Rh Ions Research Articles

Synthesis and catalytic properties of highly porous Ag-Rh nanocages

Ag-Rh nanocages are synthesised by a facile method at 190 °C using Ag nanocubes and Na3RhCl6 as sacrificial templates and precursor, respectively. Upon introduction of Na3RhCl6 into Ag nanocube suspension in ethylene glycol (EG) with poly(vinylpyrrolidone), Rh(III) ions are reduced by EG and Ag atoms via galvanic reaction; simultaneously, the released Ag(I) ions are reduced by EG. The reduction and co-deposition of both Ag and Rh atoms result in the formation of highly porous Ag-Rh nanocages when high volume of Na3RhCl6 is introduced. The Ag-Rh nanocages with Ag:Rh atomic ratio of 54.2:45.8 exhibit good catalytic activity toward the degradation of rhodamine 6G, reduction of 4-nitrophenol, and decomposition of hydrazine.

Layer-Type AxRhO2 (A = Li, Na, K, Rb, Cs) and KxMO2 (M = Co, Rh, Ir) Electrodes: Structure and Electrochemistry

Layered lithium transition-metal oxides have remained at the forefront since the first commercialization of layered LiCoO2 in lithium-ion batteries in 1991. The scientific interest in layered sodium transition-metal oxides as well as potassium transition-metal oxides has been considerably growing for application to sodium- and potassium-ion batteries. We extend our systematic studies on the series of layered oxides to AxRhO2 (A = Li, Na, K, Rb, Cs) and KxMO2 (M = Co, Rh, Ir) electrode system focusing on their crystal structure and electrochemical behaviors in non-aqueous cells as a function of A+ ion. Further studies on P2-type KxRhO2 in comparison to P2-type KxCoO2 show that larger Rh(III/IV) ion than Co(III/IV) is believed to be beneficial for reversibility and kinetic of redox process, accompanied with reversible structural evolution upon oxidation/reduction maintaining the P2 framework.

Spin-Orbit Excitons in a Correlated Metal: Raman Scattering Study of Sr_{2}RhO_{4}.

Using Raman spectroscopy to study the correlated 4d-electron metal Sr_{2}RhO_{4}, we observe pronounced excitations at 220meV and 240meV with A_{1g} and B_{1g} symmetries, respectively. We identify them as transitions between the spin-orbit multiplets of the Rh ions, in close analogy to the spin-orbit excitons in the Mott insulators Sr_{2}IrO_{4} and α-RuCl_{3}. This observation provides direct evidence for the unquenched spin-orbit coupling in Sr_{2}RhO_{4}. A quantitative analysis of the data reveals that the tetragonal crystal field Δ in Sr_{2}RhO_{4} has a sign opposite to that in insulating Sr_{2}IrO_{4}, which enhances the planar xy orbital character of the effective J=1/2 wave function. This supports a metallic ground state, and suggests that c-axis compression of Sr_{2}RhO_{4} may transform it into a quasi-two-dimensional antiferromagnetic insulator.

Study of sorption of platinum, palladium and rhodium ions on a carbon sorbent

The article is devoted to the sorption concentration of platinum (II,IV), palladium (II) and rhodium (III) ions from chloride media on a carbon synthetic sorbent. For the study of the sorption concentration of platinum group metals, the carbon synthetic sorbent Lewatit AF5 was chosen. This sorbent has high mechanical strength, high surface area, narrow pore size distribution, and low cost compared to silicate or polymer sorbents. Sorption concentration was carried out under static conditions from model chloride solutions. The concentration of analytes in the initial solutions ranged from 8 to 50 mmol/dm3. Equilibrium concentrations of metals in solutions were determined by inductively coupled plasma atomic emission spectrometry. The dependences of adsorption on contact time, free acidity and redox potential of the system were studied, and the limiting absorption values for each of the metals studied were determined. The study of the kinetic parameters of the sorption of Pt (IV), Pd (II) and Rh (III) ions was carried out from chloride solutions characterized by free acidity values of 0.01 mol/dm3. The time for establishing sorption equilibrium was determined, which was 4 hours for each of the ions. When studying the dependence of adsorption on free acidity and the oxidation-reduction potential of the system (ORP), it was revealed that with an increase in free acidity and redox potential, a decrease in sorption activity is observed, thus we can conclude that aquated complexes of platinum metals, in which metals present not in the highest oxidation state, involved in the sorption process. Processing of experimental data showed the applicability of the linear equation of the Langmuir isotherm for the description of the adsorption process, the limiting adsorption values were calculated, using which the sorption capacity of the sorbent was assessed. The sorption capacity for Pt (II, IV), Pd (II) and Rh (III) was 1.24 mmol/g; 1.16 mmol/g and 0.57 mmol/g, respectively. High values of sorption capacity, as well as a fairly short time to achieve sorption equilibrium without the use of means for the acceleration of the process, in combination with the mechanical characteristics of the sorbent, allow us to conclude that the Lewatit AF5 sorbent is promising for the concentration of platinum group metals from hydrochloric acid solutions.

Hydroxypyridinate-bridged paddlewheel-type dirhodium complex as a catalyst for photochemical and electrochemical hydrogen evolution.

Electrochemical and photochemical hydrogen (H2) evolution activities of a 6-fluoro-2-hydroxypyridinate (fhp-)-bridged paddlewheel-type dirhodium (Rh2) complex, [Rh2(fhp)4], were investigated through experimental and theoretical approaches. In DMF, the [Rh2(fhp)4] underwent a one-electron reduction (assigned to Rh24+/3+) at -1.31V vs SCE in the cathodic region. Adding trifluoroacetic acid as a proton source to the electrochemical cell containing [Rh2(fhp)4], the significant catalytic current, i.e., electrochemical H2 evolution, was observed; the turnover frequency and overpotential of electrochemical H2 evolution were 18 244s-1 and 732 mV, respectively. The reaction mechanism of electrochemical H2 evolution catalyzed by [Rh2(fhp)4] in DMF was examined in detail by theoretically predicting the redox potentials and pKa values of the reaction intermediates using density functional theory calculations. The calculations revealed that (i) the formation of a one-electron reduced species, [Rh2(fhp)4]-, triggered for H2 evolution and (ii) the protonation and reduction processes of [Rh2(fhp)4]- to further reduced hydride intermediates proceeded directly via a concerted proton-electron transfer mechanism. Moreover, [Rh2(fhp)4] was shown to be a highly efficient H2 evolution catalyst (HEC) for photochemical proton reduction reactions when combined with an artificial photosynthetic (AP) system containing [Ir(ppy)2(dtbbpy)]PF6 and triethylamine, which served as a photosensitizer and a sacrificial electron donor, respectively. Under visible light irradiation, the total amount of H2 evolved and its turnover number (per Rh ion) were 1361.0 µmol and 13 610, respectively, which are superior to those of previously reported AP systems with rhodium complexes as HEC.

Band structure engineering of Pd, Rh, Cu-Modified SrMoO4 for enhanced activity and selectivity in photocatalytic CO2 reduction to CH4

Photocatalytic CO2 reduction holds promise as a strategy to mitigate the energy crisis and greenhouse effects. However, devising cost-effective photocatalysts capable of efficiently and selectively converting CO2 to CH4 remains challenging. This study presents the synthesis of Pd, Rh, and Cu-modified SrMoO4 photocatalysts via a one-step solvothermal method. Our findings demonstrate increased CH4 activity and controlled selectivity through the modification with Pd, Rh, or Cu ions. It was determined that Pd, Rh, or Cu ions modified the SrMoO4 surface as -O-Pd-O-, -O-Rh-O-, or -O-Cu–O- species, increasing the adsorption sites and active regions on the catalyst surface. Moreover, these introduced -O-Pd-O-, -O-Rh-O-, or -O-Cu–O- species' energy level enhances visible light absorption and photogenerated charge carrier separation, and regulates the band structure for better alignment with water oxidation potential. This leads to greater water oxidation half-reaction efficiency and increased H+ generation in photocatalytic CO2 reduction. Consequently, more protons (H+) participate in CO2 photocatalytic reduction, thus promoting CH4 production and selectivity. These insights may guide the design of highly-selective photocatalysts for effective CO2 photoreduction through bandgap engineering strategies.

Synthesis, Characterization and Thermal Analysis of Cu (II), Co (II), Ru(III) and Rh(III) Complexes of a New Acidic Ligand

Hippuric acid and 3-amino phenol were used to make the 4-(2-Amino-4-hydroxy-phenylazo)-benzoylamino-acetic acid diazonium salt, a new Azo molecule that is a derivative of the (4-Amino-benzoylamino)-acetic acid diazonium salt. We found out what the ligand's chemical structures were by using information from 1HNMR, FTIR, CHN, UV-Vis, LC-mass spectroscopy, and thermal analyses. To make metal complexes of the azo ligand with Co(II), Cu(II), Ru(III), and Rh(III) ions, extra amounts of each azo ligand were mixed with metal chloride salts in a 2:2 mole ratio. The stereochemical structures and geometries of the metal complexes that were studied were guessed based on the fact that the ligand exhibited tetradentate bonding behavior when combined with the metalions. The azodye ligand is coordinated with the metal ions (Co(II), Cu(II),Ru(III), and Rh(III)) through (NNOO) the N atoms of azo and amine groups and the oxygen of carboxylic and phenolic hydroxyl groups. According to analytical results, the Ru(III) and Rh(III) complexes have binuclear octahedral geometry, whereas the Cu(II) and Co(II) complexes have binuclear distorted octahedral and binuclear tetrahedral geometry, respectively. The results indicated that the following formulas for ligand complexes should be used: [Ru2Cl2(H2O)2(LI)2], [Rh2Cl2(H2O)2(LI)2], [Co2(LI)2], and [Cu2(LI)2]. The thermal analysis conducted by TG, DTG, and DTA demonstrated partial breakdown at temperatures between 820°C and 850°C.

Study on the extraction and separation of precious metals from wastewater using a hydrophobic deep eutectic solvent

Efficient and sustainable recovery of precious metals from the acidic leaching solution of solid waste is considered to be the main solution to the scarcity of precious metal resources. In this study, a hydrophobic deep eutectic solvent (HDES) was synthesized using trioctylmethylammonium chloride (N263) and oleic acid (OA). HDES was then used for the efficient recovery of Ir, Pt, Ru, and Rh from leaching solution containing precious metals. The effects of different molar ratios between N263 and OA, the initial pH of the aqueous phase, the oscillation time, and the phase ratio O/A of the extraction process were investigated. The organic phases were characterized analytically using ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, and electrospray ionization–mass spectrometry to further investigate the reaction mechanisms of the extraction process. The single-stage extraction percentages of Ir(IV), Ru(III), Pt(IV), and Rh(III) ions were 97.57%, 94.26%, 99.55%, and 15.1%, respectively. The high saturation extraction capacity of HDES enabled a high precious metal load, reaching 18.44 g L−1. Hydrogen bonds were formed between Cl-, which was bound by electrostatic force in the N263 structure, and H in the -COOH group in the OA molecule. During the extraction process, metal chloride complex ions replaced Cl- and entered the organic phase as 2[C17H33-COOH···N263+]IrCl62-, 3[C17H33-COOH···N263+]RuCl63-, 2[C17H33-COOH···N263+]PtCl62-, and 3[C17H33-COOH···N263+]RhCl63-. After scrubbing for effective removal of Cu and Fe in the loaded organic phase, different systems were used for stripping. The stripping percentage of precious metal ions reached more than 96.3%, providing efficient separation of the four precious metals from wastewater.

Large magnetocaloric effect and magnetic properties of EuRhO3

We report on the structural, magnetic, and magnetocaloric properties of EuRhO3 powders. The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy (XPS). It is found that the Eu ions are mainly in the divalent oxidation state while the Rh ions have +4 state. EuRhO3 powders are found to be antiferromagnetic with a second order magnetic transition at Néel temperature (TN = 2.9 K). Analysis of the magnetic susceptibility versus temperature data in terms of the Curie–Weiss law: (χ = C/(T–θW)) for T > TN, yields θW = −3.1 K and effective magnetic moment μeffexp = 7.72 μB, which is close to the theoretical value μefftheo = 7.94 μB. The magnetic entropy change (–ΔSM), was determined by employing the thermodynamic Maxwell's relation. At μ0H = 5 T and near TN, (–ΔSMMax) and relative cooling power (RCP) exhibit large values of 33.7 J/(kg⋅K) and 238 J/kg, respectively. The large magnitude of –ΔSM and RCP show that the EuRhO3 compound could be a potential candidate to be used in cryogenic magnetic refrigeration.

A Novel Diamagnetic Insulating Quadruple Perovskite Oxide YCu<sub>3</sub>Rh<sub>4</sub>O<sub>12</sub>

A novel oxide YCu3Rh4O12 has been obtained using high-pressure and high-temperature conditions of 12 GPa and 1573 K. Electron diffraction and synchrotron X-ray powder diffraction data demonstrates that YCu3Rh4O12 crystallizes in a cubic AA′3B4O12-type quadruple perovskite structure. The valence state is estimated to be Y3+Cu3+3Rh3+4O12 by X-ray absorption spectroscopy. The electric resistivity and magnetization data prove that YCu3Rh4O12 is a diamagnetic insulator, which is expected from the electron configurations of Cu3+ (3d8, low spin, S = 0) and Rh3+ (4d6, low spin, S = 0) ions. The first-principle calculation displays the insulating band structure for YCu3Rh4O12. The valence state transition from Ca2+Cu2.8+3Rh3.4+4O12 to Y3+Cu3+3Rh3+4O12 indicates that the doped electrons by the substitution of Y3+ for Ca2+ are not simply injected to Cu and/or Rh ions, realizing unusual charge redistributions consisting of the simultaneous Cu oxidation (Cu2.8+ → Cu3+) and Rh reduction (Rh3.4+ → Rh3+).

One‐Pot Polyol Synthesis and Scalable Production of Rh−Pd Alloy Nanorods with Tunable Compositions

AbstractCombining different precious metals to generate alloy nanocrystals with desirable shapes and compositions remains a challenge because of the low miscibility between these metals and/or the different reduction potentials of their salt precursors. Specifically, Rh and Pd are considered to be immiscible in the bulk solid over the entire composition range. Here we demonstrate that Rh−Pd alloy nanorods with well‐distributed and tunable compositions can be synthesized using a one‐pot polyol method. The success of our synthesis relies on the introduction of bromide as a coordination ligand to tune the redox potentials of Rh(III) and Pd(II) ions for the achievement of co‐reduction. The atomic ratio of the Rh−Pd alloy nanorods can be facilely tuned by changing the molar feeding ratio between the two precursors. We also systematically investigate the effects of water on the morphology of the Rh−Pd alloy nanocrystals. In an attempt to promote future use of these alloy nanorods, we successfully scale up their synthesis in a continuous‐flow reactor with no degradation to the product quality.

Recovery of platinum group metals from aqueous solution by iron-electrocoagulation

The recovery of platinum group-metals (PGMs) has attracted increasing attention owing to their scarcity, economic importance, and criticality. Traditional techniques for PGM recovery often involve the use of toxic reagents and require strict extraction conditions, posing challenges for their implementation in complex environments. In this paper, a novel method based on iron electrocoagulation (Fe-EC) is proposed for PGM extraction. The Fe-EC process generates iron (hydr)oxide flocs in situ, which spontaneously and uniformly adsorb and reduce PGM ions. The selectivity of PGM recovery is attributed to the higher electronegativity and standard reduction potential of PGM ions compared to base metal ions. Efficient extraction of Pt, Pd, and Rh ions from aqueous solutions was achieved using Fe-EC, with extraction efficiencies of 81.26 %, 81.32 %, and 99.66 %, respectively. These results were obtained at a voltage of 2 V and residual concentrations of 0.3072, 0.0051 and 0.0049 mg L–1. TEM-EDS and XPS characterizations of the Fe-EC flocs showed that Pt, Pd, and Rh were present in the elemental form particles. The extraction performance of base metal such as Ni, Zn, Mg and Mn ions by Fe-EC was found to be poor, with minimal reduction to elemental form. Finally, the Fe-EC flocs were subjected to acid washing and filtration, resulting in the selective recovery of Pt, Pd, and Rh products with high purities of 97.43%, 97.12%, and 97.92%, respectively. This study presents a new and environmentally friendly method for the recycling of PGMs, offering a promising approach for sustainable PGM recovery.

Recovery of platinum group metal resources from high-level radioactive liquid wastes by non-contact photoreduction

Recovery of platinum group metals (PGMs) including palladium (Pd), rhodium (Rh), and ruthenium (Ru) from high-level radioactive liquid waste (HLLW) possesses enormous environmental and economic benefits. A non-contact photoreduction method was herein developed to selectively recover each PGM from HLLW. Soluble Pd(II), Rh(III), and Ru(III) ions were reduced to insoluble zero-valent metals and separated from simulated HLLW containing neodymium (Nd) as a representative for lanthanides, another main component in HLLW. Detailed investigation on the photoreduction of different PGMs revealed that Pd(II) could be reduced under 254- or 300-nm UV exposure using either ethanol or isopropanol as reductants. Only 300-nm UV light enabled the reduction of Rh(III) in the presence of ethanol or isopropanol. Ru(III) was the most difficult to reduce, which was only realized by 300-nm UV illumination in isopropanol solution. The effects of pH was also studied, suggesting that lower pH favored the separation of Rh(III) but hindered the reduction of Pd(II) and Ru(III). A delicate three-step process was accordingly designed to achieve the selective recovery of each PGM from simulated HLLW. Pd(II) was reduced by 254-nm UV light with the help of ethanol in the first step. Then Rh(III) was reduced by 300-UV light in the second step after the pH was adjusted to 0.5 to suppress the Ru(III) reduction. In the third step, Ru(III) was reduced by 300-nm UV light after isopropanol was added and the pH was adjusted to 3.2. The separation ratios of Pd, Rh, and Ru exceeded 99.8%, 99.9%, and 90.0%, respectively. Meanwhile, all Nd(III) still remained in the simulated HLLW. The separation coefficients between Pd/Rh and Rh/Ru exceeded 56,000 and 75,000, respectively. This work may provide an alternative method to recover PGMs from HLLW, which minimize the secondary radioactive wastes compared with other approaches.

Extraction of Rh(III) from hydrochloric acid by protonated NTAamide(C6) and analogous compounds and understanding of extraction equilibria by using UV spectroscopy and DFT calculations.

Extraction of Rh from hydrochloric acid is conducted using NTAamide(C6) (N,N,N´,N´,N´´,N´´-hexahexyl-nitrilotriacetamide) and other related compounds. We use the ion-pair extraction of anionic species of Rh-chloride and protonated extractant. Rh ions exist as Rh(Cl)n(H2O)6-n (n ≤ 5) and the tertiary nitrogen atom in an extractant are protonated to produce a quaternary amine in acidic condition. The D(Rh) values are changeable because the Rh-Cl-H2O complex forms from + 3 to - 2 valency. Rh-chloride ion with a peak of spectrum at 504nm can be extracted effectively, where RhCl4(H2O)- and RhCl5(H2O)2- exist from Density functional theory calculation and UV spectrum. The maximum distribution ratio (D) of Rh(III) is 16, and 85mM Rh can be extracted from 1M HCl dissolving 96mM, due to less third phase formation. Approximate 80% of Rh can be stripped by the water-soluble reagents having the activities of neutralization and solvation. The figure for the Graphical Index saved in the JPEG, PNG or TIFF format at 300 dpi should be pasted with the size adjusted to the frame below (5 cm long and 8 cm wide).

Interaction between dirhodium(II) tetraacetate and PAMAM dendrimer grafted onto magnetite nanoparticles: Effects on magnetic properties

In this study, we report on fabrication and characterization of a novel magnetic nanocarrier based on association of magnetite nanoparticles (NPs) with poly(amidoamine) (PAMAM) dendrimers loading dirhodium(II) tetraacetate complex (DiRh(II)). The pristine magnetite NP was coated with ATPS (3-aminopropyltriethoxysilane). The interaction between PAMAM dendrimer and DiRh(II) and its effects on magnetic properties were investigated. The magnetite spinel phase is confirmed via x-ray diffraction (XRD) and Raman spectroscopy data analysis. A mean crystallite size of 9.5 ± 0.3 nm of magnetite particles is assessed from XRD data, which is close to the values obtained via dynamic light scattering (DLS) and transmission electron microscopy micrographs. Our findings strongly suggest that the Rh(II) ions interact with lone electron pairs of nitrogen atoms in amide-II and primary amines of PAMAM surface-terminated moieties. The onset of an absorption peak at 283 nm in DiRh(II) containing sample, assigned to σRh-L→σ∗Rh-Rh electronic transition, revealed a direct interaction between Rh(II) ions and L moieties of PAMAM dendrimer. Magnetization results indicate that the presence of DiRh(II) attached to PAMAM dendrimer leads to the strong weakening of magnetic dipole–dipole interactions in ATPS- and ATPS + PAMAM coated magnetite nanoparticles.

Radiative Properties of Rb-Isoelectronic Technetium (Tc VII), Ruthenium (Ru VIII) and Rhodium (Rh IX) Ions for Astrophysical Applications

In this work, we present high-accuracy spectroscopic properties, such as line strengths, transition probabilities and oscillator strengths for allowed transitions among nD3/2,5/2,n′S1/2 and n′P1/2,3/2(n=4,n′=5,6) states of Rb-isoelectronic Tc (Tc VII), Ru (Ru VIII) and Rh (Rh IX) ions for their applications in the analysis of astrophysical phenomena occurring inside celestial bodies containing Tc, Ru and Rh ions. Due to the scarcity of computational data of atomic properties of these transitions, as well as considerable discrepancies within the literature about these ions, the precise determination of these properties is necessary. For this purpose, we have implemented relativistic many-body perturbation theory (RMBPT) for evaluation of the wave functions of the considered states. For better accuracy, we have accounted for electron interactions through random phase approximation, Brückner orbitals and structural radiations of wave functions in our RMBPT method for further precise evaluation of electric dipole amplitudes. Combining these values of the observed wavelengths, the above transition properties and radiative lifetimes, a number of excited states of Tc VII, Ru VIII and Rh IX ions have been calculated. For further validation of our work, we have compared our results with the data already available in the literature.

Fe-Cu-Rh ternary alloy nanofibers as an outstanding pH-universal electrocatalyst for hydrogen evolution reaction: The catalytic roles of Fe depending on pH

Fe-Cu-Rh ternary alloy nanofibers having various elemental compositions (x-Fe@Cu-Rh) were synthesized through the thermal hydrogen reduction of Fe-substituted CuRh2O4 nanofibers, which were prepared by electrospinning of a solution containing Cu and Rh precursors at a constant molar ratio (Cu:Rh = 1:2) with varying Fe precursor wt% (x = 6, 12, 24, 48 and 80). A series of x-Fe@Cu-Rh nanofibers were composed of the phases of metallic (fcc) and/or spinel CuRh2O4 where Fe ion substitutes primarily Rh ion in the octahedral site. x-Fe@Cu-Rh ternary alloy nanofibers showed higher pH-universal HER activity than pure Rh and Cu-Rh binary counterparts; and particularly, 12-Fe@Cu-Rh composed of 7.3, 27.2 and 65.5 atomic % of Fe, Cu and Rh, respectively, presented a superb activity (e.g., the most positive onset potential and the smallest Tafel slope) along with reasonable stability, even outperforming commercial Pt. The addition of Fe to Cu-Rh binary system improved alkaline HER activity substantially, proposing the crucial role of Fe-Cu-Rh interfaces for facilitating water molecule adsorption/dissociation. In acidic condition, Fe served as an excellent diluent reducing noble Rh content without deteriorating the acidic HER activity. Surprisingly, 80-Fe@Cu-Rh having only 18.5 atomic % of noble Rh exhibited decent HER activity during 24 h, demonstrating its potential as a stable and economic catalyst particularly for acidic HER.

Role of rhodium doping into lanthanum cobalt oxide (LaCoO3) perovskite and the induced bifunctional activity of oxygen evolution and reduction reactions in alkaline medium

Rhodium doping into the lanthanum cobalt oxide (LaCo 1-x Rh x O 3 ) has induced significant bifunctional electrochemical activity towards the OER and ORR in alkaline solution with a substantially lower OER/ORR onset potential of 1.36/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), low charge-transfer resistance, and an OER and ORR potential gap of only 0.65 V. Transition metal oxides, especially perovskites, have been considered effective electrocatalysts for the oxygen evolution (OER) and oxygen reduction (ORR) reactions in an alkaline solution. Here, a series of lanthanum cobalt rhodium oxide perovskites with the chemical formula LaCo 1-x Rh x O 3 (LCRO, 0.1 ≤ x ≤ 0.70) were prepared through the approach of solid-phase synthesis and their bifunctional electrocatalytic activity was assessed for both the OER and ORR. The crystallinity, morphology, surface, and electrocatalytic features of the LCRO were significantly correlated with the rhodium content. The LaCo 0.7 Rh 0.3 O 3 electrocatalysts with x = 0.3 showed enhanced electrocatalytic bifunctional performance with a substantially lower OER/ORR onset potential of 1.38/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), and low charge-transfer resistance, which is the most efficient catalyst among the other studied ratios and superior to the pristine lanthanum cobalt oxide benchmark electrocatalysts. The LaCo 0.7 Rh 0.3 O 3 electrode exhibit good bifunctional electrocatalytic behavior and long-term durability with an OER and ORR onset potential gap (ΔE = E OER − E ORR ) of only 0.65 V, which could be credited to the enriched oxygen vacancies, lattice expansion and the improved electrical conductivity upon the doping of larger size of Rh ions. The LaCo 1-x Rh x O 3 catalysts are obtained from abundant materials that have the potential of highly-active bifunctional OER and ORR electrocatalysts.

Sorption of rhodium(III) chloride complexes by silica chemically modified with γ-minopropyltriethoxysilane groups

The sorption of Rh(III) chlorocomplexes from hydrochloric acid solutions by silica chemically modified with -aminopropyltriethoxysilane groups was studied. Under static conditions, dependences of the sorption of the indicated ion on time, acid concentration, and temperature were obtained, and sorption isotherms were plotted. It was found that the time required for establishing constant sorption values for Rh(III) ions from a 1 mol/l HCl solution is 35–40 min. The maximum capacity of the sorbent with respect to rhodium(III) ions, which the authors managed to achieve, is 0.42 mmol/g. Under the same conditions, to achieve constant values of sorption of Pt(IV), Ir(III), and Ir(IV) ions, 10 min of phase contact is sufficient, while the sorption of ions of these metals does not exceed 0.06 mmol/g. Using a combination of spectral methods (IR and electron spectroscopy), it has been shown that in the process of establishing the sorption equilibrium, the Rh(III) hexachloride complex undergoes hydrolytic transformations, and an aquated ion of the [RhCl5(H2O)]2– composition passes into the sorbent phase, and with an increase in temperature — trans-[RhCl4(H2O)2]–. In this case, during the sorption of [PtCl6]2– and [IrCl6]2– ions, their complex state does not change, and they pass into the sorbent phase in the form of hexachloroplatinate (IV) ion and hexachloroiridate (IV) ion, respectively. Ir(III) ions behave similarly to Rh(III), aquatation processes occur, and the [IrCl4(H2O)2]– anion is sorbed. Since the chlorocomplexes of Ir(III) are adsorbed by the sorbent under study better than Ir(IV), in order to separate rhodium from iridium, one should not allow the reduction of Ir(IV) to a lower oxidation state. Experiments were carried out on the desorption of sorbed ions of platinum metals with a 10% ammonium chloride solution and a 3 mol/l HCl solution. It was found that the separation of the Rh(III)/Ir(IV) pair occurs at the elution stage.The work was carried out under agreement with the Ministry of Education and Science of the Russian Federation No. 075-15-2021-689 dated 09/01/2021, unique identification number 2296.61321X0010, with the participation of N. M. Bodnar, Candidate of Chemical Sciences, senior researcher (RTU MIREA), and G. V. Erlich, Doctor of Chemical Sciences, professor of the Faculty of Chemistry of Moscow State University named after M. V. Lomonosov.

Prototropic tautomerism of (E)-N-((4-((2-hydroxy-5-methoxybenzylidene) amino)phenyl)sulfonyl)acetamide and its coordination abilities towards Ru, Rh, and Ir trivalent metal ions

The Schiff base (E)-N-((4-((2-hydroxy-5-methoxybenzylidene)amino)phenyl)sulfonyl) acetamide (ScB-SAM) has been synthesized bytheir condensation at room temperature in ethanol. X-ray crystallographic analysis revealed that the keto-enol tautomerism of its solid state exists as a complex equilibria system that is stabilized intramolecular hydrogen bond. The enol, keto and mixed enol-zwitterionic forms were observed in the crystal structure. The crystallographic results were supported by ATR, and UV–Vis. Physical properties were determined in different polar and nonpolar solvents and solid state. All above experimental results were then compared with DFT calculations. Additionally, the stabilities of the trivalent: iridium, rhodium and ruthenium ions complexes with ScB-SAM have also been investigated by spectrophotometric titration methods in water. The data showed that the examined coordination compounds were stable in solution based on the values of their stability constants found.