Artículos > Grupo de Nanoestructuras de Carbono y Nanotecnología (G-CNN)

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Mono- And bimetallic metal catalysts based on Ni and Ru supported on alumina-coated monoliths for CO2 methanation

Catalysis Science and Technology 2020, 10(12), pp. 4061-4071.

Structured reactors such as monoliths have some favorable properties over fixed bed reactors such as low pressure drop, ease in handling and fast heat and mass transfer. Some of these properties make them advantageous reactors for the catalytic reduction of CO2 contained in post-combustion gases. Mono- and bimetallic Ru and Ni catalysts on alumina-washcoated cordierite monoliths have been scrutinized for CO2 methanation. The methodology for the preparation of NiRu bimetallic catalysts has been optimized to obtain an outperforming monolithic catalyst. The catalyst providing the highest CH4 productivity corresponds to a bimetallic NiRu catalyst with a small amount of Ru, prepared by consecutive impregnation of Ni and Ru precursors with an intermediate reduction step. This catalyst consists of 2–4 nm Ni nanoparticles interspersed with atomic Ru homogeneously distributed on the alumina coating. This nanostructure endows the catalyst with the highest density of basic sites of medium strength and the highest degree of Ni oxidation in the passivated catalyst compared to the other tested catalysts. The bimetallic monolithic catalyst afforded a stable CO2 methanation activity at high space velocities and with a low pressure drop, reducing energy consumption.

Slow diffusion co-assembly as an efficient tool to tune colour emission in alkynyl benzoazoles
We report here the preparation of co-assembled microcrystals by employing an easy, reproducible and cost-effective technique, namely slow diffusion. 2H-Benzo[d][1,2,3]triazole and benzo[c][1,2,5]thiadiazole were chosen as host and guest skeletons, respectively. Structural similarities allowed the correct co-assembly of the two structures. The co-assemblies were studied by different techniques that included Raman spectroscopy and X-ray diffraction, amongst others. The waveguiding properties and the emission colour of the doped organic microcrystals were also investigated. It was found that changes in the molar ratio of the different doping agents could tune the light emission. Fluorescence microscopy images of the co-assembled microcrystals revealed light colour changes from green to whitish, up to CIE coordinates of (0.370, 0.385). These tunable colour-active materials could be useful in the fields of optoelectronics or lab-on-a-chip for integrated optical circuits at micro-/nanoscale.
Reduced Graphene Oxide Aerogels with Controlled Continuous Microchannels for Environmental Remediation

ACS Appl. Nano Mater., 2019, 2 (3), pp 1210–1222

3D porous graphene microarchitectures with aligned and continuous channels are of paramount interest for several applications such as pollutant removal, energy storage, or biomedical engineering. For these applications, an accurate control over the pore microstructure is of capital importance. Freeze casting is a well-stablished technique to prepare graphene aerogels with unidirectional channels. This technique is typically applied to plain GO colloids, leading to discontinuous microchannels. Herein we have carried out the freeze process starting directly with partially reduced graphene (rGO) hydrogels prepared by a prior hydrothermal treatment in autoclave. This approach leads to the formation of aerogels with aligned and continuous microchannels, enabled by an intermediate cross-linking degree of the rGO nanosheets, carefully controlled by keeping the time of the prior hydrothermal process between the thresholds of 45–75 min. To the best of our knowledge, the effect of the degree of cross-linking in the freeze casting process is not yet reported. The resulting rGO aerogels with highly aligned microchannel structure reveal superior properties over its isotropic counterpart of randomly oriented pores for the absorption of nonpolar solvents and the selective adsorption of an aromatic compound dissolved in an alkane. Our combined hydrothermal freeze casting approach thus affords aligned microchannel rGO aerogels of enormous potential for environmental remediation.

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Electrochimica Acta,  2019, 298,  Pages 279-287

Nanostructured TiO2 and graphene-based materials constitute components of actual interest in devices related to solar energy conversion and storage. In this work, we show that a thin layer of electrochemically reduced graphene oxide (ECrGO), covering nanostructured TiO2 photoelectrodes, can significantly improve the photoactivity. In order to understand the working principle, ECrGO/TiO2 photoelectrodes with different ECrGO thicknesses were prepared and studied by a set of photoelectrochemical measurements. Methanol in alkaline conditions was employed as effective hole acceptor probe to elucidate the electronic phenomena in the electrode layers and interfaces. These studies underline the hole accepting properties of ECrGO and reveal the formation of a p-n junction at the interface between ECrGO and TiO2. It is shown for the first time that the resulting space charge region of about 10 nm defines the …

Chemical Postdeposition Treatments To Improve the Adhesion of Carbon Nanotube Films on Plastic Substrates

ACS OMEGA, 2019, 4(2), pp 2804-2811

The robust adhesion of single-walled carbon nanotubes (SWCNTs) to plastic substrates is a key issue toward their use in flexible electronic devices. In this work, semitransparent SWCNT films were prepared by spray-coating on two different plastic substrates, specifically poly(ethylene terephthalate) and poly(vinylidene fluoride). The deposited SWCNT films were treated by dipping in suitable solvents separately, namely, 53% nitric acid (HNO3) and N-methyl pyrrolidone. Direct evidence of SWCNT adhesion to the substrate was obtained by a peel-off test carried out with an adhesive tape. Moreover, these treatments caused enhanced film transparency and electrical conductivity. Electron microscopy images suggested that SWCNTs were embedded in the plastic substrates, forming a thin layer of conductive composite materials. Raman spectroscopy detected a certain level of doping in the SWCNTs after the chemical …

Capacitive and charge transfer effects of single‐walled carbon nanotubes in TiO2 electrodes

ChemPhysChem 2019, 20, 838-847

The transfer of nanoscale properties from single‐walled carbon nanotubes (SWCNTs) to macroscopic systems is a topic of intense research. In particular, inorganic composites of SWCNTs and metal oxide semiconductors are being investigated for applications in electronics, energy devices, photocatalysis, and electroanalysis. In this work, a commercial SWCNT material is separated into fractions containing different conformations. The liquid fractions show clear variations in their optical absorbance spectra, indicating differences in the metallic/semiconducting character and the diameter of the SWCNTs. Also, changes in the surface chemistry and the electrical resistance are evidenced in SWCNT solid films. The starting SWCNT sample and the fractions as well are used to prepare hybrid electrodes with titanium dioxide (SWCNT/TiO2). Raman spectroscopy reflects the optoelectronic properties of SWCNTs in the SWCNT/TiO2electrodes, while the electrochemical behavior is studied by cyclic voltammetry. A selective development of charge transfer characteristics and double‐layer behavior is achieved through the suitable choice of SWCNT fractions.

Integrating Water-Soluble Polythiophene With Transition Metal Dichalcogenides for Managing Photoinduced Processes

ACS Appl Mater. Interfaces 2019, 11(6), pp 5947-5956

Transition metal dichalcogenides (TMDs) attract increased attention for the development of donor-acceptor materials enabling improved light harvesting and optoelectronic applications. The development of novel donor-acceptor nanoensembles consisting of poly(3-thiophene sodium acetate) and ammonium functionalized MoS2 and WS2 was accomplished, while photoelectrochemical cells were fabricated and examined. Attractive interactions between the negatively charged carboxylate anion on the polythiophene backbone and the positively charged ammonium moieties on the TMDs enabled in a controlled way and in aqueous dispersions the electrostatic association of two species, evidenced upon titration experiments. A progressive quenching of the characteristic fluorescence emission of the polythiophene derivative at 555 nm revealed photoinduced intra-ensemble energy and/or electron transfer from the …

Nanoscale J-aggregates of poly (3-hexylthiophene): Key to electronic interface interactions with graphene oxide as revealed by KPFM

Nanoscale 2019, 11, 11202-11208

The performance of organic thin film optoelectronic devices strongly relies on the nanoscale aggregate structure of the employed conjugated polymer. Their impact on electronic interface interactions with adjacent layers of graphene, widely reported to improve the device characteristics, yet remains an open issue, which needs to be addressed by an appropriate benchmark system. Here, we prepared discrete ensembles of poly(3-hexylthiophene) nanoparticles and graphene oxide sheets (P3HTNPs–GO) with well defined aggregate structures of either J- or H- type and imaged their photogenerated charge transfer dynamics across their interface by Kelvin probe force microscopy (KPFM). A distinctive inversion of the sign of the surface potential and surface photovoltage (SPV) demonstrates that J-aggregates are decisive for establishing charge transfer interactions with GO. These enable efficient injection of …

A tool box to ascertain the nature of doping and photoresponse in single-walled carbon nanotubes

Physical Chemistry Chemistry Physics 2019, 21(7), pp 4063-4071

The effect of doping on the electronic properties in bulk single-walled carbon nanotube (SWCNT) samples is studied for the first time using a new in situ Raman spectroelectrochemical method, and further verified by DFT calculations and photoresponse. We use p-/n-doped SWCNTs prepared by diazonium reactions as a versatile chemical strategy to control the SWCNT behavior. The measured and calculated data testify an acceptor effect of 4-aminobenzenesulfonic acid (p-doping), and a donor effect (n-doping) in the case of benzyl alcohol. In addition, pristine and covalently functionalized SWCNTs were used for the preparation of photoactive film electrodes. The photocathodic current in the photoelectrochemical cell is consistently modulated by the doping group. These results validate the in situ Raman spectroelectrochemistry as a unique tool box for predicting the electronic properties of functionalized SWCNTs …

A versatile room-temperature method for the preparation of customized fluorescent non-conjugated polymer dots

Polymer 2019, 177, 97-101

We present a general procedure for the synthesis and in situ functionalization of highly fluorescent non-conjugated polymer dots, by exploiting the room-temperature carbodiimide-mediated condensation between citric acid and amines. The versatility of this method is proved by the preparation and characterization of a broad set of fluorescent nanoparticles with customized polymer structures and functional groups.