Tuning the Chemical Environment within the UiO-66-NH2 Nanocages for Charge-Dependent Contaminant Uptake and Selectivity

The remarkable water stability of Zr-carboxylatebased metal-organic frameworks (MOFs) stimulated considerable interest toward their utilization in aqueous phase applications. The origin of such stability is probed here through pH titration and plc modeling. A unique feature of the Zr-6(mu 3OH)(4)(mu O-3)(4)(RCO2)(12) cluster is the Zr-bridging oxo/hydroxyl groups, demonstrating several pK(a) values that appear to provide for the water stability at a wide range of pH. Accordingly, the tunability of the cage/surface charge of the MOF can feasibly be controlled through careful adjustment of solution pH. Such high stability, and facile control over cage/surface charge, can additionally be augmented through introducing chemical functionalities lining the cages of the MOF, specifically amine groups in the UiO-66-NH2 presented herein. The variable protonation states of the Zr cluster and the pendant amino groups, their H-bond donor/acceptor characteristics, and their electrostatic interactions with guest molecules were effectively utilized in controlled experiments to demonstrate high uptake of model guest molecules (137 mg/g for Cr(VI), 1275 mg/g for methylene blue, and 909 mg/g for methyl orange). Additionally, a practical form of the silica-supported MOF, UiO-66-NH2 @SiO2, constructed in under 2 h reaction time, is described, generating a true platform microporous sorbent for practical use in demanding applications

Hierarchical Corannulene‐Based Materials: Energy Transfer and Solid‐State Photophysics

We report the first example of a donor–acceptor corannulene-containing hybrid material with rapid ligand-to-ligand energy transfer (ET). Additionally, we provide the first time-resolved photoluminescence (PL) data for any corannulene-based compounds in the solid state. Comprehensive analysis of PL data in combination with theoretical calculations of donor–acceptor exciton coupling was employed to estimate ET rate and efficiency in the prepared material. The ligand-to-ligand ET rate calculated using two models is comparable with that observed in fullerene-containing materials, which are generally considered for molecular electronics development. Thus, the presented studies not only demonstrate the possibility of merging the intrinsic properties of π-bowls, specifically corannulene derivatives, with the versatility of crystalline hybrid scaffolds, but could also foreshadow the engineering of a novel class of hierarchical corannulene-based hybrid materials for optoelectronic devices

Direct Correlation between Adsorption Energetics and Nuclear Spin Relaxation in a Liquid-saturated Catalyst Material.

The ratio of NMR relaxation time constants T 1 / T 2 provides a non-destructive indication of the relative surface affinities exhibited by adsorbates within liquid-saturated mesoporous catalysts. In the present work we provide supporting evidence for the existence of a quantitative relationship between such measurements and adsorption energetics. As a prototypical example with relevance to green chemical processes we examine and contrast the relaxation characteristics of primary alcohols and cyclohexane within an industrial silica catalyst support. T 1 / T 2 values obtained at intermediate magnetic field strength are in good agreement with DFT adsorption energy calculations performed on single molecules interacting with an idealised silica surface. Our results demonstrate the remarkable ability of this metric to quantify surface affinities within systems of relevance to liquid-phase heterogeneous catalysis, and highlight NMR relaxation as a powerful method for the determination of adsorption phenomena within mesoporous solids.Catalysis@Cambridge, BP pl

Atomically dispersed single iron sites for promoting Pt and Pt3Co fuel cell catalysts: performance and durability improvements

Significantly reducing platinum group metal (PGM) loading while improving catalytic performance and durability is critical to accelerating proton-exchange membrane fuel cells (PEMFCs) for transportation. Here we report an effective strategy to boost PGM catalysts through integrating PGM-free atomically-dispersed single metal active sites in the carbon support toward the cathode oxygen reduction reaction (ORR). We achieved uniform and fine Pt nanoparticle (NP) (∼2 nm) dispersion on an already highly ORR-active FeN4 site-rich carbon (FeN4–C). Furthermore, we developed an effective approach to preparing a well-dispersed and highly ordered L12 Pt3Co intermetallic nanoparticle catalyst on the FeN4–C support. DFT calculations predicted a synergistic interaction between Pt clusters and surrounding FeN4 sites through weakening O2 adsorption by 0.15 eV on Pt sites and reducing activation energy to break O–O bonds, thereby enhancing the intrinsic activity of Pt. Experimentally, we verified the synergistic effect between Pt or Pt3Co NPs and FeN4 sites, leading to significantly enhanced ORR activity and stability. Especially in a membrane electrode assembly (MEA) with a low cathode Pt loading (0.1 mgPt cm−2), the Pt/FeN4–C catalyst achieved a mass activity of 0.451 A mgPt−1 and retained 80% of the initial values after 30 000 voltage cycles (0.60 to 0.95 V), exceeding DOE 2020 targets. Furthermore, the Pt3Co/FeN4 catalyst achieved significantly enhanced performance and durability concerning initial mass activity (0.72 A mgPt−1), power density (824 mW cm−2 at 0.67 V), and stability (23 mV loss at 1.0 A cm−2). The approach to exploring the synergy between PGM and PGM-free Fe–N–C catalysts provides a new direction to design advanced catalysts for hydrogen fuel cells and various electrocatalysis processes

Heterometallic Multinuclear Nodes Directing MOF Electronic Behavior

Metal node engineering in combination with modularity, topological diversity, and porosity of metal–organic frameworks (MOFs) could advance energy and optoelectronic sectors. In this study, we focus on MOFs with multinuclear heterometallic nodes for establishing metal−property trends, i.e., connecting atomic scale changes with macroscopic material properties by utilization of inductively coupled plasma mass spectrometry, conductivity measurements, X-ray photoelectron and diffuse reflectance spectroscopies, and density functional theory calculations. The results of Bader charge analysis and studies employing the Voronoi–Dirichlet partition of crystal structures are also presented. As an example of frameworks with different nodal arrangements, we have chosen MOFs with mononuclear, binuclear, and pentanuclear nodes, primarily consisting of first-row transition metals, that are incorporated in HHTP-, BTC-, and NIP-systems, respectively (HHTP3− = triphenylene-2,3,6,7,10,11-hexaone; BTC3− = 1,3,5-benzenetricarboxylate; and NIP2− = 5-nitroisophthalate). Through probing framework electronic profiles, we demonstrate structure–property relationships, and also highlight the necessity for both comprehensive analysis of trends in metal properties, and novel avenues for preparation of heterometallic multinuclear isoreticular structures, which are critical components for on-demand tailoring of properties in heterometallic systems

Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4-Nitrophenol in Solution

The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4-nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy-dispersive X-ray spectroscopy coupled with aberration-corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au-rich or Cu-rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an Au/Cu reference sample made by chemical impregnation

Growth Mode Study of MgCl2 on Ti (0001) and SiO2 under Ultra High Vacuum by XPS

The growth mode of MgCl2 on Ti (0001) and on SiO2 grown on Si (100) was investigated by X-ray Photoelectron Spectroscopy (XPS) under UHV conditions. Magnesium chloride grows on both Ti (0001) single crystal and SiO2 following the Frank-van der Merve, (FM) growth mode

Study of model catalytic systems using surface sensitive spectroscopies

In the present thesis two model systems, important in heterogeneous catalysis, where investigated. The study was mainly performed using surface sensitive spectroscopies , which are variations of x-ray photoelectron spectroscopy, namely XPS, SRPES and XAES. Other surface sensitive techniques employed were: Low Energy Electron Difraction (LEED), Ion Scattering Spectroscopy (ISS), Temperature Programmed Desorption (TPD) and Contact Potential Difference (CPD) measurements. The bi-metallic system Sn/Ni was initially investigated, starting with the study of surface alloying conditions of Sn on Ni(111) . It was found that the necessary condition for the formation of an epitaxial surface alloy with structure (?3x?3) R30° and 0.3 ML coverage on the Ni(111) surface, is to have an initial Sn coverage higher than one ML which then has to be annealed at 7000C for some minutes. Next, the c(4x2) and c(2x2) ordered structures were studied and found to be an intermediate step of the surface alloying process. The interaction between Sn and the Ni(111) surface was spectroscopically asserted by the 0,27 eV chemical shift of the Sn4d XPS peak and the appearance of new components at the valence band spectrum, which were also predicted by first principle calculations. The main part of the thesis was the study of surface science compatible model catalysts of the Ziegler-Natta (ZN) system. In order to study these highly complex catalytic systems in an atomic level using surface sensitive spectroscopies, the interfaces between the main components of the real catalyst were considered separately. In this concept the interface formation during evaporation of MgCl2 on Si(111)7?7, Ti(0001) and SiO2 and during the evaporation of Ti on MgCl2 /SiO2 mixed substrate were investigated. Considering the growth of MgCl2 on Si(111)7?7, it was found that it follows a layer by layer mode, while the interaction between the two materials at room temperature is rather weak. The interaction takes place through the Mg atoms, which at low coverage form a new surface structure, namely (?3x?3)R30°. At higher MgCl2 coverage the same superstructure could be observed after annealing. The interaction of MgCl2 with Si(111)7?7 was stronger after annealing, where desorption of molecular MgCl2 takes place, followed by decomposition of the remaining MgCl2 leaving submonolayer coverage of Mg atoms on the surface. The 7?7 reconstruction vanishes while a new component characteristic of the interfacial reaction products appears in the valence band. During step by step deposition of MgCl2 on Ti(0001) in was found that MgCl2 interacts strongly with the substrate even at room temperature. The interaction takes place via Cl atoms of the deposit that tend to form chemical bonds with the Ti atoms of the substrate. Annealing of the surface causes the desorption of molecular MgCl2 followed by decomposition that leaves on the surface only Cl atoms attached to Ti. Contrary to the case of the Si(111)7?7 substrate, no Mg atoms remain on the Ti(0001) surface after annealing and no new superstructure is observed. Nevertheless, the interaction leads to the appearance of a new component at the valence band spectrum. The MgCl2 / SiO2 interface models the porous mixed substrate used at the industrial ZN catalysts. Only a weak interaction was observed between MgCl2 and SiO2 while annealing the sample resulted again to the desorption and decomposition of MgCl2 leaving on the surface a sub-monolayer coverage of oxidized Mg. A final experiment was designed in order to investigate the interaction between three different components of the real ZN catalyst. Ti was evaporated on the mixed MgCl2 / SiO2 support. It was found that even at room temperature Ti appears at higher oxidation states due to the reaction with Cl and O atoms at the surface. Annealing in this case causes the partial desorption of Cl while the remaining surface chemical species contain Mg, Cl, Ti and O.Στην παρούσα διατριβή μελετήθηκαν δύο πρότυπα συστήματα με ενδιαφέρον για την ετερογενή κατάλυση. Για την μελέτη αυτή χρησιμοποιήθηκε μία σειρά από επιφανειακά ευαίσθητες τεχνικές, κυρίως παραλλαγές της φασματοσκοπίας φωτοηλεκτρονίων από ακτίνες-Χ (XPS, SRPES, XAES). Παράλληλα έγιναν πειράματα με τις τεχνικές: περίθλαση ηλεκτρονίων χαμηλής ενέργειας (LEED), φασματοσκοπία σκέδασης ιόντων (ISS), θερμοπρογραμματισμένη εκρόφηση (TPD) και μέτρησης των μεταβολών του δυναμικού επαφής (CPD). To πρώτο υπόδειγμα πρότυπου συστήματος με καταλυτικό ενδιαφέρον που μελετήθηκε εισαγωγικά, είναι το διμεταλλικό σύστημα Sn/Ni. Αρχικά μελετήθηκαν οι συνθήκες επιφανειακής κραματοποίησης του Sn στην επιφάνεια Ni(111). Βρέθηκε ότι για να σχηματιστεί το πλήρες επιφανειακό κράμα με δομή (?3x?3)R30° και με κάλυψη ακριβώς 0,33ΜΣ Sn, απαιτείται αρχική ποσότητα Sn μεγαλύτερη του ενός ισοδύναμου μονοστρώματος και θέρμανσή του στους 7000C για μερικά λεπτά. Στη συνέχεια μελετήθηκαν οι διατεταγμένες δομές c(4x2) και c(2x2) και βρέθηκε ότι αποτελούν ένα ενδιάμεσο στάδιο της επιφανειακής κραματοποίησης. Τέλος, η αλληλεπίδραση του Sn με την επιφάνεια Ni(111) επιβεβαιώθηκε φασματοσκοπικά με την παρατήρηση χημικής μετατόπισης της κορυφής Sn4d κατά 0,27eV και με την παρουσία νέων συνεισφορών στη ζώνη σθένους, οι οποίες επιβεβαιώθηκαν από θεωρητικούς υπολογισμούς από πρώτες αρχές. Το δεύτερο υπόδειγμα πρότυπου καταλυτικού συστήματος, η μελέτη του οποίου καλύπτει το μεγαλύτερο μέρος της παρούσας διατριβής, είναι η σύνθεση ρεαλιστικών πρόδρομων καταλυτικών συστημάτων Ziegler – Natta (ZN), τα οποία είναι συμβατά για μελέτη σε ατομικό επίπεδο με χρήση επιφανειακά ευαίσθητων τεχνικών. Λόγω της πολυπλοκότητας των παραπάνω συστημάτων, επιδιώχθηκε να μελετηθούν χωριστά οι κυριότερες περιπτώσεις δεπιφανειών που μπορούν να εμφανισθούν στην τελική μορφή του καταλύτη. Η δημιουργία των διεπιφανειών που μελετήθηκαν έγινε κυρίως με εξάχνωση MgCl2 σε υποστρώματα Si(111)7?7, Ti(0001) και SiO2, που αποτελούν συστατικά στοιχεία του καταλύτη. +ς πρώτο υπόστρωμα χρησιμοποιήθηκε η αναδομημένη επιφάνεια Si(111)7?7. Βρέθηκε ότι ο τρόπος ανάπτυξης του MgCl2 στο συγκεκριμένο υπόστρωμα είναι στρωματικός ενώ σε θερμοκρασία δωματίου αλληλεπιδρά ασθενώς με το υπόστρωμα. ,εν εμφανίζονται χημικές μετατοπίσεις στις φωτοκορυφές και σε χαμηλές καλύψεις διατηρείται η αναδόμηση της επιφάνειας του υποστρώματος. Η ασθενής αλληλεπίδραση λαμβάνει χώρα κυρίως μέσω των ατόμων Mg, τα οποία σε χαμηλές καλύψεις συμμετέχουν στη δημιουργία της διατεταγμένης δομής (?3x?3)R30°. Η υπερδομή αυτή παρατηρείται και μετά από θέρμανση μεγαλύτερων καλύψεων MgCl2. Η αλληλεπίδραση του MgCl2 με το Si(111)7?7 γίνεται ισχυρότερη μετά τη θέρμανση, όπου συμβαίνει εκρόφηση και διάσπαση του MgCl2 αφήνοντας στην επιφάνεια υπομονοστρωματική ποσότητα Mg. Η αναδόμηση 7?7 εξαφανίζεται και εμφανίζεται μία νέα συνεισφορά στη ζώνη σθένους χαρακτηριστική της αλληλεπίδρασης. .................

Anti-Hu antibody seropositive neuropathy with large and small fiber involvement mimicking alcoholic neuropathy: a case report

Abstract Background Anti-Hu antibody neuropathy is considered a rare acquired peripheral neuropathy, but common among paraneoplastic syndromes. Typically, is described as subacute sensory neuronopathy and electrophysiological findings are usually suggestive of a sensory axonal neuropathy. Case presentation We report the case of a 67-year-old man referred to our clinic with a 4-month history of progressive pain and paresthesias of distal lower limbs. He had a 30-year history of alcohol abuse and smoking. Alcoholic neuropathy was considered the most likely diagnosis, considering his history and evaluation. The patient’s neurological examination revealed symmetric bilateral superficial and deep sensory loss in the lower extremities, reduced Achilles tendon reflexes and wide based gait. Electrophysiological testing was suggestive of axonal sensory-motor polyneuropathy and small fiber involvement. Even though alcohol consumption was discontinued, symptoms gradually worsened. Further testing was performed and the patient was found seropositive for anti-Hu antibody. Small-cell lung cancer was detected later, but patient passed away before treatment for cancer was administrated. Conclusions The aim of our paper is to report a case of a rare paraneoplastic syndrome that can cause progressive sensory-motor neuropathy with large and small fiber involvement, which should be rapidly differentially diagnosed from other neuropathies, so that the underlying cause can be identified and, potentially, treated

Preferentially Oriented Ag Nanocrystals with Extremely High Activity and Faradaic Efficiency for CO2 Electrochemical Reduction to CO

Selective electrochemical reduction of CO2 is one of the most important processes to study because of its promise to convert this greenhouse gas to value-added chemicals at low cost. In this work, a simple anodization treatment was devised that first oxidizes Ag to Ag2CO3, then uses rapid electrochemical reduction to create preferentially oriented nanoparticles (PONs) of metallic Ag (PON-Ag) with high surface area as well as high activity and very high selectivity for the reduction of CO2 to CO. The PON-Ag catalyst was dominated by (110) and (100) orientation, which allowed PON-Ag to achieve a CO Faradaic efficiency of 96.7% at an operating potential of −0.69 V vs RHE. This performance is not only significantly higher than that of polycrystalline Ag (60% at −0.87 V vs RHE) but also represents one of the best combinations of activity and selectivity achieved to date - all with a very simple, scalable approach to electrode fabrication