Ionic Strength-Controlled Mn (Hydr)oxide Nanoparticle Nucleation on Quartz: Effect of Aqueous Mn(OH)₂

Abstract

The early formation of manganese (hydr)oxide nanoparticles at mineral-water interfaces is crucial in understanding how Mn oxides control the fate and transport of heavy metals and the cycling of nutrients. Using atomic force microscopy, we investigated the heterogeneous nucleation and growth of Mn (hydr)oxide under varied ionic strengths (IS; 1-100 mM NaNO3). Experimental conditions (i.e., 0.1 mM Mn(2+) (aq) concentration and pH 10.1) were chosen to be relevant to Mn remediation sites. We found that IS controls Mn(OH)2 (aq) formation, and that the controlled Mn(OH)2 (aq) formation can affect the system's saturation and subsequent Mn(OH)2 (s) and further Mn3O4 (s) nanoparticle formation. In 100 mM IS system, nucleated Mn (hydr)oxide particles had more coverage on the quartz substrate than those in 1 mM and 10 mM IS systems. This high IS also resulted in low supersaturation ratio and thus favor heterogeneous nucleation, having better structural matching between nucleating Mn (hydr)oxides and quartz. The unique information obtained in this work improves our understanding of Mn (hydr)oxide formation in natural as well as engineered aqueous environments, such as groundwater contaminated by natural leachate and acid mine drainage remediation.

Reliable electrochemical phase diagrams of magnetic transition metals and related compounds from high-throughput ab initio calculations

“…3b, center and right panels). Furthermore, Mn 3 O 4 is observed to be stable in solutions with pH ≳ 8.5 and [I] 10 −2 -10 −4 M, 65,66 which also strongly supports the DFT-determined phase boundary at pH 8.5~9.5 (V SHE~0 V). In addition, an operando X-ray absorption near-edge structure (XANES) spectroscopy 63 Fig.…”

“…These observations were later confirmed using multiple probes, including high-resolution X-ray diffraction, Raman spectroscopy, and Xray photoelectron spectroscopy. 66 In those experiments, MnOOH or/and Mn(OH) 2 was found to initially precipitate and then transform into Mn 3 O 4 in solutions with [I] ≲ 10 −4 M and pH 10. It should be noted that precisely distinguishing MnOOH from Mn (OH) 2 in experiment is nontrivial, due to their similar layered structures and the uncontrollable degree of hydrogenation.…”

Mechanochemical Redox: Calcination‐free Synthesis of Ceria‐hybrid Catalyst with Ultra‐High Surface Area

“…The existence of Ce 3 + ions (14.5 %) suggested the formation of surface oxygen vacancies. [56,[59][60] The Cu 2p 3/2 and 2p 1/2 binding energies of CeMnCuÀ M were found at 934.1 and 954.1 eV (with Cu satellite separation of 20 eV), which were similar to those for CuO (Figure S2). [61][62] The surface Cu species were in divalent state, which basically follow the redox equation in Table 1 [Eq.…”

“…51,53 The concentration of surface Ce 4 + was estimated to~90.6 % (Figure 3a). [55][56] Two apparent peaks (Figure 3c) around 641.5 and 653.4 eV were attributed to the ionization 2p 3/2 and 2p 1/2 electrons of Mn 2 + ions. [57][58] Therefore, the CeMnÀ M surface was dominated by Mn 2 + and Ce 4 + ions, which roughly follow the redox equation [Eq.…”

“…Raman spectra together with XPS results claimed the presence of oxygen vacancies, which can be considered to be part of the active site for CO oxidation. [56,[75][76] Accordingly, the starting configuration was constructed by removing one O atom bonded with Cu from clean CeMnCuÀ M surface (Figure 9, state i, Supporting Information). Then, CO was firmly adsorbed on top of O v (O v -top) with adsorption energy of À 0.25 eV (Table S5).…”