Papers by Author: S.K. Milonjić

Abstract: The adsorption of organic electrolytes from aqueous solutions on various adsorbents has been frequently investigated because of its importance in water purification. Phenol and substituted phenols are very common contaminants of water. In this paper, the adsorption results of some weak organic electrolytes (hydrochinon, phloroglucin and acidum gallicum) from aqueous solutions on silica are presented. The adsorption of the organics was investigated by the batch method. Effects of solution pHs (in the 2-10 range) and concentrations of these compounds on the adsorption were investigated. In the case of acidum gallicum, adsorption isotherms (in the 2-6 pH range) were determined. The obtained results indicate that the amount of adsorbed acidum gallicum increases with its increasing concentration. The maximum adsorption was recorded at pH=2-3 (pH equal to pHpzc of SiO2) with acidum gallicum molecule being undissociated (pKa= 4.41). The experimental data were fitted with different adsorption isotherms models. The maximum amount of acidum gallicum adsorbed as well as the Freundlich constants of adsorption were calculated. The adsorption of hydrochinon and phloroglucin from aqueous solutions (in the investigated pH range) on silica was negligible.

Abstract: The sorption of ferric and ferrous ions from aqueous solutions on the silica powder, obtained from colloidal dispersion of silica (silica sol), was studied as a function of their concentrations and solution pH. The amount of sorbed ferric and ferrous ions increases with increasing final pH of the solution. The sorption isotherms are of high-affinity type. A sorption mechanism of ferric and ferrous ions from aqueous solutions on silica is proposed.

Abstract: A synthetic procedure based on thermal hydrolysis of iron(III) chloride solutions for the preparation of hematite (α-Fe2O3) and ferricoxychloride (FeOCl) colloids consisting of nanoparticles (NPs) is described. Transmission electron microscopy indicated that both colloids consisted of particles smaller than 10 nm. X-ray diffraction measurements revealed transformation of FeOCl NPs into α-Fe2O3 NPs after a few months. The phase transformation was explained in terms of redissolution – recrystallization process. UV-vis spectroscopy was used for precise determination of the band gap of α-Fe2O3.

Abstract: It has been shown recently that small organic molecules, used as dispersants in the colloidal processing of ceramic powders to adjust the forces between the particles, are quite efficient in preparing aqueous suspensions of high solid loadings and low viscosity. One of them is 4,5-dihydroxy-1,3-benzenedisulfonic acid, disodium salt monohydrate, ((OH)2C6H2(SO3Na)2·H2O), commercially known as Tiron. The adsorption of Tiron, as a function of its concentration and solution pH, onto alumina was investigated by the solution depletion method, applying UV spectrophotometry. KNO3 (10-2 mol/l) was used as the background electrolyte. The obtained results indicate an increase in the amount of adsorbed Tiron with its increasing concentration. The maximum adsorption was recorded at pH≈7 when the Tiron molecule was uncharged, i.e. undissociated (pKa1=7.6). The experimental data were fitted with different adsorption isotherm models. The maximum amount of Tiron adsorbed, as well as the constants of adsorption process were calculated.

Abstract: The morphology and the capacitive properties of carbon supported hydrous ruthenium oxide (RuOxHy/C), prepared by impregnation of low-surface area carbon black VulcanÒ XC-72 R with solid phase of RuOxHy sol, were investigated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The oxide sols of different ageing times, prepared by forced hydrolysis of RuCl3, were used for composite preparation. The prepared composites show considerably higher capacitance values in acid electrolyte if compared to carbon black support. Microscopic investigations show that the extent of impregnation and the composite surface appearance depend on ageing time. The composite capacitance increases with ageing time of oxide sol. A gradual decrease in capacitance of thermally untreated composite with charging/discharging cycles was registered, which appears to be related to the extent of impregnation, too. Electrochemical impedance spectroscopy measurements indicate an in-depth capacitance distribution through the composite layer. It was found that NafionÒ layer, used to ensure the adhesion of the composite layer to the current collector, influenced the composite impedance behavior, especially on the oxide-rich parts of the composite surface.