Cationic Species Research Articles

Adsorption of Phenols from Aqueous Solution with A pH-Sensitive Surfactant-Modified Bentonite

The presence of organic pollutants in wastewater remains a prominent environmental concern due to the related ecological and health hazards. In response, this study employs an adsorptive methodology to address the removal of phenol and catechol, utilizing an organo-bentonite material modified with a pH-responsive switchable surfactant, dodecyldimethylamine oxide (C12DAO). The synthesized organo-bentonite (C12DAO-Bt) manifests commendable thermostability resulting from thermogravimetric analyses. The adsorption capacities of C12DAO-Bt concerning phenol and catechol intensify with the augmentation of the C12DAO/bentonite mass ratio. The utmost adsorption capacities of 150C12DAO-Bt, deduced through a pseudo-second-order kinetic model, stand at 5.72 mg·g−1 for phenol and 5.55 mg·g−1 for catechol, respectively. Subject to modification by a pH-responsive surfactant, conditions leaning towards weakly acidic and neutral conditions (pH = 6~7) are conducive to the adsorption of phenolic compounds. Conversely, alkaline conditions (pH = 8~9) facilitate the dissociation of adsorbates from adsorbents. The augmentation of cationic strength within the examined scope incites the adsorption procedure while impeding the desorption efficacy. In the case of cationic species with comparable ionic strengths, Na+ exhibited a superior effect on the adsorption–desorption dynamics of phenol, while Ca2+ exerts a more pronounced effect on those of catechol. Moreover, even following five consecutive acid–base regulation cycles, C12DAO-Bt retains a relatively high adsorption capacity and desorption efficacy, which underscores its exceptional regenerative capacity for removing phenolic compounds from wastewater.

The Optimization of Mechanochemical Processes toward Functional Nanocomposite Materials

Mechanochemical technology is developing rapidly, judging by the scientific information in both basic and applied studies. However, many issues and points of view remain to be discussed. This review presents some new key issues for the optimization of mechanochemical processes in terms of theoretical and practical aspects. Emphasis is placed on powder technology aspects, which are not always discussed compared to functional or microscopic viewpoints. The transfer of chemical species across the interparticle interface between dissimilar species during the mechanosynthesis of nanocomposites offers many new opportunities. Since almost all material transport is preceded by charge transfer, its driving force has been sought using terminology beyond the well-established electrochemical terms. In particular, the valence state of the cationic species involved is of importance. The role of organic compounds throughout the process is emphasized, regardless of their survival in the final product. The similarity with pharmaceutical phenomena is pointed out, although its mentality is very different from that of the synthesis of nanocomposites. The rational amorphization and stabilization of molecular dispersion states with the participation of excipients are discussed. The effects of liquids, either added or formed by mechanochemical auto-liquefaction, are presented with reference to the comparison between wet and dry grinding. The mechanisms of the apparent stabilization of the mechanically activated states of the products are elucidated to investigate the practical applicability of these mechanochemically synthesized products. Finally, the most important aspects for the optimization of the mechanochemical processes of functional nanocomposites are listed.

Spatially and Chemically Resolved Visualization of Fe Incorporation into NiO Octahedra during the Oxygen Evolution Reaction.

The activity of Ni (hydr)oxides for the electrochemical evolution of oxygen (OER), a key component of the overall water splitting reaction, is known to be greatly enhanced by the incorporation of Fe. However, a complete understanding of the role of cationic Fe species and the nature of the catalyst surface under reaction conditions remains unclear. Here, using a combination of electrochemical cell and conventional transmission electron microscopy, we show how the surface of NiO electrocatalysts, with initially well-defined surface facets, restructures under applied potential and forms an active NiFe layered double (oxy)hydroxide (NiFe-LDH) when Fe3+ ions are present in the electrolyte. Continued OER under these conditions, however, leads to the creation of additional FeOx aggregates. Electrochemically, the NiFe-LDH formation correlates with a lower onset potential toward the OER, whereas the formation of the FeOx aggregates is accompanied by a gradual decrease in the OER activity. Complementary insight into the catalyst near-surface composition, structure, and chemical state is further extracted using X-ray photoelectron spectroscopy, operando Raman spectroscopy, and operando X-ray absorption spectroscopy together with measurements of Fe uptake by the electrocatalysts using time-resolved inductively coupled plasma mass spectrometry. Notably, we identified that the catalytic deactivation under stationary conditions is linked to the degradation of in situ-created NiFe-LDH. These insights exemplify the complexity of the active state formation and show how its structural and morphological evolution under different applied potentials can be directly linked to the catalyst activation and degradation.

Enhanced Li+ Diffusion and Lattice oxygen Stability by the High Entropy Effect in Disordered-Rocksalt Cathodes.

Cation-disordered Rocksalt oxides (DRXs) are a promising new class of cathode materials for Li-ion batteries due to their natural abundance, low cost and great electrochemical performance. High entropy strategy in Mn-based DRXs appears to be an effective strategy for improving the rate capability, but it suffers from challenges including capacity degradation. The present paper reports a new group of high entropy DRXs (HE DRX) based on Ni2+ -Nb5+ pair; the structural and chemical evolution upon cycling of DRXs with an increasing transition metal (TM) species are systematically investigated. An explanation is proposed for how the crystal field stability energy determines that HE DRX could exist in single Rocksalt solid solution structures. We further reveal that the charge compensation mechanism in HE DRX is the result of various TM synergistic effect. More importantly, through various in situ and ex situ techniques and theoretical calculation, the effective integration of more TM cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, consequently increasing capacity upon cycling.

Enhanced Li+ Diffusion and Lattice oxygen Stability by the High Entropy Effect in Disordered‐Rocksalt Cathodes

AbstractCation‐disordered Rocksalt oxides (DRXs) are a promising new class of cathode materials for Li‐ion batteries due to their natural abundance, low cost and great electrochemical performance. High entropy strategy in Mn‐based DRXs appears to be an effective strategy for improving the rate capability, but it suffers from challenges including capacity degradation. The present paper reports a new group of high entropy DRXs (HE DRX) based on Ni2+‐Nb5+ pair; the structural and chemical evolution upon cycling of DRXs with an increasing transition metal (TM) species are systematically investigated. An explanation is proposed for how the crystal field stability energy determines that HE DRX could exist in single Rocksalt solid solution structures. We further reveal that the charge compensation mechanism in HE DRX is the result of various TM synergistic effect. More importantly, through various in situ and ex situ techniques and theoretical calculation, the effective integration of more TM cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, consequently increasing capacity upon cycling.

Strategy for a Rational Design of Deep-Ultraviolet Nonlinear Optical Materials from Zeolites.

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play a crucial role in cutting-edge laser technology. In order to solve the serious layered growth tendency of the sole commercial DUV NLO crystal KBe2BO3F2 (KBBF), developing alternative systems of compounds with bulk crystal habits has become an urgent task for practical applications. Herein, a novel strategy was developed by applying non-centrosymmetric (NCS) cancrinite (CAN)-type zincophosphates {Na6(OH)2(H2O)2}Cs2[ZnPO4]6 with bulk-crystal habits as the prototype to design new DUV NLO crystals. Two new anhydrous alkali zincophosphates, namely, {(Li6-xNaxO)A2}[(ZnPO4)6] (A = Cs, Rb; x = 2-3) crystallizing in the NCS hexagonal space group P63 (no. 173) with a CAN-type framework, were successfully synthesized via a modified fluoro-solvo-hydrothermal method by applying triethylamine (TEA) and concentrated NaF solution as a co-solvent. Interestingly, the rigidity of the NCS CAN-type framework acting as the host ensures the non-centrosymmetry of the resulting new compounds. Meanwhile, the replacement of water molecules by guest cationic species in the channels or cages can greatly improve the thermal stability of the resultant crystal and tune its NLO properties. The synergetic effect of the host framework and the guest species makes the two compounds transparent down to the DUV region (<200 nm) and exhibit SHG effects. Therefore, the proposed rational design strategy of applying the known zeotype NCS frameworks as prototypes together with the modified fluoro-solvo-hydrothermal method opens a great avenue for highly effectively exploring new DUV NLO materials.

Using high entropy configuration strategy to design high-temperature thermosensitive ceramics with superior thermal stability and a wide temperature range

Entropy plays a crucial role in designing new functional materials or enhancing material performance. The design of high entropy ceramics (HECs) introduces a larger composition space, thus the understanding of the correlation between the composition, entropy effect, and the performance of HECs is becoming increasingly important. In this work, to pursue superior properties, a series of CeNbO4-based solid solution ceramics with a maximum of 9 species cations in a single sublattice were synthesized by using high entropy configuration strategy. The interaction of composition, size disorder, and configurational entropy on the properties of HECs was emphasized. The potential conflict between high resistivity and low material constant of thermosensitive ceramics was overcome and thus achieving excellent thermal sensitivity properties having an extremely wide temperature range from room temperature to 1623 K and long-term high-temperature stability. This will bring innovative prospects for the design and application of high-temperature functional ceramics.

Gold-Zinc Cooperative Catalysis for Seven-exo-dig Hydrocarboxylation of Internal Alkynes.

Seven-exo-dig hydrocarboxylation of nonactivated internal alkynes with conformationally flexible linker chains was achieved with cooperative gold-zinc catalysts composed of an imidazo[1,5-a]pyridinylidene ligand including a bipyridine coordination site at the C5 position. A proximity effect of the gold and zinc sites was essential for their high catalytic activity, in which the internal alkyne activated by the cationic gold species was attacked by the carboxylic acid deprotonated by the basic zinc site. Using a gold(I)-complex with a bulky aromatic N-substituent, 2,6-dibenzhydryl-4-methylphenyl group, for the NHC ligand facilitated seven-membered ring formation while minimizing intermolecular hydrocarboxylation as an undesired side reaction. The reaction mechanism was investigated by quantum chemical calculations.

Development of mechanistic models for the description of radionuclide retention onto calcareous gravels

The retention capacity of natural calcareous gravels used as a filling material between the packages containing radioactive waste materials in the disposal cells was evaluated for Sr, U, Ni, Ag, 14C, 99Tc, 239Pu, 228Th and 152Eu. The thermodynamic calculations performed considering repository conditions indicated that the chemistry of most of these elements was dominated by neutral or cationic species, this is the case of 238Pu 152Eu, 228Th, Ni and Ag. The studied gravels presented high sorption capacities for these cationic or neutral species, but they are not efficient on retaining anionic species as in the case of 99Tc or Sr, which is already present in the composition of the studied gravels. For those elements where the predominant species are carbonated (14C and U) low distribution coefficients were obtained. A preliminary mechanistic sorption model was developed for each radionuclide considering carbonate (>CO3H) and calcium hydroxide (>CaOH) sites. Our preliminary model allowed to successfully reproduce the experimental trend of the data obtained in this work.

Sulfonato Complex Formation Rather than Sulfonate Binding in the Extraction of Base Metals with 2,2′-Biimidazole: Extraction and Complexation Studies

The application of a bidentate aromatic N,N’-donor ligand, 2,2′-biimidazole (BIIMH2), as an extractant in the form of 1-octyl-2,2′-biimidazole (OBIIMH) and related derivatives in the solvent extraction of base metal ions (Mg2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) from an acidic sulfonate medium using dinonylnaphthalene disulfonic acid (DNNDSA) as a synergist was investigated. OBIIMH with DNNDSA as a co-extractant showed a lack of selectivity for base metals ions (Mg2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) despite its similarity with a related bidentate aromatic ligand, 2,2′-pyridylimidazole, which showed preference for Ni(II) ions. The nickel(II) specificity, through stereochemical “tailor-making”, was not achieved as expected and the extracted species were isolated to study the underlying chemistry. The homemade metal sulfonate salts, M(RSO3)2·6H2O (R = Toluene and M2+ = Co2+, Ni2+, Cu2+ and Zn2+), were used as precursors of the metal complexes of BIIMH2 using toluene-4-sulfonic acid as the representative sulfonate. Spectroscopic analysis and single-crystal X-ray analysis supported the formation of similar neutral distorted octahedral sulfonato complexes through the bis coordination of BIIMH2 and two sulfonate ions rather than the formation of cationic complex species with anion coordination of sulfonates. We attributed the observation of similar complex species and the similar stability constants of the bis-complexes in solution as the cause for the lack of pH-metric separation of the later 3d metal ions.

Intra-cluster Charge Migration upon Hydration of Protonated Formic Acid Revealed by Anharmonic Analysis of Cold Ion Vibrational Spectra.

The rates of many chemical reactions are accelerated when carried out in micron-sized droplets, but the molecular origin of the rate acceleration remains unclear. One example is the condensation reaction of 1,2-diaminobenzene with formic acid to yield benzimidazole. The observed rate enhancements have been rationalized by invoking enhanced acidity at the surface of methanol solvent droplets with low water content to enable protonation of formic acid to generate a cationic species (protonated formic acid or PFA) formed by attachment of a proton to the neutral acid. Because PFA is the key feature in this reaction mechanism, vibrational spectra of cryogenically cooled, microhydrated PFA·(H2O)n=1-6 were acquired to determine how the extent of charge localization depends on the degree of hydration. Analysis of these highly anharmonic spectra with path integral ab initio molecular dynamics simulations reveals the gradual displacement of the excess proton onto the water network in the microhydration regime at low temperatures with n = 3 as the tipping point for intra-cluster proton transfer.

Electrocatalytic hydrodechlorination of 2,4-dichlorophenol on Pd catalysts supported on N-doped mesoporous carbons: Impact of electronic effects

The Pd catalysts supported on activated carbon (AC), ordered mesoporous carbon (CMK3) and N-doped mesoporous carbon (NCMK3) were prepared, and electrocatalytic hydrodechlorination (EHDC) of 2,4-dichlorophenol (2,4-DCP) was studied on the catalysts. The electronic properties of Pd particles in Pd/NCMK3 were modulated using varied reduction temperature. Increasing reduction temperature from 200 to 300 °C leads to the decrease of Pdn+/Pd0 in Pd/NCMK3 from 1.56 to 0.83. As a result, Pd/NCMK3 reduced at 200 °C exhibits substantially enhanced EHDC activity for 2,4-DCP with a peak mass activity of 3.37 min−1 mgPd−1, which is much better than previously reported catalysts. The DFT calculation shows that highly effective activation of C-Cl bonds can be achieved on cationic Pd species. Furthermore, the Pd/NCMK3 catalyst shows excellent electrocatalytic stability for EHDC of 2,4-DCP, demonstrating its great potential in the long-term application in the electrocatalytic removal of chlorinated pollutants.

Promotion of Salinity to Protonation of Amidine-based CO2-switchable Surfactant

Amidine-based switchable surfactants, whose surface activity is enabled by protonation, are a desirable candidate for the development of enhanced oil recovery methods. However, studies on the influence of salt components on the protonation of amidine-based surfactants are still very limited. In this study, it has been found that inorganic salts can induce the protonation of amidine-based surfactants, using N’-dodecyl-N and N-dimethyl acetamidine (C12-DMAA) as an example. The feasibility predictions of protonation of C12-DMAA in pure water and brines were attained by quantum chemical simulation. The occurrence of partial protonation is determined by Nuclear Magnetic Resonance (NMR). In the dispersion test, variation in conductivity and pH indicated that the water molecule plays the role of proton donor in the protonation process, and the protonation level is unaffected by the presence of cationic species. Overall, this research enhances the understanding of the switchable ability, as well as the efficient utilization of amidine-based surfactants in salt-containing systems.

EPR Sensing of a Cation Species by Aza-Crown Ethers Incorporating a Persistent Nitroxidic Radical Unit.

New nitroxides based on aza-crown ethers were prepared and employed as selective sensors for the detection of inorganic and organic cations by EPR analysis of the corresponding host-guest complexes. The nitroxide unit behaves as a sensitive probe for a number of alkali and alkaline earth metal cations affording EPR spectra differing in the value of nitrogen hyperfine constants and in the appearance of splitted signals due to the non-zero nuclear spin of some metal cation upon complexation. Owing to the remarkable EPR spectral differences between the host and the corresponding cation complex the new macrocycles are likely to act as multitasking tools to recognize several cationic species. EPR behaviour of the larger nitroxide azacrown 1⋅ when acting as a wheel in a radical synthetic bistable [2]rotaxane containing both secondary dialkylammonium and 1,2-bis(pyridinium) molecular stations, was also investigated. Reversible movements of the macrocycle between the two recognition sites in the rotaxane were promptly revealed by EPR, which shows significant changes either in nitrogen coupling constant values (aN ) or in the spectral shape in the two rotaxane co-conformations.

Sustainable hybrid biocomposite adsorbents for anion-selective or concerted removal of ionic pollutants: Organic dyes to arsenate

The controlled removal of hazardous ionizable compounds ranging from organic dyes from the textile industry to inorganic anions such as fluoride, sulfate or arsenate in aqueous media presents challenges to this day. This study devised a synthetic strategy to enable anion selective or simultaneous adsorption of anionic and cationic species. Therefore, versatile ternary metal composites (TMCs) were prepared with variable aluminum salt precursors: TMC-S for Al2(SO4)3 and TMC-N for Al(NO3)3 with variable Al3+ content from high to low values (S1>S2>S3>S4; N1≫N3) for the respective TMCs. Characterization was achieved through complementary methods: pHPZC, TGA, PXRD, XPS, 27Al/13C NMR and IR spectroscopy. The TMC surface properties were assessed via dye adsorption with methylene blue (MB) as a model cation, whereas methyl orange (MO) and reactive Black 5 (RB5) served as model anion systems. Sulfate, fluoride and arsenate represented a variety of inorganic anion target pollutant species.The maximum equilibrium adsorption capacity of MO decreased (TMC-S1 to TMC-S4; 0.67 to 0.41 mmol/g), whereas the MB adsorption capacity increased from 0.03 to 0.47 mmol/g. The arsenate adsorption capacity also decreased with decreased aluminum concentration during synthesis from 0.71 mmol/g (TMC-S1) to 0.46 mmol/g (TMC-S4). Arsenate and fluoride were chemisorbed onto the Al-centers, in contrast to the dye probes, which undergo physisorption. Additionally, arsenate was selectively removed from saline samples of groundwater with up to 6000 mg/L sulfate species, which contributes to salinity without altering the adsorption properties. This study hereby highlights the unique role of variable aluminum salt during synthesis to enable facile tailoring of the adsorbent structure and selective anion adsorption (TMC-S1) versus a more general (less selective) adsorption of ionic species (TMC-S4) for multi-component pollutant removal.

Effect of Cations on Electrocatalytic CO2-to-Methanol Conversion by Heterogenized Molecular Catalyst

Catalytic benefit and role of electrolyte cations for electrochemical CO2 reduction reaction have recently received significant research attention. It has been experimentally and theoretically demonstrated that cations can stabilize the key intermediate species, for example, *CO2 –, through mid- or short-range electrostatic interactions, facilitating the CO2 activation step.1-2 However, to date, these discussions are mostly limited to CO2-to-CO conversion (a two electron/proton transfer reaction) and electrostatic stabilization of reaction intermediate species.In present work, we show that cations play a crucial role in further reducing CO2 to methanol. We found that cations engage as a promoter in the rate determining step of the CO2-to-methanol conversion, which involves a proton-coupled electron transfer, beyond the first CO2 activation step. For this study, heterogenized molecular catalyst with a cobalt single site (Co-N4) was employed, achieving ~25% methanol selectivity at –0.78 V vs. RHE. Through an isotope labeling experiment (13CO2 reduction reaction), we validated that methanol is produced by the CO2 reduction reaction. Furthermore, electrolytes with different cation species and concentrations were tested in a systematic manner to investigate the promoting effect of cations on methanol production. In addition, using deuterated electrolytes, we studied kinetic isotope effect, proposing a reaction pathway for CO2-to-methanol conversion on the cobalt single site. Our findings offer new insights into the beneficial effect of cations on electrochemical CO2 reduction reaction kinetics besides their widely acknowledged stabilizing effect. Our discovery also opens up new research directions where non-covalent interactions between electrolyte species and reaction intermediates are utilized to enhance electrocatalytic production of a desired product in CO2 reduction reaction beyond two-electron transfer products.In this talk, I will discuss the promoting effect of cations on the electrochemical reduction of CO2 to methanol and conclude by proposing potential strategies to further improve the electrocatalytic CO2-to-methanol conversion.References Monteiro, M. C. O.; Dattila, F.; Hagedoorn, B.; García-Muelas, R.; López, N.; Koper, M. T. , Absence of CO2 electroreduction on copper, gold and silver electrodes without metal cations in solution. Nature Catalysis 2021, 4 (8), 654-662.Resasco, J.; Chen, L. D.; Clark, E.; Tsai, C.; Hahn, C.; Jaramillo, T. F.; Chan, K.; Bell, A. T., Promoter Effects of Alkali Metal Cations on the Electrochemical Reduction of Carbon Dioxide. Journal of the American Chemical Society 2017, 139 (32), 11277-11287.

Mathematical Modeling of the Performance-Degradation Mechanisms of Cation-Contaminated Proton-Exchange-Membrane Water Electrolysis

The role of hydrogen as a commercial energy carrier is dependent on the development of robust processes to convert hydrogen into usable electricity as well as produce hydrogen at large scales. Proton-exchange-membrane water electrolysis (PEMWE) is a leading technology with the potential to produce hydrogen at projected consumption rates. In PEMWE, water is electrochemically split into hydrogen and oxygen gas using a membrane—electrode assembly, which uses a membrane capable of transporting both water and protons. Reactant water containing cationic impurities have been observed to degrade cell performance. Thus, developing an understanding of the influence of cationic contaminants is important to developing mitigation and recovery strategies for PEMWE systems.In the current work, mathematical models were developed to provide insight into the mechanisms of performance degradation due to cationic contaminants. The models are non-isothermal continuum models that describe multi-phase porous flow, electrochemical reactions, and concentrated-species transport in both the gas membrane, and ionomer phases. Simulations were performed in steady-state and transient operational modes for various cationic species at several ionic concentrations. The calibration and fitting of the models were performed using experimental measurements performed by the National Renewable Energy Laboratory. The mathematical models suggest that gradients facilitate the adsorption of cationic contaminants in reactant water, which subsequently accumulate in the cathode catalyst layer, as shown in Figure 1(a), and inhibit the PEMWE hydrogen-evolution reaction (HER) that consume protons and electrons to produce hydrogen gas. The models suggest that protonic conductivity is not significantly affected by low-concentration cationic species, but access to the catalyst active sites in the cathode catalyst layer is severely impeded. As a result, the evolution of hydrogen then proceeds by an alkaline mechanism, where water and electrons combine to produce hydrogen gas and hydroxide ions. An interpolated polarization curve shown in Figure 1(b) suggests that cell operation at high current densities favor the alkaline HER reaction due to the lack of protons in the cathode catalyst layer.This research is supported by DOE Hydrogen and Fuel Cell Technologies Office, through the H2NEW Consortia. Figure 1

Alkaline Leaching: A Facile Strategy to Improve the Surface Activity of Air Electrodes for Solid Oxide Electrochemical Cells

Solid oxide electrochemical cells (SOCs) have been focused on as next-generation energy conversion devices. However, since SOCs are operated at high temperatures (>800 °C), several issues are present, such as limited material selection and high system cost. Therefore, lowering the operating temperature and developing suitable electrode materials which have high oxygen evolution/reduction reaction (OER/ORR) activity at relatively low temperatures are crucial.In this manner, surface modification methods have been researched, such as nanocatalyst decoration, surface coating, and acid etching. However, nanocatalyst decoration and surface coating require a long annealing time and complicated vacuum devices, respectively, and acid etching is not favorable for rational control on the surface of the electrode. Therefore, a cost- and time-efficient surface modification method while maintaining reasonable controllability can have a meaningful advantage.We suggest a facile method of surface modification for electrodes of SOCs: alkaline leaching. During the water splitting in a conventional 3-electrode system with an alkaline medium, cations in perovskite oxide lattice are selectively dissolved into the alkaline solution, which is called as leaching phenomenon. As a result of leaching, the composition of the perovskite oxide surface differs from the pristine condition (e.g. the transition metal-rich surface). We adopted this phenomenon as a strategy to improve the activity of air electrodes for SOCs.In this study, we chose PrBa0.8Ca0.2Co2O5+δ (PBCC) as the air electrode material for the first case-study. Recently, PBCC has gained a lot of attention due to its outstanding OER/ORR activity even at relatively low temperatures (<650 °C). We compared the reactivity of PBCC electrodes in different alkaline leaching conditions by electrochemical impedance spectroscopy. After the surface treatment, area-specific resistance of 0.018 Ω·cm2 (at 650 °C) was recorded, corresponding to the 5-fold and 53-fold enhanced ORR reactivity compared to the pristine PBCC air electrode and commercialized La0.6Sr0.4Co0.2Fe0.8O3 air electrode, respectively.To elucidate the enhanced surface activity, various analyses were carried out. Scanning electron microscopy images showed the porous structure of the PBCC electrode and the removal of Ba-containing secondary phases on the PBCC surface, which are known to degrade surface activity. Transmission electron microscopy-energy dispersive spectroscopy results demonstrated that the surface of the PBCC electrode becomes amorphous and Co-rich, which are both known to be advantageous for ORR activity. Inductively coupled plasma-mass spectrometry results of the alkaline medium in the 3-electrode system revealed that specific cation species (i.e. Ba and Ca) were selectively dissolved into the alkaline medium and were more leached out by the applied anodic bias, resulting in the Co-rich surface. X-ray photoelectron spectroscopy results suggest that surface Ba species were decreased and defective O species were increased, leading to improved ORR activity.In this case, we showcased alkaline leaching as a strategy to enhance the PBCC electrodes for SOCs, but with the sufficient current collection, our method can be further applied to various perovskite oxides in various structures. Taking the various advantages of perovskite-oxide-based materials, the alkaline leaching method will be a novel strategy to achieve a high-performance (electro)chemical catalyst.

Ruthenium arene complexes with chalcone ligands incorporating pyridyl and anthryl units: Synthesis, aqueous stability and interaction with quadruplex DNA

Twelve ruthenium(II) arene complexes incorporating chalcone ligands with pyridyl and anthryl units, as well as chlorido or oxalato ancillary ligands, have been synthesized and structurally characterized by 1H NMR spectroscopy, ESI mass spectrometry and elemental analysis. Compared to the oxalato compounds, the chlorido complexes were less stable and more susceptible to aquation in solution; the dissociation was suppressed in the presence of chloride ions. All six of the chlorido complexes and three of the oxalato complexes were able to bind to quadruplex DNA, exhibiting greater selectivity for HTelo over c-myc. The cationic species 3f, in which the chalcone chelates to the metal center, was found to bind to HTelo most strongly. These results indicate that the ancillary ligand, the location of the N-donor atom in the pyridyl ring, the position of the α,β-unsaturated ketone relative to the pyridyl and anthryl entities in the chalcone moiety, as well as the presence of the metal center all play significant roles in improving the binding of such complexes to quadruplex DNA.

Resonance Raman spectra and excited state properties of methyl viologen and its radical cation from time-dependent density functional theory.

Time-dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV2+ ). An organic dication, MV2+ has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV2+ is easily reduced by a single electron transfer to form a radical cation species (MV•+ ), which has an intense UV-visible absorption near 600 nm. The redox properties of the MV2+ /MV•+ couple and light-sensitivity of MV•+ have made the system appealing for photo-electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo-induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV2+ and MV•+ . Using a conventional hybrid exchange functional (B3-LYP) and a long-range corrected hybrid exchange functional (ωB97X-D3), including with a conductor-like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions.