This study presents the effects of the heterogeneous nucleation rate of Mn(OH)2 (s) on the structural match at the interface between quartz and Mn(OH)2 (s) in water. Mn (hydr)oxide affects the cycling of nutrients and fate of heavy metals in environmental systems due to its rich redox chemistry and sorption capacity. While the reactivity of Mn (hydr)oxide has been studied widely, thus far, technical limitations have kept us from obtaining a clear picture of how Mn (hydr)oxides start to form and how they grow on mineral surfaces. Only a few studies have considered the heterogeneous nucleation and growth behaviors of Mn (hydr)oxide. Here, we introduce the idea that the heterogeneous nucleation rate affects the structural match with a foreign substrate in an aqueous system. Among various Mn (hydr)oxide phases, Mn(OH)2 (s) forms as one of initial nuclei in environmental systems. We changed pH conditions (pH 9.8; pH 9.9; pH 10.1) to control the supersaturation of Mn(OH)2 (s). Atomic force microscopy (AFM) and grazing incident small angle X-ray scattering (GISAXS) provided the vertical and lateral dimensions of nuclei on quartz, respectively. Under varied pH conditions and elapsed times, the analyzed dimensions provided the contact angles, θ, of the heterogeneously nucleated Mn(OH)2 (s) nanoparticles, and consequently the structural match (m = cos θ). Based on the calculated contact angles, we demonstrated that faster nucleation (at high supersaturation) yields a poorer structural match (with a high contact angle) between Mn(OH)2 (s) and quartz over a 1hr reaction. The m values were around 0.96, 0.92, and 0.82 at pH 9.8, 9.9, and 10.1, respectively. For the first time, by fitting the obtained m values using heterogeneous classical nucleation theory, we quantified the interfacial energies between Mn(OH)2 (s) and water, γnf = 71 ± 7 mM/m2. The calculated m values and γnf provide the variance of the interfacial energy between Mn(OH)2 (s) and quartz, γsn = 262–272 mM/m2. This study provides new information for understanding heterogeneous nucleation, not only of Mn(OH)2 (s), but also of other minerals controlled by kinetics in environmental systems and material syntheses.

Heterogeneous nucleation rate of Mn(OH)2 (s) controls structural match between Mn(OH)2 (s) and quartz substrate

253rd National Meeting (2017)

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