Sinteza i karakterizacija platinskih legura za anodne reakcije u gorivim spregovima

Pronalazak novih materijala koji mogu da reše probleme u oblasti proizvodnje, konverzije i skladištenja energije sa ciljem da se izbegne korišćenje fosilnog goriva kao jednog od velikih zagađivača prirode je najveći izazov današnjice. Dobra altenativa fosilnom gorivu su gorive ćelije jer imaju visoku energetsku efikasnost a malu štetnost za okolinu. Iako su u dosadašnjim istraživanima najbolju efikasnost pokazale gorive ćelije sa vodonikom kao gorivom, skladištenje, rukovanje i distribucija vodonika je još uvek velika barijera za njihovu rasprostranjeniju primenu. Korišćenje tečnih goriva kao što su metanol, etanol ili mravlja kiselina može da bude dobra zamena vodoniku. Platina je odličan katalizator za dehidrogenaciju malih organskih molekula, ali sa druge strane ima nekoliko značajnih nedostataka: visoku cenu i veoma veliku osetljivost na trovanje ugljen monoksidom kao ometajućim produktom tokom oksidacije ovih organskih molekula. Napori da se poboljšaju katalitičke sposobnosti i smanji količina platine u katalizatorima su usmereni ka dodatku metala kao što su kalaj ili rodijum. Takođe, elektrokatalitička sposobnost platinskih katalizatora ne zavisi samo od prirode dodatog metala već i od mnogobrojnih uslova tokom sinteze. Predmet ove doktorske disertacije bio je da se ispita uticaj uvođenja kalaja i/ili rodijuma kod platinskih katalizatora na reakcije oksidacije etanola, ugljen monoksida i mravlje kiseline. U tu svrhu su korišćenjem mikrotalasnog modifikovanog poliol postupka sintetizovani su Pt/C, PtSn/C, Pt3Sn/C, PtRh/C i PtRhSn/C nanokatalizatori. Katalizatori su okarakterisani termogravimetrijskom analizom (TGA), rendgenostrukturnom analizom (XRD), skenirajućom tunelirajućom mikroskopijom (STM), transmisionom elektronskom mikroskopijom (TEM), energetskom disperzionom atomskom analizom (EDX) i metodom ciklične voltametrije. STM analiza koloidnog katalizatora bez ugljenične podloge je pokazala malu veličinu čestica za sve sintetizovane katalizatore (diametar oko 2 nm) sa uskom distribucijom čestica po veličini. Dobre karakteristike sintetizovanih katalizatora se mogu pripisati prednostima korišćenja mikrotalasne sinteze i modifikovanog poliol postupka. Brzim i uniformnim mikrotalasnim zagrevanjem smanjena je potreba za dugim zagrevanjem na visokim temperaturama, izbegnuti su temperaturski gradijenti i tako ubrzana redukcija metala, postignuta je homogena nukleacija i kraće vreme kristalizacije što je dovelo do formiranja malih metalnih čestica sa ujednačenom veličinom. TEM i XRD ispitivanja katalizatora sa ugljeničnom podlogom su pokazala povećanje veličine čestica nakon nanošenja na podlogu od ugljenika (prosečna veličina čestice je oko 3 nm). XRD analiza je pokazala da PtSn/C i...The development of new materials that can solve challenging problems in the areas of clean energy production, conversion and storage is topmost importance in the ques to find an altenative to enviromenttally unfriendly fossil-fuel use. Fuel cells are a valuable option since they have high energy efficiency and low pollutant emission. Although the best performance, so far, has been achieved using hydrogen as fuel, its storage, handling, and distribution appear to be important barriers for widespread application. Direct use of liquid fuels, such as methanol, ethanol and formic acid can be a convenient alternative. Pt is an excellent catalyst for dehydrogenation of small organic molecules but, on the other hand, has several significant drawbacks: high cost, extreme susceptibility to poisoning by CO and in the case of ethanol the main products of its oxidation are acetaldehyde and acetic acid, while CO2 is produced at high potentials. Efforts to improve catalyst performance and minimize quantity of Pt in the catalyst have been centered on the addition of metals such as Sn and Rh. In general, electrocatalytic performance of the Pt-based catalysts considerably depends not only on the nature of the added metal, but also on a variety of conditions of the synthesis procedures which determine surface composition and morphology of synthesized materials. In this work, carbon supported nanoparticles Pt/C, PtSn/C, Pt3Sn/C, PtRh/C and PtRhSn/C catalysts, synthesized by microwave assisted polyol method, were examined for ethanol oxidation in perchloric acid. The catalysts were characterized by thermogravimetric analysis (TGA), X-ray difraction (XRD), scsnning tunnelling microscopy (STM), TEM, EDX and cyclic voltammetry techinques. STM analysis of unsupported catalysts shows that the particles are small (diameter is ~ 2 nm) with a narrow size distribution, as a result of using polyol method with microwave heating. The fast and uniform microwave heating, reduces the temperature and concentration gradients thus accelerates the reduction of the metal ions and enables homogeneous nucleation and shorter crystallization time leading to formation of small uniform metal particles. TEM and XRD examinations of supported catalysts revealed an increase in particle size upon deposition on carbon support (diameter ~ 3 nm). XRD analysis shows that PtSn/C and Pt3Sn/C catalysts have low alloying degree and is composed of Pt and Pt3Sn phase. The rest of Sn is present in a form of very small tin oxide particles connected to Pt particles. XRD patterns of the PtRhSn/C catalyst are all broadened and diffraction peaks for Pt, Rh or Sn cannot be resolved separately, indicating a very small crystallinity. Oxidation of ethanol is significntly improved at Pt-Sn/C catalysts with the onset potential shifted for..

Nucleation and early stages of growth of lead onto copper electrodes from dilute electrolytes

The processes of nucleation and growth of lead from the dilute electrolytes on copper substrates were investigated by chronoamperometry and by scanning electron microscopic (SEM) analysis of the deposits obtained in the potentiostatic regime of electrolysis. In the dependence of electrodeposition conditions, the nucleation of Pb followed either progressive or instantaneous type. The type of nucleation changed from progressive to instantaneous one with increasing the concentration of Pb(II) ions and the overpotential of electrodeposition. Regardless of the type nucleation, a novel type of Pb particles like cobweb was formed by the potentiostatic electrodeposition in the moment of nucleation and at the early stages of growth. On the basis of the shape of cobweb-like particles and the electrodeposition conditions leading to their formation, these particles were situated in the group of spongy-like ones. Also, comparative morphological analysis of Pb deposits obtained in the conditions of progressive and instantaneous nucleation confirmed the existence of two limiting types of nucleation

Relationship between the kinetic parameters and morphology of electrochemically deposited lead

The processes of lead electrodeposition from electrolytes of various concentrations of sodium nitrate as the supporting electrolyte have been examined by chronoamperometry and by the scanning electron microscopic (SEM) analysis of deposits obtained in the potentiostatic regime of electrolysis. The good agreement between the diffusion coefficents determined by Cottrell equation and non-linear fitting method was observed. For the first time, the transition from the mixed ohmic-diffusion to the full diffusion control was defined from the analysis of Cottrell equation. The parameters, such as the number density of active sites and the nucleation rate constant, obtained by non-linear fitting method were discussed in accordance with the fact that lead belongs to the group of metals characterized by the high values of the exchange current density. The data obtained by the chronoamperometric analysis were succesfully correlated with morphologies of electrodeposited lead obtained in the different types of electrodeposition control. [Projekat Ministarstva nauke Republike Srbije, br. 172046

Voltammetric and Square-Wave Anodic Stripping Determination of Amlodipine Besylate on Gold Electrode

The oxidative behaviour of amlodipine besylate was studied. The gold electrode and Au/o-MWCNT (oxidized multi-wall carbon nanotubes) were used for determination of amlodipine besylate standard and as a content of Alopres tablet, in 0.05 M NaHCO3 and in phosphate buffer (pH=11) by cyclic voltammetry and square-wave anodic stripping voltammetry. Electrode surfaces were characterized by AFM in the presence of amlodipine and the concentrations of drugs in electrolytes were simultaneously followed by HPLC. The linear dependency of the anodic currents of amlodipine besylate as standard and in Alopres tablet vs. concentration was observed in both electrolytes, but in phosphate buffer for the higher concentrations. The peak currents obtained in all experiments are more than fifty-fold higher comparing to all previously published results concerning the glassy carbon electrode and the carbon paste electrode. The gold electrode is better catalyst for anodic oxidation of amlodipine besylate than glassy carbone. The results obtained with Au/o-MWCNT show lower anodic activity comparing to previously published GC/o-MWCNT. GC/o-MWCNT is better catalyst than Au/o-MWCNT under similar experimental conditions

Original scientific paper doi: 10.2298/JSC0812211P Photoelectrochemical properties of sol–gel obtained titanium oxide

Abstract: The photoelectrochemical properties of a sol–gel prepared titanium oxide coating applied onto a Ti substrate were investigated. The oxide coating was formed from an inorganic sol thermally treated in air at 350 °C. The coating consisted of agglomerates of narrow size distribution around 100 nm. The photoelectrochemical characteristics were evaluated by investigating the changes in the open circuit potential, current transients and impedance characteristics of a Ti/TiO 2 electrode upon illumination by UV light in H 2SO 4 solution and in the oxidation of benzyl alcohol. The electrode was found to be active for photoelectrochemical reactions in the investigated solutions

Copper(II) and zinc(II) complexes with the clinically used fluconazole

Copper(II) and zinc(II) complexes with clinically used antifungal drug fluconazole (fcz), {[CuCl$_2$(fcz)$_2$]·5H$_2$O}$_n$, 1, and {[ZnCl$_2$(fcz)$_2$]·2C$_2$H$_5$OH}$_n$, 2, were prepared and characterized by spectroscopic and crystallographic methods. The polymeric structure of the complexes comprises four fluconazole molecules monodentately coordinated via the triazole nitrogen and two chlorido ligands. With respect to fluconazole, complex 2 showed significantly higher antifungal activity against Candida krusei and Candida parapsilosis. All tested compounds reduced the total amount of ergosterol at subinhibitory concentrations, indicating that the mode of activity of fluconazole was retained within the complexes, which was corroborated via molecular docking with cytochrome P450 sterol 14α-demethylase (CYP51) as a target. Electrostatic, steric and internal energy interactions between the complexes and enzyme showed that 2 has higher binding potency to this target. Both complexes showed strong inhibition of C. albicans filamentation and biofilm formation at subinhibitory concentrations, with 2 being able to reduce the adherence of C. albicans to A549 cells in vitro. Complex 2 was able to reduce pyocyanin production in Pseudomonas aeruginosa between 10% and 25% and to inhibit its biofilm formation by 20% in comparison to the untreated control. These results suggest that complex 2 may be further examined in the mixed Candida-P. aeruginosa infections

Clinically used antifungal azoles as ligands for gold(III) complexes

In a search for novel antimicrobial metal-based therapeutic agents, mononuclear gold(III) complexes 1–7 of the general formula [AuCl$_3$(azole)], where azole stands for imidazole (im, 1), 1-isopropylimidazole (ipim, 2), 1-phenylimidazole (phim, 3), clotrimazole (ctz, 4), econazole (ecz, 5), tioconazole (tcz, 6) and voriconazole (vcz, 7) were synthesized, characterized and biologically evaluated. In all complexes, the corresponding azole ligand is monodentately coordinated to the Au(III) via the imidazole or triazole nitrogen atom, while the remaining coordination sites are occupied by chloride anions leading to the square-planar arrangement. In vitro antimicrobial assays showed that the complexation of inactive azoles, imidazole, 1-isopropylimidazole and 1-phenylimidazole, to the Au(III) ion led to complexes 1–3, respectively, with moderate activity against the investigated strains and low cytotoxicity on the human normal lung fibroblast cell line (MRC-5). Moreover, gold(III) complexes 4–7 with clinically used antifungal agents clotrimazole, econazole, tioconazole and voriconazole, respectively, have, in most cases, enhanced antimicrobial effectiveness relative to the corresponding azoles, with the best improvement achieved after complexation of tioconazole (6) and voriconazole (7). The complexes 4–7 and the corresponding antifungal azoles inhibited the growth of dermatophyte Microsporum canis at 50 and 25 μg mL$^{−1}$. Gold(III) complexes 1–3 significantly reduced the amount of ergosterol in the cell membrane of Candida albicans at the subinhibitory concentration of 0.5 × MIC (minimal inhibitory concentration), while the corresponding imidazole ligands did not significantly affect the ergosterol content, indicating that the mechanism of action of the gold(III)–azole complexes is associated with inhibition of ergosterol biosynthesis. Finally, complexes 5 and 6 significantly reduced the production of pyocyanin, a virulence factor in Pseudomonas aeruginosa controlled by quorum sensing, and increased cell survival after exposure to this bacterium. These findings could be of importance for the development of novel gold(III)-based antivirulence therapeutic agents that attenuate virulence without pronounced effect on the growth of the pathogens, offering a lower risk for resistance development

Polynuclear Silver(I) Complex with Thianthrene: Structural Characterization, Antimicrobial Activity and Interaction with Biomolecules

New silver(I) complex with thianthrene (tia), [Ag(NO3)(tia)(H2O)]n, was synthesized by the reaction of AgNO3 with an equimolar amount of tia in ethanol/dichloromethane (v/v 1:1) at room temperature, and characterized by NMR, IR and UV-Vis spectroscopy and single-crystal X-ray diffraction analysis. The antimicrobial activity of the synthesized complex was evaluated against the broad panel of Gram-positive and Gram-negative bacteria and Candida spp. This complex showed significant activity toward important human pathogens Gram-positive Staphylococcus aureus and Candida parapsilosis with minimal inhibitory concentrations (MICs) being 3.91 µg/mL. The interaction of [Ag(NO3)(tia)(H2O)]n with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) was studied to evaluate the binding affinity towards these biomolecules for possible insights on the mode of antimicrobial activity. The binding affinity of the investigated complex to BSA is higher than that for DNA, indicating that proteins could be more favorable binding sites for this complex in comparison to the nucleic acids