Reflexion M\"ossbauer analysis of the in situ oxidation products hydroxycarbonate green rust

TL;DR

This study uses miniaturized Mössbauer spectroscopy to analyze the in situ oxidation products of green rust, revealing the transformation process from FeII-III hydroxycarbonate to fully ferric deprotonated form under controlled conditions.

Contribution

It introduces a novel in situ Mössbauer measurement method that tracks green rust oxidation and deprotonation without sample degradation.

Findings

Continuous deprotonation of green rust observed.

Method enables real-time monitoring of oxidation products.

Transformation from hydroxycarbonate to ferric form demonstrated.

Abstract

The purpose of this study is to determine the nature of the oxidation products of FeII-III hydroxycarbonate FeII4FeIII2(OH)12CO3~3H2O (green rust GR(CO32-)) by using the miniaturised M\"ossbauer spectrometer MIMOS II. Two M\"ossbauer measurements methods are used: method (i) with green rust pastes coated with glycerol and spread into Plexiglas sample holders, and method (ii) with green rust pastes in the same sample holders but introduced into a gas-tight cell with a beryllium window under a continuous nitrogen flow. Method (ii) allows us to follow the continuous deprotonation of GR(CO32-) into the fully ferric deprotonated form FeIII6O4(OH)8CO3~3H2O by adding the correct amount of H2O2, without any further oxidation or degradation of the samples.