Nanomateriales que interaccionan con la luz

El presente artículo revisa algunas aplicaciones y fenómenos derivados de la interacción de los nanomateriales y la luz. Así, como ejemplos particulares se van a comentar la fotocatálisis, el efecto Tyndall y la resonancia de plasmón superficial. Se explican brevemente sus fundamentos y se recogen ejemplos divulgativos de sus usos. Algunas de estas aplicaciones se comenzaron a desarrollar hace más de una década, aunque, como se va a mostrar, continuamente se están desarrollando nuevos e interesantes usos derivados de esta interacción, en muchos casos en el ámbito de la ciencia de materiales y de la biomedicina. A pesar de que el auge de las aplicaciones en las que la luz interacciona con los (nano)materiales es reciente, y está estrechamente ligado al desarrollo de la nanociencia y nanotecnología, en este artículo se muestra que el resultado de esta interacción era conocido y empleado desde hace muchos años en una curiosa aplicación, como es la de colorear vidrieras.This article reviews some applications and phenomena derived from the interaction of nanomaterials and light. Thus, photocatalysis, the Tyndall effect and surface plasmon resonance will be particularly discussed as examples. Their fundamentals are briefly explained and an informative example of their uses is shown. Some of these applications began to be developed more than a decade ago, although, as it will be shown, new and interesting applications derived from this interaction are continually being developed, in many cases in the field of materials science and biomedicine. Despite the recent boom in applications in which light interacts with (nano)materials, closely linked to the development of nanoscience and nanotechnology, this article shows that the result of this interaction has been known for many years and used in a curious application, such as stained glass coloring

Activation of a spherical carbon for toluene adsorption at low concentration

This paper complements a previous one [1] about toluene adsorption on a commercial spherical activated carbon and on samples obtained from it by CO2 or steam activation. The present paper deals with the activation of a commercial spherical carbon (SC) having low porosity and high bed density (0.85 g/cm3) using the same procedure. Our results show that SC can be well activated with CO2 or steam. The increase in the burn-off percentage leads to an increase in the gravimetric adsorption capacity (more intensively for CO2) and a decrease in bed density (more intensively for CO2). However, for similar porosity developments similar bed densities are achieved for CO2 and steam. Especial attention is paid to differences between both activating agents, comparing samples having similar or different activation rates, showing that CO2 generates more narrow porosity and penetrates more inside the spherical particles than steam. Steam activates more from the outside to the interior of the spheres and hence produces larger spheres size reductions. With both activation agents and with a suitable combination of porosity development and bed density, quite high volumetric adsorption values of toluene (up to 236 g toluene/L) can be obtained even using a low toluene concentration (200 ppmv).Generalitat Valenciana (Prometeo/2009/047 and FEDER), MICINN and plan E (CTQ2012-3176) and MINECO (MAT-2012-32832)

Factors governing the adsorption of ethanol on spherical activated carbons

Ethanol adsorption on different activated carbons (mostly spherical ones) was investigated covering the relative pressure range from 0.001 to 1. Oxygen surface contents of the ACs were modified by oxidation (in HNO3 solution or air) and/or by thermal treatment in N2. To differentiate the concomitant effects of porosity and oxygen surface chemistry on ethanol adsorption, different sets of samples were used to analyze different relative pressure ranges (below 1000 ppmv concentration and close to unity). To see the effect of oxygen surface chemistry, selected samples having similar porosity but different oxygen contents were studied in the low relative pressure range. At low ethanol concentration (225 ppmv) adsorption is favored in oxidized samples, remarking the effect of the oxidizing treatment used (HNO3 is more effective than air) and the type of oxygen functionalities created (carboxyl and anhydride groups are more effective than phenolic, carbonyl and derivatives). To analyze the high relative pressure range, spherical and additional ACs were used. As the relative pressure of ethanol increases, the effect of oxygen-containing surface groups decreases and microporosity becomes the most important variable affecting the adsorption of ethanol.Authors thank Generalitat Valenciana – Spain (PROMETEOII/2014/010), MINECO (MAT-2012-32832), MICINN – Spain and plan E (CTQ2012-3176) for financial support

Chemical Activation of Lignocellulosic Precursors and Residues: What Else to Consider?

This paper provides the basis for understanding the preparation and properties of an old, but advanced material: activated carbon. The activated carbons discussed herein are obtained from “green” precursors: biomass residues. Accordingly, the present study starts analyzing the components of biomass residues, such as cellulose, hemicellulose, and lignin, and the features that make them suitable raw materials for preparing activated carbons. The physicochemical transformations of these components during their heat treatment that lead to the development of a carbonized material, a biochar, are also considered. The influence of the chemical activation experimental conditions on the yield and porosity development of the final activated carbons are revised as well, and compared with those for physical activation, highlighting the physicochemical interactions between the activating agents and the lignocellulosic components. This review incorporates a comprehensive discussion about the surface chemistry that can be developed as a result of chemical activation and compiles some results related to the mechanical properties and conformation of activated carbons, scarcely analyzed in most published papers. Finally, economic, and environmental issues involved in the large-scale preparation of activated carbons by chemical activation of lignocellulosic precursors are commented on as well.This research was funded by Generalitat Valenciana (PROMETEO/2018/076), European Commission/FEDER, and the University of Alicante (VIGROB-136)

Ru Catalysts Supported on Commercial and Biomass-Derived Activated Carbons for the Transformation of Levulinic Acid into γ-Valerolactone under Mild Conditions

Ru catalysts (1 wt.%) supported on commercial and biomass-derived activated carbons (AC) have been prepared, thoroughly characterized, and used in the hydrogenation of levulinic acid to produce gamma-valerolactone (GVL). This is an important platform compound that plays a key role in the production of liquid fuels and that can also be used, for example, as a food flavoring agent, antifreeze, and solvent. The study focuses on the influence of the carbon support characteristics, such as porous texture and acidity, on the properties and performance (LA conversion and selectivity to GVL) of the catalysts. Catalytic activity tests have been carried out at 170 °C and also in noticeably milder conditions (70 °C) to implement a less energy-demanding process. All the catalysts show high LA conversion and GVL yield at 170 °C, while at 70 °C, important differences between them, related to the support properties, have been found. The catalysts prepared with more acidic supports show better catalytic properties: very good catalytic performance (98% LA conversion and 77% selectivity to GVL) has been obtained in mild temperature conditions.This research was funded by the Spanish Ministry of Science, Innovation and Universities (RTI2018-095291-B-I00), Generalitat Valenciana (PROMETEO/2018/076), European ComissionFEDER, and the University of Alicante (VIGROB-136)

Mesoporous Activated Carbon Supported Ru Catalysts to Efficiently Convert Cellulose into Sorbitol by Hydrolytic Hydrogenation

Catalysts consisting of Ru nanoparticles (1 wt%), supported on mesoporous activated carbons (ACs), were prepared and used in the one-pot hydrolytic hydrogenation of cellulose to obtain sorbitol. The carbon materials used as supports are a pristine commercial mesoporous AC (named SA), and two samples derived from it by sulfonation or oxidation treatments (named SASu and SAS, respectively). The catalysts have been thoroughly characterized regarding both surface chemistry and porosity, as well as Ru electronic state and particle size. The amount and type of surface functional groups in the carbon materials becomes modified as a result of the Ru incorporation process, while a high mesopore volume is preserved upon functionalization and Ru incorporation. The prepared catalysts have shown to be very active, with cellulose conversion close to 50% and selectivity to sorbitol above 75%. The support functionalization does not lead to an improvement of the catalysts’ behavior and, in fact, the Ru/SA catalyst is the most effective one, with about 50% yield to sorbitol, and a very low generation of by-products.This research was funded by Spanish Ministry of Science, Innovation and Universities and FEDER, project of reference RTI2018-095291-B-I00, GV/FEDER (PROMETEO/2018/076) and University of Alicante (VIGROB-136)

Efficient and labor-saving Ru/C catalysts for the transformation of levulinic acid into γ-valerolactone under mild reaction conditions

Ru/C catalysts for the transformation of levulinic acid into gamma-valerolactone have been prepared using carbon materials with different textural and chemical properties, and morphology. In the mild reaction conditions used (70 °C, 15 bar H2, 1 h), all the reduced catalysts are active and selective, with similar behavior independently of the support's properties. Surprisingly, the un-reduced (as prepared) catalysts show also catalytic activity, which varies (from moderate to high) with the carbon support type, indicating that an in situ (under reaction) reduction process takes place. The catalysts prepared with the supports of lower surface chemistry are almost as active as their reduced counterparts, whereas those prepared with rich surface chemistry supports are noticeably less active, but become activated in consecutive runs. The size of the developed Ru particles depends on the reduction conditions (i.e., reduction treatment at 250 °C or reaction conditions) and is highly influenced by the support's surface chemistry, which determines the metal–support interaction.This work was supported by the following research projects: RTI2018–095291-B-100 and PID2021–123079OB-I00 (project funded by MICINN/AEI/10.13039/501100011033 and by ERDF A way of making Europe (European Union)), CIPROM/2021/070 (Generalitat Valenciana) and VIGROB-136 (University of Alicante). Z. R.-B. thanks MICINN for the pre-doctoral scholarship (PRE2019-090049). The authors thank Immutrix Therapeutics and Ingevitiy Corporation (both in the USA) for providing carbon materials. The research technical services of the University of Alicante and the University of Cádiz (both in Spain) are also acknowledged

H2 production by cellulose photoreforming with TiO2-Cu photocatalysts bearing different Cu species

TiO2-Cu photocatalysts (1 wt.% Cu) containing different copper species have been prepared and used for the generation of hydrogen by photoreforming of cellulose (the major component of biomass) in water at room temperature, using UV light. A positive effect of copper has been clearly observed, and the analysis of the role of the Cu species present shows that a mixture of Cu(I) and Cu(II) favours the process. Among the TiO2-Cu photocatalysts, the one prepared by a simple impregnation method and not heat-treated, which shows small and well dispersed copper species particles, gives the highest hydrogen production.This work was supported by the national and regional Spanish governments (RTI2018-095291-B-100, PID2021-123079OB-I00 and CIPROM/2021/070) and the University of Alicante (VIGROB-136)

The Influence of NH4NO3 and NH4ClO4 on Porous Structure Development of Activated Carbons Produced from Furfuryl Alcohol

The influence of NH4NO3 and NH4ClO4 on the porous texture and structure development of activated carbons produced from a non-porous polymeric precursor synthesized from furfuryl alcohol has been studied. The non-doped counterparts were prepared and studied for comparison purposes. NH4NO3 and NH4ClO4-doped polymers were carbonized under N2 atmosphere at 600 °C, followed by CO2 activation at 1000 °C and the obtained carbon materials and activated carbons were thoroughly characterized. The porosity characterization data have shown that NH4NO3-derived ACs present the highest specific surface area (up to 1523 m2/g in the experimental conditions studied), and the resulting porosity distributions are strongly dependent on the activation conditions. Thus, 1 h activation is optimum for the microporosity development, whereas larger activation times lead to micropores enlargement and conversion into mesopores. The type of doping salts used also has a substantial impact on the surface chemical composition, i.e., C=O groups. Moreover, NH4NO3 and NH4ClO4 constitute good sources of nitrogen. The type and contribution of nitrogen species are dependent on the preparation conditions. Quaternary nitrogen only appears in doped samples prepared by carbonization and pyrrolic, pyrydinic, and nitrogen oxide groups appear in the NH4NO3 -series. NH4NO3 incorporation has led to optimized materials towards CO2 and C2H4 sorption with just 1 h activation time.This research was funded by Rector of the West Pomeranian University of Technology in Szczecin for Ph.D. students of the Doctoral School, grant number ZUT/23/2022

Spherical activated carbons for the adsorption of a real multicomponent VOC mixture

The objective of this work is to study the adsorption of a multicomponent gaseous mixture (acetaldehyde, formaldehyde, 2-propenal, 1,3-butadiene and benzene) in which the components are present at different concentration on spherical activated carbons (SACs). Attention is paid to the influence of the carbons’ properties on such adsorption, especially their porosities and distributions. For this purpose, a series of spherical activated carbons were prepared by physical activation with CO2 of a commercial spherical carbon. Their physico-chemical properties were characterized by N2 and CO2 isotherms, temperature programmed desorption and scanning electron microscopy. Measurements of the adsorption of the volatile organic compounds (VOC) mixture on SACs were performed in a flow-typed fixed bed system at room temperature under atmospheric pressure. Regarding porosity, our results show that, for this particular mixture, SACs with narrow micropore size distribution and moderate porous texture development (surface area in the range of 1000 m2/g or even lower) exhibit higher multicomponent adsorption capacities than others with much larger porosities. This can be explained considering that the VOC present in larger concentration in the mixture, aldehydes, present low adsorption affinities and their adsorption is enhanced in adsorbents with narrow micropore size distribution.The authors would like to thank Philip Morris International (PMI) for financial support