611 research outputs found
Semiconductor nanocrystals/M(II)-phthalocyanine heterojunctions:spectroscopic and photoelectrochemical properties
No full textMechanics of active mechano-chemical responsive polymers
No full textThe need for smart materials in advanced applications, has promoted significantly
the research in the field of responsive (or active) materials. They are capable of some physical
response to external stimuli, such as temperature, pH, light, mechanical stress, etc. so they can
adapt themselves to the surrounding environment. In the present paper, we propose a
mechanical model to describe the response of polymers containing mechanically responsive
molecules (mechanophores), having the ability to assume two distinct geometrically stable
configurations under mechanical actions or due to a change of the environment’s pH. When
linked to the polymer’s chains, under a proper mechanical stress, they switch from one state to
the other, triggering a macroscopic deformation of the material. Such an internal deformation,
driven by the mechanophores’ activation, can be exploited to get a desired functionality of the
polymer. Our model starts from the mechanical behavior at the microscopic level, and through
the mechanics of a single chain and chain statistics, it is scaled-up to the (mesoscopic)
continuum level. An energy-based approach is adopted: the free energy W is obtained by
adding up the contribution of the network deformation (), of the mixing term related to the
solvent uptake () and of the switching of the hosted responsive molecules ().
Numerical simulations demonstrate that the material response under chemical or mechanical
stimuli, shows a permanent deformation due to the activation of the switchable molecules,
enabling the design of smart self-adaptive polymers
Mechanics and physics of the light-driven response of hydrogels
No full textHydrogels are versatile and environmentally sensitive materials having appealing and tunable physical-chemical-mechanical properties, similar to those encountered in natural living tissues, which enable their use in a wide range of applications, especially in the biomedical field.
In the present study, we investigate the temperature-driven responsiveness of one class of elastomeric gels, namely poly-N-isopropylacrylamide (pNIPAm), that allows for temperature-controlled swelling. In particular, we consider the mechanical behavior of temperature-sensitive hydrogels in which the temperature variation is the result of light-thermal conversion enabled by nanoparticles embedded in the material. Relying on a theoretical multi-physics-based model describing light diffusion, heat generation and transfer, fluid absorption, and mechanics, the morphing response of hydrogel elements is investigated. The complex interplay between fluid uptake (swelling) and mechanical deformation taking place at different temperatures is investigated. In particular, the light-driven swelling response of hydrogel under a time-dependent light stimulus is studied. It is shown that the self-cooling of the material influences the material responsiveness. Accordingly, we demonstrate the interplay between the generated and the dispersed heat, which is a key aspect for an efficient design of tunable devices and materials
Photoelectrochemical investigation on heterojunctions based on M(II)phthalocyanine and nanocrytalline ZnO
No full textPhotochemical sensitisation process at photosynthetic pigments/Q-sized colloidal semiconductor hetero-junctions
No full textElectrodes based on Q-sized ZnO and TiO2, synthesised by non-hydrolytic routes, were prepared and characterised. The nanostructured electrodes were modified with photosynthetic pigments, namely, chlorophyll a, carotenoids and their mixture, to probe the photochemical sensitisation process. The photocurrent response of the hetero-junctions and the current–potential (I–V) characteristics of the sensitised electrodes are presented for different dyes. The Q-sized semiconductor sensitised electrodes showed different behaviour when compared to correspondent commercial oxides. Co-sensitisation acted by chlorophyll a and carotenoids on nanostructured electrodes was found to greatly enhance the photocurrent generation
Photoelectrochemical study on photosynthetic pigments-sensitized nanocrystalline ZnO films
No full textHetero-structures formed by quantum-sized ZnO nanocrystals and photosynthetic pigments were prepared by adsorbing either chlorophyll
a, carotenoids or their mixture onto a film of organic-capped ZnO nanoparticles. Photoelectrochemical measurements were comparatively
performed on both bulk and nanocrystalline ZnO films after dye-covering in order to probe the photosensitization process occurring at the
hetero-junction. The photoconversion process was found to be greatly enhanced at the nanocrystalline electrodes upon sensitization with a
dye mixture. The sensitization process is discussed on the basis of the aggregation state of chlorophyll a, and of the specific photoprotective
action played by carotenoids
Photoelectrochemical properties of hybrid junctions based on zinc phthalocyanine and semiconducting colloidal nanocrystals
No full textIn this paper, a photoelectrochemical study of hetero-junctions formed by zinc phthalocyanine (ZnPc) and semiconductor oxide nanocrystals
(NCs), is reported. To this purpose, thin films composed of either size- and shape-controlled ZnO or TiO2 NCs, synthesized by both hydrolytic
and non-hydrolytic colloidal methods, were investigated as photo-anodes with ZnPc as the sensitizer. The effects of the oxide nature, of the
nanocrystal shape and surface chemistry, and of the modality of photo-anode preparation on the resulting photoelectrochemical response were
evaluated. In general, the photoactivity was found to be significantly enhanced when ZnO NCs were used as compared to TiO2 NCs. In the latter
case, the hetero-junctions based on non-hydrolytically prepared TiO2 provided remarkably lower photocurrents with respect to those formed by
its hydrolytically synthesized analogous. Moreover, a slight improvement of photoactivity was observed if spherical TiO2 NCs were replaced by
rod-like particles. Finally, as opposed to expectations, photo-anodes deposited from NC-ZnPc blended solutions exhibited a photoelectrochemical
response comparable to that of sensitized films prepared by layer-by-layer procedure
Photoelectrochemical properties of Zn(II) phthalocyanine/ZnO nanocrystals heterojunctions: nanocrystal surface chemistry effect
No full textHetero-junctions prepared by deposition of unsubstituted Zn(II) phthalocyanines (Zn(II)Pc) onto a film of colloidal ZnO
nanocrystals, were studied. Photoelectrochemical measurements were performed on the sensitized nanocrystalline ZnO films
deposited onto optically transparent electrodes, to characterize the photoactivity of the heterojunction. A comparison between
ZnO nanocrystals prepared by using a hydrolytic and non-hydrolytic route was performed in order to investigate the effect of
nanocrystal surface chemistry on the photoelectrical response. The photoactivity was found to be significantly enhanced when
non-hydrolytically prepared nanocrystals were used to form the heterojunction
Amino-grafted mesoporous MCM-41 and SBA-15 recyclable adsorbents: Desert-rose-petals-like SBA-15 type as the most efficient to remove azo textile dyes and their mixture from water
No full textAmino-grafted Mobil Composition of Matter N. 41 (MCM-41/NH2) and Santa Barbara Amorphous (SBA-15/NH2) type mesoporous adsorbents were successfully used and compared in this work to remove azo dyes (and their mixture) from highly colored solutions. This paper reports a very fast removal and recycle (in 5 min) of great amounts of textile dyes (about the 100%) by materials characterized by high adsorption/desorption capacities. A qmax ≈ 250 mg/g for each adsorption cycle, that should be potentially increase to ≈ 1250 mg/g, under appropriate experimental conditions, was found for the proposed adsorbents. The UV–Vis absorption spectra of dyes were used to support this finding, determining the rate of adsorption. Several parameters affecting the adsorption process were investigated: the contact time, dyes solution pH values and amount of the adsorbent materials, ranging from 0.4 mg to 12 mg, and dyes (5 × 10−5 M and 1 × 10−5 M). Further, the Nitrogen adsorption/desorption isotherms, SAXS patterns, TG analyses, Zeta-potential measurements and microscopic imaging techniques, such as SEM and TEM, were used to detail the nature of interaction between dyes and adsorbents, and to investigate the morphology and the mesoporous array of the amino grafted MCM-41 and SBA-15
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