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

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Graphene quantum dots: From efficient preparation to safe renal excretion

NANO RESEARCH 14(3) 674-683 (2021)

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.

Formation of one-dimensional quantum crystals of molecular deuterium inside carbon nanotubes

CARBON 2021, 175, 141-154. DOI:10.1016/j.carbon.2020.12.067

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.

Optical properties and carrier dynamics in Co-doped ZnO nanorods

NANOSCALE ADVANCES 3(1), 214-222 (2021).

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.

Controlling the surface chemistry of graphene oxide: Key towards efficient ZnO-GO photocatalysts

Catalysis Today 2020

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.

Towards high-efficient microsupercapacitors based on reduced graphene oxide with optimized reduction degree

ENERGY STORAGE MATERIALS 2020, 25, 740-749

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.

Ru supported on N-doped reduced graphene oxide aerogels with different N-type for alcohol selective oxidation

MOLECULAR CATALYSIS. 2020, 484, 110737

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.

Differential properties and effects of fluorescent carbon nanoparticles towards intestinal theranostics.

COLLOIDS AND SURFACES B: Biointerfaces 2020, 185, 110612

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.

In-situ growth and immobilization of CdS nanoparticles onto functionalized MoS2 for managing charge-transfer processes.

CHEMISTRY- An Asian Journal 2020, 15, 2350-2356. DOI:10.1002/asia.201901371

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.

Laser-Deposited Carbon Aerogel Derived from Graphene Oxide Enables NO2-Selective Parts-Per-Billion Gas Sensing

ACS APPL MAT & INTERFACES. 2020, 12, 35, 39541-39548

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.

Cobalt-Doped ZnO Nanorods Coated with Nanoscale Metal-Organic Framework Shells for Water-Splitting Photoanodes

ACS APPL NANO MATER 2020,3,8, 7781-7788.

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 …