Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials.

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba(OH)2 electrolyte, we find both Cu-O bonds and Cu-Ba scattering persist at potentials as low as -400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts.

Aqueous Structure of Lanthanide-EDTA Coordination Complexes Determined by a Combined DFT/EXAFS Approach.

Sustainable production of rare earth elements (REEs) is critical for technologies needed for climate change mitigation, including wind turbines and electric vehicles. However, separation technologies currently used in REE production have large environmental footprints, necessitating more sustainable strategies. Aqueous, affinity-based separations are examples of such strategies. To make these technologies feasible, it is imperative to connect aqueous ligand structure to ligand selectivity for individual REEs. As a step toward this goal, we analyzed the extended X-ray absorption fine structure (EXAFS) of four lanthanides (La, Ce, Pr, and Nd) complexed by a common REE chelator, ethylenediaminetetraacetic acid (EDTA) to determine the aqueous-phase structure. Reference structures from density functional theory (DFT) were used to help fit the EXAFS spectra. We found that all four Ln-EDTA coordination complexes formed 9-coordinate structures with 6 coordinating atoms from EDTA (4 carboxyl oxygen atoms and 2 nitrogen atoms) and 3 oxygen atoms from water molecules. All EXAFS fits were of high quality (R-factor < 0.02) and showed decreasing average first-shell coordination distance across the series (2.62-2.57 Å from La-Nd), in agreement with DFT (2.65-2.56 Å from La-Nd). The insights determined herein will be useful in the development of ligands for sustainable rare earth elements (REE) separation technologies.

Identifying the Local Atomic Environment of the "Cu3+" State in Alkaline Electrochemical Systems.

CuO-based catalysts are active for the oxygen evolution reaction (OER), although the active form of copper for the OER is still unknown. We combine operando Raman experiments and density functional theory (DFT) electronic structure calculations to determine the form of Cu(O)xOHy present under OER conditions. Raman spectra show a distinct feature related to the active "Cu3+" species, which is only present under highly oxidizing conditions. DFT is used to produce theoretical Raman standards and match the unique Raman feature of copper under OER potentials. This method identifies a range of Cu3+-containing compounds which match the distinct Raman feature. We then integrate experimental electrochemistry to progressively eliminate possible structures and determine the stoichiometry of the active form as CuOOH, which likely takes the form of a surface-adsorbed hydroxide on a CuO surface. Bader charge analysis, site-projected wavefunctions, and density of states analysis show that electron density is removed from O 2p orbitals upon hydroxide adsorption, suggesting that the electronic structure exhibits d9L Cu2+ behavior rather than the local electronic structure of a formal Cu3+.

Biodegradable microneedle patch for delivery of meloxicam for managing pain in cattle.

Microneedle patches are a promising source for transdermal diffusion of macromolecules and are designed to painlessly penetrate the skin. In this study, a biodegradable chitosan microneedle patch to deliver meloxicam for managing pain in cattle was tested. The potential of reuse of the polymeric solution to fabricate the patches, optimization of fabrication, morphological analysis of the microneedle patch and analysis of preservation of the chemical composition after sterilization were evaluated. In-vitro analysis consisted of studying in-vitro penetration mechanical properties, compression testing analysis of microneedle patch, and in-vitro drug release analysis. In-vivo studies were performed to analyze the dissolution capability of the microneedle patch. Results regarding the physical characteristics, chemical composition, and mechanical properties confirmed that rheological properties of the chitosan solution, present significant differences over time, demonstrating that reusing the solution on the fourth day results in failure patches. Morphological characteristics and chemical composition studies revealed that the process of sterilization (ethylene oxide gas) needed for implanting the patches into the skin did not affect the properties of microneedle patches. In-vitro studies showed that approximately 33.02 ± 3.88% of the meloxicam was released over 7 days. A full penetration of the microneedles into the skin can be obtained by applying approximately 3.2 N. In-vivo studies demonstrated that microneedle patches were capable of swelling and dissolving, exhibiting a dissolution percentage of more than 50% of the original height of microneedle after 7 days. No abnormal tissue, swelling, or inflammation was observed in the implanted area. The results of this work show that chitosan biodegradable microneedle patches may be useful to deliver meloxicam to improve pain management of cattle with positive effects for commercial manufacturing.

Ultrafiltration Membranes Functionalized with Copper Oxide and Zwitterions for Fouling Resistance.

Polymeric membrane fouling is a long-standing challenge for water filtration. Metal/metal oxide nanoparticle functionalization of the membrane surface can impart anti-fouling properties through the reactivity of the metal species and the generation of radical species. Copper oxide nanoparticles (CuO NPs) are effective at reducing organic fouling when used in conjunction with hydrogen peroxide, but leaching of copper ions from the membrane has been observed, which can hinder the longevity of the CuO NP activity at the membrane surface. Zwitterions can reduce organic fouling and stabilize NP attachment, suggesting a potential opportunity to combine the two functionalizations. Here, we coated polyethersulfone (PES) ultrafiltration membranes with polydopamine (PDA) and attached the zwitterionic compound, thiolated 2-methacryloyloxyethyl phosphorylcholine (MPC-SH), and CuO NPs. Functionalized membranes resulted in a higher flux recovery ratio (0.694) than the unfunctionalized PES control (0.599). Copper retention was high (>96%) for functionalized membranes. The results indicate that CuO NPs and MPC-SH can reduce organic fouling with only limited copper leaching.

Electrochemical nutrient removal from natural wastewater sources and its impact on water quality.

In this study, a suite of natural wastewater sources is tested to understand the effects of wastewater composition and source on electrochemically driven nitrogen and phosphorus nutrient removal. Kinetics, electrode behavior, and removal efficiency were evaluated during electrochemical precipitation, whereby a sacrificial magnesium (Mg) anode was used to drive precipitation of ammonium and phosphate. The electrochemical reactor demonstrated fast kinetics in the natural wastewater matrices, removing up to 54% of the phosphate present in natural wastewater within 1 min, with an energy input of only 0.04 kWh.m-3. After 1 min, phosphate removal followed a zero-order rate law in the 1 min - 30 min range. The zero-order rate constant (k) appears to depend upon differences in wastewater composition, where a faster rate constant is associated with higher Cl- and NH4+ concentrations, lower Ca2+ concentrations, and higher organic carbon content. The sacrificial Mg anode showed the lowest corrosion resistance in the natural industrial wastewater source, with an increased corrosion rate (vcorr) of 15.8 mm.y-1 compared to 1.9-3.5 mm.y-1 in municipal wastewater sources, while the Tafel slopes (ß) showed a direct correlation with the natural wastewater composition and origin. An overall improvement of water quality was observed where important water quality parameters such as total organic carbon (TOC), total suspended solids (TSS), and turbidity showed a significant decrease. An economic analysis revealed costs based upon experimental Mg consumption are estimated to range from 0.19 $.m-3 to 0.30 $.m-3, but costs based upon theoretical Mg consumption range from 0.09 $.m-3 to 0.18 $.m-3. Overall, this study highlights that water chemistry parameters control nutrient recovery, while electrochemical treatment does not directly produce potable water, and that economic analysis should be based upon experimentally-determined Mg consumption data. Synopsis Statement: Magnesium-driven electrochemical precipitation of natural wastewater sources enables fast kinetics for phosphate removal at low energy input.

Disinfection/ammonia removal from aquaculture wastewater and disinfection of irrigation water using electrochemical flow cells: A case study in Hawaii.

This field case study reports findings on disinfection/ammonia removal from aquaculture wastewater and disinfection of irrigation water carried out at an aquaculture farm and two irrigation locations in Hawaii. We used a flow cell incorporating PtRu/graphite anode and graphite cathode for the disinfection/ammonia removal from aquaculture wastewater, and a flow cell assembled with graphite plates as both anode and cathode for the disinfection of irrigation water. The removal of ammonia followed the indirect oxidation mechanism mediated by free chlorine electro-generated at the PtRu/graphite anode. Ammonia removal rate increased with the increase in NaCl concentration, applied current density, or flow rate. The disinfection of aquaculture wastewater can be readily achieved due to the presence of highly germicidal free chlorine species. The disinfection of irrigation water was realized without the addition of chemicals. The disinfection mechanism was attributed to the formation of free chlorine from the anodic oxidation of chloride ions naturally occurring in the water sources. The disinfection efficiency decreased with increasing organic matter concentration. In addition to the flow cell approach, we also successfully demonstrated the disinfection of irrigation water by adding electrolyzed NaCl solution or purging with a mixture of air and chlorine gas, both of which were generated on-site. PRACTITIONER POINTS: Field case study on disinfection/ammonia removal from aquaculture wastewater and disinfection of irrigation water was carried out in Hawaii. Electrochemical flow cell assembled with PtRu/graphite anode and graphite cathode effectively removes ammonia from aquaculture wastewater. Ammonia removal proceeds via the indirect oxidation mechanism mediated by free chlorine electro-generated at the PtRu/graphite anode. Electrochemical flow cell assembled with commercial graphite electrodes enables fast disinfection of coliform bacteria and E. coli. The primary disinfection mechanism is through chlorine species electro-generated from chloride oxidation at the graphite anode.

Electrochemical biomass upgrading: degradation of glucose to lactic acid on a copper(ii) electrode.

Biomass upgrading - the conversion of biomass waste into value-added products - provides a possible solution to reduce global dependency on nonrenewable resources. This study investigates the possibility of green biomass upgrading for lactic acid production by electrochemically-driven degradation of glucose. Herein we report an electrooxidized copper(ii) electrode which exhibits a turnover frequency of 5.04 s-1 for glucose conversion. Chronoamperometry experiments under varied potentials, alkalinity, and electrode preparation achieved a maximum lactic acid yield of 23.3 ± 1.2% and selectivity of 31.1 ± 1.9% (1.46 V vs. RHE, 1.0 M NaOH) for a room temperature and open-to-atmosphere reaction. Comparison between reaction conditions revealed lactic acid yield depends on alkalinity and applied potential, while pre-oxidation of the copper had a negligible effect on yield. Post-reaction cyclic voltammetry studies indicated no loss in reactivity for copper(ii) electrodes after a 30 hour reaction. Finally, a mechanism dependent on solvated Cu2+ species is proposed as evidenced by similar product distributions in electrocatalytic and thermocatalytic systems.

Electrochemical disinfection of irrigation water with a graphite electrode flow cell.

In this work, we report experimental studies on the disinfection of irrigation water using a flow cell assembled with low-cost graphite plates as both anode and cathode. Natural irrigation waters collected from two irrigation locations (Reservoir 225 and Bott Well Pond) in Hawaii were used, and synthetic irrigation waters were prepared based on the chemical analysis of natural irrigation waters. The concentration of chloride was 10.2 mg/L in the synthetic Reservoir 225 water and 6.9 mg/L in the synthetic Bott Well pond water. Escherichia coli K12 ER2738 was selected as a model bacterium to evaluate the disinfection capability of the flow cell. Experiments performed in the synthetic irrigation waters showed that E. coli was inactivated by free chlorine species electro-generated from oxidation of chloride ions at the graphite anode. Complete removal of E. coli was achieved within 10 min in the synthetic irrigation waters. The disinfection of the natural irrigation waters took about four times longer than the disinfection of the synthetic irrigation waters. This result is most likely due to the presence of organic matter (and possibly other oxidizable species) in the natural irrigation waters. PRACTITIONER POINTS: Electrochemical flow cell disinfects to 99.9% with commercial graphite electrodes. E. coli is removed in 10 min from synthetic irrigation water by a flow cell. E. coli removal takes 4× longer in natural irrigation water. A minimum current density of ≥1 mA/cm2 is required for disinfection. The primary disinfection mechanism is through chlorine generated from chloride ions.

Design, characterization, and modeling of a chitosan microneedle patch for transdermal delivery of meloxicam as a pain management strategy for use in cattle.

This work describes the formulation and evaluation of a chitosan microneedle patch for the transdermal delivery of meloxicam to manage pain in cattle. Microneedle patches composed of chitosan and chitosan/meloxicam were evaluated regarding their chemical composition, uniformity of physical characteristics, capacity to penetrate the skin, and response to thermal and thermo-mechanical changes. Microneedle patches were prepared by varying the percentage of acetic acid used during solution preparation, including 90% (v/v), 50% (v/v), and 10% (v/v). In addition, drug release was assessed by modeling different percentages of penetration into the skin and the number of microneedles on the microneedle patch. Scanning electron microscopy confirmed the presence of microneedles uniformly organized on the patch surface for each percentage of acetic acid used. Fourier transform infrared spectroscopy revealed that 10% (v/v) of acetic acid in the solution was a suitable condition to preserve the characteristic bands of chitosan (amide I and amide II) and meloxicam (amine NH stretch and CO stretch) as compared to 90% (v/v) and 50% (v/v) of acetic acid used during the solution preparation. The resultant microneedle patches were successful in penetrating the skin in a cow's cadaver ear. Results demonstrated that the average depth penetration measured after complete dehydration of the penetrated skin was approximately 78 ± 1 µm. Chitosan and chitosan/meloxicam microneedle patches with higher acetic acid percentages reflected greater resistance to compressive force as temperature increased. Time-dependent simulation of the transport of diluted species by COMSOL revealed that the transdermal drug delivery increases in function to the increment of the number of microneedles on the surface patch and percentage of penetration per microneedle. One patch released a drug concentration of 3.57 × 10-5 mol/m3 in the skin per week, which represents the 26.2% of what is needed for pain management in cattle, established as 1.43 × 10-4 mol/m3. These results demonstrate that chitosan/meloxicam microneedles patches may be suitable to manage pain in cattle after routine procedures.

Electroless Production of Fertilizer (Struvite) and Hydrogen from Synthetic Agricultural Wastewaters.

The drive toward sustainable phosphorus (P) recovery from agricultural and municipal wastewater streams has intensified. However, combining P recovery with energy conservation is perhaps one of the greatest challenges of this century. In this study, we report for the first time the simultaneous electroless production of struvite and dihydrogen from aqueous ammonium dihydrogen phosphate (NH4H2PO4) solutions in contact with either a pure magnesium (Mg) or a Mg alloy as the anode and 316 stainless steel (SS) as the cathode placed in a bench-scale electrochemical reactor. During the electroless process (i.e., in the absence of external electrical power), the open circuit potential (OCP), the formation of struvite on the anode, and the generation of dihydrogen at the cathode were monitored. We found that struvite is formed, and that struvite crystal structure/morphology and precipitate film thickness are affected by the concentration of the HnPO4n-3/NH4+ in solution and the composition of the anode. The pure Mg anode produced a porous 0.6-4.1 µm thick film, while the AZ31 Mg alloy produced a more compact 1.7-9.9 µm thick struvite film. Kinetic analyses revealed that Mg dissolution to Mg2+ followed mostly a zero-order kinetic rate law for both Mg anode materials, and the rate constants (k) depended upon the struvite layer morphology. Fourier-transform infrared spectrometry, X-ray diffraction, and scanning electron microscopy indicated that the synthesized struvite was of high quality. The dihydrogen and Mg2+ in solution were detected by a gas chromatography-thermal conductivity detector and ion chromatography, respectively. Furthermore, we fully demonstrate that the reactor was able to remove ∼73% of the HnPO4n-3 present in a natural poultry wastewater as mainly struvite. This study highlights the feasibility of simultaneously producing struvite and dihydrogen from wastewater effluents with no energy input in a green and sustainable approach.

Recombinant peptide fusion construction for protein-templated catalytic palladium nanoparticles.

Although peptide-enabled synthesis of nanostructures has garnered considerable interest for use in catalytic applications, it has so far been achieved mostly via Fmoc based solid phase peptide synthesis. Consequently, the potential of longer peptides in nanoparticle synthesis have not been explored largely due to the complexities and economic constraints of this chemical synthesis route. This study examines the potential of a 45-amino acid long peptide expressed as fusion to green fluorescence protein (GFPuv) in Escherichia coli for use in palladium nanoparticle synthesis. Fed-batch fermentation with E. coli harboring an arabinose-inducible plasmid produced a product containing three copies of Pd4 peptide fused to N-terminus of GFPuv ((Pd4)3 -GFPuv). Using the intrinsic fluorescence of GFPuv, expression and enrichment of the fusion product was easily monitored. Crude lysate, desalted lysate, and an ion-exchange enriched fraction containing (Pd4)3 -GFPuv were used to test the hypothesis that high purity of the biologic material used as the nanoparticle synthesis template may not be necessary. Nanoparticles were characterized using a variety of material science techniques and used to catalyze a model Suzuki-Miyaura coupling reaction. Results demonstrated that palladium nanoparticles can be synthesized using the soluble cell extract containing (Pd4)3 -GFPuv without extensive purification or cleavage steps, and as a catalyst the crude mixture is functional.

Chemical Structure of Fe-Ni Nanoparticles for Efficient Oxygen Evolution Reaction Electrocatalysis.

Bimetallic iron-nickel-based nanocatalysts are perhaps the most active for the oxygen evolution reaction (OER) in alkaline electrolytes. Recent developments in literature have suggested that the ratio of iron and nickel in Fe-Ni thin films plays an essential role in the performance and stability of the catalysts. In this work, the metallic ratio of iron to nickel was tested in alloy bimetallic nanoparticles. Similar to thin films, nanoparticles with iron-nickel atomic compositions where the atomic iron percentage is ≤50% outperformed nanoparticles with iron-nickel ratios of >50%. Nanoparticles of Fe20Ni80, Fe50Ni50, and Fe80Ni20 compositions were evaluated and demonstrated to have overpotentials of 313, 327,, and 364 mV, respectively, at a current density of 10 mA/cm2. While the Fe20Ni80 composition might be considered to have the best OER performance at low current densities, Fe50Ni50 was found to have the best current density performance at higher current densities, making this composition particularly relevant for electrolysis conditions. However, when stability was evaluated through chronoamperometry and chronopotentiometry, the Fe80Ni20 composition resulted in the lowest degradation rates of 2.9 µA/h and 17.2 µV/h, respectively. These results suggest that nanoparticles with higher iron and lower nickel content, such as the Fe80Ni20 composition, should be still taken into consideration while optimizing these bimetallic OER catalysts for overall electrocatalytic performance. Characterization by electron microscopy, diffraction, and X-ray spectroscopy provides detailed chemical and structural information on as-synthesized nanoparticle materials.

Controlling the 3-D morphology of Ni-Fe-based nanocatalysts for the oxygen evolution reaction.

Controlling the 3-D morphology of nanocatalysts is one of the underexplored but important approaches for improving the sluggish kinetics of the oxygen evolution reaction (OER) in water electrolysis. This work reports a scalable, oil-based method based on thermal decomposition of organometallic complexes to yield highly uniform Ni-Fe-based nanocatalysts with a well-defined morphology (i.e. Ni-Fe core-shell, Ni/Fe alloy, and Fe-Ni core-shell). Transmission electron microscopy reveals their morphology and composition to be NiOx-FeOx/NiOx core-mixed shell, NiOx/FeOx alloy, and FeOx-NiOx core-shell. X-ray techniques resolve the electronic structures of the bulk and are supported by electron energy loss spectroscopy analysis of individual nanoparticles. These results suggest that the crystal structure of Ni is most likely to contain α-Ni(OH)2 and that the chemical environment of Fe is variable, depending on the morphology of the nanoparticle. The Ni diffusion from the amorphous Ni-based core to the iron oxide shell makes the NiOx-NiOx/FeOx core-mixed shell structure the most active and the most stable nanocatalyst, which outperforms the comparison NiOx/FeOx alloy nanoparticles expected to be active for the OER. This study suggests that the chemical environment of the mixed NiOx/FeOx alloy composition is important to achieve high electrocatalytic activity for the OER and that the 3-D morphology plays a key role in the optimization of the electrocatalytic activity and stability of the nanocatalyst for the OER.

Post-Synthesis Separation and Storage of Zero-Valent Iron Nanoparticles.

Zero-valent iron (ZVI) nanoparticles are susceptible to oxidation and are therefore sensitive to postsynthesis processing, including both separation and storage techniques. Two separation methods, centrifugation and magnetic separation, were evaluated in this study. Nanoparticle stability during storage in ethanol-water solutions was also studied, and the influence of both water and aeration on nanoparticle oxidation was determined. Nanoparticle morphology and extent of oxidation were analyzed with electron microscopy, elemental analysis, zeta potential, and X-ray photoelectron spectroscopy. Microscopy results suggest that the separation method used affects the extent of stabilizer that remains adsorbed to the nanoparticles, but both separation methods result in minimal oxidation of the nanoparticles. However, the addition of aerated water to nanoparticle-ethanol storage solutions caused nanoparticle oxidation; an increase in the volume fraction of water added caused a linear increase in oxygen content based on elemental analysis of nanoparticle samples. X-ray photoelectron spectroscopy results suggest that organic stabilizer is incorporated into the nanoparticle structure as oxidation occurs.

Scalable Chitosan-Graphene Oxide Membranes: The Effect of GO Size on Properties and Cross-Flow Filtration Performance.

Chitosan (CS)-graphene oxide (GO) composite films were fabricated, characterized, and evaluated as pressure-driven water filtration membranes. GO particles were incorporated into a chitosan polymer solution to form a suspension that was cast as a membrane via evaporative phase inversion allowing for scale-up for cross-flow testing conditions. Morphology and composition results for nano and granular GO in the CS matrix indicate that the particle size of GO impacts the internal membrane morphology as well as the structural order and the chemical composition. Performance of the membranes was evaluated with cationic and anionic organic probe molecules and revealed charge-dependent mechanisms of dye removal. The CSGO membranes had rejections of at least 95% for cationic methylene blue with mass balances obtained from measurements of the feed, concentrate, and permeate. This result suggests the dominant mechanism of removal is physical rejection for both GO particle sizes. For anionic methyl orange, the results indicate sorption as the dominant mechanism of removal, and performance is dependent on both GO particle size and time, with micrometer-scale GO removing 68-99% and nanometer-scale GO showing modest removal of 29-64%. The pure water flux for CSGO composite membranes ranged from 2-4.5 L/m2 h at a transmembrane pressure of 344 kPa (3.44 bar), with pure water permeance ranging from 5.8 × 10-3 to 0.01 L/m2 h kPa (0.58-1.3 L/m2 h bar). Based on the 41 µm membrane thickness obtained from microscopy, the hydraulic permeability ranged from 0.24-0.54 L µm/m2 h kPa (24.4-54.1 L µm/m2 h bar).

Processing and Characterization of Nanoparticle Coatings for Quartz Crystal Microbalance Measurements.

The quartz-crystal microbalance is a sensitive and versatile tool for measuring adsorption of a variety of compounds (e.g. small molecules, polymers, biomolecules, nanoparticles and cells) to surfaces. While the technique has traditionally been used for measuring adsorption to flat surfaces and thin ridged films, it can also be extended to study adsorption to nanoparticle surfaces when the nanoparticles are fixed to the crystal surface. The sensitivity and accuracy of the measurement depend on the users' ability to reproducibly prepare a thin uniform nanoparticle coating. This study evaluated four coating techniques, including spin coating, spray coating, drop casting, and electrophoretic deposition, for two unique particle chemistries [nanoscale zero valent iron (nZVI) and titanium dioxide (TiO2)] to produce uniform and reproducible nanoparticle coatings for real-time quartz-crystal microbalance measurements. Uniform TiO2 coatings were produced from a 50 mg/mL methanol suspension via spin coating. Nanoscale zero-valent iron was best applied by spray coating a low concentration 1.0 mg/mL suspended in methanol. The application of multiple coatings, rather than an increase in the suspension concentration, was the best method to increase the mass of nanoparticles on the crystal surface while maintaining coating uniformity. An upper mass threshold was determined to be approximately 96 µg/cm(2); above this mass, coatings no longer maintained their uniform rigid characteristic, and a low signal to noise ratio resulted in loss of measurable signal from crystal resonances above the fundamental.

Kinetics of zero valent iron nanoparticle oxidation in oxygenated water.

Zero valent iron (ZVI) nanoparticles are versatile in their ability to remove a wide variety of water contaminants, and ZVI-based bimetallic nanoparticles show increased reactivity above that of ZVI alone. ZVI nanoparticles degrade contaminants through the reactive species (e.g., OH*, H(2(g)), H(2)O(2)) that are produced during iron oxidation. Measurement and modeling of aqueous ZVI nanoparticle oxidation kinetics are therefore necessary to optimize nanoparticle design. Stabilized ZVI and iron-nickel nanoparticles of approximately 150 nm in diameter were synthesized through solution chemistry, and nanoparticle oxidation kinetics were determined via measured mass change using a quartz crystal microbalance (QCM). Under flowing aerated water, ZVI nanoparticles had an initial exponential growth behavior indicating surface-dominated oxidation controlled by migration of species (H(2)O and O(2)) to the surface. A region of logarithmic growth followed the exponential growth which, based on the Mott-Cabrera model of thin oxide film growth, suggests a reaction dominated by movement of species (e.g., iron cations and oxygen anions) through the oxide layer. The presence of ethanol or a nickel shell on the ZVI nanoparticles delayed the onset of iron oxidation and reduced the extent of oxidation. In oxygenated water, ZVI nanoparticles oxidized primarily to the iron oxide-hydroxide lepidocrocite.

The effect of antiscalant addition on calcium carbonate precipitation for a simplified synthetic brackish water reverse osmosis concentrate.

The primary limitations to inland brackish water reverse osmosis (RO) desalination are the cost and technical feasibility of concentrate disposal. To decrease concentrate volume, a side-stream process can be used to precipitate problematic scaling salts and remove the precipitate with a solid/liquid separation step. The treated concentrate can then be purified through a secondary reverse osmosis stage to increase overall recovery and decrease the volume of waste requiring disposal. Antiscalants are used in an RO system to prevent salt precipitation but might affect side-stream concentrate treatment. Precipitation experiments were performed on a synthetic RO concentrate with and without antiscalant; of particular interest was the precipitation of calcium carbonate. Particle size distributions, calcium precipitation, microfiltration flux, and scanning electron microscopy were used to evaluate the effects of antiscalant type, antiscalant concentration, and precipitation pH on calcium carbonate precipitation and filtration. Results show that antiscalants can decrease precipitate particle size and change the shape of the particles; smaller particles can cause an increase in microfiltration flux decline during the solid/liquid separation step. The presence of antiscalant during precipitation can also decrease the mass of precipitated calcium carbonate.

Effect of antiscalants on precipitation of an RO concentrate: metals precipitated and particle characteristics for several water compositions.

Inland brackish water reverse osmosis (RO) is economically and technically limited by the large volume of salty waste (concentrate) produced. The use of a controlled precipitation step, followed by solid/liquid separation (filtration), has emerged as a promising side-stream treatment process to treat reverse osmosis concentrate and increase overall system recovery. The addition of antiscalants to the RO feed prevents precipitation within the membrane system but might have a deleterious effect on a concentrate treatment process that uses precipitation to remove problematic precipitates. The effects of antiscalant type and concentration on salt precipitation and precipitate particle morphology were evaluated for several water compositions. The primary precipitate for the synthetic brackish waters tested was calcium carbonate; the presence of magnesium, sulfate, minor ions, and antiscalant compounds affected the amount of calcium precipitated, as well as the phases of calcium carbonate formed during precipitation. Addition of antiscalant decreased calcium precipitation but increased incorporation of magnesium and sulfate into precipitating calcium carbonate. Antiscalants prevented the growth of nucleated precipitates, resulting in the formation of small (100-200 nm diameter) particles, as well as larger (6-10 microm) particles. Elemental analysis revealed changes in composition and calcium carbonate polymorph with antiscalant addition and antiscalant type. Results indicate that the presence of antiscalants does reduce the extent of calcium precipitation and can worsen subsequent filtration performance.