Ecotoxicity of different-shaped silver nanoparticles: Case of zebrafish embryos

As the worldwide application of silver nanomaterials in commercial products increases every year, and concern about the environmental risks of such nanoparticles also grows. A clear understanding of how different characteristics of nanoparticles contribute in their toxic behavior to organisms are imperative for predicting and control nanotoxicity. Within our research, we investigated the toxic effect of two types of silver nanoparticles (spherical and flat Ag nanoparticles) on zebrafish (Danio rerio) embryos. Particular interest was paid to proper characterization of Ag nanoparticles initially and during the experiment. A proper test medium was found and used for ecotoxicity evaluation. The behavior of flat silver nanoparticles with respect to embryos of zebrafish was analyzed and compared to the ecotoxicity of silver ionic form (AgNO₃). Both types of nanoparticles showed a more pronounced toxic effect to Danio rerio embryos than silver ions (AgNO₃), while silver nanoplates were more harmful than Ag nanospheres. While previous investigations showed that toxicity of Ag nanoparticles can be explained by the presence of Ag⁺ in solution of silver nanoparticles, our results demonstrate that the harmful effects of nanosilver may be associated with silver nanoparticles themselves than with ionic silver released into solution.

The enthalpies of vaporisation of ionic liquids: new measurements and predictions

The enthalpies of vaporisation, Δ(vap)H(298), of seven ionic liquids (ILs) (four imidazoliums, a pyridinium, a phosphonium and an isouronium) have been determined by temperature programmed desorption using line of sight mass spectrometry. They were: 1-ethyl-3-methylimidazolium bis(pentafluoroethyl)phosphinate, [C(2)C(1)Im][PO(2)(C(2)F(5))(2)]; 1-butyl-3-methylimidazolium octylsulfate, [C(4)C(1)Im][C(8)OSO(3)]; 1-butyl-3-methylimidazolium tetrafluoroborate, [C(4)C(1)Im][BF(4)]; 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, [C(6)C(1)Im][FAP]; 1-butylpyridinium methylsulfate, [C(4)Py][C(1)OSO(3)]; trihexyl(tetradecyl)phosphonium tetrafluoroborate, [P(6,6,6,14)][BF(4)] and O-ethyl-N,N,N',N'-tetramethylisouronium trifluoromethanesulfonate, [C(2)(C(1))(4)iU][TfO]. The values were found to be consistent with a previously proposed, predictive, model in which Δ(vap)H(298) is decomposed into a Coulombic component (computable from the IL density) and van der Waals components from the anion and cation. Two previously predicted values of Δ(vap)H(298) were found to be within 6 kJ mol(-1) of the measured experimental values. Values for the van der Waals components are tabulated for eleven cations and twelve anions. Predictions are made for Δ(vap)H(298) for 13 ILs with as yet unmeasured Δ(vap)H(298) values (using experimental molar volumes), and for a further 44 ILs using estimated molar volumes.

Pd-Fe nanoparticles stabilized by chitosan derivatives for perchloroethene dechlorination

A series of chitosan-stabilized Pd-NZVI (nano-zero-valent-iron) catalysts for dechlorination with variation in their composition and in the nature of the polymer has been prepared. The synthesis procedures and palladium and chitosan contents were optimized. It was demonstrated by the XPS method that Fe and Pd in Fe-Pd/chitosan samples exist in the metallic state. The positive shift of the binding energy as compared with the bulk metal shows that the iron metal in the surface layers exists as very small nanoparticles. The prepared materials were characterized also by the XAS method. The presence of O and N atoms in the first coordination shell of the central Fe atom in the Fe-Pd/chitosan samples certifies the binding of the Fe metal particles with the chitosan surface via OH and NH(2) groups. The samples are characterized by the high stability of the nanoparticles as compared to unstabilized Pd-NZVI. The materials were tested to evaluate their catalytic activity in the perchloroethene (PCE) dechlorination reaction. Some samples of chitosan-stabilized Pd-NZVI revealed a good performance in PCE degradation as compared to unstabilized Pd-NZVI.

Reaction products and transformations of intermediates in the aqueous-phase reforming of sorbitol

Aqueous phase reforming of sorbitol over Pt supported on an alumina catalyst is investigated, in order to identify the intermediates involved in the transformation of the initial feed. Parameters such as the sorbitol feed rate and temperature are studied. To identify the intermediates, an approach based on analysis of the gas and liquid phases as well as the total carbon content was developed. According to analysis by gas chromatography combined with mass spectrometry of volatile substances collected with solid-phase microextraction, over 260 compounds are involved in the transformation of sorbitol. Of these, 50 of the major products are identified with high reliability. It is shown that a great variety of compounds, bearing different functionalities, form part of the reaction network. The formation of the majority of identified compounds is explained and a reaction network for the formation of sorbitol and intermediate molecules transformation is proposed.

Peculiarities of adsorption of organic compounds and water on silicas with bonded polyfluoroalkyl groups

The adsorption isotherms of benzene revealed the low adsorption potential of polyfluoroalkyl silicas compared with both initial silica and hexadecyl silica. Hydrophobicity of all modified silicas, measured by water adsorption, was rather close at p/p(s)=1 and was significantly different in the initial p/p(s) region: polyfluoroalkyl silicas did not nearly adsorb water but alkyl silica did it gradually. Thermodynamic parameters of adsorption of organic compounds of different nature were studied at a zero surface coverage by gas chromatography (GC). The high enough contributions of specific interactions as well as polar molecular group increments to the Gibbs adsorption energy were found to be characteristic of polyfluoroalkyl silica. The selectivity of polyfluoroalkyl silicas and the commonly used fluorinecontaining liquid stationary phase for GC (OV-210) toward homologous ethers, esters, and alcohols was comparable in most cases. GC data, IR spectra, and adsorption measurements were in good agreement with each other. It was shown that residual SiOH-groups of silica do not nearly take part in the adsorption process because they are effectively screened by the attached organic groups.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.