Cationic imprinting of Pb(II) within composite networks based on bovine or fish chondroitin sulfate.

Imprinting chondroitin sulfate (CS)/silica composites with Pb(II) and Cu(II) cations was explored with CS of bovine and different fish species origin. The process was based on the assumption that particular arrangements of the linear CS chains in aqueous solution, induced so as to accommodate cross complexation with the cations, would be embodied into a tridimensional matrix created through an organoalkoxysilane sol-gel scheme. The presence of Cu(II) in the synthesis of the composites did not result in the production of significantly stronger Cu(II)-oriented binding arrangements, and therefore, the imprinting was not successful. Inversely, for Pb(II), the materials obtained exhibited a "memory" effect for the Pb(II) ions, expressed in the observation of stronger (13%-44%) binding as compared to the nonimprinted counterparts, and increased selectivity (1.5-2 folds) against Cd(II). The imprinting features observed were dependent on the CS source. However, it was not possible to identify, among a set of their properties (carboxylate and sulfate abundance, percent of disulfated units, 4S/6S ratio, and molecular weight), any that correlated directly with the observed imprinting features. The augmented selectivity provided by the cation-imprinting process may be advantageous in areas such as analytical separation, remediation, purification, sensing, and others, particularly in those cases where a certain cation is of special interest within a mixture of them.

Graphene-poly(nickel complex) as novel electrochromic nanocomposite for the fabrication of a robust solid-state device.

An electrochromic nanocomposite based on a nickel-salen polymeric film - poly[Ni(3-Mesalen)], Mesalen=N,N'-bis(3-methylsalicylideneiminate) - and graphene nanoplatelets (GFNPs) with enhanced electrochromic stability was successfully prepared by anodic electropolymerization. Although the electrochemical processes typical of the polymer film were not changed by the presence of graphene, higher electroactive surface coverages could be obtained for nanocomposite films, which suggest the incorporation of GFNPs into the polymeric network. The nanocomposite showed multi-electrochromic behavior, with color changes between yellow (reduced state) and green (oxidized state). The inclusion of GFNPs into the poly[Ni(3-Mesalen)] structure accelerates the switching process, with the response time for green coloration decreasing by 50.7% and for yellow coloration by 60.0%, for films prepared with 30 electropolymerization cycles. In terms of electrochemical stability, after 10,000 electrochemical cycles the loss of charge was 7% for the graphene nanocomposite. The nanocomposite film was used as electrochromic material to assemble a flexible solid-state electrochromic device (ECD), which exhibited an outstanding electrochemical stability - only 3% of charge loss after 15days of continuous activity.

Multicolour Electrochromic Film Based on a TiO2@poly[Ni(salen)] Nanocomposite with Excellent Electrochemical Stability.

We report the electrochromic properties of a polymeric nanocomposite prepared by potentiodynamic deposition of transition-metal complex [Ni(3-Mesalen)], designated as [1], in the presence of TiO2 nanoparticles (NPs) with an average size of 9.7 ± 1.1 nm. Entrapment of TiO2 NPs in the poly[1] matrix was confirmed by several techniques. The nanocomposite TiO2@poly[1] films showed similar electrochemical responses to the original (nanoparticle-free) poly[1] films, but with higher electroactive surface coverages (Γ), showing the advantage of the nanocomposite preparation. The results indicated that the electronic structure of poly[1] was retained in the nanocomposite; nonetheless, a lower ε value was obtained for the charge-transfer band of the former, revealing superior stability of the nanocomposite for ligand high oxidation states. The TiO2@poly[1] nanocomposite showed interesting color changes, from yellow (reduced state) to green and russet (oxidized states), with enhanced electrochemical stability, demonstrated by a charge loss of only 7.3% over ca. 10 000 redox cycles surpassing the original polymer film stability: the loss of electroactivity is a factor of ca. 2 less than for pristine poly[1]. Furthermore, an enhancement of 16.7% in the optical modulation (ΔOD = 0.48) was also observed for the nanocomposite, confirming the benefit of TiO2 incorporation into the EC properties of the original polymer film.

High-Performance Electrochromic Devices Based on Poly[Ni(salen)]-Type Polymer Films.

We report the application of two poly[Ni(salen)]-type electroactive polymer films as new electrochromic materials. The two films, poly[Ni(3-Mesalen)] (poly[1]) and poly[Ni(3-MesaltMe)] (poly[2]), were successfully electrodeposited onto ITO/PET flexible substrates, and their voltammetric characterization revealed that poly[1] showed similar redox profiles in LiClO4/CH3CN and LiClO4/propylene carbonate (PC), while poly[2] showed solvent-dependent electrochemical responses. Both films showed multielectrochromic behavior, exhibiting yellow, green, and russet colors according to their oxidation state, and promising electrochromic properties with high electrochemical stability in LiClO4/PC supporting electrolyte. In particular, poly[1] exhibited a very good electrochemical stability, changing color between yellow and green (λ = 750 nm) during 9000 redox cycles, with a charge loss of 34.3%, an optical contrast of ΔT = 26.2%, and an optical density of ΔOD = 0.49, with a coloration efficiency of η = 75.55 cm(2) C(-1). On the other hand, poly[2] showed good optical contrast for the color change from green to russet (ΔT = 58.5%), although with moderate electrochemical stability. Finally, poly[1] was used to fabricate a solid-state electrochromic device using lateral configuration with two figures of merit: a simple shape (typology 1) and a butterfly shape (typology 2); typology 1 showed the best performance with optical contrast ΔT = 88.7% (at λ = 750 nm), coloration efficiency η = 130.4 cm(2) C(-1), and charge loss of 37.0% upon 3000 redox cycles.

Novel layer-by-layer interfacial [Ni(salen)]-polyelectrolyte hybrid films.

A novel multilayer film containing a cationic phosphonium-derivatized Ni(salen)-type complex and poly(sodium-4-styrenesulfonate (NaPSS) was assembled onto quartz, mica, and metal surfaces using the layer-by-layer (LbL) technique. Spectroscopic (UV-vis) and gravimetric (QCM) responses for the multilayer films show regular stepwise growth and the signature of strong electrostatic interactions between the component layers. The gravimetric responses indicate the presence of substantial additional (net neutral) material in the PSS layers, which XPS shows is not polyelectrolyte or salt, so charge compensation is intrinsic; we deduce the presence of space-filling solvent. Direct electrostatic interaction of the two-component layers is enhanced by a secondary noncovalent interaction between the delocalized pi-systems of the two components. Permeability of the film to the redox probe [Fe(CN)(6)](3-/4-) was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Qualitatively similar results were obtained in the absence and presence of a precursor PSS/PAH multilayer, but with a general shift in kinetic and diffusional processes to longer time scales (lower frequencies) in the presence of the precursor layer and with increasing numbers of PSS/[Ni(salen)] bilayers. Quantitatively, the EIS data were interpreted using a capillary membrane model (CMM) to yield values of coverage, apparent charge transfer resistance, double-layer capacitance, pore size, and diffusion coefficient. The coverage values were consistent with a model in which there are no preferential growth sites and the surface charge density is independent of the number of bilayers.

Electrochemical impedance spectroscopy of polyelectrolyte multilayer modified gold electrodes: influence of supporting electrolyte and temperature.

Electrochemical impedance spectroscopy and cyclic voltammetry are employed to characterize poly(styrenesulfonate)/poly(allylamine hydrochloride) multilayers assembled onto cysteamine-modified gold surfaces. The influence of the supporting electrolyte and temperature on the impedance response is studied because of both its practical interest and the need to test further the capillary membrane model recently developed by Barreira et al. [J. Phys. Chem. B 2004, 108, 17973]. The results obtained are interpreted quite satisfactorily in terms of this model, thus providing additional support to its usefulness for the description of ionic transport through polyelectrolyte multilayers. It is observed that the nature of the supporting electrolyte affects the film resistance and the electrode coverage. The temperature dependence of the diffusion coefficient is shown to follow the Arrhenius law, and the activation energy is estimated as 61 kJ/mol. Experiments with a large number of layers are also included to show that the impedance response of the multilayer then resembles that of a homogeneous membrane.