Extraction of silver(i) from aqueous solutions in the absence and presence of copper(ii) with a methimazole-based ionic liquid

The ionic liquid (IL) 2-butylthiolonium bis(trifluoromethanesulfonyl)amide, [mimSBu][NTf₂], facilitates the efficient extraction of silver(i) from aqueous media via interaction with both the cation and anion components of the IL. Studies with a conventional aqueous-IL two phase system as well as microextraction of silver(i) by a thick IL film adhered to an electrode monitored in situ by cyclic voltammetry, established that [mimSBu][NTf₂] can extract electroactive silver(i) ions from an aqueous solution. The pH of the aqueous phase decreases upon addition of [mimSBu]⁺, which is attributed to partial release of the hydrogen attached to the N(3) nitrogen atom of the imidazolium ring. The presence of silver(i) further increase the acidity of the aqueous phase as a consequence of coordination with the IL cation component. Voltammetric and ¹H and ¹³C NMR techniques have been used to establish the nature of the silver(i) complexes extracted, and show that the form of interaction with the IL differs from that outlined previously for the extraction of copper(ii). Insights on the competition established when silver(i) is extracted in the presence of copper(ii) are provided. Finally, it is noted that metallic silver can be directly electrodeposited at the electrode surface after extraction of silver(i) into [mimSBu][NTf₂] and that back extraction of silver(i) into aqueous media is achieved by addition of an acidic aqueous solution.

Performance evaluation of different ultrafiltration membranes for the reclamation and reuse of secondary effluent

This study investigates and compares the performance of two different types of ultrafiltration (UF) membranes in the recovery of water from secondary treated wastewater. Filtration experiments were carried out on a pilot scale cross-flow unit using synthetic wastewater similar to the quality of secondary treated wastewater by varying the operating parameters such as transmembrane pressure (TMP), feed composition and membrane configuration. The filtration experiments demonstrated that the flux recovery through spiral polymeric UF membrane was more sensitive to the variation in TMP compared to the tubular ceramic UF membrane over the range of TMP studied. The resistance in series model was used for the evaluation of the resistance to the permeate flux. The fouling resistance, particularly irreversible resistance compared to reversible resistance plays a major role in the total resistance for the tubular ceramic membrane. In contrast clean membrane resistance is the major contributor for the total resistance of the spiral polymeric membrane. Finally, the effectiveness of the filtration treatment was determined by evaluating the rejection coefficients for various pollution indices of the wastewater. Significant differences in the performance of the membrane types were observed which are likely to impact on the selection, operation and maintenance of the membrane system.

Diatoms : self assembled silica nanostructures, and templates for bio/chemical sensors and biomimetic membranes

In this review we highlight recent advances in the understanding of biosilica production, biomodification of diatom frustules and their subsequent applications in bio/chemical sensors, and as a model membrane for filtration and separation.

Optical phase change at the interface between mica and thin silver film

We describe a simple experiment which allows unequivocal determination of optical phase change upon reflection of light at the mica-silver interface. While the physical origin of such a phase change at the dielectric-metal interface is well understood to lie in absorption of electromagnetic energy by the metal, inconsistency and ambiguity has persisted as to what its sign and magnitude should be in the field of thin film optics. Most commonly, it has been assigned to be negative for mathematical convenience or just arbitrarily. Our finding shows that with the convention exp(-iωt) for time dependence of the electromagnetic wave, the phase change at the interface between mica and the thin silver film is necessarily positive and its magnitude falls between π and 3π/2 for silver thicknesses down to nanometres. This gives a physically reasonable correspondence to an increased equivalent thickness of the dielectric material, and it clarifies the assignment of interference orders in the harmonic series in a spectrum.

Drug release rate and anti-microbial effect of controlled-diffusion biopolymer membranes

In this study, a series of fibrous membranes made from cellulose acetate (CA) and polyester urethane (PEU) by co-electrospining or blend-electrospining were evaluated for drug release kinetics, in vitro anti-microbial activity and in vivo would healing performance when used as wound dressings. To stop common clinical infections, an antibacterial agent, Polyhexamethylene Biguanide (PHMB) was incorporated into e-spun fibres. The presence of CA in the wound healing membrane was found to improve hydrophilicity and permeability to air and moisture. The in vivo tests indicated that the addition of PHMB and CA considerably improved the wound healing efficiency. CA fibres became slightly swollen upon contacting with the wound exudates. It can not only speed up the liquid evaporation but also create a moisture environment for wound recovery. The drug release dynamics of membranes was controlled by the structure of membranes and component rations within membranes. The lower ration of CA:PEU retained the sound mechanical properties of membranes, and also reduced the boost release effectively and slowed down diffusion of antibacterial agent during in vitro tests. The controlled-diffusion membranes exert long-term anti-infective effect.

Toughening of a carbon-fibre composite using electrospun poly(Hydroxyether of Bisphenol A) nanofibrous membranes through inverse phase separation and inter-domain etherification

The interlaminar toughening of a carbon fibre reinforced composite by interleaving a thin layer (~20 microns) of poly(hydroxyether of bisphenol A) (phenoxy) nanofibres was explored in this work. Nanofibres, free of defect and averaging several hundred nanometres, were produced by electrospinning directly onto a pre-impregnated carbon fibre material (Toray G83C) at various concentrations between 0.5 wt % and 2 wt %. During curing at 150 °C, phenoxy diffuses through the epoxy resin to form a semi interpenetrating network with an inverse phase type of morphology where the epoxy became the co-continuous phase with a nodular morphology. This type of morphology improved the fracture toughness in mode I (opening failure) and mode II (in-plane shear failure) by up to 150% and 30%, respectively. Interlaminar shear stress test results showed that the interleaving did not negatively affect the effective in-plane strength of the composites. Furthermore, there was some evidence from DMTA and FT-IR analysis to suggest that inter-domain etherification between the residual epoxide groups with the pendant hydroxyl groups of the phenoxy occurred, also leading to an increase in glass transition temperature (~7.5 °C).

Kinetic effects of halide ions on the morphological evolution of silver nanoplates

Time-resolved extinction spectroscopy is employed to study the reaction kinetics in the shape-conversion reaction involving halide ions (including Cl-, Br- and I-) etching (sculpturing) silver nanoplates. A series of time-resolved extinction spectra are obtained during the in situ etching process and the evolution of surface plasmon resonance (SPR) of the silver nanoparticles is analyzed. Spectral analysis indicates that the conversion of nanoprisms starts simultaneously with the emergence of nanodisks when the halide ions are added. The etching rate of different halide ions is evaluated through the in-plane dipole resonance peak intensity of silver nanoplates vs. the reaction time (dI/dt). The relationship between the etching rate and the halide ion concentration shows that the halide ion etching reaction can be considered as a pseudo-first-order reaction. The effect of different halide ions on the shape-conversion of silver nanoplates is compared in detail. The activation energy of the etching reaction is calculated, which indicates that the etching ability of different halide ions is on the order of Cl - < I- < Br-.

Photochemical formation of silver nanodecahedra : structural selection by the excitation wavelength

Silver decahedra have been successfully synthesized with high yield via a photochemical reaction using blue light-emitting diodes (LEDs) as the exciting light source. The decahedra display distinct properties with respect to the ability of light scattering. The photochemical growth process of silver decahedra was monitored by both extinction and scattering spectral evolution. A suggested formation mechanism of silver decahedron is discussed.

Photoinduced shape conversion and reconstruction of silver nanoprisms

A series of shapes of silver nanoplates were achieved by adjusting the concentration of citrate in the colloid in the photoinduced process. The local surface plasmon resonance (LSPR) of the silver nanoplates could be tuned gradually in a range from 740 to 440 nm. In contrast, the LSPR band can be photomediated again to the long wavelength region within 620-690 nm only by adding more citrate to the colloidal system. The initial silver nanoprisms converted to the discal shape under the light effect. In this conversion, the coupling effect of the plasmon resonance and the light source speeds up the photothermal reaction. Subsequently, the reconstruction of silver nanoprisms from the nanodisks took place in the presence of more citrate through the photoconversion.

The facet selectivity of inorganic ions on silver nanocrystals in etching reactions

The facet selectivity of the halide ions and chlorauric acid for several shaped silver nanocrystals is presented in this paper. Two inorganic ions show different representations when they are used for etching silver nanocrystals in the self-sacrificial template reaction. The morphological changes of the silver nanocrystals indicate that the halide ions prefer to etch the (110) facets of silver nanocrystals, while in the chlorauric acid etching reaction, gold first modifies the (110) facets and then lets chlorauric acid etch the (111) facets instead. The selective facet etching on individual nanoparticles in the solution phase has crucial significance in the control-synthesis of nanocrystals and the facet asymmetric reaction.

Real-time, in-situ, extinction spectroscopy studies on silver-nanoseed formation

In this paper, real-time extinction spectroscopy was employed to analyze in situ the fast formation process of silver seeds. The influencing factors for silver-seed formation, including the concentration of the reducer (NaBH 4), the amount of stabilizer (citrate), and the addition procedure of NaBH4, were evaluated. The configuration of the surface plasmon resonance (SPR) spectra of silver nanoparticles, which reflected the morphology of the produced silver seeds, was found to be distinctly affected by the NaBH4 concentration. Homogeneous silver nanoparticles were obtained when the added NaBH4 was lower in concentration than 2.00 mM. In contrast, higher concentrations of reducing agent (>3.00 mM NaBH4) resulted in uneven silver nanoparticles. Mie theory was applied to clarify the correlation of the SPR and the size of the silver seeds. Repeated additions of a small amount of the reducing agent could increase the monodispersity and isotropy of silver seeds. Real-time extinction spectroscopy is a convenient technique that achieves the in-situ and nondestructive measurement of intermediates in the formation process of silver nanoseeds.