Academic literature on the topic 'Nano-porous graphene membranes'

Forward osmosis (FO) membranes have the advantages of low energy consumption, high water recovery rate, and low membrane pollution trend, and they have been widely studied in many fields. However, the internal concentration polarization (ICP) caused by the accumulation of solutes in the porous support layer will reduce permeation efficiency, which is currently unavoidable. In this paper, we doped Graphene oxide (GO) nanoparticles (50~150 nm) to a polyamide (PA) active layer and/or polysulfone (PSF) support layer, investigating the influence of GO on the morphology and properties of thin-film composite forward osmosis (TFC-FO) membranes. The results show that under the optimal doping amount, doping GO to the PA active layer and PSF support layer, respectively, is conducive to the formation of dense and uniform nano-scale water channels perpendicular to the membrane surface possessing a high salt rejection rate and low reverse solute flux without sacrificing high water flux. Moreover, the water channels formed by doping GO to the active layer possess preferable properties, which significantly improves the salt rejection and water permeability of the membrane, with a salt rejection rate higher than 99% and a water flux of 54.85 L·m−2·h−1 while the pure PSF-PA membrane water flux is 12.94 L·m−2·h−1. GO-doping modification is promising for improving the performance and structure of TFC-FO membranes.

Reduced graphene oxide is a very attractive material for sensor applications. It exhibits high conductivity at room temperature and high specific surface area. Since it can be produced in many ways, its properties can be influenced by the fabrication method. In this paper, we investigated the influence of graphite precursors (flake, scalar and synthetic) on the size of reduced graphene oxide. We have shown that the size of the precursor determines the size of the obtained rGO. We have noted that the larger graphite size, the larger rGO size. Full Text: PDF ReferencesR. Peng, Y. Li, T. Liu et al., "Reduced graphene oxide/SnO2@Au heterostructure for enhanced ammonia gas sensing", Chem. Phys. Lett., 737, 136829 (2019). CrossRef S. Pei and H. M. Cheng, "The reduction of graphene oxide", Carbon N. Y., 50, 9 (2012). CrossRef N. Sharma, V. Sharma, R. Vyas et al., "A new sustainable green protocol for production of reduced graphene oxide and its gas sensing properties", J. Sci. Adv. Mater. Devices, 4, 3 (2019) CrossRef R. Tarcan, O. Todor-Boer, I. Petrovai, C. Leordean, S. Astilean, I. Botiz, "Reduced graphene oxide today", J. Mater. Chem. C, 8, 4 (2020). CrossRef X. Jiao, Y. Qiu, L. Zhang, and X. Zhang, "Comparison of the characteristic properties of reduced graphene oxides synthesized from natural graphites with different graphitization degrees", RSC Adv., 7, 82 (2017). CrossRef J.A. Quezada-Renteria, C.O. Ania, L.F. Chazaro-Ruiz, J.R. Rangel-Mendez, "Influence of protons on reduction degree and defect formation in electrochemically reduced graphene oxide", Carbon N. Y., 149 (2019). CrossRef H. Gao, Y. Ma, P. Song, J. Leng, Q. Wang, "Characterization and cytocompatibility of 3D porous biomimetic scaffold derived from rabbit nucleus pulposus tissue in vitro", J. Mater. Sci. Mater. Electron., 32, 8 (2021). CrossRef A.T. Lawal, "Graphene-based nano composites and their applications. A review", Biosens. Bioelectron., 141, 111384, (2019). CrossRef E. Aliyev, V. Filiz, M.M. Khan, Y.J. Lee, C. Abetz, V. Abetz, "Structural Characterization of Graphene Oxide: Surface Functional Groups and Fractionated Oxidative Debris", Nanomaterials, 9, 8 (2019). CrossRef S. Sali, H.R. Mackey, A.A. Abdala, "Effect of Graphene Oxide Synthesis Method on Properties and Performance of Polysulfone-Graphene Oxide Mixed Matrix Membranes", Nanomaterials, 9, 5 (2019). CrossRef G. Lu, L.E. Ocola, J. Chen, "Reduced graphene oxide for room-temperature gas sensors", Nanotechnology, 20, 44 (2009). CrossRef C. Botas, P. Alvarez, C. Blanco et al., "Critical temperatures in the synthesis of graphene-like materials by thermal exfoliation–reduction of graphite oxide", Carbon N. Y., 52, 2013. CrossRef

Pristine and doped polyvinylidene fluoride (PVDF) are actively investigated for a broad range of applications in pressure sensing, energy harvesting, transducers, porous membranes, etc. There have been numerous reports on the improved piezoelectric and electric performance of PVDF-doped reduced graphene oxide (rGO) structures. However, the common in situ doping methods have proven to be expensive and less desirable. Furthermore, there is a lack of explicit extraction of the compression mode piezoelectric coefficient (d33) in ex situ rGO doped PVDF composite films prepared using low-cost, solution-cast processes. In this work, we describe an optimal procedure for preparing high-quality pristine and nano-composite PVDF films using solution-casting and thermal poling. We then verify their electromechanical properties by rigorously characterizing β-phase concentration, crystallinity, piezoelectric coefficient, dielectric permittivity, and loss tangent. We also demonstrate a novel stationary atomic force microscope (AFM) technique designed to reduce non-piezoelectric influences on the extraction of d33 in PVDF films. We then discuss the benefits of our d33 measurements technique over commercially sourced piezometers and conventional piezoforce microscopy (PFM). Characterization outcomes from our in-house synthesized films demonstrate that the introduction of 0.3%w.t. rGO nanoparticles in a solution-cast only marginally changes the β-phase concentration from 83.7% to 81.7% and decreases the crystallinity from 42.4% to 37.3%, whereas doping increases the piezoelectric coefficient by 28% from d33 = 45 pm/V to d33 = 58 pm/V, while also improving the dielectric by 28%. The piezoelectric coefficients of our films were generally higher but comparable to other in situ prepared PVDF/rGO composite films, while the dielectric permittivity and β-phase concentrations were found to be lower.

A multifunctional nano-films of cellulose acetate (CA)/magnesium ortho-vanadate (MOV)/magnesium oxide/graphene oxide wound coverage was fabricated. Through fabrication, different weights of the previously mentioned ingredients were selected to receive a certain morphological appearance. The composition was confirmed by XRD, FTIR, and EDX techniques. SEM micrograph of Mg3(VO4)2/MgO/GO@CA film depicted that there was a porous surface with flattened rounded MgO grains with an average size of 0.31 µm was observed. Regarding wettability, the binary composition of Mg3(VO4)2@CA occupied the lowest contact angle of 30.15 ± 0.8o, while pure CA represents the highest one at 47.35 ± 0.4°. The cell viability % amongst the usage of 4.9 µg/mL of Mg3(VO4)2/MgO/GO@CA is 95.77 ± 3.2%, while 2.4 µg/mL showed 101.54 ± 2.9%. The higher concentration of 5000 µg/mL exhibited a viability of 19.23%. According to optical results, the refractive index jumped from 1.73 for CA to 1.81 for Mg3(VO4)2/MgO/GO@CA film. The thermogravimetric analysis showed three main stages of degradation. The initial temperature started from room temperature to 289 °C with a weight loss of 13%. On the other hand, the second stage started from the final temperature of the first stage and end at 375 °C with a weight loss of 52%. Finally, the last stage was from 375 to 472 °C with 19% weight loss. The obtained results, such as high hydrophilic behavior, high cell viability, surface roughness, and porosity due to the addition of nanoparticles to the CA membrane, all played a significant role in enhancing the biocompatibility and biological activity of the CA membrane. The enhancements in the CA membrane suggest that it can be utilized in drug delivery and wound healing applications.

Over the last two decades, platinum group metal-free (PGM-free) catalysts are attracting increasing attention and finding applications in several important process across many electrochemical energy technologies. Among those PGM-free materials, atomically dispersed (AD) transition metal-nitrogen-carbon (M-N-C) catalysts are gaining exceptional popularity as they demonstrate very high (for this class of materials) activity in oxygen reduction reaction (ORR)1 and are the only cathode catalysts suitable for both proton exchange membrane fuel cells (PEMFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). Over the last few years, M-N-C catalysts have shown promising activity in carbon dioxide reduction reaction (CO2RR).2 In this case, varying the transition metal in M-N-Cs opens routes for controlling the selectivity towards a list of C1 and C2 products. There are recent reports on catalytic activity of AD M-N-C materials in direct electro-reduction of molecular nitrogen (N2RR) or reactions of reduction of nitrates, nitrites or various nitrogen oxides (NOx). We have systematically investigated all these processes having as a base the M-N-C catalysts synthesized by sacrificial support method (SSM) – a hard template approach with transition metal salt and charge-transfer organic salt (nicarbazin) mixed by ball-milling, pyrolyzed at high temperature in inert atmosphere and then etched in HF after cooling. In most cases a secondary (similar) pyrolysis was performed to refine the material and ensure its AD character. The makeup and structure of the active site/sites of the AD M-N0C electrocatalysts, including geometry (coordination) and chemistry (composition and oxidation state) remain contentious to this day. There is an emerging agreement however, that the transition metal (at least for the 2nd row transitions meals) is immediately associated with (liganded by) the nitrogen functionalities, displayed on the surface if the carbonaceous substrate. It is almost universally accepted that N-coordinated AD transition metal ions, either as in-plane or edge-type defect in “graphene” sheet, are the main/principal active sites. This is often combined with a broadly accepted hypothesis that micro-porous surface area plays a critical role forming edge-type, intercalational active sites while meso-porous interface is most-likely associated with the in-plane, substitutional AD metal sites. Candidate structures participating in reativity towards O2, CO2 or nitrogen species include a list of nitrogen-containg and oxygen-containng moeties in the carbonaceous matrix. The carbon itself displays various degrees of graphitization, depending on the transition metal used in M-N-C synthesis. Additional complexity in this calss of caralysts study comes from the fact that many samples are not strictly AD materials. They often contain incorporated metal nano-particles, corresponding (native) oxides and/or carbides and nitrides (oxocabides and oxonitrides have been observed as well).These “unrefined” M-N-C materials are often used in practice and the corresponding nano-particle components of the de-facto nanocomposites do alter substantially the reactivity and selectivity of the catalysts in all these electro-reduction reactions. This talk discusses the mechanistic aspects of M-N-C catalysts in ORR, CO2RR, N2RR and electroreduction of nitrogen-containing oxo-species, obtained when cross-referencing electrochemical activity results obtained in rotating disk and rotating ring-disk electrodes setting (RDE/RRDE) with those observed in near-ambient pressure X-ray photo-electron spectroscopy (NAP-XPS) and supported by density functional theory calculations of the reagents adsorption on AD transition metal or nitrogen- or oxygen-containing moieties from the carbonaceous matrix of the M-N-Cs. The later are of particular importance as significant reactivity has been observed for most of those processes when metal-free, nitrogen-doped carbon (N-C) catalysts are used.3 We will present a case that outlines the reactivity of M-N-C in those important electro-reduction reactions in terms of (i) role of the AD transition metal, (ii) role of the surface N-groups as co-catalysts/alternative sites (iii) role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor, the last being also critically dependent on morphology.4 References: T. Asset and P. Atanassov, Joule, 2020, 4, 33. T. Asset, S.T. Garcia, S. Herrera, N. Andersen, Y. Chen, E.J. Peterson, I. Matanovic, K.Artyushkova, J. Lee, S.D. Minteer,S. Dai, X. Pan, K. Chavan, S. Calabrese Bartonand P. Atanassov, ACS Catalysis, 2019, 9, 7668 D. Hursán, A. Samu,K. Artyushkova,T. Asset, P. Atanassov and C. Janáky, Joule, 2019, 3 1719 Y. Huang, Y. Chen, M. Xu, T. Asset, P. Tieu, A. Gili, D. Kulkarni, V. de Andrade, F. de Carlo, H. S. Barnard, A. Doran, D. Y. Parkinson, X. Pan, P. Atanassov, and I. Zenyuk, Materials Today, 2021, 47, 53.