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Papers by maurizio muniz-miranda

Research paper thumbnail of Fabrication and characterization of Ag/Pd colloidal nanoparticles as stable platforms for SERS and catalytic applications

Materials Chemistry and Physics, 2015

ABSTRACT

Research paper thumbnail of Vibrational spectra and normal coordinate analysis of p-bis(dimethyl-hydroxy-silil)benzene-d0 and -d4

Spectrochimica acta, 1983

ABSTRACT

Research paper thumbnail of SERS, XPS and DFT investigation on palladium surfaces coated with 2,2′-bipyridine monolayers

Applied Surface Science, 2018

Research paper thumbnail of DFT and TD-DFT Study of the Chemical Effect in the SERS Spectra of Piperidine Adsorbed on Silver Colloidal Nanoparticles

Nanomaterials

The surface-enhanced Raman scattering (SERS) spectra of piperidine adsorbed on silver/chloride co... more The surface-enhanced Raman scattering (SERS) spectra of piperidine adsorbed on silver/chloride colloids were studied by a combined density functional theory (DFT)/time dependent DFT (TD-DFT) approach. The mechanism of chemical enhancement on the Raman signals is due to at least two contributions: the first comes from the changes in the molecular force constants and the dynamic polarizabilities of the normal modes, when the molecule is chemisorbed. DFT calculations satisfactorily reproduce the SERS spectra of piperidine adsorbed on silver, showing that the species formed on the silver particle is a complex formed by a deprotonated piperidine linked to a silver cation. A second contribution to the SERS chemical enhancement is due to a resonance Raman effect occurring when the wavelength of the Raman excitation falls within the electronic excitation band of the molecule/metal complex. Actually, the SERS spectra of piperidine show a significant dependence on the wavelength of the laser ...

Research paper thumbnail of Bifunctional Fe3O4/Ag nanoparticles obtained by two-step laser ablation in pure water

Journal of Colloid and Interface Science, 2017

Hypothesis: Bimetallic nanoparticles made of iron oxide and Ag could be fabricated by pulsed lase... more Hypothesis: Bimetallic nanoparticles made of iron oxide and Ag could be fabricated by pulsed laser ablation of iron and silver targets in pure water by a two-step route. These nanoparticles could exhibit both magnetic and plasmonic properties. Experiments: Bimetallic nanoparticles were fabricated by using a focused Nd:YAG nanosecond laser source emitting a 1064 nm wavelength radiation and characterized with f-potential, Dynamic Light Scattering (DLS), UV-vis absorption, Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM), Energy Dispersive X-ray Spectrometry (EDX), and Selected Area Electron Diffraction (SAED). The magnetic character of the nanoparticles was ascertained by observing attraction by a magnet and complete removing from the water environment, while their SERS (surface-enhanced Raman scattering) response was checked by decorating them with 2,2 0-bipyridine as molecular reporter and performing Raman tests with green (514.5 nm) and far-red (785 nm) excitation wavelengths. Findings: The observed magnetic attraction was due to magnetite (Fe 3 O 4), the only ferromagnetic iron oxide form evidenced by the characterization tests in the aqueous colloidal system, where silver nanoparticles were also embedded. UV-vis and SERS spectra confirmed the presence of nanostructured silver as plasmonic constituent of the fabricated metal nanoparticles.

Research paper thumbnail of DFT and TD-DFT Study of the Chemical Effect in the SERS Spectra of Piperidine Adsorbed on Silver Colloidal Nanoparticles

Nanomaterials, Aug 24, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Can DFT Calculations Provide Useful Information for SERS Applications?

Molecules

Density functional theory (DFT) calculations allow us to reproduce the SERS (surface-enhanced Ram... more Density functional theory (DFT) calculations allow us to reproduce the SERS (surface-enhanced Raman scattering) spectra of molecules adsorbed on nanostructured metal surfaces and extract the most information this spectroscopy is potentially able to provide. The latter point mainly concerns the anchoring mechanism and the bond strength between molecule and metal as well as the structural and electronic modifications of the adsorbed molecule. These findings are of fundamental importance for the application of this spectroscopic technique. This review presents and discusses some SERS–DFT studies carried out in Italy as a collaboration between the universities of Modena and Reggio-Emilia and of Florence, giving an overview of the information that we can extract with a combination of experimental SERS spectra and DFT modeling. In addition, a selection of the most recent studies and advancements on the DFT approach to SERS spectroscopy is reported with commentary.

Research paper thumbnail of Magneto-Plasmonic Colloidal Nanoparticles Obtained by Laser Ablation of Nickel and Silver Targets in Water

The Journal of Physical Chemistry C, 2017

Stable magneto-plasmonic nanoparticles in colloidal suspensions are fabricated by two-step nanose... more Stable magneto-plasmonic nanoparticles in colloidal suspensions are fabricated by two-step nanosecondpulsed laser ablation of nickel and silver targets in pure water and characterized by UV−visible absorption, Raman, X-ray photoelectron spectroscopic, and magnetic measurements, along with high-resolution electron microscopy analysis. These systems are constituted by a low-crystallinity matrix of ferromagnetic nickel hydroxide, where nickel oxide nanocrystals are embedded, with silver nanoparticles intimately linked to them. The surface enhanced Raman scattering activity is assessed by adsorption of adenine as probe ligand. Spectroscopic investigation and density functional theory calculations revealed that adenine is linked to nickel oxide, while nanosilver essentially plays the role of ensuring the Raman enhancement for the adsorbed organic ligand. Both magnetic and plasmonic properties allow using these nanostructured bimetallic platforms as catalysts in chemical reactions or nanosensors in biomedicine as well as in environmental research.

Research paper thumbnail of Spectroscopic and Computational Studies on Ligand-Capped Metal Nanoparticles and Clusters

Metal nanoparticles represent a bridge between single atoms and bulk materials, presenting peculi... more Metal nanoparticles represent a bridge between single atoms and bulk materials, presenting peculiar chemical and optical properties. Under irradiation with an appropriate electromagnetic wave, the conduction electrons do not oscillate freely, because they are trapped in the nanometric size of the metal particles, which exhibit collective excitations called “localized plasmons.” These latter are needed to promote enhancements for both the Raman signal and the fluorescence emission of molecules adhering to the metal surface, when the exciting radiation wavelengths match those of the plasmon bands. Hence, Raman enhancements up to 107 factors are generally observed for molecules adsorbed on silver or gold nanoparticles in the SERS (surface-enhanced Raman scattering) measurements. When, instead, metal particles have sizes below about 2 nm, they do not have metallic properties owing to the existence of discrete electronic energy levels and the loss of overlapping electronic bands. These m...

Research paper thumbnail of Spectroscopic and Microscopic Analyses of Fe3O4/Au Nanoparticles Obtained by Laser Ablation in Water

Nanomaterials, Jan 10, 2020

Magneto-plasmonic nanoparticles constituted of gold and iron oxide were obtained in an aqueous en... more Magneto-plasmonic nanoparticles constituted of gold and iron oxide were obtained in an aqueous environment by laser ablation of iron and gold targets in two successive steps. Gold nanoparticles are embedded in a mucilaginous matrix of iron oxide, which was identified as magnetite by both microscopic and spectroscopic analyses. The plasmonic properties of the obtained colloids, as well as their adsorption capability, were tested by surface-enhanced Raman scattering (SERS) spectroscopy using 2,2′-bipyridine as a probe molecule. DFT calculations allowed for obtaining information on the adsorption of the ligand molecules that strongly interact with positively charged surface active sites of the gold nanoparticles, thus providing efficient SERS enhancement. The presence of iron oxide gives the bimetallic colloid new possibilities of adsorption in addition to those inherent to gold nanoparticles, especially regarding organic pollutants and heavy metals, allowing to remove them from the aqueous environment by applying a magnetic field. Moreover, these nanoparticles, thanks to their low toxicity, are potentially useful not only in the field of sensors, but also for biomedical applications.

Research paper thumbnail of Palladium Oxide Nanoparticles: Preparation, Characterization and Catalytic Activity Evaluation

Coatings

Stable palladium oxide nanoparticles were prepared in aqueous suspension with a very simple proce... more Stable palladium oxide nanoparticles were prepared in aqueous suspension with a very simple procedure, by dissolving palladium nitrate in water at a concentration around 10−4 M. UV-visible absorption spectroscopy was adopted to follow the formation of these nanoparticles, which were characterized by TEM microscopy, along with XRD, XPS and Raman measurements. DFT calculations allowed to interpret the Raman data and to clarify the species present at the surface of the nanoparticles. The catalytic activity of the latter was evaluated by monitoring the reduction of p-nitrophenol to p-aminophenol. This investigation paves the way to the use of these colloidal nanoparticles in processes of heterogeneous catalysis, in particular those concerning the catalytic degradation of aromatic derivatives that represent a serious danger for the environment as pollutants, as in the case of p-nitrophenol.

Research paper thumbnail of Adsorption of Trans-Zeatin on Laser-Ablated Gold Nanoparticles for Transport into Plant Cells and Growth Stimulation

ACS Applied Nano Materials

Gold nanoparticles can serve as nanovectors for trans-zeatin, a natural cytokinin used in plant c... more Gold nanoparticles can serve as nanovectors for trans-zeatin, a natural cytokinin used in plant culture to stimulate growth and bud formation. Here, we have used Raman scattering, X-ray photoelectron spectroscopy, UV–vis absorption, transmission electron microscopy, and density functional theory calculations to explain the role of citrate anions in both the formation and the reactivity of the gold colloidal nanoparticles obtained by laser ablation and to go deeper inside into the interaction between metal and zeatin. In particular, the SERS (surface-enhanced Raman scattering) spectroscopy has been employed to study the adsorption of zeatin on different gold colloidal substrates. It is established that the molecule links to gold as tautomer N7(H), predominant in the aqueous suspension, in close similarity with adenine adsorbed on gold. Moreover, the laser ablation of a gold target in citrate solution results in small, stable, and reactive Au nanoparticles, able to transport zeatin inside plant cells, where...

Research paper thumbnail of A DFT Approach to the Surface-Enhanced Raman Scattering of 4-Cyanopyridine Adsorbed on Silver Nanoparticles

Nanomaterials

A Surface-Enhanced Raman Scattering (SERS) spectrum of 4-cyanopyridine (4CNPy) was recorded on si... more A Surface-Enhanced Raman Scattering (SERS) spectrum of 4-cyanopyridine (4CNPy) was recorded on silver plasmonic nanoparticles and analyzed by using Density Functional Theory (DFT) calculations. Two simple molecular models of the metal–4CNPy surface complex with a single silver cation or with a neutral dimer (Ag+–4CNPy, Ag2–4CNPy), linked through the two possible interacting sites of 4CNPy (aromatic nitrogen, N, and nitrile group, CN), were considered. The calculated vibrational wavenumbers and intensities of the adsorbate and the isolated species are compared with the experimental Raman and SERS results. The analysis of the DFT predictions and the experimental data indicates that 4CNPy adsorbs preferentially on neutral/charged active sites of the silver nanoparticles through the nitrogen atom of the aromatic ring with a perpendicular orientation.

Research paper thumbnail of SERS active Ag–SiO2 nanoparticles obtained by laser ablation of silver in colloidal silica

Beilstein Journal of Nanotechnology

Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver t... more Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver target in an aqueous colloidal dispersion of silica and examined by UV–vis absorption spectroscopy, transmission electron microscopy and Raman spectroscopy. The surface enhanced Raman scattering (SERS) activity of these nanocomposites was tested using 2,2’-bipyridine as a molecular reporter and excitation in the visible and near-IR spectral regions. The computational DFT approach provided evidence of ligand adsorption on positively charged adatoms of the silver nanostructured surface, in a very similar way to the metal/molecule interaction occurring in the corresponding Ag(I) coordination compound.

Research paper thumbnail of SERS, XPS and DFT Study of Xanthine Adsorbed on Citrate-Stabilized Gold Nanoparticles

Sensors

We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that ... more We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that is involved in important metabolic processes, on citrate-reduced gold colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS), absorption, and X-ray photoelectron spectroscopy (XPS) measurements, along with density functional theory (DFT) calculations. The citrate anions stabilize the colloidal suspensions by strongly binding the gold nanoparticles. However, these anions do not impair the adsorption of xanthine on positively-charged active sites present on the metal surface. We have obtained the Fourier transform (FT)-SERS spectra of adsorbed xanthine by laser excitation in the near infrared spectral region, where interference due to fluorescence emission does not usually occur. In fact, the addition of chloride ions to the Au/xanthine colloid induces the aggregation of the gold nanoparticles, whose plasmonic band is shifted to the near infrared region where there is...

Research paper thumbnail of Raman and Computational Study on the Adsorption of Xanthine on Silver Nanocolloids

ACS Omega

Xanthine is a nucleobase, deriving from adenine and guanine by deamination and oxidation processe... more Xanthine is a nucleobase, deriving from adenine and guanine by deamination and oxidation processes, which may deposit in the human body causing diseases, similar to uric acid. Here, we have investigated the adsorption of xanthine on silver colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS) with an exciting radiation in the near-infrared spectral region, where interference due to fluorescence does not occur, along with density functional theory calculations of molecule/metal model systems. By adopting a combined experimental and computational approach, we have identified the "marker" SERS bands of xanthine and the tautomer that preferentially binds the silver particles, as well as the molecular group involved in the interaction with metal. This investigation allows using the FT-SERS spectroscopy for biosensory and diagnostic purposes in body fluids, detecting abnormal levels of xanthine, and preventing metabolic diseases.

Research paper thumbnail of SERS and DFT investigation on push-pull molecules: 4-Dimethylamino- 4’-nitrostilbene adsorbed on silver colloidal nanoparticles

Research paper thumbnail of Spectroscopic and DFT investigation on the photo-chemical properties of a push-pull chromophore: 4-Dimethylamino-4′-nitrostilbene

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

4-Dimethylamino-4'-nitrostilbene (DANS), a π-conjugated push-pull molecule, has b... more 4-Dimethylamino-4'-nitrostilbene (DANS), a π-conjugated push-pull molecule, has been investigated by means of a combined spectroscopic and computational approach. When the Raman excitation is close to the visible electronic transition of DANS, vibrational bands not belonging to DANS appear in the spectra, increasing with the laser power. These bands are observed at room temperature in the solid phase, but not at low temperature or in solution, and we interpret them as due to a thermally-activated photoreaction occurring under laser irradiation in the visible spectral region. Density-functional calculations correctly reproducing the electronic and vibrational spectra of DANS, describe the charge-transfer process, indicate that an azo-derivative is the product of the photoreaction of DANS and provide a reasonable interpretation of this process.

Research paper thumbnail of Nanostructured carbon materials decorated with organophosphorus moieties: synthesis and application

Beilstein journal of nanotechnology, 2017

A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organoph... more A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organophosphorus moieties is presented. Three different triphenylphosphine oxide (TPPO) derivatives were used to decorate oxidized multiwalled carbon nanotubes (ox-MWCNTs) and graphene platelets (GPs). The TPPOs chosen bear functional groups able to react with the CNMs by Tour reaction (an amino group), nitrene cycloaddition (an azido group) or CuAAC reaction (one terminal C-C triple bond). All the adducts were characterized by FTIR, Raman spectroscopy, TEM, XPS, elemental analysis and ICP-AES. The cycloaddition of nitrene provided the higher loading on ox-MWCNTs and GPs as well, while the Tour approach gave best results with nanotubes (CNTs). Finally, we investigated the possibility to reduce the TPPO functionalized CNMs to the corresponding phosphine derivatives and applied one of the materials produced as heterogeneous organocatalyst in a Staudinger ligation reaction.

Research paper thumbnail of Antibacterial activity of silver nanoparticles obtained by pulsed laser ablation in pure water and in chloride solution

Beilstein Journal of Nanotechnology, 2016

Silver nanoparticles (AgNPs) have increasingly gained importance as antibacterial agents with app... more Silver nanoparticles (AgNPs) have increasingly gained importance as antibacterial agents with applications in several fields due to their strong, broad-range antimicrobial properties. AgNP synthesis by pulsed laser ablation in liquid (PLAL) permits the preparation of stable Ag colloids in pure solvents without capping or stabilizing agents, producing AgNPs more suitable for biomedical applications than those prepared with common, wet chemical preparation techniques. To date, only a few investigations into the antimicrobial effect of AgNPs produced by PLAL have been performed. These have mainly been performed by ablation in water with nanosecond pulse widths. We previously observed a strong surface-enhanced Raman scattering (SERS) signal from such AgNPs by “activating” the NP surface by the addition of a small quantity of LiCl to the colloid. Such surface effects could also influence the antimicrobial activity of the NPs. Their activity, on the other hand, could also be affected by o...

Research paper thumbnail of Fabrication and characterization of Ag/Pd colloidal nanoparticles as stable platforms for SERS and catalytic applications

Materials Chemistry and Physics, 2015

ABSTRACT

Research paper thumbnail of Vibrational spectra and normal coordinate analysis of p-bis(dimethyl-hydroxy-silil)benzene-d0 and -d4

Spectrochimica acta, 1983

ABSTRACT

Research paper thumbnail of SERS, XPS and DFT investigation on palladium surfaces coated with 2,2′-bipyridine monolayers

Applied Surface Science, 2018

Research paper thumbnail of DFT and TD-DFT Study of the Chemical Effect in the SERS Spectra of Piperidine Adsorbed on Silver Colloidal Nanoparticles

Nanomaterials

The surface-enhanced Raman scattering (SERS) spectra of piperidine adsorbed on silver/chloride co... more The surface-enhanced Raman scattering (SERS) spectra of piperidine adsorbed on silver/chloride colloids were studied by a combined density functional theory (DFT)/time dependent DFT (TD-DFT) approach. The mechanism of chemical enhancement on the Raman signals is due to at least two contributions: the first comes from the changes in the molecular force constants and the dynamic polarizabilities of the normal modes, when the molecule is chemisorbed. DFT calculations satisfactorily reproduce the SERS spectra of piperidine adsorbed on silver, showing that the species formed on the silver particle is a complex formed by a deprotonated piperidine linked to a silver cation. A second contribution to the SERS chemical enhancement is due to a resonance Raman effect occurring when the wavelength of the Raman excitation falls within the electronic excitation band of the molecule/metal complex. Actually, the SERS spectra of piperidine show a significant dependence on the wavelength of the laser ...

Research paper thumbnail of Bifunctional Fe3O4/Ag nanoparticles obtained by two-step laser ablation in pure water

Journal of Colloid and Interface Science, 2017

Hypothesis: Bimetallic nanoparticles made of iron oxide and Ag could be fabricated by pulsed lase... more Hypothesis: Bimetallic nanoparticles made of iron oxide and Ag could be fabricated by pulsed laser ablation of iron and silver targets in pure water by a two-step route. These nanoparticles could exhibit both magnetic and plasmonic properties. Experiments: Bimetallic nanoparticles were fabricated by using a focused Nd:YAG nanosecond laser source emitting a 1064 nm wavelength radiation and characterized with f-potential, Dynamic Light Scattering (DLS), UV-vis absorption, Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM), Energy Dispersive X-ray Spectrometry (EDX), and Selected Area Electron Diffraction (SAED). The magnetic character of the nanoparticles was ascertained by observing attraction by a magnet and complete removing from the water environment, while their SERS (surface-enhanced Raman scattering) response was checked by decorating them with 2,2 0-bipyridine as molecular reporter and performing Raman tests with green (514.5 nm) and far-red (785 nm) excitation wavelengths. Findings: The observed magnetic attraction was due to magnetite (Fe 3 O 4), the only ferromagnetic iron oxide form evidenced by the characterization tests in the aqueous colloidal system, where silver nanoparticles were also embedded. UV-vis and SERS spectra confirmed the presence of nanostructured silver as plasmonic constituent of the fabricated metal nanoparticles.

Research paper thumbnail of DFT and TD-DFT Study of the Chemical Effect in the SERS Spectra of Piperidine Adsorbed on Silver Colloidal Nanoparticles

Nanomaterials, Aug 24, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Can DFT Calculations Provide Useful Information for SERS Applications?

Molecules

Density functional theory (DFT) calculations allow us to reproduce the SERS (surface-enhanced Ram... more Density functional theory (DFT) calculations allow us to reproduce the SERS (surface-enhanced Raman scattering) spectra of molecules adsorbed on nanostructured metal surfaces and extract the most information this spectroscopy is potentially able to provide. The latter point mainly concerns the anchoring mechanism and the bond strength between molecule and metal as well as the structural and electronic modifications of the adsorbed molecule. These findings are of fundamental importance for the application of this spectroscopic technique. This review presents and discusses some SERS–DFT studies carried out in Italy as a collaboration between the universities of Modena and Reggio-Emilia and of Florence, giving an overview of the information that we can extract with a combination of experimental SERS spectra and DFT modeling. In addition, a selection of the most recent studies and advancements on the DFT approach to SERS spectroscopy is reported with commentary.

Research paper thumbnail of Magneto-Plasmonic Colloidal Nanoparticles Obtained by Laser Ablation of Nickel and Silver Targets in Water

The Journal of Physical Chemistry C, 2017

Stable magneto-plasmonic nanoparticles in colloidal suspensions are fabricated by two-step nanose... more Stable magneto-plasmonic nanoparticles in colloidal suspensions are fabricated by two-step nanosecondpulsed laser ablation of nickel and silver targets in pure water and characterized by UV−visible absorption, Raman, X-ray photoelectron spectroscopic, and magnetic measurements, along with high-resolution electron microscopy analysis. These systems are constituted by a low-crystallinity matrix of ferromagnetic nickel hydroxide, where nickel oxide nanocrystals are embedded, with silver nanoparticles intimately linked to them. The surface enhanced Raman scattering activity is assessed by adsorption of adenine as probe ligand. Spectroscopic investigation and density functional theory calculations revealed that adenine is linked to nickel oxide, while nanosilver essentially plays the role of ensuring the Raman enhancement for the adsorbed organic ligand. Both magnetic and plasmonic properties allow using these nanostructured bimetallic platforms as catalysts in chemical reactions or nanosensors in biomedicine as well as in environmental research.

Research paper thumbnail of Spectroscopic and Computational Studies on Ligand-Capped Metal Nanoparticles and Clusters

Metal nanoparticles represent a bridge between single atoms and bulk materials, presenting peculi... more Metal nanoparticles represent a bridge between single atoms and bulk materials, presenting peculiar chemical and optical properties. Under irradiation with an appropriate electromagnetic wave, the conduction electrons do not oscillate freely, because they are trapped in the nanometric size of the metal particles, which exhibit collective excitations called “localized plasmons.” These latter are needed to promote enhancements for both the Raman signal and the fluorescence emission of molecules adhering to the metal surface, when the exciting radiation wavelengths match those of the plasmon bands. Hence, Raman enhancements up to 107 factors are generally observed for molecules adsorbed on silver or gold nanoparticles in the SERS (surface-enhanced Raman scattering) measurements. When, instead, metal particles have sizes below about 2 nm, they do not have metallic properties owing to the existence of discrete electronic energy levels and the loss of overlapping electronic bands. These m...

Research paper thumbnail of Spectroscopic and Microscopic Analyses of Fe3O4/Au Nanoparticles Obtained by Laser Ablation in Water

Nanomaterials, Jan 10, 2020

Magneto-plasmonic nanoparticles constituted of gold and iron oxide were obtained in an aqueous en... more Magneto-plasmonic nanoparticles constituted of gold and iron oxide were obtained in an aqueous environment by laser ablation of iron and gold targets in two successive steps. Gold nanoparticles are embedded in a mucilaginous matrix of iron oxide, which was identified as magnetite by both microscopic and spectroscopic analyses. The plasmonic properties of the obtained colloids, as well as their adsorption capability, were tested by surface-enhanced Raman scattering (SERS) spectroscopy using 2,2′-bipyridine as a probe molecule. DFT calculations allowed for obtaining information on the adsorption of the ligand molecules that strongly interact with positively charged surface active sites of the gold nanoparticles, thus providing efficient SERS enhancement. The presence of iron oxide gives the bimetallic colloid new possibilities of adsorption in addition to those inherent to gold nanoparticles, especially regarding organic pollutants and heavy metals, allowing to remove them from the aqueous environment by applying a magnetic field. Moreover, these nanoparticles, thanks to their low toxicity, are potentially useful not only in the field of sensors, but also for biomedical applications.

Research paper thumbnail of Palladium Oxide Nanoparticles: Preparation, Characterization and Catalytic Activity Evaluation

Coatings

Stable palladium oxide nanoparticles were prepared in aqueous suspension with a very simple proce... more Stable palladium oxide nanoparticles were prepared in aqueous suspension with a very simple procedure, by dissolving palladium nitrate in water at a concentration around 10−4 M. UV-visible absorption spectroscopy was adopted to follow the formation of these nanoparticles, which were characterized by TEM microscopy, along with XRD, XPS and Raman measurements. DFT calculations allowed to interpret the Raman data and to clarify the species present at the surface of the nanoparticles. The catalytic activity of the latter was evaluated by monitoring the reduction of p-nitrophenol to p-aminophenol. This investigation paves the way to the use of these colloidal nanoparticles in processes of heterogeneous catalysis, in particular those concerning the catalytic degradation of aromatic derivatives that represent a serious danger for the environment as pollutants, as in the case of p-nitrophenol.

Research paper thumbnail of Adsorption of Trans-Zeatin on Laser-Ablated Gold Nanoparticles for Transport into Plant Cells and Growth Stimulation

ACS Applied Nano Materials

Gold nanoparticles can serve as nanovectors for trans-zeatin, a natural cytokinin used in plant c... more Gold nanoparticles can serve as nanovectors for trans-zeatin, a natural cytokinin used in plant culture to stimulate growth and bud formation. Here, we have used Raman scattering, X-ray photoelectron spectroscopy, UV–vis absorption, transmission electron microscopy, and density functional theory calculations to explain the role of citrate anions in both the formation and the reactivity of the gold colloidal nanoparticles obtained by laser ablation and to go deeper inside into the interaction between metal and zeatin. In particular, the SERS (surface-enhanced Raman scattering) spectroscopy has been employed to study the adsorption of zeatin on different gold colloidal substrates. It is established that the molecule links to gold as tautomer N7(H), predominant in the aqueous suspension, in close similarity with adenine adsorbed on gold. Moreover, the laser ablation of a gold target in citrate solution results in small, stable, and reactive Au nanoparticles, able to transport zeatin inside plant cells, where...

Research paper thumbnail of A DFT Approach to the Surface-Enhanced Raman Scattering of 4-Cyanopyridine Adsorbed on Silver Nanoparticles

Nanomaterials

A Surface-Enhanced Raman Scattering (SERS) spectrum of 4-cyanopyridine (4CNPy) was recorded on si... more A Surface-Enhanced Raman Scattering (SERS) spectrum of 4-cyanopyridine (4CNPy) was recorded on silver plasmonic nanoparticles and analyzed by using Density Functional Theory (DFT) calculations. Two simple molecular models of the metal–4CNPy surface complex with a single silver cation or with a neutral dimer (Ag+–4CNPy, Ag2–4CNPy), linked through the two possible interacting sites of 4CNPy (aromatic nitrogen, N, and nitrile group, CN), were considered. The calculated vibrational wavenumbers and intensities of the adsorbate and the isolated species are compared with the experimental Raman and SERS results. The analysis of the DFT predictions and the experimental data indicates that 4CNPy adsorbs preferentially on neutral/charged active sites of the silver nanoparticles through the nitrogen atom of the aromatic ring with a perpendicular orientation.

Research paper thumbnail of SERS active Ag–SiO2 nanoparticles obtained by laser ablation of silver in colloidal silica

Beilstein Journal of Nanotechnology

Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver t... more Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver target in an aqueous colloidal dispersion of silica and examined by UV–vis absorption spectroscopy, transmission electron microscopy and Raman spectroscopy. The surface enhanced Raman scattering (SERS) activity of these nanocomposites was tested using 2,2’-bipyridine as a molecular reporter and excitation in the visible and near-IR spectral regions. The computational DFT approach provided evidence of ligand adsorption on positively charged adatoms of the silver nanostructured surface, in a very similar way to the metal/molecule interaction occurring in the corresponding Ag(I) coordination compound.

Research paper thumbnail of SERS, XPS and DFT Study of Xanthine Adsorbed on Citrate-Stabilized Gold Nanoparticles

Sensors

We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that ... more We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that is involved in important metabolic processes, on citrate-reduced gold colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS), absorption, and X-ray photoelectron spectroscopy (XPS) measurements, along with density functional theory (DFT) calculations. The citrate anions stabilize the colloidal suspensions by strongly binding the gold nanoparticles. However, these anions do not impair the adsorption of xanthine on positively-charged active sites present on the metal surface. We have obtained the Fourier transform (FT)-SERS spectra of adsorbed xanthine by laser excitation in the near infrared spectral region, where interference due to fluorescence emission does not usually occur. In fact, the addition of chloride ions to the Au/xanthine colloid induces the aggregation of the gold nanoparticles, whose plasmonic band is shifted to the near infrared region where there is...

Research paper thumbnail of Raman and Computational Study on the Adsorption of Xanthine on Silver Nanocolloids

ACS Omega

Xanthine is a nucleobase, deriving from adenine and guanine by deamination and oxidation processe... more Xanthine is a nucleobase, deriving from adenine and guanine by deamination and oxidation processes, which may deposit in the human body causing diseases, similar to uric acid. Here, we have investigated the adsorption of xanthine on silver colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS) with an exciting radiation in the near-infrared spectral region, where interference due to fluorescence does not occur, along with density functional theory calculations of molecule/metal model systems. By adopting a combined experimental and computational approach, we have identified the "marker" SERS bands of xanthine and the tautomer that preferentially binds the silver particles, as well as the molecular group involved in the interaction with metal. This investigation allows using the FT-SERS spectroscopy for biosensory and diagnostic purposes in body fluids, detecting abnormal levels of xanthine, and preventing metabolic diseases.

Research paper thumbnail of SERS and DFT investigation on push-pull molecules: 4-Dimethylamino- 4’-nitrostilbene adsorbed on silver colloidal nanoparticles

Research paper thumbnail of Spectroscopic and DFT investigation on the photo-chemical properties of a push-pull chromophore: 4-Dimethylamino-4′-nitrostilbene

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

4-Dimethylamino-4'-nitrostilbene (DANS), a π-conjugated push-pull molecule, has b... more 4-Dimethylamino-4'-nitrostilbene (DANS), a π-conjugated push-pull molecule, has been investigated by means of a combined spectroscopic and computational approach. When the Raman excitation is close to the visible electronic transition of DANS, vibrational bands not belonging to DANS appear in the spectra, increasing with the laser power. These bands are observed at room temperature in the solid phase, but not at low temperature or in solution, and we interpret them as due to a thermally-activated photoreaction occurring under laser irradiation in the visible spectral region. Density-functional calculations correctly reproducing the electronic and vibrational spectra of DANS, describe the charge-transfer process, indicate that an azo-derivative is the product of the photoreaction of DANS and provide a reasonable interpretation of this process.

Research paper thumbnail of Nanostructured carbon materials decorated with organophosphorus moieties: synthesis and application

Beilstein journal of nanotechnology, 2017

A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organoph... more A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organophosphorus moieties is presented. Three different triphenylphosphine oxide (TPPO) derivatives were used to decorate oxidized multiwalled carbon nanotubes (ox-MWCNTs) and graphene platelets (GPs). The TPPOs chosen bear functional groups able to react with the CNMs by Tour reaction (an amino group), nitrene cycloaddition (an azido group) or CuAAC reaction (one terminal C-C triple bond). All the adducts were characterized by FTIR, Raman spectroscopy, TEM, XPS, elemental analysis and ICP-AES. The cycloaddition of nitrene provided the higher loading on ox-MWCNTs and GPs as well, while the Tour approach gave best results with nanotubes (CNTs). Finally, we investigated the possibility to reduce the TPPO functionalized CNMs to the corresponding phosphine derivatives and applied one of the materials produced as heterogeneous organocatalyst in a Staudinger ligation reaction.

Research paper thumbnail of Antibacterial activity of silver nanoparticles obtained by pulsed laser ablation in pure water and in chloride solution

Beilstein Journal of Nanotechnology, 2016

Silver nanoparticles (AgNPs) have increasingly gained importance as antibacterial agents with app... more Silver nanoparticles (AgNPs) have increasingly gained importance as antibacterial agents with applications in several fields due to their strong, broad-range antimicrobial properties. AgNP synthesis by pulsed laser ablation in liquid (PLAL) permits the preparation of stable Ag colloids in pure solvents without capping or stabilizing agents, producing AgNPs more suitable for biomedical applications than those prepared with common, wet chemical preparation techniques. To date, only a few investigations into the antimicrobial effect of AgNPs produced by PLAL have been performed. These have mainly been performed by ablation in water with nanosecond pulse widths. We previously observed a strong surface-enhanced Raman scattering (SERS) signal from such AgNPs by “activating” the NP surface by the addition of a small quantity of LiCl to the colloid. Such surface effects could also influence the antimicrobial activity of the NPs. Their activity, on the other hand, could also be affected by o...