Manganese Oxide Nanoarchitectures as Broad-Spectrum Sorbents for Toxic Gases

Abstract

We demonstrate that sol-gel-derived manganese oxide (MnOx) nanoarchitectures exhibit broad-spectrum filtration activity for three chemically diverse toxic gases: NH3, SO2, and H2S. Manganese oxides are synthesized via the reaction of NaMnO4 and fumaric acid to form monolithic gels of disordered, mixed-valent Na-MnOx; incorporated Na(+) is readily exchanged for H(+) by subsequent acid rinsing to form a more crystalline H-MnOx phase. For both Na-MnOx and H-MnOx forms, controlled pore-fluid removal yields either densified, yet still mesoporous, xerogels or low-density aerogels (prepared by drying from supercritical CO2). The performance of these MnOx nanoarchitectures as filtration media is assessed using dynamic-challenge microbreakthrough protocols. We observe technologically relevant sorption capacities under both dry conditions and wet (80% relative humidity) for each of the three toxic industrial chemicals investigated. The Na-MnOx xerogels and aerogels provide optimal performance with the aerogel exhibiting maximum sorption capacities of 39, 200, and 680 mg g(-1) for NH3, SO2, and H2S, respectively. Postbreakthrough characterization using X-ray photoelectron spectroscopy (XPS) and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms that NH3 is captured and partially protonated within the MnOx structure, while SO2 undergoes oxidation by the redox-active oxide to form adsorbed sulfate at the MnOx surface. Hydrogen sulfide is also oxidized to form a combination of sulfate and sulfur/polysulfide products, concomitant with a decrease in the average Mn oxidation state from 3.43 to 2.94 and generation of a MnOOH phase.

Hierarchical branched α-MnO2: one-step synthesis and catalytic activity

“…The survey spectrum shows characteristic peaks for Mn, O and C, which is similar to that reported. 30 In Fig. 1b, we can see clearly two major XPS peaks of Mn 2p 3/2 at 642.2 eV and Mn 2p 1/2 at 654.0 eV, which conrmed the presence of MnO 2 .…”

Efficient Electrochemical Water Oxidation and Oxidative Degradation of Rhodamine B: A Comparative Study Using High‐Purity Birnessites Containing Li+, Na+ or K+ Ions

“…XRD spectra suggested that the crystallinities followed a descending sequence of Na‐Bir> Li‐Bir> K‐Bir. On the one hand, a higher crystallinity generated fewer lattice defects, accompanied by lower chemical activity . On the other hand, a lower crystallinity gave smaller particles and larger reaction interface.…”

Oxidization of hydrogen sulfide in biogas by manganese (IV) oxide particles

“…Manganese dioxide is also active in the removal of sulphide [42,[48][49][50][51]. It was furthermore found that H 2 S reacts significantly faster with KMnO 4 than with MnO 2 [52], but the complex reactions between KMnO 4 and H 2 S are still not clearly understood [12].…”