Since the mid-1990s, I am of the opinion that the minute pore spaces within the sediments may have a different chemistry than the bulk media due to the surface charge of the sediment grains, their sharp curvature, and therefore enhanced electric field strength under such an environment.
In continuation of those thoughts a recent work (Ma et al., 2018) using a combination of cryo-microscopy and single-particle 3D reconstruction suggested the existence of silica cages of around 10 nm size that they christened as "silicages" with dodecahedral structure. These microenvironments are different from bulk media properties and have the potential for the separation of isotopes as these "silicages" are effective substrates for column separation. Their extended uses are in the areas of wastewater treatment and separation of organic molecules.
Such a change in the properties of bulk water within the microenvironment can be ascribed to the low dielectric constant of ~2 for the water (Fumagalli et al., 2018). The consequences of such a very low dielectric constant of water within nanoscale pore spaces has ramifications for geochemistry. Some of them include dissolution and precipitation of minerals, weathering and remobilization of major and trace elements in the hyporheic zone of the riverine environment, the hydrocarbon potential of oil-bearing formations (water shall have increased miscibility with oil in the nano-pore spaces), solubility of calcium carbonate in the karst regions, pore water chemistry and isotopic fractionation during early diagenesis, and adsorption.
I believe that the anomalous characteristics of water within the confined space is also applicable to the boundary layers of the mineral grains. For example, the leaching of trace elements from the aerosols (for a review, please read Mahowald et al., 2018) is a highly complex process. Now consider an aerosol particle in the upper atmosphere with mineral dust as a nucleus and condensed water around it. Also, assume that the aerosol has natural organic molecules such as formate and acetate that can be excited by irradiation of light (or, UV).
1) The aerosols with the fine mineral particle as nuclei can have a boundary layer around it where the properties of water shall be different from its bulk chemistry; 2) The fine mineral particles shall have the surface charges that may impact the chemical reactions occurring within the boundary layer. 3) The natural organics shall interact with dissolved trace elements in the aerosol, such as Fe and Cu, to generate reactive oxygen species by photochemical reactions. Thus, the aerosols present an exciting phase for the study of biogeochemical cycling of trace elements - especially that of Fe, Mn, Cu.)
The same principles are applicable for the trace elements speciation in the boundary layer surrounding the phytoplankton cells. The redox chemistry of the trace elements within the boundary layer is highly complex and difficult to study. However, the scattering and polarisation of light within the boundary layer may serve as a probe for the environmental conditions in the boundary layer. From those results, it could be possible to understand the speciation of trace elements. For example, the Circular Dichroism Spectroscopy (CDS) can probe the secondary structure of macromolecules like the protein. Moreover, the secondary structures of proteins are prone to environmental conditions such as pH and temperature. Similarly, the nature of the boundary layers surrounding algae cells can be probed using Vibrational Optical Activity (Vibrational Circular Dichroism, and Vibrational Raman Optical Activity). Since biological molecules are chiral, and the algal exudates meant to manipulate the speciation of trace elements are expected to exhibit chirality, studying their optical properties using the techniques mentioned above may provide more insight into the conditions prevailing within the boundary layer.
Thus, I consider that the surface change, electric field strength, the dielectric constant of water, the surface energy of "adsorption sites" or, "sites of molecular interaction" can have a tremendous impact on the properties of the interface. Understanding the chemistry of the interface has ramifications for many fields in geochemistry.
A recent investigation by Schaefer et al. (2018) of silica mineral dissolution kinetics at the "boundary layer" using surface-specific spectroscopy (V-SFG), revealed that the dissolution products reached saturation within a very short time (tens of hours) compared to silica dissolution kinetics observed using bulk solutions, indicating that the mineral-water interface has distinct properties. I am of the opinion that such an attainment of fast equilibrium conditions during silica dissolution arises from the distinctive properties of the interface (or, boundary layer) described above.
I extend that "boundary layer theory" of interface chemistry to the application of mineral dissolution. And, I state that the surface "sites of molecular interaction" of a mineral have their surface energy distribution described by the Boltzmann function, akin to that of a porous media in that, the energetic heterogeneity of the "sites of molecular interaction" can be derived from the theory of surface adsorption (Anandaraj et al., 2017). Then, I propose that the surface roughness of the mineral introduces an "energetic heterogeneity" onto the "sites of molecular interaction" that affects the Boltzmann energy distribution function of that surface. Then I suppose that the surface charge of the mineral, the electric field strength of curved surfaces that arises due to surface roughness (that introduces the geometric heterogeneity), the dielectric constant of water, the surface energy of "adsorption sites" or, "sites of molecular interaction" are the forces that play a major role in the dissolution kinetics of a mineral. The same principles are applicable to describe trace elements speciation and biological uptake within the boundary layers.
Note: This article is based on my earlier posts in the LinkedIn with most of the portions being reproduced here in a coherent way.
a) https://www.linkedin.com/feed/update/urn:li:activity:6439327245055156224
b) https://www.linkedin.com/feed/update/urn:li:activity:6417815034390474753
c) https://www.linkedin.com/feed/update/urn:li:activity:6424147843132555264
d) https://www.linkedin.com/feed/update/urn:li:activity:6422264668093546496
References:
Anandaraj, B., Eswaramoorthi, S., Rajesh, T.P., Aravind, J., Suresh Babu, P., 2018. Chromium(VI) adsorption by Codium tomentosum: evidence for adsorption by porous media from sigmoidal dose–response curve. Int. J. Environ. Sci. Technol. 15, 2595–2606. https://doi.org/10.1007/s13762-017-1488-7
Fumagalli, L., Esfandiar, A., Fabregas, R., Hu, S., Ares, P., Janardanan, A., Yang, Q., Radha, B., Taniguchi, T., Watanabe, K., Gomila, G., Novoselov, K.S., Geim, A.K., 2018. Anomalously low dielectric constant of confined water. Science 360, 1339–1342. https://doi.org/10.1126/science.aat4191
Ma, K., Gong, Y., Aubert, T., Turker, M.Z., Kao, T., Doerschuk, P.C., Wiesner, U., 2018. Self-assembly of highly symmetrical, ultrasmall inorganic cages directed by surfactant micelles. Nature 558, 577–580. https://doi.org/10.1038/s41586-018-0221-0
Mahowald, N.M., Hamilton, D.S., Mackey, K.R.M., Moore, J.K., Baker, A.R., Scanza, R.A., Zhang, Y., 2018. Aerosol trace metal leaching and impacts on marine microorganisms. Nat Commun 9, 2614. https://doi.org/10.1038/s41467-018-04970-7
Schaefer, J., Backus, E.H.G., Bonn, M., 2018. Evidence for auto-catalytic mineral dissolution from surface-specific vibrational spectroscopy. Nat Commun 9, 3316. https://doi.org/10.1038/s41467-018-05762-9
In continuation of those thoughts a recent work (Ma et al., 2018) using a combination of cryo-microscopy and single-particle 3D reconstruction suggested the existence of silica cages of around 10 nm size that they christened as "silicages" with dodecahedral structure. These microenvironments are different from bulk media properties and have the potential for the separation of isotopes as these "silicages" are effective substrates for column separation. Their extended uses are in the areas of wastewater treatment and separation of organic molecules.
Such a change in the properties of bulk water within the microenvironment can be ascribed to the low dielectric constant of ~2 for the water (Fumagalli et al., 2018). The consequences of such a very low dielectric constant of water within nanoscale pore spaces has ramifications for geochemistry. Some of them include dissolution and precipitation of minerals, weathering and remobilization of major and trace elements in the hyporheic zone of the riverine environment, the hydrocarbon potential of oil-bearing formations (water shall have increased miscibility with oil in the nano-pore spaces), solubility of calcium carbonate in the karst regions, pore water chemistry and isotopic fractionation during early diagenesis, and adsorption.
I believe that the anomalous characteristics of water within the confined space is also applicable to the boundary layers of the mineral grains. For example, the leaching of trace elements from the aerosols (for a review, please read Mahowald et al., 2018) is a highly complex process. Now consider an aerosol particle in the upper atmosphere with mineral dust as a nucleus and condensed water around it. Also, assume that the aerosol has natural organic molecules such as formate and acetate that can be excited by irradiation of light (or, UV).
1) The aerosols with the fine mineral particle as nuclei can have a boundary layer around it where the properties of water shall be different from its bulk chemistry; 2) The fine mineral particles shall have the surface charges that may impact the chemical reactions occurring within the boundary layer. 3) The natural organics shall interact with dissolved trace elements in the aerosol, such as Fe and Cu, to generate reactive oxygen species by photochemical reactions. Thus, the aerosols present an exciting phase for the study of biogeochemical cycling of trace elements - especially that of Fe, Mn, Cu.)
The same principles are applicable for the trace elements speciation in the boundary layer surrounding the phytoplankton cells. The redox chemistry of the trace elements within the boundary layer is highly complex and difficult to study. However, the scattering and polarisation of light within the boundary layer may serve as a probe for the environmental conditions in the boundary layer. From those results, it could be possible to understand the speciation of trace elements. For example, the Circular Dichroism Spectroscopy (CDS) can probe the secondary structure of macromolecules like the protein. Moreover, the secondary structures of proteins are prone to environmental conditions such as pH and temperature. Similarly, the nature of the boundary layers surrounding algae cells can be probed using Vibrational Optical Activity (Vibrational Circular Dichroism, and Vibrational Raman Optical Activity). Since biological molecules are chiral, and the algal exudates meant to manipulate the speciation of trace elements are expected to exhibit chirality, studying their optical properties using the techniques mentioned above may provide more insight into the conditions prevailing within the boundary layer.
Thus, I consider that the surface change, electric field strength, the dielectric constant of water, the surface energy of "adsorption sites" or, "sites of molecular interaction" can have a tremendous impact on the properties of the interface. Understanding the chemistry of the interface has ramifications for many fields in geochemistry.
A recent investigation by Schaefer et al. (2018) of silica mineral dissolution kinetics at the "boundary layer" using surface-specific spectroscopy (V-SFG), revealed that the dissolution products reached saturation within a very short time (tens of hours) compared to silica dissolution kinetics observed using bulk solutions, indicating that the mineral-water interface has distinct properties. I am of the opinion that such an attainment of fast equilibrium conditions during silica dissolution arises from the distinctive properties of the interface (or, boundary layer) described above.
I extend that "boundary layer theory" of interface chemistry to the application of mineral dissolution. And, I state that the surface "sites of molecular interaction" of a mineral have their surface energy distribution described by the Boltzmann function, akin to that of a porous media in that, the energetic heterogeneity of the "sites of molecular interaction" can be derived from the theory of surface adsorption (Anandaraj et al., 2017). Then, I propose that the surface roughness of the mineral introduces an "energetic heterogeneity" onto the "sites of molecular interaction" that affects the Boltzmann energy distribution function of that surface. Then I suppose that the surface charge of the mineral, the electric field strength of curved surfaces that arises due to surface roughness (that introduces the geometric heterogeneity), the dielectric constant of water, the surface energy of "adsorption sites" or, "sites of molecular interaction" are the forces that play a major role in the dissolution kinetics of a mineral. The same principles are applicable to describe trace elements speciation and biological uptake within the boundary layers.
Note: This article is based on my earlier posts in the LinkedIn with most of the portions being reproduced here in a coherent way.
a) https://www.linkedin.com/feed/update/urn:li:activity:6439327245055156224
b) https://www.linkedin.com/feed/update/urn:li:activity:6417815034390474753
c) https://www.linkedin.com/feed/update/urn:li:activity:6424147843132555264
d) https://www.linkedin.com/feed/update/urn:li:activity:6422264668093546496
References:
Anandaraj, B., Eswaramoorthi, S., Rajesh, T.P., Aravind, J., Suresh Babu, P., 2018. Chromium(VI) adsorption by Codium tomentosum: evidence for adsorption by porous media from sigmoidal dose–response curve. Int. J. Environ. Sci. Technol. 15, 2595–2606. https://doi.org/10.1007/s13762-017-1488-7
Fumagalli, L., Esfandiar, A., Fabregas, R., Hu, S., Ares, P., Janardanan, A., Yang, Q., Radha, B., Taniguchi, T., Watanabe, K., Gomila, G., Novoselov, K.S., Geim, A.K., 2018. Anomalously low dielectric constant of confined water. Science 360, 1339–1342. https://doi.org/10.1126/science.aat4191
Ma, K., Gong, Y., Aubert, T., Turker, M.Z., Kao, T., Doerschuk, P.C., Wiesner, U., 2018. Self-assembly of highly symmetrical, ultrasmall inorganic cages directed by surfactant micelles. Nature 558, 577–580. https://doi.org/10.1038/s41586-018-0221-0
Mahowald, N.M., Hamilton, D.S., Mackey, K.R.M., Moore, J.K., Baker, A.R., Scanza, R.A., Zhang, Y., 2018. Aerosol trace metal leaching and impacts on marine microorganisms. Nat Commun 9, 2614. https://doi.org/10.1038/s41467-018-04970-7
Schaefer, J., Backus, E.H.G., Bonn, M., 2018. Evidence for auto-catalytic mineral dissolution from surface-specific vibrational spectroscopy. Nat Commun 9, 3316. https://doi.org/10.1038/s41467-018-05762-9
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