Mike Hochella’s career as a teacher, a researcher, and a leader has set a shining example of the transformative power of a geosciences education. He and his students contribute to areas well beyond geology, such as soil science, physics, (micro)biology, surface science, materials science, nanotechnology, chemistry, civil and environmental engineering, and the health sciences. We geoscientists even have decades of microscopic images and other forms of ‘big data’ that represent a treasure trove for computer scientists pushing the boundaries of artificial intelligence and machine learning. In a world where lack of understanding and support for the sciences can be nothing short of deadly, it has never been more important to develop engaging model geosciences courses to provide every undergraduate with key life skills. A great geology course for non-geologists can teach students how to scientifically diagnose a problem (mineral identification), how to read a map, how to formulate an hypothesis, and how to measure, graph, and interpret environmental properties like pH. No one is better prepared than a geoscientist to teach what we might call Basic Life Skills for Earthlings. The time is ripe to seize the initiative, as Mike has done so often throughout his career, to share the transformative power of a geosciences education with students and communities everywhere. In addition to highlighting the diverse and exemplary work of Mike Hochella and his group, this talk will describe new ideas for unleashing the transformative power of a geosciences education.
Michael Hochella has been a leader in geochemistry as long as I can remember, and he is a pioneer in the field of nano-geochemistry. His work has spanned molecular- to field-scale studies and his contributions have been immense. In addition, he has always been a positive force in the geochemistry community especially through his work on NanoEarth and the Center for Environmental Impacts of NanoTechnology (CEINT). This talk will focus on DFT calculations of nanoparticles. Beginning with studies of TiO2 (anatase and rutile) nucleation and cation adsorption, the discussion will also cover goethite and ferrihydrite surface chemistry, and then move on to silica nanoparticles and radical formation.
This presentation will illustrate how the integration of laboratory experiments, X-ray photoelectron spectroscopy (XPS), and synchrotron-based X-ray absorption spectroscopy (XAS) facilitates the investigation of Mn and U nanomaterials in the environment. The integration of XPS and XAS has been essential for the determination of oxidation states of Mn-oxide and U-bearing nanoparticles to better understand redox reactions affecting metal transport and remediation. Additionally, recent advances have facilitated understanding nanoparticle accumulation in plants and cell cultures which have important implication for toxicology, risk assessment, and risk reduction. This work pays tribute to the interdisciplinary spirit and scientific curiosity of Professor Michael Hochella who has illustriously mentored and inspired a new generation of scientists interested in nanotechnology for earth and environmental sciences and engineering.
The weathering of sulfidic rock can profoundly impact watersheds through the export of acidity and metals. Here we combine analytical methods to establish a model for the principal weathering pathways and controls on element retention or release from actively weathering fractured sandstone containing disseminated iron-rich sphalerite in the Mesa Verde Formation at the Redwell Basin, Colorado. Microfocus X-ray analysis of a fracture-scale weathering profile is consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of Fe-sphalerite, chlorite and minor siderite. Although the sandstone possesses little buffering capacity from carbonate minerals, dissolution of feldspar and chlorite neutralizes the acidity generated by sulfide and iron oxidation, inducing the precipitation of jarosite, a hydrous iron(III) sulfate, and iron (oxyhydr)oxide during transport to the surface. Low-temperature magnetism data show pyrrhotite to be a proxy for unweathered sulfide minerals and the loss of pyrrhotite is associated with the extent of oxidative weathering, despite the low abundance of this phase. The combination of X-ray and magnetic measurements show nanophase goethite, mainly present in a fracture surface coating, to be an important iron(III) product. Pyrrhotite loss and nanophase goethite formation are detectable through room-temperature coercivity changes suggesting that rock magnetism measurements can determine weathering intensity in bulk rock samples. This work contributes evidence that the weathering of sulfidic sedimentary rocks follows a common geochemical pattern in which the abundance of certain mineral phases controls the generation of acidity and dissolved elements and the pH-dependent mobility of these elements controls their export.
I will describe how spherulites nucleate and grow, using scleractinian (or stony) corals as a model system, because they are well known to form their skeletons from aragonite (CaCO3) spherulites (1), and because a comparative study of crystal structures across coral species has not been performed previously. Besides the expected centers and radiating crystal fibers, we observed unexpected randomly oriented, equant crystals, which we termed sprinkles, and which stand out in Polarization-dependent Imaging Contrast maps (PIC maps(2)). Based on this discovery, we propose a spherulite formation mechanism in which randomly oriented sprinkle crystals are nucleated at the growth front and growth in competition for space. The smallest, outcompeted crystals disappear during coarsening. This model replaces the previously assumed slightly misoriented nucleations termed non-crystallographic branching (3).
Crystal orientations in a coral skeleton, as measured and displayed in color by Polarization-dependent Imaging Contrast (PIC) mapping with 20-nm resolution.
Data from Acta Biomaterialia 2021, DOI: 10.1016/j.actbio.2020.06.027
On the date of this happy occasion, it has been almost 46 years since I first worked with Mike Hochella on his M.S. thesis, which focused on the high-temperature crystal chemistry of the mineral cordierite. I was fortunate to attract Mike to Stanford University for his Ph.D. work with me and my group of grad students and postdocs, who gave Mike the moniker “The Rookie”, in part because of his boundless enthusiasm. While at Stanford, Mike worked on the structure of molecular-level structure and structure/property relationships of aluminosilicate glasses and melts for his Ph.D. degree, which he completed in 1981. His first professional position was as a Senior Scientist at Corning, Inc., where he worked on various ceramic and amorphous materials and became an expert in the application of X-ray photoelectron spectroscopy (XPS) to ceramic and mineral surfaces. After three years at Corning, he returned to Stanford in 1983 as a Senior Research Associate, working on XPS studies of mineral surfaces. From 1989 to 1992, Mike was an Associate Professor (Research) at Stanford, where he had a strong group of grad students and postdocs and was one of the first geochemists/mineralogists to apply scanning force microscopy to mineral/water interface chemistry problems. Mike returned to Virginia Tech, his undergraduate alma mater, as a tenured faculty member in 1992. Mike’s fame grew by leaps and bounds at Virginia Tech because of his pioneering studies of mineral surfaces using scanning tunneling and atomic force microscopies, which led to seminal studies of the adhesive forces of bacteria on mineral surfaces. He is also one of the pioneers in the rapidly growing field of nanogeoscience, which has benefited from his boundless energy and creativity. My talk will cover these and other exciting studies that Mike undertook until his retirement from Virginia Tech in 2019 as University Distinguished Professor Emeritus, and for which he is receiving the ACS Geochemistry Division Medal for 2021.
Mixing between cold, oxygenated seawater and hot, anoxic hydrothermal vent fluids induce the formation and/or precipitation of (nano)mineral phases. Using the NanoEarth Facility at Virginia Tech, we demonstrate the occurrence and/or formation of a wide variety of chemical constituents as nano and submicron mineral phases in the mixing zone (first 1-2 meters from the vent orifice) between high-temperature hydrothermal fluids and ambient seawater, and in diffuse flow waters at the 9° 50' N East Pacific Rise hydrothermal fields. Phases include pyrite, chalcopyrite, sphalerite, wurtzite, graphite, and silicates containing Mg and Fe (kaolinite, Fe-rich mica, and talc/lizardite).
We find that silicate (nano)particles are ubiquitous in sampled fluids and are a previously undocumented source of Fe to the global ocean. Particle size and uniformity, in addition to the inclusion of Mg, suggests that these (nano)particles form from solution in rapid reverse weathering reactions rather than representing pieces of basement rock or chimneys entrained into the flow. The formation of hydrothermal silicates may be more widespread than previously documented and have an impact on the ocean’s Si, Fe, and other element budgets. Thus, both nanoparticulate pyrite and metal-bearing (alumino)silicate phases can transport away from vent sites, and act as a source of Fe and other metals to the global ocean.
In addition to SEM/EDS and TEM/EDS data, selected area electron diffraction patterns confirm the identity of these (nano)mineral phases. We define nanoparticles in the size range from 20-200 nm based upon filtering with 200 nm filters. Filters also trap these nanoparticles as they co-occur and aggregate during filtration indicating that ICP-MS solution data underdetermine the concentration of these nanoparticles as “dissolved” species.
The controlled nucleation and growth of CaCO3 polymorphs occur extensively in biological systems within a macromolecular matrix of organic molecules. The central role of the organic matrix as a template and scaffold in regulating nucleation and subsequent biomineral growth is recognized, and simple relationships between functional group composition and influence upon crystallization are emerging. Parallel studies of in vivo systems also are providing remarkable insights. However, twenty-plus years later, our understanding of how the organic matrix directs controlled biomineralization continues to be meager. This gap in our knowledge is a significant obstacle to building a comprehensive and predictive model. This is our Ever Given.
With recent advances in natural polymer and hydrogel synthesis chemistry, the functional group chemistry of natural polysaccharides can be tailored into hydrogels with a palette of compositions. By investigating CaCO3 nucleation using these characterized materials as models for the organic matrix, we are posing testable hypotheses to quantify functional group controls on 1) the rate of CaCO3 nucleation, 2) chemical controls on the polymorph, and 3) the placement of the crystals that form.
As a 17-year-old first year college student a half century ago, I learned that pure carbon was the only ingredient in pencil “lead” (graphite), as well as diamond. That little bit of knowledge seems to have guided my professional life ever since, as my fascination with this has not waned over all these years. In the graphite-diamond example, chemists understand/explain this carbon atomic structure-property relationship using sp2/sp3 bond hybridization models, and physicists describe exactly the same thing in terms of valance and conduction band electronic structure. The latter model, developed from the standpoint of quantum mechanics, is really handy when understanding graphene (a single sheet of carbon), and other nanomaterials which I find particularly fascinating. My long-range plan was to map this atomic structure-property relationship thinking into a better understanding of environmental Earth, and to find understanding on the mechanistic and practical sides of this endeavor. But how? To the best of my ability, I will give examples in this lecture, likely using the following disparate examples from our research over the years: 1) our discovery of the atomic structure of magnesium hydroxide sulfate hydrates, helping to explain its impact on hydrothermal venting systems and life in the oceans; 2) very early experiments with calcite and sorbed cations, like aqueous cadmium, proving that sorbed species can readily move into the host calcite phase through solid state diffusion; 3) our work on pyrite surface electronic structure and reactive sites, atomically resolved, and relating that to acid mine drainage; 4) experiments concerning hematite reactivity as a function of its size in the nanoscale regime, and its effects on manganese redox chemistry and groundwater chemistry in general; 5) determining the nature of the formation and atomic structure of green rust and its reactivity for metal transport; 6) discovery of massive titanium suboxide generation, its remarkable defect atomic structure, and its human lung toxicity; and 7) expanding these themes to global impact scenarios.
Manganese (Mn) oxides possess extraordinary metal sorption and oxidation properties and thus affect environmental fate and transport of toxic metals and organic pollutants. There are more than 30 different types of Mn oxides that can be grouped into layered (LMOs), tunneled (TMOs), and low-valence (LVMOs) Mn oxides. The Mn in LMOs and TMOs is mainly Mn(IV) with some species containing Mn(III), while Mn exists as Mn(II), Mn(III) or both in LVMOs. It has been challenging to understand the formation of such a high diversity of phases in the environment. Recent studies showed that Mn(II) can promote transformation of LMOs to TMOs and LVMOs at room temperature, in which Mn(II) acts as either a catalyst, a reactant, or both. The transformation products are controlled by the Mn(II)/LMO ratio and pH. This presentation will be focused on the effects of co–existing cations (alkali, alkaline earth or transition metal cations) or oxyanions (phosphate or silicate) on the Mn(II)-driven redox transformation. We found that these cations strongly affect the phases of the transformation products. In Li+, Na+ or K+ solution, 4×4 TMO forms with or without triclinic birnessite as an intermediate product. The presence of Ca2+ or Mg2+ stabilizes triclinic birnessite without forming the TMO phase. In contrast, Cu2+ strongly inhibit the above transformation. The cation effects positively correlate with the binding strength of the cation to LMO. While not altering the phases of the transformation products, phosphate or silicate decreased the transformation rate and extent as well as the particle sizes of the products. These results suggest that adsorptive ions in natural waters can increase the stability of LMOs, contributing to their high abundance in natural environment, compared to other Mn oxide phases.
Thermal power plants using coal and solid biomass as fuel represent major sources of coarse, fine, and ultrafine particulate matter (PM) in the atmosphere. The interactions of PM with the atmosphere and the solid Earth, its hydrosphere, and its biosphere, as well as the impacts on human health depend on particle number and size as well as on other properties, such as, chemical composition, structure, surface area, and solubility of the individual particles, which therefore need to be investigated in detail. Because the individual particles emitted through smokestacks are small, they have to be studied with a variety of methods, including transmission electron microscopy. Moreover, several different experiments have to be performed in order to assess the toxicity of such particles, which can easily enter the human respiratory tract. This presentation will focus on the characterization of select solid constituents of emissions from coal and biomass combustion, including metal sulfates, magnetite, and bulk fly ash. Moreover, results from various in-vitro toxicological experiments with human lung cells (alveolar epithelial A549, bronchial epithelial BEAS-2B) and from microscopic investigations will be used to evaluate the dose-dependent cytotoxicity and genotoxicity, the formation of reactive oxygen species, and the uptake/translocation of these particles into the cells.
Methanotrophic bacteria catalyze the activation of methane using enzymes which incorporate Cu and excrete small peptides known as methanobactins for extracellular copper acquisition. In addition to Cu, these peptides interact strongly with other late transition metals including Zn, Cd, and Hg, and represent a nexus between the biogeochemistry of methane and the biogeochemical cycles of the late transition metals. We combine spectroscopic, computational, and thermodynamic data to characterize the complexation of Group 11 and 12 transition metals by methanobactins excreted by methylocystis sp. strain SB2. We propose a mechanism for a fluorescence enhancement observed complexes of mb-SB2 with specific transition metals and use the near-UV absorbance of the peptide to study competition between the methanobactins and specific organic compounds chosen as models for dissolved organic matter for complexation of Group 12 transition metals. We find that methanobactins are generally strong chelating agents for late transition metals but that out-competition of the peptide may occur in the presence of specific ligand types. Our data represents the first computational investigation of the peptides of which we are aware and creates a baseline for further study of the peptides and the intermolecular interactions which may modulate their function in extracellular copper acquisition.
Iron sulfide nanoparticles assume an important role within a wide range of geological settings as indicators of redox conditions and elemental cycling mechanisms. Initial precipitates of iron sulfide are exclusively nano-sized in low-temperature aqueous conditions and have been reported to go through diverse morphological and phase transformations, possibly leading to the ultimate deposits of pyrite. A systematic understanding of how early-stage precipitates of iron sulfide may develop into more crystalline phases is still lacking, however. The major goal of this study is to illuminate the effects of iron and sulfide sources on the formed iron sulfide and their subsequent transformation. We used comparative experimental approach to study whether the sulfide (abiogenic vs. biogenic via bacterial sulfate reduction) and iron (ferrous vs. ferric) sources affect the phase, morphology, and stability of the formed iron sulfide. The different iron sources also reflect formation processes in anoxic vs. suboxic scenarios. Based on XRD, TEM-EDX, and SAXS data, apparent variations in sizes, morphology, crystal structure, and composition were revealed for the biogenic and abiogenic iron sulfide. The abiogenic precipitates that used Fe(II) as reactants consist mainly of mackinawite and greigite nanocrystals (sized 50 nm on average) at T0; the abiogenic precipitates that used Fe(III) as reactants consist mainly of greigite (sized ~ 70 nm on average) at T0. In general, the abiogenic samples of Fe(III) systems showed higher crystallinity than those of Fe(II) systems at all examined time intervals. It is noted that pyrite was identified in the abiogenic samples of Fe(III) systems as early as T0. In comparison, the biogenic precipitates were composed mainly of amorphous phase at early stages (T0, T1m, T2m) and of greigite precipitates in aged samples (T3m). Pyrite was also detected in the biogenic samples of Fe(III) systems, but at a much later stage (T3m). These results indicated that Fe(III) species may behave as a suitable oxidant favoring the formation of pyrite and the presence of bacterial cells delays the Fe-monosulfide to polysulfide transformation, likely by providing more reducing resources and mediating the microenvironmental pH. The results of the work provide new insight into the transformation pathways of early iron sulfide precipitates into pyrite.
Chemical weathering of pyrite via oxidative dissolution can generate Fe(III)-bearing colloids at acid mine drainage (AMD) sites; however, the potential for physical weathering of pyrite-bearing materials in mine spoil and subsequent release and transport of colloidal pyrite and associated trace metals has not been studied. We monitored colloidal metal transport in soil developing on abandoned coal mine spoil to systematically study the elemental and mineralogical composition of colloids and determine their contribution to base and trace metal transport. Soil pore water samples were collected using lysimeters with a pore size of ~1.3μm, and centrifugation was used to separate the colloids (<10μm) from the solution. Metal concentrations of Na, Ca, Mg, K, Si, Al, Mn, Fe, Cu, and Zn were analyzed. Results show a higher colloidal contribution relative to total metal concentrations for the transport of Zn (54%), Mn (43%), Fe (23%), and Cu (14%) in the porewater. In contrast, all base metals were primarily present in the aqueous phase (<10% in colloidal fraction). The morphology, elemental, and mineral composition of colloids were determined by a scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). XRD analyses indicated that colloids were dominated by phyllosilicates (biotite, muscovite, and kaolinite) and contained between 1 to 10% hematite, goethite, arsenopyrite, and chalcopyrite, and SEM-EDS analyses identified the phases with composition and morphology consistent with framboidal pyrite. Our study indicates that the physical weathering of pyrite-bearing coal shale can generate colloidal pyrite which is mobilized and transported by soil porewater. Further SEM-EDS analyses of colloids present in the soils revealed that trace element (Cu, Mn, and Zn) partitioning during pyrite oxidative dissolution is controlled in part by whether subsequent Fe(III) precipitation occurs immediately (e.g. pseudomorphic replacement of pyrite) or after transport in pore water (e.g., Fe(III) coatings on primary grains and/or formation of discrete Fe(III)-bearing phases. On-going Transmission Electron Microscopic analyses of colloidal pyrite and secondary Fe mineral surface coatings prepared by a Focused Ion Beam (FIB) instrument aims to provide a better understanding of the morphology, mineralogical, and composition of these phases to more clearly elucidate the fate and transport of metals in this system.
Concentrations of sedimentary molybdenum (Mo) have been used as a proxy for paleooceanographic redox conditions based on the distinctive behavior of Mo under oxic versus euxinic (anoxic and sulfidic) conditions. However, the mechanisms that govern Mo sequestration in various euxinic settings are not fully resolved. It has been proposed that sulfate-reducing bacteria (SRB), the main driver and regulator of euxinic conditions, reductively immobilize molybdate (MoO42-), a structural analog to sulfate (SO42-). Controversially, only circumstantial evidence was provided, which contradicts the more widely accepted paradigm that Mo inhibits SRB growth. The major goal of the current study is to understand the interactions among Mo, ferrous iron (Fe2+), and SRB through systematic experimentation with a focus on combinations of conditions that may lead to reductive precipitation of Mo mediated by Fe2+ and/or SRB. Specifically, we will characterize the behavior of Mo (i.e., aqueous speciation, degree of association with SRB cells, and the composition, structure, and Mo valence state of its precipitates) in sulfidic solutions generated and maintained by SRB. Solutions and precipitates will be analyzed using UV-Vis spectrophotometry, transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). Preliminary results show that Desulfovibrio vulgaris immobilized Mo more effectively than Desulfotigum balticum, which could challenge the assumption of former studies that little distinction exists in the biological control of Mo by SRB. Moreover, upon Fe2+ addition, the D. vulgaris solutions remained unaffected, indicating the formed Mo-OM complexes were stable enough to prevent remobilization of the Mo and sulfide, suggesting a high preservation potential of thiomolybdate-OM complexes. Based on these preliminary results, we hypothesize that (1) the Mo precipitates in the biological experiments will exhibit strong association with the periplasm of SRB cell walls, (2) the initial presence of Fe2+ will induce Mo precipitation but decrease the cellular association of the precipitates, and (3) Mo(VI) will be reduced to Mo(IV) in both SRB- and Fe-mediated precipitates. The results of these biological Mo sequestration experiments will further our understanding of Mo behavior in natural euxinic environments and refine redox reconstructions.
The Auger decay and dielectric capture in differently charged sulfur ion with an initial hole in either K or L shell were simulated using relativistic multiconfiguration Dirac-Fock approaches. This configuration interaction approach enables one to model three-electron processes in an Auger decay through a careful treatment of correlation between electronic configurations, and allows computing electron spectra, the population of final-states and Auger yields. The wave function of the free electron in autoionization and radiationless electron capture rates were also calculated based on the relativistic distorted-wave and isolated resonance approximations. The quantum electrodynamic simulations reveal that the Auger kinetic energies decrease linearly as function of the charge and the Auger yield rate varies with the ionization state of sulfur ion. The electron configurations of different ionization states directly affect the Coulomb and Breit interactions differently in Auger transitions. The intensity ratios and the energy gaps between different Auger transitions were found to change with ionization state of the sulfur ions.