New trends in modelling of breakthrough curves to remove pollutants using adsorption on advanced monoliths geometries.

This work proposes a rigorous mathematical model capable of reproducing the adsorption process in dynamic regime on advanced monoliths geometries. For this, four bed geometries with axisymmetric distribution of channels and similar solid mass were proposed. In each geometry a different distribution of channels was suggested, maintaining constant the bed dimensions of 15 cm high and 5 cm radius. The mathematical modeling includes mass and momentum transfer phenomena, and it was solved with the COMSOL Multiphysics software using mass transfer parameters published in the literature. The overall performance of the column was evaluated in terms of breakthrough (CA/CA0 = 0.1) and saturation times (CA/CA0 = 0.9). The mass and velocity distributions obtained from the proposed model show good physical consistency with what is expected in real systems. In addition, the model proved to be easy to solve given the short convergence times required (2-4 h). Modifications were made to the bed geometry to achieve a better use of the adsorbent material which reached up to 80%. The proposed bed geometries allow obtaining different mixing distributions, in such a way that inside the bed a thinning of the boundary layer is caused, thus reducing diffusive effects at the adsorbent solid-fluid interface, given dissipation rates of about 323 × 10-11 m2/s3. The bed geometry composed of intersecting rings deployed the best performance in terms of usage of the material adsorbent, and acceptable hydrodynamical behavior inside the channels (maximum fluid velocity = 35.4 × 10-5 m/s and drop pressure = 0.19 Pa). Based on these results, it was found that it is possible to reduce diffusional effects and delimit the mass transfer zone inside the monoliths, thus increasing the efficiency of adsorbent fixed beds.

Enhancement of the Generation and Transfer of Active Oxygen in Ni/CeO2 Catalysts for Soot Combustion by Controlling the Ni-Ceria Contact and the Three-Dimensional Structure.

The effect of the three-dimensionally ordered macroporous (3DOM) structure and the Ni doping of CeO2 on the physicochemical properties and catalytic activity for soot combustion was studied. Moreover, the way in which Ni is introduced to the ceria support was also investigated. For this, CeO2 supports were synthesized with uncontrolled (Ref) and 3DOM-structured morphology, and their respective Ni/CeO2 catalysts were prepared by impregnation of the previously synthesized supports or by successive impregnation of both precursors (Ni and Ce) on the 3DOM template. Conclusions reached in this study are: (1) the 3DOM structure increases the surface area of the catalysts and improves the catalyst-soot contact. (2) The doping of CeO2 with Ni improves the catalytic activity because the NiO participates in the catalytic oxidation of NO to NO2, and also favors the production of active oxygen and the catalyst oxygen storage capacity. (3) Ni incorporation method affects its physicochemical and catalytic properties. By introducing Ni by successive infiltration in the solid template, the CeO2 crystal size is reduced, Ni dispersion is improved, and the catalyst reducibility is increased. All of these characteristics make the catalyst synthesized by successive infiltration to have higher catalytic activity for soot combustion than the Ni-impregnated CeO2 catalyst.

Cellulose-based materials in tailoring a novel defective titanium­carbon­phosphorus hybrid composites for highly efficient photocatalytic activity.

Until now, black titania has attracted much interest as a potential photocatalyst. In this contribution, we report the first demonstration of the effective strategy to fundamentally improve the photocatalytic performance using a novel sustainable defective titanium­carbon-phosphorous (TCPH) hybrid nanocomposite. The prepared TCPH was used for photocatalytic degradation of the main organic pollutants, which is methyl orange (MO) dye. The physico-chemical properties of as-prepared samples were characterized by various techniques to observe the transformations after carbonization and the interaction between different composite phases. The existence of Ti+3 and oxygen vacancies at the surface, and a notable increase in surface area, are all demonstrated by TCPH, together with the distinct core-shell structure. These unique properties exhibit excellent photocatalytic performance due to the boosted charge transport and separation. The highest degradation efficiency of methyl orange (MO) was attained in the case of TCPH when compared with titanium-cellulose-phosphorous (TCeP) and titanium­carbon-phosphorous (TCPN). Accordingly, the highest degradation efficiency was achieved by applying the optimal operational conditions of 1 g/L of TCPH catalyst, 10 mg/L of MO, pH of 7 and the temperature at 25 ± 3 °C after 3 min under LED lamp (365 nm) with light intensity 100 mW/cm2. The degradation mechanism was investigated, and the trapping tests showed the dominance of hydroxyl radicals in the degradation of MO. TCPH showed high stability under a long period of operation in five consecutive cycles, which renders the highly promising on an industrial scale. The fabrication of highly active defective titanium­carbon-phosphorous opens new opportunities in various areas, including water splitting, and CO2 reduction.

Facile Synthesis of Carbon-Based Inks to Develop Metal-Free ORR Electrocatalysts for Electro-Fenton Removal of Amoxicillin.

The electro-Fenton process is based on the generation of hydroxyl radicals (OH•) from hydroxide peroxide (H2O2) generated in situ by an oxygen reduction reaction (ORR). Catalysts based on carbon gels have aroused the interest of researchers as ORR catalysts due to their textural, chemical and even electrical properties. In this work, we synthesized metal-free electrocatalysts based on carbon gels doped with graphene oxide, which were conformed to a working electrode. The catalysts were prepared from organic-gel-based inks using painted (brush) and screen-printed methods free of binders. These new methods of electrode preparation were compared with the conventional pasted method on graphite supports using a binder. All these materials were tested for the electro-Fenton degradation of amoxicillin using a homemade magnetite coated with carbon (Fe3O4/C) as a Fenton catalyst. All catalysts showed very good behavior, but the one prepared by ink painting (brush) was the best one. The degradation of amoxicillin was close to 90% under optimal conditions ([Fe3O4/C] = 100 mg L-1, -0.55 V) with the catalyst prepared using the painted method with a brush, which had 14.59 mA cm-2 as JK and a H2O2 electrogeneration close to 100% at the optimal voltage. These results show that carbon-gel-based electrocatalysts are not only very good at this type of application but can be adhered to graphite free of binders, thus enhancing all their catalytic properties.

Modeling and experimental analysis of CO2 methanation reaction using Ni/CeO2 monolithic catalyst.

In this study, the effect of the cell density of monolithic catalysts was investigated and further mathematically modeled on cordierite supports used in CO2 methanation. Commercial cordierite monoliths with 200, 400, and 500 cpsi cell densities were coated by immersion into an ethanolic suspension of Ni/CeO2 active phase. SEM-EDS analysis confirmed that, owing to the low porosity of cordierite (surface area < 1 m2 g-1), the Ni/CeO2 diffusion into the walls was limited, especially in the case of low and intermediate cell density monoliths; thus, active phase was predominantly loaded onto the channels' external surface. Nevertheless, despite the larger exposed surface area in the monolith with high cell density, which would allow for better distribution and accessibility of Ni/CeO2, its higher macro-pore volume resulted in some introduction of the active phase into the walls. As a result, the catalytic evaluation showed that it was more influenced by increments in volumetric flow rates. The low cell density monolith displayed diffusional control at flow rates below 500 mL min-1. In contrast, intermediate and high cell density monoliths presented this behavior up to 300 mL min-1. These findings suggest that the interaction reactants-catalyst is considerably more affected by a forced non-uniform flow when increasing the injection rate. This condition reduced the transport of reactants and products within the catalyst channels and, in turn, increased the minimum temperature required for the reaction. Moreover, a slight diminution of selectivity to CH4 was observed and ascribed to the possible formation of hot spots that activate the reverse water-gas shift reaction. Finally, a mathematical model based on fundamental momentum and mass transfer equations coupled with the kinetics of CO2 methanation was successfully derived and solved to analyze the fluid dynamics of the monolithic support. The results showed a radial profile with maximum fluid velocity located at the center of the channel. A reactive zone close to the inlet was obtained, and maximum methane production (4.5 mol m-3) throughout the monolith was attained at 350 °C. Then, linear streamlines of the chemical species were developed along the channel.

Size Control of Carbon Xerogel Spheres as Key Factor Governing the H2O2 Selectivity in Metal-Free Bifunctional Electro-Fenton Catalysts for Tetracycline Degradation.

Carbon xerogel spheres co-doped with nitrogen and eco-graphene were synthesized using a typical solvothermal method. The results indicate that the incorporation of eco-graphene enhances the electrochemical properties, such as the current density (JK) and the selectivity for the four transferred electrons (n). Additionally, nitrogen doping has a significant effect on the degradation efficiency, varying with the size of the carbon xerogel spheres, which could be attributed to the type of nitrogenous group doped in the carbon material. The degradation efficiency improved in the nanometric spheres (48.3% to 61.6%) but decreased in the micrometric-scale spheres (58.6% to 53.4%). This effect was attributed to the N-functional groups present in each sample, with N-CNS-5 exhibiting a higher percentage of graphitic nitrogen (35.7%) compared to N-CMS-5 (15.3%). These findings highlight the critical role of sphere size in determining the type of N-functional groups present in the sample. leading to enhanced degradation of pollutants as a result of the electro-Fenton process.

Application of artificial intelligence for the optimization of advanced oxidation processes to improve the water quality polluted with pharmaceutical compounds.

Sulfamethoxazole and metronidazole are emerging pollutants commonly found in surface water and wastewater. These compounds have a significant environmental impact, being necessary in the design of technologies for their removal. Recently, the advanced oxidation process has been proven successful in the elimination of this kind of compounds. In this sense, the present work discusses the application of UV/H2O2 and ozonation for the degradation of both molecules in single and binary systems. Experimental kinetic data from O3 and UV/H2O2 process were adequately described by a first and second kinetic model, respectively. From the ANOVA analysis, it was determined that the most statistically significant variables were the initial concentration of the drugs (0.03 mmol L-1) and the pH = 8 for UV/H2O2 system, and only the pH (optimal value of 6) was significant for degradation with O3. Results showed that both molecules were eliminated with high degradation efficiencies (88-94% for UV/H2O2 and 79-98% for O3) in short reaction times (around 30-90 min). The modeling was performed using a quadratic regression model through response surface methodology representing adequately 90 % of the experimental data. On the other hand, an artificial neural network was used to evaluate a non-linear multi-variable system, a 98% of fit between the model and experimental data was obtained. The identification of degradation byproducts was performed by high-performance liquid chromatography coupled to a time mass detector. After each process, at least four to five stable byproducts were found in the treated water, reducing the mineralization percentage to 20% for both molecules.

Carbon Gels-Green Graphene Composites as Metal-Free Bifunctional Electro-Fenton Catalysts.

The Electro-Fenton (EF) process has emerged as a promising technology for pollutant removal. However, the EF process requires the use of two catalysts: one acting as an electrocatalyst for the reduction of oxygen to H2O2 and another Fenton-type catalyst for the generation of ·OH radicals from H2O2. Thus, the search for materials with bifunctionality for both processes is required for a practical and real application of the EF process. Thus, in this work, bifunctional electrocatalysts were obtained via doping carbon microspheres with Eco-graphene, a form of graphene produced using eco-friendly methods. The incorporation of Eco-graphene offers numerous advantages to the catalysts, including enhanced conductivity, leading to more efficient electron transfer during the Electro-Fenton process. Additionally, the synthesis induced structural defects that serve as active sites, promoting the direct production of hydroxyl radicals via a 3-electron pathway. Furthermore, the spherical morphology of carbon xerogels enhances the accessibility of the reagents to the active sites. This combination of factors results in the effective degradation of Tetracycline (TTC) using metal-free catalysts in the Electro-Fenton process, achieving up to an impressive 83% degradation without requiring any other external or additional catalyst.

Synthesis, characterization, and application of pristine and clay-templated carbon xerogel microspheres for removing diclofenac and heavy metals from water solution.

Organic xerogel microspheres (SX) were synthesized by inverse emulsion sol-gel polymerization and carbonized to obtain carbon xerogel spheres (SXCs). The catalyst was K2CO3 or Fe(C2H3O2)2, and the clay sodium sepiolite (SNa) or exfoliated vermiculite (Vexf) was added during the synthesis. Depending on the catalyst and clays, the SXCs were designated SXC-K, SXC-Fe, Vexf-K, Vexf-Fe, SNa-Fe, and SNa-K. At pH = 7 and T = 25 °C, the SXCs' adsorption capacities towards diclofenac (DCF) in water increased as follows: SXC-K < Vexf-Fe < SXC-Fe < SNa-Fe < SNa-K < Vexf-K and this order is associated with the SXCs' surface area and mesopore volume. The Vexf-K displayed the highest capacity for DCF due to its optimal textural and chemical properties, and the DCF maximum uptake was 560 mg/g at pH = 6 and T = 35 °C. The adsorption capacity towards Cd2+ and Pb2+ decreased as SX-K > SX-Fe > SXC-K > SXC-Fe, indicating that the non-carbonized materials (SX) presented higher adsorption capacity than the SXCs because the SXs had a higher acidic site content. Adding SNa or Vexf to SXs enhanced the adsorption capacity towards Cd(II), and SNa-SX-K presented an exceptionally high capacity of 182.7 mg/g. This synergistic effect revealed that the Cd2+ was adsorbed on the SX-K acidic sites and by cation exchange on the SNa.

Mineral Manganese Oxides as Oxidation Catalysts: Capabilities in the CO-PROX Reaction.

Cryptomelane is an abundant mineral manganese oxide with unique physicochemical features. This work investigates the real capabilities of cryptomelane as an oxidation catalyst. In particular, the preferential CO oxidation (CO-PROX), has been studied as a simple reaction model. When doped with copper, the cryptomelane-based material has revealed a great potential, displaying a comparable activity to the high-performance CuO/CeO2. Despite stability concerns that compromise the primary catalyst reusability, CuO/cryptomelane is particularly robust in the presence of CO2 and H2O, typical components of realistic CO-PROX streams. The CO-PROX reaction mechanism has been assessed by means of isotopic oxygen pulse experiments. Altogether, CuO/CeO2 shows a greater oxygen lability, which facilitates lattice oxygen enrolment in the CO-PROX mechanism. In the case of CuO/cryptomelane, in spite of its lower oxygen mobility, the intrinsic structural water co-assists as active oxygen species involved in CO-PROX. Thus, the presence of moisture in the reaction stream turns out to be beneficial for the stability of the cryptomelane structure, besides aiding into the active oxygen restitution in the catalyst. Overall, this study proves that CuO/cryptomelane is a promising competitor to CuO/CeO2 in CO-PROX technology, whose implementation can bring the CO-PROX technology and H2 purification processes a more sustainable nature.

Effect of Pr in CO2 Methanation Ru/CeO2 Catalysts.

CO2 methanation has been studied with Pr-doped Ru/CeO2 catalysts, and a dual effect of Pr has been observed. For low Pr content (i.e., 3 wt %) a positive effect in oxygen mobility prevails, while for high Pr doping (i.e., 25 wt %) a negative effect in the Ru-CeO2 interaction is more relevant. Isotopic experiments evidenced that Pr hinders the dissociation of CO2, which takes place at the Ru-CeO2 interface. However, once the temperature is high enough (200 °C), Pr improves the oxygen mobility in the CeO2 support, and this enhances CO2 dissociation because the oxygen atoms left are delivered faster to the support sink and the dissociation sites at the interface are cleaned up faster. In situ Raman spectroscopy experiments confirmed that Pr improves the creation of oxygen vacancies on the ceria lattice but hinders their reoxidation by CO2, and both opposite effects reach an optimum balance for 3 wt % Pr doping. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments showed that Pr doping, regardless of the amount, decreases the population of surface carbon species created on the catalysts surface upon CO2 chemisorption under methanation reaction conditions, affecting both productive reaction intermediates (formates and carbonyls) and unproductive carbonates.

Synthesis of Magnetic Adsorbents Based Carbon Highly Efficient and Stable for Use in the Removal of Pb(II) and Cd(II) in Aqueous Solution.

In this study, two alternative synthesis routes for magnetic adsorbents were evaluated to remove Pb(II) and Cd(II) in an aqueous solution. First, activated carbon was prepared from argan shells (C). One portion was doped with magnetite (Fe3O4+C) and the other with cobalt ferrite (CoFe2O4+C). Characterization studies showed that C has a high surface area (1635 m2 g-1) due to the development of microporosity. For Fe3O4+C the magnetic particles were nano-sized and penetrated the material's texture, saturating the micropores. In contrast, CoFe2O4+C conserves the mesoporosity developed because most of the cobalt ferrite particles adhered to the exposed surface of the material. The adsorption capacity for Pb(II) was 389 mg g-1 (1.88 mmol g-1) and 249 mg g-1 (1.20 mmol g-1); while for Cd(II) was 269 mg g-1 (2.39 mmol g-1) and 264 mg g-1 (2.35 mmol g-1) for the Fe3O4+C and CoFe2O4+C, respectively. The predominant adsorption mechanism is the interaction between -FeOH groups with the cations in the solution, which are the main reason these adsorption capacities remain high in repeated adsorption cycles after regeneration with HNO3. The results obtained are superior to studies previously reported in the literature, making these new materials a promising alternative for large-scale wastewater treatment processes using batch-type reactors.

Growing Tungsten Nanophases on Carbon Spheres Doped with Nitrogen. Behaviour as Electro-Catalysts for Oxygen Reduction Reaction.

This work shows the preparation of carbon nanospheres with a high superficial nitrogen content (7 wt.%), obtained by a simple hydrothermal method, from pyrocatechol and formaldehyde, around which tungsten nanophases have been formed. One of these nanophases is tungsten carbide, whose electro-catalytic behavior in the ORR has been evaluated together with the presence of nitrogen surface groups. Both current and potential kinetic density values improve considerably with the presence of tungsten, despite the significant nitrogen loss detected during the carbonization treatment. However, the synergetic effect that the WC has with other electro-catalytic metals in this reaction cannot be easily evaluated with the nitrogen in these materials, since both contents vary in opposite ways. Nevertheless, all the prepared materials carried out oxygen electro-reduction by a mixed pathway of two and four electrons, showing remarkable electro-catalytic behavior.

High Performance Tunable Catalysts Prepared by Using 3D Printing.

Honeycomb monoliths are the preferred supports in many industrial heterogeneous catalysis reactions, but current extrusion synthesis only allows obtaining parallel channels. Here, we demonstrate that 3D printing opens new design possibilities that outperform conventional catalysts. High performance carbon integral monoliths have been prepared with a complex network of interconnected channels and have been tested for carbon dioxide hydrogenation to methane after loading a Ni/CeO2 active phase. CO2 methanation rate is enhanced by 25% at 300 °C because the novel design forces turbulent flow into the channels network. The methodology and monoliths developed can be applied to other heterogeneous catalysis reactions, and open new synthesis options based on 3D printing to manufacture tailored heterogeneous catalysts.

Elucidating the Role of the Metal Catalyst and Oxide Support in the Ru/CeO2-Catalyzed CO2 Methanation Mechanism.

This study addresses the yet unresolved CO2 methanation mechanism on a Ru/CeO2 catalyst by means of near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) complemented with periodic density functional theory (DFT) calculations. NAP-XPS results show that the switch from H2 to CO2 + H2 mixture oxidizes both the Ru and CeO2 phases at low temperatures, which is explained by the CO2 adsorption modes assessed by means of DFT on each representative surface. CO2 adsorption on Ru is dissociative and moderately endergonic, leading to polybonded Ru-carbonyl groups whose hydrogenation is the rate-determining step in the overall process. Unlike on Ru metal, CO2 can be strongly adsorbed as carbonates on ceria surface oxygen sites or on the reduced ceria at oxygen vacancies as carboxylates (CO2 -δ), resulting in the reoxidation of ceria. Carboxylates can then evolve as CO, which is released either via direct splitting at relatively low temperatures or through stable formate species at higher temperatures. DRIFTS confirm the great stability of formates, whose depletion relates with CO2 conversion in the reaction cell, while carbonates remain on the surface up to higher temperatures. CO generation on ceria serves as an additional reservoir of Ru-carbonyls, cooperating to the overall CO2 methanation process. Altogether, this study highlights the noninnocent role of the ceria support in the performance of Ru/CeO2 toward CO2 methanation.

Functionalized Cellulose for the Controlled Synthesis of Novel Carbon-Ti Nanocomposites: Physicochemical and Photocatalytic Properties.

Carbon-Ti nanocomposites were prepared by a controlled two-step method using microcrystalline cellulose as a raw material. The synthesis procedure involves the solubilization of cellulose by an acid treatment (H3PO4 or HNO3) and the impregnation with the Ti precursor followed of a carbonization step at 500 or 800 °C. The type of acid treatment leads to a different functionalization of cellulose with phosphorus- or oxygen-containing surface groups, which are able to control the load, dispersion and crystalline phase of Ti during the composite preparation. Thus, phosphorus functionalities lead to amorphous carbon-Ti composites at 500 °C, while TiP2O7 crystals are formed when prepared at 800 °C. On the contrary, oxygenated groups induce the formation of TiO2 rutile at an unusually low temperature (500 °C), while an increase of carbonization temperature promotes a progressive crystal growth. The removal of Orange G (OG) azo dye in aqueous solution, as target pollutant, was used to determine the adsorptive and photocatalytic efficiencies, with all composites being more active than the benchmark TiO2 material (Degussa P25). Carbon-Ti nanocomposites with a developed micro-mesoporosity, reduced band gap and TiO2 rutile phase were the most active in the photodegradation of OG under ultraviolet irradiation.

Customizable Heterogeneous Catalysts: Nonchanneled Advanced Monolithic Supports Manufactured by 3D-Printing for Improved Active Phase Coating Performance.

Three-dimensional (3D)-printed catalysts are being increasingly studied; however, most of these studies focus on the obtention of catalytically active monoliths, and thus traditional channeled monolithic catalysts are usually obtained and tested, losing sight of the advantages that 3D-printing could entail. This work goes one step further, and an advanced monolith with specifically designed geometry has been obtained, taking advantage of the versatility provided by 3D-printing. As a proof of concept, nonchanneled advanced monolithic (NCM) support, composed of several transversal discs containing deposits for active phase deposition and slits through which the gas circulates, was obtained and tested in the CO-PrOx reaction. The results evidenced that the NCM support showed superior catalytic performance compared to conventional channeled monoliths (CMs). The region of temperature in which the active phase can work under chemical control, and thus in a more efficient way, is increased by 31% in NCM compared to the powdered or the CM sample. Turbulence occurs inside the fluid path through the NCM, which enhances the mass transfer of reagents and products toward and from the active sites to the fluid bulk favoring the chemical reaction rate. The nonchanneled monolith also improved heat dispersion by the tortuous paths, reducing the local temperature at the active site. Thus, the way in which reactants and products are transported inside the monoliths plays a crucial role, and this is affected by the inner geometry of the monoliths.

Design of Monolithic Supports by 3D Printing for Its Application in the Preferential Oxidation of CO (CO-PrOx).

Honeycomb-shaped cordierite monoliths are widely used as supports for a large number of industrial applications. However, the high manufacturing cost of cordierite monoliths only justifies its use for high temperatures and aggressive chemical environments, demanding applications where the economic benefit obtained exceeds the manufacturing costs. For low demanding applications, such as the preferential oxidation of CO (CO-PrOx), alternative materials can be proposed to reduce manufacturing costs. Polymeric monoliths would be an interesting low-cost alternative; however, the limitations of the active phase incorporation to the polymeric support must be overcome. In this work, the implementation and use of polymeric monolithic structures obtained by three-dimensional printing to support CuO/CeO2 catalysts for CO-PrOx have been studied. Several approaches were used to anchor the active phase into the polymeric monoliths, such as adding inorganic materials (carbon or silica) to the polymer previous to the printing process, chemical attack with solvents of the printed resin before or during the active phase incorporation, and consecutive impregnation and modification of the channel wall design. Among those approaches, best results were obtained by the addition of silica and by channel modification. Independent of the strategy followed, a subsequent thermal treatment in N2 was required to soften the resin and favor the active phase anchoring. However, catalyst particles become embedded on the polymeric resin being not active, and thus, a final cleaning thermal treatment under air was needed to recover the active phase activity, after which the supported active phase demonstrated good catalytic activity, stability, and reusability.

Cobalt oxide-carbon nanocatalysts with highly enhanced catalytic performance for the green synthesis of nitrogen heterocycles through the Friedländer condensation.

A novel series of eco-sustainable catalysts developed by supporting CoO nanoparticles on different carbon supports, highly efficient in the synthesis of quinolines and naphthyridines, through the Friedländer condensation, are reported for the first time. Textural properties, dispersion and location of the Co-phase are influenced by the nature of the carbon support, Co-precursor salt and metal loading, having a significant impact on the catalytic performance. Thus, the presence of the mesopores and macropores in carbon aerogels together with the homogeneous distribution of the active phase favours the formation of product 3a as a function of the metal loading. However, an increase in the metal content when using CNTs indicates the formation of CoO aggregates and an optimal concentration of 3 wt% CoO was observed, providing the highest conversion values. The carbon-based catalysts herein reported can be considered to be a sustainable alternative having advantages such as easy preparation, superior stability and notably enhanced catalytic performance, operating at lower temperature and under solvent-free conditions.

The use of functionalized carbon xerogels in cells growth.

In the present study carbon xerogels are used for the first time to study the fibroblast cell growth. For that, carbon xerogel microspheres are synthesized and thereafter functionalized with carbon nanofibers followed by the 1,3-dipolar cycloaddition of azomethine ylides (the so called "Prato reaction") or the addition of aryl diazonium salts (the so called "Tour reaction") to improve its wettability. The presence of nanofibers produces a huge improvement of the functionalization degree (59 versus 372 µmol/g for pristine carbon spheres and carbon spheres with 30% of carbon nanofibers, respectively) in spite of the blockage of the carbon spheres porosity caused after the nanofibers growth. This improvement was explained on the base of the increase of the number of probable active sites for the addition reactions (CC bonds) and the accessibility to these active sites (accessible surface area) by the presence of nanofibers. These high functionalization degrees reflect a promising potential of these materials in biomedical applications. Toxicity results obtained using a fibroblast cell line showed that samples are biocompatible for this kind of cells and that the presence of carbon fibers on the surface of the spheres increases the cells proliferation in a high extend reaching in some case values around 150% regarding the control. This study evidences that carbon aerogels could be interesting materials in biological applications, an unexplored field for this type of materials, being biocompatible, favouring the proliferation of cells and achieving high functionalization degrees.