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 operational functionality of the ECrGO layer. Films thinner than the space charge region act as hole transport layer (HTL), which efficiently transfers holes to the liquid interface thus leading to enhanced photoactivity. Thicker films however act as hole blocking layer (HBL), resulting in a systematic decrease of the photoactivity. The finding of a thickness dependent threshold value for the operation of ECrGO as HTL and HBL is of general interest for the fabrication of optoelectronic devices with improved performance

Intrinsic and Selective Activity of Functionalized Carbon Nanotube/Nanocellulose Platforms Against Colon Cancer Cells

[Abstract] Given their large surface area and versatile chemical reactivity, single-walled carbon nanotubes (SWCNTs) are regarded as the basis of new pharmacological complexes. In this study, SWCNTs are chemically functionalized with fluorescein, folic acid, and capecitabine, a drug that is commonly used against colorectal cancer. These functionalized SWCNTs are dispersed in water by taking advantage of their synergistic interaction with type-II nanocrystalline cellulose (II-NCC), and the resulting colloidal system is tested in vitro on both normal (differentiated) and cancerous (proliferative) human colon cells (Caco-2). The functionalized SWCNT/II-NCC hybrids show a higher activity than the reference (capecitabine) against the Caco-2 cancer cell line. However, this effect appears to be intrinsically associated with the SWCNT/II-NCC complex, particularly boosted by fluorescein, as the presence of capecitabine is not required. In addition, confocal microscopy fluorescence imaging using cell cultures highlights the enormous potential of this nanohybrid platform for colon cancer theranostics.This research was funded by the regional government of Aragón, DGA (Grupos Reconocidos DGA-T03_17R, DGA-T03_20R and DGA-A20_20R), together with associated EU Regional Development Funds, and also the Spanish MINEICO through a “Juan de la Cierva Incorporación” contract, and their associated research funds (ref. IJCI-2016–27789). A.C. thanks the Xunta de Galicia for an “Atracción de Talento” research grant (no. ED431H 2020/17)Gobierno de Aragón; DGA-T03_17RGobierno de Aragón; DGA-T03_20RGobierno de Aragón; DGA-A20_20RXunta de Galicia; ED431H 2020/1

Graphene oxide: key to efficient charge extraction and suppression of polaronic transport in hybrids with poly (3-hexylthiophene) nanoparticles

Nanoparticles (NPs) of conjugated polymers in intimate contact with sheets of graphene oxide (GO) constitute a promising class of water-dispersible nanohybrid materials of increased interest for the design of sustainable and improved optoelectronic thin-film devices, revealing properties exclusively pre-established upon their liquid-phase synthesis. In this context, we report for the first time the preparation of a P3HTNPs–GO nanohybrid employing a miniemulsion synthesis approach, whereby GO sheets dispersed in the aqueous phase serve as a surfactant. We show that this process uniquely favors a quinoid-like conformation of the P3HT chains of the resulting NPs well located onto individual GO sheets. The accompanied change in the electronic behavior of these P3HTNPs, consistently confirmed by the photoluminescence and Raman response of the hybrid in the liquid and solid states, respectively, as well as by the properties of the surface potential of isolated individual P3HTNPs–GO nano-objects, facilitates unprecedented charge transfer interactions between the two constituents. While the electrochemical performance of nanohybrid films is featured by fast charge transfer processes, compared to those taking place in pure P3HTNPs films, the loss of electrochromic effects in P3HTNPs–GO films additionally indicates the unusual suppression of polaronic charge transport processes typically encountered in P3HT. Thus, the established interface interactions in the P3HTNPs–GO hybrid enable a direct and highly efficient charge extraction channel via GO sheets. These findings are of relevance for the sustainable design of novel high-performance optoelectronic device structures based on water-dispersible conjugated polymer nanoparticles

Catalytic activity of MWCNT-based inks synthetized by different methods

Abstract of the poster presented at "Current Trends in Electrochemistry", 41st Meeting of the Electrochemistry Group of the Spanish Royal Society of Chemistry and 1st French-Spanish Atelier/Workshop on Electrochemistry, Paris (July 6 - 9, 2021).Research on new catalyst materials for the oxygen reduction reaction (ORR) is the main goal for many research groups around the world, due to its application in fuel cells and metal/air batteries. ORR mainly occurs by two pathways, in alkaline media, the direct four-electron transfer pathway from O2 to OH- or in a two-steps mechanism, where hydrogen peroxide (HO2-) is formed in the first reaction. On fuel cells and metal air batteries applications, the catalyst must be optimized to get the oxygen reduced directly to water through the 4 electrons mechanism1. Due to high price of the precious metals, new materials are tested to be used as catalyst in ORR. Among them, researchers have focused their attention mainly on metal oxides, perovskites or carbonaceous materials. In this communication, we have studied four carbonaceous-based inks synthetized by ultrasonic or hydrothermal methods2, using a rotating ring-disk electrode (RRDE) (Figure 1.A). The production of HO2- (%HO2-), transferred electrons and others parameters will be analyzed and the results will be discussed in depth. Finally, the inks were used as catalysts in the cathode of a PVA-KOH-based zinc/air batteries to replace the most widely used catalyst to date, MnO2The authors thank the financial support from Fundación Séneca (Región de Murcia, Spain; Ref: 20985/PI/18 and 19882-GERM-15), Spanish Agencia Estatal de Investigación (PID2019-104272RB-C55/ AEI/10.13039/501100011033 and PID2019-104272RB-C51/AEI/10.13039/501100011033), and Gobierno de Aragón (DGA T03_20R).Peer reviewe

Formamidinium halide salts as precursors of carbon nitrides

13 figures, 6 tables.-- Supplementary information available.Pyrolysis of formamidinium halide salts (FAI, FABr) results in a new type of amorphous carbon nitride materials with a mass fraction of 40–50% nitrogen content. Pyrolysis temperature drives final chemical composition, morphology, optical and electrical properties of the material independently of the halide precursor and identifying triazine ring, instead of typical heptazine unit, as the main building block of this material. We elaborated a temperature dependent mechanism of formation for these materials and foresee its potential value as native passivation layer in the field of perovskite solar cells.E.J.J-P acknowledges the funding support from MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR (project grants PID2019-107893RB-I00 and EIN2020-112315, respectively). M.H. acknowledges the funding support from MCIN/AEI/10.13039/501100011033 for the Ramón y Cajal fellowship (RYC-2018-025222-I) and the project PID2019-108247RA-I00. R.A. acknowledges funding from the Spanish MICINN (project grant PID2019-104739 GB-100/AEI/10.13039/501100011033). RA also acknowledge to Government of Aragon (project DGA E13-20R (FEDER, EU)) and European Union H2020 program “ESTEEM3” (823717). A.A-C acknowledges financial support from Spanish MCIN/AEI/10.13039/501100011033 under project PID2019-104272RB-C51/AEI/10.13039/501100011033 and the Diputación General de Aragón under project T03_20R (Grupo Reconocido).Peer reviewe

Frictional and mechanical behaviour of graphene/UHMWPE composite coatings

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Bulk-modified ultra-high molecular weight polyethylene (UHMWPE) is a biomaterial currently used for joint replacements. As an alternative, we assess the frictional behaviour of coatings based on graphene/UHMWPE composites and sprayed graphene, which maintain the high performance of the UHMWPE matrix. Composite coatings were prepared with 0–4.6 wt% of graphene nanoplatelets (GNP) and 1–2 layered graphene (2LG). Mechanical properties of the coatings were measured by nanoidentation and friction coefficients were determined with a ball-on-disk tribometer. The results indicate that GNP present better tribological behaviour than 2LG. Spray-coated GNP shows the lowest friction, 40% less than UHMWPE, although with low adhesion. An increase of 10% in elastic modulus and 30% in hardness was measured for composite coatings with 2–5 wt% graphene.Special thanks are directed to the Analysis Service of Instituto de Carboquímica, ICB-CSIC, in particular to M.D. Domínguez, N. Fernández and I. Fernández. This work has been funde(2016–79282-d by MINECO and European Regional Development Fund C5-1ENE -R), and Government of Aragon and European Social Fund (DGA-ESF-T66 “Grupo Consolidado”).Peer reviewe

Influence of argon ion sputtering on electric and mechanical surface properties of graphene/polyethylene composites

Abstract of the poster presented at the 30th International Conference on Diamond and Carbon Materials (ICDCM), 7-12 september 2019, in Seville (Spain).The exposure of polymers and graphene to Ar+ ion bombardment has been widely studied independently. The goal of this work is assessing the microstructural effect of Ar+ sputtering on graphene/polyethylene composites and the influence of the induced interaction mechanisms between both components on the mechanical and electrical surface properties of the composites. Composites of ultra-high molecular weight polyethylene (UHMWPE) and 4 wt% multi-layered nanoplatelet graphene (GNP) were thermo-compressed [1]. An ESCAPlus Omicron spectrometer was utilized for both Ar+ treatments and XPS measurements at different ion energies in the range of 500 to 5000 eV. The Ar+ irradiation in the unfilled polyethylene causes changes in the XPS C 1s peak position and shape profile with a narrow transition around 3000 eV related to the conversion of tetrahedral sp3 into planar sp2 carbon. Trans-vinylene groups, C=C bonds and oxygen groups were also detected by IR and Raman spectroscopy. In the composites, this graphitization effect is reduced by the presence of graphene, in spite of the low values of GNP concentration. Thermogravimetric measurements also point to the free radical trapping effect of the graphene [2], which can be related to the former behaviour. Nanoindentation and Vickers hardness indicate that ion bombardment increases the elastic modulus and hardness by 50-100 % in both raw polyethylene and composites. More relevant is the behaviour of the surface electrical resistance. For the polyethylene, it decreases from 1015 to 108 Ω by sputtering with energies higher than 3000 eV. However, an abrupt transition from insulating (1015 Ω) to conducting (104 Ω) appears when the composite is irradiated above 3000 eV. Apparently, the irradiation effect is enough to link an electrical network in the composite

Effects of argon ion sputtering on the surface of graphene/polyethylene composites

13 Figures, 1 Table.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Argon ion sputtering at various energies in the range of 500–5000 eV is performed on polymer composites of ultra-high molecular weight polyethylene (UHMWPE) with 4.6 wt% graphene nanoplatelets (GNPs). X-ray photoelectron spectroscopy (XPS) shows that irradiation above 3000 eV causes an abrupt transition from tetrahedral sp3 into planar sp2 carbon in the blank polyethylene surface. This graphitization process, as well as the formation of certain oxygen groups after the subsequent exposure to air, is delayed by graphene in the composites. Besides, both XPS and Raman spectroscopy indicate that a part of the sp2 graphene network is transformed into sp3 carbon defects by irradiation. Surface hardness and Young's modulus increase by 30–100% in blank polyethylene and the composites upon irradiation. The surface electrical resistance of polyethylene decreases from 1015 to 108 Ω by sputtering at 5000 eV. Composites that are consolidated at low temperature (175 °C) experience a transition from insulating (1015 Ω) to conducting (104 Ω) in a narrow range of Ar+ sputtering energies, while for a high consolidation temperature (240 °C) the transition is not observed. This research provides information on the induced interaction mechanisms between graphene and a polymer matrix upon ion beam irradiation.This work has been funded by the Spanish Ministry of Science and the European Regional Development Fund (ENE 2016-79282-C5-1-R), and the Government of Aragon together with the European Social Fund (DGA ESF T48-17R and T03-17R).Peer reviewe

KOH-treated single-walled carbon nanotubes as electrodes for supercapacitors

5 Figures, 1 Table.-- Carbon '04, Providence, Rhode Island, USAElectric-arc-obtained single-walled carbon nanotubes (SWNTs) have been chemically activated by treatment with KOH. It results in a development of porosity without destroying the SWNTs entangled structure. The chemically activated sample shows aspecific capacitance of ca. 100 F·g-1, maximum energy density of 4 Wh·kg-1 and maximum power density of 300 W·kg-1. The electrochemical response of the chemically activated sample is compared with the response found in the raw sample and in a physically activated sample.A. Ansón and F. Picó thank the CSIC Fuel Cell Network for their respective fellowships

Tribological and mechanical properties of graphene nanoplatelet/PEEK composites

© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Poly(ether ether ketone) (PEEK) is a relevant thermoplastic in industry and in the biomedical sector. In this work, the lubricant capability of graphene nanoplatelets (GNPs) is used for improving the PEEK wear properties. Nanocomposites were prepared by solvent-free melt-blending and injection molding at various compositions between 1 and 10 wt. % of GNPs. The Raman G band shows a progressive increment proportional to the bulk GNP percentage. From calorimetric data, the polymer matrix structure is interpreted in terms of a 3-phase model, in which the crystalline phase fluctuates from 39 to 34% upon GNP addition. Thermal conductivity varies in accordance with the polymer crystallinity. Tensile and flexural tests show a progressive increase in the modulus, as well as a decrease in the fracture strength and the work of fracture. Most important, the composite surface undergoes a substantial improvement in hardness (60%), together with a decrease in the coefficient of friction (−38%) and a great reduction in the wear factor (−83%). Abrasion and fatigue wear mechanisms are predominant at the lowest and highest GNP concentrations respectively. In conclusion, GNPs are used without any chemical functionalization as the filler in PEEK-based materials, improving the surface hardness and the tribological properties.This work has been funded by the University of Zaragoza (UZ2015-TEC-04), the MINECO together with the European Regional Development Fund (ENE 2016-79282-C5-1-R), and the Government of Aragon together with the European Social Fund (DGA T48- 17R, DGA-T03-17R and DGA E11-17R). Special thanks are directed to the Analysis Service of Instituto de Carboquímica, ICB-CSIC, in particular to A.I. Díaz-Megías.Peer reviewe