Suchergebnisse

2 Esquemas.- 5 Figuras ; A facile strategy for the controllable growth of CdS nanoparticles at the periphery of MoS 2 en route the preparation of electron donor‐acceptor nanoensembles is developed. Precisely, the carboxylic group of α‐lipoic acid, as addend of the modified MoS 2 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 MoS 2 /CdS hybrid material was characterized by complementary spectroscopic, thermal and microscopy imaging means. Absorption spectroscopy was employed to register the formation of MoS 2 /CdS, by observing a broad shoulder centered at 420 nm due to CdS nanoparticles, while the excitonic bands of MoS 2 were also evident. Moreover, based on the efficient quenching of the characteristic fluorescence emission of CdS at 725 nm by the presence of MoS 2 , strong electronic interactions at the excited state between the two species within the ensemble were identified. Photoelectrochemical assays of MoS 2 /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 MoS 2 . The superior performance of the charge‐transfer processes in MoS 2 /CdS is of direct interest for the fabrication of photoelectrochemical and optoelectronic devices. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742. Support of this work by the project "Advanced Materials and Devices" (MIS 5002409) which is implemented under the "Action for the Strategic Development on the Research and Technological Sector", which Submitted_Manuscript is implemented under the "Reinforcement of the Research and Innovation Infrastructures", funded by the Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund) is also acknowledged. A.M.B. and W.K.M. acknowledge Spanish MINEICO (project grant ENE2016-79282-C5-1-R, AEI/FEDER, UE) and the Gobierno de Aragón (Grupo Reconocido DGA T03_17R, FEDER, UE). ; Peer reviewed

Molybdenum disulfide nanosheets covalently modified with porphyrin were prepared and fully characterized. Neither the porphyrin absorption nor its fluorescence was notably affected by covalent linkage to MoS2. The use of transient absorption spectroscopy showed that a complex ping‐pong energy‐transfer mechanism, namely from the porphyrin to MoS2 and back to the porphyrin, operated. This study reveals the potential of transition‐metal dichalcogenides in photosensitization processes. ; This project has received funding from EC H2020 under the Marie Sklodowska‐Curie grant agreement No. 642742. HRSTEM and EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016‐79776‐P (AEI/FEDER, UE) and from EC H2020 programs "Graphene Flagship" (785219), FLAG‐ERA—"GATES" (JTC‐PCI2018‐093137) and "ESTEEM3" (823717). R.A. also acknowledges Government of Aragon under the project "Construyendo Europa desde Aragon" 2014‐2020 (grant number E13_17R). ; Peer reviewed

This article belongs to the Section Nanocomposite Materials. ; Environmental degradation of transition metal disulfides (TMDs) is a key stumbling block in a range of applications. We show that a simple one-pot non-covalent pyrene coating process protects TMDs from both photoinduced oxidation and environmental aging. Pyrene is immobilized non-covalently on the basal plane of exfoliated MoS2 and WS2. The optical properties of TMD/pyrene are assessed via electronic absorption and fluorescence emission spectroscopy. High-resolution scanning transmission electron microscopy coupled with electron energy loss spectroscopy confirms extensive pyrene surface coverage, with density functional theory calculations suggesting a strongly bound stable parallel-stacked pyrene coverage of ~2–3 layers on the TMD surfaces. Raman spectroscopy of exfoliated TMDs while irradiating at 0.9 mW/4 μm2 under ambient conditions shows new and strong Raman bands due to oxidized states of Mo and W. Yet remarkably, under the same exposure conditions TMD/pyrene remain unperturbed. The current findings demonstrate that pyrene physisorbed on MoS2 and WS2 acts as an environmental barrier, preventing oxidative surface reactions in the TMDs catalyzed by moisture, air, and assisted by laser irradiation. Raman spectroscopy confirms that the hybrid materials stored under ambient conditions for two years remained structurally unaltered, corroborating the beneficial role of pyrene for not only hindering oxidation but also inhibiting aging. ; This research was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742, under the "Graphene Flagship" project grant agreement No 785219 and under the ESTEEM-3 project grant agreement No 823717. This research was also partially funded by the project "Advanced Materials and Devices" (MIS 5002409), which is implemented under the "Action for the Strategic Development on the Research and Technological Sector" funded by the Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). This work was supported by the COST Action CA15107 MultiComp. This research was also supported by the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P), from the Government of Aragon and the European Social Fund under the project "Construyendo Europa desde Aragon" 2014–2020 (grant number E13_17R). ; Peer reviewed

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 tertbutyl 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. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742 ; Peer reviewed

5 Figuras, 1 Esquema, 1 Tabla .-- Información suplementaria disponible en la página web del editor. ; The preparation of MoS 2 ‐polymer carbon nanodot (MoS 2 ‐PCND) hybrid material was accomplished by employing an easy and fast bottom‐up synthetic approach. Specifically, MoS 2 ‐PCND was realized by the thermal decomposition of ammonium tetrathiomolybdate and the in‐situ complexation of Mo with carboxylic acid units present in the surface of PCNDs. The newly prepared hybrid material was comprehensively characterized by spectroscopic, thermal and electron microscopy imaging means. The electrocatalytic activity of MoS 2 ‐PCND was examined against the hydrogen evolution reaction (HER) and compared with that attributed to the hybrid material prepared by a top‐down approach, namely with MoS 2 ‐PCND(exf‐fun), in which MoS 2 was firstly exfoliated and then covalently functionalized with PCNDs. The MoS 2 ‐PCND hybrid material showed superior electrocatalytic activity against HER with low Tafel slope value and excellent electrocatalytic stability, with an onset potential at ‐0.16 V vs RHE. The superior catalytic performance of MoS 2 ‐PCND was rationalized by considering the catalytic active sites of MoS 2 , the effective charge/energy‐transfer phenomena from PCNDs to MoS 2 and the synergetic effect between MoS 2 and PCNDs within the hybrid material. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742. Support of this work by the project "Advanced Materials and Devices" (MIS 5002409) which is implemented under the "Action for the Strategic Development on the Research and Technological Sector", which is implemented under the "Reinforcement of the Research and Innovation Infrastructures", funded by the Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Ministry of Development and Investments, Greece, and the European Union (European Regional Development Fund) is also acknowledged. A.M.B. and W.K.M. acknowledge Spanish MINEICO (project grant ENE2016-79282-C5-1-R, AEI/FEDER, UE) and the Gobierno de Aragón (Grupo Reconocido DGA T03_17R, FEDER, UE). The SR-EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. The SR-EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project grant MAT2016-79776-P (AEI/FEDER, UE) from the Government of Aragon and the European Social Fund under the project "Construyendo Europa desde Aragon" 2014-2020 (grant number E13_17R) and from the European Union H2020 programs "ESTEEM3" (823717) and under the "Graphene Flagship" CORE2 project grant agreement No 785219. ; Peer reviewed

5 Figuras.- 1 Tabla.- Información complementaria disponible en línea en la página web del editor. ; 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 10 monomer units. Density functional theory calculations of these model CDs uncover the existence of a spatially separated highest occupied molecular orbital and a lowest unoccupied molecular orbital located at the amide and carboxylic groups, respectively. Photoinduced charge transfer between these groups thus constitutes the origin of the strong blue fluorescence emission. Hydrogen-bond-mediated supramolecular interactions between the polyamide chains enabling a rigid network structure further contribute to the enhancement of the radiative process. Moreover, the photoinduced charge transfer processes in the polyamide network structure easily explain the performance of CDs in applications as revealed in studies on metal ion sensing. These findings thus are of general importance to the further development of polymer CDs with tailored properties as well as for the design of technological applications. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 642742. A.M.B. and W.K.M. further acknowledge Spanish MINEICO (project ENE2016-79282-C5-1-R), the Gobierno de Aragón (Grupo Reconocido DGA T03_17R), and associated EU Regional Development Funds. E.P.U. acknowledges Gobierno de Aragón (Grupo Reconocido DGA E19_17R) and associated EU Regional Development Funds. ; Peer reviewed

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 charge-transfer between these groups thus constitutes the origin of the strong blue fluorescence emission. Hydrogen-bond mediated supramolecular interactions between the polyamide chains enabling a rigid network structure further contribute to the enhancement of the radiative process. Moreover, the photoinduced charge-transfer processes in the polyamide network structure easily explain the performance of CDs in applications as revealed in studies on metal ion sensing. These findings thus are of general importance to the further development of polymer CDs with tailored properties as well as for the design of technological applications. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 642742. AMB, and WKM further acknowledge Spanish MINEICO (project ENE2016-79282-C5-1-R), the Gobierno de Aragón (Grupo Reconocido DGA T03_17R), and associated EU Regional Development Funds). EPU acknowledges Gobierno de Aragón (Grupo Reconocido DGA E19_17R) and associated EU Regional Development Funds. Technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ ERDF and ESF) is gratefully acknowledged for assistance and generous allocation of computational resources. ; Peer reviewed

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. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742. AMB and WKM gratefully acknowledge financial support from Spanish MINECO under project ENE206-79282-C5-1-R and its associated European Regional Development Fund, as well as the Government of Aragon under project DGA-T66 and associated European Social Fund. RA gratefully acknowledges financial support from Spanish MINECO under project MAT2016 79776-P and its associated European Regional Development Fund, as well as the Government of Aragon under project DGA-E26 and associated European Social Fund. The STEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon Universidad de Zaragoza, Spain. The authors would like to thank Esteban Urriolabeitía for carrying out the NMR studies. ; Peer reviewed

The game-changing role of graphene oxide (GO) in tuning the excitonic behavior of conjugated polymer nanoparticles is described for the first time. This is demonstrated by using poly(3-hexylthiophene) (P3HT) as a benchmark conjugated polymer and employing an in-situ re-precipitation approach resulting in P3HT nanoparticles (P3HTNPs) with sizes of 50 - 100 nm in intimate contact with GO. During the self-assembly process, GO changes the crystalline packing of P3HT chains in the forming P3HTNPs from H to H/J aggregates exhibiting exciton coupling constants as low as 2 meV, indicating favorable charge separation along the P3HT chains. Concomitantly, π-π interface interactions between the P3HTNPs and GO sheets are established resulting in the creation of P3HTNPs-GO charge-transfer complexes whose energy bandgaps are lowered by up to 0.5 eV. Moreover, their optoelectronic properties, pre-established in the liquid phase, are retained when processed into thin films from the stable aqueous dispersions, thus eliminating the critical dependency on external processing parameters. These results can be transferred to other types of conjugated polymers. Combined with the possibility of employing water based "green" processing technologies, charge-transfer complexes of conjugated polymer nanoparticles and GO open new pathways for the fabrication of improved optoelectronic thin film devices. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 642742. AMB, and WKM acknowledge Spanish MINEICO (project ENE2016-79282-C5-1-R) and the Gobierno de Aragón (Grupo Reconocido DGA T03_17R), and associated EU Regional Development Funds). ; Peer reviewed