Ionogenic Groups Research Articles

KINETICS AND MECHANISM OF SORPTION OF COPPER (II) IONS BY ION EXCHANGER

In this article the kinetics of the process of sorption of copper (II) ions from aqueous solutions by polymer sulfonic cation exchanger, an elementary unit containing a heterocycle and a sulfonic group, under static conditions at a temperature of 298 K and a copper concentration of 2 mmol / mg is investigated. The sulfonic cation exchanger was preliminarily obtained by the reaction of polycondensation of diphenyl oxide and furfural with further sulfonation to obtain functional ionogenic groups in order to increase the extraction efficiency. The obtained kinetic curves of the dependence of the degree of extraction of copper ions from solution on time were processed using the Boyd, Adamson, and Myers equation, which describes diffusion in a limited volume of solution. The kinetic parameters of the sorption process (effective diffusion coefficient, etc.) are calculated, and the results obtained are compared with the data for the traditionally used industrial cation exchanger, which is a copolymer of styrene and divinyl benzene. It has been established that the process of sorption of copper (II) ions in the sulfonic cation exchanger phase is of an intra diffusion nature and corresponds to second-order kinetic equations.

Water Splitting and Transport of Ions in Electromembrane System with Bilayer Ion-Exchange Membrane.

Bilayer ion-exchange membranes are mainly used for separating single and multiply charged ions. It is well known that in membranes in which the layers have different charges of the ionogenic groups of the matrix, the limiting current decreases, and the water splitting reaction accelerates in comparison with monolayer (isotropic) ion-exchange membranes. We study samples of bilayer ion-exchange membranes with very thin cation-exchange layers deposited on an anion-exchange membrane-substrate in this work. It was revealed that in bilayer membranes, the limiting current’s value is determined by the properties of a thin surface film (modifying layer). A linear regularity of the dependence of the non-equilibrium effective rate constant of the water-splitting reaction on the resistance of the bipolar region, which is valid for both bilayer and bipolar membranes, has been revealed. It is shown that the introduction of the catalyst significantly reduces the water-splitting voltage, but reduces the selectivity of the membrane. It is possible to regulate the fluxes of salt ions and water splitting products (hydrogen and hydroxyl ions) by changing the current density. Such an ability makes it possible to conduct a controlled process of desalting electrolytes with simultaneous pH adjustment.

Physical origin of Na+/Cl− selectivity of tight junctions between epithelial cells. Nonlocal electrostatic approach

Tight junctions (TJs) of epithelial cells play a key role in regulation of the ion exchange between NaCl solutions separated by the layer of these cells. Their functioning is based on a strong difference in the permeabilities of these channels for Na+ and Cl− ion migrational fluxes owing to specific properties of the protein network inside TJs. It has been assumed in this study that this phenomenon originates from combination of two effects related to this specific TJ protein (claudin) which segments are partially located inside the TJ space. First, their ionogenic groups create a negative charge distributed inside TJs, thus inducing a difference between the Na+ and Cl− concentrations inside this spatial region. Second, the effect of these negative charges is greatly enhanced owing to high energetic barriers for penetration of both ions into TJs from the external aqueous solution, due to a significantly lower values of their solvation energies inside this spatial region, compared to the aqueous solution. This effect has been attributed to the change of the nonlocal dielectric response of the polar medium inside the TJ region where the long-range water structure is modified by the contact with segments of claudin molecules distributed in this space. Acting together, these two factors lead to pronounced permselectivity of TJs with respect to singly-charged cations and anions, i.e. to much higher Na+ concentration inside TJs, compared to the Cl− one. Derived expressions for the resolvation energies of ions as well as for their concentrations inside the TJ region on the basis of electrostatics of nonlocal dielectric media have been applied for interpretation of experimental data for the Na+/Cl− selectivity of such channels.

Cation-exchange membranes with sulfonylimide groups showing a high ionic conductivity in water/organic amide mixed systems

Cation-exchange membranes based on polystyrene block copolymer with phenylsulfonylimide ionogenic groups in the Na+-form show conductivities up to 0.2 mS cm−1 in organic amides such as N-methylpyrrolidone and N,N-dimemylacetamide. These values are 2–2.5 orders of magnitude higher compared to those of conventional sulfonated cation-exchange membranes. A strong dependence of solvation degree and ionic conductivity on dielectric permittivity, chemical structure, and composition of the solvent, as well as on the nature of the membrane functional group, was noted and discussed. Further, based on the dependence of membrane’s solvation on the dimethylacetamide or acetonitrile content in the water/organic solvent mixtures and thermodynamic properties of these solvent mixtures, the reasons for the difference in ionic conductivity with a variation in the composition of the solvent and the functional groups of membranes are described. It was shown that conductivity of the cation-exchange membranes can increase dramatically even at low water concentration in the acetonitrile solution. It was demonstrated that the membranes with phenylsulfonylimide groups have high ionic conductivity in water/dimethylacetamide mixtures of any concentrations, which opens new prospects for their applications in electrochemical desalination and metal-ion batteries.

Functionalized thermoresponsive microgels based on N-isopropylacrylamide: Energetics and mechanism of phase transitions

Nano- and micro-sized stimuli-responsive polymer containers capable of an effective controlled binding and release of ionic amphiphilic drugs are highly demanded in drug delivery. Thermoresponsive cross-linked microgels based on N-isopropylacrylamide (NIPAM) were synthesized by precipitation polymerization in aqueous media. The microgels were functionalized by the introduction of an ionic component (acrylic acid, AA, or vinyl sulfonate, VSA) either as a comonomer (NIPAM-co-AA and NIPAM-co-VSA microgels) or interpenetrating polymer network (PNIPAM-PAA microgel). The thermoresponsive behavior of the microgels was investigated by high-sensitivity differential scanning calorimetry. Thermodynamic parameters of the phase transitions (the transition temperature, enthalpy, and width) for the copolymer and interpenetrating microgels were determined. The copolymer microgels involving weak and strong ionogenic groups differ drastically by the transition energetics. This implies different types of their primary structures provided by either comonomer affinity or segregation in the reaction mixture under the polymerization conditions. The microgel functionalization via interpenetrating networks does not affect notably the transition temperature typical of the reference parent PNIPAM microgel but reduces the transition cooperativity. An analysis of the heat capacity profile of the microgel phase transition reveals some features of the mechanism of the thermoresponsivity in the microgels.

Инкапсуляция изохинолина в полимерном наноконтейнере на основе сульфокатионита КУ-2-4

The possibility of the encapsulation of isoquinoline in the nanocontainer on the matrix of the sulfonated copolymer based on styrene and divinylbenzene (CU-2-4 sulfocationite) has been researched. The encapsulation of isoquinoline in the nanocontainer on polymer matrix was performed by ion-exchange sorption from aqueous solutions. CU-2-4 sulfocationite in hydrogen and isoquinoline forms was studied by NMR and Fourier IR spectroscopy. In the 13C NMR spectra of solid-state samples of the CU-2-4 cation exchanger in the isoquinoline form is observed additional resonance absorption band of 13C in the range of chemical shift 136 ppm, corresponding to the nodal carbon atom of the pyridine ring. The IR spectrum of the polymer containing the encapsulated isoquinoline be observed bands characteristic for skeletal vibrations in the area of isoquinoline fingerprints (1300-1600 cm-1) and the band of 938 cm-1 that corresponds to the deformation vibrations of the CH-group of pyridine ring, which is not in the spectrum of the H-form sulfocationite. The ion-exchange capacity of the nanocontainer based on СU-2-4 sulfocationite for isoquinoline was 5.5 meq/g. This corresponds to the content of ionogenic groups in the polymer. The dynamic ion-exchange capacity of sulfonated CU-2-4 cation exchanger during encapsulation of isoquinoline coincides with the ion-exchange capacity of sulfonated cation exchanger upon the release of isoquinoline from the polymer nanocontainer. The content of immobilized isoquinoline in the nanocontainer on the СU-2-4 matrix reaches 71 % by weight of the polymer. It is shown that isoquinoline is encapsulated and desorbed with the solution of hydrochloric acid at the same rate. Encapsulated isoquinoline is completely released from the polymer by desorption with the aqueous hydrochloric acid solution. The half-life during sorption and desorption (release) of isoquinoline is approximately 400 seconds. It is shown that the encapsulated isoquinoline to be completely released from the polymer by desorption with an aqueous hydrochloric acid solution. The kinetics of the encapsulation and release of isoquinoline from the nanocontainer based on CU-2-4 sulfocationite is determined by its diffusion in the polymer phase.

Sorption of Uranium (VI) Ions by a Sorbent Based on a Copolymer of Maleic Anhydride with Styrene Modified by N, Nand#39;-diphenylguanidine

In this paper the results of a study on the extraction and concentration of micro-quantities of uranium (VI) with a polymeric chelating sorbent with fragments of N, N and#39;diphenylguanidine is discussed. There was studied a static sorption capacity on K+ ions ((SSC = 9.3 mmol / g) and there were determined the ionization constants of ionogenic groups ( =3.97; =8.47) by potentiometric titration. The optimal conditions of the sorption of elements (pHopt, sorption time - τ, the influence of ionic strength - μ) were determined by the dependence of the sorption capacity (SC, mg/g) on the parameter being studied; the sorption capacity of the sorbent (SC) was determined from the saturation curve constructed under optimal sorption conditions. The maximum degree of extraction of uranium by sorbents is achieved from solutions with pH 5. Sorption equilibrium is achieved within 2 hours of contact of the solution with the sorbent. With an increase in the concentration of the uranyl ion in the solution, the amount of the sorbed metal increases, and at a concentration of 8•10–3 mol/l, it becomes maximal (pH = 5, = 8•10–3 mol/l, Vgen = 20 ml, msorb. = 0.05 g, SC = 1258 mg/g). Limits of detection (3, n=20) are 13.9 ng/ml. The effect of various mineral acids(HClО4, H2SО4, HNО3, HCl) with the same concentrations on the desorption of uranium (VI) from the sorbent was studied. The developed technique was applied to determine uranium in oil sludge.

Sorption of Uranium (VI) Ions by a Sorbent Based on a Copolymer of Maleic Anhydride with Styrene Modified by N, Nand#39;-diphenylguanidine

In this paper the results of a study on the extraction and concentration of micro-quantities of uranium (VI) with a polymeric chelating sorbent with fragments of N, N and#39;diphenylguanidine is discussed. There was studied a static sorption capacity on K+ ions ((SSC = 9.3 mmol / g) and there were determined the ionization constants of ionogenic groups ( =3.97; =8.47) by potentiometric titration. The optimal conditions of the sorption of elements (pHopt, sorption time - τ, the influence of ionic strength - μ) were determined by the dependence of the sorption capacity (SC, mg/g) on the parameter being studied; the sorption capacity of the sorbent (SC) was determined from the saturation curve constructed under optimal sorption conditions. The maximum degree of extraction of uranium by sorbents is achieved from solutions with pH 5. Sorption equilibrium is achieved within 2 hours of contact of the solution with the sorbent. With an increase in the concentration of the uranyl ion in the solution, the amount of the sorbed metal increases, and at a concentration of 8•10–3 mol/l, it becomes maximal (pH = 5, = 8•10–3 mol/l, Vgen = 20 ml, msorb. = 0.05 g, SC = 1258 mg/g). Limits of detection (3, n=20) are 13.9 ng/ml. The effect of various mineral acids(HClО4, H2SО4, HNО3, HCl) with the same concentrations on the desorption of uranium (VI) from the sorbent was studied. The developed technique was applied to determine uranium in oil sludge.

Evaluation of Iminodiacetic Acid (IDA) as an Ionogenic Group for Adsorption of IgG1 Monoclonal Antibodies by Membrane Chromatography.

Iminodiacetic acid (IDA) is one of the chelating ligands most frequently employed in immobilized metal-ion affinity chromatography (IMAC) due to its ability to act as electron-pair donor, forming stable complexes with intermediate and borderline Lewis metal ions (electron acceptor). Thus, IDA can also be employed in ion exchange chromatography to purify positively charged proteins at neutral pH values. This study aimed to evaluate IDA as an ionogenic group (ion exchanger) immobilized on poly (ethylene vinyl alcohol) (PEVA) hollow fiber membranes for immunoglobulin G1 (IgG1) monoclonal antibody (MAb) purification. IDA-PEVA membranes showed considerable promise for MAb purification, since IgG1 was recovered in eluted fractions with traces of contaminants as confirmed by Western blotting and ELISA analysis. Quantification of IgG1 showed that a purity of 94.2% was reached in the elution step. Breakthrough curve and batch adsorption experiments showed that the MAb dynamic binding capacity (DBC) of 3.10mgg-1 and the maximum adsorption capacity of 70mgg-1 were of the same order of magnitude as those found in the literature. The results obtained showed that the IDA-PEVA hollow fiber membrane could be a powerful adsorbent for integrating large-scale processes for purification of MAb from cell culture supernatant.

PHYSICO-CHEMICAL PROPERTIES OF PHOSPHATE CATION-EXCHANGE RESIN

There are investigated sorption and desorption characteristics of phosphate cation-exchange resin among metals: copper, nickel, cobalt, an uranyl-ion depending on pH-environment, the ionic form of cation-exchange resin, concentration of investigated cations. Interaction of cation-exchange resin in Na- and H-forms with solutions of salts sulphate of copper, nickel, cobalt, chloride sodium, calcium and nitrate of uranyl is studied. It is shown, that ions of copper, nickel, cobalt and an uranyl-ion by phosphate cation-exchange resin sorb at the expense of an ionic exchange and partially at the expense of formation of coordination communications with ionogenic group of cation-exchange resin. A study of the sorption of uranyl ions depending on the concentration of uranyl nitrate in the range of 0.01-0.1 N showed that with an increase in the concentration of uranyl in the studied interval, the value of sorption of uranyl increases slightly. The studied phosphate cation exchanger has a sufficiently high sorption and desorption ability to the ions of the tested metals.

Characterization of the Structural Forms of Biomolecules Based on the Decomposition and Separation of the Charge-State Distributions of Their Ions

The purpose of this work is the efficient reveal and analysis of hidden information in mass spectrometric data on the structural composition of the studied solutions of biomolecules in their electrospray ionization. This paper describes the algorithm of sequential splitting combined with the decomposition of the measured charge-state distributions of biomolecules while increasing the number of individual components corresponding to the independent presence of charge carriers with the found probabilities of retention for a given number of ionogenic groups of these biomolecules. The article discusses the results of calculations for the two-dimensional and one-dimensional decompositions of the charge distributions of cytochrome c with separation, presumably corresponding to different conformations of proteins. For the first time we developed a method and a software for searching individual components and their contributions to the mass spectra of multiply charged ions when the mass spectra of these components are not known in advance.

SORPTION OF NICKEL (II) IONS BY CHELATING RESIN WITH IMINODIACETATE FUNCTIONALITY

The regularities of sorption of nickel (II) ions from a monocomponent system on macroporous weakly acidic cationite Lewatit MonoPlus TP 207 were studied. Sorption isotherms were obtained. It is shown that the extraction process can be fairly reliably described by Langmuir and Freundlich equations. The static exchange capacity (SEC) of the resin was determined. The SEC dependencies at temperatures of 305 and 328 K during the sorption process were revealed. Integral kinetic curves were obtained. It is defined that the equilibrium concentration of nickel (II) ions is reached about 13 times faster with temperature increase from 305 to 328 K. The experimental data were processed using equations that take into account the influence of external, internal diffusion, "sorbent-sorbate" and "sorbate-sorbate" chemical interactions. It was found that the main limiting stage of sorption of nickel (II) ions is the internal diffusion. The values of external and internal diffusion rate constants at the indicated temperatures were determined. The kinetic curves were processed by pseudo first and pseudo second order models, which satisfactorily describe the experimental data. According to transition-state theory the thermodynamic characteristics of the activation process (activation energy, entropy, enthalpy, and Gibbs free energy) were calculated. Relatively low activation energy indicates the decisive contribution of diffusion in the process of sorption of nickel (II) ions. Positive entropy is the evidence of nickel hydration shells destruction during the sorption process. Positive enthalpy proves an endothermic nature of interaction of nickel (II) ions and ionogenic groups. Negative Gibbs free energy witnesses to spontaneous course of the reaction in the forward direction. For known values of stability constants the contents of nickel ionic forms and SEC’s were calculated in terms of pH value. Nickel extraction from solution increases with the appearance of singly-charged NiOH+ ions in the pH range from 8 to 9.

Behavior of thermoresponsive ionogenic poly(2-isopropyl-2-oxazoline) stars and their mixture in aqueous solutions

Star-shaped eight-arm poly(2-isopropyl-2-oxazoline)s with basic and acidic groups were synthesized using a “grafting from” approach. Molar masses were 13,700 and 14,900 g mol−1 for polybase and polyacid, respectively. The aqueous solutions of synthesized polymers and their mixture were investigated by the light scattering and turbidimetry methods within wide range of temperatures and pH values. It was shown that the studied polymers separately do not exhibit pH-sensitivity due to the low content of ionogenic groups. For the solutions of mixture, one phase transition was detected, the onset temperature T1 of which lies between the phase separation temperatures for polymers. The value of T1 for mixture decreases with increasing acidity of the medium.

Sedimentation Velocity and Potential in Dilute Suspensions of Charge-Regulating Porous Spheres.

The sedimentation of a charge-regulating porous sphere surrounded by an arbitrary electric double layer, which usually models a permeable polyelectrolyte coil or an aggregate of nanoparticles, is analyzed for the first time. The hydrodynamic frictional segments and ionogenic functional groups uniformly distribute in the porous sphere, and a regulation mechanism for the dissociation and association reactions occurring at these functional groups linearly relates the local electric potential to fixed charge density. The linearized electrokinetic equations governing the ionic concentration (or electrochemical potential energy), electric potential, and fluid velocity fields are solved for the case of a small basic fixed charge density by the regular perturbation method. Analytical formulae for the sedimentation velocity of a porous sphere and sedimentation potential of a dilute suspension of porous spheres are then obtained. The charge regulation tends to reduce the electrokinetic retardation to sedimentation velocity and the sedimentation potential (can be as much as 50 and 25%, respectively) compared to the case that the fixed charge density is a constant. Both the electrokinetic retardation to sedimentation velocity and the sedimentation potential vanish at the isoelectric point of the particles. The increase in the bulk concentration of the potential-determining ions crossing the isoelectric point changes signs of the fixed charges and thus causes a reversal in the direction of the sedimentation potential. The effects of charge regulation on the sedimentation of porous particles differ substantially from those of hard particles.

О полифункциональности высокоосновных анионитов

Методом потенциометрического титрования в высокоосновном анионите АВ-17-8 установлено наличие трех типов функциональных групп. Определены константы их ионизации: pKb1=1.72÷1.78; pKb2=4.32÷4.38; pKb3=7.72÷7.82. В ионный обмен с кремниевыми кислотами вступают две функциональные группы с меньшими величинами pKb. Доля слабоосновных групп (с pKb3=7.72÷7.82) в разных партиях анионита достигает 12-34 % от полной обменной емкости. Полифункциональность анионита АВ-17-8 нужно учитывать при обсуждении различных закономерностей ионообменных процессов, а также при прогнозировании сорбции анионов слабых органических и минеральных кислот.

Features of the Formation of Interpolyelectrolyte Complexes Based on Chitosan and Pectin

Conditions for the preparation of stable to sedimentation aqueous dispersions of interpolyelectrolyte complexes based on chitosan (Chit) and pectin (Pect) with particle diameter 0.5-0.9 μm for Pect/Chit and 1.0-2.0 μm for Chit/Pect have been determined. The absolute value of the zeta potential of these complexes is >10 mV for Pect/Chit and Chit/Pect when the molar ratio of the ionogenic groups of the polymers $$ {n}_{\mathrm{COOH}}/{n}_{{\mathrm{NH}}_2} $$ is 0.4-4.6 for Pect/Chit and 0.02-0.63 for Chit/Pect. Optical spectroscopy and electrophoretic light scattering have been used to determine the effect of molecular mass and the content of the free ionogenic groups in the polysaccharide macromolecules as well as the order of mixing the solution on the formation and properties of these interpolyelectrolyte complexes.

Overlimiting current due to electro-diffusive amplification of the second Wien effect at a cation-anion bipolar membrane junction.

Numerical simulations are presented for the transient and steady-state response of a model electrodiffusive cell with a bipolar ion-selective membrane under electric current. The model uses a continuum Poisson-Nernst-Planck theory including source terms to account for the catalytic second Wien effect between ionogenic groups in the membranes and resolves the Debye layers at interfaces. The resulting electric field at the membrane junction is increased by as much as four orders of magnitude in comparison to the field external to the membrane. This leads to a significant amplification of the second Wien effect, creating an increased ionic flux due to the catalytic decomposition of water. The effect also induces an exaltation effect wherein the salt ion flux undergoes a concomitant increase as well. The interplay of effects results in a unique over-limiting current mechanism due to concentration polarization internal, rather than external, to the membranes. In addition to the case of two equal but oppositely charged membranes under the standard simplifying assumption of equal ionic diffusivities, two variations on this model are studied. Asymmetric diffusivities, representative of the actual mobility difference in dissociated water ions, and the effect of the membrane charge density ratio were also considered. The latter elucidates an overlimiting current shift mechanism for DNA adsorption on anion-selective membranes proposed by Slouka et al. [Langmuir 29, 8275 (2013)]. The former provides more realistic picture of multi-ion transport and demonstrates a surprising steady-state effect due to the asymmetry in the diffusivity of hydroxide and hydronium.

Synthesis and Antiviral Activity of Water-Soluble Polycarboxylic Derivatives of [60]Fullerene Loaded with 3,4-Dichlorophenyl Units.

We have synthesized a series of water-soluble polycarboxylic derivatives of [60]fullerene with a gradually changed polarity by combining three to five polar (ionic) malonate addends with two to zero hydrophobic dichlorobenzene units and explored their antiviral activity. It has been shown that decreasing the number of the ionogenic carboxylic groups in the molecules enhanced their antiviral activity against HIV-1 and suppressed their action against HIV-2. The obtained results implied that the charged states and hydrophobicity of the water-soluble polycarboxylic fullerene derivatives affect significantly their biological properties.

Amorphous Fe2O3 nanoparticles embedded into hypercrosslinked porous polymeric matrix for designing an easily separable and recyclable photocatalytic system

The use of polymer sorbents in wastewater treatment can generate large-scale secondary waste due to the oxidation of the polymer matrix, stemming from the ionogenic functional groups or impurities. In this work, amorphous Fe2O3 nanoparticles were embedded into a porous non-ionogenic polymer matrix (Porolas) using two different Fe(III) salts (iron nitrate and iron oxalate) for designing an easily separable and recyclable photocatalytic system. The Fe2O3-Porolas composites were prepared by a simple method: an impregnation of the Porolas by Fe(III) salts and calcination at 250 °C for 1 h. The sorption capacity and photocatalytic activity of the Fe2O3-Porolas composites were evaluated by the removal of methylene blue (MB) from model-contaminated water under UV light irradiation in the presence of oxalic acid. The characterization results, particularly from X-ray photoelectron spectroscopy and Mössbauer spectroscopy, confirmed the formation of highly dispersed amorphous Fe2O3 nanoparticles that are embedded in the Porolas matrix. An increase in the content of the embedded Fe2O3 nanoparticles decreased specific surface area (SBET), MB sorption capacity, and apparent photodegradation rate constant (kapp) but increased the photodegradation efficiency of MB. The enhancement in MB removal can be attributed to the photocatalytic activities of the Porolas and Fe2O3 nanoparticles (heterogeneous photocatalysis), sorption effect, and leaching of Fe ions in aqueous solution (homogeneous photocatalysis). The scaffold network of the Porolas and highly dispersed Fe2O3 nanoparticles additionally contributed to the enhancement of photocatalytic activity of the Fe2O3-Porolas composite. Almost complete decolorization of MB (96–98%) and more than 97% TOC were achieved in this study, confirming simultaneous mineralization of both MB and OA in aqueous solution. The Fe2O3-Porolas composite can be easily prepared and inexpensive to design an easily separable and recyclable photocatalytic system for wastewater treatment.

Comparative activity of aqueous dispersions of CdS nanocrystals stabilized by cationic and anionic polyelectrolytes in photocatalytic hydrogen production from water

The results of a study on the photocatalytic activity of aqueous dispersions of Ni-doped CdS nanocrystals (NCs) covered with an amphiphilic polyelectrolyte (PE) shell, i.e., a polycation (NC-PC) or polyanion (NC-PA), are presented for the first time. The H2 evolution rate measured under identical conditions served as a measure of activity. The NC-PC and NC-PA samples were characterized by similar PE content (~40%) and monomodal size distribution. According to our calculations based on the NC dimensions and lattice parameters, about one macromolecule of the PE is required to stabilize one NC. The average hydrodynamic diameter of the NC-PC was found to be 1.5 times larger than that of the NC-PA due to the difference between their chemical structures and different abilities of ionogenic groups to dissociate. The photocatal ytic activity of the PE-stabilized CdS nanocrystals was significantly influenced by the type of the PE, while the H2 evolution rate depended on the reducing medium used during the process. When the medium contained Na2S or when the PE-stabilized NCs were pretreated with Na2S, the effect of the shell type was more pronounced and the activity of NC-PA was 2 to 14 times higher than that of NC-PC.