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Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics

When they are in put in contact with carbonate minerals dangerous environmental pollutants such as Pb2+ and Cd2+ are taken up by the solid phase assemblage and can be removed from aqueous solutions.*

As carbonates can be found almost everywhere and are easily exploitable this makes them interesting materials for environmental remediation.*

However, magnesite ( MGS ) is well-known for the slow dissolution and growth kinetics at room temperature conditions in the so-called dolomite problem.*

In their article “Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics” Fulvio Di Lorenzo, Tobias Arnold and Sergey V. Churakov use in situ atomic force microscopy (AFM) to investigate the growth of {10.4} magnesite surfaces in the absence and in the presence of Pb2+ as well as the effect of solution ageing.*

In their study the authors attempt to answer the question if and under which circumstances magnesium carbonate could be used in removing Pb from wastewater.*

The experimental results presented in above mentioned article have the object to discuss and evaluate the theoretical possibilities and the practical limitations that must be taken into account for the development of environmental remediation technologies based on magnesite.*

The experiments conducted in this study by Fulvio Di Lorenzo et al. demonstrate that, although the thermodynamic conditions are encouraging, the transformation reaction between magnesite and cerrusite makes it improbably that it will play a crucial role in the development of remediation processes for Pb^II pollution.*

The authors of the study conclude that, although the thermodynamic conditions are encouraging, an environmental remediation process based on MGS as the substrate for a solvent-mediated transformation reaction is unlikely to play a crucial part in industrial applications due to the slow kinetics of MGS dissolution. However, the sluggish kinetics of MGS precipitation is favourable for Pb entrapment by the precipitation of carbonate from Mg2+ and Pb2+-bearing solutions, leading to a strong PbII enrichment in the solid phase even in far-from-equilibirum conditions.*

The in situ flow-through Atomic Force Microscopy was performed using Arrow-UHFAuD AFM probes in tapping mode.

Figure 8 from “Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics” by Fulvio Di Lorenzo et al:
In situ observation of {10.4} surfaces of MGS in contact with acidic solution, pH 4 (HNO3). The images were acquired in tapping mode. The first row corresponds to height channels, while the second row reports the respective amplitude channels. (A) The dissolution at 25 °C is sluggish and it is not possible to detect any dissolution feature. (B) In the same conditions but at higher temperature (60 °C), dissolution features are observed on the {10.4} surfaces of MGS, despite the retrograde solubility. Yellow and blue lines of constant size are used to highlight the evolution of etch pits and step edges, respectively. This evidence demonstrates that the existence of kinetic barriers controls the dissolution of MGS at room temperature conditions. NanoWorld Arrow-UHFAuD AFM probes were used. — Figure 8 from “*Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics*” by Fulvio Di Lorenzo et al:
In situ observation of {10.4} surfaces of MGS in contact with acidic solution, pH 4 (HNO3). The images were acquired in tapping mode. The first row corresponds to height channels, while the second row reports the respective amplitude channels. (A) The dissolution at 25 °C is sluggish and it is not possible to detect any dissolution feature. (B) In the same conditions but at higher temperature (60 °C), dissolution features are observed on the {10.4} surfaces of MGS, despite the retrograde solubility. Yellow and blue lines of constant size are used to highlight the evolution of etch pits and step edges, respectively. This evidence demonstrates that the existence of kinetic barriers controls the dissolution of MGS at room temperature conditions.

*Fulvio Di Lorenzo, Tobias Arnold, and Sergey V. Churakov
Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics
Minerals 2021, 11(4), 415
DOI: https://doi.org/10.3390/min11040415

Please follow this external link to read the full article: https://www.mdpi.com/2075-163X/11/4/415

Open Access : The article “Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics” by Fulvio Di Lorenzo, Tobias Arnold, and Sergey V. Churakov is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Influence of orientation and ferroelectric domains on the photochemical reactivity of La2Ti2O7

In the article “Influence of orientation and ferroelectric domains on the photochemical reactivity of La₂Ti₂O₇” Mingyi Zhang, Paul A. Salvador and Gregory S. Rohrer describe how they measured the effects of crystal orientation and ferroelectric domain structure on the photochemical reactivity of La₂Ti₂O_7.*

The reactivity is greatest on (001) surfaces (this is the orientation of the layers in this (110)p layered perovskite structure) while surfaces perpendicular to this orientation have the least reactivity. Complex domain structures were observed within the grains, but they appeared to have no effect on the photocathodic reduction of silver, in contrast to previous observations on other ferroelectrics. La₂Ti₂O₇ is an example of a ferroelectric oxide in which the crystal orientation has a greater influence on the photochemical reactivity than polarization from the internal domain structure. *

NanoWorld™ conductive Platinum Iridium coated Arrow-EFM AFM probes were used for the Piezo-force microscopy (PFM) that was used to determine the ferroelectric domain structure on the surface. *

The ferroelectric domains on the surface were found to have irregular shapes and there was no correlation between the pattern of silver reduction and the domain shape. The results indicate that the ferroelectric polarization of La2Ti2O7 does not alter the reactivity enough to overcome the influence of the anisotropic crystal structure. *

Fig. 6 a and b from “Influence of orientation and ferroelectric domains on the photochemical reactivity of La2Ti2O7” by Mingyi Zhang et al.
A La2Ti2O7 grain imaged with different modalities. (a) a PFM out-of-plane amplitude image. (b) a PFM out-of-plane phase image. A meandering black line in (a), marked by the arrow, corresponds to a change from light to dark contrast in the phase image. The dark (light) contrast corresponds to regions with -180° (0°) phase shift. NanoWorld conductive Arrow-EFM AFM probes were used for the piezo-force microscopy.

Please have a look at the full article cited below for the full figure — Fig. 6 a and b from “Influence of orientation and ferroelectric domains on the photochemical reactivity of La2Ti2O7” by Mingyi Zhang et al.
A La2Ti2O7 grain imaged with different modalities. (a) a PFM out-of-plane amplitude image. (b) a PFM out-of-plane phase image. A meandering black line in (a), marked by the arrow, corresponds to a change from light to dark contrast in the phase image. The dark (light) contrast corresponds to regions with -180° (0°) phase shift. Please have a look at the full article cited below for the full figure

*Mingyi Zhang, Paul A. Salvador and Gregory S.Rohrer
Influence of orientation and ferroelectric domains on the photochemical reactivity of La₂Ti₂O₇
Journal of the European Ceramic Society (2020)
DOI: https://doi.org/10.1016/j.jeurceramsoc.2020.09.020

Please follow this external link to read the full article https://www.sciencedirect.com/science/article/pii/S0955221920307445

Open Access : The article “Influence of orientation and ferroelectric domains on the photochemical reactivity of La₂Ti₂O₇” by Mingyi Zhang, Paul A. Salvador, Gregory S. Rohrer is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation

Phonon polaritons (PhPs) have attracted significant interest in the nano-optics communities because of their nanoscale confinement and long lifetimes. Although PhP modification by changing the local dielectric environment has been reported, controlled manipulation of PhPs by direct modification of the polaritonic material itself has remained elusive.*

In the article “Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation” Yingjie Wu, Qingdong Ou, Yuefeng Yin, Yun Li, Weiliang Ma, Wenzhi Yu, Guanyu Liu, Xiaoqiang Cui, Xiaozhi Bao, Jiahua Duan, Gonzalo Álvarez-Pérez, Zhigao Dai, Babar Shabbir, Nikhil Medhekar, Xiangping Li, Chang-Ming Li, Pablo Alonso-González and Qiaoliang Bao demonstrate an effective chemical approach to manipulate PhPs in α-MoO3 by the hydrogen intercalation-induced perturbation of lattice vibrations.*

Their methodology establishes a proof of concept for chemically manipulating polaritons, offering opportunities for the growing nanophotonics community.*

The surface topography and near-field images presented in this article were captured using a commercial s-SNOM setup with a platinum iridium coated NanoWorld Arrow-NCPt AFM probe in tapping mode.*

Fig. 2 a) from “Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation” by Yingjie Wu et al. :
Reversible switching of PhPs in the L-RB of α-MoO3 a Schematic of the s-SNOM measurement and PhP propagation in a typical H-MoO3/α-MoO3 in-plane heterostructure.
2 a Schematic of the s-SNOM measurement and PhP propagation in a typical H-MoO3/α-MoO3 in-plane heterostructure. P — Fig. 2 a) from “*Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation*” by Yingjie Wu et al. :
Reversible switching of PhPs in the L-RB of α-MoO3 a Schematic of the s-SNOM measurement and PhP propagation in a typical H-MoO3/α-MoO3 in-plane heterostructure.
2 a Schematic of the s-SNOM measurement and PhP propagation in a typical H-MoO3/α-MoO3 in-plane heterostructure. Please follow this external link for the full figure: https://www.nature.com/articles/s41467-020-16459-3/figures/2

*Yingjie Wu, Qingdong Ou, Yuefeng Yin, Yun Li, Weiliang Ma, Wenzhi Yu, Guanyu Liu, Xiaoqiang Cui, Xiaozhi Bao, Jiahua Duan, Gonzalo Álvarez-Pérez, Zhigao Dai, Babar Shabbir, Nikhil Medhekar, Xiangping Li, Chang-Ming Li, Pablo Alonso-González & Qiaoliang Bao
Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation
Nature Communications volume 11, Article number: 2646 (2020)
DOI: https://doi.org/10.1038/s41467-020-16459-3

Please follow this external link to read the full article https://rdcu.be/b46eT

Open Access The article “ Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation “ by Yingjie Wu, Qingdong Ou, Yuefeng Yin, Yun Li, Weiliang Ma, Wenzhi Yu, Guanyu Liu, Xiaoqiang Cui, Xiaozhi Bao, Jiahua Duan, Gonzalo Álvarez-Pérez, Zhigao Dai, Babar Shabbir, Nikhil Medhekar, Xiangping Li, Chang-Ming Li, Pablo Alonso-González and Qiaoliang Bao is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.