Ping‐pong energy transfer in covalently linked porphyrin‐MoS2 architectures

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 reviewe

Pyrene coating transition metal disulfides as protection from photooxidation and environmental aging

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 reviewe

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 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 642742Peer reviewe

Integrating water-soluble polythiophene with transition-metal dichalcogenides for managing photoinduced processes

6 Figuras. Información complementaria disponible en la página web del editor.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 intraensemble energy and/or electron transfer from the polymer to the conduction band of the two TMDs. Photoelectrochemical assays further confirmed the establishment of photoinduced charge-transfer processes in thin films, with distinct responses for the MoS2- and WS2-based systems. The MoS2-based ensemble exhibited enhanced photoanodic currents offering additional channels for hole transfer to the solution, whereas the WS2-based one displayed increased photocathodic currents providing supplementary pathways of electron transfer to the solution. Moreover, scan direction depending on photoanodic and photocathodic currents suggested the existence of yet unexploited photoinduced memory effects. These findings highlight the value of electrostatic interactions for the creation of novel donor–acceptor TMD-based ensembles and their relevance for managing the performance of photoelectrochemical and optoelectronic processes.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 642742. Support of this work by the projects “Advanced Materials and Devices” (MIS 5002409), which is implemented under the “Action for the Strategic Development on the Research and Technological Sector”, and “National Infrastructure in Nanotechnology, Advanced Materials and Micro-/Nanoelectronics” (MIS 5002772), 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 cofinanced by Greece and the European Union (European Regional Development Fund) to N.T. is acknowledged. A.M.B. and W.K.M. further acknowledge Spanish MINEICO (project grant ENE2016-79282-C5-1-R), the Gobierno de Aragón (Grupo Reconocidos DGA-T03_17R), and associated EU Regional Development Funds. E.P.U. thanks Gobierno de Aragón (Grupo de Investigación de Referencia E19_17R). The authors are thankful for SEC measurements carried out at Laboratories de Chime des Polymères Organiques (LCPO), University of Bordeaux, CNRS, Bordeaux INP. We would like to thank Dr. C. Chochos of the Institute of Biology, Medicinal Chemistry and Biotechnology/National Hellenic Research Foundation (IBMCB/NHRF) for helping with SEM images acquisition. NHRF acknowledges the General Secretariat for Research and Technology (GSRT) for the financial support through the Research Programs for Excellence under the Programmatic Agreement between Research Centers − GSRT (2015−2017), funded by Siemens SA.Peer reviewe

Bottom-up synthesized MoS 2 interfacing polymer carbon nanodots with electrocatalytic activity for hydrogen evolution

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 reviewe

Fluorescence in non-conjugated polymeric carbon dots

Resumen del trabajo presentado a la Conferencia NanoteC (Carnon Nanoscience and Nanotechnology), celebrada en la Universidad de Sussex (UK) del 29 de agosto al 1 de septiembre de 2018.Peer reviewe

Supramolecular-enhanced charge-transfer within entangled polyamide chains as the 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 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 reviewe

Interfacing transition metal dichalcogenides with carbon nanodots for managing photoinduced energy and chargetransfer 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 electron 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, investigated 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 CNDMoS2, was observed. However, such process in CND-WS2 was found to be absent due to energetic reasons. The present study highlights the importance of TMD-derived donor-acceptor hybrids in light energy harvesting and optoelectronic applications. Furthermore, the fundamental information obtained from the current results will benefit design strategies and impact the development of additional TMD-based hybrid materials to efficiently manage and perform in electron-transfer processes.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”, funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" co-financed by Greece (Ministry of Economy and Development, NSRF 2014-2020) and EU (European Regional Development Fund) to N. T. and the US-NSF (grant 1401188 to F. D.) is acknowledged. The HR-STEM and STEM-EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Spain. R. A. acknowledges support from Spanish MINECO grant MAT2016- 79776-P (AEI/FEDER, UE) and from EU H2020 “Graphene Flagship” grant agreement 785219. W. K. M. and A. M. B. acknowledge Spanish MINECO grant ENE2016-79282-C5-1-R (AEI/FEDER, EU) and the Covernment of Aragon through project DGA-T03_17R (FEDER, EU).Peer reviewe

Tungsten Disulfide-Interfacing Nickel-Porphyrin For Photo-Enhanced Electrocatalytic Water Oxidation

11 figures, 2 tables.-- Supporting information available.Covalent functionalization of tungsten disulfide (WS2) with photo- and electro-active nickel-porphyrin (NiP) is reported. Exfoliated WS2 interfacing NiP moieties with 1,2-dithiolane linkages is assayed in the oxygen evolution reaction under both dark and illuminated conditions. The hybrid material presented, WS2−NiP, is fully characterized with complementary spectroscopic, microscopic, and thermal techniques. Standard yet advanced electrochemical techniques, such as linear sweep voltammetry, electrochemical impedance spectroscopy, and calculation of the electrochemically active surface area, are used to delineate the catalytic profile of WS2−NiP. In-depth study of thin films with transient photocurrent and photovoltage response assays uncovers photo-enhanced electrocatalytic behavior. The observed photo-enhanced electrocatalytic activity of WS2−NiP is attributed to the presence of Ni centers coordinated and stabilized by the N4 motifs of tetrapyrrole rings at the tethered porphyrin derivative chains, which work as photoreceptors. This pioneering work opens wide routes for water oxidation, further contributing to the development of non-noble metal electrocatalysts.Financial support by the Hellenic Foundation for Research and Innovation HFRI under the “2nd Call for HFRI Research Projects to support Faculty Members and Researchers” (Project Number: 2482) to N.T. is acknowledged. [...] R.A. acknowledges support from Spanish MCIN (PID2019-104739GB-I00/AEI/10.13039/501100011033), Government of Aragon (projects DGA E13-20R) and from EU H2020 “ESTEEM3” (Grant number 823717) and Graphene Flagship (881603). W.K.M and A.M.B acknowledge support from Spanish MCIN (PID2019-104272RB-C51/AEI/10.13039/501100011033), and the Government of Aragon (Grupos Reconocidos DGA T03_20R).Peer reviewe