The Influence of Polymer—Selenium Complex Components and the Molecular Weight of the Ionogenic Polymeric Matrix on the Morphologic Characteristics of Selenium-Containing Nanostructures

Several optical methods were used to study nanostructures formed in the reduction of selenium ions in the selenite—ascorbate redox system in an aqueous solution of the poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate polycation. The relation between the molecular weight of the polymeric matrix, which varied over a wide range, M _w = (0.03?13) × 10⁶, and the morphologic characteristics of nanostructures (molecular weight, density, shape, and statistical and hydrodynamic dimensions) was established. The weight ratio between the components of the polymer: selenium complex and the concentration of the polymer in the reaction mixture were shown to substantially influence certain morphologic characteristics of nanostructures. In the region of the formation of stable dispersions, the Gibbs energy of macromolecule—Se⁰ nanoparticle interactions was calculated. The thermodynamic state of solutions of nanostructures was characterized.     

Morphological characteristics of selenium-containing nanostructures based on rigid-chain molecules

Selenium-containing nanostructures of rigid-chain polymers with close molecular masses were studied by flow birefringence (FB) and static and dynamic light scattering at a fixed selenium to polymer mass ratio ν = 0.1 in solution. The group of polymers under study included the cationic polyelectrolyte poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate, anionic polyelectrolyte carboxymethylcellulose, and nonionogen polymer oxyethylcellulose. High-molecular selenium-containing polymer nanostructures were found in all cases. Nanostructures with a maximum molecular mass and the largest number of constituent macromolecules were obtained using oxyethylcellulose. At ν = 0.1 the mean square radii of inertia of the nanostructures were almost independent of the nature of the polymer matrix. The thermodynamic state of the solutions of nanostructures was close to the ideal one in all cases. For the region where stable dispersions formed, the Gibbs energies of macromolecule-selenium nanoparticle interactions were calculated and shown to be almost independent of the nature of the polymer matrix at ν = 0.1. The close mean square radii of inertia R _g^* of the nanostructures, the Gibbs energies of interaction, and the equivalence of the thermodynamic state of the solutions of nanostructures obtained for all polymer matrices at ν = 0.1 suggest that ν = 0.1 corresponds to the ultimate adsorption capacity of selenium nanoparticles; the considerable differences between the molecular masses (for close R _g ^* values), mean densities, and structural conformation parameters ρ* point to different packings of macromolecules in the nanostructures under study.     

Formation and morphological characteristics of selenium-containing nanostructures based on rigid-chain cellulose derivatives

Nanostructures arising from the reduction of ionic selenium by a selenite-ascorbate redox system in aqueous solutions of oxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose have been studied by using a set of optical methods (flow birefringence and static and dynamic light scattering) and viscometry. The adsorption of a substantial amount of macromolecules (up to 3200) on selenium nanoparticles has been experimentally discovered. This effect leads to the formation of superhigh-molecular-mass spherical nanostructures with a high density of the polymer shell. The thermodynamic state of solutions of nanostructures has been characterized. In the region of occurrence of stable dispersions, the values of the free energy of macromolecule-selenium nanoparticle interaction have been calculated for polymer nanostructures. Radii of amorphous selenium nanoparticles occurring in the nuclei of nanostructures and the thickness of the polymer shell have been estimated. Given the fixed molecular mass and comparable rigidity of a polymer matrix, the structure of the monomer unit of the cellulose derivative defines the morphology of the nanostructure being formed.     

The influence of the nature of a nanoparticle and polymer matrix on the morphological characteristics of polymeric nanostructures

Comparative studies of the morphological characteristics of selenium- and platinum-containing nanostructures were performed by molecular optics methods. The nanostructures were based on an ionogenic polymeric stabilizer, poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate, and a non-ionogenic polymeric stabilizer, oxyethylcellulose. Studies were performed in aqueous solutions at a fixed ratio between components. The adsorption of a considerable number of polymer macromolecules on nanoparticles with the formation of superhigh-molecular-weight nanostructures with shapes close to spherical was observed for all the nanosystems studied. The thermodynamic state of nanosystems was characterized. Certain morphological characteristics of nanostructures were substantially influenced by the nature of both nanoparticles and polymer matrix.     

The effect of polymer architecture on the nano self-assemblies based on novel comb-shaped amphiphilic poly(allylamine)

Twelve novel poly(allylamine) (PAA)-based, comb-shaped amphiphilic polymers have been developed. Hydrophobic groups of cetyl, palmitoyl and cholesteryl were randomly grafted to PAA and quaternisation was carried out on some modified polymers. Polymers were characterised using ¹H NMR, elemental analysis and differential scanning calorimetry. All polymers formed nano self-assemblies in the aqueous solution with a positive zeta potential and were able to encapsulate a hydrophobic agent, methyl orange, in the core. The critical aggregation concentration (CAC) and the microviscosity were found to be dependent on the polymer hydrophobicity. Being the most hydrophobic polymer, cholesteryl-grafted PAA had the lowest CAC (0.02 mg mL⁻¹) and the highest microviscosity. They appeared to form dense nanoparticles and were transformed into novel nanostructures in the presence of free cholesterol. Palmitoyl-grafted polymers formed nanoparticles while cetyl-grafted polymers formed polymeric micelles. The flexibility of cetyl chains possibly resulted in the formation of multicore polymeric micelles.     

Self-organization and morphological characteristics of selenium-containing nanostructures based on rigid-chain polymers

Macroinitiators containing β-diketonate fragments were prepared by copolymerization of styrene with cobalt(II) 5-Formation and morphological characteristics of selenium-containing nanostructures formed by reduction of selenious acid with ascorbic acid in the presence of ionic or nonionic polymeric stabilizer in aqueous solutions were studied by methods of nonlinear optics and flow birefringence at widely varied selenium to polymer weight ratio in solution ν. The molecular weights, root-mean-square and hydrodynamic sizes, and mean density of the nanostructures were calculated, and the trends in variation of these quantities were compared.     

A General and High‐Yield Galvanic Displacement Approach to Au?M (M=Au,Pd, and Pt) Core–Shell Nanostructures with Porous Shells and Enhanced Electrocatalytic Performances

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au? M (M=Au, Pd, and Pt) core–shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au? Au, Au? Pd, and Au? Pt core–shell nanostructures with typical porous shells. Moreover, the Au? Au isomeric core–shell nanostructure is reported for the first time. The lower oxidation states of Au^I, Pd^II, and Pt^II are supposed to contribute to the formation of porous core–shell nanostructures instead of yolk‐shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au? Pd core–shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core–shell nanostructures. As expected, the Au? Pd core–shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I_f/I_b is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au? M (M=Au, Pd, and Pt) core–shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface‐enhanced Raman scattering, and so forth.     

Adsorption of Hydroxyethyl Cellulose Selenium Nanoparticles during Their Formation in Water

Two previously unknown phenomena were observed in studying the reduction of selenious acid with ascorbic acid in an aqueous hydroxyethyl cellulose solution: (1) formation of nanoparticles of amorphous Se⁰ with uniform particle size distribution and mean particle radius of 15 ± 4 nm and (2) adsorption of more than 3000 macromolecules on these nanoparticles with formation of spherical nanostructures.     

Influence of the nature of the stabilizing polymeric matrix on the self-organization of selenium nanoclusters

The size characteristics and formation kinetics of selenium-containing nanosystems based on various polymeric matrices (nonionic polymers: polyvinylpyrrolidone, oxyethylated cellulose; cationic polyelectrolyte: poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate; anionic polyelectrolytes: poly-2-acrylamido-2-methylpropanesulfonic acid, polymethacrylic acid) were studied by methods of molecular optics and spectrophotometry. The influence of the nature of the polymeric matrix and of the selenium: polymer weight ratio on the rate constant and hydrodynamic radius was determined.     

Morphology and thermodynamic characteristics of selenium-containing nanostructures based on polymethacrylic acid

The morphology and thermodynamic characteristics of nanostructures formed as a result of the reduction of the selenium ion in a selenite-ascorbate redox system in water solutions of polymethacrylic acid were studied by molecular optics and atomic-force microscopy. The dependence of the morphology of the selenium-containing nanostructures on the mass selenium-to-polymer ratio (ν) in solution was determined. It was established that a large number of macromolecules (up to 4300) is adsorbed on the selenium nanoparticles, leading to the formation of nanostructures with super-high molecular mass and an almost spherical form. It was shown that the density of the nanostructures, as calculated on the basis of the experimental data on the size and molecular mass of the nanocomposite, depends substantially on the selenium concentrations in the solution. The thermodynamic state of the solutions of nanostructures is described.     

Interfacially formed organized planar inorganic, polymeric and composite nanostructures

This paper discusses synthetic strategies for fabrication of new organized planar inorganic, polymeric, composite and bio-inorganic nanostructures by methods based on chemical reactions and physical interactions at the gas-liquid interface, Langmuir monolayer technique, interfacial ligand exchange and substitution reactions, self-assembling and self-organization processes, DNA templating and scaffolding. Stable reproducible planar assemblies of ligand-stabilized molecular nanoclusters containing definite number of atoms have been formed on solid substrate surfaces via preparation and deposition of mixed Langmuir monolayers composed by nanocluster and surfactant molecules. A novel approach to synthesis of inorganic nanoparticles and to formation of self-organized planar inorganic nanostructures has been introduced. In that approach, nanoparticles and nanostructures are fabricated via decomposition of insoluble metal-organic precursor compounds in a layer at the gas-liquid interface. The ultimately thin and anisotropic dynamic monomolecular reaction system was realized in that approach with quasi-two-dimensional growth and organization of nanoparticles and nanostructures in the plain of Langmuir monolayer. Photochemical and redox reactions were used to initiate processes of interfacial nucleation and growth of inorganic phase. It has been demonstrated that morphology of resulting inorganic nanostructures can be controlled efficiently by variations of growth conditions via changes in state and composition of interfacial planar reaction media, and by variations of composition of adjacent bulk phases. Planar arrays and chains of iron oxide and ultrasmall noble metal (Au and Pd) nanoparticles, nanowires and new organized planar disk, ring, net-like, labyrinth and very high-surface area nanostructures were obtained by methods based on that approach. Highly organized monomolecular polymeric films on solid substrates were obtained via deposition of Langmuir monolayer formed by water-insoluble amphiphilic polycation molecules. Corresponding nanoscale-ordered planar polymeric nanocomposite films with incorporated ligand-stabilized molecular metallic nanoclusters and interfacially grown nanoparticles were fabricated successfully. Novel planar DNA complexes with amphiphilic polycation monolayer were formed at the gas-aqueous phase interface and then deposited on solid substrates. Toroidal and new net-like conformations were discovered in those complexes. Nanoscale supramolecular organization of the complexes was dependent on cationic amphiphile monolayer state during the DNA binding. These monolayer and multilayer DNA/amphiphilic polycation complex Langmuir-Blodgett films were used as templates and nanoreactors for generation of inorganic nanostructures via metal cation binding with DNA and following inorganic phase growth reactions. As a result, ultrathin polymeric nanocomposite films with integrated DNA building blocks and organized inorganic semiconductor (CdS) and iron oxide quasi-linear nanostructures were formed. It has been demonstrated that interaction of deposited planar DNA/amphiphilic polycation complexes with bulk phase colloid inorganic cationic ligands (CdSe nano-rods) can result in formation of new highly organized hybrid bio-inorganic nanostructures via interfacial ligand exchange and self-organization processes. The methods developed can be useful for investigation of fundamental mechanisms of nanoscale structural organization and transformation processes in various inorganic and molecular systems including bio-molecular and bio-inorganic nanostructures. Also, those methods are relatively simple, environmentally safe and thus could prove to be efficient practical instruments of molecular nanotechnology with potential of design and cost-effective fabrication of new controlled-morphology organized planar inorganic and composite nanostructured materials. Possible applications of obtained nanostructures and future developments are also discussed.     

Self‐assembly of N‐carboxyethylchitosan near the isoelectric point

For the first time the possibility to obtain nanostructures by self‐assembly of chitosan polyampholytic derivative was demonstrated. The self‐assembly of N‐carboxyethylchitosan (CECh) took place only near its isoelectric point (pH 5.0–5.6). Out of the pH range 5.0–5.6, CECh aqueous solutions behaved as real solutions. Dynamic light scattering and atomic force microscopy analyses revealed that spherically shaped or rod/worm‐like nanosized assemblies were formed depending on the polymer molar mass, pH value, and polymer concentration. CECh of two different molar masses was studied in concentrations ranging from 0.01 to 0.1 mg/mL. The structures from CECh of weight‐average molar mass (M_w ) 4.5 × 10³ g/mol were spherical regardless the pH and polymer concentration. In contrast, CECh of high molar mass (HMMCECh, M_w = 6.7 × 10⁵ g/mol) formed self‐assemblies with spherical shape only at pH 5.0 and 5.6. At pH 5.2 spherical nanoparticles were obtained only at polymer concentration 0.01 mg/mL. The mean hydrodynamic diameter (D_h) of the obtained nanoparticles was in the range from 30 to 980 nm. On increasing the concentration, aggregation of the nanoparticles appeared, and at HMMCECh concentration 0.1 mg/mL, rod/worm‐like structures were obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6712–6721, 2008     

Vibrational energy transfer from N2 to CO on electron excitation of N2-CO solids at 4.2 K

Spectra emitted from 0.1% CO-N₂ solids excited with high energy electrons at 4 K show evidence for resonant transfer of vibrational energy from highly excited vibrational levels of N₂ to CO in the process N₂(X¹Σ_g⁺, ν) + CO(ν = 0) → N₂(X¹Σ_g⁺, ν - 1) + CO(ν = 1) + phonons. Energy transfer from levels with ν ? 9 has been observed.     

A completely green approach to the synthesis of dendritic silver nanostructures starting from white grape pomace as a potential nanofactory

A simple, eco-friendly, cost-effective and rapid microwave-assisted method has been developed to synthetize dendritic silver nanostructures, composed of silver nanoparticles (AgNPs), using white grape pomace aqueous extract (WGPE) as both reducing and capping agent. With this aim, WGPE and AgNO₃ (1 mM) were mixed at different ratio, and microwave irradiated at 700 W, for 40 s. To understand the role of bioactive compounds involved in the green synthesis of AgNPs, preliminary chemical characterization, FT-IR analysis and ¹H NMR metabolite profiling of WGPE were carried out. The effects of bioactive extract concentration and stability over time on AgNPs formation were also evaluated. WGPE-mediated silver nanostructures were then characterized by UV–vis, FTIR analyses, and scanning electron microscopy. Interestingly, the formation of dendritic nanostructures, originated from the self-assembly of Ag rounded nanoparticles (average diameter of 33 ± 6 nm), was observed and ascribed to the use of microwave power and the presence of organic components within the used WGPE, inducing an anisotropic crystal growth and promoting a diffusion-limited aggregation mechanism. The bio-dendritic synthetized nanostructures were also evaluated for potential applications in bio-sensing and agricultural fields. Cyclic voltammetry measurements in 0.5 M phosphate + 0.1 M KCl buffer, pH 7.4 showed that green AgNPs possess the electroactive properties typical of AgNPs produced using chemical protocol. The biological activity of synthetized AgNPs was evaluated by in-vitro antifungal activity against F. graminearum. Additionally, a phytotoxicity evaluation of synthetized green nanostructures was carried out on wheat seed germination. Results highlighted the potential of WGPE as green agent for bio-inspired nanomaterial synthesis, and of green Ag nanostructures, which can be used as antifungal agent and in biosensing applications.     

Elemental Selenium Enriched Nanofiber Production

This study aimed to produce electrospun nanofibers from a polyvinyl butyral polymer (PVB) solution enriched with red and grey selenium nanoparticles. Scanning electron microscopic analysis was used to observe the samples, evaluate the fiber diameters, and reveal eventual artifacts in the nanofibrous structure. Average fiber diameter is determined by manually measuring the diameters of randomly selected fibers on scanning electron microscopic (SEM) images. The obtained nanofibers are amorphous with a diameter of approximately 500 nm, a specific surface area of approx. 8 m² g⁻¹, and 5093 km cm⁻³ length. If the red and grey selenium nanoparticles were produced in powder form and suspended to the ethanolic solution of PVB then they were located inside and outside the fiber. When selenium nanoparticles were synthesized in the PVB solution, then they were located only inside the fiber. These nanofiber sheets enriched with selenium nanoparticles could be a good candidate for high-efficiency filter materials and medical applications.     

Sorption-spectroscopic determination of selenium using a PANV-AV-17 fibrous ion-exchanger

The possibility of determining selenium on the solid phase of polyacrylonitrile fibers impregnated by an AV-17 anion-exchanger ([PANV-AV-17]) were examined by virtue of diffuse reflectance spectroscopy. Reactions of a complex formation between selenium(IV) and organic reagents on solid phase as well as the formation of an elemental selenium sol both on the solid phase and in solution followed by absorption were studied. The best analytical parameters were achieved in the adsorption of selenium sol formed in solution upon the addition of ascorbic acid. The comparison of the batch and dynamic adsorption modes revealed greater advances of the dynamic one. The optimal conditions for determining selenium were proved as follows: the formation of a selenium sol in a 1% ascorbic acid solution at pH 2 and dynamic adsorption at a flow rate of 5 mL/min. A procedure was developed for determining selenium with a limit of detection of 0.1 mg/L. The procedure was validated by the added-found method in the analysis of river and well natural waters and also the standard specimen OSO-200-90, which also contained As, Bi, Sb, and PO₄³⁻. The duration of analysis for 5–6 samples of the volume 100 mL was 30 min approximately, RSD < 20%.     

Experimental study of the D + H2(ν = 1) reaction

The D + H₂(ν = 1) reaction, D + H₂(ν = 1) → K_a HD(ν = 1) + H, → K_n HD(ν = 0) + H, → K_r D + H₂(ν = 0) has been studied. The measurements were made in a flow-tube apparatus at 300 K. Vibrationally excited H₂ was generated in a furnace and D atoms in a microwave discharge. EPR and thermometric techniques were used for the detection of D and H atoms and H₂(ν = 1). The product branching rate constants (in CM³/Molecule s) were found to be K_a = (10.7 ± 4.1) × 10^?13. K_n = (5.4 ± 2.7) × 10^?13, K_r, < 2.7 × 10^?13.     

The flocculation of kaolin suspensions with cationic polyacrylamides of varying molar mass but the same cationic character

Cationic polyacrylamides of varying molar masses but of similar charge density were tested as flocculants for kaolin suspensions. Flocculant performance was assessed by determining the extent of polymer adsorption, the subsidence rates of the flocculated suspensions and the residual turbidities of the resulting supernatants. The sol concentration was kept constant at 20 g kaolin dm⁻³ in 10⁻³ mol dm⁻³ NaCl solution; pH was varied from 3 to 10. It was found that the subsidence rates did not reflect the trends of polymer adsorption. Polymer adsorption decreased while subsidence rates increased as the molar mass of the polymers increased. Increased adsorption of polymer with pH did not result in higher rates of subsidence. The principal effect of the quaternary cationic charge is to produce a partially extended polymer molecule at all values of the pH. The positive polymeric charge is of secondary importance to the length of the molecule in determining the efficacy of flocculation by polymer bridging and does not counteract the increasing self-repulsion of the clay particles with increasing pH which produced poor floc formation.     

Perturbation-enhanced quenching of laser-excited CS A1π(ν = 0) by atomic oxygen

Quenching of CS A¹Π(ν = 0) by O³ P is enhanced by perturbations due to á ³Σ⁺(ν = 10) and d³ Δ (ν = 4) The rotational-state dependence is linear in the singlet-triplet mixing coefficients and indicates an orientation-dependent interaction Symmetry correlations suggest that the perturbations promote formation of an attractive collision complex with quenching by intersystem crossing or chemical reaction.     

New Strategies for the Simple and Sensitive Voltammetric Direct Quantification of Se(IV) in Environmental Waters Employing Bismuth Film Modified Glassy Carbon Electrode and Amberlite Resin

An analytical procedure regarding the determination of selenium(IV) by anodic stripping voltammetry exploiting the in situ plated bismuth film electrode is described. Since organics are commonly present in untreated natural water samples, the use of Amberlite XAD-7 resin turns out to be quite important to avoid problems such as the adsorption of these compounds on the working electrode. The optimum circumstances for the detection of selenium in water using differential pulse voltammetry techniques were found to be as follows: 0.1 mol L⁻¹ acetic acid, 1.9 × 10⁻⁵ mol L⁻¹ Bi(III), 0.1 g Amberlite XAD-7 resin, and successive potentials of −1.6 V for 5 s and −0.4 V for 60 s, during which the in situ formation of the bismuth film on glassy carbon and the accumulation of selenium took place. The current of the anodic peak varies linearly with the selenium concentration ranging from 3 × 10⁻⁹ mol L⁻¹ to 3 × 10⁻⁶ mol L⁻¹ (r = 0.9995), with a detection limit of 8 × 10⁻¹⁰ mol L⁻¹. The proposed procedure was used for Se(IV) determination in certified reference materials and natural water samples, and acceptable results and recoveries were obtained.