Effect of Zn(II) coprecipitation on Mn(II)-induced reductive transformation of birnessite

Coupled Substitutions in Natural MnO(OH) Polymorphs: Infrared Spectroscopic Investigation

“…Feitknechtite has been synthesized in the reaction of nanocrystalline vernadite (δ-MnO 2 ) with aqueous solutions containing Mn 2+ cations, at a pH below 9 [41]. It was shown [37] that in the presence of Mn 2+ cations, transformation of a birnessite-type MnO 2 compound into manganite (Mng) proceeds via the intermediate unstable feitknechtite (Ftk) phase in accordance with the scheme Mn 2+ (aq) + MnO 2 + 2H 2 O → 2Ftk + 2H + (aq); Ftk → Mng. The formation of the intermediate feitknechtite phase was faster for Zncoprecipitated birnessite than for pure birnessite.…”

“…The broad absorption bands at 2010 and 2600 cm −1 correspond to stretching vibrations of OH groups forming strong hydrogen bonds. The distinct narrow bands at 1085, 1114, and 1150 cm −1 are due to Mn 3+ •••O-H bending vibrations and are considered to be characteristic bands of manganite [37]. The absorptions in the range of 400-600 cm −1 correspond to Mn 3+ -O stretching modes, and the shoulder at 950 is an overtone or a Mn 3+ -O stretching combination mode.…”

Understanding the role of manganese oxides in retaining harmful metals: Insights into oxidation and adsorption mechanisms at microstructure level

“…For instance, reproducing todorokite under low temperatures and neutral environmental conditions in the lab is difficult. The current methods for synthesizing todorokite from layered Mn oxides typically require conditions that significantly differ from those in nature, such as elevated pH levels [ 18 , 105 , 255 , 256 ]. The aforementioned observation outcome exhibits a notable disparity from the prevailing occurrence of todorokite in naturally occurring low-temperature settings [ 18 ].…”