73 research outputs found
Electro-osmotic flow in coated nanocapillaries: a theoretical investigation
Motivated by recent experiments, we present a theoretical investigation of
how the electro-osmotic flow occurring in a capillary is modified when its
charged surfaces are coated by charged polymers. The theoretical treatment is
based on a three dimensional model consisting of a ternary fluid-mixture,
representing the solvent and two species for the ions, confined between two
parallel charged plates decorated by a fixed array of scatterers representing
the polymer coating. The electro-osmotic flow, generated by a constant electric
field applied in a direction parallel to the plates, is studied numerically by
means of Lattice Boltzmann simulations. In order to gain further understanding
we performed a simple theoretical analysis by extending the Stokes-Smoluchowski
equation to take into account the porosity induced by the polymers in the
region adjacent the walls. We discuss the nature of the velocity profiles by
focusing on the competing effects of the polymer charges and the frictional
forces they exert. We show evidence of the flow reduction and of the flow
inversion phenomenon when the polymer charge is opposite to the surface charge.
By using the density of polymers and the surface charge as control variables,
we propose a phase diagram that discriminates the direct and the reversed flow
regimes and determine its dependence on the ionic concentration.Comment: 15 pages, 6 figures in Physical Chemistry Chemical Physics, 201
The role of ceria/precious metal interfaces in catalysis
The popularity of ceria (CeO2) supports has been increasing over the last three decades on account of the rich redox chemistry of such an oxide. The ability to act as an oxygen buffer and switch the oxidation state of Ce depending on conditions implies that the role of this oxide goes beyond the conventional function of stabilizing nanoparticles. In fact, ceria can actively participate in catalytic reactions by interacting with the supported metal, in particular precious metals, promoting various types of dynamic processes that are beneficial for catalysis. This perspective put into light such interfacial synergy, and the effects in several catalytic processes, encompassing the most traditional applications up to the most modern reaction schemes
Synthesis and study of novel zwitterionic transition metal complexes and their application as olefin polymerisation catalysts
The synthesis, characterization and coordination chemistry of novel zwitterionic late
transition metal complexes has been carried out, and an investigation of their ability to
act as olefin polymerisation catalysts has been conducted. These systems are based on 6-
aminofulvene-2-aldiminate ligands (R2AFA¯) which are capable of binding metal
centres via two nitrogen donors, delocalising the negative charge into their
cyclopentadienyl moiety, thus resulting in the formation of neutral zwitterionic
complexes. Preparation and characterisation of mono- and di-substituted complexes such
as Ph2AFACuPPh3, (Ph2AFA)2Zn, (Ph2AFA)2Co, (Ph2AFA)2Ni and (Ph2AFA)2Pd have
revealed that this type of ligand has enough flexibility to distort upon coordination to the
metal depending on geometrical or steric restrictions. As a result, when the ligand
coordination involves narrow binding angle of the metal chelate, as it happens in the
square-planar species, a severe loss of planarity of the ligand framework is observed, in
contrast with the tetrahedral structures where such binding angles are wider.
Although the coordination of the ligand primarily occurs through the nitrogen donors,
once they have been occupied by the metal centre, it is possible to exploit the aromatic
Cp ring for coordination to a Cp*Ru+ unit. In this way, the synthesis and characterisation
of two- and tri-metallic complexes [(Cp*Ru)(Ph’2AFA)Pd(η3-C3H5)][BF4] (where Ph’=
2,4,6-trimethylphenyl) and [(Cp*Ru)2(Ph2AFA)2Pd][BF4]2 has been achieved, featuring
the R2AFA¯ molecule acting as an ambidentate ligand, binding the palladium atom in a
diimine fashion and the ruthenium centres by means of the C5 ring. The synthesis of the
complex Cp*RuPh2AFA where the two N atoms are vacant was also achieved and it was
found that this compound acts as a proton sponge in the presence of protic solvents.
In an effort to prepare AFA-metal complexes which could be of potential use in olefin
polymerisation catalysis, two novel species, [(Ph2AFA)Pd(Me)PPh3] and
[(Ph’2AFA)Pd(C3H5)] (where Ph’= 2,4,6-trimethylphenyl) have been synthesised and characterised, and polymerisation tests with ethylene have been carried out. Some
preliminary screening of other molecules as monomers for polymerisation catalysis has
also been conducted
Wire Up on Carbon Nanostructures! How To Play a Winning Game
Carbon nanotubes and graphene possess a unique extended \u3c0-system that makes them stand out among carbon nanostructures. The resulting electronic properties enable electron or charge flow along one or two directions, respectively, thus offering the opportunity to connect electronically different entities that come into contact, be they living cells or catalytic systems. Using these carbon nanostructures thus holds great promise in providing innovative solutions to address key challenges in the fields of medicine and energy. Here, we discuss how chemical functionalization of these carbon nanostructures is a crucial tool to master their properties and deliver innovation
Into the carbon: A matter of core and shell in advanced electrocatalysis
Electrocatalysis, particularly related to fuel cell applications or other processes related to sustainability, has been steadily advanced by the design of new hierarchical materials involving two or more phases. One particularly appealing type of structure features metal species confined within carbon layers. These materials combine the benefits of the two components, which often work in synergy. However, given the intrinsic catalytic activity of carbon and the fact that the metal may be chemically inaccessible, in many cases, which of the two phases is the truly active site is not fully clear. Particularly for pure core–shell systems, where the metal is completely covered by carbon, the identification of the specific task of each component is not trivial. Many reported works on this type of bi-component catalyst are speculative in this regard. It is important for catalyst development that future studies on these systems will include a thorough cross-check of the reactivity aspects by means of combination of suitable techniques or experiments to unravel probable mechanisms and that assumptions are avoided.Electrocatalysis, particularly related to fuel cell applications or other processes related to sustainability, has been steadily advanced by the design of new hierarchical materials involving two or more phases. One particularly appealing type of structure features metal species confined within carbon layers. These materials combine the benefits of the two components, which often work in synergy. However, given the intrinsic catalytic activity of carbon and the fact that the metal may be chemically inaccessible, in many cases, which of the two phases is the truly active site is not fully clear. Particularly for pure core–shell systems, where the metal is completely covered by carbon, the identification of the specific task of each component is not trivial. Many reported works on this type of bi-component catalyst are speculative in this regard. It is important for catalyst development that future studies on these systems will include a thorough cross-check of the reactivity aspects by means of combination..
The Unexpected Advantages of Using D-Amino Acids for Peptide Self- Assembly into Nanostructured Hydrogels for Medicine
Self-assembled peptide hydrogels have brought innovation to the medicinal field, not only as responsive biomaterials but also as nanostructured therapeutic agents or as smart drug delivery systems. D-amino acids are typically introduced to increase the peptide enzymatic stability. However, there are several reports of unexpected effects on peptide conformation, self-assembly behavior, cytotoxicity and even therapeutic activity. This mini-review discusses all the surprising twists of heterochiral self-assembled peptide hydrogels, and delineates emerging key findings to exploit all the benefits of D-amino acids in this novel medicinal area
Nanostructured Ceria: Biomolecular Templates and (Bio)applications
4Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.Part of the described research was funded by the University of Trieste (FRA2021 to M.M.).openopenRozhin, Petr; Melchionna, Michele; Fornasiero, Paolo; Marchesan, SilviaRozhin, Petr; Melchionna, Michele; Fornasiero, Paolo; Marchesan, Silvi
Design of dye-sensitized TiO2 materials for photocatalytic hydrogen production: light and shadow
Visible light-driven production of fuels and value-added chemicals is currently one of the most
intensely investigated research topics across various scientific disciplines, due to its potential to ease the
World\u2019s dependence on fossil fuels. In this perspective, we recapitulate some of the main features of dyesensitized
photocatalytic systems aimed at solar H2 production, focusing in particular on TiO2-based threecomponent
assemblies with organic sensitizers. Relevant aspects include the structural and electronic
properties of the sensitizers, the nature of the semiconductor and the hydrogen evolution catalysts, the role
of the sacrificial donor and the effect of the reaction parameters on H2 production rate and stability. Besides
presenting the most significant recent developments of the field, we also analyse some of its common
practices in terms of experimental design, laboratory procedures and data presentation, trying to highlight
their weaknesses and suggesting possible improvements. We then conclude with a short paragraph
discussing the possible future development of this exciting research area
The Covalent Functionalization of Graphene on Substrates
The utilization of grown or deposited graphene on solid substrates offers key benefits for functionalization processes, but especially to attain structures with a high level of control for electronics and \u201csmart\u201d materials. In this review, we will initially focus on the nature and properties of graphene on substrates, based on the method of preparation. We will then analyze the most relevant literature on the functionalization of graphene on substrates. In particular, we will comparatively discuss radical reactions, cycloadditions, halogenations, hydrogenations, and oxidations. We will especially address the question of how the reactivity of graphene is affected by its morphology (i.e., number of layers, defects, substrate, curvature, etc.)
Graphitic carbon nitride meets molecular oxygen: New sustainable photocatalytic ways for the oxidation of organic molecules
In recent years, organic chemists have taken a resolute step toward green photocatalytic synthesis. In this regard, the oxidation of organic compounds with molecular oxygen is one of the most important classes of transformations, as it increases molecular complexity while avoiding the use of toxic and harmful oxidants. To this aim, the development of new and efficient photocatalysts capable of driving valuable oxidative reactions in a sustainable manner is highly desirable. These novel photocatalytic systems need to be metal-free, easy-to-prepare, and potentially recyclable. Carbon nitride (CN) fulfills all these requirements because of its outstanding physicochemical properties, thus emerging as a promising heterogeneous photocatalytic platform. The growing popularity of this material is also substantiated by its fast and facile preparation from readily available and inexpensive molecular precursors. This Review aims at highlighting the recent advances in synthesis of carbon nitride-based materials and their applications in organic photocatalysis for the oxidation of organic molecules in presence of molecular oxygen. Lastly, forward-looking opportunities within this intriguing research field are
mentioned
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