Search

Layered double hydroxides (LDHs) are 2D ionic lamellar nanomaterials, which attract increasing interest for applications in different fields. This paper shows that their morphology is strongly affected by the microstructure of the substrate on which they grow. Zn–Al LDHs were grown in the same conditions on Al substrates with different microstructural features obtained from cold-rolled sheets by annealing at 265 °C for increasing soaking time up to 1 h. LDH morphology was then investigated through scanning electron microscopy observations. The homogeneous distribution of petals on the substrate surface mainly depends on grain size distribution. A bimodal grain size distribution in the substrate leads to the formation of petal clusters and a not complete covering of the surface. In the case of grains of large size the nucleation sites are the dislocations forming the walls of the cells, while owing to their low density, the dislocations inside the grains are not a relevant factor in determining the LDH morphology.

The fluorescence quenching effect of unfolded-fullerene nanoparticles (UFNPs) in the presence of Cu2+ ions in water solution has been investigated for a broad range of fluorophore/quencher concentrations. The experimental Stern-Volmer plot exhibited a nonlinear behaviour with an initial upward curvature even though carbon nanoparticles are known to form stable complexes with metal ions and thus a dominant static quenching with a linear plot is expected according to the classical Stern-Volmer equation. A generalized model for static quenching, applicable to any value of fluorophore/quencher concentrations, provided a very good fit with the experimental data without the need to introduce any second-order effect, such as in the sphere of action model or diffusion-limited processes. Moreover, by changing the dilution of the UFNP solution, we could study how the quenching ratio depended on the fluorophore concentration, whereas it is predicted to be constant by the standard model. In addition to providing a significant test of the nonlinear model for static quenching, we believe this study could help find the best parameters for the optimization of sensitivity and signal-to-noise ratio in applications such as fluorescence sensing.

We have realized a 3D substrate for surface-enhanced Raman scattering (SERS) sensor with DELIL (Double Exposure Laser Interference Lithography) technique and silver nanoparticles (Ag-NPs) functionalized with an appropriate aptamer. The 3D substrates were obtained by means of soft mold technique in thin layer of sol-gel Ti/TMSPM on silicon substrate using intermediate stamp fabricated in a photosensitive material. The stamp was in turn produced with a Lloyd's mirror set up by means of double exposition (Ar+ laser at 364 nm, 23 mW) of a photopolymerizable thin film at two mutually orthogonal orientation.The obtained 3D gratings have regular cross-weave texture with holes and pillars. The Ag-NPs were deposited by drop-casting on the 3D substrates and they arranged themselves inside the holes. This controlled Ag-NPs distribution allows the system to be a potential candidate for a good SERS sensor. The easy replication of the 3D substrates from a single stamp makes this technique attractive for applications in analytic and environmental fields.

We investigated the adsorption of heavy metal ions on a nanostructured coating of zinc-aluminum layered double hydroxides (Zn-Al LDHs) grown on aluminum foam by one-step hydrothermal process. This approach aimed to increase the interactive surface and provide a more practical medium for removal of toxic heavy metals from aqueous media. The foam coated with LDH was characterized by using scanning electron microscopy and X-ray diffraction. After immersion in a copper-rich water solution, X-ray photoelectron spectroscopy demonstrated the occurrence of adsorbed copper on the LDH-coated foam with two oxidation states: particles of metallic copper Cu(0)with oxidized surface Cu+1. X-ray diffraction showed the presence of Cu(+2)in the LDH structure.

Zn Al Layered Double Hydroxide (LDH) films were grown on aluminum substrates with different anions by a one-step, hydrothermal process at 80 °C, in which the metal substrate acts as both reactant and support. Since the films are made of partially-oriented nanoplatelets with controllable size and density, this approach can be a promising strategy for the fabrication of functionalized 3D electrodes and patterns on any surface. The presence of the different anions was confirmed by XPS measurements. Electrochemical Impedance Spectroscopy measurements were performed in order to study the electrical behavior of the films, with different inorganic anions intercalated in the LDH interlamellar space. The values of ionic conductivity are correlated to the anion type and the growth time of the films. F− intercalated LDHs present a higher conductivity than those with chloride and nitrate anions, which might be related to the lower hydration of the latter. Growth times around 8 h provided the best trade-off between shorter times, which affected the reproducibility of results, and longer periods, which induced formation of aggregates with a resulting lower conductivity.

Metal nanoclusters (MNCs) are small aggregates of metal atoms with a mean diameter up to 2 nm, that when excited by electromagnetic radiation of suitable energy present an intense florescence. This optical property can be exploited in many fields such as bioimaging, drug delivery and optical sensing in environmental monitoring. In the present work, we synthesized silver nanoclusters (AgNCs) in water starting from AgNO3 and exploiting poly (methacrylic acid) (PMAA) as capping agent. The reduction of the silver ions Ag(I) to Ag(0) was promoted by the exposition of the solution to UV light radiation for 6 minutes. We studied the UV-Vis absorption and the fluorescence spectra for different pH values. The morphological characterization of the solution was accomplished by Transmission Electron Microscopy (TEM) and the statistical analysis showed that the mean diameter of the AgNCs was around 2 nm for the solution at pH = 4 which presented also the strongest fluorescence. Moreover, we studied the time stability of the absorption and fluorescence spectra. AgNCs stored in the dark at 4 °C were stable for more than 60 days. A possible application of the synthesized AgNCs deals with water monitoring by optical sensing based on the change of the fluorescence property in presence of heavy metal ions. Preliminary investigations show a high sensitivity to Pb(II) ions.Metal nanoclusters (MNCs) are small aggregates of metal atoms with a mean diameter up to 2 nm, that when excited by electromagnetic radiation of suitable energy present an intense florescence. This optical property can be exploited in many fields such as bioimaging, drug delivery and optical sensing in environmental monitoring. In the present work, we synthesized silver nanoclusters (AgNCs) in water starting from AgNO3 and exploiting poly (methacrylic acid) (PMAA) as capping agent. The reduction of the silver ions Ag(I) to Ag(0) was promoted by the exposition of the solution to UV light radiation for 6 minutes. We studied the UV-Vis absorption and the fluorescence spectra for different pH values. The morphological characterization of the solution was accomplished by Transmission Electron Microscopy (TEM) and the statistical analysis showed that the mean diameter of the AgNCs was around 2 nm for the solution at pH = 4 which presented also the strongest fluorescence. Moreover, we studied the time stability ...

Graphene quantum dots (GQDs) have recently been proposed as fluorescent sensors for metal ions dissolved in water. The physical origin of this fluorescence is still not completely clear, therefore further studies on GQDs and their properties are required. Graphene-like quantum dots were prepared by oxidation and unfolding of commercial buckminsterfullerene. This process was carried out by a modified Hummers method. After dialysis, the solution was diluted with deionized water to obtain the reference solution for optical measurements. Part of the solution was dried to obtain the unfolded fullerene powder. The metal ions were allowed to interact with GQDs by adding the metal-salt water solution to the stock solution of unfolded fullerene. The properties of GQDs before and after incorporation of metal ions (Hg, Cd, Pb, Cu, Ni and As) were characterized by using X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy, UV–vis and fluorescent spectroscopies. In XPS, a particular attention was given to the analysis of photoemission C 1 s and Auger C KVV spectra in order to determine the carbon electronic configuration and its changes after incorporation of metal ions into GQDs. Obtained quantum dots were composed of graphene with oxidized borders. Optical measurements showed that the interaction with metal ions was changing the fluorescence intensity and optical absorbance, with different characteristics for each distinct ionic species. This behavior could be used for a selective multiple sensor detecting different heavy metals in water solutions.

We have synthesized fluorescent and stable silver nanoclusters (AgNCs) capped with poly (methacrylic acid), PMAA, by UV irradiation process. The NCs are well dispersed in aqueous solution and present a uniform distribution with an average dimension of 1.45 ± 0.26 nm. The fluorescence excited at 340 nm was found to be sensitive to the presence of heavy metal ions in solution. In particular, a peculiar fluorescence enhancement was detected upon interaction with lead(II) ions. A linear behavior of the fluorescence intensity as a function of the Pb2+ concentration was measured and a detection limit of 60 nM was estimated. A possible mechanism of the interaction between AgNCs and metal ions is discussed.

We have synthesized two-dimensional carbon nanoparticles by oxidative unfolding of C60 fullerene and demonstrated that the selective sensitivity of this material to the presence of Cu2+ and Pb2+, resulting in variations of the fluorescence intensity and optical absorbance, is related to nanoparticle aggregation processes. This mechanism occurs through coordination of the metal ions and, above a certain ion concentration, leads to precipitation of the carbon material that reduces the metal content in solution. The effect has been characterized by optical measurements while Atomic Absorption Spectroscopy have been carried out for a precise assessment of the real ion concentration in solution.We have synthesized two-dimensional carbon nanoparticles by oxidative unfolding of C60 fullerene and demonstrated that the selective sensitivity of this material to the presence of Cu2+ and Pb2+, resulting in variations of the fluorescence intensity and optical absorbance, is related to nanoparticle aggregation processes. This mechanism occurs through coordination of the metal ions and, above a certain ion concentration, leads to precipitation of the carbon material that reduces the metal content in solution. The effect has been characterized by optical measurements while Atomic Absorption Spectroscopy have been carried out for a precise assessment of the real ion concentration in solution.

Layered double hydroxides (LDHs) are anionic clays composed by host layers of positively charged metal hydroxide, in which anions are intercalated to neutralize the charge of the positive layers. Because of the positive charge of the structure and because of their properties of anion exchanges, different anions can be intercalated into the structure. In recent years the ionic conductivity of LDHs was studied for use as the anode material in lithium-ion batteries or PVA/LDH hybrid membranes for fuel cells. However, such studies have reported very low values of the electrical conductivity that is less than 10-3 S cm-1 near room temperature. However, the ion conductivities of LDHs depends on the intercalated anion species and may be affected by difference in the synthesis condition. Moreover, the anion conductivity increases with increasing interlayer distance and as more water is adsorbed by LDH. Within this framework, we have intercalated two ionic liquids, tetramethylammonium hydroxide (TMAH) and 1-buthyl-3-methylimidazolium hydrogen sulfate (Bmim-HSO4) in the interlamellar space with the purpose of increasing the ionic conductivity and decreasing the dependence from the water content. LDH was prepared using the co-precipitation method with controlled pH. The introduction of IL was performed by the intercalation methods. The increase of conductivity was around an order of magnitude in the case of Bmim-HSO4. The LDH-IL can be an interesting material to prepare composite membranes for electrochemical applications.

Meso-tetraphenylporphyrin connected with a ferrocene molecule in the beta-position of the macrocycle through a triple carbon@carbon bond has been bound to carbon spheres using the Prato@Maggini reaction. The ethynyl or/and phenylene ethynylene subunits were chosen as a linking bridge to give a high conjugation degree between the donor (i. e., ferrocene), the photoactive compound (i. e., porphyrin), and the acceptor (i. e., carbon spheres). The molecular bridges have been directly linked to the beta-pyrrole positions of the porphyrin ring, generating a new example of a long-range donor@acceptor system. Steady-state fluorescence studies together with Raman and XPS measurements helped understanding the chemical and physical properties of the porphyrin ring in the new adduct. The spectroscopic characteristics were also compared with those obtained from a similar compound bearing fullerene instead of carbon spheres. &nbsp

A novel type of graphene-like quantum dots, synthesized by oxidation and cage-opening of C60buckminsterfullerene, has been studied as a fluorescent and absorptive probe for heavy-metal ions. The lattice structure of such unfolded fullerene quantum dots (UFQDs) is distinct from that of graphene since it includes both carbon hexagons and pentagons. The basic optical properties, however, are similar to those of regular graphene oxide quantum dots. On the other hand, UFQDs behave quite differently in the presence of heavy-metal ions, in that multiple sensitivity to Cu2+, Pb2+and As(III) was observed through comparable quenching of the fluorescent emission and different variations of the transmittance spectrum. By dynamic light scattering measurements and transmission electron microscope (TEM) images we confirmed, for the first time in metal sensing, that this response is due to multiple complexation and subsequent aggregation of UFQDs. Nonetheless, the explanation of the distinct behaviour of transmittance in the presence of As(III) and the formation of precipitate with Pb2+require further studies. These differences, however, also make it possible to discriminate between the three metal ions in view of the implementation of a selective multiple sensor.

A novel type of graphene-like quantum dots, synthesized by oxidation and cage-opening of C60 buckminsterfullerene, has been studied as a fluorescent and absorptive probe for heavy-metal ions. The lattice structure of such unfolded fullerene quantum dots (UFQDs) is distinct from that of graphene since it includes both carbon hexagons and pentagons. The basic optical properties, however, are similar to those of regular graphene oxide quantum dots. On the other hand, UFQDs behave quite differently in the presence of heavy-metal ions, in that multiple sensitivity to Cu2+, Pb2+ and As(III) was observed through comparable quenching of the fluorescent emission and different variations of the transmittance spectrum. By dynamic light scattering measurements we confirmed, for the first time in metal sensing, that this response is due to multiple complexation and subsequent aggregation of UFQDs. Nonetheless, the explanation of the distinct behaviour of transmittance in the presence of As(III) and the formation of precipitate with Pb2+ require further studies. These differences, however, also make it possible to discriminate between the three metal ions in view of the implementation of a selective multiple sensor.

In this study, we have carried out a characterization of the quenching effect produced by some commonly encountered metal ions (Co2+, Cu2+, Ni2+, Pb2+, Cd2+, As5+) on the photoluminescence of water suspensions of open-cage fullerene quantum dots prepared with a modified Hummers method. The response to heavy-metal ions occurs through a selective quenching of the PL emission and modifications of the absorption spectrum.

The 2,12 pyrrole positions of meso-tetraphenylporphyrin were functionalized through triple carbon–carbon bonds by C60 and ferrocene giving new electron donor–acceptor triads which have been characterized and studied by photophysical methods. The fluorescence spectra of the new compounds have been compared to those previously reported for similar compounds giving as a result an increase of the quantum efficiency based on the larger separation of fullerene from the porphyrin ring. On the contrary the efficiency decreases with the presence of a phenylene spacer between ferrocene and the macrocycle.

CsPbBr3 and Cs4PbBr6 perovskite powders have been synthesized through a relatively simple low-temperature and low-cost method. Nanocrystalline films have also been deposited from solutions with four different molar compositions of binary salt precursors. Optical absorption, emission and excitation spectra have been performed in the UV-visible spectral range while X-ray diffraction (XRD) has been recorded to characterize the nanocrystal morphology for the different molar compositions. A preferential orientation of crystallites along the (024) crystalline plane has been observed as a function of the different deposition conditions in films growth. All the crystals show an absorption edge around 530 nm, Tauc plots of the absorption returned bandgaps ranging from 2.29 to 2.35 eV characteristic of CsPbBr3 phase. We attribute the UV absorption band peaked at 324 nm to the fundamental band-to-band transition for Cs4PbBr6. It was observed that the samples with the most ordered Cs4PbBr6 crystals exhibited the most intense emission of light, with a bright green emission at 520 nm, which are however due to the luminescence of the inclusion of CsPbBr3 nanoclusters into the Cs4PbBr6. The latter shows instead an intense UV emission. Differently, the pure CsPbBr3 powder did not show any intense fluorescent emission. The excitation spectra of the green fluorescent emission in all samples closely resemble the CsPbBr3 absorption with the peculiar dip around 324 nm as expected from density of state calculations reported in the literature.