Mykola T. Kartel

Evaluation of pectin binding of heavy metal ions in aqueous solutions

Evaluation of adsorption performance of several industrially manufactured pectins towards some toxic heavy metals was carried out. Adsorption isotherms for divalent cations in simulant aqueous solutions were measured and corresponding distribution coefficients were calculated. The following selectivity sequences we found for pectins: Pb2+ >> Cu2+ > Co2+ > Ni2+ >> Zn2+ > Cd2+. It was shown that a beet pectin exhibits a high affinity for Pb2+ and Cu2+ ions, an apple pectin for Co2+ ion and a citrus pectin for Ni2+ ion. The binding properties of all pectins towards Zn2+ and Cd2+ ions are extremely poor. The quantitative data on adsorption performance of pectins suggest their applicability as food additives or remedies for efficient removal of Pb2+, Cu2+, Co2+, and Ni2+ ions from different biological systems, including human and animal organisms.

Adsorption of anionic and cationic dyes by activated carbons, PVA hydrogels, and PVA/AC composite

The textural and adsorption characteristics of a series of activated carbons (ACs), porous poly(vinyl alcohol) (PVA) gels, and PVA/AC composites were studied using scanning electron microscopy, mercury porosimetry, adsorption of nitrogen (at 77.4 K), cationic methylene blue (MB), anionic methyl orange (MO), and Congo red (CR) from the aqueous solutions. Dye-PVA-AC-water interactions were modeled using the semiempirical quantum chemical method PM6. The percentage of dye removed (C(rem)) by the ACs was close to 100% at an equilibrium concentration (C(eq)) of less than 0.1 mM but decreased with increasing dye concentration. This decrease was stronger at C(eq) of less than 1 mM, and C(rem) was less than 50% at a C(eq) of 10-20 mM. For PVA and the PVA/AC composite containing C-7, the C(rem) values were minimal (<75%). The free energy distribution functions (f(ΔG)) for dye adsorption include one to three peaks in the -ΔG range of 1-60 kJ/mol, depending on the dye concentration range used and the spatial, charge symmetry of the hydrated dye ions and the structural characteristics of the adsorbents. The f(ΔG) shape is most complex for MO with the most asymmetrical geometry and charge distribution and adsorbed at concentrations over a large C(eq) range. For symmetrical CR ions, adsorbed over a narrow C(eq) range, the f(ΔG) plot includes mainly one narrow peak. MB has a minimal molecular size at a planar geometry (especially important for effective adsorption in slit-shaped pores) which explains its greater adsorptive capacity over that of MO or CR. Dye adsorption was greatest for ACs with the largest surface area but as molecular size increases adsorption depends to a greater extent on the pore size distribution in addition to total and nanopore surface areas and pore volume.

Morphological and chemical features of nano and macroscale carbons affecting hydrogen peroxide decomposition in aqueous media

Chemical and structural factors of carbon materials affect their activity in adsorption and surface reactions in aqueous media. Decomposition of hydrogen peroxide studied is a probe reaction for exploring parameters of carbons that might be involved, such as specific surface area, nitrogen and oxygen doping and conformational changes. To date, a detailed comparison of the behavior of carbon nanoscale (Carbon Nanotubes, CNT, Single Layer Graphene Oxide, SLGO) with macroscale (Activated carbons, AC) materials in this reaction has not been forthcoming. Herein, we demonstrate that on their first cycle, ACs in doped and undoped forms outperform all nanoscale carbons tested in the H(2)O(2) decomposition. Among the nanocarbons, nitrogen-doped CNT exhibited the highest activity in this reaction. However, subsequent recycling of each carbon, without chemical regeneration between uses, reveals SLGO exhibits greater reaction rate stability over an extended number of cycles (n>8) than other carbons including nitrogen-doped CNT and ACs. The effects of pH, temperature and concentration on the reaction were analyzed. Quantum-chemical modeling and reaction kinetics analysis reveal key processes likely involved in hydrogen peroxide decomposition and show evidence that the reaction rate is linked to active sites with N-and O-containing functionalities.

Catalytic performance of carbon nanotubes in H2O2 decomposition: Experimental and quantum chemical study

The catalytic performance of multi-walled carbon nanotubes (MWCNTs) with different surface chemistry was studied in the decomposition reaction of H2O2 at various values of pH and temperature. A comparative analysis of experimental and quantum chemical calculation results is given. It has been shown that both the lowest calculated activation energy (∼18.9 kJ/mol) and the highest rate constant correspond to the N-containing CNT. The calculated chemisorption energy values correlate with the operation stability of MWCNTs. Based on the proposed quantum chemical model it was found that the catalytic activity of carbon materials in electron transfer reactions is controlled by their electron donor capability.

Influence of the “wetting–drying” compaction on the adsorptive characteristics of nanosilica A-300

The methods of low-temperature 1H NMR and IR spectroscopy, densitometry, and adsorption from solutions are applied to study the influence of “wetting–drying” compaction on the adsorptive characteristics of the nanosilica A-300 in relation to water and gelatin. It was shown that if the bulk density changes from 0.05 to 0.25 g/ml, the protein adsorptive capacity of the nanosilica decreases no more than by 30%, which, apparently, is connected with the decrease of the part of the surface, available for the protein molecules. Interfacial energy in relation to water increases from 37 to 52 mJ/m2 if the bulk density increases and this is connected with the increase of the contribution from minor clusters (nanodrops) adsorbed on the surface water.

Kinetics of Valeric Acid Ketonization and Ketenization in Catalytic Pyrolysis on Nanosized SiO2, γ-Al2O3, CeO2/SiO2, Al2O3/SiO2 and TiO2/SiO2

Valeric acid is an important renewable platform chemical that can be produced efficiently from lignocellulosic biomass. Upgrading of valeric acid by catalytic pyrolysis has the potential to produce value added biofuels and chemicals on an industrial scale. Understanding the different mechanisms involved in the thermal transformations of valeric acid on the surface of nanometer-sized oxides is important for the development of efficient heterogeneously catalyzed pyrolytic conversion techniques. In this work, the thermal decomposition of valeric acid on the surface of nanoscale SiO2 , γ-Al2 O3 , CeO2 /SiO2 , Al2 O3 /SiO2 and TiO2 /SiO2 has been investigated by temperature-programmed desorption mass spectrometry (TPD MS). Fourier transform infrared spectroscopy (FTIR) has also been used to investigate the structure of valeric acid complexes on the oxide surfaces. Two main products of pyrolytic conversion were observed to be formed depending on the nano-catalyst used-dibutylketone and propylketene. Mechanisms of ketene and ketone formation from chemisorbed fragments of valeric acid are proposed and the kinetic parameters of the corresponding reactions were calculated. It was found that the activation energy of ketenization decreases in the order SiO2 >γ-Al2 O3 >TiO2 /SiO2 >Al2 O3 /SiO2 , and the activation energy of ketonization decreases in the order γ-Al2 O3 >CeO2 /SiO2 . Nano-oxide CeO2 /SiO2 was found to selectively catalyze the ketonization reaction.

Factors Determining the Catalytic Activity of Multi-walled Carbon Nanotubes in the Decomposition of Diacyl Peroxides in Non-aqueous Media (DPDec)

The catalytic activity of multi-walled carbon nanotubes (CNT) with different surface chemistry was investigated in the decomposition of benzoyl and lauroyl peroxides (BP and LP respectively) at room temperature in non-aqueous media. Calculated diffusion coefficients (Deff) indicate that catalysis is not limited by internal diffusion. CNT demonstrate a moderate catalytic activity that ordering in the raw: N-CNT > CNTini > CNTox. Surface chemistry analysis displays the dependence of catalytic ability of CNT on their surface electron donor properties. Operation stability experiments and TPD–MS analysis reveal that reactions proceeding via the single electron transfer (SET) mechanism.Graphical Abstract

Water Interactions with Hydrophobic versus Hydrophilic Nanosilica

It is well-known that interaction of hydrophobic powders with water is weak, and upon mixing, they typically form separated phases. Preparation of hydrophobic nanosilica AM1 with a relatively large content of bound water with no formation of separated phases was the aim of this study. Unmodified nanosilica A-300 and initial AM1 (A-300 completely hydrophobized by dimethyldichlorosilane), compacted A-300 (cA-300), and compacted AM1 (cAM1) containing 50-58 wt % of bound water were studied using low-temperature 1H NMR spectroscopy, thermogravimetry, infrared spectroscopy, microscopy, small-angle X-ray scattering, nitrogen adsorption, and theoretical modeling. After mechanical activation (∼20 atm) upon stirring of AM1/water mixture at the degree of hydration h = 1.0 or 1.4 g of distilled water per gram of dry silica, all water is bound and the blend has the bulk density of 0.7 g/cm3. The temperature and interfacial behaviors of bound water depend strongly on a dispersion media type (air, chloroform, and chloroform with trifluoroacetic acid (4:1)) because the boundary area between immiscible water and chloroform should be minimal. Water and chloroform molecules are of different sizes affecting their distribution in pores (voids between silica nanoparticles in their aggregates) of different sizes. Structural, morphological, and textural characteristics of silicas, and environmental features affect not only the distribution of bound water, but also the amounts of strongly (frozen at T < 260 K) and weakly (frozen at 260 K < T < 273 K) bound and strongly (chemical shift δH = 4-6 ppm) and weakly (δH = 1-2 ppm) associated waters. Despite the changes in the characteristics of cAM1, it demonstrates a flotation effect. The developed system with cAM1/bound water could be of interest from a practical point of view due to controlled interactions with aqueous surroundings.

FERROCYANIDE BIOSORBENTS BASED ON LIGNOCELLULOSE WASTE PRODUCTS FOR MULTIFUNCTIONAL PURPOSE

New composite biosorbents based on lignocellulose complex, derived from the waste of food industry – apricot pits, and ferrocyanides of d-metals were synthesized. An influence of pretreatment of initial apricot pits by acid-alkali scheme was established. It was found out that such pretreatment leads to an increase in the specific surface area of the lignocellulose material in two times and the total pore volume up to six times. The physical, chemical, structural properties of the obtained materials were investigated. The sorption behavior of initial materials and lignocellulose-inorganic samples toward cesium-137, heavy metals, Methylene blue, gelatin, vitamin B12 was studied. Comparative analysis of the sorption properties of obtained biosorbents based on different ferrocyanides towards different ecotoxicants was carried out. Obtained results allow to state that new composite biosorbents are universal materials for adsorption of radionuclides, heavy metals and organic pollutants from water solutions and can be used in radiochemistry, analytical chemistry, industry, medicine and veterinary.