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Symposium in Honor of Prof. Michael Hochella, 2021 Geochemistry Medal Recipient:
10:30am - 12:30pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 36
Nadine Kabengi, Organizer, Georgia State University; Gordon Brown, Organizer, Stanford Univ; Nadine Kabengi, Presider, Georgia State University; Gordon Brown, Presider, Stanford Univ; Udo Becker, Organizer, Presider, University of Michigan
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Division/Committee: [GEOC] Division of Geochemistry
Wednesday
Still plenty of room at the bottom: A snapshot of current nanoscience in geochemistry
10:30am - 10:55am USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 36
Andrew Stack, Presenter, Oak Ridge National Laboratory
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Echoing Feyman, Dr. Hochella once wrote about how "There’s plenty of room at the bottom: Nanoscience in geochemistry" (Hochella, 2002). I will endeavor to show that understanding nanoscale processes in geochemistry is just as important today as it was twenty years ago when Dr. Hochella wrote that. For example, I'll show how the extended solvation structure of aqueous ions affects their reactivity. Everything from thermodynamics of complex formation to the reaction mechanisms seemingly changes as a function of concentration. In some systems, we even see that the extended solvation structure determines induction times for precipitate nucleation and phase selection. These results may help us learn how to better treat legacy tank wastes and deal with flowback water from hydraulic fracturing. In the second half of the talk, I will show how nanoporous materials display different nucleation behavior than in open solution. Nanopores, or pores less than 100 nm in diameter, are ubiquitous in the subsurface and constitute the majority of pores in shales. Reactivity in nanopores are known to be affect the nucleation of minerals, ion selection, and phase selection, among others. It is hypothesized that the anomalous reactivity in nanopores stems from the mineral-water interface that dominates the pore volume. In all of these cases, nanoscale phenomena lead to macroscopic differences in reactivity. Achieving an understanding of these systems requires us to probe reactivity and processes with their origins at the nanoscale. In other words, there's still plenty of room at the bottom!
Wednesday
Effects of hydroxyl and carboxyl functional groups on the calcite surface wettability using AFM and computational modeling
10:55am - 11:15am USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 36
Sooyeon Kim, Presenter, University of Michigan; Maria Marcano; Udo Becker, University of Michigan
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Surface-active compounds, which are mostly in asphaltene fraction of crude oil, are responsible for binding the oil components to mineral surfaces and, therefore, control wettability changes on reservoir rock/mineral surfaces. Surface wettability change occurs mainly through polar functional groups in these compounds, such as hydroxyl, carboxyl, or carbonyl functional groups. Using an asphaltene removed crude oil (i.e., maltenes), we investigate the effect of hydroxyl and carboxyl functional groups on wettability changes of calcite surfaces. AFM images show significantly increased adsorbates of maltenes for the calcite sample pretreated with two asphaltene surrogates (phenol with a hydroxyl group and benzoic acid with a carboxyl group) than the one treated with water. However, the adsorbate patterns are different between those two asphaltene surrogates, suggesting different aggregation mechanisms. We observed formations of bigger surface-adsorbed droplets on the phenol- or benzoic acid-treated calcite samples even for relatively short exposure times (< 30 min.) to maltenes. Quantum-mechanical calculations were performed to calculate which asphaltene surrogate works better to adsorb oil molecules onto the calcite surface for both terraces and step edges. And classical molecular dynamics simulations show that phenol can behave as an agent to separate oil from the water phase and help bind the oil phase to the calcite surface in the water/oil mixture.1
Wednesday
Lateritic nanophases: Witnesses of the fragility and promises of tropical soils
11:15am - 11:40am USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 36
Georges Calas, Presenter
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Laterites cover about one third of the Earth surface, corresponding to extreme weathering conditions under present and/or past humid tropical to sub-tropical climates. Leading to thick weathering profiles, such intense weathering causes a massive exportation of Si, soluble elements and reactive natural nanophases. This mobility is enhanced by the presence of organic matter (humic colloids), as illustrated in the Amazon basin: the concentration of Al- and Fe3+- bound organic nanos rises from soils to river colloids, with a specific spectroscopic signature. Such a translocation and massive exportation of chemical elements to rivers result in a progressive degradation of tropical soils.
On the other hand, surface reactions on lateritic minerals are at the origin of the concentration of strategic metals, such as heavy REE's adsorbed on clay minerals or Ni, Co, and Sc adsorbed on or sequestered within lateritic Fe- and Mn-oxides (60-70% of the world’s Ni resources). This has recently been illustrated by the unusually high-grade Sc-containing laterites from Eastern Australia. Concentration processes are often mediated by Fe-oxide nanophases, but the surface reactivity and the intrinsic nanoscale porosity of lateritic minerals play also a major role. Such diversity underlines the importance of a multiscale approach based on various spectroscopic and microscopic approaches. This will be helpful to model and predict the concentration processes of strategic elements in this new kind of mineral deposits that will receive increasing attention due the growing demand of strategic metals.

Wednesday
Rate-limiting step of dissimilatory microbial iron oxide nanoparticle reduction
11:40am - 12:05pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 36
Eric Roden, Presenter
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Experiments were conducted with synthetic iron oxide nanoparticles to gain insight into the rate-limiting step during the initial stages of dissimilatory microbial iron oxide reduction (DIR) in the presence of excess electron donor for microbial respiration. Ten iron oxide phases with a range of surface areas and thermodynamic properties were reduced by Geobacter sulfurreducens under nongrowth conditions with excess H2 as an energy source. Analogous experiments were conducted in the presence of 100 mM of the soluble electron shuttling compound AQDS. Other experiments examined the short-term kinetics of abiotic iron oxide reduction by excess (10 mM) AH2DS. Longer term abiotic reduction experiments with 10 mM AH2DS were used to estimate the reduction potential (Eh0) of the different oxide phases. There was a significant correlation between oxide Eh0 and short-term surface-area normalized rates of abiotic reduction by AH2DS. In contrast, there was no correlation between oxide Eh0 and initial surface area-normalized DIR rates, either the presence or absence of AQDS. Separate experiments with amorphous hydrous ferric oxide showed that 1 mM AQDS was sufficient to saturate rates of DIR. Thus, the concentration of AQDS did not limit DIR in the reaction systems with 1 mM AQDS. These results, together with other data sets, suggest that the rate of electron flow from cytoplasmic metabolism to redox active components (i.e. multiheme cytochromes) in the outer membrane limits the rate of DIR in both the absence and presence of soluble electron shuttles. This conclusion is supported by the documented rapid electron transfer kinetics between isolated outer membrane multiheme cytochrome systems (e.g. mtrCAB in Shewanella oneidensis) and iron oxide nanoparticles. The analysis highlights the previously demonstrated (or inferred) importance of particle surface properties – as opposed to bulk thermodynamic properties – on the kinetics of biological electron transport to iron oxide surfaces.

Wednesday
Role of nanoscale materials in environmental pollution and remediation
12:05pm - 12:30pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 36
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Naturally occurring nanoscale materials in soils include clays, organic matter, and iron oxides and each can play an important role in contaminant transport and remediation. Incidental nanomaterials, including metals and plastic released through waste streams and agricultural processes, are emerging terrestrial pollutants of particular concern. In order to understand the behavior of natural and incidental nanomaterials, and to harness the potential to engineer them for contaminant sequestration, it is necessary to fully characterize these materials in terms of their structure and reactivity with various chemical/biological components in the environment. Within single particles, elemental distribution can vary from the interior to the surface, thus surface sensitive techniques must be employed. Here, we illustrate how the use of model materials, as well as field samples, in combination with high-resolution spectroscopic and microscopic capabilities, can be used to interrogate interfacial reactivity of nanomaterials, including with redox-active contaminants and at microbe-nanomaterial interfaces.
Symposium in Honor of Prof. Michael Hochella, 2021 Geochemistry Medal Recipient:
02:00pm - 04:00pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 41
Nadine Kabengi, Organizer, Georgia State University; Gordon Brown, Organizer, Stanford Univ; Nadine Kabengi, Presider, Georgia State University; Gordon Brown, Presider, Stanford Univ; Udo Becker, Organizer, Presider, University of Michigan
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Division/Committee: [GEOC] Division of Geochemistry
Wednesday
Metal-containing nanoparticles in coal flyash: Identification, quantification and environmental implications
02:00pm - 02:25pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 41
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Identification and quantitative characterization of nanoparticles (NPs) in coal flyash (CFA) is critical for a better understanding of the eco-environmental and health related risks caused by CFA. In the present study, various metal-containing NPs were identified based on electron microscopy techniques, among which Fe- and Ti-containing NPs are dominant. Iron oxides, including hematite, magnetite and goethite particles, as well as titanium oxides, including rutile, anatase, and Magnéli phases (TixO2x-1), were found to be ubiquitous in CFA samples. Based on single particle-ICP-MS technique, the particle number concentrations of Fe- and Ti- containing NPs were investigated ranging from 2.5 × 107 to 2.5 × 108 particles/mg, and their concentrations were regulated by the feed coals and combustion conditions of various CFAs tested. In cases where these NPs in CFAs become airborne and are inhaled, they can be taken up in pulmonary interstitial fluids. In the analyzed Gamble’s solution (a pulmonary fluid simulant), 51-87 % of Fe and 63-89 % of Ti existed in NP-oxide form and remained suspended in solution. These NP are bioavailable and have been ignored in past traditional risk assessment methods for metals, which has resulted in underestimates when evaluating the risks caused by CFA related metals.
Wednesday
Reactive metal impurities in low valent manganese oxides: Their effects and significance in surficial geochemical processes
02:25pm - 02:50pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 41
Dr. Bojeong Kim, Presenter, Temple University
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Metal impurities are common in low valent manganese (oxyhydr)oxides (hereafter, Mn oxides), yet their effects on the reactivity of the oxides have not been experimentally assessed. In this work, we investigate such effects for the first time by measuring the redox ability of the oxides toward arsenite (As(III)), by varying both the type (redox-inactive nickel vs redox-labile cobalt) and concentration (0–3 wt%) of metal impurities in the mineral structure, as well as by the type of Mn mineral (mixed valence spinel hausmannite vs Mn(III)-only monoclinic manganite). A series of mineral batch reactions were run with As(III) for 8 hrs at pH 5, with regular sampling for total dissolved metal (or metalloid) and [As(V)] by inductively-coupled plasma optical emission spectroscopy and ion chromatography. Mineral characterization was made before and after reaction by X-ray diffraction, Brunauer-Emmett-Teller methods, scanning electron microscopy, transmission electron microscopy, and X-ray absorption spectroscopy (XAS). Especially, XAS analyses were used to detect structural changes by metal impurity substitution, and also examine changes in the oxidation states and coordination chemistry of structural impurities upon As(III) oxidation to As(V). Attenuated total reflectance Fourier transform infrared spectroscopy was also used for in-situ observation of interactions between As species and mineral surfaces. The results of this work demonstrate that Mn oxides with metal impurities exhibit a higher oxidizing ability toward As(III) than pristine ones. After the redox reaction, As(V) was the dominant As species found in the solution and on mineral surfaces. At the equivalent loading, greater impurity effects were found in hausmannite than manganite due to smaller particle sizes and higher surface areas. Ni substitution resulted in more profound impacts in the stability and reactivity of the mineral than Co, with greater impact at higher wt%. During the As(III) oxidation reaction, the release of structural metals occurred, with more Ni released than Co, but overall the majority of the impurities remained in the mineral structure. The present study highlights the importance of considering effects of impurities in mineral reactivity, and thus helps improve our understanding of fate and cycling of transition metals and metalloids that are closely associated with natural Mn oxides in surficial environments.
Wednesday
Quantum mechanical models to electrochemistry: Understanding the redox properties of uranyl peroxides
02:50pm - 03:15pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 41
Dr. Benjamin Gebarski, Presenter; Udo Becker, University of Michigan
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
The redox behavior, thermodynamics, and redox kinetics of the simple uranyl (UO2) complex are well documented within the literature. However, less common and newly synthesized complexes of uranium do not receive the same thorough treatment due to the resources that must be devoted in order to reach a similar understanding. One of the most efficient ways to study this electrochemical behavior is through the use of powder microelectrodes (cavity microanalysis), allowing for rapid characterization of solids in direct contact with the electrode surface. A drawback of this method, is that electrochemical responses often represent a highly complex system in which redox transition, diffusion, adsorption/desorption, and a myriad of other processes occur simultaneously. To analyze these processes individually can require exhaustive experimental design and represent a bottleneck in an otherwise efficient analytical tool.
This study explores the use of atomistic theoretical approaches to aid in the interpretation of experimental electrochemical results. Complexation and adsorption of uranyl leads to differing voltammetric responses in electrochemistry, evident in the wide-ranging standard reduction potentials of different uranyl complexes. Peaks in cyclic voltammetry related to redox transitions are shifted by the difference in binding energy, bonding environments, and differing ligands between uncommon uranyl complexes (like uranyl peroxides) and simple uranyl complexes. The change in Gibbs free energy (ΔG) of adsorption and complexation as calculated using computational models is shown to correlate with the measured redox transitions in electrochemistry. These changes in ΔG can then be converted to electrochemical potentials using the Nernst equation, allowing for the accurate prediction of electrochemical potentials using computational modeling. Our results show that the U(IV)/U(V) switching potential of uranyl peroxides can be predicted to within 0.1 V of electrochemical measurements and identifies the primary interactions occurring at the solid/electrolyte/electrode interface (complexation, adsorption, and reduction). This methodology not only streamlines the process of electrochemical experimental design, but offers a more detailed understanding of electrochemical results at the molecular level.

Wednesday
Dissolution of iron oxide at the nanoscale revealed using in situ liquid cell transmission electron microscopy
03:15pm - 03:40pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 41
Dr. Juan Liu, Presenter, Peking University
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Nanosized iron oxide minerals are widespread in natural environment and play an important role in a variety of biogeochemical processes. Studying dissolution processes of nanosized iron oxide minerals is essential to understand their bioavailability, transformation, reactivity, and fate, as well as biogeochemical cycle of iron in the Earth's surface environment. The conventional methods for dissolution studies, such as batch dissolution experiments, cannot distinguish the effects of different factors, such as particle size distribution, aggregation state, and surface defects, on apparent dissolution rates. Whether nanosized minerals can exhibit special dissolution behavior or have distinct thermodynamic properties controlling dissolution processes are still unclear. We studied dissolution processes of hematite (α-Fe2O3) nanoparticles and goethite (α-FeOOH) nanorods using in situ liquid cell transmission electron microscopy (LCTEM) that allows us to observe dissolution behavior of each nanocrystal with well-defined properties (including aggregation state, shape, size, and defects) at high spatial and temporal resolution. The results of this study present that the initial surface-area normalized dissolution rates (RSA,Int) of isolated hematite nanoparticles exponentially increase as particle size linearly decreases, indicating a linear relationship of RSA,Int and degree of chemical non-equilibrium. Interface free energy of hematite particle was derived from the correlation between the measured RSA,Int and the primary sizes, suggesting a new method to measure interfacial surface energy of nanocrystals. The effects of crystal defects and aggregation state on the dynamic dissolution processes were revealed at nanoscale by LCTEM. Anisotropic dissolution of goethite nanorods were also presented using LCTEM, which quantitatively described the distinct surface properties of different goethite facets. More generally, this study illustrates an integrated method, involving in situ LCTEM, conventional batch experiments, and computational simulation, for probing interfacial reactions of iron oxide minerals at nanoscale.
Wednesday
Roles of bicarbonate in arsenopyrite dissolution and nanoscale secondary iron mineral precipitation in managed aquifer recharge systems
03:40pm - 04:00pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 41
Ping-I Chou, Presenter; Xuanhao Wu; Yaguang Zhu; Zhenwei Gao; Young-Shin Jun, Washington University in St. Louis
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Managed aquifer recharge (MAR) is viable method for water storage, recycling, and reuse, alleviating the stress of groundwater over-extraction. However, water injected during MAR can trigger unexpected oxidative dissolution of arsenic-bearing iron sulfide minerals, releasing arsenic into groundwater. In particular, the effect of bicarbonate on sulfide mineral dissolution and subsequent secondary mineral precipitation under conditions relevant to groundwater is still unclear. Using arsenopyrite, one of the most common arsenic-bearing minerals in subsurface environments, here we examined the effects of bicarbonate concentrations (0.01 mM, 0.1 mM, 1 mM, and 10 mM) on the dissolution of arsenopyrite and the precipitation of iron-containing secondary minerals. Furthermore, to mimic aquifer environments with and without CO2 exchange, the dissolution experiments were conducted in both open and closed systems. In the open system, the mobilization of arsenic in the short term (< 6 hours) was similar for all bicarbonate concentrations, while in long term (7 days), the aqueous arsenic concentrations were reduced by increasing bicarbonate concentrations. This long-term arsenic dissolution trend is attributed to the equilibrium pH at different bicarbonate concentrations, because a high bicarbonate concentration will result in high pH and will slow the proton-promoted dissolution of arsenopyrite. We also measured the total arsenic concentrations dissolved from arsenopyrite. When we delineated aqueous and adsorbed arsenic concentrations, we found that most of the dissolved arsenic was adsorbed on the surface of arsenopyrite and iron(III) oxide minerals. In addition, higher bicarbonate concentrations reduced both the absorbed and total dissolved arsenic. Based on nanoscale observations using atomic force microscopy, the increased bicarbonate concentrations promoted secondary mineral precipitation. Raman spectroscopy confirmed that newly formed mineral phases were maghemite and magnetite. The results in the closed system revealed that, due to similar equilibrium pH values for the bicarbonate concentrations of 0.1 mM, 1 mM, and 10 mM, arsenic mobilization in all the bicarbonate concentration systems was similar during the entire 7-day reaction. These new observations of bicarbonate’s effects on arsenopyrite reactions illuminate the role of bicarbonate in arsenic mobilization in groundwater systems and can aid in designing safe and sustainable MAR operations.
Symposium in Honor of Prof. Michael Hochella, 2021 Geochemistry Medal Recipient:
04:30pm - 06:20pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 40
Nadine Kabengi, Organizer, Georgia State University; Gordon Brown, Organizer, Stanford Univ; Nadine Kabengi, Presider, Georgia State University; Gordon Brown, Presider, Stanford Univ; Udo Becker, Organizer, Presider, University of Michigan
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Division/Committee: [GEOC] Division of Geochemistry
Wednesday
Comparing the ability of microbial communities within Great Lake sediment ecosystems to degrade light synthetic crude
04:30pm - 04:55pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 40
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Research in marine environments has shown that microbes can play an active role in degrading hydrocarbons, yet, very few studies have examined freshwater ecosystems. The Laurentian Great Lakes comprises over 90% of the surface freshwater in North America and concerns of crude impacts have recently increased due to a pipeline that crosses the Straits of Mackinac, the intersection of Lakes Michigan and Huron. To examine the impacts of crude on microbial communities in the Great Lakes, sediments and water collected from three different ecosystems (beach, coastal wetland, and profundal benthic sediments) were used in microcosm experiments amended with light synthetic crude. Ecosystems with greater diversity (wetland sediments) had a greater ability to resist community change (based on beta diversity) relative to lower diversity sites (sand). When microcosms were exposed to crude, all three ecosystems did show an enrichment of taxa (gammaproteobacterial and Pseudomonas) that have been previously known to degrade crude. Hydrocarbon degradation byproducts, such as methane and ethane, were also documented in the headspace of microcosms when exposed to crude, with coastal wetland sediments having the greatest concentrations. Taken together, these data document a high potential for microbial communities in sites with greater diversity (such as wetlands) to degrade crude, but a more limited ability for microbes in lower diversity sites, like beach sand. Current metagenomic analysis is underway to examine the genetic pathways that wetland communities could be using to degrade this crude.
Wednesday
New insights on the detection and sulfidation of Ag nanoparticles in a natural freshwater environment: performance of two new biomonitors
04:55pm - 05:15pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 40
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Discharge of man engineered metal-based nanoparticles (NPs) from various sources into freshwater environment is inevitable. This requires the development of sampling techniques in order to detect, quantify, and characterise NPs in natural waters. Major sampling difficulties are associated with speciation effects. NPs in the aquatic environment are exposed daily to different factors (UV irradiation, natural organic matter, pH, etc.) which affect their stability and may lead to their chemical transformation. This directly impacts the fate of NPs, including the release of metal ions from particles (i.e., the toxicity of NPs). Since 2014, the fate of 15 kg of poly(vinylpyrrolidone)-coated silver nanoparticles (Ag-NPs) (size 30±50 nm), introduced into a small boreal lake (L222) in the Experimental Lakes Area (ELA) in western Ontario (Canada), is under continuous observations by the research community. In 2019, adult unionid mussels, Pyganodon grandis (Say), were collected from control lake (L375) and L222. Their shells and soft tissues were analysed with ICP-MS. In specimens from L375, Ag concentrations are < 1 ppm, whereas samples from L222 contain ~ 150 ppm. In shells, > 99% of Ag was associated with external proteinaceous periostracum (organic substrate) rather than with the underlying mineral layer. Shells were also studied with optical microscopy, LA-ICP-MS and TEM. Brush-like micromorphology of intact periostracum in this species promoted the capture and storage of silica diatom shells (silica substrate) which resided in the surrounding water during the mussels live. In the studied shells, Ag-NPs (individual particles with d= 20-60 nm and aggregates with d= ~100 nm) were partially transformed (sulfidation) to Ag2S and adhered to both periostracum and diatoms. Ag-NPs are randomly distributed on the surface of both organic and silica substrates. In this study, attention to shell micromorphology led, for the first time, to the incidental discovery of two biomonitors, mussel shell periostracum and diatoms, which showed good results in the detection and characterisation of engineered nanoparticles introduced into a freshwater ecosystem. These findings may lead to more effective strategies for the detection of engineered and incidental nanoparticles, characterization of their toxicity and fate in natural water environments.
Wednesday
Using imogolite to adsorb emerging organic pollutants from water samples
05:15pm - 05:40pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 40
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Imogolite is a nanomineral, with the general formula (OH)3Al2O3SiOH and tubular shape, that can be obtained from glassy volcanic ash soils or be synthesized at mild conditions in aqueous solutions. In nature, imogolite can be found as hollow nanotubes with an outer diameter of ~2.5 nm, an inner diameter of less than 1 nm and lengths between several hundred nanometers to one micrometer. It also has amphoteric groups of aluminol and silanol inducing very interesting acid-base properties. All these properties make this nanomineral a highly attractive adsorbents for emerging contaminants in aqueous solutions.

In this study the adsorption capacity of Imogolite was tested using different concentrations of the hormone 17β-estradiol in aqueous solution. The presence of this pollutant was detected and quantify by spectrofluorimetry. Solid phase microextraction studies were performed and a chemometric approach was used to adjust the most relevant variables (rotation time, pH and imogolite mass). A maximum adsorption of 95.5% was obtained, using purified imogolite under the following experimental condition: pH 7, 17β-estradiol concentration of 350 µg/L, adsorbent dose of 0.017g per 5.0 mL of solution and an agitation at 1250 rpm for 10.0 minutes.

To the best of our knowledge, this is the second time that the imogolite's adsorption capacity has been confirmed using an emerging organic pollutant. Our study also opens very promising applications of imogolite as green ecosorbent in analytical chemistry as well as other applications in the remediation of water organic pollution.

Wednesday
Facet-specific oxidation of Mn(II) and heterogeneous growth of manganese (oxyhydr)oxides on hematite nanoparticles
05:40pm - 06:00pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 40
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
It is recognized that different facets of minerals vary distinctively in their chemical reactivity with aqueous solutions. However, detailed molecular and atomistic understandings of these phenomena are relatively limited. This study investigated the interaction of aqueous Mn2+ and dissolved oxygen on various facets of two morphology-types of iron oxide (hematite) nanocrystals. These interactions result in the oxidation of Mn(II) and heterogeneous growth of Mn(II)/Mn(III) and Mn(III) oxides. The nanoscale morphology and atomic structure of the manganese oxide products were characterized in detail. Our results, for the first time, directly demonstrate the facet-specific oxidation of Mn(II) and nucleation of Mn(II/III) oxides, followed by their epitaxial growth on hematite. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction measurements reveal the growth of MnOx nanowires on {113} of hematite nanoplates (HNP) and {012} facets of hematite nanocubes (HNC), while the basal {001} facets on the HNP particles do not produce precipitates. The average oxidation states of the MnOx on HNP and HNC determined using electron energy-loss spectroscopy (EELS) show that both Mn(II) and Mn(III) are present. The mineral composition and growth mechanisms of MnOx catalyzed by HNP and HNC are similar. High-resolution TEM analysis reveals the presence of both hausmannite and manganite on HNP and HNC. The crystallographic relationship between the heterogeneously formed manganite with hematite, which has not been reported before, proves that hematite provides reaction sites and can function as an atomic template for the formation of MnOx nanowires. These findings advance our understanding of the redox chemistry and heterogeneous growth of minerals as controlled by the surficial structure of the substrate mineral. This has important geochemical implications as the catalytic growth of less common, highly reactive phases like MnOx are known to be consequential in complex natural and anthropogenic environments.
Wednesday
Effect of quaternary ammonium disinfectants upon hematite nanoparticle solution stability
06:00pm - 06:20pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 40
Division: [GEOC] Division of Geochemistry
Session Type: Oral - Virtual
Disinfectant use has increased worldwide due to the COVID-19 pandemic. Quaternary ammonium compounds (QACs) are some of the most common disinfectants used for surface cleaning, as well as being used in everyday personal care products. QACs contain cations with the general formula NR4+, where R corresponds any alkyl or aryl group. Those used as disinfectants have surfactant activity, namely with at least one long-chain alkyl group (R = CnH2n+1 with n ≥ 8). Increased QAC use leads to greater release of QACs to environmental systems. As such, understanding the interaction between QACs and environmental compounds is critical. One major class of environmental substances is mineral nanoparticles, which has been the focus of our studies.

We present preliminary data from our investigation into the impact of QACs upon mineral nanoparticle (NP) stability in solution, based upon the hypothesis that bilayer formation might impact the degree of NP aggregation. Hematite (a-Fe2O3) nanoparticles were exposed to QACs with varying alkyl group lengths: hexadecyltrimethylammonium chloride (denoted as Q-16), octyltrimethylammonium chloride (Q-8), and tetramethylammonium chloride (Q-1). We also exposed nanoparticles to benzalkonium chloride (BZC), a commonly used QAC containing a mixture of alkyl chain lengths. Along with controls (no QACs), three environmentally-relevant QAC concentrations were tested: for BZC, 1000 μg / L, 100 μg / L, 10 μg / L, and for Q-16, Q-8, and Q-1, 3.13 μM, 0.313 μM and 0.0313 μM. The Q-16 and BZC-exposed NPs were stabilized in solution at the two highest concentrations; Q-8 exposed NPs were stabilized at 3.13 μM only and Q-1 did not stabilize NPs at any concentration. We shall discuss our hypotheses on QAC stabilization of NPs in the context of characterization with scanning electron microscopy, dynamic light scattering, and Fourier transform infrared spectroscopy.

Symposium in Honor of Prof. Michael Hochella, 2021 Geochemistry Medal Recipient:
07:00pm - 09:00pm USA / Canada - Eastern - August 25, 2021 | Room: B2 - EXHIBIT HALL
Adam Wallace, Organizer, University of Delaware; Nadine Kabengi, Organizer, Georgia State University
Division: [GEOC] Division of Geochemistry
Session Type: Poster - In-person
Division/Committee: [GEOC] Division of Geochemistry
Wednesday
Withdrawn
07:00pm - 09:00pm USA / Canada - Eastern - August 25, 2021 | Room: B2 - EXHIBIT HALL
Division: [GEOC] Division of Geochemistry
Session Type: Poster - In-person

Thursday
Virtual Networking Event: Symposium in Honor of Prof. Michael Hochella, 2021 Geochemistry Medal Recipient
02:00pm - 03:00pm USA / Canada - Eastern - August 26, 2021 | Room: Virtual Room
Division: [GEOC] Division of Geochemistry
Session Type: Networking Events - Virtual
Division/Committee: [GEOC] Division of Geochemistry