Platinum In Water Research Articles

Why Methanol Electro-Oxidation on Platinum in Water Takes Place Only in the Presence of Adsorbed OH

To optimize fuel cells performance using alcohols as fuel it is essential to untangle the mechanism of the methanol electro-oxidation on platinum in aqueous medium as a model reaction. Recent studies have pointed out the particular necessity of adsorbed OH for this electro-oxidation process to take place1. The here reported results, carefully obtained under low methanol concentrations on the three basal planes of platinum at different scan rates to discriminate between oxidation and adsorption processes, confirm such an unforeseen preceding observation2. It is elucidated that only when adsorbed OH is already present on the surface, adsorbed CO from methanol is formed. This observation is a clear indication that adsorbed OH is involved in the mechanism beyond providing the oxygen group required to oxidize adsorbed CO, which has never been considered before. The role played by adsorbed OH in the methanol electro-oxidation to CO on platinum in aqueous medium is supported by DFT calculations, as well as the reason why this reaction is not observed in the absence of adsorbed OH. A combination of kinetic and thermodynamic factors, such as the presence of multiple water molecules per methanol molecule, the high adsorbed OH mobility on the surface, the favorable co-adsorption of methanol in the presence of adsorbed OH, and the favorable and virtually barrier-less hydrogen transference from the hydroxy group of methanol to adsorbed OH to yield water, result in the immediate activation of methanol (as soon as the molecule approaches the surface) through the favorable substitution of adsorbed OH by adsorbed methoxy. In this contribution it will be presented a change of paradigm in the understanding of how alcohols are electro-oxidized in reference systems thus having crucial implications in the search for better electrocatalysts.

Why Methanol Electro-oxidation on Platinum in Water Takes Place Only in the Presence of Adsorbed OH

Untangling the mechanism of the methanol electro-oxidation on platinum in water as a model reaction is essential to optimize fuel cells using alcohols as fuel. Recent experiments unexpectedly suggested that this electro-oxidation process would take place only in the presence of adsorbed OH. The here reported results, carefully obtained under low methanol concentrations on the three basal planes of platinum at different scan rates to discriminate between oxidation and adsorption processes, confirm such an unexpected preliminary observation. It is found that adsorbed CO from methanol is only formed when adsorbed OH is already present on the surface. This observation is a clear indication that adsorbed OH is involved in the mechanism beyond providing the oxygen group required to oxidize adsorbed CO, which has never been considered before. Supported by density functional theory calculations, the role played by adsorbed OH in the methanol electro-oxidation to CO on platinum in water and the reason why this reaction is not observed in the absence of adsorbed OH are also here both elucidated. A combination of kinetic and thermodynamic factors, such as the presence of multiple water molecules per methanol molecule, the high adsorbed OH mobility on the surface, the favorable coadsorption of methanol in the presence of adsorbed OH, and the favorable and virtually barrier-less hydrogen transference from the hydroxy group of methanol to adsorbed OH to yield water result in the immediate activation of methanol (as soon as the molecule approaches the surface) through the favorable substitution of adsorbed OH by adsorbed methoxy. This contribution represents a change of paradigm in the understanding of how alcohols are electro-oxidized in reference systems and have crucial implications in the search for better electrocatalysts.

Solvent-specific reduction of Na2PtI6 in acetone

Oxidation state of iodide complexes of PtII and PtIV in large excess of NaI with respect to platinum in water and acetone solution has been determined by means of 195Pt NMR spectroscopy. In acetone, iodide complexes of PtIV are almost quantitatively reduced into PtII, and iodine is bound in a poorly soluble polymeric complex with sodium iodide and acetone. Iodometric titration has revealed the formation of equivalent amount of iodine. Reduction of platinum has not been observed in aqueous medium.

Improving the Voltammetric Quantification of Ill-Defined Peaks Using Second Derivative Signal Transformation: Example of the Determination of Platinum in Water and Sediments

The determination of trace elements using stripping voltammetry may be seriously affected by the presence of intensive matrix background or interfering peaks, leading to poorer detection limits and/or inaccurate quantitative results. In this work, we have tested the use of signal transformation (e.g., second derivative) in the analysis of platinum in seawater and sediment digests by means of catalytic adsorptive stripping voltammetry. In natural waters, the limit of detection of Pt is affected by a broad background wave due to the formazone complex used in the sample matrix for its determination, while in sediment digests, the Pt peak may be interfered with due to the presence of elevated concentrations of Zn, affecting the accuracy of the determination. Results applying second derivative signal transformation revealed a significant improvement (2-3-fold) of the detection limit in water due to the minimization of background effects, therefore allowing shorter accumulation times and faster determinations. In the presence of interfering peaks, the inaccuracy resulting from erroneous baseline selection in the original signal is eliminated when the second derivative is used. Signal processing should be considered as a useful tool for other voltammetric methodologies where more accurate or faster determinations are needed.

Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)

Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)

Removal of platinum from water by precipitation or liquid–liquid extraction and separation from gold using ionic liquids

Precipitation and liquid–liquid extraction of PtX62− (X = Cl−, Br−, SCN−) in acidified aqueous solutions ranging from 0.1 M to 9 M HBr or 11 M of HCl have been studied using water-soluble or hydrophobic ionic liquids. Divalent hexachloroplatinate(IV) anions appear to be extracted much less efficiently than tetrachloroaurate(III) complexes. At a concentration of 11 M HCl, values of 15 and 800 for the distribution coefficients of PtCl62− and PtBr62− in [OMIM][NTf2] have been obtained accordingly. The presence of a labile hydrogen on the imidazolium ring has been found to play a specific role in the extraction of platinum(IV) complexes in concentrated HCl or HBr. Pt(SCN)62− appears to be very efficiently extracted at pH 1 using [OMIM][NTf2], exhibiting a distribution coefficient of 6150. Finally, two methods for quantitative separation of gold and platinum in water using in each method two extraction steps have been proposed. The back extraction of platinum(IV) during the second separation process was also discussed.

Selective extraction of gold and platinum in water using ionic liquids. A simple two-step extraction process

We report an all-ionic liquid process for the separation of tetrachloroaurate and hexachloroplatinate complexes. In a first step, gold is removed from water by liquid-liquid extraction with a hydrophobic ionic liquid, 1,2-dimethyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide. Platinum is subsequently extracted from the solution in the presence of KSCN using 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide.

Study of Solid Phase Extraction Prior to Spectrophotometric Determination of Platinum with N-(3,5-Dimethylphenyl)-N′-(4-Aminobenzenesulfonate)-Thiourea

A highly sensitive, selective and rapid method for the determination of platinum based on the rapid reaction of platinum(IV) with N-(3,5-dimethylphenyl)-N′-(4-aminobenzenesulfonate)-thiourea (DMMPT) and the solid phase extraction of the Pt(IV)-DMMPT complex with C18 membrane disks was developed. In the presence of pH = 3.8 buffer solution and cetyl trimethylammonium bromide (CTMAB) medium, DMMPT reacts with platinum to form a violet complex of a molar ratio of 1:3 (platinum to DMMPT). This complex was enriched by solid phase extraction with C18 membrane disks, and an enrichment factor of 200 was obtained. The molar absorptivity of the complex is 9.51 × 104 L · mol−1 · cm−1 at 755 nm, and Beer’s law is obeyed in the range of 0.01–3.0 µg mL−1 in the measured solution. The relative standard deviation for eleven replicate samples of 0.01 µg mL−1 level is 1.79%. The detection limit reaches 0.02 µg L−1 in the original samples. This method was applied to the determination of platinum in water and soil samples. The relative standard deviations are 2.9–3.4%. The recoveries are 94–105%. The values of determination obtained agree with those of the ICP-MS method. The results are satisfactory.

Simultaneous Determination of Palladium and Platinum by On-Line Enrichment Followed by Rapid Column High Performance Liquid Chromatography

In this paper, a new method for the simultaneous determination of palladium and platinum ions was developed using a rapid column high performance liquid chromatograph equipped with an on-line enrichment technique. The palladium and platinum ions were pre-column derivatized with 5-(p-aminobenzylidene)-thiorhodanine (ABTR) to form colored chelates. The Pd-ABTR, Pt-ABTR chelates can be absorbed onto the front of an enrichment column when they were injected into the injector and sent to the enrichment column [ZORBAX Stable Bound, 4.6 × 10 mm, 1.8 μm] with a buffer solution of 0.05 mol/L sodium acetate-acetic acid buffer solution (pH 3.5) as mobile phase. After the enrichment had finished, by switching the six-ports switching valve, the retained chelates were back-flushed by mobile phase and traveled towards the analytical column. These chelates separation on the analytical column [ZORBAX Stable Bound, 4.6 × 50 mm, 1.8 μm] was satisfactory with 65% methanol (containing 0.05 mol/L of pH 3.5 sodium acetate-acetic acid buffer salt and 0.01 mol/L of tritonX-100) as mobile phase. The palladium and platinum were separated completely within 2 min. The detection limits (S/N = 3) of palladium and platinum are 1.4 ng/L and 1.6 ng/L, respectively. This method was applied to the determination of palladium and platinum in water and urine samples with good results.

Preconcentration of Trace Amounts of Platinum in Water on Different Sorbents

Three different sorbents for platinum preconcentration in water were investigated: alumina, silica gel with bonded aminopropyl groups and Cellex-T. The sorbents were tested in a microcolumn at the flow rate 3 ml/min. Elution was performed with 2.0 mol/l ammonia, 2.0 mol/l hydrochloric acid and 1.2 mol/l thiourea solution, respectively. The optimal enrichment factor was 400 for the alumina column, when the eluent volume was 25 μl. Satisfactory precision was obtained for all sorbents. As the detection technique was used either FAAS or GFAAS, depending on the concentration of platinum in the eluate.

Electrode kinetics of the Cu(II)/Cu(I) system at platinum in water + dimethylsulphoxide (DMSO) mixtures

The electroreduction of Cu(II) at platinum was studied in water + DMSO mixtures using rotating disc and ring-disc voltammetry. In the whole composition range, the voltammetric curves obtained at the disc electrode exhibit a pre-wave whose height increases with increasing DMSO concentration. Quantitative measurements of the collection efficiency proved that the pre-wave corresponds to the reduction of Cu(II) to soluble Cu(I) with a current efficiency of 100%. The diffusion coefficients of Cu(II) and the kinetic parameters of the Cu(II)/Cu(I) system were determined. The change of the kinetics with the solvent composition is discussed taking into account the solvation of Cu(II) and Cu(I) ions as well as the coverage of the electrode surface by DMSO.

Elevated Temperature Potential-pH Diagrams for the Cr-H2O, Ti-H2O, Mo-H2O, and Pt-H2O Systems

Abstract This paper describes the potential-pH diagrams of chromium, molybdenum, titanium, and platinum in water at temperatures from 25 to 300 C. The diagrams can be utilized to predict the stability of these metals in aqueous solutions over this temperature range. A computer program written by D. D. Macdonald, et al, was utilized to perform the thermodynamic calculations and to construct the diagrams. In general, the diagrams indicate that the metals are more active at higher temperatures and that the area of the stable metal oxide domains decreases with increasing temperature.

On the galvanic polarization of platinum in water

"On the galvanic polarization of platinum in water." The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 5(32), p. 400