Magnetic-Field-Induced Painting-Out of Precipitation Bands of Mn–Fe-Based Prussian Blue Analogues in Water–Glass Gels

Abstract

The effect of magnetic fields on the precipitation patterns of Mn–Fe-based Prussian blue analogues in water–glass gels was studied using X-ray fluorescence and X-ray absorption near-edge structure spectroscopies. Three sets of two glass tubes, A, B, and C, were prepared using 1.20 M Mn 2+ /0.24 M [Fe(CN) 6 ] 3– , 0.60 M Mn 2+ /0.12 M [Fe(CN) 6 ] 3– , and 0.30 M Mn 2+ /0.06 M [Fe(CN) 6 ] 3– solutions, respectively. From each of these sets, one tube was subjected to a magnetic field of 0.5 T, whereas the other was not. The magnetic field barely affected the Liesegang bands in the tube from Set A, but there were noticeable differences in the tubes from sets B and C, where (1) the amounts of electrolytes were small, (2) the dominant Mn species was [Mn(H 2 O) 6 ] 2+ , and (3) there was stochasticity of the band formation. In these regions, the magnetic field painted out the spaces between the precipitation bands, even enhancing the formation of additional bands.

Low-Cost, High-Performance Sample Cell for X-Ray Spectroscopy of Solutions and Gels Made from Plastic Straw

“…The relative XRF intensity, where the Fe Kα intensity at the bottom of the samples in the initial stages (∼1 h after the addition of the outer electrolyte sols; not shown here for simplicity), was set to 1, according to the procedure used in previous studies. [13][14][15] In Gel-1 ( Fig. 6(a)), a peak in the Fe Kα distribution at the gel boundary (X ≈ 0 mm), similar to one previously found, 10 was observed, suggesting Fe accumulation near the boundary.…”

“…The combined use of X-ray fluorescence (XRF) spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy was experimentally proven to be useful for obtaining such in situ, elemental-selective information, 9 particularly for selforganized, discrete precipitation banding of Prussian blue analogs (PBA) in water-glass gels. [10][11][12][13][14][15] In previous X-ray spectroscopic studies on self-organized systems, [9][10][11][12][13][14][15] quartz capillary tubes have been employed as sample cells. These have also been widely used for X-ray diffraction measurements of protein, liquids, liquid crystals, and single crystals and powder specimens that can be degraded by air and moisture.…”

An Electrochemical System for Forming Periodic Precipitation Bands of Cu-Fe-Based Prussian Blue Analogues

“…Second, the optimal experimental conditions to produce well-controlled periodic bands should be further explored. Conventional precipitation banding of PBA in gels (using the setup in Figure 1a) is known to be dependent on the experimental conditions, including the gel type, gel density [29], and presence of magnetic fields [37]. The precipitation patterns formed using the proposed electrochemical setup should be examined while varying these factors (as well as the initial concentration of [Fe(CN)6] 3-and the gel length).…”

Highly Resolved Mn Kβ Emission: A Potential Probe in Laboratory for Analysis of Ligand Coordination around Mn Atoms in Gels and Solutions

“…Note also that linefocused X-ray beams, which are produced by the curved monochromator, are preferable to examine position dependence of HR-XRF in (pseudo-) one-dimensional systems, such as Liesegang bands in gels. [25][26][27]29 In addition, line-focused, monochromatic X-ray incidence allows us to easily incorporate the HR-XRF setup with other X-ray instruments, such as smallangle X-ray scattering (SAXS) diffractometers 34 (SAXS is a standard technique to study structural properties of gels and solutions). 35 Mn Kβ emission from the sample was analyzed and focused by a Ge (440) spherically bent Johann-type crystal (Saint-Gobain Crystals; bending radius, 820 mm; diameter, 75 mm).…”

“…9,10,12 Furthermore, the selection of Mn Kβ emission is also justified by the following. Recently, Mn-Fe-based Prussian blue analogs (Mn-Fe PBAs) have been found to show several interesting crystallization/precipitation phenomena in gels, [25][26][27][28][29] and their local structure around Mn atoms (examined by XAFS spectroscopy at SR facilities) has become the subject of intense research interest. [25][26][27]30 Meanwhile, the local structure during the development of Mn-Fe PBA precipitation bands (which can significantly influence the quality of Mn-Fe PBAs finally formed 31 ) has not been explored yet, because the time required for their full development (∼10 days) is too long to continuously monitor their XAFS at SR facilities.…”