Comparison of the activities of C2N and BCNO towards Congo red degradation

An n-type organic carbon nitride semiconductor, C2N, was synthesized by the pyrolysis of uric acid, and its properties were investigated by scanning electron and transmission electron microscopies, X-ray powder diffraction, and vibrational, UV-visible and X-ray photoelectron spectroscopies. This novel material, composed of crystalline flakes, featured a broad absorption centered at 700¿nm, possibly due to charge transfer, and a 2.49¿eV band gap. Its catalytic performance was assessed for the treatment of effluents with the diazo dye Congo red, comparing it with that of boron carbon nitrogen oxide, BCNO. Both wide band gap semiconductors exhibited decolorizing activity in the dark, although the mechanisms were different and were not photocatalytic: BCNO was more effective towards the adsorption-coordination due to the presence of B-O, while C2N was effective towards the adsorption and the advancement of the oxidation reaction. Their kinetic constants (0.19 and 0.02 min-1 for BCNO and C2N, respectively) were comparable to those of intermetallic compounds studied for azo dyes degradation in dark conditions. In view of the high color removal efficiency (97% after 20¿min) and good reusability of BCNO, this study suggests a potential application of this catalyst for wastewater treatment, alone or in combination with C2N

Nitrogen-carbon graphite-like semiconductor synthesized from uric acid

A new carbon-nitrogen organic semiconductor has been synthesized by pyrolysis of uric acid. This layered carbon-nitrogen material contains imidazole-, pyridine (naphthyridine)- and graphitic-like nitrogen, as evinced by infrared and X-ray photoelectron spectroscopies. Quantum chemistry calculations support that it would consist of a 2D polymeric material held together by hydrogen bonds. Layers are stacked with an interplanar distance between 3.30 and 3.36 Å, as in graphite and coke. Terahertz spectroscopy shows a behavior similar to that of amorphous carbons, such as coke, with non-interacting layers. This material features substantial differences from polymeric carbon nitride, with some characteristics closer to those of nitrogen-doped graphene, in spite of its higher nitrogen content. The direct optical band gap, dependent on the polycondensation temperature, ranges from 2.10 to 2.32 eV. Although in general the degree of crystallinity is low, in the material synthesized at 600 °C some spots with a certain degree of crystallinity can be found

Influence de l'adsorption de protéine (BSA) sur le comportement électrochimique et la composition de surface d'un alliage Fe-17Cr en solution aqueuse

ABSTRACT: The aim of this work was to study the interactions between a model protein, the bovine serum albumin (BSA), and the surface of a ferritic stainless steel, Fe-17Cr, during the initial stages of oxide layer formation in aqueous solution. Different parameters have been tested: potential (corrosion potential Ecor and passive potential), pH (values ranging from 1.3 to 10), and absence/presence of chloride ions in solution. For this purpose, electrochemical methods (polarization curves, electrochemical impedance spectroscopy (EIS)) and X-ray photoelectron spectroscopy (XPS) were coupled. In the absence of chlorides, impedance measurements reveal a corrosion inhibition by the BSA at pH 1.3 and Ecor. XPS analyses show that the BSA layer adsorbed on the stainless steel surface (chemically intact molecules; thickness of about 4 nm) has no influence either on the chemical composition or on the thickness of the oxide and hydroxide layers. Thus, the corrosion inhibition effect evidenced at pH 1.3 and Ecor is due to the protein and not to a change in the chemical composition and/or thickness of the surface layers. In the presence of chlorides (NaCl 0.5M), the protein accelerates the localized corrosion of the passivated Fe-17Cr alloy at pH 5.5; moreover, the pitting potential Ep is lower when passivation and exposure to the BSA are simultaneous. The pitting potential is all the more cathodic as the amount of adsorbed protein is large.L'objectif de ce travail était d'étudier les interactions entre une protéine modèle, l'albumine de sérum bovin (BSA), et la surface d'un acier inoxydable ferritique, le Fe-17Cr, lors des toutes premières étapes de formation de la couche d'oxyde en solution aqueuse. Différents paramètres ont été testés : potentiel (potentiel de corrosion Ecor et potentiel passif), pH (compris entre 1,3 et 10) et absence/présence d'ions chlorures en solution. Pour atteindre cet objectif, des méthodes électrochimiques (courbes de polarisation, spectroscopie d'impédance électrochimique (SIE)) et la spectroscopie de photoélectrons induits par rayons X (XPS) ont été couplées. En absence de chlorures, les mesures d'impédance révèlent une inhibition de la corrosion par la BSA, à pH 1,3 et Ecor. Les analyses XPS montrent que la couche de BSA adsorbée sur la surface d'acier inoxydable (molécules chimiquement intactes ; épaisseur d'environ 4 nm) n'a d'effet ni sur la composition chimique ni sur l'épaisseur des couches d'oxyde et d'hydroxyde. Par conséquent, l'inhibition de la corrosion mise en évidence à pH 1,3 et Ecor est due à la protéine elle-même et non pas à un changement de composition chimique et/ou d'épaisseur des couches de surface. En présence de chlorures (NaCl 0,5M), la protéine accélèrerait la corrosion localisée du Fe-17Cr passivé à pH 5,5 ; de plus, le potentiel de piqûration Ep est plus faible quand la passivation et l'exposition à la BSA sont simultanées. Le potentiel de piqûration est d'autant plus cathodique que la quantité de protéine adsorbée est importante

Influence de l'adsorption de protéine (BSA) sur le comportement électrochimique et la composition de surface d'un alliage Fe-17Cr en solution aqueuse

L objectif de ce travail était d étudier les interactions entre une protéine modèle, l albumine de sérum bovin (BSA), et la surface d un acier inoxydable ferritique, le Fe-17Cr, lors des toutes premières étapes de formation de la couche d oxyde en solution aqueuse. Différents paramètres ont été testés : potentiel (potentiel de corrosion Ecor et potentiel passif), pH (compris entre 1,3 et 10) et absence/présence d ions chlorures en solution. Pour atteindre cet objectif, des méthodes électrochimiques (courbes de polarisation, spectroscopie d impédance électrochimique (SIE)) et la spectroscopie de photoélectrons induits par rayons X (XPS) ont été couplées. En absence de chlorures, les mesures d impédance révèlent une inhibition de la corrosion par la BSA, à pH 1,3 et Ecor. Les analyses XPS montrent que la couche de BSA adsorbée sur la surface d acier inoxydable (molécules chimiquement intactes ; épaisseur d environ 4 nm) n a d effet ni sur la composition chimique ni sur l épaisseur des couches d oxyde et d hydroxyde. Par conséquent, l inhibition de la corrosion mise en évidence à pH 1,3 et Ecor est due à la protéine elle-même et non pas à un changement de composition chimique et/ou d épaisseur des couches de surface. En présence de chlorures (NaCl 0,5M), la protéine accélèrerait la corrosion localisée du Fe-17Cr passivé à pH 5,5 ; de plus, le potentiel de piqûration Ep est plus faible quand la passivation et l exposition à la BSA sont simultanées. Le potentiel de piqûration est d'autant plus cathodique que la quantité de protéine adsorbée est importante.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Effect of Chitosan on the Performance of NiMoP-Supported Catalysts for the Hydrodesulfurization of Dibenzothiophene

Chitosan-added NiMoP catalysts supported on alumina and alumina-titania were studied in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The preparation of catalysts containing Mo (12 wt%), Ni (3 wt%), P (1.6 wt%), and chitosan/nickel = 2 (mol ratio) was accomplished by sequential pore-filling impregnation varying the order of chitosan integration. Materials were characterized by DRIFTS, TPR, TG-DTA, and XPS techniques. The TG-DTA study showed that the nature of the support influences the degradation of chitosan onto the catalytic materials and also influences the HDS of DBT and the product distribution as well. The series of catalysts supported on alumina presented the most remarkable effect of chitosan, in which the OH and NH groups of the organic molecule interact with acid sites of the support weakening the interaction between alumina and deposited metal phases. In all cases, DBT was converted mainly through direct sulfur removal. The catalysts ChP3/A (alumina support impregnated with chitosan in phosphoric acid solution, prior to NiMoP deposition) and ChP4/AT (alumina-titania support impregnated with NiMoP solution, prior to contacting with a solution comprising chitosan and phosphorus) exhibited the best performance in HDS reactions and also showed the highest selectivity in biphenyl formation. Presence of carbonaceous residua on the catalyst’s surface, as shown by XPS, could enhance the HDS activity over the ChP4/AT sample

Synthesis of porphyrins as precursors to PAMAM dendrimers and their metal chelating properties

Novel meso-porphyrins were synthesized via microwave assistance and implemented as centers to polyamide amine (PAMAM) dendrimers. The molecular structures of the porphyrins were characterized by UV-Vis, 1H and 13C NMR spectroscopy. In addition, porphyrin-PAMAM dendrimers were characterized by 1H and 13C NMR spectroscopy. The molecular weight of the prepared dendrimers were confirmed by MALDI-TOF mass spectrometry. These porphyrin-core-PAMAM-modified dendrimers were used as templates to form Ag0 species and doped nylon membranes, using the XPS technique to confirm the chemical reduction of the metal cation

Experimental and Theoretical Analysis Accounting for Differences of Pyrite and Chalcopyrite Oxidative Behaviors for Prospective Environmental and Bioleaching Applications

The oxidative processes of pyrite (FeS₂) and chalcopyrite (CuFeS₂) of interest for bioleaching and/or bioremediation applications are evaluated in growing medium conditions to account for differences in their reactions mechanisms proposed with chemical and electrochemical analysis, and their electronic structures calculated with density functional theory (DFT). Electrochemical (chronoamperometry, cyclic voltammetry), spectroscopic (Raman, XPS) and microscopic techniques (SEM-EDS, AFM) are used to comprehensively characterize complex surface transformations of secondary species arising during the electrochemical oxidation of these minerals. Early oxidation steps of both sulfides involve the formation of passive polysulfide species (e.g., Fe_1–<i>x</i>S₂, Cu_1–<i>x</i>Fe_1–<i>y</i>S₂), with the additional formation of Covelite-(CuS)-like species on a more passive chalcopyrite surface. Subsequent stages indicate the formation of semiconductive compounds including elemental sulfur (S⁰). DFT reveals that there are significant differences between pyrite and chalcopyrite densities of states (DOS), that support the fact that pyrite oxidation is more facile than chalcopyrite, as experimentally described. The DOS shows that near to the Fermi energy level of both sulfide minerals, there are few states that explain the oxidation limitations observed in the experimental region of low overpotential. At higher energies, the oxidation of pyrite is mainly due to iron species and sulfur species to a minor extent, while the chalcopyrite passivation is attributed to sulfur species and copper