Insights into the Structural Dynamics of Pt/CeO2_{2} Single-Site Catalysts during CO Oxidation

Despite their high atomic dispersion, single site catalysts with Pt supported on CeO$_{2}$ were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO$_{2}$ single site catalyst under more complex gas mixtures, including CO, C$_{3}$H$_{6}$ and CO/C$_{3}$H$_{6}$ oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt$^{4+}$ to Pt$^{2+}$ due to the increase of temperature, CO adsorbs and reduces Pt$^{2+}$ to Pt$^{δ+}$ and assists its migration with final formation of Pt$_{x^Δ+}$ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria

Tuning the activity of a hybrid polymer–oxocluster catalyst: A composition—selectivity correlation

Zr-based oxoclusters M$_{x}$O$_{y}$(OR)$_{w}$(OOR’)$_{z}$ are promising catalysts for the activation of hydrogen peroxide. However, they need to be integrated into suitable matrices to increase their hydrolytic stability and allow for their recovery after use. Polymeric materials can be successfully employed for this aim, since they modify the properties of the resulting hybrid materials, in terms of polarity and chemical affinity for the substrates, improving the catalytic activity. Herein, we report the synthesis of different acrylic polymers based on various co-monomers (methyl methacrylate (MMA), 2,2,2-trifluoroethylmethacrylate (TFMA) and 3-methacryloxypropyltrimethoxylsilane (MAPTMS)) covalently cross-linked by a Zr$_{4}$-based oxocluster, whose composition was tuned to optimise the catalytic oxidation of methyl p-tolyl sulphide. To assess their properties and stability, the materials were characterised via Fourier Transform Infrared (FT-IR) and Raman spectroscopies, Thermogravimetric Analysis (TGA), Solid-State NMR (SS-NMR) and X-Ray Absorption Spectroscopies XAS, before and after catalytic turnover

The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

For the production of chemicals from biomass, new selective processes are required. The selective oxidation of 5-(Hydroxymethyl)furfural (HMF), a promising platform molecule in fine chemistry, to 2,5-furandicarboxylic acid (FDCA) is considered a promising approach and requires the oxidation of two functional groups. In this study, Au/ZrO2 catalysts with different mean particle sizes were prepared by a chemical reduction method using tetrakis(hydroxymethyl)phosphonium chloride (THPC) and tested in HMF oxidation. The catalyst with the smallest mean particle size (2.1 nm) and the narrowest particle size distribution was highly active in the oxidation of the aldehyde moiety of HMF, but less active in alcohol oxidation. On the other hand, increased activity in FDCA synthesis up to 92% yield was observed over catalysts with a larger mean particle size (2.7 nm), which had a large fraction of small and some larger particles. A decreasing FDCA yield over the catalyst with the largest mean particle size (2.9 nm) indicates that the oxidation of both functional groups require different particle sizes and hint at the presence of an optimal particle size for both oxidation steps. The activity of Au particles seems to be influenced by surface steps and H bonding strength, the latter particularly in aldehyde oxidation. Therefore, the presence of both small and some larger Au particles seem to give catalysts with the highest catalytic activity

Effective Space Confinement by Inverse Miniemulsion for the Controlled Synthesis of Undoped and Eu3+^{3+} -Doped Calcium Molybdate Nanophosphors: A Systematic Comparison with Batch Synthesis

The possibility to precisely control reaction outcomes for pursuing materials with well-defined features is a main endeavor in the development of inorganic materials. Confining reactions within a confined space, such as nanoreactors, is an extremely promising methodology which allows to ensure control over the final properties of the material. An effective room temperature inverse miniemulsion approach for the controlled synthesis of undoped and Eu3+-doped calcium molybdate crystalline nanophosphors was developed. The advantages and the efficiency of confined space in terms of controlling nanoparticle features like size, shape, and functional properties are highlighted by systematically comparing miniemulsion products with calcium molybdate particles obtained without confinement from a typical batch synthesis. A relevant beneficial impact of space confinement by miniemulsion nanodroplets is observed on the control of size and shape of the final nanoparticles, resulting in 12 nm spherical nanoparticles with a narrow size distribution, as compared to the 58 nm irregularly shaped and aggregated particles from the batch approach (assessed by TEM analysis). Further considerable effects of the confined space for the miniemulsion samples are found on the doping effectiveness, leading to a more homogeneous distribution of the Eu$^{3+}$ ions into the molybdate host matrix, without segregation (assessed by PXRD, XAS, and ICP-MS). These findings are finally related to the photoluminescence properties, which are evidenced to be closely dependent on the Eu$^{3+}$ content for the miniemulsion samples, as an increase of the relative intensity of the direct f–f excitation and a shortening of the lifetime (from 0.901 ms for 1 at. % to 0.625 ms for 7 at. % samples) with increasing Eu$^{3+}$ content are observed, whereas no relationship between these parameters and the Eu$^{3+}$ content is evidenced for the batch samples. All these results are ascribed to the uniform and controlled crystallization occurring inside each miniemulsion nanodroplet, as opposed to the less controlled nucleation and growth for a classic nonconfined approach

Covalent Graft of Lipopeptides and Peptide Dendrimers to Cellulose Fibers

Introduction: Bacterial proliferation in health environments may lead to the development of specific pathologies, but can be highly dangerous under particular conditions, such as during chemotherapy. To limit the spread of infections, it is helpful to use gauzes and clothing containing antibacterial agents. As cotton tissues are widespread in health care environments, in this contribution we report the preparation of cellulose fibers characterized by the covalent attachment of lipopeptides as possible antimicrobial agents. Aim: To covalently link peptides to cotton samples and characterize them. Peptides are expected to preserve the features of the fabrics even after repeated washing and use. Peptides are well tolerated by the human body and do not induce resistance in bacteria. Materials and Methods: A commercially available cotton tissue (specific weight of 150 g/m2, 30 Tex yarn fineness, fabric density of 270/230 threads/10 cm in the warp and weft) was washed with alkali and bleached and died. A piece of this tissue was accurately weighed, washed with methanol (MeOH) and N,N-dimethylformamide (DMF), and air-dried. Upon incubation with epibromohydrin, followed by treatment with Fmoc-NH-CH2CH2-NH2 and Fmoc removal, the peptides were synthesized by incorporating one amino acid at a time, beginning with the formation of an amide bond with the free NH2 of 1,2\u2013diaminoethane. We also linked to the fibers a few peptide dendrimers, because the mechanism of action of these peptides often requires the formation of clusters. We prepared and characterized seven peptide-cotton samples. Results: The new peptide-cotton conjugates were characterized by means of FT-IR spectroscopy and X-ray Photoelectron Spectroscopy (XPS). This latter technique allows for discriminating among different amino acids and thus different peptide-cotton samples. Some samples maintain a pretty good whiteness degree even after peptide functionalization. Interestingly, these samples also display encouraging activities against a Gram positive strain. Conclusions: Potentially antimicrobial lipopeptides can be covalently linked to cotton fabrics, step-by-step. It is also possible to build on the cotton Lys-based dendrimers. XPS is a useful technique to discriminate among different types of nitrogen. Two samples displaying some antibacterial potency did also preserve their whiteness index

Nanoparticle Exsolution from Nanoporous Perovskites for Highly Active and Stable Catalysts

Nanoporosity is clearly beneficial for the performance of heterogeneous catalysts. Although exsolution is a modern method to design innovative catalysts, thus far it is predominantly studied for sintered matrices. A quantitative description of the exsolution of Ni nanoparticles from nanoporous perovskite oxides and their effective application in the biogas dry reforming is here presented. The exsolution process is studied between 500 and 900 °C in nanoporous and sintered La$_{0.52}$Sr$_{0.28}$Ti$_{0.94}$Ni$_{0.06}$O$_{3±δ}$. Using temperature-programmed reduction (TPR) and X-ray absorption spectroscopy (XAS), it is shown that the faster and larger oxygen release in the nanoporous material is responsible for twice as high Ni reduction than in the sintered system. For the nanoporous material, the nanoparticle formation mechanism, studied by in situ TEM and small-angle X-ray scattering (SAXS), follows the classical nucleation theory, while on sintered systems also small endogenous nanoparticles form despite the low Ni concentration. Biogas dry reforming tests demonstrate that nanoporous exsolved catalysts are up to 18 times more active than sintered ones with 90% of CO$_2$ conversion at 800 °C. Time-on-stream tests exhibit superior long-term stability (only 3% activity loss in 8 h) and full regenerability (over three cycles) of the nanoporous exsolved materials in comparison to a commercial Ni/Al$_2$O$_3$ catalyst

Tracking the formation, fate and consequence for catalytic activity of Pt single sites on CeO2

Platinum single sites are highly attractive due to their high atom economy and can be generated on CeO$_2$ by an oxidative high-temperature treatment. However, their location and activity are strongly debated. Furthermore, reaction-driven structural dynamics have not been addressed so far. In this study, we were able to evidence platinum-induced CeO$_2$ surface restructuring, locate platinum single sites on CeO$_2$ and track the variation of the active state under reaction conditions using a complementary approach of density functional theory calculations, in situ infrared spectroscopy, operando high-energy-resolution fluorescence detected X-ray absorption spectroscopy and catalytic CO (as well as C$_3$H$_6$ and CH$_4$) oxidation. We found that the onset of CO oxidation is linked to the migration of platinum single sites from four-fold hollow sites to form small clusters containing a few platinum atoms. This demonstrates that operando studies on single sites are essential to assess their fate and the resulting catalytic properties

A multicentre outcome analysis to define global benchmarks for donation after circulatory death liver transplantation

BACKGROUND: To identify the best possible outcomes in liver transplantation from donation after circulatory death donors (DCD) and to propose outcome values, which serve as reference for individual liver recipients or patient groups. METHODS: Based on 2219 controlled DCD liver transplantations, collected from 17 centres in North America and Europe, we identified 1012 low-risk, primary, adult liver transplantations with a laboratory MELD of ≤20points, receiving a DCD liver with a total donor warm ischemia time of ≤30minutes and asystolic donor warm ischemia time of ≤15minutes. Clinically relevant outcomes were selected and complications were reported according to the Clavien-Dindo-Grading and the Comprehensive Complication Index (CCI). Corresponding benchmark cut-offs were based on median values of each centre, where the 75(th)-percentile was considered. RESULTS: Benchmark cases represented between 19.7% and 75% of DCD transplantations in participating centers. The one-year retransplant and mortality rate was 5.23% and 9.01%, respectively. Within the first year of follow-up, 51.1% of recipients developed at least one major complication (≥Clavien-Dindo-Grade-III). Benchmark cut-offs were ≤3days and ≤16days for ICU and hospital stay, ≤66% for severe recipient complications (≥Grade-III), ≤16.8% for ischemic cholangiopathy, and ≤38.9CCI points at one-year posttransplant. Comparisons with higher risk groups showed more complications and impaired graft survival, outside the benchmark cut-offs. Organ perfusion techniques reduced the complications to values below benchmark cut-offs, despite higher graft risk. CONCLUSIONS: Despite excellent 1-year survival, morbidity in benchmark cases remains high with more than half of recipients developing severe complications during 1-year follow-up. Benchmark cut-offs targeting morbidity parameters offer a valid tool to assess the protective value of new preservation technologies in higher risk groups, and provide a valid comparator cohort for future clinical trials. LAY SUMMARY: The best possible outcomes after liver transplantation of grafts donated after circulatory death (DCD) were defined using the concept of benchmarking. These were based on 2219 liver transplantations following controlled DCD donation in 17 centres worldwide. The following benchmark cut-offs for the most relevant outcome parameters were developed: ICU and hospital stay: ≤3 and ≤16 days; primary non function: ≤2.5%; renal replacement therapy: ≤9.6%; ischemic cholangiopathy: ≤16.8% and anastomotic strictures ≤28.4%. One-year graft loss and mortality were defined as ≤14.4% and 9.6%, respectively. Donor and recipient combinations with higher risk had significantly worse outcomes. The use of novel organ perfusion technology achieved similar, good results in this high-risk group with prolonged donor warm ischemia time, when compared to the benchmark cohort

Synthesis and Chemico-Physical and Structural Characterization of Nanocrystalline Inorganic Materials obtained via Miniemulsions

In this PhD thesis, several inorganic nanostructures were synthesized through a wetchemistry synthetic route. In particular, the miniemulsion approach was exploited to induce the formation in confined space of pure and doped binary (oxides, sulfides and fluorides) and ternary (hydroxides) compounds, of metal/oxide nanocomposites and of hybrid organic/inorganic nanoparticles. Through this methodology, the investigated systems were obtained in crystalline form already at room temperature. Various miniemulsion formulations were used to control the size and morphology of the investigated systems, achieving different emulsion stabilities and yields of crystalline powders. The obtained materials were thoroughly characterized through a wide array of techniques from the compositional, structural and functional points of view. In particular, XRD (X-Ray Diffraction) was employed to assess the formation of crystalline materials and to calculate average crystallite sizes (through Rietveld refinement), and the data thus obtained were compared with micrographs collected through TEM (Transmission Electron Microscopy). This latter microscopy, coupled with SEM (Scanning Electron Microscopy), was also used to investigate the morphology of the synthesized nanostructures. In addition, the surface composition was explored through XPS (X-ray Photoelectron Spectroscopy) and, especially in the case of systems doped with transition metal or lanthanide ions, atomic ratios were compared to those obtained through ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) or ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) allowed to evaluate the presence and amount of residual surfactant moieties adsorbed on the materials surfaces. In the case of the doped systems, XAS (X-ray Absorption Spectroscopy) measurements were performed in order to study in detail the local structure of the doping ions, also with respect to the hosting matrices. The obtained data were further correlated to the photoluminescence properties. These materials, also due to the biocompatibility of the selected matrices, might indeed be potentially applied for optical bioimaging. At this regard, cytotoxicity and cell viability assays were also performed on selected systems.In questa tesi di dottorato, diverse nanostrutture inorganiche sono state sintetizzate mediante un approccio sintetico per via umida. In particolare, l’approccio della miniemulsione è stato sfruttato per indurre la formazione in spazio confinato di composti binari (ossidi, solfuri e fluoruri) e ternari (idrossidi), sia in forma pura che drogati, e di nanocompositi metallo/ossido e nanoparticelle ibride organiche/inorganiche. Attraverso questa metodologia, i sistemi investigati sono stati ottenuti in forma cristallina già a temperatura ambiente. Miniemulsioni con varie formulazioni sono state usate per controllare le dimensioni e la morfologia dei sistemi investigati, ottenendo emulsioni con stabilità differenti e diversa resa in termini di prodotti cristallini. I materiali ottenuti sono stati caratterizzati in dettaglio attraverso numerose tecniche, sia dal punto di vista composizionale che da quello strutturare e funzionale. In particolare, l’XRD (X-Ray Diffraction) è stato utilizzato per valutare la formazione di materiali cristallini e, attraverso rifinimento Rietveld, calcolare le dimensioni medie dei cristalliti; i dati così ottenuti sono stati confrontati con le micrografie TEM (Transmission Electron Microscopy). Quest’ultima microscopia, affiancata al SEM (Scanning Electron Microscopy), è stata anche utilizzata per investigare la morfologia delle nanostrutture sintetizzate. In aggiunta, la composizione superficiale è stata esplorata attraverso XPS (X-ray Photoelectron Spectroscopy) e, specialmente nel caso dei sistemi drogati con ioni di metalli di transizione o lantanidi, i rapporti molari registrati sono stati confrontati con quelli ottenuti attraverso ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) o ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). Analisi TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) hanno invece permesso di valutare la presenza e la quantità di residui di tensioattivi adsorbiti sulla superficie del materiale. Nel caso dei sistemi drogati, sono state effettuate misure XAS (X-ray Absorption Spectroscopy) al fine di studiare in dettaglio la struttura locale intorno agli ioni droganti, in relazione alle matrici ospitanti. I dati così ottenuti sono stati inoltre correlati con le proprietà di fotoluminescenza. Questi materiali, anche grazie alla biocompatibilità delle matrici selezionate, potrebbero potenzialmente essere utilizzati nel campo del bioimaging ottico. A questo riguardo sono state quindi effettuate prove di citotossicità e di influenza sulla vitalità cellulare su alcuni dei sistemi sintetizzati

Synthesis and Chemico-Physical and Structural Characterization of Nanocrystalline Inorganic Materials obtained via Miniemulsions

In this PhD thesis, several inorganic nanostructures were synthesized through a wetchemistry synthetic route. In particular, the miniemulsion approach was exploited to induce the formation in confined space of pure and doped binary (oxides, sulfides and fluorides) and ternary (hydroxides) compounds, of metal/oxide nanocomposites and of hybrid organic/inorganic nanoparticles. Through this methodology, the investigated systems were obtained in crystalline form already at room temperature. Various miniemulsion formulations were used to control the size and morphology of the investigated systems, achieving different emulsion stabilities and yields of crystalline powders. The obtained materials were thoroughly characterized through a wide array of techniques from the compositional, structural and functional points of view. In particular, XRD (X-Ray Diffraction) was employed to assess the formation of crystalline materials and to calculate average crystallite sizes (through Rietveld refinement), and the data thus obtained were compared with micrographs collected through TEM (Transmission Electron Microscopy). This latter microscopy, coupled with SEM (Scanning Electron Microscopy), was also used to investigate the morphology of the synthesized nanostructures. In addition, the surface composition was explored through XPS (X-ray Photoelectron Spectroscopy) and, especially in the case of systems doped with transition metal or lanthanide ions, atomic ratios were compared to those obtained through ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) or ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) allowed to evaluate the presence and amount of residual surfactant moieties adsorbed on the materials surfaces. In the case of the doped systems, XAS (X-ray Absorption Spectroscopy) measurements were performed in order to study in detail the local structure of the doping ions, also with respect to the hosting matrices. The obtained data were further correlated to the photoluminescence properties. These materials, also due to the biocompatibility of the selected matrices, might indeed be potentially applied for optical bioimaging. At this regard, cytotoxicity and cell viability assays were also performed on selected systems.In questa tesi di dottorato, diverse nanostrutture inorganiche sono state sintetizzate mediante un approccio sintetico per via umida. In particolare, l’approccio della miniemulsione è stato sfruttato per indurre la formazione in spazio confinato di composti binari (ossidi, solfuri e fluoruri) e ternari (idrossidi), sia in forma pura che drogati, e di nanocompositi metallo/ossido e nanoparticelle ibride organiche/inorganiche. Attraverso questa metodologia, i sistemi investigati sono stati ottenuti in forma cristallina già a temperatura ambiente. Miniemulsioni con varie formulazioni sono state usate per controllare le dimensioni e la morfologia dei sistemi investigati, ottenendo emulsioni con stabilità differenti e diversa resa in termini di prodotti cristallini. I materiali ottenuti sono stati caratterizzati in dettaglio attraverso numerose tecniche, sia dal punto di vista composizionale che da quello strutturare e funzionale. In particolare, l’XRD (X-Ray Diffraction) è stato utilizzato per valutare la formazione di materiali cristallini e, attraverso rifinimento Rietveld, calcolare le dimensioni medie dei cristalliti; i dati così ottenuti sono stati confrontati con le micrografie TEM (Transmission Electron Microscopy). Quest’ultima microscopia, affiancata al SEM (Scanning Electron Microscopy), è stata anche utilizzata per investigare la morfologia delle nanostrutture sintetizzate. In aggiunta, la composizione superficiale è stata esplorata attraverso XPS (X-ray Photoelectron Spectroscopy) e, specialmente nel caso dei sistemi drogati con ioni di metalli di transizione o lantanidi, i rapporti molari registrati sono stati confrontati con quelli ottenuti attraverso ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) o ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy). Analisi TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) hanno invece permesso di valutare la presenza e la quantità di residui di tensioattivi adsorbiti sulla superficie del materiale. Nel caso dei sistemi drogati, sono state effettuate misure XAS (X-ray Absorption Spectroscopy) al fine di studiare in dettaglio la struttura locale intorno agli ioni droganti, in relazione alle matrici ospitanti. I dati così ottenuti sono stati inoltre correlati con le proprietà di fotoluminescenza. Questi materiali, anche grazie alla biocompatibilità delle matrici selezionate, potrebbero potenzialmente essere utilizzati nel campo del bioimaging ottico. A questo riguardo sono state quindi effettuate prove di citotossicità e di influenza sulla vitalità cellulare su alcuni dei sistemi sintetizzati