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Une série de nanosphères poreuses acides avec une taille de particules controlée a été préparée grâce à une synthèse rapide (30min), directe et durable (température ambiante). La taille des particules a été réduite à 25nm et plusieurs Si/Ga ratios (dans la gamme 35 à 137) ont été investigués. Les matériaux ont été testés comme catalyseurs pour la conversion du glycerol en solketal. Le ratio le plus favorable correspond à un Si/Ga ratio de 74. La stabilité du solide a été testée sur plusieurs cycles et il présentait un E-factor particulièrement faible et des propriétés catalytiques significativement améliorée par rapport à d'autres matériaux dont d'autres gallosilicates. Il était encore très actif en présence des impurités principales du glycerol brut (eau, methanol). L'impact de l'eau a pû être réduit grâce à la functionalisation de la surface du catalyseur par 5 mol.% F., A series of acidic porous nanospheres with highly controllable particle size were prepared through a rapid (30 min), straightforward (one pot) and sustainable (room temperature) synthetic procedure. The particle size was reduced down to 25 nm and various Si/Ga ratios (in the range of 35 to 137) were investigated. The materials were tested as catalysts for the conversion of glycerol to solketal. The most favorable Si/Ga ratio corresponds to 74 and this solid was reusable over multiple cycles. Importantly, the best catalyst displayed a particularly low E-factor and outstanding catalytic activity compared to previously reported materials including other gallosilicates. The solid was still highly active in the presence of reaction mixtures simulating the crude glycerol composition. The impact of water on the catalytic activity was further mitigated through the functionalization of the catalyst surface with 5 mol% fluorine moieties, leading to a significant increase in the yield of solketal.

An unprecedented type of Hf-doped silica nanotubes was synthesized using a straightforward one-pot sol–gel procedure. The well-defined nanotubes with a diameter of 14–20 nm exhibited high specific surface area and a widely open texture. The method – involving a key pH adjustment step – allowed a quantitative insertion of hafnium in the materials (Si/Hf = 74) and favored the insertion of Hf as dispersed species. Depending on the synthesis parameters, the chemical environment around Hf was modified, as evidenced by XPS, NH3-TPD and NH3-IR. Hf-doped silica nanotubes showed excellent activity in the conversion of glycerol to solketal, a reaction of high relevance in the context of biorefineries. Importantly, the turnover frequency and the acidity were unambiguously correlated with the insertion of Hf in the silica matrix. The best catalyst was proven to be stable and recyclable, and this sustainable reaction was also amenable to further catalytic enhancement upon optimized reaction conditions.

A set of Cu-ZSM-5 samples (Si/Al = 25) was synthesized by wetness impregnation, aqueous phase ion exchange and solid-state ion exchange, SSIE. Copper(II) acetate was used as precursor during both wetness impregnation and aqueous phase ion exchange to prepare excessively-exchanged samples (i.e. Cu/Al > 1), whereas SSIE was carried out by sublimating copper(I) chloride. Additionally, a Cu-ZSM-5 sample with extremely low Al content (Si/Al = 500) was prepared by impregnation. The samples were tested in the catalytic decomposition of N2O, with the aim of studying possible effects of the preparation technique on the isothermal oscillatory behavior of the reaction rate in a series of tests carried out by varying both the temperature and the residence time. The SSIE sample led to a non-oscillating system, whereas the highest Cu content samples prepared by the two aqueous procedures exhibited clear oscillations of the reaction rate. The Cu-ZSM-5 with Si/Al = 500 was quite inactive, but, surprisingly, gave rise to oscillations of both unconverted N2O and produced O2 concentrations at the reactor outlet. A combined IR spectroscopy and H2-TPR study showed the role of oligomeric CuxOy species with extra-lattice oxygen close to the Al atoms on the observed oscillations. Such species are much more abundant in the samples prepared by either impregnation or ion-exchange, when Cu/Al > 1. In contrast, the sample prepared by SSIE resulted to be rich in Cu+ isolated species, active for the reaction, but not inducing oscillation.

Enabling green fabrication processes for energy storage devices is becoming a key aspect in order to achieve a sustainable fabrication cycle. Here, the focus was on the exploitation of the tragacanth gum, an exudated gum like arabic and karaya gums, as green binder for the preparation of carbon‐based materials for electrochemical capacitors. The electrochemical performance of tragacanth (TRGC)‐based electrodes was thoroughly investigated and compared with another water‐soluble binder largely used in this field, sodium‐carboxymethyl cellulose (CMC). Apart from the higher sustainability both in production and processing, TRGC exhibited a lower impact on the obstruction of pores in the final active material film with respect to CMC, allowing for more available surface area. This directly impacted the electrochemical performance, resulting in a higher specific capacitance and better rate capability. Moreover, the TRGC‐based supercapacitor showed a superior thermal stability compared with CMC, with a capacity retention of about 80 % after 10000 cycles at 70 °C., Towards greener supercapacitors: Tragacanth gum is proposed as alternative to state‐of‐the‐art green binder for supercapacitors. Tragacanth presents greener extraction procedure than CMC synthesis, reducing the overall impact in the electrode production. Remarkable results are obtained cycling cells at high temperature compared to standard electrode technology.

In this study, self-standing and flexible Li-ion battery negative electrodes made of interconnected two-dimensional carbonized cotton fibers are developed by using a controlled pyrolysis method, and their electrochemical performance in laboratory-scale lithium-based cells is investigated at ambient temperature. By applying this binder- and current collector-free cotton-based carbon fiber electrode, both the Li+-ion intercalation and capacity decay mechanisms are explored using conventional organic carbonate-based liquid electrolyte. The cotton-based carbon fiber electrode shows excellent cycling performance and delivers a high discharge capacity in the voltage range of 0.02 - 1.2 V. The post cycling analysis of carbon fiber using HR-TEM shows the major SEI layer components formed at the surface of the active fibers during the charge/discharge process. The same electrode is used to assemble a lab-scale Li-ion full cell with high mass loading LiFePO4-based composite electrode, which demonstrates excellent cycling stability, high Coulombic efficiency and remarkable rate capability at ambient temperature.

International audience; A comprehensive study of the effect of Mg loading on the performances in Dry Reforming of Methane of a series of mesoporous Ni 6-Mg x-Al 2 O 3 catalysts containing 6 wt% Ni and 0 to 26 wt% Mg is presented. Complementary characterizations by N 2 sorption, XRD, SEM/TEM, FT-IR, H 2-TPR and H 2-TPD of the materials, synthesized by one-pot EISA method and studied in their calcined and reduced forms, reveal excellent porous ordering and high and homogeneous chemicals distribution up to an intermediate Mg content, afterwards MgO segregation occurs, associated to some structural loss, nickel sintering due to the disappearance of the stabilizing nickel aluminate species, and to strong basic sites formation. In line with these physicochemical changes, all catalytic results reveal the existence of volcano curves in which the optimum Mg content is between 5 and 10 wt%. This optimum is also discussed in view of turn over frequencies and activation energy values.

Different sol‐gel synthesis methods were used to obtain four nanostructured mesoporous TiO2 samples for an efficient photocatalytic degradation of the emerging contaminant N‐phenylurea under either simulated solar light (1 Sun) or UV light. Particularly, two TiO2 samples were obtained by means of as many template‐assisted syntheses, whereas other two TiO2 samples were obtained by a greener template‐free procedure, implying acidic conditions and, then, calcination at either 200 °C or 600 °C. In one case, anatase was obtained, whereas in the other three cases mixed crystalline phases were obtained. The four TiO2 samples were characterized by X‐ray powder diffraction (followed by Rietveld analysis); Transmission Electron Microscopy; N2 adsorption/desorption at −196 °C; Diffuse Reflectance UV/Vis spectroscopy and ζ‐potential measurements. A commercial TiO2 powder (i. e., Degussa P25) was used for comparison. Differences among the synthesized samples were observed not only in their quantitative phase composition, but also in their nanoparticles morphology (shape and size), specific surface area, pore size distribution and pHIEP (pH at isoelectric point), whereas the samples band‐gap did not vary sizably. The samples showed different photocatalytic behavior in terms of N‐phenylurea degradation, which are ascribed to their different physico‐chemical properties and, especially, to their phase composition, stemming from the different synthesis conditions., Three different sol‐gel synthesis methods were adopted to produce four TiO2 samples with different phase composition. A greener template‐free method working under acidic conditions led to the formation of high‐brookite content mixed phases. Under solar light, these substances revealed a fair photocatalytic activity towards the degradation of a pollutant of environmental concern.

Made available in DSpace on 2020-12-12T01:15:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-02-01 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. Center for Sustainable Future Technologies Istituto Italiano di Tecnologia, Via Livorno 60 Department of Applied Science and Technology Politecnico di Torino, C. so Duca degli Abruzzi 24 Interdisciplinary Laboratory of Electrochemistry and Ceramics (LIEC) Institute of Chemistry São Paulo State University-UNESP Interdisciplinary Laboratory of Electrochemistry and Ceramics (LIEC) Institute of Chemistry São Paulo State University-UNESP

In this study, the adsorption capacity of the low-cost zeolite clinoptilolite was investigated for capturing carbon dioxide (CO2) emitted from industrial processes at moderate temperature. The CO2 adsorption capacity of clinoptilolite (a commercial natural zeolite) and ion-exchanged (with Na+ and Ca2+) clinoptilolite were tested under both dynamic (using a fixed-bed reactor operating with 10% vol. CO2 in N2) and equilibrium conditions (measuring single component adsorption isotherms). The dynamic CO2 adsorption capacity of bare clinoptilolite and ion-exchanged clinoptilolite were evaluated in the temperature range from 293 K to 338 K and the obtained breakthrough curves were compared with those of the commercial zeolite 13X (Z13X). Although the adsorption capacity of Z13X exceeded those of bare clinoptilolite and ion-exchanged clinoptilolite at 293 K, the clinoptilolite exhibited the highest CO2 uptake at a moderate temperature of 338 K (i.e. 25 % higher than Z13X). This feature appears in agreement with the lower isosteric heat of CO2 adsorption on clinoptilolite compared to the other samples. The surface species affecting the qiso and adsorption capacity were investigated through the FTIR spectroscopy using CO2 as probe molecule. As a whole, it has been observed that CO2 forms linear adducts onto K+ and Mg2+ cations of the bare clinoptilolite, and carbonate-like species onto its basic sites. With the Na-exchanged clinoptilolite, Na+ ions led to a decrease in surface basicity and to the formation of both single (Na+···O C O) and dual (Na+···O C O⋯Na+) cationic sites available for the formation of linear adducts. As a result of the remarkable adsorption capacity of clinoptilolite at 338 K, this material appears to be a promising adsorbent for the direct CO2 removal from different flue gases sources operating at such temperatures.

Different sol‐gel synthesis methods were used to obtain four nanostructured mesoporous TiO2 samples for an efficient photocatalytic degradation of the emerging contaminant N‐phenylurea under either simulated solar light (1 Sun) or UV light. Particularly, two TiO2 samples were obtained by means of as many template‐assisted syntheses, whereas other two TiO2 samples were obtained by a greener template‐free procedure, implying acidic conditions and, then, calcination at either 200 °C or 600 °C. In one case, anatase was obtained, whereas in the other three cases mixed crystalline phases were obtained. The four TiO2 samples were characterized by X‐ray powder diffraction (followed by Rietveld analysis); Transmission Electron Microscopy; N2 adsorption/desorption at −196 °C; Diffuse Reflectance UV/Vis spectroscopy and ζ‐potential measurements. A commercial TiO2 powder (i. e., Degussa P25) was used for comparison. Differences among the synthesized samples were observed not only in their quantitative phase composition, but also in their nanoparticles morphology (shape and size), specific surface area, pore size distribution and pHIEP (pH at isoelectric point), whereas the samples band‐gap did not vary sizably. The samples showed different photocatalytic behavior in terms of N‐phenylurea degradation, which are ascribed to their different physico‐chemical properties and, especially, to their phase composition, stemming from the different synthesis conditions.

International audience; Methylimogolite nanotubes (Me-IMO NTs, chemical composition (OH)3Al2O3SiCH3) are characterized by having an inner hydrophobic (fully-methylated) surface. Conversely, the outer surface is hydrophilic and positively charged below the point of zero charge (at pH = 8.6), due to the Al(OH)Al + H+ = Al(OH)2+Al equilibrium occurring at the outer surface of the NTs when they are dispersed in water.In this work, adsorption of MCPA (2-methyl-4-chlorophenoxyacetic acid) and of dichloromethane (DCM) on Me-IMO NTs was studied by means of both adsorption/desorption measurements in batch conditions (at room temperature and at different pH value) and Small Angle X-rays Scattering (SAXS).MCPA, which partially dissociates in water (pKa = 2.90), is mainly adsorbed at the outer surface of the NTs, although measurements in batch conditions show that other types of interaction occur (i.e. H-bond) at higher MCPA concentration. SAXS measurements confirm that MCPA has not entered the NTs inner pores.Interaction of the NTs with DCM, instead, is more complex: SAXS measurements show that DCM molecules interact with the NTs inner surface, whereas batch experiments indicate that additional interactions take place with the outer surface of the NTs.

Made available in DSpace on 2020-12-12T01:25:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-07-01 Regione Piemonte A versatile and efficient surface-enhanced Raman scattering (SERS) substrate based on a hybrid aerogel composed of reduced graphene oxide (rGO) decorated with silver nanoparticles (AgNPs), suitable for highly sensitive label-free detection of chemical and biological species, is presented. The simple and low-cost one-pot hydrothermal synthesis allows obtaining of a 3D nanostructured spongy-like matrix that shows good spatial distribution of Ag nanoparticles in intimate contact with rGO flakes, characterized by means of several morphological, structural, and compositional techniques. The nanostructured material, tested by SERS analysis with both rhodamine 6G (R6G) and 4-mercaptobenzoic acid (MBA), shows a satisfying SERS efficiency, quantified in terms of minimum detectable concentration of 10−10 and 10−7 m, corresponding to on- and off-resonant excitation, respectively. The versatility of chemical/biochemical functionalization is successfully demonstrated by exploiting different routes, by immobilizing both protoporphyrin IX (PRPIX) and hemin (H) that take advantage of π−π non-covalent bonding with the graphene layers, as well as thiol-ended oligonucleotides (DNA probes/aptamers) directly grafted on the AgNPs. Finally, after the successful integration of the hybrid aerogel into a microfluidic chip, the biorecognition of miR222 is obtained demonstrating the reliability of the aerogel substrate as SERS platform for biosensing. CDMF – Functional Materials Development Center Institute of Chemistry São Paulo State University-UNESP DISAT-Department of Applied Science and Technology Politecnico di Torino, C.so Duca degli Abruzzi 24 Center for Sustainable Future Technologies IIT-Istituto Italiano di Tecnologia, Via Livorno 60 CDMF – Functional Materials Development Center Institute of Chemistry São Paulo State University-UNESP

The state-of-the-art Cu-SSZ-13 was mixed with CeO2-SnO2 to form a Composite catalyst which was resistant towards hydrocarbon poisoning of the NH3-mediated NOx-SCR reaction. The Composite was prepared via a solid-state synthesis through ball milling, which did not influence the final morphology. The resistance towards propylene poisoning was remarkably enhanced as the NOx conversion over the Composite catalyst decreased only 9% compared to 40 % over the unmodified Cu-SSZ-13. Transient and dynamic reactivity studies showed that the coke formed during the C3H6 protolytic polymerization was dispersed inside the zeolite pores and the addition of CeO2-SnO2 did not prevent its formation nor enhance its oxidation with O2. The ion-exchanged Cu was the principal active component for the coke and hydrocarbon oxidation and the hydrocarbon poisoning prevention was attributed to the complex interaction between the three primary active sites (Cu – CeO2-SnO2 – protonic sites). Propylene oxidation over Cu-SSZ-13 was inhibited when NO was included in the reaction stream, while over the H-Composite (mixture of H-SSZ-13 and CeO2-SnO2) it had the reverse effect, since C3H6 and NOx oxidation did not compete for the same active sites on CeO2-SnO2. Basing on reactivity studies coupled with IR analysis, a deactivation and poisoning prevention mechanism was proposed, whereby the HONO/nitrate intermediates formed over the CeO2-SnO2 catalyst re-activated the zeolitic copper for the SCR reaction.

The effect of both pH and surface oxidation of nanoparticles is studied on the interaction between a commercial slurry of Nanoscale Zerovalent Iron (NZVI) and the azo dye Acid Orange 7 (AO7). NZVI is a reducing agent used for the degradation of several pollutants, including azo dyes: during pollutant degradation, it undergoes progressive oxidation and dissolution. Though it is generally acknowledged that NZVI consists of core-shell nanoparticles, where the core of metallic iron is covered by FexOy shell, it still remains a poorly defined system. In this work, the solid fraction recovered by filtration and drying was characterized by means of XRD diffraction with Rietveld refinement, N2 isotherms at 77 K, FE-SEM and TEM observation, EDX analysis, and IR spectroscopy. Powders were obtained from both the parent slurry and the same slurry pretreated with HCl in order to remove FexOy shell, finally reactivating the nanoparticles. The aforementioned physicochemical characterization allowed figuring out some correlations between the properties of the studied nanomaterial and the processes occurring when it is in contact with AO7 in aqueous phase. The type of interaction occurring within the NZVI/AO7 system (adsorption and type of redox reactions) strongly depends not only on the pH of the starting solution, but also on the surface oxidation of the nanoparticles.

TiO2 nanoparticles containing 0.0, 1.0, 5.0, and 10.0 wt.% Mo were prepared by a reverse micelle template assisted sol&ndash, gel method allowing the dispersion of Mo atoms in the TiO2 matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N2 adsorption/desorption isotherms at &minus, 196 &deg, C, energy dispersive X-ray analysis coupled to field emission scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV&ndash, Vis spectroscopy, and &zeta, 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 MoOx species occurring only at a higher Mo content.

TiO2 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 TiO2 matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N2 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 MoOx species occurring only at a higher Mo content.

An overview of the different sacrificial oxidants used in literature is reported, paying particular attention to the “sacrificial pair” \(\text{Ru}(\text{bpy})_{3}^{2 + } \text{/S}_{2} \text{O}_{8}^{2 - }\), a photosystem made of a Ru-dye (Tris(bipyridine)ruthenium(II) dichloride, working as “antenna” for visible light) and a final electron acceptor (i.e. the persulfate ion). Such sacrificial oxidant is one of the most common in the literature and it was used in all the experiments described in Chap. 4. Different configurations of batch reactors can be used in the sacrificial-oxidant-driven water oxidation (WO) reaction, and three of them (i.e. the Clark-electrode Cell, the Stripping Flow Reactor and the Bubbling Reactor) are described in detail. The effects of both mass transfer limitations and side reactions on the determination of the two parameters describing the activity of water oxidation catalysts (i.e. the O2 production rate and the total evolved O2) are discussed, evidencing how such undesired phenomena occur to a different extent with the three reactor configurations.

In the current chapter, the use of a bubbling reactor for investigating the activity of different manganese oxides (i.e. Mn2O3, Mn3O4 and MnO2) is described. The most important aspects of water oxidation reaction considered are the role of the catalyst specific surface area (SSA), and the effect of the irradiance on the \({\text{Ru}} ({\text{bpy}})_{3}^{2 + } /{\text{S}}_{2} {\text{O}}_{8}^{2 - }\) system. The former was investigated by preparing and testing samples with the same crystal structure, but with different SSA values. Notably, water oxidation catalyst activity does not strictly increase with SSA, but rather depends on the preparation route, which affects the nature of the surface. The effect of the irradiance was studied by using three irradiances conditions (i.e. 0.3, 0.5 and 1.0 sun) and three different catalyst contents (i.e. 10, 20 and 40 mg), evidencing how the increase in irradiance enhances the degradation processes rather than the O2 evolution. On this basis, a kinetic model imposing steady state conditions on transient species was developed, yielding a simple linear combination of two exponentials as expression of \(R_{{{\text{O}}_{2} }}\). The results show that the ratio between the kinetic constants of the desired (i.e. O2 formation) and undesired path (i.e. dye degradation) decreases at increasing irradiance, evidencing how the role of parasitic reactions, far from being negligible, tends to be overwhelming.

In actual water splitting devices, the WOC will be deposited on an anode surface. Therefore, whatever the results obtained with WOC particles suspended in stirrer tank reactors, it becomes necessary to study WOC performances by means of electrochemical experimental setups. The WOCs deposition on an anode will depend on their physico-chemical nature, therefore several deposition methods, including wet and dry approaches, are found in literature. This Chapter reviews the available electrochemical techniques that can be adopted to study WOCs that are deposited on an electrode. In addition, the parameters used in literature to compare the different WOC materials will be explained. At the end of the Chapter, an example of the performance of different MnOx films will be reported. The water oxidation activity of three MnOx crystalline phases prepared by two deposition techniques will be compared. The aim of the comparison is to determine whether two electrodes having the same crystalline phase behave differently or not when they are deposited by two different techniques.

This chapter focuses on some aspects concerning the realization of an actually sustainable H2 production, and especially the need for earth abundant, environmental friendly, solar driven heterogeneous catalysis for the Water Oxidation reaction: the catalyst shall be thermodynamically and mechanically stable to allow cyclic long-term operations. The focus will be mainly on Mn- and Co-compounds, though reference will be made to other compounds, when appropriate.

This chapter will address the main issues related to the scaling up of a WS process. Currently, only few examples of pilot-scale water splitting (WS) devices are available in literature: low efficiencies and high costs are the main aspects that limit the use of this technology at industrial level, since results obtained at lab-scale are difficult to reproduce in larger configurations. The main factors that influence the device efficiency, which include activity and stability of catalysts and photoabsorbing materials, synthesis procedures, operational conditions and device configuration, will be examined. By the end of this chapter, a case of a pilot-scale photoelectrochemical (PEC) device will be presented and a prospective development of this technology will be discussed.

The lack of low-cost, durable and highly efficient electrocatalysts to perform oxygen reduction reaction (ORR) still represents a significant challenge for the development of fuel cells cathodes. Recently, Pt-free metalloporphyrins supported on N-doped reduced graphene oxide (N-rGO) have been proposed as innovative ORR catalysts characterized by notable stability and superior performance. In this paper, we propose a fast and green microwave-assisted method to synthetize manganese-nitrogen co-doped rGO, characterized by catalytic activity comparable to Pt-containing materials and improved long-term stability. Theoretical calculations and experimental results showed that our synthetic method produces N-rGO matrices which coordinate Mn2+ ions in porphyrin-like structures. These Mn/N-rGO complexes are responsible for the outstanding performance of the proposed catalyst, being able to weaken O–O molecular bond, thus effectively reducing the activation energy towards oxygen catalytic reaction. Our findings open the path to a green co-doping process of graphene for the production of low-cost and efficient alternatives to noble metals-based ORR catalysts.

This chapter will cover the most important aspects concerning the water splitting reaction by providing an overall description of the main solutions, as reported in the literature, addressing the improvement of the efficiency of solar driven hydrogen production. The natural water splitting system will be considered as a starting point, in order to gain a better understanding of the main challenges that material scientists are facing towards the development of novel catalysts of water oxidation, mainly. The attention will focus on the water oxidation half-reaction, since it is the most complex and demanding process from both the kinetic and thermodynamic points of view. In addition, some general aspects of the photocatalytic water splitting and the principal semiconductors studied for such process will be reviewed.

A hybrid aerogel, composed of MoS2 sheets of 1T (distorted octahedral) and 2H (trigonal prismatic) phases, finely mixed with few layers of reduced graphene oxide (rGO) and obtained by means of a facile environment-friendly hydrothermal cosynthesis, is proposed as electrode material for supercapacitors. By electrochemical characterizations in three- and two-electrode configurations and symmetric planar devices, unique results have been obtained, with specific capacitance values up to 416 F g–1 and a highly stable capacitance behavior over 50000 charge–discharge cycles. The in-depth morphological and structural characterizations through field emission scanning electron microscopy, Raman, X-ray photoelectron spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, and transmission electron microscopy analysis provides the proofs of the unique assembly of such 3D structured matrix. The unpacked MoS2 structure exhibits an excellent distribution of 1T and 2H phase sheets that are highly exposed to interaction w...

The adsorption and catalytic properties are reported of aluminosilicate nanotubes (NTs) of the imogolite-type both bare (IMO, (OH) 3 Al 2 O 3 SiOH) and Fe-doped. Iron-doped NTs were obtained by either direct synthesis (Fe- x -IMO) or post synthesis loading (Fe-L-IMO), with 0.70 wt.% Fe (Fe-0.70-IMO) and 1.4 wt.% Fe content (both Fe-1.4-IMO and Fe-L-IMO). The samples were characterized by X-ray diffraction (XRD); N 2 sorption isotherms at −196 °C; diffuse reflectance (DR) UV–vis spectroscopy; IR spectroscopy, and electrophoretic mobility in water (ζ-potential). In water, the intrinsic acidity of Fe(OH)Al groups, formed by isomorphic substitution (IS) of Fe 3+ for Al 3+ , is only marginally different from that of parent Al(OH)Al groups, as shown by ζ-potential measurements. Substitution of one octahedral Al 3+ site, however, gives rise to the formation of three Fe–O–Al groups and three Fe(OH)Al groups: such process modifies the adsorption and catalytic properties of NTs outer surface, as shown by adsorption of the azo-dye Acid Orange 7 (NaAO7) from water solutions and by AO7 − catalytic degradation by H 2 O 2 . Interaction with AO7 − anions in water occurs in different ways: (i) with bare IMO, AO7 − anions preferentially adsorb by electrostatic interaction with the positively charged surface, and by H-bonding; (ii) with Fe-1.4-IMO, IS Fe 3+ cations act as coordination centres for N atoms in the AO7 − moiety, through a ligand displacement mechanism; (iii) with Fe-L-IMO, AO7 − adsorption is hindered by the presence of Fe 2 O 3 clusters. Concerning AO7 − degradation by H 2 O 2 , the outer surface of proper IMO is much more reactive than Fe-doped IMO towards hydrogen peroxide, by forming very reactive Al-OOH bridges. IS Fe 3+ species are probably not accessible to H 2 O 2 , and (the expected) Fenton reaction between Fe 3+ and H 2 O 2 is not observed.

The Cover Feature shows how brookite in TiO(2) mixed phases has a positive effect on the photocatalytic degradation of the emerging contaminant N‐phenylurea under solar light. When different sol‐gel methods were used to produce mesoporous TiO(2) with different phase composition, a template‐free green synthesis at acidic pH allowed obtaining high brookite content TiO(2), with fair photocatalytic activity under either UV or simulated solar light (1 Sun). The activity of a low surface area (ca. 30 m(2) g(‐1)) sample obtained by such procedure showed that heterojunctions between closely interconnected mixed phases, rather than surface area, improve TiO(2) photocatalytic activity, likely due to the stabilization of photogenerated e(‐)/h(+) pairs. More information can be found in the Full Paper by Francesca S. Freyria et al.[Image: see text]

Morphological, textural and surface properties are reported of Fe-doped aluminosilicate nanotubes (NTs) of the imogolite type (IMO, (OH) 3 Al 2 O 3 SiOH). Two samples with 1.4 wt% Fe were obtained by either direct synthesis (Fe-1.4-IMO) or post synthesis loading (Fe-L-IMO). Since formation of Fe 2 O 3 clusters was observed in both cases, a third sample with a lower Fe content corresponding to 0.70 wt% Fe was prepared by direct synthesis, with the aim of preventing clusters formation (Fe-0.70-IMO). The samples were characterized by: High Resolution Transmission Electron Microscopy (HRTEM); X-ray Diffraction (XRD); N 2 sorption isotherms; Thermo-Gravimetric Analysis (TGA); Diffuse Reflectance (DR) UV–vis and IR spectroscopies; electrophoretic mobility in water (ζ-potential) and adsorption of the azo-dye Acid Orange 7 (NaAO7) from water solutions. With Fe-0.70-IMO, Al 3+ isomorphic substitution by Fe 3+ was the main process occurring, leading to a material with formula (OH) 3 Al 1.975 Fe 0.025 O 3 SiOH, in which formation of Fe(OH)Al groups occurred at NTs outer surface. With Fe-1.4-IMO, some of the formed Fe(OH)Al groups probably acted as nucleation seeds, due to the natural tendency of iron to form Fe–O–Fe bridges, being responsible of the (undesired) formation of some Fe 2 O 3 clusters. Comparison with Fe-L-IMO, in which only the formation of Fe 2 O 3 clusters was, in principle, expected, showed on the contrary that some isomorphic substitution occurred also by post-synthesis loading. The intrinsic acidity of Fe(OH)Al groups was marginally different from that of Al(OH)Al groups, as shown by both IR spectroscopy and ζ-potential measurements, but the presence of iron modified the adsorption properties of IMO. Interaction with AO7 − anions in water, indeed, occurred in different ways: i) with proper IMO, besides electrostatic interaction with the positively charged external surface of nanotubes, AO7 − anions preferentially adsorb via H-bonding on inner SiOH groups; ii) with both Fe-0.70-IMO and Fe-1.4-IMO, Fe 3+ cations of Fe(OH)Al groups act as coordination centres for N atoms in the AO7 − moiety; iii) with Fe-L-IMO, larger Fe 2 O 3 clusters likely hinder AO7 − adsorption.

The integration of NOx reduction and catalytic soot oxidation was investigated for the SCRoF (Selective Catalytic Reduction on Filter) applications. By physically mixing a commercial SCR catalyst (either Fe-ZSM-5 and Cu-ZSM-5) with a soot oxidation catalyst (K/CeO2-PrO2), it was possible to lower the soot oxidation temperature by more than 150 degrees and, by optimizing the catalysts mass ratio in the mixture, NOx conversion simultaneously increased, because NO oxidation induced a fast SCR reaction pathway, unlike during standard SCR. Such an improvement in NOx conversion was more pronounced with the Fe-ZSM-5 than with the Cu-ZSM-5 zeolite, as the latter was more sensitive to the NO2/NOx ratio. In order to make the soot oxidation catalyst inactive towards ammonia oxidation, poisoning of the surface acid sites with 3.0 wt.% K2CO3 (corresponding to only 1.0 wt.% K) was performed. In the soot oxidation and SCR catalysts physical mixture, the soot was oxidized mainly by O2 and the contribution of NO2 to oxidation was negligible, as NO2 itself was a key reactant in the (kinetically much faster) SCR reaction.

Pure and V-loaded mesoporous titania (with 2.5 wt-% V) were prepared by template-assisted synthesis and compared to commercial titania (Degussa P25), both as such and after vanadium loading. Mesoporous TiO2 occurred as pure anatase nanoparticles with higher surface area (SSA = 150 m2 g−1) than P25 (SSA = 56 m2 g−1).Degradation of the azo dye Acid Orange 7 by H2O2 was used as a test reaction: under UV light, no difference emerged between mesoporous TiO2 and P25, whereas in dark conditions, higher SSA of the mesoporous sample resulted in higher conversions. Under UV illumination, surface V5+ species inhibited photocatalytic activity, by forming inactive V4+ species. Similarly, in dark conditions, V5+ surface species reacted with H2O2, likely yielding ·O2H radicals and reducing to V4+. On the contrary, V-containing catalysts were very active after pretreatment with ascorbic acid, which reduced V5+ species to V3+species, the latter promoting very lively a Fenton-like reaction.

Commercial Mn2O3, Mn3O4 and MnO2 and the same after thermal or ball-milling treatments have been examined as catalysts for the photocatalytic water oxidation reaction, using [Ru(bpy)3]2+ as photosensitizer and S2O82− as sacrificial electron acceptor. Tests were performed in a bubbling reactor, allowing the calculation of the actual rate of O2 evolution as a function of time from raw data (oxygen flow, concentration of dissolved oxygen, DO) through a model able to take into account mass transfer phenomena Hernandez et al. [19]. A few parameters are proposed for measuring activity, and comparison among them is made. The activity per unit mass of commercial samples is Mn2O3 > MnO2 > Mn3O4, in agreement with the literature. Increase in the surface area brought about by milling correspond, as expected, to a steady increase in activity in the case of Mn3O4, whereas had no effect with Mn2O3. The markedly higher specific surface of Mn2O3 and Mn3O4 samples obtained by thermal treatment of MnO2 and a home-made sample, respectively, correspond surprisingly to activities lower than low surface area ball milled samples. Reasons for this are proposed to be a different nature of the surfaces arrived at, because of the different preparation route. A similar study of the effect of surface area for MnO2 specimens is prevented by their largely amorphous nature. Comparison of present data with those already reported gives further support to the bounty of the model taking into account mass transfer.

Imogolite-like nanomaterials were tested as heterogeneous catalysts for the photo-catalytic degradation of tartrazine (a food dye recalcitrant to biodegradation and responsible of allergic and/or intolerance reactions) in the presence of H 2 O 2 . Methyl-imogolite, a hybrid organic/inorganic material with chemical composition (OH) 3 Al 2 O 3 SiCH 3 , occurs as single-walled nanotubes with an inner surface lined by Si-CH 3 groups and an aluminum oxo-hydroxide outer surface, where octahedral Al 3+ ions may be isomorphically substituted by Fe 3+ ions. Besides bare methyl-imogolite, novel Fe doped nanotubes (with nominal composition (OH) 3 Al 2-x Fe x O 3 SiCH 3 , where x = 0.025 or 0.050) were prepared by ion exchange of preformed methyl-imogolite with FeCl 3 × 6H 2 O in water. Physico-chemical characterization of the materials showed that Fe doping positively modifies nanotubes light absorption capacity by lowering the band gap of methyl-imogolite from 4.9 eV to 2.4 eV. At higher Fe content (sample with nominal composition (OH) 3 Al 1.950 Fe 0.050 O 3 SiCH 3 ), some Fe oxo-hydroxide clusters form, due to the natural tendency of Fe to form aggregates. Photo-degradation tests of tartrazine show that both bare and Fe-doped methyl-imogolite efficiently remove the dye from aqueous mixtures through different mechanisms. With bare methyl-imogolite, under UV light almost 65% Total Organic Carbon (TOC) is removed within 2 h, likely due to the formation of reactive AlOOH groups promptly generating HO radicals. With sample having nominal composition (OH) 3 Al 1.975 Fe 0.025 O 3 SiCH 3 , Fe 3+ species undergo efficient photo-Fenton reaction under UV light, leading to 90% TOC removal after 2 h. Conversely, the Fe oxo-hydroxide clusters at nanotubes outer surface likely worsen the photo-Fenton activity of the sample with (OH) 3 Al 1.950 Fe 0.050 O 3 SiCH 3 nominal composition as far as the TOC removal is concerned.

Five different bimetallic non-precius metal catalysts for oxygen reduction reaction (ORR) are synthesized by different combinations of two transition metal (Fe, Co, Cu, Zn) phthalocyanine precusrsors. The aim of this study is to investigate the effects of the different combinations of two transition metals on the physico-chemical and ORR electrocatalytic activity of the catalysts. The precursors were mixed, impregnated on a mesoporous silica used as a hard template, and pyrolyzed under inert atmosphere at 800 °C. After the template removal, the catalysts were characterized via BET, FESEM, and XPS. TGA-MS analysis was also performed on the catalysts precursors to simulate their behaviour during the pyrolysis, detecting the evolved gases. The results show that both the physico-chemical features and the ORR activity and selectivity in acidic medium (measured by RDE-RRDE technique) are strongly influenced by the transition metals pair used. In particular, the most effective transition metals pair to get a more performing ORR catalyst is Co-Zn. The catalysts are also tested in direct methanol fuel cell, including a short-term durability test. The durability of the best perfroming Co-Zn catalyst is improved compared to a similar catalyst synthesized using Fe. The possibility of tuning the catalysts features by combining different transition metals enables to increase the catalyst durability, the production yield during the synthesis (enabling to recover more material after the pyrolysis), and the surface N fixation.

The photoreduction of nitrate ions was studied for the abatement of N-containing compounds from waste and drinking water. A new processwas developed in semibatch mode, aiming at maximum selectivity towards N2. Different photocatalysts have been prepared with two different methods and their photocatalytic performance has been compared with commercial nanostructured TiO2 (P25). TiO2 has been prepared in nanosized form by using an innovative flame pyrolysis (FP) approach, and mesoporous TiO2 was prepared by sol-gel method. Pd has been added to TiO2 by post synthesis impregnation. The physical/chemical properties of the photocatalysts were studied by means of XRD, BET and UV-Vis spectroscopy. The results show that the flame pyrolysis procedure is a viable technique for the preparation of nanosized TiO2 for this application, leading to ca. double conversion with respect to P25. Furthermore, the addition of a small amount of Pd (0.1 mol %), likely enhanced the lifetime of the photoproduced charges by electron trapping and resulted in higher conversion and selectivity toward N2. The best performance was obtained with Pd doped on TiO2 (FP), with 13% conversion and ca. 27% selectivity, only, toward ammonia formation.

We report on a fast and simple protocol for the electrodeposition of Fe-MnOx films used as catalysts for the water oxidation (WO) reaction at neutral pH, and showing the beneficial effect of iron in terms of both activity and stability of the catalyst. While most electrodeposited MnOx WO catalysts are obtained starting from Mn(II) precursors, the proposed protocol consists in the galvanostatic cathodic deposition of Fe-MnOx onto conductive FTO glasses, using KMnO4 and Fe(NO3)3 as Mn and Fe precursors, respectively. In the absence of Fe, the Tafel slope drastically increases from 103 to 270 mV dec−1 when passing from low to high overpotentials. The slope change, instead, is progressively reduced when the Fe precursor is added to the deposition solution and a constant slope of 105 mV dec−1 is obtained in the whole overpotential range with an optimal Fe concentration of 1.00 mM, Accordingly, Electrochemical Impedance Spectroscopy (EIS) shows that Fe addition improves both charge transfer and transport properties of the electrodeposited films. In particular, a five-fold decrease in charge transfer resistance at the catalyst/electrolyte interface was observed, suggesting a more facile oxygen evolving kinetics for Fe containing samples. Furthermore, the lower the iron content, the lower the film stability, as pointed out by chronopotentiometric measurements, and confimed by FESEM analysis and EIS as measured both before and after water electrolysis experiments. To establish structure activity relationships, an extended characterization of the electrodeposited films was carried out by means of Raman Microscopy, Transmission Electron Microscopy, UV–vis and X-ray Photoelectron Spectroscopies. The ensemble of the characterization results suggests that Fe3+ ions are actually incorporated within the electrodeposited film, with limited effects on the final Fe-MnOx structure, consisting in a defective MnO2 birnessite-type structure with significant fraction of surface Mn3+ species.

The hydrothermal synthesis of a nanosized cobalt doped aluminum phosphate CoAPO-5 (CoAPO-5-N) in a water-surfactant-organic solvent mixture (emulsion method) is reported, along with its physico-chemical characterization and comparison with a sample obtained by conventional synthesis (CoAPO-5-C). Both XRD (X-ray Diffraction) peak widths and FESEM (Field Emission Scanning Electron Microscopy) pictures of CoAPO-5-N are in agreement with a nanoscale structure, although the aggregation of nanoparticles occurred. EDX analysis shows a more homogeneous distribution of cobalt in CoAPO-5-N, not attainable by conventional synthesis. The specific surface area, as measured by nitrogen adsorption at 77 K, shows a limited increase in CoAPO-5-N (242 m(2) g(-1)) with respect to CoAPO-5-C (216 m(2) g(-1)), whereas the external surface area is almost tripled. Such a definite increase in the outer surface of CoAPO-5-N is also evidenced by the fourfold increase in the rate of a reaction only involving the exterior surface of particles, the light-driven oxidation of water by persulfate anions, as activated by the bulky Ru(bipy)3(2+) complex, unable to enter CoAPO-5 micropores. Two new features were also noted, adding to the knowledge of CoAPO-5 systems: (i) tetrahedral Co(3+) species may coordinate ammonia molecules, assuming an octahedral configuration, as determined by UV-vis spectroscopy; (ii) Co(2+) species in trigonal coordination occur, able to coordinate either CO molecules at a low temperature or ammonia (or water) at room temperature, as evidenced by IR and UV-vis spectroscopy, respectively.

The [Ru(bpy)3]2+/persulfate photosystem is the most common dye/sacrificial reagent pair used to study the catalyzed water oxidation half-reaction. Recently, we developed a bubbling reactor along with its modelling, and we used it with the aforementioned photosystem to measure the actual rate of reaction (RO2) over time. In the present work, the same method is employed to investigate the kinetics of the reaction occurring through several steps, i.e. not only water oxidation, but also parasitic reactions due to chemical instability of the intermediate [Ru(bpy)3]3+ species, which degrade over time finally decreasing the reaction rate. O2 evolution as catalyzed by Mn2O3 is examined at three irradiance conditions, and for three different catalyst contents. Qualitatively, whereas the increase of catalyst amount yields the expected increase of O2 production and evolution rate, the increase in irradiance enhances the degradation processes, thus giving a “paradoxical” effect of decreasing the chemical yields. Chemical kinetics are applied, and predictions are compared to experimental data derived from bubbling-reactor. The development of the kinetic model imposing steady state condition on transient species yields as expression of RO2 a simple linear combination of two exponentials. It is found that the main activity indicators obtained from the bubbling reactor tests can be related in an expression that is independent of the amount catalytic sites, i.e. the ratio between the O2 evolution rate and the total amount of O2 evolved during the reaction. Results show that the ratio between the kinetic constants of the desired (i.e. O2 formation) and undesired path (i.e. dye degradation) decreases at increasing irradiance, evidencing how the role of parasitic reactions, far from being negligible, tends to be overwhelming.

Solar energy, along with other renewable resources, is going to play a key role in waste treatments and CO2 conversion. Photocatalytic technologies can be considered an effective solution for these purposes. This work summarises the setup of two different reactor configurations for two challenging processes: nitrate/ammonia abatement from water and CO2 photoreduction. The project goal was the setup of proper photoreactors and the preliminary investigation of some critical operating process parameters. Concerning the CO2 photoreduction, large efforts have been devoted to study an innovative high-pressure reactor developed properly to overcome the main limitation of the reaction, i.e. the limited solubility of carbon dioxide in water. On the other hand, nitrate and ammonia conversion was investigated, exploring the reactor setup and the analysis of critical products such as nitrogen.

A sample of pure CeO2 and two samples of Fe-doped CeO2 containing either 3 or 6 at.% Fe were obtained by microwave assisted combustion synthesis. The powders were extensively characterized by several techniques and tested as catalysts for both CO oxidation and soot combustion. As-synthesized CeO2 nanoparticles have a mostly squared shape and size well below 100 nm; they are characterized by the presence of surface Ce3+ species likely due to the occurrence of very defective ceria crystalline phases, as revealed by HR-TEM. Oxidation at 400 °C leads to the formation of a hydroxyls-rich surface, with several types of OH groups related to both Ce4+ and Ce3+ species; reduction in H2 at mild temperature (200 °C) leads both to reduction of surface Ce4+ to Ce3+ and formation of new OH groups. With respect to CeO2 nanoparticles, Fe-doped ones have, as a whole, a larger size and less abundant surface OH species. A core-shell structure is inferred where Fe is mostly present in the shell, both in a secondary phase (CeFeO3) and as a dopant, finally lowering the band gap of the material. The presence of Fe improved samples reducibility, as shown by the lowering of the onset of temperature programmed reduction. Catalytic tests of CO oxidation showed that surface Fe species significantly improve the catalytic performance of the samples, by lowering the onset of CO conversion to CO2 especially at low Fe content (i.e. 3 at.%), whereas at 6 at.% Fe loading, the preferential formation of the secondary phase CeFeO3 occurs, finally lowering the CO conversion with respect to the sample containing 3 at.% Fe. Conversely, the soot combustion activity was higher for pure CeO2 nanoparticles, likely due to their smaller size, which increases the amount of solid–solid contact points between soot and the catalyst. However, a positive effect of the presence of surface Fe species on the catalytic activity towards soot combustion was observed, as well.

Four carbonaceous materials (acetylene black, multi-walled carbon nanotubes, and two carbon materials synthesized by hard-template method) were used as a support to synthesize four Fe-N/C non-noble metal (NNM) catalysts for oxygen reduction reaction (ORR) by impregnation with a FeIII–1,10-phenanthroline complex and subsequent pyrolysis in inert atmosphere. The catalysts were characterized by N2 physisorption, XPS, Raman and TGA, and their ORR activity was measured by rotating disk electrode (RDE) in both acidic and alkaline conditions. The catalysts were tested in an acidic direct methanol fuel cell (DMFC) and in an alkaline direct ethanol fuel cell (DEFC). Due to the slower ORR kinetics at low pH, the features of the carbon support have an important influence on the performance in acidic DMFC. Conversely, the enhanced ORR kinetics at high pH, makes the influence of the C-support less evident in alkaline DEFC. Moreover, the short-term durability test in DMFC for our best Fe-N/C catalysts showed better results compared to Pt/C benchmark catalyst. The durability in alkaline DEFC is poor, even though the initial performance can be partially recovered after purge-drying and reactivation.