Physicochemical Characteristics of the Birnessite and Todorokite Synthesized Using Various Methods

Abstract

The synthesis methods used to produce todorokite (10 Å manganate, OMS-1) and birnessite (7 Å manganate), which are abundant in marine manganese nodules, have been studied to confirm whether pure mineral phases can be obtained and to compare their physicochemical characteristics. The physicochemical characteristics of todorokite and its precursor Na–birnessite can vary widely based on the precursors used during their synthesis. Birnessite can be synthesized via three mechanisms, i.e., the oxidation of Mn2+, a redox reaction between Mn2+ and MnO4−, or the reduction of MnO4−. Herein, four precursors are used to synthesize birnessite using different methods before being transformed into todorokite. The characteristics of the birnessite and todorokite synthesized using different methods are investigated via X-ray diffraction (XRD), chemical analysis, Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (SEM). Based on the method used, birnessite and todorokite exhibit distinct physicochemical features, including crystallinity, crystal structure, specific surface area, oxidation state of manganese, thermal stability, and morphology. Thus, the characteristics of birnessite and todorokite are closely correlated, indicating the importance of designing suitable methods to synthesize them for specific applications.

Study of Mono- and Bimetallic Fe and Mn Oxide-Supported Clinoptilolite for Improved Pb(II) Removal

“…1%. Only the MnOx-zeolite spectrum was enriched characteristically with a 1445 cm −1 and a small 876 cm −1 absorption band, likely assigning MnO 2 minerals [ 20 , 21 , 22 ]. These absorption bands were not ob-served in the FeO(OH)-MnOx-zeolite spectrum, probably due to strong alkalic treatment of MnOx-zeolite and the covering of its surface with FeO(OH).…”

“…These absorption bands were not ob-served in the FeO(OH)-MnOx-zeolite spectrum, probably due to strong alkalic treatment of MnOx-zeolite and the covering of its surface with FeO(OH). The bands appearing at 400–800 cm −1 in the IR spectrum of MnOx-zeolite may have reflected the properties of the Mn-O stretching vibrations [ 21 , 22 ]. The bands in the range of 748–764 cm −1 , which are missing in our MnOx-zeolite spectrum, are, according to literature [ 21 ], the characteristic bands of tunnel-structured pyrolusite.…”

“…The bands appearing at 400–800 cm −1 in the IR spectrum of MnOx-zeolite may have reflected the properties of the Mn-O stretching vibrations [ 21 , 22 ]. The bands in the range of 748–764 cm −1 , which are missing in our MnOx-zeolite spectrum, are, according to literature [ 21 ], the characteristic bands of tunnel-structured pyrolusite. This fact might support the occurrence of birnessite in our sample.…”

“…An inhomogeneous dispersion of Fe(III) and Mn(IV) oxihydroxides in the clinoptilolite rock was deduced. Although the crystal size and detailed morphology of the samples was different, birnessite generally shows an irregular plate-like morphology [ 21 , 24 ]. The morphology of the synthetic K-birnessite sample has a fairly similar SEM image to that of a baerite rose [ 24 ].…”

“…Pb(II) ions from solutions may also intercalate mechanically between its parallel layers (inner sphere complex adsorption), which is typical for some manganese oxide structure (birnessite), and likely also occurs on the zeolite surface ( Figure 6 , Table 3 ). According to some literature [ 21 , 23 , 24 ], synthetic birnessite removes almost an order of magnitude more Pb(II) from solution than the Fe oxides do and the natural pyrolusite removes a similar amount of Pb(II) from solution as many Fe oxides. This statement, correlated with Table 3 and Figure 6 , might support the predominant occurrence of birnessite on the surface of our MnOx-zeolite (see also Section 3.2 ).…”