Graphene-based composite with high stable dispersion in ethanol.

In the last few years a lot of applicative research studies are focused on graphene, a 2D carbo-material with very particular physical features like electro-conductivity, thermo-conductivity, mechanical stability, and its particular aspect ratio with a high surface and a negligible thickness (1–3). For that features the spectra of possibilities to make a new application with this material, are big and grow time after time. In addition, with climate change, the focus of research to make new technologies greener and with less impact, on the environment, than now has moved to increase the study of that material and most researchers have focused their studies on the possibility to disperse that material in a green solvent with low boiling point. One problem with pristine Graphene is that it could be dispersed with high concentration only in polar aprotic solvent as n-methyl-2-pyrrolidone or Dimethyl formamide (4), a solvent with a high boiling point and with high toxicity for the humans and the environment. Usually for that reason is preferred to use the oxidized form of graphene GO, most easy to disperse, and reduce in rGO. The reduced form has the problem of having more defects on the surface than pristine graphene losing a part of the natural performance of the graphene. Another method studied is the use of a surfactant (5)or making nano-composite material with the use of polar polymer such as the PVP (6–8) has permitted to disperse of the material with a good concentration in water. This research has moved used to investigate how to make new composite graphene-based, easy to disperse in an organic polar solvent such as ethanol. We made an uncontrolled growth of polymer (ethyl maleate derivate) on the surface of the material, for making that we use the support of the microwave reactor that, with the particular characteristic of the graphene to be a radical initiator, permits the formation of different particles of polymer maleate based on the surface of the graphene. This material has good stability in ethanol and maintains that feature after a long time. That dispersion opens the possibility to make ink graphene-based or coating on other surfaces and other different applications with the fast removal of the solvent. At the same time the uncontrolled growing permit the removal of the composite with the heating of the material in an inert atmosphere to obtain pristine graphene with a low number of defects. Bibliography 1. Clancy AJ, Bayazit MK, Hodge SA, Skipper NT, Howard CA, Shaffer MSP. Charged Carbon Nanomaterials: Redox Chemistries of Fullerenes, Carbon Nanotubes, and Graphenes. Chem Rev. 2018;118(16):7363-7408. doi:10.1021/acs.chemrev.8b00128 2. Randviir EP, Brownson DAC, Banks CE. A decade of graphene research: Production, applications, and outlook. Mater Today. 2014;17(9):426-432. doi:10.1016/j.mattod.2014.06.001 3. Wei W, Qu X. Extraordinary physical properties of functionalized graphene. Small. 2012;8(14):2138-2151. doi:10.1002/smll.201200104 4. Vacacela Gomez C, Guevara M, Tene T, et al. The liquid exfoliation of graphene in polar solvents. Appl Surf Sci. 2021;546(December 2020):149046. doi:10.1016/j.apsusc.2021.149046 5. Wang S, Yi M, Shen Z, Zhang X, Ma S. Adding ethanol can effectively enhance the graphene concentration in water-surfactant solutions. RSC Adv. 2014;4(48):25374-25378. doi:10.1039/c4ra03345k 6. Laaksonen P, Kainlauri M, Laaksonen T, et al. Interfacial engineering by proteins: Exfoliation and functionalization of graphene by hydrophobins. Angew Chemie - Int Ed. 2010;49(29):4946-4949. doi:10.1002/anie.201001806 7. Perumal S, Lee HM, Cheong IW. High-concentration graphene dispersion stabilized by block copolymers in ethanol. J Colloid Interface Sci. 2017;497:359-367. doi:10.1016/j.jcis.2017.03.027 8. Wajid AS, Das S, Irin F, et al. Polymer-stabilized graphene dispersions at high concentrations in organic solvents for composite production. Carbon N Y. 2012;50(2):526-534. doi:10.1016/j.carbon.2011.09.00

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virtual European Symposium of Photopolymer Science 202

Electrospun PEO/PEDOT:PSS Nanofibers for Wearable Physiological Flex Sensors

Flexible sensors are fundamental devices for human body monitoring. The mechanical strain and physiological parameters coupled sensing have attracted increasing interest in this field. However, integration of different sensors in one platform usually involves complex fabrication process-flows. Simplification, even if essential, remains a challenge. Here, we investigate a piezoresistive and electrochemical active electrospun nanofibers (NFs) mat as the sensitive element of the wearable physiological flex sensing platform. The use of one material sensitive to the two kinds of stimuli reduces the process-flow to two steps. We demonstrate that the final NFs pH-Flex Sensor can be used to monitor the deformation of a human body joint as well as the pH of the skin. A unique approach has been selected for pH sensing, based on Electrochemical Impedance Spectroscopy (EIS). A linear dependence of the both the double layer capacitance and charge transfer re-sistance with the pH value was obtained by EIS, as well as a linear trend of the electrical resistance with the bending deformation. Gauge factors values calculated after the bending test were 45.84 in traction and 208.55 in compression mode, reflecting the extraordinary piezoresistive behavior of our nanostructured NFs

Determination of reliable resistance values for electrical double-layer capacitors

The power capabilities of supercapacitors are strongly influenced by their passive elements. Within this study, we investigate methods to address resistive components out of galvanostatic measurements and we compared literature methods with the aim to provide a guide to correctly exploit the resistance of supercapacitors. The impact of the sampling conditions of galvanostatic measurements is analyzed and related to electrochemical impedance spectroscopy. Further, a novel method based on the instantaneous power analysis is provided to get real-time information concerning the actual cell resistance during the measurement without altering the gal- vanostatic experiment. Measurements show that literature methods can provide values close to the series resistance, while the newly proposed power method results in a good estimate of the actual dissipative value

Design and Optimization of Piezoresistive PEO/PEDOT:PSS Electrospun Nanofibers for Wearable Flex Sensors

Flexible strain sensors are fundamental devices for application in human body monitoring in areas ranging from health care to soft robotics. Stretchable piezoelectric strain sensors received an ever-increasing interest to design novel, robust and low-cost sensing units for these sensors, with intrinsically conductive polymers (ICPs) as leading materials. We investigated a sensitive element based on crosslinked electrospun nanofibers (NFs) directly collected and thermal treated on a flexible and biocompatible substrate of polydimethylsiloxane (PDMS). The nanostructured active layer based on a blend of poly(ethylene oxide) (PEO) and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) as the ICP was optimized, especially in terms of the thermal treatment that promotes electrical conductivity through crosslinking of PEO and PSS, preserving the nanostructuration and optimizing the coupling between the sensitive layer and the substrate. We demonstrate that excellent properties can be obtained thanks to the nanostructured active materials. We analyzed the piezoresistive response of the sensor in both compression and traction modes, obtaining an increase in the electrical resistance up to 90%. The Gauge Factors (GFs) reflected the extraordinary piezoresistive behavior observed: 45.84 in traction and 208.55 in compression mode, which is much higher than the results presented in the literature for non-nanostructurated PEDOT

Leveraging substrate flexibility and product selectivity of acetogens in two-stage systems for chemical production

Carbon dioxide (CO2 ) stands out as sustainable feedstock for developing a circular carbon economy whose energy supply could be obtained by boosting the production of clean hydrogen from renewable electricity. H2 -dependent CO2 gas fermentation using acetogenic microorganisms offers a viable solution of increasingly demonstrated value. While gas fermentation advances to achieve commercial process scalability, which is currently limited to a few products such as acetate and ethanol, it is worth taking the best of the current state-of-the-art technology by its integration within innovative bioconversion schemes. This review presents multiple scenarios where gas fermentation by acetogens integrate into double-stage biotechnological production processes that use CO2 as sole carbon feedstock and H2 as energy carrier for products' synthesis. In the integration schemes here reviewed, the first stage can be biotic or abiotic while the second stage is biotic. When the first stage is biotic, acetogens act as a biological platform to generate chemical intermediates such as acetate, formate and ethanol that become substrates for a second fermentation stage. This approach holds the potential to enhance process titre/rate/yield metrics and products' spectrum. Alternatively, when the first stage is abiotic, the integrated two-stage scheme foresees, in the first stage, the catalytic transformation of CO2 into C1 products that, in the second stage, can be metabolized by acetogens. This latter scheme leverages the metabolic flexibility of acetogens in efficient utilization of the products of CO2 abiotic hydrogenation, namely formate and methanol, to synthesize multicarbon compounds but also to act as flexible catalysts for hydrogen storage or production

Crown-Ether Functionalized Graphene Oxide Membrane for Lithium Recovery from Water

The massive worldwide transition of the transport sector to electric vehicles has dramatically increased the demand for lithium. Lithium recovery by means of ion sieves or supramolecular chemistry has been extensively studied in recent years as a viable alternative approach to the most common extraction processes. Graphene oxide (GO) has also already been proven to be an excellent candidate for water treatment and other membrane related applications. Herein, a nanocomposite 12-crown-4-ether functionalized GO membrane for lithium recovery by means of pressure filtration is proposed. GO flakes were via carbodiimide esterification, then a polymeric binder was added to improve the mechanical properties. The membrane was then obtained and tested on a polymeric support in a dead-end pressure setup under nitrogen gas to speed up the lithium recovery. Morphological and physico-chemical characterizations were carried out using pristine GO and functionalized GO membranes for comparison with the nanocomposite. The lithium selectivity was proven by both the conductance and ICP mass measurements on different sets of feed and stripping solutions filtrated (LiCl/HCl and other chloride salts/HCl). The membrane proposed showed promising properties in low concentrated solutions (7 mg(Li)/L) with an average lithium uptake of 5 mg(Li)/g in under half an hour of filtration time

Effect of electrode materials on resistive switching behaviour of NbOx-based memristive devices

Memristive devices that rely on redox-based resistive switching mechanism have attracted great attention for the development of next-generation memory and computing architectures. However, a detailed understanding of the relationship between involved materials, interfaces, and device functionalities still represents a challenge. In this work, we analyse the effect of electrode metals on resistive switching functionalities of NbOx-based memristive cells. For this purpose, the effect of Au, Pt, Ir, TiN, and Nb top electrodes was investigated in devices based on amorphous NbOx grown by anodic oxidation on a Nb substrate exploited also as counter electrode. It is shown that the choice of the metal electrode regulates electronic transport properties of metal–insulator interfaces, strongly influences the electroforming process, and the following resistive switching characteristics. Results show that the electronic blocking character of Schottky interfaces provided by Au and Pt metal electrodes results in better resistive switching performances. It is shown that Pt represents the best choice for the realization of memristive cells when the NbOx thickness is reduced, making possible the realization of memristive cells characterised by low variability in operating voltages, resistance states and with low device-to-device variability. These results can provide new insights towards a rational design of redox-based memristive cells

Production of Graphene Stably Dispersible in Ethanol by Microwave Reaction

Graphene is a 2D carbon material with peculiar features such as high electrical conductivity, high thermal conductivity, mechanical stability, and a high ratio between surface and thickness. Applications are continuously growing, and the possibility of dispersing graphene in low-boiling green solvents could reduce its global environmental impact. Pristine graphene can be dispersed in high concentration only in polar aprotic solvents that usually have high boiling points and high toxicity. For this reason, the oxidized form of graphene is always used, as it is easier to disperse and to subsequently reduce to reduced graphene oxide. However, compared to pristine graphene, reduced graphene oxide has more defects and has inferior properties respect to graphene. In this work, the polymerization of (diethyl maleate derivate) on graphene obtained by sonication was performed in a microwave reactor. The obtained material has good stability in ethanol even after a long period of time, therefore, it can be used to deposit graphene by mass production of inks or by casting and easy removal of the solvent. The thermal annealing by heating at 300–400 ◦C in inert atmosphere allows the removal of the polymer to obtain pristine graphene with a low number of defects