Graphene Aerogel Research Articles

Role of nitrogen dual reaction sites in N-doped graphene aerogels for synergistic sulfamethoxazole adsorption and peroxymonosulfate activation in Fenton-like process

Persulfate-based advanced oxidation technology is widely used in water treatment, and the key is to develop catalysts showing excellent performance. In this study, an N-doped graphene aerogel (N-GA-2) with a three-dimensional macroscopic structure was prepared by chemically reducing graphene oxide using ethylenediamine (EDA) and was used to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. N-GA-2 has high pyridinic N content (5.84 at.%), and shows excellent catalytic performance in the activation of PMS. The SMX degradation rate was 94.11% within 90 min, and the first-order reaction rate constant was 0.0231 min−1. Furthermore, the adsorption of SMX on N-GA-2 was chemisorption, and the maximum adsorption capacity (qm) was 250.00 mg/g. Quenching experiments and electrochemical tests confirmed that the electron-transfer pathway was the main reason for SMX degradation. X-ray photoelectron spectroscopy and density functional theory revealed that pyridinic N, adjacent C atoms and electron-rich C = O functional groups were involved in the degradation of SMX. Specially, pyridinic N functioned as dual reaction sites for both SMX adsorption and PMS activation. The formation of SMX/N-GA-2* and N-GA-2/PMS* complexes, dominated by pyridinic N, enabled the completion of electron-transfer pathways. In addition, N-GA-2/PMS/SMX system demonstrated superior continuous catalytic performance in fluidized-bed experimental facility simulating practical applications, which can stably and sustainedly degrade SMX. This study focuses on the mechanism of electron transfer pathway induced by nitrogen dual reaction site in N-doped graphene aerogel and explores its potential application in engineering. This will provide basic theoretical support for the practical application of N-GA-2/PMS catalytic system.

Comparative study on the H2S gas-sensing properties of graphene aerogels synthesized through hydrothermal and chemical reduction

BackgroundIn this study, graphene aerogels (GAs) were successfully prepared through hydrothermal reduction (GA-HR) and chemical reduction (GA-CR) to determine the effect of two reduction approaches on the properties of GAs in gas-sensing applications. MethodsThe GA thin films were used for the detection of H2S, and the gas-sensing performances were investigated at room temperature. Significant findingsThe H2S gas sensitivity of GA-HR and GA-CR were 0.255 and 0.3984 ppm−1 H2S gas, respectively. GA-CR had a more compact surface morphology and slightly lower reduction degree than GA-HR. The high electrical conductivity of GA-CR, which resulted from its strong sp2 character as indicated by its ID/IG ratio (intensity ratio of D an G band in Raman spectrum), was an essential factor for its high sensitivity to H2S gas. Moreover, simulation based on density functional theory was employed to investigate the various adsorption sites for H2S gas molecules on the GAs. The theoretical calculations based on adsorption energy, charge transfer, and density of states were consistent with the experimental results indicating that the GAs had strong H2S gas-sensing characteristics.

Multi-layer wrapping functionalized silicon via graphene aerogels regenerated from spent graphite anode achieves high efficient lithium storage

The large volume expansion and severe pulverization of silicon nanoparticles (SiNPs) during cycling have significantly hindered its application into lithium-ion batteries (LIBs). Graphene, for its excellent mechanical strength and high conductivity, has been widely applied to alleviate the swelling effect and enhance the ion conductivity of electrode materials. Herein, a facile and low-cost method to wrap Si by graphene aerogels with multiple shells is proposed in this work. Specifically, graphene oxide (GO) is synthesized by an improved Hummers’ method with waste graphite anode as raw material, the surface of SiNPs are modified with an amino group to achieve electrostatic attraction with an abundant carboxyl group on GO. Then a two-step reduction is carried out to synthesize a 3D graphene aerogel structure with uniformly distributed SiNPs, the inner rGO shell enhances the transport of ions on the surface of Si, the outer shell provides excellent confinement against the volume expansion during battery cycling.

Towards metal-free nitrogen-doped graphene aerogels as efficient electrocatalysts in hydrogen evolution reaction

Graphene-based materials have been researched to substitute traditional Pt-based electrocatalysts in the hydrogen evolution reaction (HER) due to its strong electrical conductivity, easy functionalization, and cheaper synthesis. Doping graphene with heteroatom is a simple way of obtaining original and active electrocatalysts. Moreover, the nitrogen on it had a positive effect on HER performance. By using a reducing agent with nitrogen while synthesising graphene-based aerogels nitrogen-doped catalysts were obtained. In addition, a better reduction rate, higher crystallography parameters and a more porous material structure were reached. The aerogels were synthesised in an one-pot hydrothermal process, in which the graphene sheets were assembled. This was followed by freeze-drying, which fixed the carbon matrix structure. As a result, the final aerogel had a 3D structure that eased mass transfer and enhanced catalytic activity, reaching an overpotential of −10 mAcm−2 at 101 mV vs RHE (η10 = 101 mV). The amount of quaternary type nitrogen generated during synthesis had a strong influence on electrocatalytic behaviour in HER. Then, quaternary nitrogen and surface area (up to 397 m2/g) were maximized to ensure a higher current density. Moreover, an effective aerogel was prepared with half the solvent per batch, as this was essential for expanding the synthesis to an industrial scale. A final calcination step resulted crucial to improve the metal-free aerogel HER performance.

Function Graded Carbon Micro‐Structures for Powerless Photon Sensing with Intriguing µm‐Scale Position Sensitivity

AbstractPartial laser treatment is introduced to carbon‐based microfibers to generate excellent photon sensing capability without bias. This treatment brings about a Seebeck coefficient distribution along the sample's length, out of which a photovoltage with no external bias is generated and sensed. Using a line‐shaped laser spot, carbon microfiber (CMF), graphene microfiber (GMF), and graphene aerogel fiber (GAF) are investigated for their response to µm‐scale photon irradiation. A higher sensitivity for the incident photon is found for the GAF with no position sensitivity. More Seebeck coefficient variation is also observed for the GAF considering the amount of laser power used for the laser treatment. A weaker Seebeck coefficient spatial variation is observed for the GMF compared with the GAF. However, its photovoltage shows an abrupt magnitude change from the laser‐treated region to the non‐treated one. Despite the low spatial variation of the Seebeck coefficient for the CMF, it features an excellent and accurate position‐sensitive photoresponse with polarization change over a distance of ≈100 µm. Such unique capability prompts novel applications in using partially annealed CMF for sensing the position of optical beams at the microscale.

New choice of energy battery electrode materials in new energy vehicles: preparation of graphene aerogels by γ ray irradiation method

Graphene aerogel are frequently employed as electrode materials for power batteries due to their high specific surface area and excellent properties. This paper presents a method for preparing graphene aerogel by radiolytic reduction in a water and isopropanol system. In this study, the authors used radiolytic reduction technology to reduce graphene oxide to graphene aerogel and investigated the effects of various factors in the water and isopropanol system on its preparation process and properties. The experimental results showed that the water and isopropanol system could effectively prepare graphene aerogel with a high specific surface area, and the isopropanol concentration and irradiation time in the isopropanol system had important effects on its properties. This preparation method has the advantages of simplicity, rapidity, and low cost, providing a new idea for the large-scale preparation of graphene aerogel.

Ultralight covalent organic frame graphene aerogels modified platinum-magnetite nanostructure for direct methanol fuel cell

In order to fully utilise porous structures, the production of structures from covalent organic frameworks is of great importance. At this point, graphene aerogel (GA) production with ascorbic acid, a green reducing agent, is presented. It was observed that the GAs obtained in this context were stacked in 3D and exhibited an ultralight and highly porous structure. In addition, GAs were modified with PtFe3O4 for methanol oxidation studies and compared with PtFe3O4 to observe the effect of GA. The obtained nanostructure was characterised by TEM, SEM, FTIR, Raman and XRD. Also, the particle size was found to be 12.53 nm according to Debye Scherer formula. Electrochemical analyses were performed for the obtained structures. According to the results; electrocatalytic activity increased 8.72 times with the inclusion of GAs in the structure. In addition, according to long-term stability tests, it was observed that it showed 3 times more current at the end of 4000 s and provided high stability in the 500 cycle test. It was determined by EIS and CO stripping tests that GAs increased the electrical conductivity in the structure and offered higher surface area. With this study, it was shown that aerogel offers a very high potential in methanol oxidation studies using its porous structure.

Graphene aerogel-supported Na3V2(PO4)3/C cathodes for sodium-ion batteries

Na3V2(PO4)3 (NVP) is a preferred cathode material for Na-ion batteries due to its good thermal stability and long cycle life, but its low electrical conductivity limits its use. The carbon coating method is widely available in the literature but can solve the problem to a limited extent. Graphene aerogel-based composite materials with lightweight, high surface area and 3-dimensional (3D) porous structure are prepared, and the properties are tried to be improved further. In this study, carbon-coated Na3V2(PO4)3 (NVP/C) and graphene aerogel-carbon-coated Na3V2(PO4)3 (GA-NVP/C) composite have been synthesized. The produced samples have been analyzed using Field emission scanning electron microscopy, X-ray diffraction, Raman spectrum, Thermal Gravity Analysis, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller and Transmission electron microscopy. Then, the effect of graphene aerogel additive on electrochemical performances as cathode materials has been investigated. Even though GA-NVP/C and NVP/C have similar discharge capacities in the first cycle, GA-NVP/C shows high cycle stability when compared to NVP/C after 250 cycles. The GA-NVP/C cathode also has a higher discharge capacity than the NVP/C cathode at different current rates. The diffusion coefficient calculated using the cyclic voltammetry curve of GA-NVP/C is also high, supporting the graphene aerogel's positive results. In conclusion, we show that adding GA with a 3-dimensional porous structure greatly improves the electrochemical properties of the cathode in Na-ion batteries.

A Review of Nitrogen-Doped Graphene Aerogel in Electromagnetic Wave Absorption.

Graphene aerogels (GAs) possess a remarkable capability to absorb electromagnetic waves (EMWs) due to their favorable dielectric characteristics and unique porous structure. Nevertheless, the introduction of nitrogen atoms into graphene aerogels can result in improved impedance matching. In recent years, nitrogen-doped graphene aerogels (NGAs) have emerged as promising materials, particularly when combined with magnetic metals, magnetic oxides, carbon nanotubes, and polymers, forming innovative composite systems with excellent multi-functional and broadband absorption properties. This paper provides a comprehensive summary of the synthesis methods and the EMW absorption mechanism of NGAs, along with an overview of the absorption properties of nitrogen-doped graphene-based aerogels. Furthermore, this study sheds light on the potential challenges that NGAs may encounter. By highlighting the substantial contribution of NGAs in the field of EMW absorption, this study aims to facilitate the innovative development of NGAs toward achieving broadband absorption, lightweight characteristics, and multifunctionality.

Multifunctional nanocomposites reinforced by aligned graphene network via a low-cost lyophilization-free method

Compared with a disordered network, the ordered framework is more beneficial to improving the multifunctional properties (including thermal, electrical, and mechanical properties) of epoxy-based composites. However, current methods for building aligned structures are both energy and time-consuming on account of the tedious and lengthy lyophilization process. Herein, a new strategy is proposed to obtain low-density graphene aerogels (GAs) with long-range oriented structures through a lyophilization-free processes. Due to the minimum thermal boundary resistance, the prepared aligned graphene/epoxy composite exhibits an ultrahigh thermal conductivity of ∼11.6 W/(m·K) at a graphene content of 1.84 vol%, i.e., an enhancement efficiency of 3640% per 1 vol%. In addition, the compressive strength of the composite is increased by 2.6 times compared to epoxy (from 0.29 MPa to 0.76 MPa). Because the composite shows a modulus as low as 0.5–1.0 MPa, it has excellent deformability and compression performance. Moreover, the obtained 3-mm-thick composite achieves an electromagnetic interference shielding effectiveness (EMI SE) of 40 dB due to the interconnected graphene network structure, which meets the requirements of commercial EMI shielding applications. Hence, this strategy can be used to synthesize aligned graphene/epoxy composites with excellent multifunctional performances, which can be simultaneously used as elastic thermal interface materials (TIMs) and EMI shielding materials in the fields of advanced electronic packaging.

An aerogel-based adsorption structure for a high-performance adsorption heat pump system

Efforts to address global warming and fossil fuel depletion have driven the development of environmentally friendly and efficient energy systems. Adsorption heat pumps, which use thermal energy, are becoming popular since they can use renewable energy sources such as solar, geothermal, and waste heat. To effectively deliver thermal energy to the adsorbent medium in the heat pump systems, two methods are often utilized: packing the adsorbent between the fins or coating the adsorbent on the fin surfaces. The packing type exhibits a higher refrigerant adsorption capacity than the coating type. However, the heat transfer ability is low in the former, and the adsorbent quantity is limited in the latter. Therefore, we developed aerogel-based structures as an alternative to fin structures—a breakthrough that offers improved heat transfer capabilities compared to packing, and it overcomes the quantity limitations of coating representing a significant advancement beyond the existing literature. As a result, our innovation presents a promising avenue for enhancing thermal energy delivery in heat pump systems. In our study, we impregnated sodium bromide (NaBr) adsorbent into graphene aerogel (GA). The GA-based structure achieved a significantly improved specific cooling power of adsorption (SCPads) of 3.043 [kW/kg], compared to the conventional NaBr-packed finned flat plate structure with 0.065 [kW/kg]. We also conducted a numerical analysis to gain a deeper understanding of the experimental behavior. Additionally, we conducted a sensitivity analysis using the numerical model, revealing the pivotal role of adsorbent structure porosity in influencing SCPads. This research demonstrates the potential of using aerogels impregnated with adsorbent materials in adsorption reactors, leading to enhanced performance of heat pumps. The proposed adsorbent structure could be applied in future adsorption and desorption reactors.

Three-dimensional graphene aerogel mitigated the toxic impact of chloramphenicol wastewater on microorganisms in an EGSB reactor

Anaerobic treatment of chloramphenicol wastewater holds significant promise due to its potential for bioenergy generation. However, the high concentration of organic matter and residual toxic substances in the wastewater severely inhibit the activity of microorganisms. In this study, a three-dimensional graphene aerogel (GA), as a conductive material with high specific surface area (114.942 m2 g−1) and pore volume (0.352 cm3 g−1), was synthesized and its role in the efficiency and related mechanism for EGSB reactor to treat chloramphenicol wastewater was verified. The results indicated that synergy effects of GA for Chemical Oxygen Demand (COD) removal (increased by 8.17 %), chloramphenicol (CAP) removal (increased by 4.43 %) and methane production (increased by 70.29 %). Furthermore, GA increased the average particle size of anaerobic granular sludge (AGS) and promoted AGS to secrete more redox active substances. Microbial community analysis revealed that GA increased the relative abundance of functional bacteria and archaea, specifically Syntrophomonas, Geobacter, Methanothrix, and Methanolinea. These microbial species can participate in direct interspecific electron transfer (DIET). This research serves as a theoretical foundation for the application of GA in mitigating the toxic impact of refractory organic substances, such as antibiotics, on microorganisms during anaerobic treatment processes.

Microwave Gas Sensor Based on Graphene Aerogels

Microwave Gas Sensor Based on Graphene Aerogels

Enhancing Effect of Boron-Doping on the Activity of Nife-MOF-74 Towards Oxygen Evolution Reaction in Alkaline

Water splitting has drawn significant attention due to the capability of mass-producing hydrogen, which is considered a promising alternative to fossil fuels in the future.[1] The development of electrochemical energy conversion and storage technologies, such as water electrolyzers, metal-air batteries, and regenerative fuel cells, is of great importance to support the transition to clean and renewable energy.[2] Based on the merits of high surface area, 3D periodic porous structure, large porosities, diverse composition and well-defined metal centers, metal–organic frameworks (MOFs) and their derivatives have been widely exploited as OER electrocatalysts.[3]However, MOFs have some limitation to be used as a OER catalysts, considering their poor stabilities (in water, especially basic/acidic conditions) and low electrical conductivities. Incorporation of boron atoms into an aromatic carbon framework offers a wide variety of functionalities. [4] In this work, the flower-like bimetallic NiFe-MOF-74 dopped with boron were fabricated, and they exhibit superior catalytic activity with a very low overpotential of 318 mV for OER at a laboratory grade current density of 10 to 100 mA/cm2 and fast reaction kinetics with a small Tafel slope of 89 mV dec-1 in 1.0 M KOH using a catalyst fabrication process that is scalable to commercial levels. Additional work is required to demonstrate current densities at commercial levels. Reference [1] L. Fan, Z. Kang, M. Li, D. Sun, Recent progress in pristine MOF-based catalysts for electrochemical hydrogen evolution, oxygen evolution and oxygen reduction, Dalton Trans. 50 (2021) 5732–5753. https://doi.org/10.1039/D1DT00302J.[2] Bimetallic metal–organic frameworks and MOF-derived composites: Recent progress on electro- and photoelectrocatalytic applications - ScienceDirect, (n.d.). https://www.sciencedirect.com/science/article/pii/S0010854521005385 (accessed April 27, 2022).[3] J. Du, F. Li, L. Sun, Metal–organic frameworks and their derivatives as electrocatalysts for the oxygen evolution reaction, Chem. Soc. Rev. 50 (2021) 2663–2695. https://doi.org/10.1039/D0CS01191F.[4] Y. Xie, Z. Meng, T. Cai, W.-Q. Han, Effect of Boron-Doping on the Graphene Aerogel Used as Cathode for the Lithium–Sulfur Battery, ACS Appl. Mater. Interfaces. 7 (2015) 25202–25210. https://doi.org/10.1021/acsami.5b08129.

(Invited) Graphene-Based Scaffolds for Electrochemical Energy Storage

The efficient transport of charge species within energy storage devices is critical to realizing both large power and energy densities, especially when operating under extreme conditions (e.g. ultralow temperatures, high charge/discharge rates, etc.). A number of resistances can contribute to sluggish ion/electron transport in a cell such as charge transfer at interfaces, electrolyte resistance, electrode resistance, and diffusive transport within porous electrodes. Several strategies have been pursued to address these transport limitations. Electrolyte engineering is an effective approach as it can influence both electrolyte resistance and charge transfer resistances. Electrode materials discovery and development is another popular strategy as the charge storage mechanism and electrode resistance play a key role in kinetics of the device. Within electrode materials development, engineering of the electrode pore architecture is an extremely effective strategy to decrease the diffusive transport lengths and electrode resistances. This pore engineering can be achieved through synthetic chemistry for small pores (e.g. <10 um) and via additive manufacturing for larger pores (> 10 um). Here we show how electrolyte engineering and electrode materials development can be used to overcome sluggish transport in graphene-based electrodes. Particular focus will be given to the use of synthetic means to tune to the properties of a graphene aerogel scaffold (e.g. surface area, pore size, mechanical properties) and additive manufacturing to define the larger pore structure to facilitate uniform deposition of active materials (e.g. MnO2) and improve energy density and rate capability of the energy storage device. We explore a number of additive manufacturing techniques (e.g. direct ink write, projection microstereolithography, etc.) to print a variety of lattice structures and computer-guided designs to determine the optimal electrode architecture.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Study of Metal–Graphene Aerogel for Efficient Solar Energy Interface Evaporation Based on One‐Step Thermal Reduction Method

Freshwater resources can be sustainably harvested through interfacial evaporation by solar energy. To enhance the efficiency of solar interfacial evaporation, a metal–graphene alcohol gel is synthesized using a one‐step thermal reduction technique. Subsequently, a metal–graphene aerogel (GA) is produced using freeze‐drying technology. The hydrothermal treatment method is applied to introduce asymmetric moisture and roughness on the upper and lower surfaces of the aerogel. The unique structure of the aerogel plays a significant role in facilitating continuous water transport to the interface for evaporation. The top layer, being hydrophobic, and the bottom layer, being hydrophilic, contribute to this process. Importantly, the top layer's design ensures that an excessively thick water film does not form, thereby preventing any adverse effects on light‐absorption efficiency. The aerogel exhibits that an outstanding water‐evaporation rate is 1.75 kg m−2 h−1 and a remarkable photothermal conversion efficiency (PTCE) is 93.17% under one solar radiation intensity. This is because the aerogel has a unique 3D structure. This special 3D structure has an interconnected microporous‐like appearance inside, which increases the evaporation area. Metal–GA is based on the electric field dielectric evaporation mechanism of metal nanoparticles localized surface plasmon resonance effect and the thermal mediated evaporation mechanism of graphene full spectrum. Under the double action, the PTCE is significantly improved. The meticulously created metallic GA performs exceptionally well at evaporating water. As a result, it presents a promising and practical avenue for exploring effective solar interfacial evaporation.

Adsorption Ability of Graphene Aerogel and Reduced Graphene Aerogel toward 2,4-D Herbicide and Salicylic Acid.

Within this work, new aerogels based on graphene oxide are proposed to adsorb salicylic acid (SA) and herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous media. Graphene oxide aerogel (GOA) and reduced graphene oxide aerogel (rGOA) were obtained by freeze-drying processes and then studied by Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and Brunauer-Emmett-Teller (BET) analysis. The influence of contact time and the concentration of the adsorbates were also assessed. It was found that equilibrium for high adsorption is reached in 150 min. In a single system, the pseudo-first-order, pseudo-second-order kinetic models, Intraparticle diffusion, and Elovich models were used to discuss the detail of the aerogel adsorbing pollutant. Moreover, the Langmuir, Freundlich, and Temkin adsorption models were applied to describe the equilibrium isotherms and calculate the isotherm constants.

Plastic-Swelling Preparation of Functional Graphene Aerogel Fiber Textiles

Plastic-Swelling Preparation of Functional Graphene Aerogel Fiber Textiles

N-Octadecane Encapsulated by Assembled BN/GO Aerogels for Highly Improved Thermal Conductivity and Energy Storage Capacity.

The rapid development of industry has emphasized the importance of phase change materials (PCMs) with a high latent-heat storage capacity and good thermal stability in promoting sustainable energy solutions. However, the inherent low thermal conductivity and poor thermal-cycling stability of PCMs limit their application. In this study, we constructed three-dimensional (3D) hybrid graphene aerogels (GBA) based on synergistic assembly and cross-linking between GO and modified hexagonal boron nitride (h-BN). Highly thermally conductive GBA was utilized as the supporting optimal matrix for encapsulating OD, and further implied that composite matrix n-octadecane (OD)/GBA composite PCMs were further prepared by encapsulating OD within the GBA structure. Due to the highly thermally conductive network of GBA, the latent heat of the composite PCMs improved to 208.3 J/g, with negligible changes after 100 thermal cycles. In addition, the thermal conductivity of the composite PCMs was significantly enhanced to 1.444 W/(m·k), increasing by 738% compared to OD. These results sufficiently confirmed that the novel GBA with a well-defined porous structure served as PCMs with excellent comprehensive performance offer great potential for thermal energy storage applications.

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption.

Graphene-based aerogels have garnered considerable attention for their lightweight and efficient microwave absorption (MA) properties; however, optimizing the relationship between impedance matching and attenuation capability at low frequencies remains a challenge. In this study, a three-dimensional (3D) silicon carbonitride (SiCN) nanoceramic-coated graphene aerogel with conformal heterogeneous interfaces is constructed by precursor infiltration and pyrolysis to optimize MA performance at low frequencies. Thanks to the enhanced impedance matching and significant interfacial polarization of the two-dimensional sandwiched SiCN/graphene/SiCN cell walls and multiple scattering occurring within the 3D porous skeleton, the aerogel achieves a minimum reflection loss of -57.9 dB at an ultralow frequency of 4.92 GHz (C-band) and a broad bandwidth of 5.0 GHz at an ultralow thickness of 1.7 mm. The strategy developed here provides a method for enhancing dielectric polarization loss in graphene aerogels by the joint optimization of interfacial polarization and impedance matching, inspiring the design of high-performance graphene-based materials for low-frequency MA.