Biljana Babić

Point of zero charge and intrinsic equilibrium constants of activated carbon cloth

Surface properties of cellulose-based activated carbon cloth were investigated. The point of zero charge was determined by batch equilibrium method. Surface charge densities were obtained from potentiometric titrations. The site-binding model was applied to calculate the intrinsic acidity constants.

Adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth

The adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth was studied as a function of their concentrations and solution pH. For that purpose, pertinent adsorption isotherm data was collected at different pH values. The amount of adsorbed zinc and cadmium ions increases while the amount of adsorbed mercury remains constant with an increase in the equilibrium pH of the solution. The adsorption mechanisms of metal ions on activated carbon cloth are discussed. Under the conditions investigated, these primarily involve adsorption of monovalent cations (Zn and Cd) or precipitation of metal hydroxides (Cd and Hg) on the activated carbon cloth tested.

Nanocrystalline CeO2-δ as effective adsorbent of azo dyes.

Ultrafine CeO2-δ nanopowder, prepared by a simple and cost-effective self-propagating room temperature synthesis method (SPRT), showed high adsorption capability for removal of different azo dyes. Batch type of adsorption experiments with fixed initial pH value were conducted for the removal of Reactive Orange 16 (RO16), Methyl Orange (MO), and Mordant Blue 9 (MB9). The equilibrium adsorption data were evaluated using Freundlich and Langmuir isotherm models. The Langmuir model slightly better describes isotherm data for RO16 and MO, whereas the Freundlich model was found to best fit the isotherm data for MB9 over the whole concentration range. The maximum adsorption capacities, determined from isotherm data for MO, MB9, and RO16 were 113, 101, and 91 mg g(-1) respectively. The adsorption process follows the pseudo-second-order kinetic model indicating the coexistence of chemisorption and physisorption. The mechanism of azo dye adsorption is also discussed.

Comparison of structural, textural and thermal characteristics of pure and acid treated bentonites from Aleksinac and Petrovac (Serbia)

Bentonite samples collected from vicinity of Petrovac and Aleksinac were treated with different sulfuric acid molarities. Acid attack dissolved the octahedral sheets by interlayer and edge attack. The effects of the H(2)SO(4) acid caused an exchange of Al(3+), Fe(3+) and Mg(2+) with H(+) ions leading to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheets promoted the dispersion of corresponding layers and formation of amorphous silicon. The activated bentonites, after the treatment of sulfuric acid, exhibited a lower cation-exchange capacity (CEC) and significant increase of specific surface area from 6 to 387 m(2) g(-1) (bentonite from Petrovac) and from 11 to 306 m(2) g(-1) (bentonite from Aleksinac). The acid reaction caused a splitting of particles within the octahedral sheet which led to an increase in specific surface area and decrease in CEC in both bentonites.

Adsorption of malathion on mesoporous monetite obtained by mechanochemical treatment of brushite

Mesoporous monetite (CaHPO4), obtained by mechanochemical treatment of previously synthesized brushite (CaHPO4·2H2O), was used as efficient adsorbent for the organic pesticide malathion. The structure of brushite was confirmed by Raman spectroscopy. The phase transformation process was investigated by X-ray powder diffraction (XRD) and Fourier transformation infra-red spectroscopy (FTIR). The microstructure and morphology were determined by scanning electron microscopy (SEM) and the nitrogen adsorption–desorption method. It was found that five minutes of milling induces brushite–monetite phase transformation. Adsorption of malathion from aqueous solutions showed that this pesticide can be successfully adsorbed on surface of this material.

Pt nanoparticles on tin oxide based support as a beneficial catalyst for oxygen reduction in alkaline solutions

A platinum nanocatalyst on Sb doped tin oxide support (Sb–SnO2) was synthesized and characterized as a catalyst for oxygen reduction reaction in 0.1 mol dm−3 NaOH solution at 25 °C. Sb (5%) doped tin oxide support was synthesized by a modified hydrazine reduction procedure. The platinum nanocatalyst (20% Pt) on Sb–SnO2 support was synthesized by a borohydride reduction method. The synthesized support and catalyst were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) and X-ray diffraction technique (XRD). X-ray photoelectron spectroscopy was applied to characterize the chemical status of elements before and after Pt-treatment. XPS spectra of Sn 3d, Pt 4f, Sb 3d and O 1s revealed that the Pt-deposition on Sb–SnO2 support induced the reduction of the Sn(4+) oxidation state to Sn(2+) and Sn(0) states, while Pt remained in the metallic state and Sb was in the (3+) oxidation state. Homogenous Pt nanoparticle distribution over the support, without pronounced particle agglomeration, was confirmed by HRTEM technique. The average Pt particle size was 2.9 nm. The electrochemically active Pt surface area of the catalyst was determined by the integration of the cyclic voltammetry curve in the potential region of underpotential deposition of hydrogen, after double layer charge correction, taking into account the reference value of 210 μC cm−2 for full monolayer coverage. This calculation gave the value of 51 m2 g−1. The kinetics of the oxygen reduction reaction with Pt/Sb–SnO2 catalyst was studied by cyclic voltammetry and linear sweep voltammetry using a rotating gold disc electrode. Two different Tafel slopes were observed: one close to 60 mV dec−1 in the low current density region, and another at ∼120 mV dec−1 in the higher current densities region, as was already referred in previous reports for the oxygen reduction reaction with polycrystalline Pt, as well as with different Pt based nanocatalysts. The specific activities for oxygen reduction, expressed in terms of kinetic current densities per electrochemically Pt active surface area, as well as per mass of Pt loaded, at the constant potential of practical interest (0.85 V and 0.90 V vs. RHE), were compared to a carbon supported (Vulcan XC-72) catalyst. The Pt/Sb–SnO2 catalyst exhibited similar catalytic activity for oxygen reduction reaction like carbon supported one. The advantages of the carbon free support application in terms of the durability and stability of the catalysts were proved by accelerated stability tests.

Preparation of Porous Silica Ceramics Using the Wood Template

Porous silica (SiO2) ceramic with a wood-like structure was prepared by wet impregnation tetraethyl orthosilicate (TEOS) into biological template that was derived from linden wood (tilia amurensis). After repeated pressure impregnation the subsequent annealing in air atmosphere at 800°C resulted in burn out of the template and consolidation of the oxide layers. The products exhibit structures corresponding to negative replication of biological templates. X-ray diffraction (XRD), scanning electron microscopy (SEM), infra red (IR), and Brunauer Emmett Teller (BET) measurements were employed to characterize the phases and crystal structure of biomorphic ceramics. It was found that the bio-organic structure was converted into oxide ceramics (SiO2). At low temperature (800°C), pore radius varied between 2 and 10 nm indicating that the samples were mostly mesoporous. Samples treated at higher temperature (1300°C) lost the mesoporous character; however, they were still porous having the microstructural features of the biological perform.

Characterization of Carbon Cryogel Synthesized by Sol-Gel Polycondensation and Freeze-Drying

Resorcinol-formaldehyde (RF) cryogels were synthesized by sol-gel polycondensation of resorcinol with formaldehyde and freeze-drying carried out with t-butanol. Carbon cryogels were obtained by pyrolyzing RF cryogels in an inert atmosphere. Characterization by nitrogen adsorption showed that carbon cryogels were micro- and mesoporous materials with high surface areas (500 m2/g< SBET <700 m2/g). Cyclic voltammetry experiments at various scan rates (2 to 200 mV s-1) were carried out to study the electrical double-layer charging of carbon cryogel electrodes in 0.5 mol dm-3 HClO4 solution. It has been demonstrated that the total specific capacitance can further be divided into mesoporous and microporous specific capacitance by analyzing the linear dependence of the specific capacitance (C) on the reciprocal of the square root of the potential scan rate ( ν -1/2), as well as linear dependence of the reciprocal specific charge (1/C) on the square root of the potential scan rate ( ν 1/2).

REMOVAL OF HEAVY METALS FROM AQUEOUS SOLUTION USING NATURAL AND Fe(III) OXYHYDROXIDE CLINOPTILOLITE

The increasing levels of industrial wastewater released to the environment present a serious threat to human health, living resources, and ecological systems. Fe-modified zeolites were developed and tested for removal of Cu2+ and Zn2+ from contaminated water. The surfaces of the naturally occurring zeolite, clinoptilolite, were modified with Fe(III) oxyhydroxides using three different methods, denoted I, II, and III (FeCli1, FeCli2, and FeNaCli1, respectively). The oxyhydroxides were prepared in Method I using 0.1 M FeCl3·6H2O in an acetate buffer (pH = 3.6); in Method II, using 10ai] FeCl3·6H2O solution in 0.1 M KOH (pH = 10); and Method III was the same as Method I except the clinoptilolite was pretreated with NaCl. Newly synthesized materials from these three methods were then tested for their ability to enhance the sorption capacity for Cu and Zn compared to the natural sample (Cli). Powder X-ray diffraction measurements and the chemical composition of these modified samples confirmed that clinoptilolite maintained its structure while amorphous Fe3+ species were synthesized. The specific surface area (BET method) of both the natural and modified clinoptilolite increased by 2 and 7.5 times for Methods I and II, respectively. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed that CaO was formed during Method I (FeClii). Throughout the adsorption process, the hydrolysis of CaO and the release of OH− caused the precipitation of Cu and Zn hydroxide, which made the determination of the sorption capacity of FeClii impossible. This phenomenon was avoided in Method III (FeNaClii) because of the absence of exchangeable Ca2+. The adsorption experiments with Method II resulted in double-enchanced adsoprtion capacity. Laboratory batch experiments revealed that the sorption capacities increased in the following order: Cli < FeCli2 < FeNaCli1, for Cu: 0.121 mmol/g < 0.251 mmol/g < 0.403 mmol/g and for Zn: 0.128 mmol/g < 0.234 mmol/g < 0.381 mmol/g.

Heteroatom-doped mesoporous carbons as efficient adsorbents for removal of dimethoate and omethoate from water

Extensive use of organophosphate pesticides (OPs) invokes development of efficient procedures for their removal from the environment. By introducing low levels (<1 at%) of B, N or P into the structure of mesoporous carbons, we have produced a series of materials with different surface chemical composition, textural properties and level of structural disorder. These adsorbents were applied for removal of dimethoate and its oxo-analogue omethoate from aqueous solutions under batch adsorption conditions and by filtration using modified nylon membrane filters. Adsorption capacities up to 164 mg g−1 were measured, with OPs uptake typically above 80% for dimethoate concentration as high as 5 × 10−3 mol dm−3. After the adsorption, neurotoxic effects of OP-containing water samples were significantly reduced or completely removed. The level of structural disorder was identified as a key parameter for efficient removal of dimethoate and omethoate while in the filtration experiments surface area of adsorbents also played an important role. While the presented research appeals to new fundamental studies of OP–carbon surface interactions, it also indicates a possible strategy in designing new efficient adsorbents for OPs removal from water.