Rosa Arrigo

Tuning the acid/base properties of nanocarbons by functionalization via amination

The surface chemical properties and the electronic properties of vapor grown carbon nanofibers (VGCNFs) have been modified by treatment of the oxidized CNFs with NH(3). The effect of treatment temperature on the types of nitrogen functionalities introduced was evaluated by synchrotron based X-ray photoelectron spectroscopy (XPS), while the impact of the preparation methods on the surface acid-base properties was investigated by potentiometric titration, microcalorimetry, and zeta potential measurements. The impact of the N-functionalization on the electronic properties was measured by THz-Time Domain spectroscopy. The samples functionalized via amination are characterized by the coexistence of acidic and basic O and N sites. The population of O and N species is temperature dependent. In particular, at 873 K nitrogen is stabilized in substitutional positions within the graphitic structure, as heterocyclic-like moieties. The surface presents heterogeneously distributed and energetically different basic sites. A small amount of strong basic sites gives rise to a differential heat of CO(2) adsorption of 150 kJ mol(-1). However, when functionalization is carried out at 473 K, nitrogen moieties with basic character are introduced and the maximum heat of adsorption is significantly lower, at approximately 90 kJ mol(-1). In the latter sample, energetically different basic sites coexist with acidic oxygen groups introduced during the oxidative step. Under these conditions, a bifunctional acidic and basic surface is obtained with high hydrophilic character. N-functionalization carried out at higher temperature changes the electronic properties of the CNFs as evaluated by THz-TDS. The functionalization procedure presented in this work allows high versatility and flexibility in tailoring the surface chemistry of nanocarbon material to specific needs. This work shows the potential of the N-containing nanocarbon materials obtained via amination in catalysis as well as electronic device materials.

Dynamic surface rearrangement and thermal stability of nitrogen functional groups on carbon nanotubes

Dynamic surface rearrangement and thermal stability of N-functional groups on carbon nanotubes (CNTs), obtained by functionalization of pristine CNTs with NH(3), were studied by temperature-programmed XPS and MS: a link between the stability of the functional group and decomposition temperature have been established and a conversion into graphitic nitrogen was observed.

Gold catalyzed liquid phase oxidation of alcohol: the issue of selectivity.

Commercial carbon nanotubes (CNTs) and carbon nanofibers (CNFs) modified in various ways at the surface have been used as supports for gold nanoparticles (AuNPs) in order to study their influence on the activity/selectivity of catalysts in the aqueous oxidation of alcohol. Particularly oxidative treatment was used to introduce carboxylic functionalities, whereas subsequent treatment with NH3 at different temperatures (473 K, 673 K and 873 K) produced N-containing groups leading to an enhancement of basic properties as the NH3 treatment temperature was increased. The nature of the N-containing groups changed as the temperature increased, leading to an increase in the hydrophobicity of the support surface. Similar Au particle size and similar textural properties of the supports allowed the role of chemical surface groups in both the activity and the selectivity of the reaction of glycerol oxidation to be highlighted. An increase of basic functionalities produced a consistent increase in the activity of the catalyst, which was correlated to the promoting effect of the basic support in the alcoholate formation and the subsequent C-H bond cleavage. The selectivity towards primary oxidation products (C3 compounds) was the highest for the catalysts treated with NH3 at 873 K, which presented the most hydrophobic surface. The same trend in the catalyst activity has been obtained in the aqueous benzyl alcohol base-free oxidation. As in the case of glycerol, the increasing of basicity and/or hydrophobicity increased the consecutive reactions.

In Situ Study of the Gas-Phase Electrolysis of Water on Platinum by NAP-XPS

Chasing down the active state: Near-ambient-pressure X-ray photoelectron spectroscopy was used to study the surface of a Pt electrode during the oxygen evolution reaction (OER). A hydrated Pt metal phase with dissolved oxygen in the near-surface region is OER-active and considered to be the precursor of the analytically detected PtO2 , which is in fact the deactivation product of the electrode.

Photoelectron Spectroscopy at the Graphene–Liquid Interface Reveals the Electronic Structure of an Electrodeposited Cobalt/Graphene Electrocatalyst

Electrochemically grown cobalt on graphene exhibits exceptional performance as a catalyst for the oxygen evolution reaction (OER) and provides the possibility of controlling the morphology and the chemical properties during deposition. However, the detailed atomic structure of this hybrid material is not well understood. To elucidate the Co/graphene electronic structure, we have developed a flow cell closed by a graphene membrane that provides electronic and chemical information on the active surfaces under atmospheric pressure and in the presence of liquids by means of X-ray photoelectron spectroscopy (XPS). We found that cobalt is anchored on graphene via carbonyl-like species, namely Co(CO)x , promoting the reduction of Co(3+) to Co(2+), which is believed to be the active site of the catalyst.

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H2O2

This work aims to clarify the nanostructural transformation accompanying the loss of activity and selectivity for the hydrogen peroxide synthesis of palladium and gold-palladium nanoparticles supported on N-functionalized carbon nanotubes. High-resolution X-ray photoemission spectroscopy (XPS) allows the discrimination of metallic palladium, electronically modified metallic palladium hosting impurities, and cationic palladium. This is paralleled by the morphological heterogeneity observed by high-resolution TEM, in which nanoparticles with an average size of 2 nm coexisted with very small palladium clusters. The morphological distribution of palladium is modified after reaction through sintering and dissolution/redeposition pathways. The loss of selectivity is correlated to the extent to which these processes occur as a result of the instability of the particle at the carbon surface. We assign beneficial activity in the selective hydrogenation of oxygen to palladium clusters with a modified electronic structure compared with palladium metal or palladium oxides. These beneficial species are formed and stabilized on carbons modified with nitrogen atoms in substitutional positions. The formation of larger metallic palladium particles not only reduces the number of active sites for the synthesis, but also enhances the activity for deep hydrogenation to water. The structural instability of the active species is thus detrimental in a dual way. Minimizing the chance of sintering of palladium clusters by all means is thus the key to better performing catalysts.

Characterization and use of functionalized carbon nanotubes for the adsorption of heavy metal anions

The Carbon nanotubes (CNTs) have been chemically functionalized with various oxygen-containing surface groups. The feature of abundant oxygen-containing surface functional groups on the functionalized CNTs is characterized by X-ray photoelectron spectroscopy and temperature- programmed desorption analysis. Results indicate that the functionalized CNTs have a superior adsorption capacity toward anionic chromate CrO4 2- , a typical toxic heavy metal ion in waste water, as compared with the unmodified ones. The excellent adsorption ability of CrO4 2- is at- tributed to the interaction of CrO4 2- with the surface oxygen-containing functional groups on the modified CNTs. The functionalized CNTs can be potentially used as an alternatively viable and promising adsorbent for the removal of heavy metal anions in waste water. 2- ; Adsorption; Chemically functionalization

Comprehensive evaluation of in vitro toxicity of three large-scale produced carbon nanotubes on human Jurkat T cells and a comparison to crocidolite asbestos

Abstract This study has evaluated the effects of three industrially relevant multi-walled carbon nanotubes (MWNTs) on human Jurkat T cells and compared them to those of crocidolite asbestos. No overt acute toxicity was observed for all MWNTs tested although signs of oxidative stress were evident. MWNTs did not activate resting Jurkat cells and only slightly stimulated the release of the cytokine interleukin-2 (IL-2) in activated cells. Similar to MWNTs, crocidolite had little toxic effects on Jurkat cells but neither induced the formation of reactive oxygen species nor changes in IL-2 signaling. These findings suggest that, in contrast to many other cell types, T cells are relatively resistant to stress induced by high-aspect ratio particles.

New Insights from Microcalorimetry on the FeOx/CNT‐Based Electrocatalysts Active in the Conversion of CO2 to Fuels

Fe oxide nanoparticles show enhanced electrocatalytic performance in the reduction of CO(2) to isopropanol when deposited on an N-functionalized carbon nanotube (CNT) support rather than on a pristine or oxidized CNT support. XRD and high-resolution TEM were used to investigate the nanostructure of the electrocatalysts, and CO(2) adsorptive microcalorimetry was used to study the chemical nature of the interaction of CO(2) with the surface sites. Although the particles always present the same Fe(3)O(4) phase, their structural anisotropy and size inhomogeneity are consequences of the preparation method of the carbon surface. Two types of chemisorption sites have been determined by using microcalorimetry: irreversible sites (280 kJ mol(-1)) at the uncoordinated sites of the facets and reversible sites (120 kJ mol(-1)) at the hydrated oxide surface of the small nanoparticles. N-Functionalization of the carbon support is advantageous, as it causes the formation of small nanoparticles, which are highly populated by reversible chemisorbing sites. These characteristic features correlate with a higher electrocatalytic performance.

On the Nature of Selective Palladium-Based Nanoparticles on Nitrogen-Doped Carbon Nanotubes for the Direct Synthesis of H2O2

Catalysts based on Pd and Pd–Au nanoparticles supported on N‐doped carbon nanotubes (N‐CNTs) are studied in the direct synthesis of H2O2. The initial selectivity in H2O2 formation is rather high (>95 %); however, there is a fast initial decrease during the first hour of time on stream. This was due to the initial presence of an organic capping agent (polyvinyl alcohol, which is used in the catalyst synthesis to obtain a high dispersion of metal particles). The removal of this capping agent during the reaction leads to a high mobility of metal nanoparticles. The high initial selectivity, when the capping agent is present, is due to small Pd terraces fully covered with chemisorbed O2 and limited H2 chemisorbed sites that consecutively hydrogenate the formed H2O2. The alloying of Pd with Au decreases the intrinsic reaction rate (per mg of Pd) and increases the selectivity in H2O2 formation, whereas Au alone is inactive. Au also has a minor effect on the consecutive conversion of H2O2 in both the decomposition and hydrogenolysis (in the presence of H2 only) reactions. These results suggest that Au does not block the unselective sites of H2O2 conversion but mainly creates isolated small terraces of Pd that can limit H2 chemisorption sites, which thus leads to higher selectivity to H2O2 under given reaction conditions.