Yuriy L. Zub

Removal of Pb(II) ions from aqueous systems using thiol-functionalized cobalt-ferrite magnetic nanoparticles

We have investigated the removal of Pb2+ ions from water using thiol-functionalized, cobalt-ferrite, magnetic nanoparticles. These magnetic nanoparticles were prepared using the co-precipitation method and their surfaces were modified with tetraethoxy silane and 3-mercaptopropyl trimethoxysilane in order to provide a sufficient surface concentration of the thiol (–SH) functional groups. The adsorption of the Pb2+ ions from the aqueous solutions onto the thiol-functionalized, cobalt-ferrite, magnetic nanoparticles was studied. The investigated parameters include the pH value of the model water, the concentration of the adsorbent, the contact time and the temperature of adsorption. The removal of the Pb2+ was found to be greater at the higher pH values and increasing the temperature was also found to increase the removal of Pb2+ ions.

Immobilization of urease on magnetic nanoparticles coated by polysiloxane layers bearing thiol- or thiol- and alkyl-functions

Magnetically retrievable formulations of urease potentially promising for biomedical and environmental applications were constructed by immobilization of the enzyme on the surface of magnetite nanoparticles functionalized by siloxane layers with active thiol or thiol-and-alkyl moieties. The latter were deposited using a hydrolytic polycondensation reaction of tetraethoxysilane with either 3-mercaptopropyltrimethoxysilane, or with 3-mercaptopropyltrimethoxysilane and methyltriethoxysilane, or alternatively n-propyltriethoxysilane. Immobilization of urease was carried out in different ways for comparison: by adsorption, by entrapment during the hydrolytic polycondensation reaction, or by covalent bonding. For entrapment the enzyme was introduced into solution before functionalization of the magnetite. Entrapment bound high amounts of enzyme (more than 700 mg per g of carrier), but its activity was decreased compared to the native form to between 18 and 10%. In the case of covalent binding of urease using Ellmans Reagent, binding of the enzyme was almost as efficient as in the case of entrapment but its residual activity was 75%. The residual activity of urease immobilized by adsorption on the surface of thiol-functionalized particles was truly high as compared to that of the native enzyme (97%), but binding was significantly less efficient (46%). Introduction of alkyl functions permitted increase of the amounts of the adsorbed enzyme but its activity was somewhat decreased.

Molecular insight into the mode-of-action of phosphonate monolayers as active functions of hybrid metal oxide adsorbents. Case study in sequestration of rare earth elements

The insight into the molecular aspects of ligand grafting and potential maximal capacity of hybrid organic–inorganic adsorbents bearing phosphonate ligand monolayers as active functions was obtained by single crystal X-ray studies of ligand-functionalized titanium alkoxide complexes. The attachment of molecules occurs generally in the tripodal vertical fashion with the minimal distance between them being about 8.7 A, resulting in 0.19 nm2 as the minimal surface area per function. In the present experimental work the theoretical loading capacity could almost be achieved for functionalization of mesoporous nanorods of anatase with imino-bis-methylphosphonic acid (IMPA, NH(CH2PO3H2)2) or aminoethylphosphonic acid (AEPA, H2NC2H4PO3H2). The products had the same morphology as the starting material, as was established by SEM and optical microscopy. The size and structure of the individual nanoparticles of the constituting inorganic component of the material were preserved and practically unchanged through the surface modification, as established by powder XRD and EXAFS studies. The surface area of the inorganic–organic hybrids decreased somewhat from the initial ∼250 m2 g−1, on adsorption of AEPA (0.21 mmol g−1) to ∼240 m2 g−1, and on adsorption of IMPA (0.17 mmol g−1) to ∼190 m2 g−1. The ligands were bound effectively to the surface according to TGA, EDS and FTIR analyses and remained in the mono-deprotonated form. The produced hybrid adsorbents had for the selected pH (3.5) high capacities towards adsorption of Rare Earth Element (REE) cations, but with equilibria achieved relatively slowly. The composition of the surface complexes was determined as M : L = 1 : 1 for IMPA, but varied for the AEPA from 1 : 3 to 1 : 1 dependent on the REE, which can be interpreted in terms of charge compensation as the major driving force behind binding. The cation desorption in strongly acidic media for recuperation of the adsorbed REE and the relative capacity of the re-used adsorbent have been quantified.

Design of Functionalized Polysiloxane Adsorbents and Their Environmental Applications

Here we consider the routes of synthesis (which is performed by use of sol-gel method) of a new class of sorbents, namely: polysiloxane xerogels functionalized with nitrogen-, oxygen-, phosphorus- and sulfur chapter ligand groups. Applying a number of physical methods (SEM, TEM, AFM, IR and Raman spectroscopy, 1H, 13C, 29Si and 31P CP/MAS NMR, EPR spectroscopy, ERS, thermal analysis) we established the structure of both: the xerogels and their surface. An influence of some factors on the structural-adsorption characteristics of such xerogels and their sorption properties is analyzed.

Enzyme immobilization on a nanoadsorbent for improved stability against heavy metal poisoning

Magnetic nanoparticles modified with siloxane layers bearing amino and thiol functions have been used for immobilization of urease either by adsorption or via surface grafting. The activity of the immobilized enzyme in the hydrolysis of urea extended to the levels typical of the native enzyme, while its long-term stability in combination with magnetic retraction opened for its repeated use in both analysis and detoxification of bio-fluids. The immobilized urease revealed strongly enhanced stability and 65% activity in the presence of 0.1mmol/l of Hg(2+) or 0.3mmol/l of Cu(2+) while the native urease did not retain any activity at all. The enzyme grafting was shown to be a potentially perspective tool in alleviation of heavy metal poisoning and to be providing an opportunity for use of the developed adsorbents as both biosensors and bio-reactants for removal of urea from biofluids.

Mesoporous silica containing ≡Si(CH2)3NHC(S)NHC2H5 functional groups in the surface layer.

One-step synthesis technique of mesoporous SBA-15 type silica with thiourea ≡Si(CH(2))(3)NHC(S)NHC(2)H(5) groups in the surface layer was developed. According to elemental analysis, the content of surface groups is 1.25 mmol/g, which is consistent with TGA data. FT-IR spectra of the obtained sample contain characteristic absorption bands of thiourea groups (-NH-C(S)-NH-), as well as polysiloxane network (SiOSi). The synthesized sample was studied by XRD, TEM, SEM, and adsorption method. It was demonstrated that the sample features porous microspheres ~0.5 μm with well-ordered internal spatial structure of the hexagonal lattice type due to the usage of template P123 during synthesis. According to XRD and TEM, the diameter of pores is 4.2-5 nm and the wall thickness between them is 2.6 nm. These data are consistent with the structural-adsorption characteristics calculated from nitrogen adsorption-desorption isotherms: S(sp.)=510 m(2)/g, V(s)=0.47 cm(3)/g, and d=4.3 nm. Equilibrium is established within 60 min during sorption of silver(І) and mercury(ІІ) ions from acidified aqueous solutions for this sample, and with the complexes are formed 1.1/1 for Ag(+) and 0.8/1 for Hg(2+) at metal/ligand ratio.

Synthesis of Functionalized Mesoporous Silicas, Structure of Their Surface Layer and Sorption Properties

The routes of synthesis of polysiloxane xerogels functionalized by nitrogen-, oxygen-, phosphorus- and sulphur content ligand groups were investigated. Applying a number of physical methods (SEM, TEM, AFM, IR and Raman spectroscopy, 1H, 13C, 29Si and 31P CP/MAS NMR spectroscopy, EPR spectroscopy, ERS and thermal analysis) the structure of xerogels and their surface was established. The influence of some factors on the structural-adsorption characteristics of such xerogels and their sorption properties were analysed.

Silica-Coated Magnetite Nanoparticles Modified with 3-Aminopropyl Groups for Solid-Phase Extraction of Pd(II) Ions from Aqueous Solutions

Here we report a simple two-step synthesis of magnetite nanoparticles (NPs) coated with silica shell functionalized with 3-aminopropyl groups. The content of surface amino groups within the range of 0.7–2.8 mmol g−1 was established by elemental analysis and acid–base titration. The materials obtained are hydrolytically stable in acidic medium and are rapidly separated from the solution using an external magnetic field. It was shown that the prepared NPs efficiently extract palladium(II) ions in the form of [PdCl4]2– from the solution. The kinetics of adsorption was well described by the second-order model with the rate constant of approximately 0.76 g mmol−1 minute−1. The isotherm of adsorption is fitted by the Langmuir model with the maximum [PdCl4]2– adsorption capacity of 0.158 mmol g−1.

Application of Sol-Gel Method for Synthesis of a Biosensitive Polysiloxane Matrix

Sol-gel method was used to synthesize polysiloxane hydrogel with encapsulated urease (immobilization degree in the range of 79–88%) which preserved the enzymatic activity at the level of 56–84%. The nature of functional groups was shown to influence the pore structure parameters. Immobilization degree and preservation of adsorbed urease activity depend on the structural-adsorption characteristics of matrices. The possibility of “double immobilization” of urease on silica gel by sol-gel method and the opportunity of reuse of the synthesized formulations was investigated. Urease immobilization on the surface of magnetite (FeO·Fe2O3) was also studied by adsorption method.

Factors Influencing the Adsorption Properties of Silicas Functionalized by Macrocyclic Ligands

The adsorbents (polysiloxane xerogel, silicagel Davisil, mesoporous silica SBA-15) containing macroligands, such as calix[4]arenes, diaminodibenzo-18-crown-6-ethers, α- and β-cyclodextrins, have been obtained by the sol-gel method and the surface modification method. The influence of the synthesis conditions, the nature of macrocyclic compounds and routes of their grafting on the structural-adsorption characteristics of the obtained polysiloxane materials and their sorption properties toward Cs+ (137Cs) and Na+, K+, Sr2+ (90Sr), and organic compounds of different kind, has been investigated.