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Among the many potential applications of graphene and graphene-based materials, their use as protective films or as additives in coatings for corrosion protection has seen an increased level of interest in the last decade. Much of this interest is motivated by the need to implement additional functionalities, to enhance anti-corrosion performance and to ultimately extend the service life of metallic structures. Pristine graphene films, with their impermeable nature allied to flexibility and mechanical strength, appear as particularly attractive candidates for barrier films against corrosive agents, while graphene-based materials such as graphene oxide and reduced graphene oxide offer a wide range of opportunities for their dispersion in polymeric matrices for composite anti-corrosive coatings. Simultaneously, considerable progress in the development of scalable graphene and graphene-based materials production techniques has been made during the last several years. Currently, a broad range of graphene materials with different morphologies and properties is available, making the need for an adequate fit between the production method and the desired application even more evident. This review article aims to give the reader a general overview of the recent trends in both the production of graphene and graphene-based materials, and their implementation in different anti-corrosion solutions. Moreover, the present work provides a critical look on this subject, highlighting the areas in need of further exploration. published

The ability to synthesize laser-induced graphene (LIG) on cellulosic materials such as paper opens the door to a wide range of potential applications, from consumer electronics to biomonitoring. In this work, strain and bending sensors fabricated by irradiation of regular filter paper with a CO

Laser-induced graphene (LIG) is a foam-like porous material consisting of few-layer graphene obtained by laser irradiation of a wide range of carbon-containing substrates. Among these, the ability to synthesize LIG from paper and other cellulose-related materials is particularly exciting, as it opens the door to a wide assortment of potential applications in the form of low-cost, flexible, and biodegradable devices. Here, the synthesis of this material, dubbed paper-LIG, on different types of filter papers and xylan biopolymer is discussed. In particular, we report the formation of paper-LIG by single-step irradiation, providing an improvement over the conventional multiple lasing approach and giving an explanation of the conditions that allow this simplified synthesis. All the relevant process parameters are covered, assessing their effect on the resulting electrical properties, structure, and morphology. Additionally, we demonstrate the application of LIG obtained from xylan, an abundant and often underutilized biopolymer, for temperature sensing. These results provide a better understanding of the conditions required for the synthesis of highly conductive LIG from paper and related materials, paving the way for its application, with reduced cost and low environmental impact, in fields ranging from biomonitoring to consumer electronics. published

In chemical vapor deposition of graphene, low nucleation density and large domain sizes are desirable. In the particular case of growth on copper, throughout recent years, several works have reported the oxidation of the substrate through various means, which leads to a reduced nucleation density. In this work, an in situ oxidation and reduction treatment is explored, establishing its connection with the removal of carbon impurities from the copper bulk, as well as clarifying the role of these impurities as graphene nucleation sites. The extent of the contribution of these impurities to the growth of graphene is inferred by experiments using carbon-13 methane feed. The effect of the oxidation and reduction treatment on the substrate’s surface roughness is also addressed. Lastly, the synthesis recipe based on this treatment is supplemented with a growth stage splitting, an increased argon flowrate and a short etching stage, resulting in millimeter sized hexagonal graphene domains (diameters 2–3 mm) with improved electrical transport properties. Thus, the deposition process presented here stands out on account of its streamlined nature, which makes it an attractive candidate for industrial scale-up.

Carbon-based electrodes have demonstrated great promise as electrochemical transducers in the development of biosensors. More recently, laser-induced graphene (LIG), a graphene derivative, appears as a great candidate due to its superior electron transfer characteristics, high surface area and simplicity in its synthesis. The continuous interest in the development of cost-effective, more stable and reliable biosensors for glucose detection make them the most studied and explored within the academic and industry community. In this work, the electrochemistry of glucose oxidase (GOx) adsorbed on LIG electrodes is studied in detail. In addition to the well-known electroactivity of free flavin adenine dinucleotide (FAD), the cofactor of GOx, at the expected half-wave potential of −0.490 V vs. Ag/AgCl (1 M KCl), a new well-defined redox pair at 0.155 V is observed and shown to be related to LIG/GOx interaction. A systematic study was undertaken in order to understand the origin of this activity, including scan rate and pH dependence, along with glucose detection tests. Two protons and two electrons are involved in this reaction, which is shown to be sensitive to the concentration of glucose, restraining its origin to the electron transfer from FAD in the active site of GOx to the electrode via direct or mediated by quinone derivatives acting as mediators.

Unobtrusive physiological monitoring in daily routines and workplaces can play an important role in assessing the wellbeing of workers. Here, fiber Bragg grating (FBG) sensors are used to monitor the respiratory rate. Two instrumented structures, in form of a pillow and a sponge, were characterized to applied force and tested by three volunteers, positioned in the seat or backrest of an office desk chair. The experimental results are promising, with the proposed systems allowing to detect the respiratory signals in the different positions.

Zinc oxide (ZnO)/laser-induced graphene (LIG) composites were prepared by mixing ZnO, grown by laser-assisted flow deposition, with LIG produced by laser irradiation of a polyimide, both in ambient conditions. Different ZnO:LIG ratios were used to infer the effect of this combination on the overall composite behavior. The optical properties, assessed by photoluminescence (PL), showed an intensity increase of the excitonic-related recombination with increasing LIG amounts, along with a reduction in the visible emission band. Charge-transfer processes between the two materials are proposed to justify these variations. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy evidenced increased electron transfer kinetics and an electrochemically active area with the amount of LIG incorporated in the composites. As the composites were designed to be used as transducer platforms in biosensing devices, their ability to detect and quantify hydrogen peroxide (H2O2) was assessed by both PL and CV analysis. The results demonstrated that both methods can be employed for sensing, displaying slightly distinct operation ranges that allow extending the detection range by combining both transduction approaches. Moreover, limits of detection as low as 0.11 mM were calculated in a tested concentration range from 0.8 to 32.7 mM, in line with the values required for their potential application in biosensors.

Graphene presents unique opto-electronic properties which makes it useful for a wide range of applications and devices, such as high-speed photodetectors, that rely on the relaxation dynamics of photoexcited charge carriers. These demand reliable and reproducible methods for synthesis of high quality graphene. Here we present ultrafast degenerate pump-probe measurements of multilayer graphene coatings grown by microwave plasma chemical vapour deposition (MPCVD) and analyse the impact of the synthesis growth time on the material’s nonequilibrium optical response.

Integrating different carbon allotropes, namely graphene and nanocrystalline diamond, into a hybrid structure is highly desirable for a synergistic approach envisaging a field emission material. In this work, this was accomplished by a simultaneous synthesis of both allotropes by microwave plasma CVD on copper substrates, using a CH 4 pulsed flow modulation strategy. This approach enabled tailoring the density (from 1.01 × 10 6 to 4.48 × 10 6 /cm 2 ) and diameter (from 1.06 to 3.09 μm) of nanocrystalline diamond clusters nucleated on the underlying graphene layer. Since morpho-structural aspects are critical regarding the field emission behavior, an exhaustive characterization was undertaken using scanning and transmission electron microscopy, Raman spectroscopy and optical profillometry. The field emission data were analyzed using the Fowler-Nordheim model and the electrical activation fields, ranging from ∼4.6 to ∼8.4 V/μm, were found to decrease with increasing NCD cluster content. Two emission regimes were observed, each corresponding to a distinct field enhancement factor, reaching values as high as 2204. The dependency of these factors with the total NCD cluster surface area suggests emission from both the background graphene and the protruded NCD clusters.

In this work, suspended 4-mm-wide graphene membranes are obtained through a sublimation-assisted transfer process, using few-layer films grown by microwave plasma chemical vapor deposition. This result is achieved by a new approach involving the removal of the graphene-transfer supporting layer in vacuum. The membranes produced by this procedure show the largest area-to-thickness ratio described in the literature with a 2-fold improvement when compared to the best results using the conventional PMMA-assisted transfer, and a five orders of magnitude increase when compared to previous sublimation-assisted processes. This breakthrough allows the implementation of a wide variety of technological applications where 2D materials with atomic thickness and large areas are required. As large-area free-standing membranes are difficult to obtain, a new figure of merit is defined to benchmark the various methods of suspending graphene. A high transfer yield is achieved, and the mechanical and optical properties of the 3.7 nm thick membranes are evaluated. Finally, a prototype condenser microphone is built and tested, and found to exhibit an enhanced specific response.

An innovation is reported in the synthesis of a hybrid carbon structure resulting from the simultaneous growth of graphene and nanocrystalline diamond (NCD) by the microwave plasma chemical vapor deposition technique. This strategy allows to take advantage of the complementary electronic behavior of each carbon allotrope, a key feature in new nanostructured materials for electronics under the graphene/insulator all-carbon approach. The graphene-diamond hybrid structures were grown on copper and transferred to a glass substrate to be further characterized. Raman analysis puts in evidence the signature of both phases and the high crystallinity of the graphene layer, based on band intensity and width measurements. Raman mapping and SEM observations show a uniform distribution of the NCD clusters, confirmed by AFM/EFM measurements. Additionally, HRTEM analysis permitted to detail the diamond nanocrystalline structure, revealing a close link to the graphene layer on the basis of which a diamond on graphene nucleation mechanism is proposed. (C) 2015 Elsevier Ltd. All rights reserved.

In this paper, we are proposing for the first time the partial laser treatment of a self-lubricating coating in order to optimize its frictional performance from the very first moments of the sliding contact. W-S films alloyed with carbon were deposited by closed field unbalanced magnetron sputtering. The coatings were treated using two types of lasers, with peak emissions in the UV and IR, under different laser power conditions and patterning. The structure, mechanical and tribological properties of the treated coatings were analysed using X-ray diffraction (XRD), Raman spectroscopy, nanoindentation and reciprocating ball-on-disk tribometry. Although XRD diffractograms illustrated an overall amorphous structure in all as-deposited and treated samples, their Raman spectra confirmed the presence of WS2 crystalline phase in some of the treated areas. Furthermore, in the samples where WS2 Raman peaks were detected, the friction coefficient was in the initial part of the test lower than that of untreated coating. Previous crystallization of the W-S phase before tribological testing has a key role for shortening the self-adaption process improving the overall friction performance of the coatings.

No abstract available.

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.bios.2018.10.015., Graphene has emerged as a novel material with enhanced electrical and structural properties that can be used for a multitude of applications from super-capacitors to biosensors. In this context, an ultra-sensitive biosensor was developed using a low-cost, simple and mask-free method based on laser-induced graphene technique for electrodes patterning. The graphene was produced on a polyimide substrate, showing a porous multi-layer structure with a resistivity of 102.4?±?7.3??/square. The biosensor was designed as? a 3-electrode system. Auxiliary and working electrodes were made of graphene by laser patterning and the reference electrode was handmade by casting a silver ink. A molecularly-imprinted polymer (MIP) was produced at the working electrode by direct electropolymerization of eriochrome black T (EBT). As proof-of-concept, the MIP film was tailored for chloramphenicol (CAP), a common contaminant in aquaculture. The resulting device was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy readings against a redox standard probe?. The limit of detection (LOD) was 0.62?nM and the linear response ranged from 1?nM to 10?mM. These analytical features were better than those produced by assembling the same biorecognition element on commercial graphene- and carbon-based screen-printed electrodes. Overall, the simplicity and quickness of the laser-induced graphene technique, along with the better analytical features obtained with the graphene-based electrodes, shows the potential to become a commercial approach for on-site sensing., The authors acknowledge funding from project PTDC/AAG-TEC/5400/2014, POCI-01-0145-FEDER-016637 and POCI-01-0145-FEDER007688, UID/CTM/50025/2013 funded by European funds, through FEDER (European Funding or Regional Development) via COMPETE2020 – POCI (operational program for internationalization and competitively) and by national funding through the Fundação para a Ciência e Tecnologia, I.P., Portugal (FCT-MCTES). ARC, ACM and AFC also acknowledge funding to National Foundation for Science and Technology, I.P., Portugal (FCT-MCTES) through the Ph.D. Grant SFRH/BD/130107/2017, SFRH/BD/115173/2016 and DAEPHYS-FCT PD/BD/114063/2015, respectively. AFC also acknowledges the funding from “Programa de Estímulo à Investigação 2016” from Fundação Calouste Gulbenkian., info:eu-repo/semantics/publishedVersion