Efficient adsorption and photocatalytic degradation of Congo red onto hydrothermally synthesized NiS nanoparticles

The influence of the length of the cation alkyl chain on the dispersibility by ultrasonic treatment of TiO₂ nanopowders in hydrophilic imidazolium-based room temperature ionic liquids was studied for the first time by dynamic light scattering and advanced rheology. TiO₂ nanopowders had been synthesized by chemical vapor synthesis (CVS) under varied conditions leading to two different materials. A commercial nanopowder had been used for comparison. Characterizations had been done using transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Primary particle sizes were about 6 and 8 nm for the CVS-based and 26 nm for the commercial materials. The particle size distribution in the dispersion was strongly influenced by the length of the cation alkyl chain for all the investigated powders with different structural characteristics and concentrations in the dispersion. It was found that an increase of the alkyl chain length was beneficial, leading to a narrowing of the particle size distribution and a decrease of the agglomerate size in dispersion. The smallest average nanoparticle sizes in dispersion were around 30 nm. Additionally, the surface functionality of the nanoparticles, the concentration of the solid material in the liquid, and the period of ultrasonic treatment control the dispersion quality, especially in the case of the ionic liquids with the shorter alkyl chain. The influence of the nanopowders characteristics on their dispersibility decreases considerably with increasing cation alkyl chain length. The results indicate that ionic liquids with adapted structure are candidates as absorber media for nanoparticles synthesized in gas phase processes to obtain liquid dispersions directly without redispergation.     

In situ bioconjugation—Novel laser based approach to pure nanoparticle-conjugates

The generation and characterization of nanoparticulate carrier systems is important for drug delivery, biosensing and in vivo or in vitro diagnostics. Conventional nanoparticle generation is based on chemical synthesis methods requiring time intensive reaction and additive design for each material. Successive purification and surface functionalisation is often required after the nanoparticle generation to achieve pure nanoparticle-bioconjugates. We established a novel single step method, which allows the generation of pure nanoparticles and their in situ conjugation with biomolecules bearing electron donating moieties using pulsed laser ablation in liquids. For comparison between unspecific binding and binding through strong dative bonds (here: S-Au), we applied this preparation method to the conjugation of gold nanoparticles with unmodified and thiolated oligonucleotides. In order to determine optimal parameters (laser pulse energy, focus diameter), the influence on productivity of nanoparticle generation and their interaction with oligonucleotides is studied. We report quenching of nanoparticle growth and modification of the surface plasmon resonance as evidence of a successful functionalisation. Their stability in ionic solutions is evidenced with relevance to biological and medical assays. Negligible differences between the two model bioconjugations evidence the universality of the established in situ bioconjugation method.     

Side-chain effects on the capacitive behaviour of ionic liquids in microporous electrodes

Classical density functional theory (cDFT) is used to investigate electrosorption of ionic liquids in porous electrodes within the framework of a coarse-grained model. The purpose of this study is to clarify the influence of the side alkyl chains of imidazolium cations on the electric double layer (EDL) capacitance that was studied in a number of recent investigations but with contradictory trends. For an ionic liquid near a planar electrode, cDFT predicts that the capacitance falls by extending the alkyl chain length of cations because neutral segments reduce the packing density of counterions thus the charge density. The side-chain effect is more complicated for ionic liquids in micropores owing to space-charge competition. Adding neutral segments to imidazolium cations always reduces the capacitance in cases where the surface electrical potential of micropores is sufficiently large. However, the capacitance shows a nonmonotonic dependence on the alkyl chain length at intermediate surface potentials. Surprisingly, addition of neutral segments to the cations has the most pronounced effect on the EDL capacitance in cases when the surface potential is positively charged. These findings challenge the conventional assumption that the alkyl side chains of imidazolium ions only negatively impact ionic liquid performance in charge storage.     

Dispersions of silica nanoparticles in ionic liquids investigated with advanced rheology

The colloidal stabilities of dispersions of unmodified and surface-functionalized SiO₂ nanoparticles in hydrophobic and hydrophilic imidazolium-based ionic liquids were studied with advanced rheology at three temperatures (25, 100, and 200 °C). The rheological behavior of the dispersions was strongly affected by the ionic liquids hydrophilicity, by the nanoparticles surface, by the concentration of the nanoparticles in the dispersion as well as by the temperature. The unmodified hydrophilic nanoparticles showed a better compatibility with the hydrophilic ionic liquid. The SiO₂ surface functionalization with hydrophobic groups clearly improved the colloidal stability of the dispersions in the hydrophobic ionic liquid. The temperature increase was found to lead to a destabilization in all studied systems, especially at higher concentrations. The results of this study imply that ionic liquids with tailored properties could be used in absorbers directly after reactors for gas-phase synthesis of nanoparticles or/and as solvents for their further surface functionalization without agglomeration or aggregation.     

Parametric analysis of the growth of colloidal ZnO nanoparticles synthesized in alcoholic medium

The growth kinetics of nanosized ZnO was studied considering the influence of different parameters (mixing degree, temperature, alcohol chain length, reactant concentration and Zn/OH ratios) on the synthesis reaction and modelling the outputs using typical kinetic growth models, which were then evaluated by means of a sensitivity analysis. The Zn/OH ratio, the temperature and the alcohol chain length were found to be essential parameters to control the growth of ZnO nanoparticles, whereas zinc acetate concentration (for Zn/OH = 0.625) and the stirring during the ageing stage were shown to not have significant influence on the particle size growth. This last operational parameter was for the first time investigated for nanoparticles synthesized in 1-pentanol, and it is of outmost importance for the implementation of continuous industrial processes for mass production of nanosized ZnO and energy savings in the process. Concerning the nanoparticle growth modelling, the results show a different pattern from the more commonly accepted diffusion-limited Ostwald ripening process, i.e. the Lifshitz–Slyozov–Wagner (LSW) model. Indeed, this study shows that oriented attachment occurs during the early stages whereas for the later stages the particle growth is well represented by the LSW model. This conclusion contributes to clarify some controversy found in the literature regarding the kinetic model which better represents the ZnO NPs’ growth in alcoholic medium.     

Insight into the activity of efficient acid–base bifunctional catalysts for the coupling reaction of CO2

The fixation of carbon dioxide with epoxide catalysed by a series of carboxylic acidic functionalised ionic liquids (ILs) catalysts is investigated by density functional theory method. Except for the catalysts reported by the experiment, the catalytic activity of a new designed catalyst (4c see Scheme 1) is also explored. These ILs are categorised into four groups according to the different cation structures and number of functional groups. The effects of different chain length, anion, and cation structure on the catalytic activity are explored. The elongation of alkyl chain length in cation will increase the product yield, while increasing the chain bulk has almost negligible effect on the enhancement of catalytic activity. Utilisation of imidazole group as the cation is better than pyridine group. And the cation with two functional groups will have a better catalytic activity than that with one functional group.     

Effect of Different Ionic Surfactants on the Structural,Photophysical, and Morphological Properties of Water-Based P3HT:PCBM Nanoparticle Dispersions and Films

Aqueous suspensions of composite nanoparticles of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) are fabricated by miniemulsion method using three different ionic surfactants. The aim is to study how the length and conformation of the surfactants alkyl chains affect the properties of the nanoparticles. While the morphology and dimensions of the nanoparticles are similar, UV–vis spectroscopy evidences that the internal aggregation and ordering of the P3HT chains varies within the three nanoparticle formulations. The surfactant with branched alkyl chains promote the highest degree of ordering of P3HT chains in the nanoparticles (leading to increased conjugation length). In contrast, the lowest ordering is found for the nanoparticles with the surfactant having the shortest linear alkyl chain. The optical/structural properties of nanoparticles are partially retained in the films. Besides, the surfactant with branched alkyl chains favors the strongest coalescence of nanoparticles in the thin film, promoting a further ordering of the polymeric chains in the most external shell of the nanoparticles as evidenced by steady-state and time-resolved UV–vis spectroscopy and confocal fluorescence microscopy. These findings might guide the engineering of new surfactants for composite nanoparticles for optoelectronic applications.     

Theoretical investigation of imidazolium based ionic liquid/alcohol mixture: a molecular dynamic simulation

In this work, molecular dynamic simulation of the mixture of imidazolium based ionic liquids with alcohols is implemented in order to investigate mixing excess properties and some structural and physical properties of the mixture. Excess volumes and enthalpies are evaluated for 11 different mole fractions of ionic liquids at each 0.1, in the range of 0 to 1. Radial distribution function, cohesive energy density, potential of mean force, solvation energy, and diffusion coefficient are reported and analysed. The effects of the cationic alkyl chain length, in comparison with changes of the anions, on these properties are reported. Results reveal that the methanol molecule participates with its hydrophilic characteristics in the mixing process and tends to aggregate around anion part of the ionic liquids, especially in the case of Cl.     

Chemical sensing based on the plasmonic response of nanoparticle aggregation: anion sensing in nanoparticles stabilized by amino-functional ionic liquid

We report the synthesis, characterization and modellization of optical anion sensors based on gold nanoparticles (Au NPs) stabilized by amino-functional imidazolium ionic liquids (AFIL). The addition of different salts results in anion exchange of the imidazolium ionic liquid stabilizer leading to a change in the optical response of the original nanoparticle aqueous solution. In all cases except with dodecylbenzenesulfonic acid sodium salt, a sufficient amount of salt concentration (5 times larger than equimolar) leads to the appearance of an absorption band between 600 and 700 nm in the ultravioletvisible (UV-vis) spectrum. The presence of the salt produces aggregation of the particles that localise the optical response and produce a large spectral red shift. Transmission electron microscopy images demonstrated that this optical change was due to the aggregation of the nanoparticles. We simulate the optical response of both situations, before and after salt addition, and interpret the experimental observations in terms of the different response of metallic single nanoparticles and nanoparticle aggregates. Theoretical calculations for single nanoparticle and single nanoparticle dimers demonstrate that the colour change is not due to the enlargement or structural changes of the Au NPs, but due to the formation of NP aggregation. These results show the potential of nanoparticle plasmonics to perform effective chemical sensing.     

Ionic liquids: Liquid structure

The objective of this paper is the elaboration of liquid structure model for ionic liquids (IL) with cation:anion ratio 1:1. Described model consists of ionic and alkyl domains. The ionic domain is neutral. It has octupole structure: 4 cations and 4 anions are distributed in cube vertexes. The alkyl domains are formed by alkyl chains of cations. Elaborated model explains properties of IL: low melting points, hygroscopicity (including hydrophobic IL), and viscosity.     

Chemical sensing based on the plasmonic response of nanoparticle aggregation: Anion sensing in nanoparticles stabilized by amino-functional ionic liquid

We report the synthesis, characterization and modellization of optical anion sensors based on gold nanoparticles (Au NPs) stabilized by amino-functional imidazolium ionic liquids (AFIL). The addition of different salts results in anion exchange of the imidazolium ionic liquid stabilizer leading to a change in the optical response of the original nanoparticle aqueous solution. In all cases except with dodecylbenzenesulfonic acid sodium salt, a sufficient amount of salt concentration (5 times larger than equimolar) leads to the appearance of an absorption band between 600 and 700 nm in the ultravioletvisible (UV-vis) spectrum. The presence of the salt produces aggregation of the particles that localise the optical response and produce a large spectral red shift. Transmission electron microscopy images demonstrated that this optical change was due to the aggregation of the nanoparticles. We simulate the optical response of both situations, before and after salt addition, and interpret the experimental observations in terms of the different response of metallic single nanoparticles and nanoparticle aggregates. Theoretical calculations for single nanoparticle and single nanoparticle dimers demonstrate that the colour change is not due to the enlargement or structural changes of the Au NPs, but due to the formation of NP aggregation. These results show the potential of nanoparticle plasmonics to perform effective chemical sensing.     

Physicochemical characterization of paramagnetic ionic liquids 1‐vinyl‐3‐alkylimidazolium tetrahalogenidoferrate(III) [VRIM][FeClmBr4 − m]

Using microwave‐assisted synthesis method, a series of paramagnetic ionic liquids comprising 1‐vinyl‐3‐alkylimidazolium VRIM⁺ cation and tetrahalogenidoferrate (III) FeCl_mBr_{4 ? m}^? anion were designed and synthesized. The structure was analyzed using ¹H NMR and Raman spectroscopy. Ultraviolet–visible absorption spectra, thermal stability, magnetic susceptibility, viscosity, ionic conductivity, and solubility were characterized. Results show that elongation of the alkyl chain leads to replacement of bromides with a small amount of chlorides in the anion, shifting of UV maximum absorption peaks to shorter wavelengths, reduction of ionic conductivity, and solubility in polar solvents, as well as increase in fluidity, magnetic susceptibility, and solubility in nonpolar solvents. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanoparticle composites: FePt with wide-band-gap semiconductor

We present a simple way to synthesize FePt and ZnO (wide-band-gap semiconductor) nanoparticle composites. The FePt nanoparticles were fabricated using the method reported by Sun et al. By controlling the heating rate, 3 nm FePt nanoparticles were synthesized. Well-dispersed FePt and ZnO nanoparticle composites were prepared by further adding zinc acetate and oleyl amine into the 3 nm FePt nanoparticle dispersion. By controlling the molar ratio of the FePt and zinc acetate, FePt and ZnO nanoparticle composites with different FePt particle fractions were obtained. The intensity of photo luminescence spectra of the nanoparticle composites increases very much with decreasing FePt particle fraction, whereas the peak position shifts a little. After annealing at 550 °C for half an hour, the nanoparticle composites become magnetically hard or semi-hard with coercivity much dependent on the FePt particle volume fraction. The coercivity of the composites increases with annealing temperature. The composites hold the promise of applications in new generation recording and/or optical devices.     

ZnO-ionic liquid nanostructures

The mixture of nanostructures derived from the surface interactions and reactivity of ZnO nanoparticles with the room-temperature ionic liquid (IL1) 1-hexyl, 3-methylimidazolium hexafluorophosphate has been studied. Results are discussed on the basis of transmission electron microscopy (TEM) observations, energy dispersive spectroscopy (EDS) analysis, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) determinations. Size and morphology changes in ZnO nanoparticles by surface modification with IL1 are observed. ZnF₂ crystalline needles due to reaction with the hexafluorophosphate anion are also formed.     

Amine-capped gold nanoparticles: reaction steps during the synthesis and the influence of the ligand on the particle size

Alkylamine-capped gold nanoparticles were synthesised using the Leff method. In order to investigate the influence on the complexes formed during the synthesis and the final size of the protected nanoparticles the chain length of the stabilizing ligands varied. Phase transfer and amine complex formation were studied in solution with X-ray absorption spectroscopy. The phase transfer complexes retain the quadratic planar conformation whilst all alkyl amines form a linear coordinated gold(I) complex. After reduction, the particles were characterised in solution with EXFAS, UV–Vis spectroscopy, and compared to TEM measurements. The size of the particles was determined from the coordination number of the first gold shell. The position of the UV–Vis plasmon band and the distance of the first gold shell were used to qualitatively compare the effects of the ligands on the particle size. The size of the particles decreases with increasing chain length.     

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH₃CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH₃CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH₃CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν₁ (CD₃ ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of alkyl chain length in protic ionic liquids: an AIMD perspective

In this study we have explored, by means of ab initio molecular dynamics, a subset of three different protic ionic liquids (ILs). We present both structural and dynamical information of the liquid state of these compounds as revealed by accurate ab initio computations of the interactions. Our analysis figures out the presence of a strong hydrogen bond network in the bulk state, that is more stable in those ILs characterised by a longer alkyl side chain. Indeed it becomes more long-lasting passing from ethyl ammonium to butyl ammonium, owing to the hydrophobic effects stemming from alkyl chain contacts. Furthermore, the relative free energy landscape of the cation–anion interaction exhibits a progressively deeper well as the side chain of the cation gets longer. The hydrogen bond interaction, as already mentioned in previous works, leads to loss of degeneracy of the asymmetric stretching vibrations of the nitrate anions. The resulting frequency splitting between the two normal modes is about 90 cm^?1.     

Hybridization of surface-modified metal nanoparticles and a resin

Mercapto-terminated linear polymers, which were prepared by a reversible addition-fragmentation chain transfer (RAFT) technique, were used to modify metal nanoparticle surfaces. Au and Ag nanoparticles which are approximately 3–6 nm were used. This modification resulted in easy dispersion of the nanoparticles in polymer resins by simple mixing. The quality of the dispersion was confirmed by UV–Vis spectroscopy and transmission electron microscopy.     

Sonochemical synthesis, photocatalytic activity and optical properties of silica coated ZnO nanoparticles

In this paper, we report the synthesis of silica coated ZnO nanoparticles by ultrasound irradiation of a mixture of dispersion of ZnO, tetraethoxysilane (TEOS), and ammonia in an ethanol-water solution medium. The silica coating layer formed at the initial TEOS/ZnO loading of 0.8 for 60 min ultrasonic irradiation was uniform and extended up to 3 nm from the ZnO surface as revealed from HR-TEM images. Silica coated ZnO nanoparticles demonstrated a significant inhibition of photocatalytic activity against photodegradation of methylene blue dye in aqueous solution. The effects of silica coating on the UV blocking property of ZnO nanoparticles were also studied.     

Transforming single domain magnetic CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles from hydrophobic to hydrophilic by novel mechanochemical ligand exchange

Single-phase uniform-sized (~9 nm) cobalt ferrite (CFO) nanoparticles have been synthesized by hydrothermal synthesis using oleic acid as a surfactant. The as-synthesized oleic acid-coated CFO (OA-CFO) nanoparticles were well dispersible in nonpolar solvents but not dispersible in water. The OA-CFO nanoparticles have been successfully transformed to highly water-dispersible citric acid-coated CFO (CA-CFO) nanoparticles using a novel single-step ligand exchange process by mechanochemical milling, in which small chain citric acid molecules replace the original large chain oleic acid molecules available on CFO nanoparticles. The OA-CFO nanoparticle’s hexane solution and CA-CFO nanoparticle’s water solution remain stable even after 6 months and show no agglomeration and their dispersion stability was confirmed by zeta-potential measurements. The contact angle measurement shows that OA-CFO nanoparticles are hydrophobic whereas CA-CFO nanoparticles are superhydrophilic in nature. The potentiality of as-synthesized OA-CFO and mechanochemically transformed CA-CFO nanoparticles for the demulsification of highly stabilized water-in-oil and oil-in-water emulsions has been demonstrated.