Iron Oxide with Different Crystal Phases (α- and γ-Fe₂O₃) in Electroanalysis and Ultrasensitive and Selective Detection of Lead(II): An Advancing Approach Using XPS and EXAFS

Abstract

Iron oxide with different crystal phases (α- and γ-Fe2O3) has been applied to electrode coatings and been demonstrated to ultrasensitive and selective electrochemical sensing toward heavy metal ions (e.g., Pb(II)). A range of Pb(II) contents in micromoles (0.1 to 1.0 μM) at α-Fe2O3 nanoflowers with a sensitivity of 137.23 μA μM(-1) cm(-2) and nanomoles (from 0.1 to 1.0 nM) at γ-Fe2O3 nanoflowers with a sensitivity of 197.82 μA nM(-1) cm(-2) have been investigated. Furthermore, an extended X-ray absorption fine structure (EXAFS) technique was applied to characterize the difference of local structural environment of the adsorbed Pb(II) on the surface of α- and γ-Fe2O3. The results first showed that α- and γ-Fe2O3 had diverse interaction between Pb(II) and iron (hydro)oxides, which were consistent with the difference of electrochemical performance. Determining the responses of Cu(II) and Hg(II) as the most appropriate choice for comparison, the stripping voltammetric quantification of Pb(II) with high sensitivity and selectivity at γ-Fe2O3 nanoflower has been demonstrated. This work reveals that the stripping performances of a nanomodifier have to be directly connected with its intrinsic surface atom arrangement.

The evaluation of the photocatalytic activity of magnetic and non-magnetic polymorphs of Fe 2 O 3 in natural sunlight exposure: A comparison of photocatalytic activity

“…The intensity of the peak corresponding to the surface oxygen was significantly higher for γ as compared to α-Fe 2 O 3 that depicted the higher tendency of γ-Fe 2 O 3 towards surface O-H formation. The observation was in compliance with that reported earlier[61,62]. The deconvoluted, fitted Fe 2p peaks of both the polymorphs are compared inFig.…”

The effect of Fe2O3 crystal phases on CO2 hydrogenation

“…In these studies, iron oxide almost presents in α-Fe 2 O 3 [15,21,26] or Fe 3 O 4 [25] crystal phase in the as-prepared catalysts. Considering that γ-Fe 2 O 3 is one kind of iron oxide as common as α-Fe 2 O 3 [27,28], it is surprising that there are very few reports about the behavior of γ-Fe 2 O 3 in CO 2 hydrogenation. Al-Dossary et al found γ-Fe 2 O 3 coexisted with α-Fe 2 O 3 in the catalysts, but no benefit from γ-Fe 2 O 3 was disclosed [21].…”

“…Al-Dossary et al found γ-Fe 2 O 3 coexisted with α-Fe 2 O 3 in the catalysts, but no benefit from γ-Fe 2 O 3 was disclosed [21]. However, it has been confirmed that γ-Fe 2 O 3 is superior to α-Fe 2 O 3 in other catalytic reactions, such as photodecomposition of H 2 S [29], selective catalytic reduction of NO X with NH 3 [30], electroanalysis and ultrasensitive detection of Pb 2+ [27], WGS reaction [31] and so on. The lack on the performance of γ-Fe 2 O 3 in CO 2 hydrogenation makes it necessary to study Fe catalyst in γ-Fe 2 O 3 phase, not only to supply the knowledge about γ-Fe 2 O 3 in the reaction, but also to find active catalyst to make CO 2 profitable.…”

The crystal facet-dependent electrochemical performance of TiO2 nanocrystals for heavy metal detection: Theoretical prediction and experimental proof

“…Adsorption-release model is often used to describe the stripping voltammetric technique [35]. Scheme 1 illuminates how adsorption-release process affects the heavy metal ions sensing on the TiO2 (001) and (101) facets.…”