Expanded graphite applied in the catalytic process as a catalyst support

The potential of thermally expanded graphite in oil sorption applications

An oil spill occurs when liquid petroleum hydrocarbons are released into the environment, whether accidentally or intentionally, in substantial quantities. The impact of an oil spill on the ecosystem is significant and should not be underestimated. Various techniques are employed to address oil spills, including mechanical, physical, biological, and physicochemical methods. Among these techniques, adsorption is considered the most suitable approach. Adsorption is promising due to its simplicity, ease of use, high removal capacity, and rapid pollutant removal. An excellent adsorbent material exhibits unique characteristics that enhance its efficacy in liquid adsorption. Sorbents are categorized into synthetic and natural types. Porous carbon materials, especially expanded graphite, are widely utilized in wastewater treatment due to their micropores and exceptional adsorption capacity. The distinctive properties of expanded graphite, including its low density, high porosity, and electrical conductivity, have garnered significant global attention for various potential applications. In essence, expanded graphite offers a powerful and practical approach to oil spill cleanup due to its efficient oil adsorption, selective targeting, ease of use, and potential reusability. This review article summarizes the preparation techniques, structure, and properties of expanded graphite. It also delves into recent advancements in using expanded graphite for oil spill cleanup. The article concludes by outlining potential future directions in this field and discussing the commercial viability of some of these techniques.

Modification of thermally expanded graphite and its effect on the properties of the amperometric biosensor

The work considered the properties of a biosensor based on a novel nanomaterial-modified thermally expanded graphite (TEGM). The main focus was on whether the procedure of additional graphite thermal expansion would affect the electrochemical properties of biosensors based on membrane fractions of acetic acid bacteria Gluconobacter oxydans. Raman spectroscopy, scanning electron microscopy and electrochemical analysis were used for the study. Raman spectra showed that the formation of TEGM led to its stratification into smaller particles and a better orderly layered structure with high "graphenization" degree. Modification of TEG led to the formation of additional cavities into which bacterial cells or bacterial membrane fractions could be immobilized and affect the electrical conductivity of the biosensors positively. Calculation of the heterogeneous charge transfer constants showed that processes occurring on the electrodes are quasi-reversible. The limiting stage of these processes is the transfer of an electron from a biological component on the electrode surface, not the diffusion of the analyte from the solution to the active centers of the enzyme. We showed the possibility of developing third-generation mediator-free biosensors for glucose detection based on TEGM, as well as of second-generation mediator biosensors for glucose, ethanol and glycerol detection.

Adsorption of Transition Metal Catalysts on Carbon Supports: A Theoretical Perspective : Understanding the interaction between catalyst and catalyst supports

Adsorption is a fundamental process which takes place on a catalyst surface before it dissociates, diffuses over the surface and recombines with other adsorbed species to form the final product. Therefore, in theoretical chemistry understanding of the local geometrical and electronic properties of the adsorbed species on the catalyst surface has been a topic of core focus. In this short review we briefly summarise some of the important developments on theoretical studies related to the adsorption properties of transition metal (TM) catalysts on graphene and graphene-related carbon materials. Prior to this, we will present a discussion on various forms of carbon materials used as catalyst supports, which will be followed by a brief discussion of the fundamentals of the density functional theory (DFT).

Highly Porous Expanded Graphite: Thermal Shock vs. Programmable Heating

Highly porous expanded graphite was synthesized by the programmable heating technique using heating with a constant rate (20 °C/min) from room temperature to 400–700 °C. The samples obtained were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy, thermogravimetry, and differential scanning calorimetry. A comparison between programmable heating and thermal shock as methods of producing expanded graphite showed efficiency of the first one at a temperature 400 °C, and the surface area reached 699 and 184 m²/g, respectively. The proposed technique made it possible to obtain a relatively higher yield of expanded graphite (78–90%) from intercalated graphite. The experiments showed the advantages of programmable heating in terms of its flexibility and the possibility to manage the textural properties, yield, disorder degree, and bulk density of expanded graphite.

Recent trends in the applications of thermally expanded graphite for energy storage and sensors - a review

Carbon nanomaterials such as carbon dots (0D), carbon nanotubes (1D), graphene (2D), and graphite (3D) have been exploited as electrode materials for various applications because of their high active surface area, thermal conductivity, high chemical stability and easy availability. In addition, due to the strong affinity between carbon nanomaterials and various catalysts, they can easily form metal carbides (examples: ionic, covalent, interstitial and intermediate transition metal carbides) and also help in the stable dispersion of catalysts on the surface of carbon nanomaterials. Thermally expanded graphite (TEG) is a vermicular-structured carbon material that can be prepared by heating expandable graphite up to 1150 °C using a muffle or tubular furnace. At high temperatures, the thermal expansion of graphite occurred by the intercalation of ions (examples: SO4 2-, NO3 -, Li+, Na+, K+, etc.) and oxidizing agents (examples: ammonium persulfate, H2O2, potassium nitrate, potassium dichromate, potassium permanganate, etc.) which helped in the exfoliation process. Finally, the obtained TEG, an intumescent form of graphite, has been used in the preparation of composite materials with various conducting polymers (examples: epoxy, poly(styrene-co-acrylonitrile), polyaniline, etc.) and metal chlorides (examples: FeCl3, CuCl2, and ZnCl2) for hydrogen storage, thermal energy storage, fuel cells, batteries, supercapacitors, sensors, etc. The main features of TEG include a highly porous structure, very lightweight with an apparent density (0.002-0.02 g cm-3), high mechanical properties (10 MPa), thermal conductivity (25-470 W m-1 K-1), high electrical conductivity (106-108 S cm-1) and low-cost. The porosity and expansion ratio of graphite layers could be customized by controlling the temperature and selection of intercalation ions according to the demand. Recently, TEG based composites prepared with metal oxides, chlorides and polymers have been demonstrated for their use in energy production, energy storage, and electrochemical (bio-) sensors (examples: urea, organic pollutants, Cd2+, Pb2+, etc.). In this review, we have highlighted and summarized the recent developments in TEG-based composites and their potential applications in energy storage, fuel cells and sensors with hand-picked examples.

Synthesis and Microwave Absorption Properties of Sulfur-Free Expanded Graphite/Fe3O4 Composites

In this study, sulfur-free expanded graphite (EG) was obtained by using flake graphite as the raw material, and EG/Fe₃O₄ composites with excellent microwave absorption properties were prepared by a facile one-pot co-precipitation method. The structure and properties of as-prepared EG/Fe₃O₄ were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectrometry (XPS), thermogravimetric (TG), and vibrating sample magnetometry (VSM) characterizations. The Fe₃O₄ intercalated between the layers of expanded graphite forms a sandwich-like structure which is superparamagnetic and porous. When applied as a microwave absorber, the reflection loss (R_L) of EG/Fe₃O₄ reaches −40.39 dB with a thickness of 3.0 mm (10 wt% loading), and the effective absorption bandwidth (EAB < −10 dB) with R_L exceeding −10 dB is 4.76–17.66 GHz with the absorber thickness of 1.5–4.0 mm. Considering its non-toxicity, easy operation, low cost, suitability for large-scale industrial production, and excellent microwave absorbing performance, EG/Fe₃O₄ is expected to be a promising candidate for industrialized electromagnetic absorbing materials.

Adsorption isotherm, kinetic and mechanism of expanded graphite for sulfadiazine antibiotics removal from aqueous solutions

The adsorption of sulfadiazine from water by expanded graphite (EG), a low cost and environmental-friendly adsorbent, was investigated. Several adsorption parameters (including the initial sulfadiazine concentration, contact time, pH of solution, ionic strength and temperature) were studied. Results of equilibrium experiments indicated that adsorption of sulfadiazine onto EG were better described by the Langmuir and Tempkin models than by the Freundlich model. The maximum adsorption capacity is calculated to be 16.586 mg/g at 298 K. The kinetic data were analyzed by pseudo-first-order, pseudo-second-order and intraparticle models. The results indicated that the adsorption process followed pseudo-second-order kinetics and may be controlled by two steps. Moreover, the pH significantly influenced the adsorption process, with the relatively high adsorption capacity at pH 2-10. The electrostatic and hydrophobic interactions are manifested to be two main mechanisms for sulfadiazine adsorption of EG. Meanwhile, the ionic concentration of Cl^- slightly impacted the removal of sulfadiazine. Results of thermodynamics analysis showed spontaneous and exothermic nature of sulfadiazine adsorption on EG. In addition, regeneration experiments imply that the saturated EG could be reused for sulfadiazine removal by immersing sodium hydroxide.

Cu-Expanded Graphite Composite Material Preparation and Thermal Properties

A composite material based on expanded graphite (EG) and copper compounds was obtained by natural graphite oxidation with 95% nitric acid, copper (II) nitrate and granular carbamide addition with further rapid heat treatment at three different exfoliation temperatures: 800, 1000 and 1200 °С. It was found that the composition of copper containing graphite material depends on the temperature and the atmosphere of thermal expansion. The formation of copper oxides can be eliminated if rapid heat treatment is conducted in nitrogen at 1200 °С. Thermal conductive properties: thermal diffusivity and specific heat capacity of obtained Cu-expanded graphite samples were measured. It was revealed that the dependence of thermal conductivity (TC) of Cu-graphite material has non-linear character in the studied range of copper content. The incorporation of 3% copper into expanded graphite allows to increase its thermal conductivity by 20% while the further Cu content growth leads to the TC decrease from 6 to 4.5 W/(m∙K). The specific heat capacity is constant at ω(Cu)<3% and reduces in the range (3‒8)% Cu. The advantage of proposed technique of Cu-expanded graphite materials preparation is exclusion graphite intercalation compounds hydrolysis step with further drying because of carbamide addition.

Synergetic adsorption and catalytic oxidation performance originating from leafy graphite nanosheet anchored iron(ii) phthalocyanine nanorods for efficient organic dye degradation

Leafy graphite nanosheet anchored iron(ii) phthalocyanine nanorods (FePc@LGNS) were facilely synthesized without using a complex covalent anchoring procedure.

Preparation and Its Adsorptive Property of Modified Expanded Graphite Nanomaterials

Modified expanded graphite (MEG) samples were prepared by strong acid treatment modification. As-prepared MEG samples were characterized by the means of FE-SEM, XRD, FT-IR, N2physical adsorption measurements, and TG-DTA. The influences of expanded volume and oil viscosity on adsorptive property of MEG samples were investigated. The results suggest that MEG samples have high crystallinity. The pores of MEG samples can be divided into three levels from FE-SEM images. All of the functional groups of MEG samples are nonpolar. The expansion temperature of modified expansible graphite starts at about 700°C. The sorption capacity of MEG increases gradually with expanded volume and oil viscosity increase. When the expanded volume of MEG samples is 320 mL/g, its maximum sorption capacity is up to 84.681 g/g for gear oil with the highest viscosity.

Synthesis of 14-aryl-14H-dibenzo[a,j]xanthene Derivatives Catalysed by Expanded Graphite under Solvent-Free Condition

A convenient eco-friendly procedure has been developed for the synthesis of 14-aryl-14 H-dibenzo[ a,j]xanthene derivatives by one-pot condensation of 2-naphthol and aryl aldehydes catalysed by expanded graphite under solvent-free conditions. The present methodology offers several advantages such as excellent yields, shorter reaction times, low cost and reusability of the catalyst.