Multiple polymorphs (anatase, brookite and rutile) of titanium dioxide nanoparticles (TiO2-NPs) with variable structures were quantified in environmental matrices via microwave-based hydrofluoric (HF) and nitric (HNO3) mixed acid digestion and muffle furnace (MF)-based potassium hydroxide (KOH) fusion. The environmental matrices encompassed stream bed sediments, kaolinite and bentonite. The percentage of Titanium (Ti) recovered from the mixed acid digestion was not statistically different from KOH fusion when anatase and brookite TiO2-NPs were blended in all three environmental matrices. However, the percentage of Ti recovery from the mixed acid digestion for rutile TiO2-polymorph 23 (±5), 12 (±6), 11 (±0.6) was significantly lower than KOH fusion 74 (±4), 53 (±7), 75 (±2) in sediments, kaolinite and bentonite, respectively. Exposing the TiO2-NP spiked samples to elevated heat and pressure reduced the recovery of Ti from all three polymorphs via mixed acid digestion. In contrast, Ti recoveries from the KOH fusion improved after heat and pressure treatment. A narrowing of the X-ray diffraction (XRD) peaks for anatase and brookite after heat and pressure treatment indicated an increase in the aggregation or particle interaction of the TiO2-NPs. The XRD peaks for rutile TiO2-NP polymorph was similar before and after heat and pressure treatment. The current work indicated that mixed acid digestibility of TiO2-NPs is polymorph dependent and the effectiveness of the mixed acid further decreased when Ti-NPs were exposed to heat and pressure perhaps due to Ti-NPs aggregation. The KOH-fusion digestibility is polymorph independent and the effectiveness of the KOH-fusion increased when Ti-NPs were exposed to heat and pressure indicating the positive influence of KOH-fusion on aggregated TiO2-NP polymorphs.