Biomolecule-assisted exfoliation and dispersion of graphene and other two-dimensional materials: a review of recent progress and applications

Direct liquid-phase exfoliation of layered materials by means of ultrasound, shear forces or electrochemical intercalation holds enormous promise as a convenient, cost-effective approach to the mass production of two-dimensional (2D) materials, particularly in the form of colloidal suspensions of high quality and micrometer- and submicrometer-sized flakes. Of special relevance due to environmental and practical reasons is the production of 2D materials in aqueous medium, which generally requires the use of certain additives (surfactants and other types of dispersants) to assist in the exfoliation and colloidal stabilization processes. In this context, biomolecules have received, in recent years, increasing attention as dispersants for 2D materials, as they provide a number of advantages over more conventional, synthetic surfactants. Here, we review research progress in the use of biomolecules as exfoliating and dispersing agents for the production of 2D materials. Although most efforts in this area have focused on graphene, significant advances have also been reported with transition metal dichalcogenides (MoS2, WS2, etc.) or hexagonal boron nitride. Particular emphasis is placed on the specific merits of different types of biomolecules, including proteins and peptides, nucleotides and nucleic acids (RNA, DNA), polysaccharides, plant extracts and bile salts, on their role as efficient colloidal dispersants of 2D materials, as well as on the potential applications that have been explored for such biomolecule-exfoliated materials. These applications are wide-ranging and encompass the fields of biomedicine (photothermal and photodynamic therapy, bioimaging, biosensing, etc.), energy storage (Li- and Na-ion batteries), catalysis (e.g., catalyst supports for the oxygen reduction reaction or electrocatalysts for the hydrogen evolution reaction), or composite materials. As an incipient area of research, a number of knowledge gaps, unresolved issues and novel future directions remain to be addressed for biomolecule-exfoliated 2D materials, which will be discussed in the last part of this review.Financial support from the Spanish MINECO and the European Regional Development Fund (ERDF) through project MAT2015-69844-R as well as from “Plan de Ciencia, Tecnología e Innovación 2013-2017 del Principado de Asturias” and ERDF (project GRUPIN14-056) is gratefully acknowledged.Peer reviewe

Caracterización lingüística de publicidad para turistas de habla inglesa: Estudio de A Mariña

Traballo Fin de Máster en Servizos Culturais. Curso 2018-2019El presente trabajo tiene como objetivo analizar algunos materiales comunicativos publicitarios actuales producidos para promocionar A Mariña lucense y dirigidos a turistas potenciales de habla inglesa. Se propondrá una valoración del destino turístico de A Mariña y las amenazas para la imagen del mismo. Posteriormente, serán estudiados el concepto teórico de la publicidad, el rol del traductor como mediador cultural publicitario y los tipos de recursos publicitarios disponibles sobre A Mariña para al turista anglófono. A continuación, se analizará la efectividad de la presentación promocional de la marca A Mariña para dicho turismo, estudiando la dependencia de la imagen con dos aspectos conectados: la caracterización lingüística y la gestión de la marca. Por último, se finalizará el estudio con una valoración profesional de las posibles especializaciones y algunas líneas de actuación de futuro.O presente traballo ten como obxecto analizar algúns materiais comunicativos publicitarios actuais producidos para a promoción da Mariña lucense e dirixidos aos turistas potenciais de fala inglesa. Proporase unha valoración do destino turístico da Mariña e as ameazas para a imaxe do mesmo. Con posterioridade, estudarase o concepto teórico da publicidade, o rol do tradutor como mediador cultural publicitario e os tipos de recursos publicitarios dispoñibles sobre A Mariña para o turista anglófono, poñendo o foco nas novas tecnoloxías. A continuación, analizarase a efectividade da presentación promocional da marca A Mariña para dito turismo, estudando a dependencia da imaxe cos dous aspectos conectados: a caracterización lingüística e a xestión da marca. Para rematar, achegarase unha valoración profesional das posibles especializacións e algunhas liñas de actuación no futuro.The main aim of this study is to analyse some contemporary communicative publicity materials produced for promoting A Mariña (Lugo) and directed to potential English-speaking tourists. Firstly, the tourist destination A Mariña will be assessed and the menaces to its image will be pondered. Secondly, there will be some in-depth analysis about the theoretical concept of publicity, the translator’s role as a publicity cultural mediator and the type of available publicity resources about A Mariña for the anglophone tourist, focusing on new technologies. Thirdly, the promotional presentation of A Mariña brand will be studied as regards its effectiveness and the dependence which its image has with two other interconnected aspects: linguistic characterisation and brand management. Finally, some professional opinions concerning possible segmentation and future lines of action will be offered

From graphene oxide to pristine graphene: revealing the inner workings of the full structural restoration

Producción CientíficaHigh temperature annealing is the only method known to date that allows the complete repair of a defective lattice of graphenes derived from graphite oxide, but most of the relevant aspects of such restoration processes are poorly understood. Here, we investigate both experimentally (scanning probe microscopy) and theoretically (molecular dynamics simulations) the thermal evolution of individual graphene oxide sheets, which is rationalized on the basis of the generation and the dynamics of atomic vacancies in the carbon lattice. For unreduced and mildly reduced graphene oxide sheets, the amount of generated vacancies was so large that they disintegrated at 1773–2073 K. By contrast, highly reduced sheets survived annealing and their structure could be completely restored at 2073 K. For the latter, a minor atomic-sized defect with six-fold symmetry was observed and ascribed to a stable cluster of nitrogen dopants. The thermal behavior of the sheets was significantly altered when they were supported on a vacancy-decorated graphite substrate, as well as for the overlapped/stacked sheets. In these cases, a net transfer of carbon atoms between neighboring sheets via atomic vacancies takes place, affording an additional healing process. Direct evidence of sheet coalescence with the step edge of the graphite substrate was also gathered from experiments and theory.Ministerio de Economía, Industria y Competitividad (Project AT2011-26399 and MAT2011-22781)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA158A11-2

MoS2 flakes stabilized with DNA/RNA nucleotides: in vitro cell response

Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS2 and WS2, have recently emerged as nanomaterials with potential use in biomedicine. An attractive means to favor their interaction with biological media is the use of proper biomolecules as exfoliating/dispersing agents. Here, MoS2 flakes were stabilized with different small functional biomolecules such as adenosine monophosphate (AMP), guanosine monophosphate (GMP) and flavin mononucleotide (FMN) through the strong nucleotide-MoS2 interaction of Lewis acid-base type, rather than just on the weak dispersive and hydrophobic forces commonly associated with the use of many surfactants. The impact of the nucleotide-stabilized MoS2 flakes on the viability and cell proliferation, on the production of intracellular reactive oxygen species (ROS), and on the preosteoblast differentiation process (early stage) has been also evaluated, as well as the incorporation and intracellular localization of the nanomaterials by MC3T3-E1 and Saos-2 cells. The nucleotide-stabilized MoS2 flakes were found to exhibit excellent biocompatibility. Furthermore, their incorporation did not affect the integrity of the cell plasma membrane, which makes them ideal candidates for delivering drug/gene directly into cells. The in vitro cell response of tumor cells to these nanomaterials differs from that of undifferentiated cells, which provides the basis for their potential use in cancer therapy.publishe

Heterogenity of Graphite Oxide Particles Obtained with Wet Oxidative Exfoliation

Wet oxidative exfoliation of graphite is one of the most frequently applied techniques to obtain aqueous dispersions of hydrophilic graphene derivatives as required, e.g., in 3D printing, wet spinning or film casting. Due to the harsh conditions of the process, the resulting suspension is a mixture of particles with a wide distribution range both of physical dimensions and chemical properties. An aqueous graphite oxide suspension was obtained by an improved Hummers method and separated into five fractions by controlled centrifugation. The fractions were characterized and compared by various methods, revealing their diversity in size, chemical properties and application-related viscosity. The characterization methods (powder XRD, Raman spectroscopy, ATR-FTIR spectroscopy, XPS, potentiometric titration, rheology) exhibited subtle but measurable differences that exceeded the standard deviation of the techniques employed, but no systematic trend was found across the fractions in any of the properties investigated. The conditions of our centrifugal separation hardly meet the constrains of the ideal of Stokes’s law, the polydispersity of the high aspect ratio particles as well as their concentration close to the percolation limit challenge the independent sedimentation of the platelets

Impact of Covalent Functionalization on the Aqueous Processability, Catalytic Activity, and Biocompatibility of Chemically Exfoliated MoS2 Nanosheets

Chemically exfoliated MoS2 (ce-MoS2) has emerged in recent years as an attractive two-dimensional material for use in relevant technological applications, but fully exploiting its potential and versatility will most probably require the deployment of appropriate chemical modification strategies. Here, we demonstrate that extensive covalent functionalization of ce-MoS2 nanosheets with acetic acid groups (∼0.4 groups grafted per MoS2 unit) based on the organoiodide chemistry brings a number of benefits in terms of their processability and functionality. Specifically, the acetic acid-functionalized nanosheets were furnished with long-term (>6 months) colloidal stability in aqueous medium at relatively high concentrations, exhibited a markedly improved temporal retention of catalytic activity toward the reduction of nitroarenes, and could be more effectively coupled with silver nanoparticles to form hybrid nanostructures. Furthermore, in vitro cell proliferation tests carried out with murine fibroblasts suggested that the chemical derivatization had a positive effect on the biocompatibility of ce-MoS2. A hydrothermal annealing procedure was also implemented to promote the structural conversion of the functionalized nanosheets from the 1T phase that was induced during the chemical exfoliation step to the original 2H phase of the starting bulk material, while retaining at the same time the aqueous colloidal stability afforded by the presence of the acetic acid groups. Overall, by highlighting the benefits of this type of chemical derivatization, the present work should contribute to strengthen the position of ce-MoS2 as a two-dimensional material of significant practical utility.Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (FEDER) through project MAT2015-69844-R is gratefully acknowledged, as well as partial support of the ERDF/FEDER. Operative Program of the Región de Murcia 2007–2013. We also acknowledge partial funding by Plan de Ciencia, Tecnología e Innovación 2013-2017 del Principado de Asturias and FEDER through grant GRUPIN14-056.Peer reviewe

Graphene oxide modified with PMMA via ATRP as a reinforcement filler

Graphene is a two-dimensional new allotrope of carbon, which is stimulating great curiosity due to its superior mechanical, electrical, thermal and optical properties. Particularly attractive is the availability of bulk quantities of graphene (G) which can be easily processed by chemical exfoliation, yielding graphene oxide (GO). The resultant oxygenated graphene sheets covered with hydroxyl, epoxy and carboxyl groups offer tremendous opportunities for further functionalization opening plenty of opportunities for the preparation of advanced composite materials. In this work poly(methyl methacrylate) (PMMA) chains have been grafted from the GO surface via atom transfer radical polymerization (ATRP), yielding a nanocomposite which was soluble in chloroform. The surface of the PMMA grafted GO (GPMMA) was characterized by AFM, HRTEM, Raman, FTIR and contact angle. The interest of these novel nanocomposites lies in their potential to be homogenously dispersed in polymeric dense matrices and to promote good interfacial adhesion, of particular relevance in stress transfer to the fillers. PMMA composite films were prepared using different percentages of GPMMA and pristine GO. Mechanical analysis of the resulting films showed that loadings as low as 1% (w/w) of GPMMA are effective reinforcing agents, yielding tougher films than pure PMMA films and even than composite films of PMMA prepared with GO. In fact, addition of 1% (w/w) of GPMMA fillers led to a significant improvement of the elongation at break, yielding a much more ductile and therefore tougher material. Thermal analysis showed an increase of the thermal stability properties of these films providing evidence that strong interfacial interactions between PMMA and GPMMA are achieved. In addition, AFM analysis, in friction force mode, is demonstrated to be an effective tool to analyse the surface filler distribution on polymer matrices

Consequences of Nitrogen Doping and Oxygen Enrichment on Titanium Local Order and Photocatalytic Performance of TiO2 Anatase

This work was financially supported by Spanish MINECO (MAT2013-40950-R, MAT2016-78155-C2-1-R, and CTQ2014-52956-C3-1-R), Gobierno del Principado de Asturias (GRUPIN14-060 and GRUPIN14-078), FEDER and South Ural State University thanks for the support the Ministry of Education and Science of the Russian Federation (grant No 16.2674.2014/K

Efficient Pt electrocatalysts supported onto flavin mononucleotide–exfoliated pristine graphene for the methanol oxidation reaction

Due to its large surface area, high electrical conductivity as well as mechanical and thermal stability, pristine graphene has the potential to be an excellent support for metal nanoparticles (NPs), but the scarce amount of intrinsic chemical groups/defects in its structure that could act as anchoring sites for the NPs hinders this type of use. Here, a simple strategy based on the stabilization of pristine graphene in aqueous dispersion with the assistance of a low amount of flavin mononucleotide (FMN) is shown to yield a material that combines high electrical conductivity and abundance of extrinsic anchoring sites, so that pristine graphene–metal (Pd and Pt) NP hybrids with good dispersion and metal loading can be obtained from FMN–stabilized graphene. The activity of these hybrids towards the methanol oxidation reaction (MOR) both in acidic and alkaline media is studied by cyclic voltammetry (CV) and their stability investigated by chronoamperometry. The pristine graphene–Pt NP hybrid prepared by this simple, eco–friendly protocol is demonstrated to outperform most previously reported pristine graphene– and reduced graphene oxide–metal NP hybrids as electrocatalyst for the MOR, both in terms of catalytic activity and stability, avoiding at the same time the use of harsh chemicals or complex synthetic routes.Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (FEDER) through projects MAT2015-69844-R and MAT2016-76595-R is gratefully acknowledged. We also acknowledge partial funding by Plan de Ciencia, Tecnología e Innovación 2013-2017 del Principado de Asturias and FEDER through grant GRUPIN14-056. M.A-V. is thankful to MINECO and for his pre-doctoral contract. R.R.R acknowledges financial support from MINECO through “Juan de la Cierva” program (JCI-2012-12664)

Grafting of adipic anhydride to carbon nanotubes through a Diels-Alder cycloaddition/oxidation cascade reaction

Accepted ManuscriptDifferent reactions have been reported for the successful functionalization of carbon nanotubes (CNT). The Diels-Alder cycloaddition is recognized as a plausible chemical approach, but few reports are known where this strategy has been used. In this study, the functionalization was performed by 1,3-butadiene generated from 3-sulfolene under heating conditions in diglyme. This simple and easily scalable method resulted in functionalized CNT with mass losses of 10 - 23 % by thermogravimetric analysis (nitrogen atmosphere). The functionalization was also supported by acid-base titration, elemental analysis, temperature programmed desorption and X-ray photoelectron spectroscopy. The high content in oxygen detected on the CNT surface was assigned to anhydride formation due to a cascade oxidation of the alkene groups generated in the cycloaddition reaction. The complete evolution of the alkene leads to a grafting density of 4.2 mmol g-1 for the anhydride moiety. Ab-initio calculations in CNT model systems indicate that the Diels-Alder addition of butadiene is a feasible process and that subsequent oxidation reactions may result in the formation of the anhydride moiety. The presence of the anhydride group is a valuable asset for grafting a multitude of complex molecules, namely through the nucleophilic addition of amines.Centro de Química and Instituto de Polímeros e Compósitos of the University of Minho and Fundação para a Ciência e Tecnologia (FCT) through the Portuguese NMR network (RNRMN), the Project F-COMP-01-0124-FEDER-022716 (ref. FCT PEst-C/QUI/UI0686/2011) FEDER-COMPETE, Project PEst-C/CTM/LA0025/2013 (Strategic Project - LA 25-2013-2014) and also Project Scope UID/CEC/00319/2013. TG Castro acknowledges FCT for a doctoral grant (SFRH/BD/79195/2011) RF Araújo for a Post-doc grant (SFRH/BPD/88920/2012) and MMF also acknowledges FCT through the program Ciência 2008. Access to computing resources funded by the Project "Search-ON2: Revitalization of HPC infrastructure of UMinho" (NORTE-07-0162-FEDER-000086) is also gratefully acknowledged