Photoelectrochemical water splitting suffers from limited light absorption, low charge separation and transport. To deal such challenges alkali metals (Li, Na, K) doping in BiVO4 was carried out systematically to demonstrate enhanced light absorption, high diffusion length of electron-hole pairs, enhanced charge separation in the bulk and charge transport at the surface, with their unique placements in the crystal structure. The nanostructured porous grain of alkali metals doped BiVO4 thin film photoanodes exhibited 8-20 times photocurrent density higher than pristine BiVO4. Li:BiVO4, Na:BiVO4 achieved 4.2 ± 0.18 mAcm-2 and 3.2 ±0.15 mAcm-2 with OER catalyst in 0.1 M K2HPO4 electrolytes at 1.23 V under 1 sun illumination. Through XPS analysis, it was noticed that the bond formation between alkali metals and oxygen are significant. From that, it was speculated that alkali metals are getting placed in the interstitial void of the BiVO4 crystal structure. Diffusion length of charge particles was measured by implementing a positron at the surface of the thin films. It was observed that diffusion length of positron increased ~ 4 times in Na:BiVO4 and 6 times in Li:BiVO4 compared to pristine BiVO4. It is also concluded that the Bi and V based defects density is minimum in Na:BiVO4. The density functional theory calculations confirm this through interbands formation (Figure 1) on Li and Na doping along with the reduction in the optical bandgap.

Effect of alkali metals placement in the interstitial void of BiVO4 structure

Synthesis of new configurationally stable twisted-acenes that takes advantage of the recently reported “Torque, Lock, and Propagate” approach will be illustrated with efforts to make heli-acenes, 1 and 2. Key benzoquinone homologation and Mallory photocyclization steps will be described in detail. We will also describe computational studies that focus on the comparison of structural features and the electronic character of these heliacenes to pentacene and tetracene. We anticipate that these new twisted acenes will provide promise as chiral organic semiconductors with increased stability towards oxidation, dimerization, and polymerization that decrease the utility of planar acene homologues.

Comparison of structural and electronic character of Heli-acenes and acenes

Understanding the role f-electrons play in coordination and bonding has been a central focus of research in the lanthanides and actinides for decades, with particular relevance to applications in lanthanide-actinide separations. An interesting ligand for studying lanthanide and actinide bonding is 2,2’:6,2’-terpyridine (terpy) because the nitrogens in terpy could potentially act as a soft electron donor, with differences in bonding between the ligand and a central actinide (An) as compared to a central lanthanide (Ln). Additionally, changes in the metal ionic radius can affect how the ligand coordinates with the central atom. Soft x-ray absorption spectroscopy measurements have been performed on Ln-terpy complexes (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) at the nitrogen K-edge and lanthanide M4,5-edges. These experiments were performed at the Advanced Light Source (ALS) Scanning Transmission X-ray Microscopes (STXMs) at Beamlines 11.0.2 and Beamlines 5.3.2. Preliminary results indicate a clear difference in electronic structure between the lighter and heavier lanthanides. Interpretation of these results, including preliminary density functional theory (DFT) calculations are discussed, along with ongoing efforts to extend this system to An-terpy compounds.

Lanthanide electronic structure explored through soft x-ray spectromicroscopy of Ln-2,2’:6,2’-terpyridine coordination compounds

Although cannabis products are legal for medicinal or recreational use in many US states and in Canada, there are currently no harmonized guidelines for pesticide residue tolerances. Consequently, each state or nation with legalized cannabis has its own pesticide residue list with limits that may be quite different in each region. The AOAC has issued a Standard Method Performance Requirements document (SMPR 2018.011) that describes minimum recommended performance characteristics to be used to evaluate methods for determination of pesticides in cannabis. AOAC has used the lowest tolerance level from any of the US states or Canada as the target action level for any proposed method with a recommended LOQ at 50% of the action level. Although most of the target pesticides are amenable to LC-MS/MS analysis, many compounds have much lower detection limits using GC-MS/MS methods. Therefore, both LC-MS (ESI and APCI) and GC-MS (EI and API) methodologies designed to meet AOAC requirements will be discussed.

LC-MS/MS and GC-MS/MS to meet AOAC method performance requirements for multi-residue pesticide analysis in cannabis

Purification of recombinant AAV9 from cell lysates remains a technical challenge and an economic burden for commercial manufacturing of novel gene therapeutics. Currently available affinity resins for AAV9 purification are plagued by poor reduction in Host Cell Protein (HCP) and the inability to use NaOH solutions for Clean-In-Place (CIP). To support the rapidly-expanding gene therapy industry we described the development of AVIPureTM – AAV9, a novel affinity chromatography resin with ability to perform single-step purification of AAV9 from cell lysates with excellent yield and purity. Key distinguishing features are the ability to clean with NaOH and being based on an agarose bead for improved non-specific absorption. The large diameter agarose bead enables high flow rates and excellent resistance to fouling, important features when a typical purification cycle involves loading the column with up to 200 column volumes of host cell culture fluid. The order of magnitude improvement in resin lifetime promises to dramatically decrease resin costs for AAV programs requiring annual production of very large amounts of capsids. The affinity ligand is a novel peptide with exquisite specificity for rAAV9, binding the virus with picomolar affinity. A long, flexible spacer molecule attaches the ligand to the resin, enabling efficient capture of virus. Elution of several variants of AAV9 capsids elution was achieved in the range pH 4.5 – 3. Overall, AVIPureTM – AAV9 resin provides excellent yield, purity and throughput for single-step purification of rAAV9 and enables the use of sodium hydroxide as a cleaning agent for multiple cycles.

Development of AVIPureTM - AAV9: The first affinity resin for AAV production that can be cleaned with sodium hydroxide enables high resin reusability and decreases annual resin costs for high scale production

Of the 3 main protein secondary structures, β-sheets have proven the hardest to model and study. Although a number of model systems have been explored for creating β-sheets, they have been plagued by problems of aggregation and insolubility. These problems can be traced to the flat, two-dimensional shapes of the existing models systems, which allow for the model β-sheets to associate either side to side, or above and below, or both. To prevent such aggregation and improve solubility, a model system that includes a 3-dimensional shape might be useful. Research has shown that 1 has a rigid conformation with the two alkyne ligands spaced 3.3 A apart, which is close to the spacing of the two peptide strands in a β-sheet. Current work has been exploring whether peptides appended to the two alkynes in the rigid, bimetallic ring 1 will associate with each other to form β-sheets, as indicated in 2. It has been found that placing a phenyl spacer between the alkynes and the peptides prevents the formation of intramolecular hydrogen bonds between the two peptides, but a methylene spacer does allow for this intramolecular hydrogen bonding. Whether the methylene spacer is attached to a primary amine or a carboxyl group does affect the nature of the hydrogen bonding. The conformations of these species have been explored using both spectroscopic and DFT experiments, and the data indicates that these molecules adopt a conformation that has the peptides in a β-sheet conformation with the ferrocene rings located above the nascent sheet. This gives the model a unique 3-dimensional shape. Details regarding the preparation and behavior of these novel bioorganometallic models for β-sheets will be detailed.

Using a rigid, organometallic ring system to nucleate β-sheets

Biofouling attachment on submerged surfaces presents a serious economic and ecological problem for the marine industry. When a substrate-bonded dielectric elastomer (DE) is subjected to high voltage, deformations in the form of creases can be formed at the surface of the DE. This deformation, has been already demonstrated for the prevention and detachment of biofouling from the surface of DEs. In this work we add sensing capabilities to the anti-biofouling effect of active DE surfaces. A device consisting of a metallic plate, a Kapton sheet, and a thin silicone film, was immersed in saltwater. The water acted as one electrode, with the metal plate being the second electrode. Because silicone film was bonded to a rigid substrate, and because silicones are incompressible, voltages below the creasing threshold created no deformation in the film, and therefore no change in capacitance. However, when a critical value of voltage was reached, instabilities appeared at the surface of the silicone in the form of creases. Formation of creases increased the capacitance of the device. The voltage at which the capacitance increases is identified as the threshold voltage for creasing instabilities. We propose that when biofouling material (e.g. barnacles) is attached to the surface of the silicone elastomer, it will change the stiffness of the surface of the silicone elastomer and influence the threshold voltage necessary to develop creases. Measuring the capacitance versus voltage will enable the identification of the voltage threshold, and therefore provide a monitor of biofouling growth.

Creasing instabilities of dielectric elastomer for monitoring of biofouling

Molten salts have broad applications in high-temperature energy systems such as advanced nuclear reactors and concentrated solar power systems. However, it is known that molten salts are corrosive to most of the structural materials, and the corrosion by molten salts is one of the major concerns in their applications. Impurities, especially, non-metal impurities such as moisture, hydroxide and oxygen, are known to accelerate the material corrosion. The present study focused on measurements of the fundamental data such as diffusion coefficients of non-metal ions and reaction constants of the redox reactions that may influence the corrosion kinetics. The study investigated the following non-metal ions: OH-, O2- and I-. In addition, the study also investigated how to removal these ions from molten fluoride salts electrochemically. It was found that the oxygen ion can be removed by using a graphite anode in the form of carbon oxides, and the iodine ion can be removed by using graphite anode in the form iodine gas. The study also showed the anodic effects on a graphite anode which would affect the separation efficiency for iodine removal from a fluoride molten salt.

Properties and removal of non-metal ions in molten salts

The exact nature of uranium oxides in spent nuclear fuel is a primary concern in the storage of nuclear fuels resulting from both the volumetric expansion of uranium oxides and change in solubility with an increase in oxygen content. In particular, the growth of hyper–stoichiometric uranium dioxide has been linked to fracturing of spent fuel, resulting in further oxidation and the release of short-lived radionuclides trapped within the UO2 matrix. Oxygen K-edge x-ray absorption spectroscopy (XAS), utilizing a scanning transmission x-ray microscope (STXM) at the Advanced Light Source, is an excellent method to distinguish between different uranium oxide stoichiometries, but specimens must be extremely thin as a result of the short penetration length of soft x-rays. Low burnup pressurized water reactor spent nuclear fuel pins were processed at Idaho National Laboratory utilizing focused ion beam (FIB) sectioning, resulting in specimens ideal for soft x-ray spectroscopy. Measurements of oxygen K-edge near-edge XAS, using the Beamline 11.0.2 STXM have been conducted on several FIB sections of spent nuclear fuel. The FIB sections present challenges in normalization and data analysis. The sensitivity of the oxygen K-edge XAS spectrum between the different uranium oxides has allowed for species-specific mapping of the spent nuclear fuel at the sub-micron scale, showing UO2 as the bulk of the fuel, with U3O7 localized near defects. Additionally, spectral results at the uranium N4,5 edges and the cerium M4,5 edges are analyzed and will be discussed.

Oxygen K-edge spectromicroscopy of uranium oxides in spent nuclear fuel

Bio-mass derived oils have the potential to offset our dependence on fossil fuels. However, bio-oils contain compounds with various functional groups that can be corrosive to structural alloys. As such, bio-oil materials compatibilities for long-term production and storage of bio-oils need to be qualified. Analysis of corrosion products formed on the surfaces of alloy specimens helped identify some of the corrosive species in bio-oils. Our preliminary results showed that small organic carboxylic acids are the primary corrosive species found in fast pyrolysis bio-oils. Quantification of these species using various analytical tools is important for assessment of the level of corrosiveness of bio-oils. This presentation will highlight some of our analytical techniques used to speciate and quantify corrosive compounds in bio-derived oils. In addition, mitigation of corrosion by pre-treatment of bio-oils will be presented. The results of this work will help in understanding the corrosion mechanism and ultimately deciding which materials are most suitable as structural components for production and storage of bio-oils.

Alloy corrosion studies and analysis of corrosive compounds in bio-derived oils

Alkali and alkaline-earth fluoride salts have the potential to be used as 1) heat transfer fluids for power generation and 2) as solvents for fissile material in molten salt reactors (MSRs). However, because of their hygroscopicity, these salts tend to be corrosive to structural alloys due to in situ formation of corrosive hydrofluoric (HF) acid in the presence of water. Reliable methods to quantify low level oxygen and hydrogen in these salts have not been developed or require impractical conditions such as the use of explosive oxidizers. Quantification of oxygen and hydrogen has been routinely done in organic and inorganic samples using commercial combustion analysis instruments. Quantification of oxygen and hydrogen in halide salts using combustion methods is challenging due to formation of corrosive gases which can damage the internal parts of the instrument and produce inconsistent results. In this presentation, we will show our methodology for reproducible quantification of oxygen and hydrogen in fluoride salts using commercial combustion analysis. In addition, quantification of impurity anionic species in halide salts, such as SO42-, NO3-, CO32-, Br-, etc., will be presented.

Analysis of oxygen, water and inorganic anions in fluoride salts

Biomass derived pyrolysis oils is a renewable energy source that could gradually replace fossil-based oils in multiple industrial sectors. However, bio-oils can cause a corrosion risk for structural steels due to their organic acids and water content. A recent work tested different structural steels in 0.1 molal lactobionic and formic acids, i.e. potential corrosive constituents in common bio-oils, and determined that type 410 stainless steel (11.8 wt% Cr) would be the minimum requirement for corrosion resistance. According to this result, type 410 and three more stainless steels with higher Cr contents (&gt; 12 wt%) were selected in this work for corrosion study in a low ash and low moisture (LALM) bio-oil, produced by National Renewable Energy Laboratory. For a quick evaluation of corrosion behavior, electrochemical impedance spectroscopy (EIS) measurements were made for each steel type in the LALM oil. The analysis of impedance data indicted that the bio-oil is more corrosive than formic and lactobionic acids, so a stainless steel with 14.5 wt% Cr is the minimum requirement to avoid corrosion. Currently, EIS measurements are underway for the selected stainless steels in LALM bio-oils added with formic and lactobionic acids, to further investigate the role of the organic acids for the bio-oil corrosivity.

Corrosion behavior of structural stainless steels in LALM biomass pyrolysis oil

Horizontal drilling and hydraulic fracturing techniques have experienced a rapid increase over the past decade with regard to conventional and unconventional energy production. The produced water generated contains a broad variety of hazardous substances classified as a major concern for the environment and human health. In this sense, many countries have implemented stringent regulatory standards for discharging produced water from oil and gas extraction process. For their treatment, most of the technologies studied have presented unveiled disadvantages mainly due to their acquisition and exploitation costs. The use of eco-friendly water technologies can contribute to decrease the load of hazardous chemicals entering into the environment whilst minimizing the energy consumption. However, while many studies have evaluated the elimination of target pollutants, few attention has been paid to the study of the transformation products (TPs) generated. In this study, eco-friendly microalgae treatments have been performed for the elimination of the surfactant benzalkonium chloride in spiked seawater and produced water. The experiments were carried out in an own-design photobioreactor using eight different marine microalgae strains. Samples were analyzed in a liquid-chromatography system coupled to high-resolution mass spectrometry (LC-HRMS) using in-source ion fragmentation for the identification of the isomer intermediates generated. Results reveal complete elimination of benzalkonium chloride after 14 days of treatment using T. suecica microalga stain in fortified seawater. However, this microalga achieved lower removal rates (54%) treating real produced water. In both cases, the major intermediates generated were isomeric hydroxyl compounds and unsaturated intermediates generated through further dehydration step. The intermediates generated were evaluated in terms of anticorrosion activity regarding their estimated hydrophobicity in water. As a conclusion, T. suecica was the only microalgae capable to biodegrade the parent compound into a more hydrophilic intermediates decreasing their amphiphilic properties, and thus, their activity as surfactants and corrosion inhibitors.

Microalgae-based technology for removal of benzalkonium chloride in oil and gas produced water: Biotransformation and environmental effects

To minimize the lifetime of salt facing components, it is important to understand the material and chemical factors that affect corrosion. Dating back to the MSRE, efforts toward controlling corrosion in molten fluoride salts focused on careful alloy selection, thorough salt purification, and additives for redox control. This work highlights recent findings showing how controlling salt chemistry affects corrosion in fluoride and chloride salts. New developments in salt purification and redox control additives are shown to have direct and measurable effects on corrosion. Model alloys are used to isolate the effects of alloy composition and microstructure. Spectroscopic techniques are used in conjunction with traditional characterization to measure new salt properties. This talk will discuss the state of the art, and highlight new progress toward understanding what matters most when controlling corrosion in nuclear and concentrating solar systems that use molten salt coolants.

Alloy corrosion in molten salts: What matters, what doesn't, and what can we do about it?

ACS Fall 2020 Virtual Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.