Convocatoria: G.ARAGON (proyectos estratégicos de los grupos de investigación reconocidos por el gobierno de Aragón). Reconocimiento Grupo.
Reconocimiento como grupo de investigación consolidado y financiación de las líneas de investigación.
The controlled modification of the electronic properties of ZnO nanorods via transition metal doping is reported. A series of ZnO nanorods were synthesized by chemical bath growth with varying Co content from 0 to 20 atomic% in the growth solution. Optoelectronic behavior was probed using cathodoluminescence, time-resolved luminescence, transient absorbance spectroscopy, and the incident photon-to-current conversion efficiency (IPCE). Analysis indicates the crucial role of surface defects in determining the electronic behavior. Significantly, Co-doping extends the light absorption of the nanorods into the visible region, increases the surface defects, and shortens the non-radiative lifetimes, while leaving the radiative lifetime constant. Furthermore, for 1 atomic% Co-doping the IPCE of the ZnO nanorods is enhanced. These results demonstrate that doping can controllably tune the functional electronic properties of ZnO nanorods for applications.
Crystallization under stringent cylindrical confinement leads to novel quasi-one-dimensional materials. Substances with strong cohesive interactions can eventually preserve the symmetries of their bulk phase compatible with the restricted geometry, while those with weak cohesive interactions develop qualitatively different structures. Frozen molecular deuterium (D2), a solid with a strong quantum character, is structurally held by weak dispersive forces. Here, the formation of one-dimensional D2 crystals under carbon nanotube confinement is reported. In contradiction with its weak cohesive interactions, their structures, scrutinized using neutron scattering, correspond to definite cylindrical sections of the hexagonal close-packed bulk crystal. The results are rationalized on the grounds of numerical calculations, which point towards nuclear quantum delocalization as the physical mechanism responsible for the stabilization of such outstanding structures.
Carbon nanomaterials offer excellent prospects as therapeutic agents, and among them, graphene quantum dots (GQDs) have gained considerable interest thanks to their aqueous solubility and intrinsic fluorescence, which enable their possible use in theranostic approaches, if their biocompatibility and favorable pharmacokinetic are confirmed. We prepared ultra-small GQDs using an alternative, reproducible, top-down synthesis starting from graphene oxide with a nearly 100% conversion. The materials were tested to assess their safety, demonstrating good biocompatibility and ability in passing the ultrafiltration barrier using an in vitro model. This leads to renal excretion without affecting the kidneys. Moreover, we studied the GQDs in vivo biodistribution confirming their efficient renal clearance, and we demonstrated that the internalization mechanism into podocytes is caveolae-mediated. Therefore, considering the reported characteristics, it appears possible to vehiculate compounds to kidneys by means of GQDs, overcoming problems related to lysosomal degradation.
Mono- And bimetallic metal catalysts based on Ni and Ru supported on alumina-coated monoliths for CO2 methanation
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.
Controlling the physicochemical properties of nanoparticles in fluids directly impacts on their liquid phase processing and applications in nanofluidics, thermal engineering, biomedicine and printed electronics. In this work, the temperature dependent viscosity of various aqueous nanofluids containing carbon nanotubes (CNTs) or graphene oxide (GO), i.e. 1D and 2D nanoparticles with extreme aspect ratios, is analyzed by empirical and predictive physical models. The focus is to understand how the nanoparticle shape, concentration, motion degrees and surface chemistry affect the viscosity of diluted dispersions. To this end, experimental results from capillary viscosimeters are first examined in terms of the energy of viscous flow and the maximum packing fraction applying the Maron–Pierce model. Next, a comparison of the experimental data with predictive physical models is carried out in terms of nanoparticle characteristics that affect the viscosity of the fluid, mostly their aspect ratio. The analysis of intrinsic viscosity data leads to a general understanding of motion modes for carbon nanoparticles, including those with extreme aspect ratios, in a flowing liquid. The resulting universal curve might be extended to the prediction of the viscosity for any kind of 1D and 2D nanoparticles in dilute suspensions.
Modification of Physicochemical Properties and Boosting Electrical conductivity or reduced graphene oxide Aerogels by Post-Synthesis Treatment
Electrically conductive graphene aerogels are attracting great interest as functional materials. Nevertheless, graphene aerogels synthesized from graphene oxide usually exhibit low electrical conductivity. In order to increase conductivity, herein a postsynthesis thermal treatment at several temperatures (from 300 to 1000 °C) has been applied to pristine reduced graphene oxide aerogels under two different atmospheres, namely, inert Ar flow and isopropanol+H2 flow. Upon thermal treatment under Ar flow, the electrical conductivity of aerogel upscales with the treatment temperature. More remarkably, the electrical conductivity becomes 1 order of magnitude larger when the thermal treatment is carried out under isopropanol+H2 instead of under Ar, while maintaining a very low density and porous structure. The electrical conductivity achieved is exceptionally high for such a lightweight and porous material. The exhaustive characterization allowed disclosing that the generation of carbon links between the reduced graphene oxide nanosheets is the reason for this enhancement. The electrically conductive aerogels have excellent prospects for application as scaffolds for energy storage or biomedical applications.
Carbon Nanotube film electrodes with acrylic additives: Blocking electrochemical charge transfer reactions
Carbon nanotubes (CNTs) processed into conductive films by liquid phase deposition technologies reveal increasing interest as electrode components in electrochemical device platforms for sensing and energy storage applications. In this work we show that the addition of acrylic latex to water-based CNT inks not only favors the fabrication of stable and robust flexible electrodes on plastic substrates but, moreover, sensitively enables the control of their electrical and electrochemical transport properties. Importantly, within a given concentration range, the acrylic additive in the films, being used as working electrodes, effectively blocks undesired faradaic transfer reactions across the electrode–electrolyte interface while maintaining their capacitance response as probed in a three-electrode electrochemical device configuration. Our results suggest a valuable strategy to enhance the chemical stability of CNT film electrodes and to suppress non-specific parasitic electrochemical reactions of relevance to electroanalytical and energy storage applications.
Bottom-up synthesized MoS2 interfacing polymer carbon nanodots with electrocatalytic activity for hydrogen evolution
The preparation of an MoS2–polymer carbon nanodot (MoS2‐PCND) hybrid material was accomplished by employing an easy and fast bottom‐up synthetic approach. Specifically, MoS2‐PCND was realized by the thermal decomposition of ammonium tetrathiomolybdate and the in situ complexation of Mo with carboxylic acid units present on the surface of PCNDs. The newly prepared hybrid material was comprehensively characterized by spectroscopy, thermal means, and electron microscopy. The electrocatalytic activity of MoS2‐PCND was examined in the hydrogen evolution reaction (HER) and compared with that of the corresponding hybrid material prepared by a top‐down approach, namely MoS2‐PCND(exf‐fun), in which MoS2 was firstly exfoliated and then covalently functionalized with PCNDs. The MoS2‐PCND hybrid material showed superior electrocatalytic activity toward the HER with low Tafel slope, excellent electrocatalytic stability, and an onset potential of −0.16 V versus RHE. The superior catalytic performance of MoS2‐PCND was rationalized by considering the catalytically active sites of MoS2, the effective charge/energy‐transfer phenomena from PCNDs to MoS2, and the synergetic effect between MoS2 and PCNDs in the hybrid material.
Functionalized carbon dots on TiO2 for perovskite photovoltaics and stable photoanodes for water splitting
Various types of fluorescent carbon nanoparticles, often called carbon dots (CDs), are synthesized by different polycondensation methods: microwave irradiation, hydrothermal conditions or solution chemistry at ambient temperature with subsequent chemical functionalization. The CDs are deposited on TiO2 films to be probed as electron transport layers in perovskite photovoltaics and the anode for photoelectrochemical water splitting. Nitrogen CDs, which do not contain oxygen, lead to an increase of around 50 mV in the open circuit voltage of perovskite solar cells. All the CD types produce an improved photocurrent in water splitting, particularly CDs that are functionalized with thiol groups and butyl chains. It is demonstrated that the modified electrode is stable under continuous operation. Other electrochemical characteristics of the electrode, such as the voltammogram shape, onset potentials and open circuit potentials, remain nearly unchanged upon the deposition of CDs. Only the incident photon to current conversion efficiency improves clearly, extending the absorption range by around 20 nm towards longer wavelengths. This study provides new data about mechanisms and electrode arrangements for improving the performance of n-type semiconductors in photovoltaic cells and photoelectrochemical hydrogen production.
Cobalt-Doped ZnO Nanorods Coated with Nanoscale Metal-Organic Framework Shells for Water-Splitting Photoanodes
Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal–organic framework (MOF). The light absorption of the ZnO NRs is engineered toward the visible region by Co-doping, while the MOF significantly improves the stability and charge separation and transfer properties of the NRs. This …
Laser-Deposited Carbon Aerogel Derived from Graphene Oxide Enables NO2-Selective Parts-Per-Billion Gas Sensing
Laser-deposited carbon aerogel is a low-density porous network of carbon clusters synthesized using a laser process. A one-step synthesis, involving deposition and annealing, results in the formation of a thin porous conductive film which can be applied as a chemiresistor. This material is sensitive to NO2 compared to ammonia and other volatile organic compounds and is able to detect ultra-low concentrations down to at least 10 parts-per-billion. The sensing mechanism, based on the solubility of NO2 in the water layer adsorbed on the aerogel, increases the usability of the sensor in practically relevant ambient environments. A heating step, achieved in tandem with a microheater, allows the recovery to the baseline, making it operable in real world environments. This, in combination with its low cost and scalable production, makes it promising for Internet-of-Things air quality monitoring.
In-situ growth and immobilization of CdS nanoparticles onto functionalized MoS2 for managing charge-transfer processes.
A facile strategy for the controllable growth of CdS nanoparticles at the periphery of MoS2 en route the preparation of electron donor‐acceptor nanoensembles is developed. Precisely, the carboxylic group of α‐lipoic acid, as addend of the modified MoS2 obtained upon 1,2‐dithiolane functionalization, was employed as anchor site for the in situ preparation and immobilization of the CdS nanoparticles in an one‐pot two‐step process. The newly prepared MoS2/CdS hybrid material was characterized by complementary spectroscopic, thermal and microscopy imaging means. Absorption spectroscopy was employed to register the formation of MoS2/CdS, by observing a broad shoulder centered at 420 nm due to CdS nanoparticles, while the excitonic bands of MoS2 were also evident. Moreover, based on the efficient quenching of the characteristic fluorescence emission of CdS at 725 nm by the presence of MoS2, strong electronic interactions at the excited state between the two species within the ensemble were identified. Photoelectrochemical assays of MoS2/CdS thin‐film electrodes revealed a prompt, steady and reproducible anodic photoresponse during repeated on‐off cycles of illumination. A significant zero‐current photopotential of −540 mV and an anodic photocurrent of 1 μA were observed, underlining improved charge‐separation and electron transport from CdS to MoS2. The superior performance of the charge‐transfer processes in MoS2/CdS is of direct interest for the fabrication of photoelectrochemical and optoelectronic devices.
Differential properties and effects of fluorescent carbon nanoparticles towards intestinal theranostics.
Given the potential applications of fluorescent carbon nanoparticles in biomedicine, the relationship between their chemical structure, optical properties and biocompatibility has to be investigated in detail. In this work, different types of fluorescent carbon nanoparticles are synthesized by acid treatment, sonochemical treatment, electrochemical cleavage and polycondensation. The particle size ranges from 1 to 6 nm, depending on the synthesis method. Nanoparticles that were prepared by acid or sonochemical treatments from graphite keep a crystalline core and can be classified as graphene quantum dots. The electrochemically produced nanoparticles do not clearly show the graphene core, but it is made of heterogeneous aromatic structures with limited size. The polycondensation nanoparticles do not have CC double bonds. The type of functional groups on the carbon backbone and the optical properties, both absorbance and photoluminescence, strongly depend on the nanoparticle origin. The selected types of nanoparticles are compatible with human intestinal cells, while three of them also show activity against colon cancer cells. The widely different properties of the nanoparticle types need to be considered for their use as diagnosis markers and therapeutic vehicles, specifically in the digestive system.
Ru supported on N-doped reduced graphene oxide aerogels with different N-type for alcohol selective oxidation
Reduced graphene oxide aerogels doped with nitrogen have been prepared via two different strategies, namely, direct doping of rGO nanosheets with NH3 (GANH3) and coating the rGO nanosheets with an N-containing amorphous carbon derived from polydopamine (GADA). Both methods lead to comparable N/C ratios (3.4–4.7 %) but the relative contribution of quaternary nitrogen is 30 % for GADA while only 15 % for GANH3. Moreover, the N is incorporated within graphene lattice for GANH3 while it is within an amorphous carbon layer on top of graphene nanosheets for GADA. The Ru catalyst supported on the aerogels exhibited very distinct performance in the selective oxidation of benzyl alcohol depending on the support material despite having similar Ru particle size. The best performance for 5 wt% Ru on GADA can be explained by the larger reduction extent of Ru and the more hydrophobic surface. The open macroporosity of the aerogel makes it an excellent platform for using as structured catalyst in a continuous flow process.
Towards high-efficient microsupercapacitors based on reduced graphene oxide with optimized reduction degree
Reduced graphene oxide aerogels synthetized using different times of hydrothermal treatment have been tested as raw material to prepare electrochemical supercapacitors. The gravimetric electrochemical capacitance measured using 1M Na2SO4 as electrolyte was maximized for aerogels that underwent 45 min of hydrothermal treatment. The aerogels synthetized for longer durations of hydrothermal treatment exhibited higher electrical conductivity but the gravimetric capacitance drops dramatically due to an increasing resistance to diffusion of the electrolyte ions. The impeded diffusion is boosted by the intensified crosslinking between graphene sheets, which narrows the pores between them in the prepared electrode. The rGO aerogel attained for 45 min of hydrothermal treatment provided a high gravimetric capacitance of 400 F g-1 and 100 F g-1 at 50 A g-1 for three-electrode and two electrodes configuration, respectively, as well as good cyclic stability, competing with other similar carbon materials. Activation pretreatments or adding a second component (glucose, dopamine, Mn, Fe, CNT) did not provide significant change of capacitance respect to pristine rGO aerogel.
Unique Properties and Behavior of Nonmercerized Type-II Cellulose Nanocrystals as Carbon Nanotube Biocompatible Dispersants
Nanocellulose is increasingly being investigated as a paradigm of a sustainable nanomaterial because of its extraordinary physical and chemical properties, together with its renewable nature and worldwide abundance. The rich structural diversity of cellulose materials is represented by different crystalline allomorphs, from which types I and II stand out. While type I is naturally and ubiquitously present, type II is man-made and requires harsh and caustic synthesis conditions such as the so-called mercerization process. Here, we provide an optimal scenario to obtain either type-I or II nanocrystalline cellulose (NCC) by a mercerization-free method consisting only of the acid hydrolysis commonly used to produce nanocellulose from microcellulose. The possibility of having nonmercerized type-II NCC acquires a great relevance since this nanostructure shows particularly appealing properties. Moreover, an entangled and wrapped system arises when used as a dispersing agent for single-walled carbon nanotubes (SWCNTs), significantly different from that of type I. The biological testing of each NCC type and their respective SWCNT–NCC dispersions in human intestinal (Caco-2) cells reveals a general innocuous behavior in both cancer and normal stages of differentiation; however, the type-II-based SWCNT–NCC dispersions display cytotoxicity for cancer cells while enhancing mitochondrial metabolism of normal cells.
ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 2019, Vol 257, Meeting Abst 647
INCLUCIENCIA es un proyecto de divulgación científica e innovación educativa que tiene como meta convertirse en una herramienta eficaz para ayudar a reducir lo que denominamos exclusión académica (entendida como fracaso y/o abandono escolar), que constituye uno de los grandes problemas al que los responsables de la política educativa nacional se deben enfrentar, así como combatir la falta de motivación de los alumnos adolescentes por materias científicas…
The effect of graphene oxide reduction temperature on the kinetics of low-temperature sorption of hydrogen
Graphene oxide (GO) and related materials are widely reported to enhance the photocatalytic activity of zinc oxide. However, the origin of the observed performance improvements remains elusive and studies contributing to a deeper understanding of this critical issue are largely missing. In this work, we have prepared a set of benchmark ZnO-GO hybrid materials in order to systematically put under closer scrutiny the influence of the surface chemistry of GO on the photocatalytic degradation of methylene blue. The set of ZnO-GO hybrids has been synthesized in an ultrasonication process involving ZnO nanoparticles obtained in a microwave synthesis process and GO with three distinct oxidation degrees, employed in three different loading fractions. Structural and physical-chemical characterization by XRD, FTIR, Raman, UV–vis, photoluminescence and spectroscopy and XPS, consistently demonstrate the importance of the surface chemistry of GO for establishing photo-induced charge-transfer interface interactions with ZnO, facilitating the enhancement of the catalytic activity of the ZnO-GO catalyst. Optimized interface interactions thus enabled the design of a ZnO-GO catalyst exhibiting a conversion rate of 80% obtained in a time of 70 min and at a catalyst concentration of only 0.045 mg/mL.
A versatile room-temperature method for the preparation of customized fluorescent non-conjugated polymer dots
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.
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 …
Nanoscale J-aggregates of poly (3-hexylthiophene): Key to electronic interface interactions with graphene oxide as revealed by KPFM
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 …
Integrating Water-Soluble Polythiophene With Transition Metal Dichalcogenides for Managing Photoinduced Processes
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 …
Reduced graphene oxide (rGO) is widely seen as the most promising route for the low-cost mass production of graphene for many applications ranging from ultrathin electrodes to structural nanocomposites. The Hummers and Marcano methods are the two most successful approaches for producing high-performance rGO, but have been criticized for producing toxic emissions. We have applied life cycle assessment methodology to evaluate the environmental impacts of both production routes for GO and rGO in the context of applications requiring bulk materials or thin coatings. We find no current obstacle to the industrial scale production of graphene arising from its environmental impact. The cumulative energy demand is found to have a cap value between 20.7 and 68.5 GJ/Kg, a relatively high value; impact in other categories (such as human toxicity or resource depletion) is lower, and materials inventory …
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.
Chemical Postdeposition Treatments To Improve the Adhesion of Carbon Nanotube Films on Plastic Substrates
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 …
Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide
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 …
Reduced Graphene Oxide Aerogels with Controlled Continuous Microchannels for Environmental Remediation
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.
Supramolecular-enhanced charge-transfer within entangled polyamide chains as origin of the universal blue fluorescence of polymer carbon dots
The emission of a bright blue fluorescence is a unique feature common to the vast variety of polymer carbon dots (CDs) prepared from carboxylic acid and amine precursors. However, the difficulty to assign a precise chemical structure to this class of CDs yet hampers the comprehension of their underlying luminescence principle. In this work, we show that highly blue fluorescent model types of CDs can be prepared from citric acid and ethylenediamine through low temperature synthesis routes. Facilitating controlled polycondensation processes, the CDs reveal sizes of 1 – 1.5 nm formed by a compact network of short polyamide chains of about ten monomer units. Density functional theory calculations of these model CDs uncover the existence of spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital located at the amide and carboxylic groups, respectively. Photoinduced …
Interfacing transition metal dichalcogenides with carbon nan-odots for managing photoinduced energy and charge-transfer processes
Exfoliated semiconducting MoS2 and WS2 were covalently functionalized with 1,2-dithiolane-modified carbon nanodots (CNDs). The newly synthesized CND-MoS2 and CND-WS2 hybrids were characterized by spectroscopic, thermal and elec-tron microscopy imaging methods. Based on electronic absorption and fluorescence emission spectroscopy, modulation of the optoelectronic properties of TMDs by interfacing with CNDs was accomplished. Electrochemical studies revealed facile oxidation of MoS2 over WS2 in the examined hybrids, suggesting it to be better electron donor. Excited state events, inves-tigated by femtosecond transient absorption spectroscopic studies, revealed ultrafast energy transfer from photoexcited CNDs to both MoS2 and WS2. Interestingly, upon MoS2 photoexcitation charge transfer from an exciton dissociation path of MoS2 to CNDs, within CND-MoS2, was observed. However, such …
Conjugated Polymer Nanoparticle-Graphene Oxide Charge-Transfer ComplexesAdvanced Functional Materials
Carbon nanofoam (CNF) is a highly porous, amorphous carbon nanomaterial that can be produced through the interaction of a high-fluence laser and a carbon-based target material. The morphology and electrical properties of CNF make it an ideal candidate for supercapacitor applications. In this paper, we prepare and characterize CNF supercapacitor electrodes through two different processes, namely, a direct process and a water-transfer process. We elucidate the influence of the production process on the microstructural properties of the CNF, as well as the final electrochemical performance. We show that a change in morphology due to capillary forces doubles the specific capacitance of the wet-transferred CNF electrodes.
Three-Dimensional Conductive Scaffolds as Neural Prostheses Based on Carbon Nanotubes and Polypyrrole
Three-dimensional scaffolds for cellular organization need to enjoy a series of specific properties. On the one hand, the morphology, shape and porosity are critical parameters and eventually related with the mechanical properties. On the other hand, electrical conductivity is an important asset when dealing with electroactive cells, so it is a desirable property even if the conductivity values are not particularly high. Here, we construct three-dimensional (3D) porous and conductive composites, where C8-D1A astrocytic cells were incubated to study their biocompatibility. The manufactured scaffolds are composed exclusively of carbon nanotubes (CNTs), a most promising material to interface with neuronal tissue, and polypyrrole (PPy), a conjugated polymer demonstrated to reduce gliosis, …
Control of microstructure and surface chemistry of graphene aerogels via pH and time manipulation in hydrothermal method
Three-dimensional graphene aerogels of controlled pore size have emerged as important platform for several applications such as energy storage or oil-water separation. The aerogels of reduced graphene oxide are mouldable and lightweight, with porosity up to 99.9% consisting mainly of macropores. Graphene aerogels preparation by self-assembling in liquid phase is a promising strategy due to its tunability and sustainability. For graphene aerogels prepared by hydrothermal method, it is known that the pH value has an impact on its properties but it is unclear how the pH affects the autoassembling process leading to the final properties. We have monitored the time evolution of the chemical and morphological properties of aerogel as a function of initial pH value. In the hydrothermal treatment process, the hydrogel is precipitated earlier and with less oxygen content for basic pH (~ 13 wt% O …
Percolating Metallic Structures Templated on Laser-deposited Carbon Nanofoams derived from Graphene Oxide: Applications in Humidity Sensing
Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation
of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings which form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to four orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the gold-sputtered CNF …
Electronic interactions in illuminated carbon dots/MoS2 ensembles and electrocatalytic activity towards hydrogen evolution
We report on the preparation, characterization and photophysical and electrocatalytic properties of carbon dots (CDs)/MoS2 ensembles. Based on electrostatic interactions, ammonium functionalized MoS2, prepared upon reaction of 1,2‐dithiolane tert‐butyl carbamate with MoS2 followed by acidic deprotection, was coupled with CDs bearing multiple carboxylates on their periphery as derived upon microwave‐assisted polycondensation of citric acid and ethylenediamine followed by alkaline treatment. Insights into electronic interactions between the two species within CDs/MoS2 emanated from absorption and photoluminescence titration assays. Efficient fluorescence quenching of CDs by MoS2 was observed and attributed to photoinduced electron/energy transfer as the decay mechanism for the transduction of the singlet excited state of CDs. Finally, the electrocatalytic performance of CDs/MoS2 was assessed towards the hydrogen evolution reaction and found superior as compared to that owed to the individual CDs species.
Charge-transfer characteristics in carbon nanostructure/metal oxide photoelectrodes efficiently probed by hydrogen peroxide
The charge-transfer characteristics of nanostructured carbon/TiO2 electrodes are studied by cyclic voltammetry under photoelectrochemical conditions exploiting the electrooxidation and electroreduction of H2O2 in an alkaline medium. Films of composites were prepared by physically mixing TiO2 with 5 wt% of either single-walled carbon nanotubes (SWCNTs) or reduced graphene oxide (rGO). In addition, a layer-by-layer rGO/TiO2 electrode was prepared. Under dark conditions, both mixed SWCNTs and rGO facilitate H2O2 reduction. Under light irradiation, the blank TiO2 electrode shows a cathodic photopotential, the SWCNT/TiO2 an anodic photopotential, and the mixed rGO/TiO2 an increased cathodic photopotential. This scenario unambiguously reveals a photoelectron acceptor behavior for SWCNTs and a photohole acceptor performance for rGO. The latter one also agrees with the photoactivity observed in …
Unravelling the hydration mechanism in a multi-layered graphene oxide paper by in-situ X-ray scattering
Hydration of a multi-layered graphene oxide (GO) paper in water vapor atmosphere was studied by in-situ X-ray scattering over a wide range of relative humidity (RH). The intercalation of water molecules physically adsorbed between GO layers induces the expansion of the interlayer distance. Two regimes of adsorption are clearly evidenced according to the variation of the interlayer distance as a function of the relative humidity. The expansion of the interlayer distance is limited to ∼1 Å for RH ranging from 6 to 53%, whereas it is ∼3.5 Å for RH 75–100%. The hydration mechanism corresponds to the progressive adsorption of water molecules onto hydrophilic sites at the surface of GO layers in the low-RH regime, then an additional water monolayer is formed in the high-RH regime.
Quantification of signal-to-noise ratio in cerebral cortex recordings using flexible MEAs with co-localized platinum black, carbon nanotubes, and gold electrodes.
Developing new standardized tools to characterize brain recording devices is critical to evaluate neural probes and for translation to clinical use. The signal-to-noise ratio (SNR) measurement is the gold standard for quantifying the performance of brain recording devices. Given the drawbacks with the SNR measure, our first objective was to devise a new method to calculate the SNR of neural signals to distinguish signal from noise. Our second objective was to apply this new SNR method to evaluate electrodes of three different materials (platinum black, Pt; carbon nanotubes, CNTs; and gold, Au) co-localized in tritrodes to record from the same cortical area using specifically designed multielectrode arrays. Hence, we devised an approach to calculate SNR at different frequencies based on the features of cortical slow oscillations (SO). Since SO consist in the alternation of silent periods (Down states) and active periods (Up states) of neuronal activity, we used these as noise and signal, respectively. ..
Cysteine functionalized bio-nanomaterial for the affinity sensing of Pb(II) as an indicator of environmental damage.
This work aims at the development of an electrochemical affinity biosensor for Pb(II) quantification using a platform that combines glassy carbon electrodes (GCE) and an aqueous dispersion of single-walled carbon nanotubes (SWCNT) covalently modified with cysteine residues (Cys). The biosensing protocol includes the accumulation of Pb(II) at the electrode surface through the affinity interaction promoted by Cys residues at open circuit potential, followed by the reduction of the accumulated Pb(II) at ‐0.900 V and the transduction step performed by linear sweep-adsorptive stripping voltammetry (LSAdSV) in a 0.020 M acetate buffer solution pH 5.00. There is a linear relationship between Pb(II) oxidation peak current and Pb(II) concentration. The dynamic linear range extends from 5.0 to 125.0 μg·L−1, exhibiting a sensitivity of 0.061 μAμg−1L and a detection limit of 0.69 μg·L−1. In addition, the selectivity of the biosensor was evaluated in the presence of high concentrations of possible interferents such as Cu(II), Cd(II), Ni(II), Hg(II), Rh(II), Ru(II), Zn(II), Ir(IV), Co(II) and As(III) demonstrating a high discrimination of Pb(II) in complex samples. The sensor was challenged with tap and rain water samples enriched with Pb(II), demonstrating outstanding properties in terms of recovery percentages showing an excellent agreement with ICP- MS.
Mesoporous carbon doped with N,S heteroatoms prepared by one-pot auto-assembly of molecular precursor for electrocatalytic hydrogen peroxide synthesis
A bottom-up approach based on hydrothermal carbonization of organic molecules has been used to prepare carbon materials doped with either nitrogen or sulfur or both. To generate mesopores, ZnCl2 has been used as removable structure-directing agent. The final mean mesopore size depended on the type of dopant element. The doped materials exhibited remarkable activity as electrocatalyst in oxygen reduction reaction with nearly complete selectivity to H2O2 synthesis. Two pyrolysis temperatures (973 K and 1173 K) were used that yield materials with different electric conductivity, dopant content and porosity but comparable electrocatalytic performance. N-doped catalyst with an intermediate nitrogen content (4 wt%) and around 80% of pore volume in the mesopore range provided the best performance among the catalysts tested.
How does phosphoric acid interact with cherry stones? A discussion on overlooked aspects of chemical activation
The fabrication of activated carbon (AC) is widely carried out by the so-called chemical activation method, in which the biomass substratum is put in touch with an impregnating chemical agent prior to the carbonization stage. Even though this methodology is known for a long time, there are many features that are still poorly understood, particularly those regarding the details of the underlying mechanisms involved during the interaction of the activating agent with the precursor, eventually leading to the development of AC. Previous research conducted in the laboratories dealt with the use of cherry stones (CS) and phosphoric acid, toward ACs with tailored porous structures, finding out that the experimental variables of the impregnation stage were crucial for their eventual characteristics. …
International Summer School on “Carbon and related mnanomaterials: Synthesis, characterization and properties”.
Del 23 al 27 de Julio de 2018 tuvo lugar en Jaca (Huesca) el curso internacional de verano “Nanomateriales a base de carbón y próximos en estructura: Síntesis, caracterización y estudio de propiedades” que ha sido dirigido por el Dr. Raúl Arenal (INA-LMA-Universidad de Zaragoza) y por el Dr. Wolfgang Maser (Instituto de Carboquímica, ICB-CSIC, Zaragoza). El curso estaba dirigido a estudiantes universitarios, de máster o doctorandos de ciencias (física, química e ingeniería, preferentemente) con interés en la nanociencia y la nanotecnología. …
The family of carbon nanostructures includes a great number of forms with different properties derived from their reduced dimensionality. In particular, carbon nanotubes (CNTs) and graphene show special electronic, optical, mechanical and chemical properties that allow their potential application in new materials and devices. The real possibilities of pristine CNTs and graphene depend on their synthetic origin, which can be roughly classified into methods starting from graphite and chemical vapor deposition (CVD) processes. Applications of CNTs and graphene encompass electronics, energy devices, multifunctional composites, catalysis and sensors. Their reduced size and weight suggest potential uses in portable, wearable and mobile equipment with a high added value.
Preparation of Metallic and Semiconducting SWCNT Inks by a Simple Chromatographic Method: A Two-Parameter Study
Single-walled carbon nanotubes (SWCNTs) show either metallic or semiconducting character, and are potential candidates for the development of small electronic devices. However, commercial SWCNT materials consist of a mixture of many different SWCNT conformations and certain impurities. In this work, SWCNTs are dispersed in an aqueous medium, purified by centrifugation, and finally separated into metallic and semiconducting inks by a gel chromatography method. The separation is directly performed at ambient conditions, and the influence of the ink concentration and the chromatography column length are thoroughly evaluated. The most efficient separation, distinguishing between families of semiconducting SWCNT with different diameters, is achieved at the lowest concentration and with the longest column. These results provide a promising base for availability of SWCNTs with well-defined …
Dielectric behavior and electrical conductivity of PVDF filled with functionalized single-walled carbon nanotubes
Polyvinylidene fluoride (PVDF)/single-walled carbon nanotube (SWCNT) composites are characterized by X-ray diffraction and scanning calorimetry, and studied by dielectric relaxation spectroscopy (DRS) in the temperature range of −75 to 150 °C. The effects of SWCNTs and SWCNT functionalization are analyzed in terms of α and αc relaxation, dielectric permittivity, loss tangent, and AC electrical conductivity. Some small changes are detected in α relaxation with the addition of SWCNTs, and a strong influence of SWCNTs is observed in the other relaxation αc. Below the percolation threshold, the dielectric permittivity of functionalized SWCNT composites increases compared to blank PVDF, without notable changes in the dielectric loss. All the composite systems show an electrical percolation behavior with different thresholds depending on SWCNT functionalization. Threshold concentrations remain nearly unchanged in the whole temperature and frequency ranges. The base PVDF conductivity strongly depends on temperature and frequency, while the maximum conductivity above the percolation remains nearly unchanged (∼10−2 S/m) for all the systems, temperatures and frequencies.
Fizika Nizkikh Temperatur 2016, 42(1), 75-78
Electron Trap States and Photopotential of Nanocrystalline Titanium Dioxide Electrodes Filled with Single-Walled Carbon Nanotubes
Hybrid film electrodes were made of nanocrystalline titanium dioxide (TiO2) and various percentages of single‐walled carbon nanotube (SWCNT) fillers up to 5.5 wt%. A complete photoelectrochemical study was performed in both alkaline and acidic conditions by using cyclic voltammetry, potentiostatic photocurrent measurements, and open‐circuit‐potential measurements under UV/Vis irradiation. Dark voltammograms show a transition from a capacitive to a resistive behavior in the TiO2 accumulation region upon increasing SWCNT percentages. In addition, the energy levels of deep electron traps change inside the TiO2 bandgap. The new peak positions correspond to the reduction potentials of SWCNTs, and their associated charge capacities increase with the SWCNT percentage. The modifications observed in dark experiments directly impact on the shape profile of cyclic voltammograms under irradiation. As a consequence, reduction potentials of SWCNTs appear near the cathodic peaks of certain water oxidation intermediates, and may be interacting with them. On the other hand, open‐circuit photopotentials reach maximum values for small SWCNTs percentages around 0.02 wt%. An increase in potentiodynamic and potentiostatic photocurrents is observed for the electrode containing 0.02 wt% SWCNTs, compared to reference TiO2 in acidic conditions.
Self-Assembled Core-Shell CdTe/Poly(3-hexylthiophene) Nanoensembles as Novel Donor-Acceptor Light-Harvesting Systems
The self-assembly of novel core-shell nanoensembles consisting of regioregular poly(3-hexylthiophene) nanoparticles (P3HTNPs) of 100 nm as core and semiconducting CdTe quantum dots (CdTeQDs) as shell with a thickness of a few tens of nanometres was accomplished by employing a re-precipitation approach. The structure, morphology and composition of CdTeQDs/P3HTNPs nanoensembles were confirmed by high-resolution scanning transmission microscopy and dynamic light scattering studies. Intimate interface contact between the CdTeQDs shell and the P3HTNPs core leads to the stabilization of the CdTeQDs/P3HTNPs nanoensemble as probed by steady-state absorption spectroscopy. Effective quenching of the characteristic photoluminescence of CdTeQDs at 555 nm, accompanied by simultaneous increase of emission of P3HTNPs at 660 and 720 nm, reveals photoinduced charge-transfer processes. Probing the redox properties of films of CdTeQDs/P3HTNPs further proves the formation of a stabilized core-shell system in the solid-state. Photoelectrochemical assays on CdTeQDs/P3HTNPs films show a reversible on-off photoresponse at a bias voltage of +0.8 V with a three times increased photocurrent compared to CdTeQDs. The improved charge separation is directly related to the unique core-shell configuration, in which the outer CdTeQDs shell forces the P3HTNPs core to effectively act as electron acceptor. The creation of novel donor-acceptor core-shell hybrid materials via self-assembly is transferable to other types of conjugated polymers and semiconducting nanoparticles. This work, therefore, opens new pathways for the design of improved optoelectronic devices.