Platinum Group Metal Ions Research Articles

Synthesis of Some Eco-Friendly Materials for Gold Recovery.

The aim of this study was to develop new materials with adsorbent properties that can be used for the adsorption recovery of Au(III) from aqueous solutions. To achieve this result, it is necessary to obtain inexpensive adsorbent materials in a granular form. Concomitantly, these materials must have a high adsorption capacity and selectivity. Other desired properties of these materials include a higher physical resistance, insolubility in water, and materials that can be regenerated or reused. Among the methods applied for the separation, purification, and preconcentration of platinum-group metal ions, adsorption is recognised as one of the most promising methods because of its simplicity, high efficiency, and wide availability. The studies were carried out using three supports: cellulose (CE), chitosan (Chi), and diatomea earth (Diat). These supports were functionalised by impregnation with extractants, using the ultrasound method. The extractants are environmentally friendly and relatively cheap amino acids, which contain in their structure pendant groups with nitrogen and sulphur heteroatoms (aspartic acid-Asp, l-glutamic acid-Glu, valine-Val, DL-cysteine-Cys, or serine-Ser). After preliminary testing from 75 synthesised materials, CE-Cys was chosen for the further recovery of Au(III) ions from aqueous solutions. To highlight the morphology and the functionalisation of the material, we physicochemically characterised the obtained material. Therefore, the analysis of the specific surface and porosity showed that the CE-Cys material has a specific surface of 4.6 m2/g, with a porosity of about 3 nm. The FT-IR analysis showed the presence, at a wavelength of 3340 cm-1, of the specific NH bond vibration for cysteine. At the same time, pHpZc was determined to be 2.8. The kinetic, thermodynamic, and equilibrium studies showed that the pseudo-second-order kinetic model best describes the adsorption process of Au(III) ions on the CE-Cys material. A maximum adsorption capacity of 12.18 mg per gram of the adsorbent material was achieved. It was established that the CE-Cys material can be reused five times with a good recovery degree.

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.

Half-Sandwich Type Platinum-Group Metal Complexes of C-Glucosaminyl Azines: Synthesis and Antineoplastic and Antimicrobial Activities

While platinum-based compounds such as cisplatin form the backbone of chemotherapy, the use of these compounds is limited by resistance and toxicity, driving the development of novel complexes with cytostatic properties. In this study, we synthesized a set of half-sandwich complexes of platinum-group metal ions (Ru(II), Os(II), Ir(III) and Rh(III)) with an N,N-bidentate ligand comprising a C-glucosaminyl group and a heterocycle, such as pyridine, pyridazine, pyrimidine, pyrazine or quinoline. The sugar-containing ligands themselves are unknown compounds and were obtained by nucleophilic additions of lithiated heterocycles to O-perbenzylated 2-nitro-glucal. Reduction of the adducts and, where necessary, subsequent protecting group manipulations furnished the above C-glucosaminyl heterocycles in their O-perbenzylated, O-perbenzoylated and O-unprotected forms. The derived complexes were tested on A2780 ovarian cancer cells. Pyridine, pyrazine and pyridazine-containing complexes proved to be cytostatic and cytotoxic on A2780 cells, while pyrimidine and quinoline derivatives were inactive. The best complexes contained pyridine as the heterocycle. The metal ion with polyhapto arene/arenyl moiety also impacted on the biological activity of the complexes. Ruthenium complexes with p-cymene and iridium complexes with Cp* had the best performance in ovarian cancer cells, followed by osmium complexes with p-cymene and rhodium complexes with Cp*. Finally, the chemical nature of the protective groups on the hydroxyl groups of the carbohydrate moiety were also key determinants of bioactivity; in particular, O-benzyl groups were superior to O-benzoyl groups. The IC50 values of the complexes were in the low micromolar range, and, importantly, the complexes were less active against primary, untransformed human dermal fibroblasts; however, the anticipated therapeutic window is narrow. The bioactive complexes exerted cytostasis on a set of carcinomas such as cell models of glioblastoma, as well as breast and pancreatic cancers. Furthermore, the same complexes exhibited bacteriostatic properties against multiresistant Gram-positive Staphylococcus aureus and Enterococcus clinical isolates in the low micromolar range.

Flexible and Transparent Luminescent Cellulose-Transition Metal Cluster Composites.

Red-NIR luminescent polymers are principally obtained from petroleum-based derivatives in which emitters, usually a critical raw material such as rare-earth or platinum group metal ions, are embedded. Considering the strong ecological impact of their synthesis and the major risk of fossil fuel energy shortage, there is an urgent need to find alternatives. We describe a luminescent nanocomposite based on red-NIR phosphorescent molybdenum nanoclusters, namely Cs2Mo6I8(OCOC2F5)6, embedded in an eco-friendly cellulose biopolymer matrix that is obtained by a simple solvent casting technique. While homogeneity is kept up to 20 wt% of cluster complex doping, annealing hybrids leads to a large increase of their emission efficiency, as demonstrated by quantum yield measurements.

Deuterated Malonamide Synthesis for Fundamental Research on Solvent Extraction Systems

ABSTRACT Malonamide derivatives, which are the most extensively investigated extractants for solvent extraction of lanthanides, actinides, and platinum group metal ions, were deuterated by using Pd/C and Rh/C catalysts in a D2O/2-propanol mixture. This method replaces 1H atoms in the malonamides with 2H atoms at a controllable deuteration rate. The maximum rate reached about 75%, determined by nuclear magnetic resonance and electrospray ionization – mass spectrometry. The extraction behavior of metal ions by the malonamides was unchanged by the deuteration. Deuterated malonamides are a powerful tool for fundamental research on solvent extraction systems and for structural analysis of organic phases. The large difference in the cross section of coherent neutron scattering between 1H and 2H leads to a large difference in neutron scattering length density of malonamide derivatives before and after the deuteration. Therefore, using deuterated malonamides in small-angle neutron scattering and neutron reflectivity studies may help to reveal the microscopic structure of the specific solute species in the bulk organic phase and at the liquid–liquid interface, respectively. In this paper, we report the advantage of the deuterated malonamides for a contrast-matching method in the SANS experiment. This deuteration method could be generalized and extended to a wide variety of extractant molecules.

Mutual separation of platinum group metals via seed-mediated growth on a polymer with metal-coordination unit

• Mutual separation of platinum group metals (PGMs) • Seed-mediated growth of platinum or palladium atoms on a polymer with a metal-coordination unit. • Selective separation of platinum from PGM mixture. • Selective separation of palladium from PGM mixture. • Various target platinum group metals are able to be selectively separated by selection of nucleation site. Platinum group metals (PGMs) are extremely difficult to separate from each other because of the similarity in their chemical and physical properties. We report here the effective mutual separation of PGMs utilizing a seed-mediated growth approach on a polymer with a metal-coordination unit (PMCU). Nucleation of Pt 4+ ions by sodium borohydride produced Pt 0 seeds on the metal-coordination unit (thiocarbonyl group) of PMCU. The Pt seeds-attached polymer was added into a solution containing Pt 4+ and other PGM ions, and reduction with L-ascorbic acid selectively assembled Pt atoms around the Pt seeds. The resulting polymer was removed from the mixture and washed to remove Pt and other PGMs that were only physically adsorbed, achieving selective separation of Pt. By changing the nucleation site from Pt to Pd, the immersion of Pd seeds-attached polymer in the mixed solution containing Pd 2+ and other PGM ions and reduction with L-ascorbic acid selectively separated Pd. Therefore, this approach is applicable to selective separation of various target PGMs by the selection of nucleation sites on PMCU.

Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic Ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal Ions PdII, PtII, and RhIII.

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L1-L3 towards Platinum Group metal ions PdII, PtII, and RhIII. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H2O or MeOH/H2O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and 1H- and 13C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L1)Cl]2[Pd2Cl6], [Pt(L1)Cl](BF4), [Rh(L1)Cl2](PF6), and [Rh(L3)Cl2](BF4)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the PdII/PtII, and RhIII complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L3 with PtCl2 in MeCN/H2O gave by serendipity the complex [Pt(L3)(μ-1,3-MeCONH)PtCl(MeCN)](BF4)2·H2O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d8-d8 PtII-PtII ground-state nature for this compound, rather than the alleged d9-d7 PtI-PtIII mixed-valence character reported for related dinuclear Pt-complexes.

Multicomponent Polymerization of Alkynes, Sulfonyl Azide, and Iminophosphorane at Room Temperature for the Synthesis of Hyperbranched Poly(phosphorus amidine)s

The construction of functional hyperbranched polymers with unique topological structures and distinct properties remains a great challenge. Multicomponent polymerization, as a fascinating polymer synthetic approach, has proved to be a powerful tool for the synthesis of polymers with diverse structures and multifunctionalities, which is a great advantage for the preparation of hyperbranched polymers. In this work, a multicomponent polymerization of alkynes, sulfonyl azide, and iminophosphorane is utilized for the construction of heteroatom-rich hyperbranched poly(phosphorus amidine)s with different topological structures and fluorescence response toward platinum group metal ions.

Ionic Liquids with Amino Moieties: Selective and Reversible Extraction/Back-Extraction for Platinum Group Metal Ions from Aqueous Solutions

Ionic liquids (ILs) with amino moieties were designed and synthesized as extractants for the selective extraction of platinum group metal (PGM) ions into IL phases from mixed aqueous HCl solutions with PGM and other transition metal ions. The loaded PGM ions in the IL phase were successfully back-extracted into an ammonia solution. The back-extraction ability enabled us to apply the current system for a multi-cycle green PGM-extraction process.

Microbial Recycling of Precious and Rare Metals Sourced from Post-Consumer Products

We have focused on the metal-reducing bacterium, Shewanella algae that are able to reduce and deposit platinum group metals (Pt (IV), Pd (II) and Rh (III)) and gold (Au (III)) in neutral solutions at room temperature under anaerobic conditions. When processing the aqua regia solution of spent automotive catalysts, the solution pH was adjusted to the optimal range for S. algae activity between pH 4 and 7. After this pH adjustment, the S. algae cells were able to rapidly and selectively reduce and accumulate the platinum group metal ions from the leaching solution into the bacterial cells as metallic nanoparticles. The biotechnological procedure also has the potential to allow the recovery of Au (III) ions from the leaching solution of electronic waste. We also found that the S. algae cells were also applicable to the adsorption of rare metal ions from acidic solutions. We achieved selective adsorption of indium (In (III)) ions on the bacterial cells from the leaching solution of waste liquid crystal displays by adjusting its pH, because the pH range necessary for S. algae to act as an effective adsorbent differs for different metal ions. Our proposed microbial methods enable the rapid and highly efficient recovery of precious and rare metals sourced from post-consumer products.

Highly selective separation and recovery of Pd(II) from the automotive catalyst residue with the thiocarbamoyl substituted azothiacalix[4]arene derivative

ABSTRACTNew ligand, namely, 5, 11, 17, 23-tetrakis-((p-chlorophenyl) azo)-25,26,27,28-tetrakis ((dimethylthio carbamoyl)oxy) thiacalix[4]arene (CADTTCA), has been investigated for separation and recovery of Pd(II) through solvent extraction technique. Experimental parameters such as contact time, diluents, effect of H+ and Cl− concentration, and acid durability have been thoroughly investigated. The loading capacity toward Pd(II) was determined to be 113 mg/L using 0.25 mM CADTTCA. The extractant showed high selectivity and extractability for Pd(II) than the other metal ions present in automotive catalyst residue (ACR) solution containing platinum group (PGMs) metal ions (i.e., Pd(II), Pt(IV), Rh(II), La(III), Al(III) and Ce(III)). The recovery percentage of Pd(II) was 98% after five extraction-scrubbing-stripping cycles. The probable extraction mechanisms were established through the FT-IR spectral analysis.

Extraction and separation of gold(III) from hydrochloric acid solutions using long chain structurally tailored monoamides

Abstract A series of long chain symmetrical and unsymmetrical monoamides have been prepared with different substituting groups and their extracting ability for Au(III), selected platinum-group and base metal ions like Pt(IV), Pd(II), Rh(III), Cu(II), Fe(III), and Ni(II) from hydrochloric acid solutions has been studied. The structure reactivity relationship with extraction of Au(III) was investigated. A systematic investigation has been carried out on the extraction of Au(III) using N-methyl-N-butylhexylamide (MBHA), N,N-dihexyloctainamide (DHOA), and N,N-di-hexyl-2-ethylhexainamide (DHEHA), which were chosen for further studies. The quantitative extraction of Au(III) with the investigated monoamides is observed at less than 5 min. Au(III) was strongly extracted by these extractants and the extraction increased with increasing hydrochloric acid concentration. Under similar extraction conditions Pt(IV), Pd(II), Rh(III), Cu(II) and Ni(II) were found poorly extracted. Fe(III) was significant extracted only at high hydrochloric acid concentration ⩾5 M. The dominate extracted species of Au(III) is HAuCl4(amide)2. Effective separation of Au(III) from other investigated elements is possible in the whole range of hydrochloric acid medium used (0.5–7 M), and the quantitative back extraction of Au(III) from the organic phase is obtained by using thiourea- HCl solution

Reduced Graphene Oxide Impregnated Antimony Nanoparticle Sensor for Electroanalysis of Platinum Group Metals

AbstractA very sensitive electrochemical sensor based on a reduced graphene oxide film impregnated with antimony nanoparticles was prepared and applied to the electroanalysis of platinum group metal ions of Pd(II), Pt(II) and Rh(III). The electrochemical behavior of platinum group metals at the modified electrode was studied by adsorptive differential pulse cathodic stripping voltammetry in the presence of dimethylglyoxime as chelating agent. Several operational parameters were optimised to enhance the electroanalytical performance of the modified glassy carbon electrode sensor. The results showed sharp stripping peaks and a relatively constant peak potential with a good linear behaviour in the examined concentration range from 40 to 400 pg L−1 for all metal ions investigated. The detection limit was found to be 0.45, 0.49 and 0.49 pg L−1 (S/N=3) for Pd(II), Pt(II) and Rh(III), respectively. The developed electrochemical sensor also exhibited good precision with a relative standard deviation of 4.2 %, 2.55 % and 2.67 % for 5 successive measurements for Pd(II), Pt(II) and Rh(III), respectively. The proposed nanostructure showed good sensitivity and stability, which has promising potential applications in electrochemical sensors.

ケナフを材料とした弱酸性型陽イオン交換体の合成とその銅（II）及び白金族金属イオン吸着特性

ケナフを材料とした弱酸性型陽イオン交換体の合成とその銅（II）及び白金族金属イオン吸着特性

PdCl2 Catalyzed and Uncatalyzed N-Oxidation of Naratriptan with Alkaline Chloramine-T: Delineation of Reaction Mechanisms and Kinetic Modelings

Naratriptan (NTT), chemically known as N-methyl-2-[3-(1-methyl piperidin-4-yl)-1-H-indol-5-yl] ethane sulfonamide, is an indole derivative widely used in the treatment of migraine headaches. The literature survey indicates that there is no report on the oxidation of NTT from the view point of its kinetic and mechanistic aspects. Also none has examined the task of platinum group metal ions as catalysts in the oxidation of this drug. Therefore, in the present research, oxidation of NTT with chloramine-T (CAT) in alkaline medium has been investigated at 298 K through systematic kinetic study in order to explore the mechanistic picture of this redox system in presence and absence of palladium (II) chloride (Pd(II)) catalyst. The reaction shows a first-order dependence of rate each on [CAT]0 and [NTT]0, and an inverse-fractional-order dependence on [NaOH] for both the Pd(II) catalyzed and uncatalyzed reactions. The order with respect to Pd(II) catalyst is fractional. Addition of P-toluenesulfonamide decreases the rate. The dielectric effect is negative. 2-[3-(1-methyl-1-oxidopiperidin-4-yl)-1H-indol-5-yl]ethanesulfonic acid and methylamine were identified as oxidation products of NTT. Activation parameters were deduced. The Pd(II) catalyzed reactions are about five-fold faster than the uncatalyzed reactions. The observed results have been explained by plausible mechanisms and the related rate laws have been worked out. The Stoichiometry of the reaction is

Extraction and Separation of Selected Platinum-Group and Base Metal Ions from Nitric Acid Solutions Using Thiodiglycolamides (TDGA) as Novel Extractants

A new three-structurally related thiodiglycolamides (TDGA), namely, N,N,N′,N′-tetra-n-hexyl-thiodiglycolamide (THTDGA), N,N,N′,N′-tetra-2-ethylhexyl-thiodiglycolamide (TEHTDGA), and N,N,N′,N′-tetra-n-octyl-thiodiglycolamide (TOTDGA) have been synthesized and studied for their extraction behavior towards Pd(II), Pt(IV), Rh(III), Cu(II), Ni(II), and Fe(III) from nitric acid medium. The structure reactivity relationship with extraction of investigated metal ions is studied. The synthesized thiodiglycolamides showed great extractability and selectivity for palladium than the other investigated metal ions. Pd(II) was found to be easily separated from other investigated metal ions in a single extraction step. A systematic investigation has been carried out on the extraction of Pd(II) using both TOTDGA and TEHTDGA. The main extracted species of Pd(II) was found to be Pd(TDGA)2(NO3)2, and IR spectra of the extracted species have been also investigated. The values of thermodynamics functions for the extraction of Pd(II) were calculated.

Regioselective cyclometallation with some platinum group metal ions

Reactions of [Rh(PPh3)3Cl], [Ir(PPh3)3Cl], Li2[PdCl4] and K2[PtCl4] with the corresponding 4-R-Nʹ-(arylidene)benzohydrazides (H2Ln; n = 1 and 2 for arylidene = 1-pyrenylidene and R = H and Cl, respectively and n = 3 for arylidene = 1-naphthylidene and R = H) in presence of NaOAc·3H2O in methanol/toluene provide the complexes with general formula trans-[Rh(Ln)(PPh3)2H] (1 and 2), trans-[Ir(Ln)(PPh3)2H] (3 and 4), [Pd(HLn)Cl] (5) and [Pt(HLn)Cl] (6), respectively. Reactions of 5 and 6 with PPh3 in acetone produce the complexes [Pd(Ln)(PPh3)] (7) and [Pt(Ln)(PPh3)] (8), respectively. All the complexes have been characterized with the help of microanalysis (CHN), spectroscopic (infrared, NMR, electronic and emission) and cyclic voltammetric measurements. Molecular structures of 1–5 and 8 have been confirmed with single crystal X-ray crystallography. In 5 and 6, (HL1)− acts as a monobasic CNO-donor ligand, whereas in each of 1–4, 7 and 8, the (Ln)2− acts as a dibasic CNO-donor ligand. In 1, 2, 5 and 7, metallation at the peri position of the 1-pyrenyl moiety of the pincer like ligand leads to the formation of 6,5-membered fused chelate rings, whereas in 3, 4, 6 and 8 metallation takes place at ortho position of the 1-pyrenyl/1-naphthalenyl moiety of the ligand with the formation of 5,5-membered fused chelate rings.

ChemInform Abstract: Chemistry of Precious Metal Oxides Relevant to Heterogeneous Catalysis

AbstractReview: 155 refs.

Chemistry of precious metal oxides relevant to heterogeneous catalysis

The platinum group metals (PGMs) are widely employed as catalysts, especially for the mitigation of automotive exhaust pollutants. The low natural abundance of PGMs and increasing demand from the expanding automotive sector necessitates strategies to improve the efficiency of PGM use. Conventional catalysts typically consist of PGM nanoparticles dispersed on high surface area oxide supports. However, high PGM loadings must be used to counter sintering, ablation, and deactivation of the catalyst such that sufficient activity is maintained over the operating lifetime. An appealing strategy for reducing metal loading is the substitution of PGM ions into oxide hosts: the use of single atoms (ions) as catalytic active sites represents a highly atom-efficient alternative to the use of nanoparticles. This review addresses the crystal chemistry and reactivity of oxide compounds of precious metals that are, or could be relevant to developing an understanding of the role of precious metal ions in heterogeneous catalysis. We review the chemical conditions that facilitate stabilization of the notoriously oxophobic precious metals in oxide environments, and survey complex oxide hosts that have proven to be amenable to reversible redox cycling of PGMs.

Biological activity of ruthenium and osmium arene complexes with modified paullones in human cancer cells

In an attempt to combine the ability of indolobenzazepines (paullones) to inhibit cyclin-dependent kinases (Cdks) and that of platinum-group metal ions to interact with proteins and DNA, ruthenium(II) and osmium(II) arene complexes with paullones were prepared, expecting synergies and an increase of solubility of paullones. Complexes with the general formula [MIICl(η6-p-cymene)L]Cl, where M=Ru (1, 3) or Os (2, 4), and L=L1 (1, 2) or L2 (3, 4), L1=N-(9-bromo-7,12-dihydroindolo[3,2-d][1]-benzazepin-6(5H)-yliden-N′-(2-hydroxybenzylidene)azine and L2=N-(9-bromo-7,12-dihydroindolo[3,2-d][1]benzazepin-6-yl)-N′-[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl-methylene]azinium chloride (L2*HCl), were now investigated regarding cytotoxicity and accumulation in cancer cells, impact on the cell cycle, capacity of inhibiting DNA synthesis and inducing apoptosis as well as their ability to inhibit Cdk activity. The MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) assay yielded IC50 values in the nanomolar to low micromolar range. In accordance with cytotoxicity data, the BrdU assay showed that 1 is the most and 4 the least effective of these compounds regarding inhibition of DNA synthesis. Effects on the cell cycle are minor, although concentration-dependent inhibition of Cdk2/cyclin E activity was observed in cell-free experiments. Induction of apoptosis is most pronounced for complex 1, accompanied by a low fraction of necrotic cells, as observed by annexin V–fluorescein isothiocyanate/propidium iodide staining and flow cytometric analysis.