Emil B. Milosavljević

Affinity of activated carbon towards some gold(I) complexes

Abstract The adsorption of dicyanoaurate(I), dithioureaaurum(I), dithiocyanatoaurate(I), and dithiosulfatoaurate(I) complexes onto activated carbon has been investigated. A flow-through miniature column connected on-line to a flow injection analysis system with a flame atomic absorption spectrometry detector provided information on the relative rates and extent of adsorption of gold(I) complexes. The corresponding adsorption isotherms have also been determined. Scanning electron micrographs of the barren and loaded carbon surfaces (from K[Au(SCN)2]) are presented. These show that Au(SCN)2−1 is reduced to metallic gold on the carbon surface. It is established that the effectiveness of activated carbon in removing complexed gold from aqueous solutions decreases in the following ligand order: SCN− > SC(NH2)2 > CN− ⪢ S2O32−.

Photocatalytic oxidation of cyanide to nitrate at TiO2 particles

Abstract The photocatalytic oxidation of cyanide at titanium(IV) oxide powder induced by UV irradiation was investigated. It is verified that cyanide is first oxidized to cyanate. However, contrary to earlier studies, it is established that cyanate is subsequently further photocatalytically oxidized via nitrite all the way to nitrate. Experimental conditions were varied and the effects of various sparging gases and pH, as well as the concentrations of both cyanide and photocatalyst, were investigated. As nitrate is a significantly less hazardous contaminant than cyanide, complete photocatalytic oxidation of cyanide to nitrate may be a viable method for decontamination of cyanide wastes.

Photocatalytic oxidation of aqueous ammonia (ammonium ion) to nitrite or nitrate at TiO2 particles

SummaryThe photocatalytic oxidation of ammonia (ammonium ion) in the presence of air or pure oxygen at titanium(IV) oxide powder surfaces and induced by UV light was investigated. Experimental conditions were varied and the effect ofpH, sparging gas, as well as the concentration of both ammonia (ammonium ion) and photocatalyst were investigated. It has been established that the principal product of photocatalytic oxidation depends onpH, and is either nitrite or nitrate. A gas-diffusion flow injection analysis system with conductivity detection was used for on-line monitoring of ammonia concentration. In addition, ion-chromatography with UV detection was utilized for offline monitoring of nitrite and nitrate concentrations. The use of a photocatalyst such as TiO2 may prove to be a viable method for conversion of ammonia (ammonium ion) to either nitrite or nitrate.ZusammenfassungEs wurde die photokatalytische Oxidation von Ammoniak (Ammoniumion) mittels Luft oder reinem Sauerstoff an Titan(IV)oxid-Pulveroberflächen unter Induktion von UV-Licht untersucht. Die experimentellen Bedingungen wurden variiert, wobei der Effekt despH-Wertes, des Spülgases und sowohl die Ammoniak- als auch die Photokatalysator-Konzentration berücksichtigt wurde. Dabei ergab sich, daß das Hauptprodukt der photokatalytischen Oxidation vompH abhängt und entweder Nitrit oder Nitrat ist. Ein Gasdiffusions-Fließinjektions-Analysensystem wurde zur on-line-Kontrolle der Ammoniak-Konzentration verwendet. Off-line-Ionenchromatographie mit UV-Detektion wurde zur Konzentrationsbestimmung für Nitrit und Nitrat herangezogen. Die Verwendung von Photokatalysatoren wie Titanoxid könnte sich als gangbarer Weg erweisen, um Ammoniak (Ammoniumion) entweder zu Nitrit oder zu Nitrat umzusetzen.

Phosphole complexes of gold(III) halides : synthesis, structure, electrochemistry and ligand redistribution reactions

Abstract The complexes LAuCl3 [L = 1-phenyl-3,4-dimethylphosphole(DMPP), 1- phenyldibenzophosphole(DBP) and triphenylphosphine], LAuBr3 (L = DBP, Ph3P) and LAuClBr2 (L = DBP, Ph3P) were prepared and characterized by physical properties, cyclic voltammetry, far IR, 31P {1H} and CP/MAS 31P{1H} NMR spectroscopy. Ligand redistribution, reactions of the types: LAuCl + L′AuBr ⇌L′AuCl + LAuBr; LAuCl3 + LAuBr3⇌ LAuClnBr3−n; LAuCl3 + L′AuBr3⇌ LAuCl nBr3−n +L′AuClnBr3−n; and LAu Cl+L′AuBr3⇌ LAuBr+L′AuCl+L′AuBr+LAuClnBr3−n +L′AuClnBr3−n all occur rapidly and have been studied by 31P{1H} NMR spectroscopy. These reactions all appear to proceed by way of halide-bridged intermediates. The solid state identities of LAuClBr2 were established by a combination of far IR and CP/MAS 31P{1H} NMR spectroscopies and single crystal X-ray crystallography for Ph3PAuBr2Cl. The R3PAuBr2Cl complexes are substitutionally disordered, probably with two-thirds bromine and one-third chlorine in each site. Ph3PAuBr2Cl crystallized in the monoclinic space group P21/c with a = 9.086(2), b = 11.410(2), c = 18.734(4) A, β = 95.01°(2), and Z = 4. The structure was solved by least-squares methods with RF = 0.074 for 1919 unique reflections with I/σ(I)

Electrochemistry of (R3P)2Ru(CO)2Cl2 and (R3P)3Ru(CO)Cl2 complexes

3.0. The gold atom has nearly regular square-planar coordination with AuP = 2.314(6) A° and AuX = 2.399(3), 2.413(3) and 2.415(4) A°.

Photochemistry of Aqueous Solutions of Dicyanomercury(II) and Potassium Tetracyanomercurate(II)

Abstract The redox behavior of a series of sixteen ruthenium(II) complexes of the types (R 3 P) 2 Ru(CO) 2 Cl 2 (R 3 P  Me 3 P, Ph 2 MeP and (R 3 P) 2 Ru(CO)Cl 2 (R 3 P = Me 3 P,Ph 2 MeP and PhMe 2 P) has been studied by cyclic and differential pulse voltammetry at a stationary platinum electrode in dichloro-methane. The redox potentials for the Ru II /Ru III processes are a function of complex geometry, stoichiometry and the nature of the phosphine. This process is electrochemically reversible and is followed by a chemical step, the rate of which is a function of the complex geometry and the nature of the phosphine. The chemical step is fast for the cis -(R 3 P) 3 Ru(CO)Cl 2 and cct -(R 3 P) 2 Ru(CO) 2 Cl 2 complexes whereas for the corresponding trans and ttt complexes it is slow. For some of the latter complexes, the rate constants for the chemical step have been determined. A few of the complexes also underwent irreversible Ru II /Ru I and Ru III /Ru IV processes in the accessible potential range. There is no correlation between the redox behavior of these complexes and their activity as homogeneous hydrogenation catalysts.

Indirect determination of bromide by diffusion flow injection analysis with amperometric detection

Photochemically induced reactions of dicyanomercury(II) and potassium tetracyanomercurate(II) in alkaline aqueous solutions were investigated in detail. The studies were conducted in the presence or absence of a titanium(IV) oxide semiconductor photocatalyst utilizing sunlight as the irradiation source. It was established that the cyanide ion liberated from the thermodynamically stable mercury-cyano species can be photocatalytically oxidized via cyanate and nitrite to nitrate. In addition, the process removes over 99 mol% of mercury from the solution. In the absence of the photocatalyst, no photoproducts were detected and mercury remained in solution. The results obtained may have ramifications for the use of solar power for the efficient treatment of large quantities of precious metals mill tailings wastes containing various cyanide species. In addition, in order to follow the fate of cyanide in these experiments, a novel gas-diffusion flow injection analysis system for the determination of cyanide from the thermodynamically stable mercury-cyano complexes was utilized.

Simultaneous flow injection speciation of iron(II) and iron(III) cyano complexes utilizing electrochemical and atomic absorption detectors in series

SummaryA rapid, indirect diffusion flow injection analysis (FIA) method with amperometric detection has been developed for the selective and sensitive determination of Br−. The method is based on permanganate oxidation of Br− to bromine. Bromine diffuses through a PTFE membrane and is quantified amperometrically at a platinum working electrode. Calibration graphs were linear up to the maximum concentration of Br− investigated (10.0 mmol/l). The precision of the technique was better than a relative standard deviation of 0.7% at 10.0 μmol/l, with a throughput of 30 samples per hour. The effects of temperature, acidity, working potential, composition of the reagent solution and interferents on the FIA signals were studied. The catalytic effect of Cl− on the permanganate oxidation of the analyte was utilized to lower the detection limit to 1 μmol/l (16 ng Br−). Similar detection limits were achieved by combining the effects of higher acidity (4.0 mol/l H2SO4) and elevated temperatures (40°C). The method was successfully applied to the determination of Br− in chloride and other reagents, as well as in natural waters.

Indirect determination of tetrahydroborate (BH−4) by gas-diffusion flow injection analysis with amperometric detection

SummaryA method is described for the simultaneous speciation of Fe(CN)64−and Fe(CN)63−in a flow injection (FIA) system comprising electrochemical (EC) and flame atomic absorption spectrometry (AAS) detectors in series. One of these species is detected amperometrically at a Pt-electrode by applying the required potential and measuring the resulting reduction or oxidation current of the appropriate iron cyanide complex. Total iron in both species is determined by an AAS detector. The EC detector is inherently more sensitive, with a detection limit of 0.5 Μg Fe l−1 and a relative standard deviation of 1.0% for a 0.040 Μg Fe ml−1 sample. The limit of detection for the AAS detector is 0.5 Μg Fe ml−1, and the relative standard deviation for a 5.70 Μg Fe ml−1 sample is 0.40%. The method enables up to 60 analyses (120 speciations) per hour and obviates the problem of easy oxidation of Fe(CN)64−.

Iron-promoted intramolecular [4 + 2] Diels-Alder cycloadditions of 1-phenyl-3,4-dimethylphosphole with selected dienophiles

A rapid, indirect gas-diffusion flow injection analysis (FIA) method with amperometric detection has been developed for the selective and sensitive determination of tetrahydroborate (BH(-)(4)). The injected analyte reduces arsenic(III) to arsine. The arsine formed diffuses through the PTFE (polytetrafluoroethylene) membrane and is quantified amperometrically at a platinum working electrode. The precision of the technique was better than a relative standard deviation of 2.1% at 60 muM levels and better than 0.5% at 0.1 mM, with a throughput of 60 samples/hr. The detection limit of the method was found to be 1 muM (1.5 ng BH(-)(4)) with a linear range up to 1 mM. The dynamic range extends over five orders of magnitude in BH(-)(4) concentration. The effects of working potential, concentration of As(III) and HCl in the reagent stream, type and flow rate of the acceptor solution, temperature and interferents on the FIA signals were studied.