Marija Vukčević

Biosorption of heavy metal ions from aqueous solutions by short hemp fibers: Effect of chemical composition

Sorption potential of waste short hemp fibers for Pb(2+), Cd(2+) and Zn(2+) ions from aqueous media was explored. In order to assess the influence of hemp fiber chemical composition on their heavy metals sorption potential, lignin and hemicelluloses were removed selectively by chemical modification. The degree of fiber swelling and water retention value were determined in order to evaluate the change in accessibility of the cell wall components to aqueous solutions due to the fiber modification. The effects of initial ion concentration, contact time and cosorption were studied in batch sorption experiments. The obtained results show that when the content of either lignin or hemicelluloses is progressively reduced by chemical treatment, the sorption properties of hemp fibers are improved. Short hemp fibers are capable of sorbing metal ions (Pb(2+), Cd(2+) and Zn(2+)) from single as well as from ternary metal ion solutions. The maximum total uptake capacities for Pb(2+), Cd(2+) and Zn(2+) ions from single solutions are the same, i.e. 0.078mmol/g, and from ternary mixture 0.074, 0.035 and 0.035mmol/g, respectively.

Surface characteristics and antibacterial activity of a silver-doped carbon monolith

Abstract A carbon monolith with a silver coating was prepared and its antimicrobial behaviour in a flow system was examined. The functional groups on the surface of the carbon monolith were determined by temperature-programmed desorption and Boehms method, and the point of zero charge was determined by mass titration. The specific surface area was examined by N2 adsorption using the Brunauer, Emmett and Teller (BET) method. As a test for the surface activity, the deposition of silver from an aqueous solution of a silver salt was used. The morphology and structure of the silver coatings were characterized by scanning electron microscopy and x-ray diffraction. The resistance to the attrition of the silver deposited on the carbon monolith was tested. The antimicrobial activity of the carbon monolith with a silver coating was determined using standard microbiological methods. Carbon monolith samples with a silver coating showed good antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans, and are therefore suitable for water purification, particularly as personal disposable water filters with a limited capacity.

Influence of chemically modified short hemp fiber structure on biosorption process of Zn2+ ions from waste water

Short hemp fibers, acquired as a waste from textile industry, were used as an efficient biosorbent for removal of zinc ions from polluted water. In order to obtain the material with better sorption properties, short hemp fibers were subjected to oxidative and alkali treatment. The following factors that may influence the sorption properties of short hemp fibers were examined: fiber structure and morphology were characterized by iodine sorption, water retention and scanning electron microscopy, while specific surface area was determined by BET method. Additionally, the amount of carboxyl groups was determined by calcium-acetate method, and the point of zero charge of the short hemp fibers samples was determined by the solid addition method. Biosorption of zinc ions was evaluated through the total uptake capacity, equilibrium and kinetic data. Obtained data were analyzed by nonlinear Langmuir and Freundlich isotherms, as well as pseudo-first and pseudo-second order kinetic models, and the best fitting model was chosen using Akaike information criterion. Chemical modification, used in this work, leads to structural and morphological changes of short hemp fibers, and improvement of their sorption properties. It was found that sorption properties of short hemp fibers are predominantly influenced by surface acidity and the amount of functional groups, while fiber structure and specific surface area have a secondary role in the biosorption of zinc ions. Akakike information criterion values showed that biosorption of zinc ions on all tested hemp fiber samples obey the pseudo-second order adsorption kinetics, while experimental isotherm data fit better with Langmuir model. Biosorption of zinc ions on the hemp fibers is a predominantly chemical process, which mainly follows the mechanism of ion exchange on acidic functional groups, and occurs through the fast surface adsorption, intraparticle diffusion and final equilibrium stage.

Photocatalytic Performance of Carbon Monolith/TiO2 Composite

The new and simple approach for deposition of catalytically active TiO2 coating on carbon monolith (CM) carrier was presented. CM photocatalysts were impregnated with TiO2 using titanium solution and thermal treatment, and their photocatalytic activity was investigated in the process of methylene blue (MB) photodegradation. For the purpose of comparison, CM composite photocatalysts were prepared by dip-coating method, which implies binder usage. The presence of TiO2 on CM carrier was confirmed by Raman spectroscopy and scanning electron microscopy. The sorption characteristics of CM and the role of adsorption in the overall process of MB removal were evaluated through amount of surface oxygen groups obtained by temperature-programmed desorption and specific surface area determined by BET method. CM has shown good adsorption properties toward MB due to high amount of surface oxygen groups and relatively high specific surface area. It was concluded that photocatalytic activity increases with CM disc thickness due to increase of MB adsorption and amount of deposited TiO2. Good photocatalytic activity achieved for samples obtained by thermal treatment is the result of better accessibility of MB solution to the TiO2 particles induced by binder absence.

Influence of hemicelluloses and lignin content on structure and sorption properties of flax fibers (Linum usitatissimum L.)

In this work, alkali and oxidative treatments were employed to obtain flax fibers with different content of hemicelluloses and lignin, in order to study the influence of chemical composition on structure and sorption properties of flax fibers. The flax fibers were characterized using FTIR spectroscopy and FESEM microscopy, and by determination of chemical composition, carboxyl group content, electrokinetic and sorption properties. Adsorption of silver ions was used to evaluate flax fiber sorption properties, but also to obtain antimicrobial fibers whose antimicrobial activity was tested against Gram-negative bacteria Escherichia coli, Gram-positive bacteria Staphylococcus aureus and fungi Candida albicans. The progressive removal of hemicelluloses or lignin influenced the sorption properties through the increased liberation of elementary fibers and accessibility of functional surface groups of flax fibers. Removal of hemicelluloses led to increase of iodine sorption without significant change in functional groups content and electrokinetic properties. On the other hand, lignin removal led to an increase of functional groups content, namely carboxyl groups, which in turn influenced better moisture and silver ions sorption. Flax fibers with incorporated silver exhibit fair antimicrobial activity against Gram (−) E. coli, Gram (+) S. aureus and fungi C. albicans.