Long-term leaching kinetics and solution chemistry of aqueous BaTiO3 powder suspensions: a numerical model supported experiment

The advent of lead-free perovskite materials with favorable toxicity profiles has made them candidates for in vivo and environmental applications. However, their tendency to leach A-site cations raises concerns about toxicity, catalytic efficiency, and slurry properties. The present study investigates the long-term leaching kinetics of BaTiO3 powders over 31 days in aqueous solutions of varying pH levels. Using ICP-MS analysis and a numerical model based on the Unreacted Shrinking Core (USC) principle. The study extends the understanding of BaTiO3 stability beyond previously reported timeframes. The findings highlight the material's long-term stability, with implications for biomedical and environmental applications.

Investigation of the formation and variability of dissolved inorganic carbon and dissolved organic carbon in the water of a small river (on the example of the Styr River, Ukraine)

This paper presents the results of a study on the dynamics in the concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in water samples collected from the Styr River between 2019 and 2022. The concentrations of DIC and DOC were measured using an Elementar liqui TOC II analyzer. The study methodology involved analyzing the changes in DIC and DOC concentrations and their relationship with flow rates, temperature, seasonality, and other indicators such as hydrogen pH levels, total alkalinity (TA), and total dissolved solids (TDS). The purpose of this article is to identify patterns in the formation and changes of DIC and DOC concentrations in the Styr River. The concentrations of DIC and DOC in the samples ranged from 1.55 to 4.93 mM and 0.49 to 1.43 mM, respectively, with DOC accounting for an average of 22% of the total dissolved carbon content. The highest DOC concentrations were observed in summer, while the highest DIC concentrations were observed in winter. Based on the results, it can be concluded that water flow and temperature have an impact on DOC concentration, while flow, temperature, and pH affect DIC concentration. There was no correlation between DIC and DOC concentrations, but a strong positive relationship (r = 0.9056, p < 0.001) was found between DIC and TA concentrations. Therefore, the main factors influencing DIC in the Styr River are those that affect the carbonate equilibrium, such as leaching of carbonate and silicate rocks, CO2 absorption from the atmosphere, and changes in pH. Additionally, the concentration of DOC is influenced by biological activity and is higher during the warm season. These findings can be used to develop a strategy for managing water resources in the Styr River basin and to assess and predict the ecological state of the river.

Cell-Free Systems Biology: Characterizing Central Metabolism of Clostridium thermocellum with a Three-Enzyme Cascade Reaction

Genetic approaches have been traditionally used to understand microbial metabolism, but this process can be slow in nonmodel organisms due to limited genetic tools. An alternative approach is to study metabolism directly in the cell lysate. This avoids the need for genetic tools and is routinely used to study individual enzymatic reactions but is not generally used to study systems-level properties of metabolism. Here we demonstrate a new approach that we call "cell-free systems biology", where we use well-characterized enzymes and multienzyme cascades to serve as sources or sinks of intermediate metabolites. This allows us to isolate subnetworks within metabolism and study their systems-level properties. To demonstrate this, we worked with a three-enzyme cascade reaction that converts pyruvate to 2,3-butanediol. Although it has been previously used in cell-free systems, its pH dependence was not well characterized, limiting its utility as a sink for pyruvate. We showed that improved proton accounting allowed better prediction of pH changes and that active pH control allowed 2,3-butanediol titers of up to 2.1 M (189 g/L) from acetoin and 1.6 M (144 g/L) from pyruvate. The improved proton accounting provided a crucial insight that preventing the escape of CO2 from the system largely eliminated the need for active pH control, dramatically simplifying our experimental setup. We then used this cascade reaction to understand limits to product formation in Clostridium thermocellum, an organism with potential applications for cellulosic biofuel production. We showed that the fate of pyruvate is largely controlled by electron availability and that reactions upstream of pyruvate limit overall product formation.

Reaction-diffusion modeling provides insights into biophysical carbon-concentrating mechanisms in land plants

Carbon-concentrating mechanisms (CCMs) have evolved numerous times in photosynthetic organisms. They elevate the concentration of CO2 around the carbon-fixing enzyme rubisco, thereby increasing CO2 assimilatory flux and reducing photorespiration. Biophysical CCMs, like the pyrenoid-based CCM (PCCM) of Chlamydomonas reinhardtii or carboxysome systems of cyanobacteria, are common in aquatic photosynthetic microbes, but in land plants appear only among the hornworts. To predict the likely efficiency of biophysical CCMs in C3 plants, we used spatially resolved reaction-diffusion models to predict rubisco saturation and light use efficiency. We found that the energy efficiency of adding individual CCM components to a C3 land plant is highly dependent on the permeability of lipid membranes to CO2, with values in the range reported in the literature that are higher than those used in previous modeling studies resulting in low light use efficiency. Adding a complete PCCM into the leaf cells of a C3 land plant was predicted to boost net CO2 fixation, but at higher energetic costs than those incurred by photorespiratory losses without a CCM. Two notable exceptions were when substomatal CO2 levels are as low as those found in land plants that already use biochemical CCMs and when gas exchange is limited, such as with hornworts, making the use of a biophysical CCM necessary to achieve net positive CO2 fixation under atmospheric CO2 levels. This provides an explanation for the uniqueness of hornworts' CCM among land plants and the evolution of pyrenoids multiple times.

Phytoremediation of formaldehyde by three selected non-native indoor plant species

Formaldehyde is an organic volatile compound and a commonly used chemical in various construction materials thus causing dwellers to be exposed to it inside a building. Its remediation from indoor air has been carried out through various techniques where potted plants and living walls are at the front foot. It is necessary to study plants under various conditions for their efficiency. We selected three plant species Epipremnum aureum, Chlorophytum comosum, and Spathiphyllum wallisii non-native of Bahrain. These plants were tested under normal conditions in a sealed fumigation box where formaldehyde concentration was kept ∼3 ppm, CO2 ∼ 450 ppm, light intensity 1000 Lx (equal to 13.5 µmol.m-2.s-1), irrigated with tap water. Analysis of Variance (ANOVA) statistical method was performed to test the significant differences of purification efficiencies of the tested indoor plants against HCHO. In addition, the statistical method was used to test the significant difference, if any, of the plants to CO2 emission because of absorbing HCHO. The physical health of plants and their short-term remediation ability reveals that all plants exhibited up to 70% remediation potential and tolerance to remediate the target chemical. It is evident that the impact of local environmental factors on the plants is negligible.

The chemical state of the watershed in Ras Elma region (South of Taza, Morocco) one of the parameters responsible for the decline in the formation of the current travertine formations

The Ras Elma region, situated to the south of the city of Taza in northern Morocco, boasts abundant travertine formations that continue to develop, albeit selectively in specific sheltered sites. This development is influenced by various parameters, including the role of water chemistry. This article presents a spatio-temporal analysis of various hydrochemical parameters, including conductivity, pH, temperature, magnesium, calcium, and others. It's worth noting that the water from the Ras Elma Vauclusian spring, a key driver of travertinization in the region, is sourced from water infiltrating through faults and flowing into Lake Tompraire, known as Dayat Chikker near the Bab Boudir area. The findings suggest that the water in Ras Elma has turned aggressive, as revealed by the examination of the calcaro-carbonic equilibrium. CaCO3 precipitation occurs predominantly in the summer, significantly impacting the formation of travertines, particularly those of the spring and dam types. However, valley-type travertines exhibit more extensive development compared to the other two types.

Advancing sustainable materials in a circular economy for decarbonisation

This research paper delves into the intricate interplay between decarbonisation and sustainability, focusing on adopting chemical looping technologies. Deep decarbonisation scenarios necessitate a profound transformation in various sectors to mitigate climate change, and oil refineries, as pivotal players, must adapt to these changes. Employing the BLUES integrated assessment model, we evaluate the evolution of the refining sector in decarbonisation pathways, emphasising its potential for sustainability through repurposing and emissions mitigation. Additionally, we delve into chemical looping technologies, including Solar Thermal Chemical Looping (STCL), Reverse Water Gas Shift Chemical Looping (RWGS-CL), Chemical Looping Reforming (CLR), and Super Dry Reforming (SDR), elucidating their principles and contributions to carbon dioxide (CO2) conversion. These technologies offer promising routes for CO2 capture and present opportunities for sustainable carbon loop cycles, potentially revolutionising industries' emissions reduction efforts. In a world of climate change, this research illuminates a sustainable path forward by integrating decarbonisation and innovative CO2 management strategies.

Biophysical carbon concentrating mechanisms in land plants: insights from reaction-diffusion modeling

Carbon Concentrating Mechanisms (CCMs) have evolved numerous times in photosynthetic organisms. They elevate the concentration of CO2 around the carbon-fixing enzyme rubisco, thereby increasing CO2 assimilatory flux and reducing photorespiration. Biophysical CCMs, like the pyrenoid-based CCM of Chlamydomonas reinhardtii or carboxysome systems of cyanobacteria, are common in aquatic photosynthetic microbes, but in land plants appear only among the hornworts. To predict the likely efficiency of biophysical CCMs in C3 plants, we used spatially resolved reaction-diffusion models to predict rubisco saturation and light use efficiency. We find that the energy efficiency of adding individual CCM components to a C3 land plant is highly dependent on the permeability of lipid membranes to CO2, with values in the range reported in the literature that are higher than used in previous modeling studies resulting in low light use efficiency. Adding a complete pyrenoid-based CCM into the leaf cells of a C3 land plant is predicted to boost net CO2 fixation, but at higher energetic costs than those incurred by photorespiratory losses without a CCM. Two notable exceptions are when substomatal CO2 levels are as low as those found in land plants that already employ biochemical CCMs and when gas exchange is limited such as with hornworts, making the use of a biophysical CCM necessary to achieve net positive CO2 fixation under atmospheric CO2 levels. This provides an explanation for the uniqueness of hornworts' CCM among land plants and evolution of pyrenoids multiple times.

Microbial gas fermentation technology for sustainable food protein production

The development of novel, sustainable, and robust food production technologies represents one of the major pillars to address the most significant challenges humanity is going to face on earth in the upcoming decades - climate change, population growth, and resource depletion. The implementation of microfoods, i.e., foods formulated with ingredients from microbial cultivation, into the food supply chain has a huge potential to contribute towards energy-efficient and nutritious food manufacturing and represents a means to sustainably feed a growing world population. This review recapitulates and assesses the current state in the establishment and usage of gas fermenting bacteria as an innovative feedstock for protein production. In particular, we focus on the most promising representatives of this taxon: the hydrogen-oxidizing bacteria (hydrogenotrophs) and the methane-oxidizing bacteria (methanotrophs). These unicellular microorganisms can aerobically metabolize gaseous hydrogen and methane, respectively, to provide the required energy for building up cell material. A protein yield over 70% in the dry matter cell mass can be reached with no need for arable land and organic substrates making it a promising alternative to plant- and animal-based protein sources. We illuminate the holistic approach to incorporate protein extracts obtained from the cultivation of gas fermenting bacteria into microfoods. Herein, the fundamental properties of the bacteria, cultivation methods, downstream processing, and potential food applications are discussed. Moreover, this review covers existing and future challenges as well as sustainability aspects associated with the production of microbial protein through gas fermentation.

Adsorption of Nickel Ions on the γ-Alumina Surface: Competitive Effect of Protons and Its Impact on Concentration Profiles

Mesoporous γ-alumina is used as an adsorbent in the decontamination of water from heavy metals (e.g., nickel and cobalt) and as a support for heterogeneous catalysts prepared by impregnation. In these cases, alumina extrudates are in contact with aqueous solutions containing precursors of the active metal phase to be deposited. The proton concentration (or pH) in the metal solution in contact with alumina can impact the adsorption efficiency of decontamination processes and the activities of catalysts. Yet, it is difficult to quantify the effect of the pH inside the pores since protons are not detected by classical imaging techniques. In this article, the effect of protons on nickel adsorption on alumina is evaluated using a novel technique coupling liquid analysis (pH, conductivity, and UV/vis) and laser-induced breakdown spectroscopy (or LIBS) analysis of concentration gradients inside the solid. Both methods are in excellent agreement. The results show a slow diffusion of protons inside alumina pores (diffusion continues even after 940 min), yielding high proton concentration gradients. On the other hand, the nickel species penetrate the extrudates faster but are slowly displaced by protons under certain operating conditions. As a result, different metal concentration profiles are obtained, depending on the initial pH and contact time. These findings are interesting in catalysis since they prove the possibility of controlling the deposition of the active metal on catalysts by regulating the operating conditions of impregnation. For typical industrial impregnation times (a few minutes to 1 to 2 h), protons do not have enough time to deeply penetrate inside extrudates, so the initial pH of the metal solution will have nearly no effect on the metal distribution. Conversely, decontamination processes have much longer contact times; therefore, lower initial pH values should have negative impacts on the adsorption efficiency due to the protons displacing the adsorbed nickel.

Towards green carbon capture and storage using waste concrete based seawater: A microfluidic analysis

Carbon capture and utilization technology is the research stream dedicated to mitigating the pressing effect of rising atmospheric carbon dioxide (CO2). The present study investigates a potential environmentally conscious solvent to capture and utilize CO2 using waste concrete and seawater under reactor conditions. Although seawater's CO2 soubility is low due to salinity, waste concrete raises seawater's pH and alkalinity, acting as a feedstock for CO2 dissolution and offsetting the adverse effects of salinity. To evaluate the performance of the novel natural seawater-concrete solutions for CO2 capture, time-dependent pH changes of solutions exposed to CO2 were measured in a microchannel using fluorescence microscopy. The concentration of dissolved CO2 in the solution was derived from pH change, revealing a 4-fold increase in the total dissolved carbon from 0.034 to 0.13 M and a 57.54% increase in the CO2 dissolution coefficient from 530 to 835 μm2/s in seawater upon concrete addition. Electrolysis further enhanced the CO2 capture capacity of the seawater-concrete solution by increasing the pH, enabling the solid precipitation of carbonate minerals. Raman spectroscopy and scanning electron microscopy showed that electrolysis-driven precipitates are mainly amorphous calcium carbonates, useful building blocks for seashells and coral reefs.

The ocean carbon sinks and climate change

The oceans act as major carbon dioxide sinks, greatly influencing global climate. Knowing how these sinks evolve would advance our understanding of climate dynamics. We construct a conceptual box model for the oceans to predict the temporal and spatial evolution of CO2 of each ocean, and the time-evolution of their salinities. Surface currents, deep water flows, freshwater influx, and major fluvial contributions are considered, as also the effect of changing temperature with time. We uncover the strongest carbon uptake to be from the Southern Ocean, followed by the Atlantic. The North Atlantic evolves into the most saline ocean with time and increasing temperatures. The Amazon River is found to have significant effects on CO2 sequestration trends. An alternative flow scenario of the Amazon is investigated, giving interesting insights into the global climate in the Miocene epoch.

Natural spider silk nanofibrils produced by assembling molecules or disassembling fibers

Spider silk is biocompatible, biodegradable, and rivals some of the best synthetic materials in terms of strength and toughness. Despite extensive research, comprehensive experimental evidence of the formation and morphology of its internal structure is still limited and controversially discussed. Here, we report the complete mechanical decomposition of natural silk fibers from the golden silk orb-weaver Trichonephila clavipes into ≈10 nm-diameter nanofibrils, the material's apparent fundamental building blocks. Furthermore, we produced nanofibrils of virtually identical morphology by triggering an intrinsic self-assembly mechanism of the silk proteins. Independent physico-chemical fibrillation triggers were revealed, enabling fiber assembly from stored precursors "at-will". This knowledge furthers the understanding of this exceptional material's fundamentals, and ultimately, leads toward the realization of silk-based high-performance materials. STATEMENT OF SIGNIFICANCE: Spider silk is one of the strongest and toughest biomaterials, rivaling the best man-made materials. The origins of these traits are still under debate but are mostly attributed to the material's intriguing hierarchical structure. Here we fully disassembled spider silk into 10 nm-diameter nanofibrils for the first time and showed that nanofibrils of the same appearance can be produced via molecular self-assembly of spider silk proteins under certain conditions. This shows that nanofibrils are the key structural elements in silk and leads toward the production of high-performance future materials inspired by spider silk.

Plasma activated water: a study of gas type, electrode material, and power supply selection and the impact on the final frontier

An in-depth study of plasma activated water (PAW) generation was conducted to link changes in power supply, electrode material, input gas, and treatment time to the resulting reaction chemistry, all while maintaining a consistent electrode geometry. These changes in chemistry can help tailor PAW for different space applications. An AC, DC, and nanosecond pulsed power supply were each used to generate PAW with stainless steel, copper, tungsten, or platinum electrodes while utilizing air, nitrogen, carbon dioxide, helium, or argon as the feed gas. Tap or deionized (DI) water was treated for 1 to 15 minutes, and the generated PAW was tested for changes in pH, conductivity, and concentration of nitrates, nitrites, and ammonium. Calculations indicated that the production of reactive nitrogen species was the leading cause of the pH and conductivity changes. The DC generated air plasma, with a voltage between 2.5-3.14 kV and currents of 85-100 mA, was able to reduce the pH of DI water to 2.88 and generate 128 ppm of nitrates. The AC supply was less effective, producing a pH of 4.22 for DI water and 5 ppm of nitrates. The pulsed supply, operating at 20% of the input power of the DC supply, lowered the pH to 3.34 and generated 26 ppm of nitrates. When a simulated Martian gas mixture of 95% CO₂ and 5% N₂ was used as the feed gas, 24.8 ppm and 3.82 ppm of nitrates were generated with the DC and pulsed supplies, respectively.

Probing dissolved CO2(aq) in aqueous solutions for CO2 electroreduction and storage

CO₂ dissolved in aqueous solutions CO₂(aq) is important to CO₂ capture, storage, photo-/electroreduction in the fight against global warming and to CO₂ analysis in drinks. Here, we developed microscale infrared (IR) spectroscopy for in situ dynamic quantitating CO₂(aq). The quantized CO₂(g) rotational state transitions were observed to quench for CO₂(aq), accompanied by increased H₂O IR absorption. An accurate CO₂ molar extinction coefficient ε was derived for in situ CO₂(aq) quantification up to 58 atm. We directly measured CO₂(aq) concentrations in electrolytes under CO₂(g) bubbling and high-pressure conditions with high spectral and time resolutions. In KHCO₃ electrolytes with CO₂(aq) > ~1 M, CO₂ electroreduction (CO₂RR) to formate reached >98% Faradaic efficiencies on copper (Cu₂O/Cu)-based electrocatalyst. Furthermore, CO₂ dissolution/desolvation kinetics showed large hysteresis and ultraslow reversal of CO₂(aq) supersaturation in aqueous systems, with implications to CO₂ capture, storage, and supersaturation phenomena in natural water bodies.

Carbonic anhydrase for CO2 capture, conversion and utilization

Carbonic anhydrase (CA) enzymes, catalyzing the CO₂ hydration at a high turnover number, can be employed in expediting CO₂ capture, conversion and utilization to aid in carbon neutrality. Despite extensive research over the last decade, there remain challenges in CA-related technologies due to poor stability and suboptimal use of CAs. Herein, we discuss recent advances in CA stabilization by protein engineering and enzyme immobilization, and shed light on state-of-the-art of in vitro and in vivo CA-mediated CO₂ conversion for improved production of value-added chemicals using CO₂ as a feedstock.

Microalgal photosynthesis induces alkalization of aquatic environment as a result of H+ uptake independently from CO2 concentration - New perspectives for environmental applications

The photosynthetic process in microalgae and the extracellular proton environment interact with each other. The photosynthetic process in microalgae induces a pH increase in the aquatic environment as a result of cellular protons uptake rather than as an effect of CO₂ consumption. The photosynthetic water photolysis and the reduction/oxidation cycle of the plastoquinone pool provide lumen with protons. Weak bases act as "permeant buffers" in lumen during the photosynthetic procedure, converting the ΔpH to Δψ. This is possibly the main reason for continuous light-driven proton uptake from the aquatic environment through cytosol and stroma, into the lumen. The proton uptake rate and, therefore, the microalgal growth is proportional to the light intensity, cell concentration, and extracellular proton concentration. The low pH in microalgae cultures, without limitation factors related to light and nutrients, strongly induces photosynthesis (and proton uptake) and, consequently, growth. In contrast, the mitochondrial respiratory process, in the absence of photosynthetic activity, does not substantially alter the culture pH. Only after intensification of the respiratory process, using exogenous glucose supply leads to significantly reduced pH values in the culture medium, almost exclusively through proton output. Enhanced dissolution of atmospheric CO₂ in water causes the phenomenon of ocean acidification, which prevents the process of calcification, a significant process for numerous phytoplankton and zooplankton organisms, as well for corals. The proposed interaction between microalgal photosynthetic activity and proton concentration in the aquatic environment, independently from the CO₂ concentration, paves the way for new innovative management strategies for reversing the ocean acidification.

Pb Mineral Precipitation in Solutions of Sulfate, Carbonate and Phosphate: Measured and Modeled Pb Solubility and Pb2+ Activity

Lead (Pb) solubility is commonly limited by dissolution–precipitation reactions of secondary mineral phases in contaminated soils and water. In the research described here, Pb solubility and free Pb2+ ion activities were measured following the precipitation of Pb minerals from aqueous solutions containing sulfate or carbonate in a 1:5 mole ratio in the absence and presence of phosphate over the pH range 4.0–9.0. Using X-ray diffraction and Fourier-transform infrared spectroscopic analysis, we identified anglesite formed in sulfate-containing solutions at low pH. At higher pH, Pb carbonate and carbonate-sulfate minerals, hydrocerussite and leadhillite, were formed in preference to anglesite. Precipitates formed in the Pb-carbonate systems over the pH range of 6 to 9 were composed of cerussite and hydrocerussite, with the latter favored only at the highest pH investigated. The addition of phosphate into the Pb-sulfate and Pb-carbonate systems resulted in the precipitation of Pb3(PO4)2 and structurally related pyromorphite minerals and prevented Pb sulfate and carbonate mineral formation. Phosphate increased the efficiency of Pb removal from solution and decreased free Pb2+ ion activity, causing over 99.9% of Pb to be precipitated. Free Pb2+ ion activities measured using the ion-selective electrode revealed lower values than predicted from thermodynamic constants, indicating that the precipitated minerals may have lower KSP values than generally reported in thermodynamic databases. Conversely, dissolved Pb was frequently greater than predicted based on a speciation model using accepted thermodynamic constants for Pb ion-pair formation in solution. The tendency of the thermodynamic models to underestimate Pb solubility while overestimating free Pb2+ activity in these systems, at least in the higher pH range, indicates that soluble Pb ion-pair formation constants and KSP values need correction in the models.

Large pH oscillations promote host defense against human airways infection

The airway mucosal microenvironment is crucial for host defense against inhaled pathogens but remains poorly understood. We report here that the airway surface normally undergoes surprisingly large excursions in pH during breathing that can reach pH 9.0 during inhalation, making it the most alkaline fluid in the body. Transient alkalinization requires luminal bicarbonate and membrane-bound carbonic anhydrase 12 (CA12) and is antimicrobial. Luminal bicarbonate concentration and CA12 expression are both reduced in cystic fibrosis (CF), and mucus accumulation both buffers the pH and obstructs airflow, further suppressing the oscillations and bacterial-killing efficacy. Defective pH oscillations may compromise airway host defense in other respiratory diseases and explain CF-like airway infections in people with CA12 mutations.

Can CO2 and Steam React in the Absence of Electrolysis at High Temperatures?

The fundamental question of whether CO₂ can react with steam at high temperatures in the absence of electrolysis or high pressures is answered. These two gases are commonly co-present as industrial wastes. Herein, a simple experiment by flowing CO₂ and steam through a CaCl₂ matrix at 500-1000 °C and atmospheric pressure was designed. Comprehensive characterizations and density functional theory calculations were conducted. Meanwhile, this study aims to recover HCl from CaCl₂ via a low-emission oxy-pyrohydrolysis process. As confirmed, CO₂ and steam interact strongly on the CaCl₂ surface, leading to an explicit formation of CaCO₃ /CaO and a nearly complete release of HCl. This is mainly contributed to a halved energy required for the splitting of H₂ O, resulting from the formation of a bicarbonate-like structure to replace Cl^- out of CaCl₂ , an otherwise industrial waste, whilst an important dopant for carbon capture, utilization and storage, and medium for electrochemical synthesis.

Origin of the Drastic Current Decay during Potentiostatic Alkaline Methanol Oxidation

The current production from the alkaline methanol electro-oxidation reaction does not reach a steady state on a smooth platinum catalyst under potentiostatic conditions. We investigated two possible explanations for this phenomenon: changes on the catalyst surface and changes in the solution near the electrode. In situ Fourier transform infrared spectroscopy experiments were conducted to evaluate the adsorbed species on the catalyst surface and a simulation model was set up to describe the changes of concentrations inside the solution. Linear- and bridge-bonded carbon monoxide are the only organic compounds which can be detected by in situ spectroscopy at fixed potentials, but their amount does not increase over time. The simulation shows that the consumption of hydroxide ions and production of carbonaceous species during alkaline oxidation causes a local pH shift near the catalyst surface. Assuming a one-electron transfer as the limiting step, this pH shift was found to contribute to the observed current loss at a potential of 0.77 V.

Heterogeneous Electrofreezing Triggered by CO2 on Pyroelectric Crystals: Qualitatively Different Icing on Hydrophilic and Hydrophobic Surfaces

By performing icing experiments on hydrophilic and hydrophobic surfaces of pyroelectric amino acids and on the x-cut faces of LiTaO₃ , we discovered that the effect of electrofreezing of super cooled water is triggered by ions of carbonic acid. During the cooling of the hydrophilic pyroelectric crystals, a continuous water layer is created between the charged hemihedral faces, as confirmed by impedance measurements. As a result, a current of carbonic acid ions, produced by dissolved environmental CO₂ , flows through the wetted layer towards the hemihedral faces and elevates the icing temperature. This proposed mechanism is based on the following: (i) on hydrophilic surfaces, water with dissolved CO₂ (pH 4) freezes at higher temperatures than pure water of pH 7. (ii) In the absence of the ionic current, achieved by linking the two hemihedral faces of hydrophilic crystals by a conductive paint, water of the two pH levels freeze at the same temperature. (iii) On hydrophobic crystals with similar pyroelectric coefficients, where there is no continuous wetted layer, no electrofreezing effect is observed.

Simple ions control the elasticity of calcite gels via interparticle forces

Suspensions of calcite in water are employed in many industrial fields such as paper filling, pharmaceutics or heritage conservation. Whereas organics are generally used to tune the rheological properties of the paste, we also expect simple ions to be able to control the suspension rheology via the interparticle forces. We have thus investigated the impact of calcium, sodium and hydroxide ions on the elasticity of a colloidal gel of nanocalcite. We confront our macroscopic measurements to DLVO interaction potentials, based on chemical speciation and measurements of the zeta potential. Upon addition of calcium hydroxide, we observe a minimum in shear modulus, correlated to a maximum in the DLVO energy barrier, due to two competing effects: Calcium adsorption onto calcite surface rises the zeta potential, while increasing salt concentration induces stronger electrostatic screening. We also demonstrate that the addition of sodium hydroxide completely screens the surface charge and leads to a more rigid paste. A second important result is that carbonation of the calcite suspensions by the atmospheric CO₂ leads to a convergent high elasticity of the colloidal gels, whatever their initial value, also well rationalized by DLVO theory and resulting from a decrease in zeta potential.

Two Experimental Protocols for Accurate Measurement of Gas Component Uptake and Production Rates in Bioconversion Processes

Bioconversion processes offer many economic, environmental, and societal advantages for production of fuels and chemicals. Successful commercialization of any biotechnology usually requires accurate characterization of cell growth dynamics, substrate conversion and production excretion rates. Despite recent advancements in analytical equipment, obtaining accurate measurement of gas component uptake or production rates remains challenging due to their high sensitivity to system pressure or volume changes. Specifically, the consumption and production of various gases will result in changes in system pressure (for batch operations) or off-gas flow rate (for continuous operations). These changes would cause significant errors in the estimated gas component uptake and production rates if they were not accounted for. In this work, we propose two easy-to-implement experimental protocols and associated calculation procedures to obtain accurate measurements of gas component consumption and production rates; one is for batch operation and one is for continuous operation. For depressurized (i.e., system pressure below 1 atm) batch cultures, nitrogen (or other inert gases) is used to repressurize the system to 1 atm before taking sample; while for continuous cultures, He (or other inert gases) is used as an internal tracer to accurately measure off-gas flow rate. The effectiveness and accuracy of the two protocols and associated calculation procedures are demonstrated using several case studies with both abiotic and biotic systems.