Electron Paramagnetic Relaxation Enhancement Produced on T1 by Anisotropic g-tensors in Rigid Systems.

International audienceParamagnetic relaxation enhancement is a fundamental molecular physical phenomenon, manifested as an acceleration of the relaxation times of a slowly relaxing spin Sslow due to the magnetic interaction, dipolar or exchange, with a fast relaxing spin Sfast. Here, we examine the general case of the enhancement of T1slow due to a fast relaxer Sfast with rhombic g-tensor. By using the formalism of Kubo and Tomita we derive an analytical expression for the dipolar effect on T1slow

Double-Nozzle Flame Spray Pyrolysis as a Potent Technology to Engineer Noble Metal-TiO2 Nanophotocatalysts for Efficient H2 Production

Noble metal-TiO2 nanohybrids, NM0-TiO2, (NM0 = Pt0, Pd0, Au0, Ag0) have been engineered by One-Nozzle Flame Spray Pyrolysis (ON-FSP) and Double-Nozzle Flame Spray Pyrolysis (DN-FSP), by controlling the method of noble metal deposition to the TiO2 matrix. A comparative screening of the two FSP methods was realized, using the NM0-TiO2 photocatalysts for H2 production from H2O/methanol. The results show that the DN-FSP process allows engineering of more efficient NM0-TiO2 nanophotocatalysts. This is attributed to the better surface-dispersion and narrower size-distribution of the noble metal onto the TiO2 matrix. In addition, DN-FSP process promoted the formation of intraband states in NM0-TiO2, lowering the band-gap of the nanophotocatalysts. Thus, the present study demonstrates that DN-FSP process is a highly efficient technology for fine engineering of photocatalysts, which adds up to the inherent scalability of Flame Spray Pyrolysis towards industrial-scale production of nanophotocatalysts

Modelling the humification process and the humic acid molecule

The structural origin of the properties of humic acids (HA) is of great importance. Natural humic acids (HA) consist of several major functional groups, predominantly carboxylic (R-COOH) and phenolic (R-OH), as well as carbonyl (C=O) and quinoid. Carboxylic and phenolic functionalities determine the H-binding, metal binding and charge properties of HA. In addition, all HA of diverse geographic and climatic origins contain stable organic radicals which are considered to play a key-role on the transformation of humic acid itself. Presently, the oxidative polymerization of polyphenols in soils is thought to be among the major processes of formation of natural humic substances. Given the acknowledged structural complexity and heterogeneity of natural HA, an approach adopted by various groups was the production of ‘‘synthetic HA”. Recently we have presented a method for performing a Humic Acid Like Polymer (HALP) at significant yields with no use of a catalyst. Herein we present a detailed study off the mechanism of the polymerization in conjunction with S.E.C. data of the evolution of the molecular size of the HALP. Finally the relation of the structures with physicochemical properties is discussed

Isolation and H-Binding Study of Humic Substances from Greek Soil and Lignite: NICA-Donnan Model Parameters

Humic acids from soil and lignite, from different locations of Greece were isolated according to the International Humic Substances Society (IHSS) isolation protocol. An analytical proton binding study of these humic acids using NICA model gives us a wide range of parameters compared to the parameter values of IHSS reference samples

UNDERSTANDING OF THE STRUCTURE AND FUNCTION OF THE IRON-QUINONE COMPLEX (QAFE2+QB) WHICH FUNCTIONS AS A STABLE ELECTRON ACCEPTOR OF PHOTOSYSTEM II OF THE HIGHER PLANTS

THE NON PROTEINIC LIGAND OF THE NON-HEME IRON OF PSII IS BICARBONATE, HCO3. REMOVAL OR REPLACEMENT OF HCO3 CAUSES A DRASTIC SLOWING OF THE ELECTRON TRANSFERIN PSII. IN THIS THESIS IT IS STUDIED THE MECHANISM OF HCO3 ACTION, BY REPLACING IT WITH STRUCTURALLY SIMILAR MOLECULES. A RATHER INDIRECT ROLE OF HCO3 ISREVEALED, THROUGH THE PKΑ OF A NEARLY RESIDUE. FURTHERMORE, THE REDOX AND CRYSTAL FIELD PROPERTIES OF THE NON-HEME IRON ARE STUDIED, AS WELL AS THE MAGNETIC INTERACTION BETWEEN QA AND FE2+. THROUGH THE STUDY OF THE ORIENTATION OF THE SYMMETRY AXES OF THE IRON, IT IS PROPOSED A STRUCTURAL MODEL FOR THE ARRANGEMENT OF THE QAFE2+QB COMPLEX IN THE THYLACOID MEMBRANE.Ο ΜΗ ΠΡΩΤΕΙΝΙΚΟΣ ΥΠΟΚΑΤΑΣΤΑΤΗΣ ΤΟΥ ΜΗ-ΑΙΜΙΚΟΥ ΣΙΔΗΡΟΥ ΤΟΥ ΦΩΤΟΣΥΣΤΗΜΑΤΟΣ ΙΙ (ΦΣΙΙ) ΕΙΝΑΙ ΤΟ ΑΝΙΟΝ HCO3. ΑΦΑΙΡΕΣΗ Η ΑΝΤΙΚΑΤΑΣΤΑΣΗ ΤΟΥ ΠΡΟΚΑΛΕΙ ΔΡΑΣΤΙΚΗ ΕΜΠΛΟΚΗ ΣΤΗ ΡΟΗ ΗΛΕΚΤΡΟΝΙΩΝ ΣΤΟ ΦΣΙΙ. ΣΤΗ ΔΙΑΤΡΙΒΗ ΑΥΤΗ ΜΕΛΕΤΑΤΑΙ Ο ΜΗΧΑΝΙΣΜΟΣ ΔΡΑΣΗΣ ΤΟΥ HCO3, ΜΕΣΩ ΤΗΣ ΑΝΤΙΚΑΤΑΣΤΑΣΗΣ ΤΟΥ ΜΕ ΔΟΜΙΚΑ ΠΑΡΟΜΟΙΑ ΜΟΡΙΑ. ΔΙΑΠΙΣΤΩΝΕΤΑΙ ΟΤΙ ΤΟ HCO3 ΕΠΗΡΕΑΖΕΙ ΤΗ ΡΟΗ ΗΛΕΤΡΟΝΙΩΝ ΕΜΜΕΣΑ, ΜΕΣΩ ΤΟΥ ΡΚΑ ΓΕΙΤΟΝΙΚΟΥ ΚΑΤΑΛΟΙΠΟΥ. ΕΠΙΠΛΕΟΝ ΓΙΝΕΤΑΙ ΣΥΣΤΗΜΑΤΙΚΗ ΜΕΛΕΤΗ ΤΩΝ ΟΞΕΙΔΟΑΝΑΓΩΓΙΚΩΝ ΧΑΡΑΚΤΗΡΙΣΤΙΚΩΝ, ΤΟΥ ΚΡΥΣΤΑΛΛΙΚΟΥ ΠΕΔΙΟΥ ΤΟΥ ΣΙΔΗΡΟΥ ΚΑΙ ΤΗΣ ΜΑΓΝΗΤΙΚΗΣ ΑΛΛΗΛΕΠΙΔΡΑΣΗΣ ΜΕΤΑΞΥ QA ΚΑΙ FE2+. ΤΕΛΟΣ ΜΕΛΕΤΑΤΑΙ Ο ΠΡΟΣΑΝΑΤΟΛΙΣΜΟΣ ΤΩΝ ΑΞΟΝΩΝ ΣΥΜΜΕΤΡΙΑΣ ΤΟΥ ΣΙΔΗΡΟΥ ΩΣ ΠΡΟΣ ΤΗ ΘΥΛΑΚΟΕΙΔΗ ΜΕΜΒΡΑΝΗ ΚΑΙ ΠΡΟΤΕΙΝΕΤΑΙ ΔΟΜΙΚΟ ΜΟΝΤΕΛΟ ΔΙΕΥΘΕΤΗΣΗΣ ΤΟΥ ΣΥΓΚΡΟΤΗΜΑΤΟΣ QAFE2+QB ΣΤΗ ΜΕΜΒΡΑΝΗ

Lattice Defects Engineering in W-, Zr-doped BiVO4 by Flame Spray Pyrolysis: Enhancing Photocatalytic O2 Evolution

A flame spray pyrolysis (FSP) method has been developed, for controlled doping of BiVO4 nanoparticles with W and Zr in tandem with the oxygen vacancies (Vo) of the BiVO4 lattice. Based on XPS and Raman data, we show that the nanolattice of W-BiVO4 and Zr-BiO4 can be controlled to achieve optimal O2 evolution from H2O photocatalysis. A synergistic effect is found between the W- and Zr-doping level in correlation with the Vo-concentration. FSP- made W-BiVO4 show optimal photocatalytic O2-production from H2O, up to 1020 μmol/(g × h) for 5%W-BiVO4, while the best performing Zr-doped achieved 970 μmol/(g × h) for 5%Zr-BiVO4. Higher W-or Zr-doping resulted in deterioration in photocatalytic O2-production from H2O. Thus, engineering of FSP-made BiVO4 nanoparticles by precise control of the lattice and doping-level, allows significant enhancement of the photocatalytic O2-evolution efficiency. Technology-wise, the present work demonstrates that flame spray pyrolysis as an inherently scalable technology, allows precise control of the BiVO4 nanolattice, to achieve significant improvement of its photocatalytic efficiency

A Water Soluble Polymer as a Working Structural Model for Humic Acids: H-binding and Spectroscopic Properties

HA occur ubiquitously in terrestrial and aquatic environments, indicating that many precursors and several formation pathways exist. Distinguishing among these pathways has been difficult because individual scientists have tended to concentrate their efforts on specific types of samples (e.g. soil, sediment or water) for which different isolation or fractionation methods are often used. Humic acids ultimately result from abiotic and biotic polymerization and polycondensation reactions involving such small precursors. The relative importance of abiotic and biotic processes in humification in soils and sediments still remains obscure even though much research has been devoted to them. For example the oxidative polymerization of phenols, which is an important precursor reaction in the formation of HA, is catalysed both by enzymes and abiotic (inorganic) catalysts. Polyphenols have been shown to be important precursors in the abiotic formation of HA. More particularly, the oxidative polymerization of polyphenols in soils is thought to be one of the major processes of formation of humic substances. According to the polyphenolic theory, humic acids are formed from simple phenols and phenolic acids via the formation of a semiquinone radical. Coupling of semiquinones originating from diphenols can lead to the formation of stable humic polymers under the catalytic action of Mn (IV) oxides. In the present case, we have focused our work on molecules bearing both carboxy and phenolic moieties as well as radical activity. In this model, protocatechuic acid (3,4-dihydroxybenzoic acid), and gallic acid (3,4,5-trihydroxybenzoic acid) are among the main low molecular weight aromatic acids formed after lignin degradation. As we have reported recently polymerization of the mono-, di-, and trihydroxyphenolic compounds may occur in alkaline media i.e. under ambient O2. i.e. under conditions where radicals are formed. In the present work, we have investigated the oxidative co-polymerization of some simple hydrobenzoic molecules which have been shown to be good models certain physicochemical properties of humic acids. As we show by controlling the pH, redox potential and the ratio of the polyphenolics, a water soluble polymer is produced that mimics certain key- physicochemical and spectroscopic properties of humic acids

Cu-Based Materials as Photocatalysts for Solar Light Artificial Photosynthesis: Aspects of Engineering Performance, Stability, Selectivity

Cu-oxide nanophases (CuO, Cu2O, Cu0) constitute highly potent nanoplatforms for the development of efficient Artificial Photosynthesis catalysts. The highly reducing conduction band edge of the d-electrons in Cu2O dictates its efficiency towards CO2 reduction under sunlight excitation. In the present review, we discuss aspects interlinking the stability under photocorrosion of the (CuO/Cu2O/Cu0) nanophase equilibria, and performance in H2-production/CO2-reduction. Converging literature evidence shows that, because of photocorrosion, single-phase Cu-oxides would not be favorable to be used as a standalone cathodic catalyst/electrode; however, their heterojunctions and the coupling with proper partner materials is an encouraging approach. Distinction between the role of various factors is required to protect the material from photocorrosion, e.g., use of hole scavengers/electron acceptors, band-gap engineering, nano-facet engineering, and selectivity of CO2-reduction pathways, to name a few possible solutions. In this context, herein we discuss examples and synthesis efforts that aim to clarify the role of interfaces, faces, and phase stability under photocatalytic conditions

Humic Acid: Aggregate, Floc, Macromolecule, Micelle, Polymer, or Supramolecule?

Two humic acids, extracted from an Alfisol forest soil and a lignite mined in Greece, were purified of ash components, size fractionated by membrane dialysis, and polarity fractionated by adsorption chromatography on XAD-8 resin to determine binding mechanisms of humic acid constituents. Humic acids, contained in 12,000 to 15,000 dialysis membranes, were successively dialyzed against 0.1 M HCl, 0.2M HF, 0.1M sodium citrate at pH 10, and 0.1 M NaOH to remove ash components and disaggregate and size fractionate with increasing pH. A part of humic acid did not permeate the dialysis membranes during the acid treatment, while the humic acid that permeated during the sodium citrate and NaOH treatments, was polarity fractionated by a decreasing pH gradient on XAD-8 resin. The resulting fractions were characterized by mass balance, elemental analyses, pH titration, and FT-IR spectrometry. Certain fractions of the lignite humic acid had characteristics very similar to molecular condensates formed by radical coupling of phenolic acid precursors of lignin. Significant differences between the composition and fractionation patterns of the soil and lignite humic acids were interpreted in terms of binding mechanisms within the humic acid precipitates