Search

Metal-free electrocatalysts for the electrochemical conversion of gases constitute an important asset for a sustainable energy transition. Nucleotides act as redox mediators in the electron transport chain to reduce oxygen in cellular respiration. The biomimicry of such an efficient natural mechanism could be utilized to address the challenges associated with electrochemical gas conversion technologies, such as sluggish kinetics and high overpotentials. Multiple descriptors are generally reported to benchmark the activity of electrocatalysts where the turnover frequency (TOF) is claimed to be the most accurate criterion. Here, a library of graphene nanosheets-nucleotide hybrid materials was prepared, and the electrocatalytic performance towards ORR/OER reactions of a graphene-flavin mononucleotide hybrid was evaluated by rotating disc electrode experiments and TOF estimation. The determination of catalyst loading and dispersion is especially relevant when assessing the intrinsic activity of a catalyst and, therefore, the amount of nucleotide electrocatalyst loaded into the graphene support was thoroughly quantified by a combination of characterization techniques. Density functional theory calculations supported the observed experimental trends, both on the adsorption rate of a given nucleotide on graphene and the catalytic activity of a specific hybrid material. This work constitutes an avenue to predict nature-mimicking electrocatalysts for efficient energy storage.

Layered transition-metal dichalcogenides (LTMDs) in two-dimensional (2D) form are attractive for electrochemical energy storage, but research efforts in this realm have so far largely focused on the best-known members of such a family of materials, mainly MoS2, MoSe2, and WS2. To exploit the potential of further, currently less-studied 2D LTMDs, targeted methods for their production, preferably by cost-effective and sustainable means, as well as control over their nanomorphology, are highly desirable. Here, we report a quick and straightforward route for the preparation of 2D NbSe2 and other metallic 2D LTMDs that relies on delaminating their bulk parent solid under aqueous cathodic conditions. Unlike typical electrochemical exfoliation methods for 2D materials, which generally require an additional processing step (e.g., sonication) to complete delamination, the present electrolytic strategy yielded directly exfoliated nano-objects in a very short time (1-2 min) and with significant yields (∼16 wt %). Moreover, the dominant morphology of the exfoliated 2D NbSe2 products could be tuned between rolled-up nanosheets (nanorolls) and unfolded nanosheets, depending on the solvent where the nano-objects were dispersed (water or isopropanol). This rather unusual delamination behavior of NbSe2 was explored and concluded to occur via a redox mechanism that involves some degree of hydrolytic oxidation of the material triggered by the cathodic treatment. The delamination strategy could be extended to other metallic LTMDs, such as NbS2 and VSe2. When tested toward electrochemical lithium storage, electrodes based on the exfoliated NbSe2 products delivered very high capacity values, up to 750-800 mA h g-1 at 0.5 A g-1, where the positive effect of the nanoroll morphology, associated to increased accessibility of the lithium storage sites, was made apparent. Overall, these results are expected to expand the availability of fit-for-purpose 2D LTMDs by resorting to simple and exped

Nowadays, Ni@C nanostructured materials are attracting a great deal of attention due to their multiple catalytic or magnetic functionalities. In this article we report on the investigation of the correlation between the microstructure and magnetic properties of Ni nanoparticles embedded in a carbon matrix. The samples were obtained following a two-step procedure that ensures protection against nanoparticle oxidation, and was carried out in the following way: (i) the synthesis of a nickel-imidazole-based metal-organic framework (MOF) by a simple method in an aqueous medium at moderate temperature (95 °C); and (ii) carbonization of the MOF at different temperatures between 400 and 600 °C to obtain a carbon-supported hybrid material, containing Ni nanoparticles with an “artichoke-like” morphology, where a Ni-FCC core is surrounded by “bracts” of Ni-HCP and Ni3C. The average size of the nanoparticle slightly changes from 7 to 10 nm as the carbonization temperature is increased, but the Ni-FCC core diameter ranges from 3 to around 6 nm. We show how the information obtained on the evolution of the magnetic behaviour with carbonization temperature, using X-ray diffraction and electron microscopy, complements each other by providing consistent structural and magnetic characteristics of the investigated Ni@C nanoparticles. In fact, this joint analysis allows us to explain the formation and transformation of different Ni-based crystalline phases along the synthesis process, including Ni3C and Ni with both hexagonal and cubic crystalline structures. The amount of conventional Ni-FCC is below 10 wt% for the sample treated at 400 °C and it can reach up to 50 wt% for that treated at 600 °C. Finally, based on our current findings we propose an explanation for understanding the magnetic properties of Ni@C, in which the Ni-FCC core spins mainly govern the magnetic coupling of the whole system.

Two-dimensional (2D) MoSe2 nanosheets were investigated as a catalyst for nitroarene reduction in the context of water treatment and demonstrated to exhibit a higher activity than their more studied MoS2 counterpart. Density functional theory (DFT) calculations disclosed a feasible nitroarene reduction pathway on 2D MoSe2, which involved passivation of the active site by oxygen from the nitro group and its reactivation by a reducing hydride. DFT analysis also provided an explanation for the isomer selectivity displayed by the 2D MoSe2 catalyst (towards, e.g., 2-, 3- and 4-nitroaniline). To facilitate their practical implementation, the bare MoSe2 nanosheets were coated with colloidal stabilizers, and were also immobilized on polymer foam, where they could be re-used for several consecutive catalytic cycles with no significant loss of activity. Overall, the present results open the prospect of 2D transition metal dichalcogenides beyond MoS2 as competitive nanocatalysts for the reduction of nitroarenes and other organic compounds.

To overcome the challenges of Na-O2 batteries with respect to efficiency, capacity, and cycle life as well as to develop cheap, metal-free, and abundant electrocatalysts, we explored boron and nitrogen-functionalized graphene aerogels prepared by the hydrothermal self-assembly of graphene oxide with subsequent thermal reduction. The results showed an improve of both the cycling overpotential and the coulombic efficiency for the functionalized graphene aerogels. However, the nitrogen-containing cathode presented a shortened cycle life and decreased charging stability. The postmortem analysis of the full discharge, and the full discharge and charge cathodes demonstrated that nitrogen functionalization triggered the formation of solid parasitic products that passivate the cathode surface, thus resulting in a poorer electrochemical performance. By contrast, functionalization with boron-containing groups demonstrated to be a more promising strategy due to minimized parasitic products, leading to lower oxygen reduction and evolution overpotentials with a concomitantly enhanced cell efficiency vs. the undoped cathodes. This resulted in a cycle life of 70 cycles at a relatively high current density of 0.1 mA cm−2 with a capacity cut-off of 0.5 mAh cm−2. Our study underscores that functionalization with heteroatoms simultaneously alters multiple characteristics of graphene-based materials, including their chemistry, texture and morphology, which in turn presents a critical impact on the electrochemical response of the resultant Na-O2 cells.

Holey graphene nanosheets are potentially useful in several relevant technological applications, including electrochemical energy storage and molecular separation. Access to this material is mostly accomplished by resorting to standard graphene oxides obtained by common routes (e.g., the Hummers method). However, such a type of highly oxidized graphenes may not be the best option as a precursor to holey graphene on account of their chemical/structural heterogeneity and harsh synthesis conditions. Here, we report the use of highly oxidized graphene nanosheets derived by an electrochemical exfoliation/oxidation strategy as an alternative precursor to holey graphene. Compared to a standard graphene oxide with the same extent of oxidation, the electrochemically derived precursor exhibited larger aromatic domains, which provided a structural basis for its higher electrical conductivity, as well as smaller and denser oxidized regions, associated to a higher chemical homogeneity and lability of its oxygen-containing functional groups. Through selective chemical etching of the oxidized domains, the latter feature was exploited to afford holey graphene nanosheets having smaller and more uniform holes. When used as an electrode material for electrochemical charge storage, the electrochemically derived holey graphene outperformed its standard graphene oxide-based counterpart in terms of capacity and energy density. Overall, boasting distinct structural and chemical characteristics, highly oxidized graphene obtained by electrochemical means can be regarded as a prospective advantageous precursor to many graphene-based materials whose preparation has traditionally relied on the processing of graphene oxides.

Composites of polymer and graphene-based nanomaterials (GBNs) combine easy processing onto porous 3D membrane geometries due to the polymer and cellular differentiation stimuli due to GBNs fillers. Aiming to step forward to the clinical application of polymer/GBNs composites, this study performs a systematic and detailed comparative analysis of the influence of the properties of four different GBNs: (i) graphene oxide obtained from graphite chemically processes (GO); (ii) reduced graphene oxide (rGO); (iii) multilayered graphene produced by mechanical exfoliation method (Gmec); and (iv) low-oxidized graphene via anodic exfoliation (Ganodic); dispersed in polycaprolactone (PCL) porous membranes to induce astrocytic differentiation. PCL/GBN flat membranes were fabricated by phase inversion technique and broadly characterized in morphology and topography, chemical structure, hydrophilicity, protein adsorption, and electrical properties. Cellular assays with rat C6 glioma cells, as model for cell-specific astrocytes, were performed. Remarkably, low GBN loading (0.67 wt%) caused an important difference in the response of the C6 differentiation among PCL/GBN membranes. PCL/rGO and PCL/GO membranes presented the highest biomolecule markers for astrocyte differentiation. Our results pointed to the chemical structural defects in rGO and GO nanomaterials and the protein adsorption mechanisms as the most plausible cause conferring distinctive properties to PCL/GBN membranes for the promotion of astrocytic differentiation. Overall, our systematic comparative study provides generalizable conclusions and new evidences to discern the role of GBNs features for future research on 3D PCL/graphene composite hollow fiber membranes for in vitro neural models.

This paper presents a series of surface experiments simulating underground coal gasification (UCG). The main goal of the experiments was to investigate the influence of the gasification medium and the coal rank on the gasification process. Four multi-day trials were carried out using a laboratory gasification facility designed for the large-scale experimental simulations of UCG and located in the Experimental Mine “Barbara”, located at Mikołów, Poland. Two Polish bituminous coals were investigated: coal sourced from “Piast-Ziemowit” mine and coal sourced from “Wesoła” mine. Each of the two coals was gasified in two separate experiments using oxygen-enriched air (OEA) and pure oxygen as the respective gasifying agents. Gasification with oxygen resulted in significantly higher gas quality and higher process efficiency than gasification with OEA. Higher concentrations of hydrogen (23.2% and 25.5%) and carbon monoxide (31.8% and 33.4%) were obtained when oxygen was used as a gasifying reagent, while lower concentrations were obtained in the case of gasification with OEA (7.1% and 9.5% of hydrogen; 6.4% and 19.7% of carbon monoxide). Average gas calorific values were 7.96 MJ/Nm3 and 9.14 MJ/Nm3 for the oxygen experiments, compared to 2.25 MJ/Nm3 and 3.44 MJ/Nm3 for the OEA experiments (“Piast-Ziemowit” coal and “Wesoła” coal, respectively). The higher coalification degree of “Wesoła” coal (82.01% of carbon) compared to the “Piast-Ziemowit” coal (68.62% of carbon) definitely improves the gas quality and energy efficiency of the process. The rate of water condensate production was higher for the oxygen gasification process (5.01 kg/h and 3.63 kg/h) compared to the OEA gasification process (4.18 kg/h and 2.63 kg/h, respectively), regardless of the type of gasified coal. Additionally, the textural characteristics (porosity development) of the chars remaining after coal gasification experiments were analyzed. A noticeable development of pores larger than 0.7 nm was only obser

[EN] The main aim of this thesis is the preparation by liquid-phase methods of two-dimensional materials, such as graphene and MoS2 nanosheets, as well as the exploration of their use in energy and environmental applications. Using bulk graphite and MoS2 pieces as the starting materials, two-dimensional graphene and MoS2 nanosheets were obtained, respectively, via cathodic exfoliation in aqueous medium. Different parameters of the process were optimized. Among the different starting graphite materials used to produce graphene (graphite foil, graphite rod and highly oriented pyrolytic graphite), graphite foil shows the highest yields, while electrolytes comprising quaternary ammonium salts of intermediate size afford graphene yields close to 50 wt% in optimal conditions. Graphene obtained by this process has a low content of oxygen, a high structural quality and a good electrical conductivity. The cathodically exfoliated graphene was used as an electrode for supercapacitors in the form of a hybrid that incorporated a small amount of vertically oriented cobalt oxide nanosheets. The latter provide pseudocapacitance and act as a spacer, thus preventing the re-stacking of graphene. The hydrophobic graphene obtained by cathodic exfoliation was used as an absorbent of aqueous pollutants, such as oils and dyes. A low-density, easy-to-handle macroscopic structure was prepared by coating melamine foam with cathodic graphene. This strategy prevents the re-stacking of the nanosheets and thus a dramatic loss of specific surface area, thus facilitating the regeneration of the adsorbent. The cathodic exfoliation of bulk MoS2 was carried out using common salts, such as KCl, as the electrolyte in apropiate conditions. The resulting two-dimensional MoS2 nanosheets retained the original 2H phase of the starting material and do not undergo oxidation at any substantial extent. The obtained material was studied as catalyst for the reduction of nitroarenes and as an electrode for supercap, [ES] El objetivo de esta tesis consiste en la preparación y procesado, mediante métodos en fase líquida, de nanoláminas bidimensionales de grafeno y MoS2 para aplicaciones energéticas y medioambientales. Utilizando como cátodo piezas de grafito y MoS2 se obtuvieron, mediante exfoliación electroquímica en medio acuoso, grafeno y nanoláminas de MoS2, respectivamente. Se optimizaron diferentes parámetros del proceso. Entre los distintos tipos de grafito de partida utilizados para la producción de grafeno (grafito flexible, barras de grafito y grafito pirolítico altamente orientado), el grafito flexible es el que condujo a mayor rendimiento en producto expandido. En cuanto al electrolito, ciertas sales de amonio cuaternario de tamaño apropiado resultaron óptimas para maximizar la expansión del electrodo y el rendimiento en grafeno, alcanzándose valores de cerca del 50%. El grafeno obtenido mediante este proceso posee un bajo grado de oxidación, una alta calidad estructural y una buena conductividad eléctrica. Se empleó el grafeno obtenido por exfoliación catódica como electrodo para supercondensadores, fabricando un híbrido mediante la adición de una pequeña cantidad de óxido de cobalto en forma de nanoláminas verticalmente orientadas. Éstas últimas proporcionan pseudocapacitancia y funcionan como espaciador, impidiendo el reapilamiento del grafeno. El alto grado de hidrofobicidad del grafeno obtenido lo hace también útil como adsorbente de contaminantes acuosos, tales como aceites y colorantes. En este caso, se recubrió una esponja de melamina con el grafeno exfoliado, evitando así el reapilamiento de las láminas y la consecuente pérdida de superficie específica, obteniéndose una estructura macroscópica de baja densidad y fácilmente manejable, lo que a su vez facilitaba su regeneración tras el uso. La exfoliación electroquímica catódica de MoS2 se llevó a cabo utilizando como electrolitos sales comunes, como el KCl, en las condiciones adecuadas. La exfoliación no provo

Activated ordered mesoporous carbon (AOMC) sorbents for CO2 capture have been synthesized, characterized and evaluated. They were obtained using low-value products from the distillation of coal tar and following a hard templating method to achieve an ordered mesoporous structure. Both physical and chemical activation processes were applied. It was observed that neither physical nor chemical activation affected the mesopore structure of the samples. Regarding the CO2 capture, the best chemical AOMC was the one activated at 850 °C with a KOH:carbon ratio of 4:1 (2.48 mmol/g AOMC), whilst the best physical activated one was obtained upon activation during 48 h with a burn-off degree of 48% and dissolving the template afterwards (2.38 mmol/g AOMC). In the present case the ordered mesoporous structure was thought to facilitate CO2 diffusion into the micropores of the porous carbons. The best samples were tested for CO2 capture at different operational conditions, considering capture temperatures up to 150 °C and CO2 partial pressures between 5 and 90% (balance N2). Their performance was also tested over six adsorption-desorption cycles, and it was determined that the working capacity remained constant and the mesoporous structure was not modified.

Hyper-crosslinked polymers (HCPs) have been produced by the Friedel-Crafts reaction using anthracene, benzene, carbazole or dibenzothiophene as precursors and dimethoxymethane as crosslinker, and the effect of graphene oxide (GO) addition has been studied. The resulting HCPs were highly microporous with BET areas (ABET) between 590 and 1120 m2g-1. The benzene-derived HCP (B1FeM2) and the corresponding composite with GO (B1FM2-GO) exhibited the highest ABET and were selected to study their hydrogen adsorption capacities in the pressure range of 0.1 - 14 MPa at 77 K. The maximum H2 excess uptake was 2.1 and 2.0 wt% for B1FeM2 and B1FeM2-GO, respectively, at 4 MPa and 77 K. The addition of GO reduced the specific surface area but increased the density of the resultant HCP-GO composites, which is beneficial for practical applications and proves that materials giving higher gravimetric storage capacities are not necessarily those that offer higher volumetric capacities. H2 adsorption-desorption cycles up to 14 MPa showed irreversible deformation of both HCP and HCP-GO materials, which calls into question their application for hydrogen adsorption at pressures above 4 MPa.

Graphene oxide (GO) is emerging as an excellent next generation material for water purification membranes. Its ability to be fabricated cost-effectively in large quantities and featured characteristics, such as hydrophilicity, makes it an equitable graphene alternative in respective nanometric applications, including nanofiltration. In this study, the influence of key properties of the GO sheets, such as lateral size, surface chemistry and colloid stability, on the successful fabrication and subsequent water purification performance of crosslinked nanofiltration membranes is analysed. GO water suspensions with nanosheets of different lateral sizes and distribution of oxygenated functional groups were prepared by controlling the sonication time (from 0 to 180 min) starting from commercial GO. The variation of the physicochemical characteristics of the resulting GO sheets was comprehensively studied by means of atomic force microscopy, UV–Vis absorption spectroscopy, zeta potential measurements and X-Ray photoelectron spectroscopy. The morphology of the subsequently fabricated membranes was hereafter examined via scanning electron microscopy, while their nanofiltration performance was investigated against methylene blue solution. The influence of GO's physicochemical characteristics on membrane performance was apparent, with the average rejection values ranging from 59.8% to 98.4% at a changing lateral size and surface chemistry.

Sodium-oxygen batteries (SOBs) have the potential to provide energy densities higher than the state-of-the-art Li-ion batteries. However, controlling the formation of sodium superoxide (NaO2) as the sole discharge product on the cathode side is crucial to achieve durable and efficient SOBs. In this work, the discharge efficiency of two graphene-based cathodes was evaluated and compared with that of a commercial gas diffusion layer. The discharge products formed at the surface of these cathodes in a glyme-based electrolyte were carefully studied using a range of characterization techniques. NaO2 was detected as the main discharge product regardless of the specific cathode material while small amounts of Na2O2⋅2H2O and carbonate-like side-products were detected by X-ray diffraction as well as by Raman and infrared spectroscopies. This work leverages the use of X-ray diffraction to determine the actual yield of NaO2 which is usually overlooked in this type of batteries. Thus, the proper quantification of the superoxide formed on the cathode surface is widely underestimated; even though is crucial for determining the efficiency of the battery while eliminating the parasitic chemistry in SOBs. Here, we develop an ex-situ analysis method to determine the amount of NaO2 generated upon discharge in SOBs by transmission X-ray diffraction and quantitative Rietveld analysis. This work unveils that the yield of NaO2 depends on the depth of discharge where high capacities lead to very low discharge efficiency, regardless of the used cathode. We anticipate that the methodology developed herein will provide a convenient diagnosis tool in future efforts to optimize the performance of the different cell components in SOBs.

Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O60 (P2W18) heteropolyacids (HPAs) are photo(catalysts) for various acid-promoted and redox catalytic reactions. Their activity increases if they are deposited on certain supports as metal oxides or carbon materials. Although the surface area and acid-base interactions of the HPAs with supports are considered as key factors for the performance of the binary material, the role of the local structure changes in the HPAs upon their immobilization on solids must be also of primary importance, directly affecting both acidity and photoredox properties. Here, the (photo)catalytic performance of Keggin and Wells-Dawson heteropolytungstates supported on boron nitride (BN) and two types of carbon nitride (C3N4) in the gas-solid 2-propanol dehydration to propene has been studied. Apart from characterizing the materials by a set of conventional laboratory-scale structural and physical-chemical techniques, an insight into the variations of the local structure of supported HPAs is provided by means of X-ray absorption spectroscopy (XAS), and their influence on the supported HPAs (photo)catalytic activity is discussed. The irradiation with UV light increased the activity of both heteropolytungstates with respect to the catalytic experiments. The apparent activation energy calculated for the photo-assisted process resulted always lower with respect to that obtained for the catalytic one alone. Moreover, the materials that showed the highest apparent turnover frequency (TOF) were those in which the HPAs were impregnated on graphitic C3N4 or on BN and, in particular, the highest TOF values were observed at the highest temperature for the PW12/BN and P2W18/BN samples. Interestingly, the highest activity of HPAs supported on BN seems to be due to the stabilization of the W octahedral coordination, according to the XAS data.

The molecular functionalization of two-dimensional MoS2 is of practical relevance with a view to, for example, facilitating its liquid-phase processing or enhancing its performance in target applications. While derivatization of metallic 1T-phase MoS2 nanosheets has been relatively well studied, progress involving their thermodynamically stable, 2H-phase counterpart has been more limited due to the lower chemical reactivity of the latter. Here, we report a simple electrolytic strategy to functionalize 2H-phase MoS2 nanosheets with molecular groups derived from organoiodides. Upon cathodic treatment of a pre-expanded MoS2 crystal in an electrolyte containing the organoiodide, water-dispersible nanosheets derivatized with acetic acid or aniline moieties (∼0.10 molecular groups inserted per surface sulfur atom) were obtained. Analysis of the functionalization process indicated it to be enabled by the external supply of electrons from the cathodic potential, although they could also be sourced from a proper reducing agent, as well as by the presence of intrinsic defects in the 2H-phase MoS2 lattice (e.g., sulfur vacancies), where the molecular groups can bind. The acetic acid-functionalized nanosheets were tested as a non-noble metal-based catalyst for nitroarene and organic dye reduction, which is of practical utility in environmental remediation and chemical synthesis, and exhibited a markedly enhanced activity, surpassing that of other (1T- or 2H-phase) MoS2 materials and most non-noble metal catalysts previously reported for this application. The reduction kinetics (reaction order) was seen to correlate with the net electric charge of the nitroarene/dye molecules, which was ascribed to the distinct abilities of the latter to diffuse to the catalyst surface. The functionalized MoS2 catalyst also worked efficiently at realistic (i.e., high) reactant concentrations, as well as with binary and ternary mixtures of the reactants, and could be immobilized on a polymeric sc

Graphene aerogels derived from a biomolecule‐assisted aqueous electrochemical exfoliation route are explored as cathode materials in sodium–oxygen (Na–O2) batteries. To this end, the natural nucleotide adenosine monophosphate (AMP) is used in the multiple roles of exfoliating electrolyte, aqueous dispersant, and functionalizing agent to access high quality, electrocatalytically active graphene nanosheets in colloidal suspension (bioinks). The surface phenomena occurring on the electrochemically derived graphene cathode is thoroughly studied to understand and optimize its electrochemical performance, where a cooperative effect between the nitrogen atoms and phosphates from the AMP molecules is demonstrated. Moreover, the role of the nitrogen atoms in the adenine nucleobase of AMP and short‐chain phosphate is unraveled. Significantly, the use of such cathodes with a proper amount of AMP molecules adsorbed on the graphene nanosheets delivers a discharge capacity as high as 9.6 mAh cm−2 and performs almost 100 cycles with a considerably reduced cell overpotential and a coulombic efficiency of ≈97% at high current density (0.2 mA cm−2). This study opens a path toward the development of environmentally friendly air cathodes by the use of natural nucleotides which offers a great opportunity to explore and manufacture bioinspired cathodes for metal–oxygen batteries.

This work aims at understanding the effect of the mesopore volume of ordered mesoporous carbons (OMCs) on their behavior as anodes for Li-ion batteries. To that purpose, the hard-templating method was used as an enabling tool, with the controlled partial etching of the silica template to prepare a series of OMCs with a wide range of mesopore volumes. The formed carbon-silica hybrids were processed into electrodes using a water-based ink preparation route in the presence of xanthan gum as a binder, which retained access to the pores after formation of the electrodes. The pore texture of the latter was compared to that of the starting powders. A very good linear relationship could be evidenced between the mesopore volume of the electrodes and the first insertion capacity of Li-ions. The lithium de-insertion also followed a linear trend, but its behavior was dependent on the final applied potential. Indeed, the higher the mesopore volume, the higher the contribution of de-insertion at elevated voltages. This study further points out the importance of the textural characterization of electrodes (instead of just the starting material) as well as the conditions at which the electrochemical measurements are carried out, especially the maximum applied de-insertion voltage.

Carbon-supported, non-noble metal-based catalysts derived from metal-organic frameworks (MOFs) are attractive alternatives to noble metal-based systems, but typical syntheses of the starting MOFs are not desirable from an environmental and practical perspective (e.g., they rely on non-innocuous organic solvents and long reaction times). Here, we report the preparation of a Ni-based MOF in aqueous medium, at moderate temperature (95 °C) and in a short reaction time (<30 min), which was used as a sacrificial template to access a family of Ni nanoparticle/carbon hybrids that were then tested as catalysts in the reduction of 4-nitrophenol (4-NP). The MOF-derived hybrids exhibited a mesoporous texture, with specific surface areas between 250 and 450 m2 g−1 depending on the carbonization temperature applied to the MOF, as well as high Ni contents (between 36 and 57 wt%). Notwithstanding the latter, the metal was homogeneously distributed throughout the carbon matrix in the hybrid and was quite resistant to extensive agglomeration and sintering, even at temperatures as high as 1000 °C. With increasing carbonization temperature, the Ni component was seen to go through different crystal phases, i.e., Ni3C phase Ni hexagonal close-packed phase Ni face-centered cubic phase. The results of the catalytic tests suggested the former and latter phases to be the most active towards the reduction of 4-NP, with catalytic activity values as high as 0.039 mol4-NP molNi−1 min−1.

Two-dimensional 2H-phase MoS2 nanosheets can be used as a non-noble metal-based catalyst for nitroarene and organic dye reduction, thus being of potential utility towards the treatment of industrial wastewater. However, their activity is severely limited by the inertness of their pristine basal surface. We report here a simple approach for the catalytic activation of solvent-dispersed MoS2 nanosheets based on the introduction of sulfur vacancies by hydrazine treatment. MoS2 nanosheets boasting markedly improved catalytic activities in the reduction of 4-nitrophenol, 4-nitroaniline, methyl orange and methylene blue by NaBH4 could be obtained, outperforming many prior non-noble metal-based catalysts developed for such reactions. Notably, the improvement in catalytic activity was not compromised by the use of a proper dispersant to colloidally stabilize the activated nanosheets in the aqueous reaction medium. Substrate-supported catalysts could be prepared by immobilizing the nanosheets on melamine foam, facilitating their handling and reutilization. The chemical processes taking place between the investigated reagents and the MoS2 catalyst were also discussed and rationalized, based on which a mechanism for nitroarene/dye reduction mediated by the sulfur vacancies was proposed.

Las técnicas de nanomoldeo son una potente herramienta para la preparación de una variedad de materiales con propiedades avanzadas que difícilmente pueden ser obtenidos por otras técnicas más convencionales. Estas técnicas permiten, por ejemplo, ejercer un alto control sobre la estructura porosa del material. En este trabajo, se utilizó el método conocido como hard-templating para la preparación de un carbón mesoporoso ordenado utilizando como plantilla una sílice mesoporosa. Como precursor se utilizó una creosota, una sustancia de precio modesto obtenida de la destilación de alquitrán de hulla, demostrándose la posibilidad de revalorización de este tipo de productos para la preparación de materiales avanzados. La red porosa de la plantilla se infiltró mediante un método simple de un solo paso en medio ácido a una temperatura moderada. La optimización de las condiciones de síntesis condujo a materiales con una porosidad muy bien ordenada y con una distribución de tamaño de poro muy estrecha en la región del mesoporo, junto con una alta área superficial. Este material se probó como electrodo para dispositivos de almacenamiento de energía electroquímica y como adsorbente para la eliminación de contaminantes. Debido a su red de poros jerárquica bien desarrollada, el carbón mesoporoso ordenado mostró un buen comportamiento como electrodo en supercondensadores en electrolito acuoso y como adsorbente de colorantes.

Graphitic carbon nitride (g-C3N4) is promising as adsorbent for water remediation as its chemical structure allows a variety of mechanisms to interact with wastewater pollutants. However, several issues, such as low specific surface area and insufficient dispersibility in water, have to be tackled to achieve a competitive performance in such use. Previous attempts to improve the features of g-C3N4as an adsorbent have relied on carbon doping and exfoliation in the solid phase by thermal expansion. Here, we demonstrate that exfoliation in the liquid phase by a combination of oxidation and sonication allows preparing g–C3N4–based materials with improved dispersibility in water, increased exposed surface, and abundance of surface functional groups. The obtained oxidized g-C3N4 adsorbents exhibited high adsorption capacities which were remarkable towards organic dyes (∼70–600 mg/g) and excellent in the case of the antibiotic tetracycline (895 mg/g) in aqueous solution. The present results should open new opportunities for the use of oxidized g-C3N4 materials as adsorbents for water remediation.

[EN] The main objective of this thesis is the development of preparation and functionalization methods of liquid phase 2D materials, particularly graphene, molybdenum disulfide (MoS2) and cobalt oxide (Co3O4). Anodic electrochemical exfoliation of graphite using potassium sulfate as the electrolyte was studied, evaluating the use of different graphites and the impact of the choice over the characteristics of the obtained graphene. Among the materials studied, graphite foil showed the best results. Aromatic sulfonates were also studied as electrolytes for the preparation of graphene, acting as the intercalating agents, colloidal stabilizers, antioxidants and anchoring points for the formation of graphene-based hybrids with very low oxidation degree (~2%). A pretreatment of the graphite foil with sulfuric acid was studied, and it increased the yield of electrochemical exfoliation from ~10% to more than 50%. Sodium halides were identified as efficient anodic exfoliation electrolytes, yielding graphenes with lower oxygen content than those obtained using sulfate. This discovery led to the development of electrolyte additives acting as antioxidants, with chloride anion standing out, allowing to obtain very high quality anodic graphene with a very limited degree of oxidation. Functionalization of MoS2 obtained through the lithium intercalation route with acetic acid groups was studied, obtaining 1T phase nanosheets with long-term colloidal stability in water that were tested as catalysts for the reduction of nitroarenes, maintaining their catalytic activity longer than the non-functionalized material. Finally, activated Co3O4 2D nanosheets were synthesized through a micellar phase directed solvothermal process. This material was tested as charge storage electrode, catalyst in the reduction of nitroarenes and dye adsorbant in water solutions, showing comparable or better results in all cases compared to those of other nanostructured cobalt oxide materials., [ES] La presente tesis tiene como objetivo central el desarrollo de métodos de preparación y funcionalización en fase líquida de materiales bidimensionales (2D), concretamente grafeno, disulfuro de molibdeno (MoS2) y óxido de cobalto (Co3O4). Se ha estudiado la exfoliación electroquímica anódica de grafito para obtener grafeno con sulfato potásico como electrolito, investigándose el uso de diferentes grafitos como ánodo y su influencia en las características del grafeno resultante. Entre los materiales estudiados, el grafito flexible mostró los mejores resultados. Asimismo, se utilizaron como electrolitos en exfoliación anódica sulfonatos aromáticos, que actúan como agentes intercalantes, estabilizantes, antioxidantes y centros de anclaje para la preparación de materiales híbridos basados en grafeno con un grado de oxidación muy bajo (~2%). Se estudió también el pretratamiento del grafito flexible con ácido sulfúrico, lo que permitió aumentar el rendimiento de exfoliación electroquímica anódica del ~10% a más del 50%. En el contexto de la exfoliación anódica se indentificó a los halogenuros de sodio como electrolitos eficientes de exfoliación, con resultados similares a los sulfatos utilizados habitualmente, pero con un grado de oxidación menor. Este descubrimiento llevó al desarrollo de aditivos de electrolito con función antioxidante, destacando entre ellos el anión cloruro, para obtener grafeno anódico de muy alta calidad con un grado de oxidación muy limitado. Se estudió también la funcionalización de MoS2 obtenido mediante la ruta de intercalación de litio con grupos de ácido acético, obteniéndose láminas en fase 1T coloidalmente estables a largo plazo que se utilizaron como catalizadores de la reducción de nitroarenos, reteniendo su actividad durante más tiempo que las láminas no funcionalizadas. Por último, mediante un proceso solvotérmico en medio micelar laminar se prepararon láminas 2D de Co3O4 activado sin necesidad de activación posterior. Este material

The production of MoS2 nanosheets by electrochemical exfoliation routes holds great promise as a means to access this two-dimensional material in large quantities for different practical applications. However, the use of electrolytes based on synthetic organic salts and solvents, as well as issues related to the unwanted oxidation and/or phase transformation of the exfoliated nanosheets, constitute significant obstacles that hinder the industrial adoption of the electrochemical approach. Here, we introduce a safe and sustainable method for the cathodic delamination of MoS2 that makes use of aqueous solutions of very simple and widely available salts, mainly KCl, as the electrolyte. Combined with an appropriate biomolecule-based solvent transfer protocol, such an electrolytic exfoliation route is shown to afford colloidally dispersed, oxide-free, and phase-preserved MoS2 nanosheets of high structural quality in considerable yields. The mechanisms behind the efficient aqueous delamination of the bulk MoS2 cathode are also discussed and rationalized on the basis of the penetration of hydrated cations from the electrolyte between its layers and the immediate reduction of the accompanying water molecules. An asymmetric supercapacitor assembled with a cathodic MoS2 nanosheet–single walled carbon nanotube hybrid as the positive electrode and activated carbon as the negative electrode delivered energy densities (e.g., 26 W h kg–1 at 750 W kg–1 in 6 M KOH) that were competitive with those of other MoS2-based asymmetric devices. When used as a catalyst for the reduction of nitroarenes, the present cathodically exfoliated nanosheets exhibited one of the highest activities reported so far with MoS2 nanostructures, the origin of which is accounted for as well. Overall, by facilitating access to this two-dimensional material through a particularly simple, efficient, and cost-effective technique, these results should expedite the practical implementation of MoS2 nanosheets in ener

Ordered mesoporous carbons (OMCs) obtained by the hard-templating method are usually prepared using complicated infiltration procedures and/or relatively high-priced carbon precursors. In this work, OMCs were obtained using creosote, a modestly priced substance obtained from the distillation of coal tar, as a carbon precursor and an ordered mesoporous silica (SBA-15) as the template. The porous network of the template was infiltrated using a simple, one-step method in acidic medium at a moderate temperature, making it potentially scalable for mass production. Optimization of the synthesis conditions led to OMCs with a very well ordered porosity with a very narrow pore size distribution in the mesopore region, together with a high surface area. This material was tested as an electrode for electrochemical energy storage devices and as an adsorbent for pollutant removal. Owing to its well-developed hierarchical pore network, the present OMC showed a good performance as a supercapacitor electrode in aqueous electrolyte and high rate of methylene blue dye adsorption.

The electrochemical exfoliation of graphite in aqueous medium stands out as an attractive, scalable approach for the production of graphenes for different applications, due to its simplicity, cost-effectiveness and environmental friendliness. In particular, cathodic exfoliation in water should allow access to high quality, non-oxidized graphene flakes, as it avoids the intrinsic oxidizing conditions that typically plague the anodic route, but this possibility has been limited by a poor intercalation ability of aqueous cations. Here, we demonstrate that with a proper choice of starting graphite and electrolyte, high quality graphene flakes can be obtained in substantial yields via cathodic delamination in water. Graphites having some pre-expanded edges and interlayer voids (e.g., graphite foil) were found to be critical for a successful exfoliation. Large differences in the efficiency of a range of aqueous quaternary ammonium-based electrolytes were observed, quantitatively compared and rationalized on the basis of their chemical structure. Graphene yields up to 40–50 wt% were attained with the most efficient cations (tetrapropylammonium and hexyltrimethylammonium). Hydrophobic sponges made up of cathodic graphene-coated melamine foam exhibited a notable capacity towards the sorption of oils and organic solvents from water with good re-usability. Hybrids comprised of cathodically exfoliated graphite and a small amount of vertically oriented cobalt oxide nanosheets displayed good electrochemical charge storage behavior. Overall, the ability to access graphene flakes in considerable yields by the aqueous cathodic route disclosed here should raise the prospects of cathodic exfoliation as a competitive method for the industrial manufacturing of high quality graphene for practical applications.

Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS2 and WS2, have recently emerged as nanomaterials with potential use in biomedicine. An attractive means to favor their interaction with biological media is the use of proper biomolecules as exfoliating/dispersing agents. Here, MoS2 flakes were stabilized with different small functional biomolecules such as adenosine monophosphate (AMP), guanosine monophosphate (GMP) and flavin mononucleotide (FMN) through the strong nucleotide−MoS2 interaction of Lewis acid-base type, rather than just on the weak dispersive and hydrophobic forces commonly associated with the use of many surfactants. The impact of the nucleotide-stabilized MoS2 flakes on the viability and cell proliferation, on the production of intracellular reactive oxygen species (ROS), and on the preosteoblast differentiation process (early stage) has been also evaluated, as well as the incorporation and intracellular localization of the nanomaterials by MC3T3-E1 and Saos-2 cells. The nucleotide-stabilized MoS2 flakes were found to exhibit excellent biocompatibility. Furthermore, their incorporation did not affect the integrity of the cell plasma membrane, which makes them ideal candidates for delivering drug/gene directly into cells. The in vitro cell response of tumor cells to these nanomaterials differs from that of undifferentiated cells, which provides the basis for their potential use in cancer therapy.

Phosphate-functionalized carbon-based nanomaterials have attracted significant attention in recent years owing to their outstanding behavior in electrochemical energy-storage devices. In this work, we report a simple approach to obtain phosphate-functionalized graphene (PFG) via anodic exfoliation of graphite at room temperature with a high yield. The graphene nanosheets were obtained via anodic exfoliation of graphite foil using aqueous solutions of H3PO4 or Na3PO4 in the dual role of phosphate sources and electrolytes, and the underlying exfoliation/functionalization mechanisms are proposed. The effect of electrolyte concentration was studied, as low concentrations do not lead to a favorable graphite exfoliation and high concentrations produce fast graphite expansion but poor layer-by-layer delamination. The optimal concentrations are 0.25 M H3PO4 and 0.05 M Na3PO4, which also exhibited the highest phosphorus contents of 2.2 and 1.4 at. %, respectively. Furthermore, when PFG-acid at 0.25 M and PFG-salt at 0.05 M were tested as an electrode material for capacitive energy storage in a three-electrode cell, they achieved a competitive performance of ∼375 F/g (540 F/cm3) and 356 F/g (500 F/cm3), respectively. Finally, devices made up of symmetric electrode cells obtained using PFG-acid at 0.25 M possess energy and power densities up to 17.6 Wh·kg-1 (25.3 Wh·L-1) and 10,200 W/kg; meanwhile, PFG-salt at 0.05 M achieved values of 14.9 Wh·kg-1 (21.3 Wh·L-1) and 9400 W/kg, with 98 and 99% of capacitance retention after 10,000 cycles, respectively. The methodology proposed here also promotes a circular-synthesis process to successfully achieve a more sustainable and greener energy-storage device.

The production of graphene through anodic exfoliation of graphite in water is regarded as a competitive approach in the efforts to scale-up the manufacturing of this two-dimensional material for different practical uses. However, issues related to oxidative attack of the nanosheets inherent to this delamination process have traditionally precluded the attainment of high quality materials, with the use of proper electrolyte additives as oxidation-preventing agents being proposed as a possible way out. Here we demonstrate that sodium chloride (table salt) can be used as a highly efficient additive (co-electrolyte) of common sulfate-based electrolytes, yielding anodically exfoliated graphene with minimal oxidation (O/C ratio ∼0.02–0.03) and thus a high structural quality. As an oxidation-preventing co-electrolyte, sodium chloride clearly outperformed other tested additives, including sodium borohydride, sulfite, citrate, bromide and iodide, ascorbic acid or ethanol, as well as other recently reported chemical species of a more complex nature and/or less readily available. The apparently contradicting ability of the chloride anion to avert oxidation of anodic graphene without negatively interfering with the exfoliation process itself was also discussed and ultimately ascribed to the different chemical reactivity of graphite edges and basal planes. The as-prepared, low-oxidized graphene exhibited a notable adsorption capacity toward organic dyes in aqueous solution (e.g., ∼450 mg g−1 for methyl orange), a substantial ability to absorb oils and non-polar organic solvents (15–30 g g−1), and displayed a good capacitive energy storage behavior (e.g., ∼120 F g−1 at 0.1 A g−1), all without the need of any post-processing steps that are so common for graphene-based materials. Overall, the demonstration that low-oxidized anodic graphene can be obtained by resorting only to inexpensive and widely available reagents should facilitate the implementation of this methodology in the i

Two-dimensional Co3O4 nanosheets have emerged as attractive materials for use in a number of relevant technological applications. To exhibit a competitive performance in such uses, however, their structure needs to be activated, which is frequently accomplished via post-synthesis reduction strategies that introduce oxygen vacancies and increase the number of active Co(II) sites. Here, we investigate a direct route for the synthesis of activated Co3O4 nanosheets that avoids reduction post-treatments, yielding materials with a high potential towards energy- and environment-related applications. The synthesis relied on an interim amorphous cobalt oxide material with nanosheet morphology, which upon calcination afforded Co3O4 nanosheets having Co(II) sites in quantities similar to those usually found for Co3O4 nanostructures activated by reduction post-treatments. When tested as electrodes for charge storage, the nanosheets demonstrated a competitive behavior in terms of both capacity and rate capability, e.g., a gravimetric capacity of ∼293 mAh g−1 at 1 A g−1 with 57% retention at 60 A g−1 was measured for nanosheets calcined at 350 °C. The materials were shown to be efficient catalysts for the reduction of nitroarenes (4-nitrophenol and 4-nitroaniline), outperforming other Co3O4 nanostructures, as well as effective adsorbents for the removal of organic dyes (methyl orange, methylene blue) from water.

Coal tar is a highly viscous liquid obtained as a by-product of coal carbonization, consisting mainly of complex mixtures of polycyclic aromatic hydrocarbons (including sulfur- and nitrogen-containing heterocycles) and phenolic compounds. Separation of coal tar into different fractions by distillation affords high-value products. Thus, naphthalene, anthracene oil or pitch are widely employed in, e.g., the manufacturing of polymers, dyes and resins (naphthalene), the synthesis of carbon black for use as a pigment or tire reinforcement (anthracene oil), or the production of carbon fibers for plastic reinforcement and synthetic graphites to be employed as electrodes in the steel and aluminum industries (pitch). In addition to these fractions, a number of liquids are also produced from coal tar distillation, including creosotes, light oils, phenolic oils and wash oils, as well as several rejects or by-products obtained from the purification of higher-value fractions such as naphthalene oils. Although some of the mentioned liquids have found a few practical uses, high-end applications for such liquids and rejects have been generally lacking. Some of these liquids and rejects are enriched in certain aromatic compounds and/or heterocycles with a potential to be exploited towards valuable applications. Therefore, the aim of this work was to investigate the use of a number of coal-derived liquids and rejects as precursors for the synthesis of ordered mesoporous carbons and carbon gels, including the exploration of innovative solutions to make the most of the multi-component nature of these products, as well as their potential use in energy- and environment-related applications. The investigation was carried out in collaboration with partners from the European industrial stakeholders at both ends of the value chain, from the producer of coal tar-derived products to the commercial porous carbon distributer. The preparation, characterization and evaluation of the porous carbon

Graphene and graphene-based materials have shown great promise in many technological applications, but their large-scale production and processing by simple and cost-effective means still constitute significant issues in the path of their widespread implementation. Here, we investigate a straightforward method for the preparation of a ready-to-use and low oxygen content graphene material that is based on electrochemical (anodic) delamination of graphite in aqueous medium with sodium halides as the electrolyte. Contrary to previous conflicting reports on the ability of halide anions to act as efficient exfoliating electrolytes in electrochemical graphene exfoliation, we show that proper choice of both graphite electrode (e.g., graphite foil) and sodium halide concentration readily leads to the generation of large quantities of single-/few-layer graphene nanosheets possessing a degree of oxidation (O/C ratio down to ∼0.06) lower than that typical of anodically exfoliated graphenes obtained with commonly used electrolytes. The halide anions are thought to play a role in mitigating the oxidation of the graphene lattice during exfoliation, which is also discussed and rationalized. The as-exfoliated graphene materials exhibited a three-dimensional morphology that was suitable for their practical use without the need to resort to any kind of postproduction processing. When tested as dye adsorbents, they outperformed many previously reported graphene-based materials (e.g., they adsorbed ∼920 mg g-1 for methyl orange) and were useful sorbents for oils and nonpolar organic solvents. Supercapacitor cells assembled directly from the as-exfoliated products delivered energy and power density values (up to 15.3 Wh kg-1 and 3220 W kg-1, respectively) competitive with those of many other graphene-based devices but with the additional advantage of extreme simplicity of preparation.

The ability to use RNA/DNA nucleotides as colloidal stabilizers for graphene would be an important asset, as a close graphene-nucleotide association would facilitate access to hybrid systems where the rich covalent and supramolecular chemistry of these biomolecules could be exploited alongside graphene in a number of applications. Unfortunately, single RNA/DNA nucleotides are inefficient graphene dispersants. Here we propose and demonstrate a supramolecular strategy which overcomes this limitation, affording aqueous dispersions of high quality graphene flakes with much improved colloidal stability. A nucleotide is combined with its complementary nucleobase yielding stable hydrogen-bonded supramolecular entities that adsorb more strongly on the graphene surface than their individual components. Based on this approach, graphene-nucleotide hybrid hydrogels could be readily obtained, where the graphene flakes were intimately and uniformly intermixed with the nucleotide-based gel phase. Such hydrogels exhibited higher uptakes and/or slower release profiles of dyes and drugs (rhodamine B, methylene blue and tetracycline) than their graphene-free counterparts. Cell proliferation tests suggested the graphene materials obtained with nucleotide-nucleobase stabilizers to be biocompatible. The present results constitute a novel strategy in the processing and molecular integration of graphene that could be extended to other (bio)molecules of interest towards the realization of functional materials for different applications.