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1. Anisotropic oxidative growth of goethite-coated sand particles in column reactors during 4-chloronitrobenzene reduction by Fe( ii )/goethite

   https://doi.org/10.1039/D1EN00788B  

   Soroush, Adel ; Penn, R. Lee ; Arnold, William A. ( January 2022 , Environmental Science: Nano)

   Reduction of nitroaromatic compounds (NACs), an important class of groundwater pollutants, by Fe( ii ) associated with iron oxides, a highly reactive reductant in anoxic aquifers, has been studied widely, but there are significant differences between the well-controlled, batch reactor conditions of the laboratory and the complicated conditions encountered in the field. Continuous flow column reactors containing goethite-coated sand and aqueous carbonate buffer were continuously exposed to 0.05 mM 4-chloronitrobenzene (4-ClNB) and 0.5 mM Fe( ii ) to emulate more realistic scenarios and to allow study of the oxidative growth of goethite particles using both saturated and unsaturated flow conditions. The experiments were designed to test how attachment to a surface affected particle growth and how particle growth affected the extent of reaction over time. After reaction, particles from different sections of each column were collected, and the goethite was detached from the sand grains for characterization using transmission electron microscopy. The amount of oxidative growth varied as a function of distance from the column inlet, with the most growth observed at the inlet end (bottom) of the column. Similar to previous work using batch reactors, newly oxidized Fe( iii ) was mostly added to the goethite particle tips, resulting in up to an 81% increase in length under saturated flow and a 50% increase in length under unsaturated flow after 220 pore volumes. With saturated flow, reactant concentrations and the extent of the reaction are important factors determining the extent of mineral growth. For unsaturated column conditions, however, flow path substantially impacts mineral growth in the column. Reactors sacrificed after 220 pore volumes under saturated flow conditions resulted in an overall 70% increase in goethite mass while the unsaturated flow column resulted in a 40% increase in goethite mass, more variable mineral growth as a function of distance from the inlet, and overall, 50% less 4-ClNB conversion. The results demonstrate that quantitative characterization of oxidative mineral growth of goethite nanoparticles attached to an underlying mineral is practical and elucidates the major variables impacting the reactivity of mineral nanoparticles in contaminated groundwater systems. 

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2. Suppressing alkali-silica reaction through incorporation of calcined kaolinite–montmorillonite clay blends

   Wei, Jianqiang ( September 2019 , 15th International Congress on the Chemistry of Cement)

   Cement substitution with calcined kaolinite–montmorillonite clay blends as an effective way to suppress alkali-silica reaction in cement composites containing reactive aggregates is investigated. Expansion, cracking behavior, mechanical properties and microstructure of the cement composites were investigated. Hydration of the ternary cement blends was also characterized. The results indicate that cement modification with a combination of calcined kaolinite–montmorillonite clays can effectively mitigate alkali-silica reaction-induced deteriorations. By incorporating 30% clays, the volume expansion of the cement composites was decreased from deleterious to innocuous level. Amount of cracks was decreased with increasing clay incorporations. In the presence of combined calcined clays, the strength gain of the cement composites is more significant the strength loss caused by alkali-silica reaction indicating the effective mitigation of this virulent reaction in concrete. 

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3. Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treat-ment and Spectroscopy

   Thomas S. Varner, Harshad V. ( September 2023 , Minerals)

   Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained de-posits rich in organic matter, clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a use-ful indicator of pore-water As concentrations. The pore-waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment have been extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment col-lected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concen-trations of sedimentary As and Fe were measured by X-Ray Fluorescence and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treat-ment, sediment samples were placed in a preheated furnace at 600C for 3 hours. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change of color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicat-ed that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40% whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals. 

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4. Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy

   https://doi.org/10.3390/min13070889  

   Varner, Thomas S. ; Kulkarni, Harshad V. ; Bhuiyan, Mesbah Uddin ; Cardenas, M. Bayani ; Knappett, Peter S. ; Datta, Saugata ( July 2023 , Minerals)

   Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 °C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals. 

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5. Enhancing ROS‐Inducing Nanozyme through Intraparticle Electron Transport

   https://doi.org/10.1002/smll.202305974  

   Yi, Zhongchao ; Yang, Xiaoyue ; Liang, Ying ; Chapelin, Fanny ; Tong, Sheng ( September 2023 , Small)

   Iron oxide nanoparticles (IONPs) have garnered significant attention as a promising platform for reactive oxygen species (ROS)‐dependent disease treatment, owing to their remarkable biocompatibility and Fenton catalytic activity. However, the low catalytic activity of IONPs is a major hurdle in their clinical translation. To overcome this challenge, IONPs of different compositions are examined for their Fenton reaction under pharmacologically relevant conditions. The results show that wüstite (FeO) nanoparticles exhibit higher catalytic activity than magnetite (Fe₃O₄) or maghemite (γ‐Fe₂O₃) of matched size and coating, despite having a similar surface oxidation state. Further analyses suggest that the high catalytic activity of wüstite nanoparticles can be attributed to the presence of internal low‐valence iron (Fe⁰and Fe²⁺), which accelerates the recycling of surface Fe³⁺to Fe²⁺through intraparticle electron transport. Additionally, ultrasmall wüstite nanoparticles are generated by tuning the thermodecomposition‐based nanocrystal synthesis, resulting in a Fenton reaction rate 5.3 times higher than that of ferumoxytol, an FDA‐approved IONP. Compared with ferumoxytol, wüstite nanoparticles substantially increase the level of intracellular ROS in mouse mammary carcinoma cells. This study presents a novel mechanism and pivotal improvement for the development of highly efficient ROS‐inducing nanozymes, thereby expanding the horizons for their therapeutic applications.

    

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