Exchange Equilibrium Research Articles

Alkoxy Exchange Strategy for the Synthesis of N,N'-Dimethylated (Alkoxy)triazinediones as Solid Reagents for Acid-Catalyzed O-Alkylation.

N,N'-Dimethylated (alkoxy)triazinediones (DMATs-R) with eight different O-alkyl groups (R), such as benzyl, allyl, and tert-butyl groups, were synthesized in 61-94% yield through the alkoxy exchange reaction of DMAT-Me with the corresponding alcohol. Molecular sieves were added to the reaction mixture to shift the alkoxy exchange equilibrium toward the product via the absorptive removal of the methanol formed in situ. All the DMATs-R were obtained as stable solids, in contrast to previously reported N,N'-diallyl analogs that included oil compounds. The treatment of alcohols with DMATs-R in the presence of an acid catalyst afforded the corresponding alkyl ethers in up to 92% yield. A base-labile bromoalkyl group is compatible with these reactions. The O-tert-butylation of a sterically hindered tert-alcohol with DMAT-tBu yielded the di-tert-butyl ether product. The DMATs-R are suitable reagents for the O-alkylative protection of alcohols under nonbasic conditions.

A facile synthesis procedure for Engelhard titanosilicate (ETS-4) and its Cs+ and Sr2+ ion exchange properties

This manuscript reports an environmentally benign method for the synthesis of Engelhard titanosilicate (ETS-4) using titanium isopropoxide or anatase as titanium source and citric acid as complexing agent. Slow release of Ti from the hydroxide or oxide precursors through the citric acid complex plays crucial role in formation of titanosilicate. Characterizations of the prepared material were carried out by powder X-ray diffraction (XRD), Scanning Electron Microscope – Energy Dispersive X-ray spectroscopy (SEM-EDS), Thermogravimetric – Differential Thermal Analysis (TG-DTA) and ion exchange studies. Caesium and strontium exchange capacities of the synthesised ETS-4 were found to be 220 mg/g and 76.2 mg/g, respectively. The saturation exchange equilibrium was attained within 60 min.

Adsorption and ion exchange of toxic metals by Brazilian clays: clay selection and studies of equilibrium, thermodynamics, and binary ion exchange modeling.

In this study, four Brazilian clays (Bofe, Verde-lodo, commercial Fluidgel, and expanded commercial vermiculite) were evaluated for their adsorptive capacity and removal percentage in relation to different toxic metals (Ni2+, Cd2+, Zn2+, and Cu2+). The best results were obtained by expanded vermiculite, with cadmium removal reaching values of 95%. The most promising clay was modified by the sodification process, and the metal cadmium was used to evaluate the ion exchange process. The clays expanded vermiculite (EV) and VNa-sodified vermiculite were evaluated by equilibrium study at 25, 35, and 45 °C. At 25 °C, EV obtained a maximum adsorption capacity of 0.368 mmol/g and sodified vermiculite 0.480 mmol/g, which represents an improvement of 30.4% in modified clay capacity. At 45 °C, the sodified vermiculite reached 0.970 mmol/g adsorption capacity. The Langmuir, Redlich-Peterson Freundlich, and Dubinin-Raduskevich models were adjusted to the results. Langmuir provided the best fit among the models. The thermodynamic quantities (ΔS, ΔH, and ΔG) demonstrated that the process is spontaneous and endothermic and the metal is captured by physisorption and chemisorption in the studied temperature range. For the ion exchange equilibrium, the binary Langmuir and binary Langmuir-Freundlich models were adjusted to the expanded vermiculite and sodified vermiculite isotherms, respectively. Both models were predictive. Thermal analysis indicated good heat resistance even after material modification. The apparent and real densities demonstrated that after each treatment or contamination, the clayey material undergoes contraction in its structure. An improved efficiency of the adsorbent was found after sodification.

Composition effects on equilibrium oxygen isotope fractionation factors between garnets and quartz/calcite/olivine: Implication from vibration frequencies of garnets at high temperatures and high pressures

Garnet-group minerals, with their wide range of compositions, play a significant role in Earth's crust and upper mantle, participating in various petrological and geochemical processes. Oxygen isotope fractionation factors between garnets and other minerals hold crucial implications in these contexts. In this work, vibration frequencies were measured via Raman spectra on five garnet mineral samples in the pyrope-almandine-spessartine ternary system and four synthetic pyrope-grossular solid solutions at temperatures up to 1000 °C and pressures up to 17 GPa. Isobaric (γiP) and isothermal (γiT) mode Grüneisen, as well as anharmonic (ai) parameters, were determined for the observed modes. Our study shows that the vibration bands tend to shift to lower frequencies with increasing temperature and to higher frequencies with increasing pressure. Moreover, the anharmonic correction has been found to contribute positively to equilibrium oxygen isotope fractionation β factors in garnets, typically within 0.5 ‰ above 1000 K. The 103∙lnβ(T) factors calculated from vibration spectra (considering Г points only) align closely with those from theoretical calculations (including all frequencies in the Brillouin zone). Contributions from phonon dispersion (including none-Г points) are typically smaller than the uncertainties propagated from frequency measurements. Additionally, the pressure effect on the oxygen isotope fractionation in garnet, evaluated from the isothermal Grüneisen parameters, is found to be insignificant under crustal and upper mantle conditions, consistent with thermodynamic expectations. Using published oxygen isotope fractionation β factors for quartz and calcite, the equilibrium oxygen isotope fractionation factors (103∙lnα) are calculated between garnets of diverse compositions and any of these phases as functions of temperature, pressure and fraction of garnet endmembers. Considering composition effects helps to reduce the discrepancies among experimental and empirical calibrations of oxygen isotope fractionation factors between garnet and quartz. As an example application, oxygen isotope fractionation factors 103∙lnα(P, T) between garnets and forsterite were calculated under upper mantle conditions. Our findings suggest that these fractionation factors are predominantly dependent on temperature and garnet compositions, with minor influence from pressure. Compared with our calculated fractionation factors between garnet and olivine, the oxygen isotope exchange equilibrium may have been reached in some in kimberlite and mantle xenolith samples between garnet and olivine. However, in other samples, the fractionation factors cannot be explained solely by the composition effect, likely due to metasomatism. Our results underscore the importance of considering garnet compositions when interpreting their oxygen isotope compositions.

Enhancing CO2 Capture via Metal-Ligand Cooperativity: Tuning Ligand Basicity and Zn(II) Lewis Acidity.

A series of thiosemicarbazonato-hydrazinatopyridine zinc(II) complexes were evaluated as direct air CO2 capture agents. The complexes sequester CO2 in a methanol solution as a metal-coordinated methylcarbonate. The reaction is reversible upon sparging of solutions with an inert gas (N2 or Ar). The capture process involves metal-ligand cooperativity with the noncoordinating nitrogen of the hydrazinatopyridine functional group serving as a Brønsted-Lowry base and the zinc acting as a Lewis acid. In this study, the pendent amine of the thiosemicarbazonato group was varied to include 4-phenyl (ZnL5), 4-(trifluoromethyl)phenyl (ZnL6), 4-cyanophenyl (ZnL7), 4-tolyl (ZnL8), and 4-naphthyl (ZnL9). Hyperconjugation between the pendent group and the ligand core resulted in modulation of the metal ion acidity, as quantified by ligand exchange equilibrium constants (K3 = 193-511) and ligand basicity (pKa,MeOH = 11.09-11.94). Variations in electronic structure that decreased ligand basicity were more than offset by increases in Lewis acidity. The equilibrium constant (K1) for CO2 capture varied from 46300 to 73700. Overall, the value of K1 was directly related to the relative Lewis acidity of the complexes (K3). Notably, there was an overall inverse relationship between K1 and the ligand basicity. The results provide insights into ligand design to further improve CO2 capture.

Nitrate Uptake from Water Using Amine‐Functionalized Meso‐ and Macroporous Carbons

AbstractMeso‐ and macroporous carbon materials modified with protonated amino groups (−NH3+Cl−) for aqueous nitrate (NO3−) uptake were prepared by surface functionalization with aminopropylsilane. Although the silane coupling treatment decreased the specific surface area of the carbons, surface modification with the −NH3+Cl− group improved the NO3− uptake capacity of both meso‐ and macroporous carbons. The amount of NO3− adsorbed depends on the specific surface area of the adsorbent; an adsorbent with a larger specific surface area exhibits a larger uptake capacity. Enhanced NO3− adsorption onto the NH3+Cl−‐modified surface occurred through an ion‐exchange mechanism. Changes in the pH of the sample solutions before and after NO3− uptake revealed the competitive exchange of NO3− and OH−. NO3− uptake is inhibited by the coexistence of anions other than NO3− (excess Cl−, SO42−, CO32− and HCO3−) and/or OH− at high pH. In particular, the influence of excess Cl− reveals that NO3− uptake through ion exchange is not irreversible, and the adsorption capacity is determined based on the ion exchange equilibrium.

Numerical evaluation of mercury concentration by using a distributional multimedia model in the Lake Biwa-Yodo River Basin, Japan

A distributional multimedia model was developed and applied to the Lake Biwa-Yodo River Basin in Japan to reproduce the mercury level in different environmental media. This model was developed based on a Level III steady-state fugacity model, and the space was divided into four environmental media (atmosphere, water, soil, and sediment). The mass transfer of Hg in this model consists of emission, deposition, sedimentation inside one medium, and advection between different media. The dissolution rate and ion exchange equilibrium have also been considered. We estimated Hg emissions in the Lake Biwa-Yodo River Basin from 1957 to 2009 based on the Pollutant Release and Transfer Registry (PRTR) system and the domestic usage of Hg in Japan. The distribution of emission was based on land data, including industrial land area, industrial location, and proportion of the population. The calculated and observed Hg concentrations were compared to evaluate the model. At both large scale and small scale, results showed that the distributional model could predict Hg concentrations in all environmental media. Sediment and soil media showed the accumulation of Hg by showing the higher concentrations than that of other media. In terms of geographical distribution, the urban area and downstream of the river showed high Hg concentrations owing to high Hg emissions. The Hg concentration in the atmosphere was affected by the transboundary pollution. Thus, the distributional multimedia model could reliably calculate the environmental Hg concentration and be utilized in environmental monitoring and management.

Thermal adaptability of neonatal piglets: Early life welfare crisis

Thermal adaptability of neonatal piglets: Early life welfare crisis

A novel method for estimation of electrode kinetics parameters

PurposeThe purpose of this paper is to extract electrochemical reaction kinetics parameters, such as Tafel slope, exchange current density and equilibrium potential, which cannot be directly measured, this study aims to propose an improved particle swarm optimization (PSO) algorithm.Design/methodology/approachIn traditional PSO algorithms, each particle’s historical optimal solution is compared with the global optimal solution in each iteration step, and the optimal solution is replaced with a certain probability to achieve the goal of jumping out of the local optimum. However, this will to some extent undermine the (true) optimal solution. In view of this, this study has improved the traditional algorithm: at each iteration of each particle, the historical optimal solution is not compared with the global optimal solution. Instead, after all particles have iterated, the optimal solution is selected and compared with the global optimal solution and then the optimal solution is replaced with a certain probability. This to some extent protects the global optimal solution.FindingsThe polarization curve plotted by this equation is in good agreement with the experimental values, which demonstrates the reliability of this algorithm and provides a new method for measuring electrochemical parameters.Originality/valueThis study has improved the traditional method, which has high accuracy and can provide great support for corrosion research.

Halide Perovskites Breathe Too: The Iodide-Iodine Equilibrium and Self-Doping in Cs2SnI6.

The response of an oxide crystal to the atmosphere can be personified as breathing-a dynamic equilibrium between O2 gas and O2- anions in the solid. We characterize the analogous defect reaction in an iodide double-perovskite semiconductor, Cs2SnI6. Here, I2 gas is released from the crystal at room temperature, forming iodine vacancies. The iodine vacancy defect is a shallow electron donor and is therefore ionized at room temperature; thus, the loss of I2 is accompanied by spontaneous n-type self-doping. Conversely, at high I2 pressures, I2 gas is resorbed by the perovskite, consuming excess electrons as I2 is converted to 2I-. Halide mobility and irreversible halide loss or exchange reactions have been studied extensively in halide perovskites. However, the reversible exchange equilibrium between iodide and iodine [2I-(s) ↔ I2(g) + 2e-] described here has often been overlooked in prior studies, though it is likely general to halide perovskites and operative near room temperature, even in the dark. An analysis of the 2I-(s)/I2(g) equilibrium thermodynamics and related transport kinetics in single crystals of Cs2SnI6 therefore provides insight toward achieving stable composition and electronic properties in the large family of iodide perovskite semiconductors.

Continental Arc Accumulation Mafic Rocks in the Mid-Upper Crust: Constraints From the Early Eocene Hornblende Gabbro–Diorite in the Tengchong Block, Southeastern Extension of Tibet

Abstract Magmatic activity in the syn-collision stage is key for net crustal growth. To understand the mechanism of accretion–differentiation and compositional change of the continental crust, it is important to focus on the magmatic activity during the syn-collision stage. Early Eocene mafic–ultramafic rock assemblages found in the western part of the Tengchong Block resulted from a continuous series of arc magmatic evolution, thoroughly recording the continental arc magmatic system during the subduction of the Neo-Tethys Ocean and syn-collision of the Indian-Asian continents. Early Eocene hornblende gabbro–diorite in the Tengchong Block formed at 53 Ma, and the primitive magma was derived from an enriched mantle source due to the enriched Nd–Hf isotopes. The amphibole and biotite thermobarometer measurements indicate that the mafic magma reservoirs in the Tengchong Block occurred at a mid-upper crust. Petrography, amphibole Fe/Mg exchange coefficient (KD), Rayleigh fractionation, and equilibrium melt calculation indicate that the Early Eocene hornblende gabbro–diorite in the Tengchong Block was created due to plagioclase-dominated accumulation at the mid-upper crust level. Based on the calculation, the corresponding amphibole equilibrium melt is more silicic (dacitic–rhyolitic in composition) than the bulk rocks, indicating a more evolved composition in the mid-upper crust. Three types of plagioclases reveal the multi-recharging and dissolution–reprecipitation promoting the further evolution of these mafic rocks. Therefore, this study concludes that magma recharge and plagioclase-dominated accumulation processes may be important mechanisms for the formation and evolution of mafic magma and the further crustal differentiation at the mid-upper crust level in a continental margin arc.

CsBr-Triggered Reversible Phase Transition of Perovskite Nanocrystals for Advanced Information Encryption and Decryption.

Luminescent perovskite nanocrystals (NCs), possessing the advantages of low cost, easy detection, and excellent luminescence, are becoming more and more significant in the fields of information encryption and decryption. Most hydrochromic perovskite NCs for information encryption have moderate reversibility and are easily passively decrypted by water in the moist air, limiting their practical applications. Herein, a lyochromic material is synthesized based on reversible phase transition between luminescent CsPbBr3-HBr (pretreating CsPbBr3 with HBr) and nonluminescent Cs4PbBr6, exhibiting excellent reversibility in 50 cycles triggered by CsBr solution. HBr treatment boosts the ion migration of NCs via diminishing surface ligands and passivating Br vacancy, assisting CsBr concentration acting as a crucial factor in dynamic ion exchange equilibrium between the trigger solution and CsPbBr3-HBr. By utilizing CsPbBr3-HBr as a safety ink, the CsBr-triggered photoluminescence switch has been demonstrated to be reproducible, stable, and reliable for information encryption and decryption.

Application of gas chromatography-stable isotope mass spectrometry to determine the oxygen isotope ratio of water in concentrated fruit juice

In this study, we developed a method to determine the authenticity of concentrated fruit juice using the δ18O ratio of water. We utilized the gas chromatography-isotope ratio mass spectrometry (GC-IRMS) technique along with the offline isotope exchange equilibrium method to pretreat and measure the oxygen isotopes in water in concentrated apple juice. This innovative approach uses anhydrous ethanol as a solvent to dissolve concentrated juices, thereby facilitating a more comprehensive reaction between the water in the sample and the CO2 standard gas. Additionally, the reaction vessel exhibits excellent air tightness, ensuring rapid equilibrium time and enabling accurate determination of δ18O in the water content of concentrated juice. The reaction vessel had excellent air tightness and rapid equilibration time, enabling accurate measurement of δ18O of water in concentrated fruit juice. The reaction vessel used had excellent air tightness and rapid equilibration time, ensuring accurate measurement of the δ18O of water in concentrated fruit juice. We analyzed 40 samples of concentrated apple juice and found that the range of δ18O values in the water of concentrated apple juice was between 1.29 ‰ and 7.59 ‰. Additionally, we used prepared sucrose syrup as a simulated sample and found that the δ18O distribution range was between −10.43 ‰ and −10.53 ‰. Furthermore, we conducted adulteration simulation experiments on randomly selected real samples and discovered a linear negative correlation between the adulteration ratio and the δ18O value of water in the samples.

Elemental composition and speciation trends in Upper Mazowe River, a typical sub-tropical river ecosystem impacted by gold mining and agriculture in Zimbabwe

This study was carried on Upper Mazowe River in Zimbabwe which connects with Luenha River in Mozambique, which is a tributary of the Zambezi River. Zambezi River is the fourth longest river in Africa flowing into the Indian Ocean, which makes the study of regional and global interest. Heavy metal aqueous speciation has received relatively little attention compared to sediment speciation in the Upper Mazowe River, and yet heavy metal behaviour and fate in surface waters are greatly affected by the heavy metal chemical form in solution. The aim of the study was to determine the elemental composition and speciation of heavy metal(oid)s. This study focused on water and sediment speciation of Al, As, Cu, Hg, Mn, Fe, and Pb using Visual MINTEQ Version 3.1 computer modelling and sequential extraction techniques. Twenty-eight different water column elemental species, comprising 3, 2, 3, 1, 7, 7 and 5 species each, and 35 sediment phase elemental species, comprising 6, 6, 6, 2, 6, 5, and 4 species each for Al, As, Cu, Hg, Mn, Fe, and Pb respectively, were identified. Of note is the fact that Hg, mainly derived from artisanal gold mining activities, exists entirely as the fulvic acid complex, FA2Hg (aq), and As exists as H3AsO3 and H2AsO3− in the water phase. Exchange equilibrium reactions across the water-sediment interface were observed for Mn2+, Fe2+, Cu2+, and Pb2+. Reactions leading to the formation of the species were identified. Species interactions within the water column and sediment phase and species interrelationships with physicochemical parameters are discussed. H3AsO3 formation is predicted to be temperature sensitive and the aluminium hydroxide-fulvic acid complex /FA2(AlOH) (aq) is oxic favourable.

A preference for heterolepticity - Schlenk type equilibria in organometallic beryllium systems.

The reactions of beryllium halides with diphenyl beryllium were investigated in the N- and O-donor solvents NEt3 and THF, as well as in benzene and dichloromethane in the presence of the Lewis basic ligands THF, NEt3 and N-heterocyclic carbenes with various steric demand. In all cases the selective formation of heteroleptic beryllium Grignard compounds of the general formula [(L)1-2BePhX]1-2 (X = Cl, Br, I; L = C-, N-, O-donor ligand) was observed. The stability of these complexes was investigated computationally, while the differences between homo- and heteroleptic systems were also evaluated NMR spectroscopically and with single crystal X-ray diffraction. Mechanistic studies on the formation and speciation of these beryllium Grignard complexes in solution were performed.

Revealing the Equilibrium of Lithium Cations Across a Solid–Electrolyte Interface by T_1 NMR Relaxation

Battery fast charging is pivotal for broader acceptance of electric mobility. While demonstrated for lithium titanate (text {Li}_4text {Ti}_5text {O}_{12}, LTO) anodes, the underlying mechanisms are still poorly understood. Recently, NMR T_1 relaxation time constants of {}^7text {Li} in the bulk of LTO were found to change if the surrounding electrolyte was altered. It was explained by interdiffusion of mobile lithium ions between the two phases, facilitated by unpinning of polarons from surface defects and leading to a pseudocapacitive effect that potentially influences fast charging. This effect is explored further by systematically varying the lithium salt concentration in an aprotic electrolyte in contact with LTO. Spectrally resolved {}^7text {Li}T_1 NMR relaxation times were used as a measure for bulk concentration changes of paramagnetic polaronic charges in LTO. Correlation of electrolyte concentration and {}^7text {Li}T_1 showed qualitatively different behavior above and below a salt concentration of about 5 mM, leading to a relaxation dispersion maximum in the LTO bulk. At intermediate concentrations, relaxation was consistent with a {}^7text {Li} exchange equilibrium between LTO and electrolyte. Upon contact of the two phases, yet without insertion into an electrochemical cell or applying an external potential, lithium ions redistributed between LTO bulk and liquid electrolyte. The results can be understood analogously to the distribution of mobile lithium ions between two phases separated by a text {Li}^{+} permeable membrane. This is the first demonstration of such an equilibrium for non-faradaic lithium exchange at an interface between a solid ceramic electrode and a liquid electrolyte outside an electrochemical cell, substantiating our previous hypothesis of a polaron-supported mechanism. This study provides a basis for more quantitative (surface)-defect engineering, which is key to optimize battery fast-charging properties.

Characterizing the Semiconductor Nanocrystal Surface through Chemical Reactivity.

ConspectusMany desirable and undesirable properties of semiconductor nanocrystals (NCs) can be traced to the NC surface due to the large surface-to-volume ratio. Therefore, precise control of the NC surface is imperative to achieve NCs with the desired qualities. Ligand-specific reactivity and surface heterogeneity make it difficult to accurately control and tune the NC surface. Without a molecular-level appreciation of the NC surface chemistry, modulating the NC surface is impossible and the risk of introducing deleterious surface defects is imminent. To gain a more comprehensive understanding of the surface reactivity, we have utilized a variety of spectroscopic techniques and analytical methods in concert.This Account describes our use of robust characterization techniques and ligand exchange reactions in effort to establish a molecular-level understanding of NC surface reactivity. The utility of NCs in target applications such as catalysis and charge transfer hangs on precise tunability of NC ligands. Modulating the NC surface requires the necessary tools to monitor chemical reactions. One commonly utilized analytical method to achieve targeted surface compositions is 1H nuclear magnetic resonance (NMR) spectroscopy. Here we describe our use of 1H NMR spectroscopy to monitor chemical reactions at CdSe and PbS NC surfaces to identify ligand specific reactivity. However, seemingly straightforward ligand exchange reactions can vary widely depending on the NC materials and anchoring group. Some non-native X-type ligands will irreversibly displace native ligands. Other ligands exist in equilibrium with native ligands. Depending on the application, it is important to understand the nature of exchange reactions. This level of understanding can be obtained by extracting exchange ratios, exchange equilibrium, and reaction mechanism information from 1H NMR spectroscopy to establish precise NC reactivity.Reactivity that occurs through multiple, parallel ligand exchange mechanisms can involve both the liberation of metal-based Z-type ligands in addition to reactivity of X-type ligands. In these reactions, 1H NMR spectroscopy fails to discern between an X-type oleate or a Z-type Pb(oleate)2 because only the alkene resonance of the organic constituent is probed by this method. Multiple, parallel reaction pathways occur when thiol ligands are introduced to oleate-capped PbS NCs. This necessitated the use of synergistic characterization methods including 1H NMR spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS) to characterize both surface-bound and liberated ligands.Similar analytical methods have been employed to probe the NC topology, which is an important, but often overlooked, component to NC reactivity given the facet-specific reactivity of PbS NCs. Through the tandem use of NMR spectroscopy and ICP-MS, we have monitored the liberation of Pb(oleate)2 as an L-type ligand is titrated to the NC to determine the quantity and equilibrium of Z-type ligands. By studying a variety of NC sizes, we correlated the number of liberated ligands with the size-dependent topology of PbS NCs.Lastly, we incorporate redox-active chemical probes into our toolbox to study NC surface defects. We describe how the site-specific reactivity and relative energetics of redox-active surface-based defects are elucidated using redox probes and show that this reactivity is highly dependent on the surface composition. This Account is designed to encourage readers to consider the necessary characterization techniques needed establish a molecular-level understanding of NC surfaces in their own work.

Proton solvation: competition between acetone and dimethyl sulfoxide

This paper presents results of quantum-chemical study of proton exchange equilibrium between acetone (AC) and dimethyl sulfoxide (DMSO). Basing on the previous study of acid-base equilibria in AC with small additives of DMSO, the most probable composition of the lyonium ion is taken as H(DMSO)2+. The equilibrium geometries and energies of solvents molecules and all possible combinations of proton complexes with one or two solvent molecules were calculated in DFT level of theory using B3LYP functional and 6-31G++(d,p) basis set. The energies of solvated proton complexes were then calculated using PCM method. The energy change corresponding to the equilibrium H(AС)2+ + 2 DMSO ⇄ H(DMSO)2+ + 2 AС is –63.1 kJ mol–1 in the gas phase, which is in qualitative agreement with the standard Gibbs energy data, obtained experimentally in the gas phase by Kebarle’s group, –77.6 kJ mol–1, and with ΔGo298 = –49.3 kJ mol–1 for AC solution with small additions of DMSO, determined by the Guss and Kolthoff method.

Sustainable recovery of lithium from spent LiFePO4 via proton circulation

Excessive chemical consumption and its concomitant secondary pollution have become persistent issues in the wet chemical recycling process of spent LiFePO4 batteries (sLFP). In this study, a prospective recycling strategy is proposed based on sustainable proton circulation between organic leachants, extractants, and strippants, whereby expensive organic leachants can be regenerated and secondary pollutants are reduced. The leaching dependence of the sLFP powder on the structure of the organic leachants is determined. Monocarboxylic acids with low pKa and short carbon chains exhibit preferable lithium leaching performance (98.7 % for formic acid), and the leaching behavior of metal impurities (Al, Cu) are coupled with organic acid complexation and solution pH. The direct separation of lithium from organic leachates is explored with acidic extractants for the first time. Benefitting from the buffering capacity toward protons and the salt-out effect of organic acid anions, Li element could be successfully extracted with di-(2-ethylhexyl) phosphoric acid and the organic acids can be significantly regenerated by proton exchange equilibrium. Dilute H3PO4 is employed to selectively strip Li and contribute protons to regenerate the extractant, where the separation factors of Li/Cu and Li/Al are 148.9 and 54.1, respectively. Through two-stage counter-current extraction and stripping processes, the extraction and stripping efficiency of Li could enhance to 98.62 % and 99.38 %, respectively. Thus, the Li overall yield in the leaching-extraction-stripping processes is calculated as 96.73 %, exhibiting promising prospects for proposed proton circulation strategy.

Microscale Catalytic Hydrogenation of Cyclopropane with Nanoparticle Palladium

Cyclopropane can be hydrogenated to produce propane under moderately high temperatures (∼175 °C). Using a nanoparticle palladium catalyst, undergraduate students can explore the reaction and draw conclusions regarding the conditions for reaction. When deuterium is used, conclusions pertaining to the reaction mechanism are possible. The full complexity of the hydrogen–deuterium exchange equilibrium on the metal surface is indicated by the observation of all nine possible hydrogen–deuterium isotopologues, propane-dx (x = 0–8), as products. To think about the reaction mechanism, the unusual bonding in cyclopropane and its interactions with a metal surface are considered. Differences between cyclopropane and propane in terms of their physical and chemical properties are discussed. The use of this activity as a multisemester research project across all levels of undergraduate students is discussed in terms of logistics, expectations, and outcomes. The catalyst tube consists of nanoparticle palladium beads (0.5%) on alumina, is inexpensive and easy to construct, and lasts indefinitely. Product analysis is by mass spectrometry and 1H NMR spectroscopy. Suggestions are provided for undergraduate exploration and inquiry-based research activities.