Application of reverse micelle sol-gel synthesis for bulk doping and heteroatoms Surface Enrichment in Mo-Doped TiO 2 nanoparticles

TiO 2 nanoparticles containing 0.0, 1.0, 5.0, and 10.0 wt.% Mo were prepared by a reverse micelle template assisted sol-gel method allowing the dispersion of Mo atoms in the TiO 2 matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N 2 adsorption/desorption isotherms at -196 °C, energy dispersive X-ray analysis coupled to field emission scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV-Vis spectroscopy, and ζ-potential measurement. The photocatalytic degradation of Rhodamine B (under visible light and low irradiance) in water was used as a test reaction as well. The ensemble of the obtained experimental results was analyzed in order to discover the actual state of Mo in the final materials, showing the occurrence of both bulk doping and Mo surface species, with progressive segregation of MoO x species occurring only at a higher Mo content

«Ricondurre gli uomini alla ragione e alla morale»: Condorcet e Voltaire a confronto

The text reproduces the introductory essay to Condocert, Vita di Voltaire, edited by Marco Armandi, Roma, Editori Riuniti, 1999, p. 7-47

A new method for studying activity and reaction kinetics of photocatalytic water oxidation systems using a bubbling reactor

A novel method is proposed for studying kinetics and overall activity of water oxidation (WO) catalysts using a bubbling reactor, where oxygen concentration is measured simultaneously in the liquid and in the gaseous phase. Total oxygen evolution is obtained from direct integration. The actual rate of oxygen formation as a function of time, RO2(t) not accessible to direct measurement with batch reactors, is calculated from raw data through a simple but comprehensive mathematical model, taking into account mass transfer phenomena occurring in the system. Data concerning the activity of a nanostructured Co3O4 catalyst dispersed on a mesoporous silica (MSU-H), in the presence of tris(2,2'-bipyridyl)Ruthenium [Ru(bpy)3]2+ as sensitizer and Na2S2O8 as sacrificial reactant, are used to illustrate data processing. Behaviour of the system is complicated by the occurrence, besides WO reaction, of the degradation of the sensitizer. Increase of sweeping gas flow increases RO2(t), by decreasing diffusional limitations to the reactions in the system: conditions for minimizing those were established. Data reported show that the assumption generally made of equilibrium between gaseous and liquid phase through Henry's law is incorrect, the more so the smaller the apparent mass transfer coefficient, kLa. An additional reason for removing oxygen from the liquid phase through bubbling is the occurrence of a parasitic reaction of molecular oxygen with the sensitizer. The method seems to yield reliable values of both kLa and the set of RO2(t) values: the former scales with the flow of sweeping gas, as expected; RO2(t) curves are in qualitative agreement with accepted reaction mechanisms. Results concerning RO2(t) lend support to our previous kinetic studies (M. Armandi et. al., ACS Catal. 2013, 3, 1272) where the reaction rate was assumed as constant for the first ~ 15 min. Availability of RO2(t) data not too biased by diffusional limitations opens the way to realistic studies of the kinetic features of WO heterogeneous reactions, in the present case as well as in many other

A Facile and Green Synthesis of a MoO2-Reduced Graphene Oxide Aerogel for Energy Storage Devices

A simple, low cost, and "green" method of hydrothermal synthesis, based on the addition of l-ascorbic acid (l-AA) as a reducing agent, is presented in order to obtain reduced graphene oxide (rGO) and hybrid rGO-MoO2 aerogels for the fabrication of supercapacitors. The resulting high degree of chemical reduction of graphene oxide (GO), confirmed by X-Ray Photoelectron Spectroscopy (XPS) analysis, is shown to produce a better electrical double layer (EDL) capacitance, as shown by cyclic voltammetric (CV) measurements. Moreover, a good reduction yield of the carbonaceous 3D-scaffold seems to be achievable even when the precursor of molybdenum oxide is added to the pristine slurry in order to get the hybrid rGO-MoO2 compound. The pseudocapacitance contribution from the resulting embedded MoO2 microstructures, was then studied by means of CV and electrochemical impedance spectroscopy (EIS). The oxidation state of the molybdenum in the MoO2 particles embedded in the rGO aerogel was deeply studied by means of XPS analysis and valuable information on the electrochemical behavior, according to the involved redox reactions, was obtained. Finally, the increased stability of the aerogels prepared with l-AA, after charge-discharge cycling, was demonstrated and confirmed by means of Field Emission Scanning Electron Microscopy (FESEM) characterization

Spin-Coated vs. Electrodeposited Mn Oxide Films as Water Oxidation Catalysts

Manganese oxides (MnOx), being active, inexpensive and low-toxicity materials, are considered promising water oxidation catalysts (WOCs). This work reports the preparation and the physico-chemical and electrochemical characterization of spin-coated (SC) films of commercial Mn2O3, Mn3O4 and MnO2 powders. Spin coating consists of few preparation steps and employs green chemicals (i.e., ethanol, acetic acid, polyethylene oxide and water). To the best of our knowledge, this is the first time SC has been used for the preparation of stable powder-based WOCs electrodes. For comparison, MnOx films were also prepared by means of lectrodeposition (ED) and tested under the same conditions, at neutral pH. Particular interest was given to -Mn2O3-based films, since Mn (III) species play a crucial role in the electrocatalytic oxidation of water. To this end, MnO2-based SC and ED films were calcined at 500 C, in order to obtain the desired -Mn2O3 crystalline phase. Electrochemical impedance spectroscopy (EIS) measurements were performed to study both electrode charge transport properties and electrode–electrolyte charge transfer kinetics. Long-term stability tests and oxygen/hydrogen evolution measurements were also made on the highest-performing samples and their faradaic efficiencies were quantified, with results higher than 95% for the Mn2O3 SC film, finally showing that the SC technique proposed here is a simple and reliable method to study the electrocatalytic behavior of pre-synthesized WOCs powders

Spin-Coated vs. Electrodeposited Mn Oxide Films as Water Oxidation Catalysts

Manganese oxides (MnOx), being active, inexpensive and low-toxicity materials, are considered promising water oxidation catalysts (WOCs). This work reports the preparation and the physico-chemical and electrochemical characterization of spin-coated (SC) films of commercial Mn2O3, Mn3O4 and MnO2 powders. Spin coating consists of few preparation steps and employs green chemicals (i.e., ethanol, acetic acid, polyethylene oxide and water). To the best of our knowledge, this is the first time SC has been used for the preparation of stable powder-based WOCs electrodes. For comparison, MnOx films were also prepared by means of lectrodeposition (ED) and tested under the same conditions, at neutral pH. Particular interest was given to -Mn2O3-based films, since Mn (III) species play a crucial role in the electrocatalytic oxidation of water. To this end, MnO2-based SC and ED films were calcined at 500 C, in order to obtain the desired -Mn2O3 crystalline phase. Electrochemical impedance spectroscopy (EIS) measurements were performed to study both electrode charge transport properties and electrode-electrolyte charge transfer kinetics. Long-term stability tests and oxygen/hydrogen evolution measurements were also made on the highest-performing samples and their faradaic efficiencies were quantified, with results higher than 95% for the Mn2O3 SC film, finally showing that the SC technique proposed here is a simple and reliable method to study the electrocatalytic behavior of pre-synthesized WOCs powders

New insights in large-pores mesoporous silica microspheres for hemostatic application

Hemorrhages are still considered a common cause of death and despite the availability of different hemostatic agents it is still necessary to develop more effective hemostats for bleeding managements in emergency situations. Herein, large-pores mesoporous silica microspheres (MSM) were synthesized, and their surface was modified to enrich the hydroxyls population with the aim of achieving a material with enhanced water adsorption capacity and high hemostatic ability. The success of surface modification was investigated by Fourier Transform Infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA), which confirmed the increase in the amount of surface hydroxyl groups. A hemolysis assay as well as a clotting test were carried out to evaluate the hemocompatibility and hemostatic ability, respectively. It was found that the modified material presented the lowest hemolytic ratio and the lowest clotting time. The novelty of the paper is mainly due to the coupling of the hemostatic ability test with the adsorption microcalorimetry of water. In fact, being the water adsorption on the material surface a crucial factor in the hemostatic activity, microcalorimetry was used for the first time to study the adsorption of water and estimate its heat of adsorption. The data obtained showed that the modified MSM presents a surface able to adsorb a higher amount of water, compared to the pristine MSM, with a low molar heat of adsorption (about 35 kJ/mol), which renders the modified MSM presented in the present study an excellent candidate for producing novel hemostats

CO2 conversion into hydrocarbons via modified Fischer-Tropsch synthesis by using bulk iron catalysts combined with zeolites

To effectively address the challenges posed by global warming, a prompt and coordinated effort is necessary to conduct an extensive study aimed at reducing CO2 emissions and overcoming the obstacles presented by expensive and scarce fossil fuel resources. This study primarily focuses on comparing two different methodologies for preparing Na-promoted Fe3O4-based catalysts for the CO2 hydrogenation into hydrocarbon mixtures. Three catalysts were synthesized and tested: two samples were impregnated with a different amount of Na (1 wt% and 5 wt%), while a third one was obtained via coprecipitation with NaOH. As the latter catalyst exhibited the best performance, it was combined with zeolites in two ways: physical mixtures and core-shell structures. MFI-type zeolites were used in both configurations and a conventional structure was compared to a hierarchical one. As a result, mesopores increased successfully both the CO2 conversion from 37% to 40% and the liquid hydrocarbon (C6+) selectivity from 29% to 57%, doubling the C6+ yield. On the other hand, NH3-TPD and XPS measurements demonstrated that the intimate contact between the two materials in the core-shell structures led to the migration of Na from the oxide to the zeolite reducing the concentration of strong acid sites and, consequently, the liquid hydrocarbon yield