Preparation of expanded graphite for malachite green dye removal from aqueous solution

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.

Efficient removal of cationic dye using ZIF-8 based sodium alginate composite beads: Performance evaluation in batch and column systems

The environmental and health risks associated with dye contamination in water sources are alarming. Recently, researchers have been focusing on developing an innovative and susceptible solution using composite beads that effectively combat this issue. In this paper, beads were synthesized using a sodium alginate (SA) and zeolitic imidazolate framework-8 (ZIF-8) through a simple dipping process. Several characterization tests were performed including XRD, FTIR, BET, TGA, and SEM-EDX. The SEM images confirmed that SA effectively coated the cubical structure of the ZIF-8, ensuring optimal performance. The efficiency of the resulting SA@ZIF-8 composite beads was tested on both synthetic malachite green dye and real industrial wastewater samples using batch and fixed bed column reactors. The findings revealed that maximum adsorption of 95.5% was achieved at pH 6 in 120 min of reaction time. FTIR and SEM analysis also confirmed the adsorption of MG dye onto the beads. The Freundlich isotherm model (R2 > 0.99) has a better fit than the Langmuir (R2 > 0.96) for describing the adsorption process. The PSO model predicted the kinetics of the system, whereas the intraparticle diffusion study supported the system's mechanistic analysis. Furthermore, the study also investigated the efficacy of the beads in treating real wastewater effluent samples collected from the dye industry. Overall, using sodium alginate-coated ZIF-8 beads was found to have many advantages over powdered ZIF-8, including higher selectivity, stability, reusability, and practicality, making them a promising alternative for adsorption applications. Therefore, these composite beads have the potential for the removal of the dye from wastewater, which could be widely applied in various industries.

Leaching characteristics and solidification strategy of heavy metals in solid waste from natural graphite purification

The tailings and fluorine-containing sludge were produced during the physical and chemical purification of natural crystalline graphite, containing heavy metals in different occurrence forms. To evaluate the threat of different heavy metals to the environment, this work uses the modified sequential extraction method (BCR) to study the presence of heavy metals in two solid wastes and their dissolution characteristics in different environments. The results show that the pollution risk of heavy metals in graphite tailings to the environment is ranked as Mn > Cr > Ni > Zn, and the pollution risk of Mn in fluorine-containing sludge is higher than that of Cr. This is because the Mn in the two solid wastes mainly exists in the form of weak acid extraction. The leaching number of heavy metals in the two solid wastes is directly proportional to the soaking time and soaking temperature, and inversely proportional to the pH value and the solid-to-liquid ratio. The number of heavy metals dissolved in solid waste landfills is significantly higher than that of acid rain and surface water environments. Based on the above results and the distribution of graphite solid waste, solidification agent was suggested to prevent heavy metal dissolution and reduce environmental risks.

Efficient removal of azo dyes by Enterococcus faecalis R1107 and its application in simulated textile effluent treatment

This study aimed to exploit the potential of Enterococcus faecalis R1107 in the bioremediation of azo dyes. The maximal decolorization of Congo Red (CR), Reactive Black 5 (RB5), and Direct Black 38 (DB38) were 90.17%, 96.82%, and 81.95%, respectively, with the bacterial treatment for 48 h. 65.57% of CR and 72.64% of RB5 could be decolorized by E. faecalis R1107 within 48 h when the concentration of azo dyes increased up to 1000 mg/L. FTIR analysis confirmed that E. faecalis R1107 could effectively break down the chemical structures of three azo dyes. E. faecalis R1107 alleviated the phytotoxicity of azo dyes and improved seed germination, which contributed to the increase in the lengths of roots, stems, and leaves of Vigna radiata seedlings. Transcriptomic analysis suggested that the gene regulatory networks in E. faecalis R1107 synergistically improved the degradation and detoxification of RB5, including the major metabolic pathways, the secondary metabolism, the transport system, the amino acid metabolic pathways, and the signal transduction systems. Simulated textile effluent (STE) was used to mimic real textile effluent to evaluate the bioremediation potential of E. faecalis R1107, and 72.79% STE can be decolorized after E. faecalis R1107 treatment for 48 h. In summary, our study demonstrated that E. faecalis R1107 might be well suitable for potential applications in the bioremediation of textile effluent.

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.

A reusable mesoporous adsorbent for efficient treatment of hazardous triphenylmethane dye wastewater: RSM-CCD optimization and rapid microwave-assisted regeneration

In this research, mesoporous calcium aluminate nanostructures (meso-CaAl2O4) were synthesized using a citric acid-assisted sol-gel auto-combustion process as the potential adsorbent to eliminate toxic triphenylmethane dye malachite green (MG) from synthetic/real effluent. The surface morphology of meso-CaAl2O4 was highly porous with nanometric size and non-homogeneous surface. The specific surface area, total pore volume, and BJH pore diameter of meso-CaAl2O4 were 148.5 m2 g-1, 1.39 cm3 g-1, and 19 nm, respectively. The meso-CaAl2O4 also showed a very high heat resistance, due to losing only 7.95% of its weight up to 800 °C, which is mainly related to the moisture loss. The optimal adsorption conditions were obtained based on response surface methods (RSM)-central composite design (CCD) techniques. The Langmuir isotherm model was used for fitting the adsorption measurements, which presented 587.5 mg g-1 as the maximum adsorption capacity of the dye. The data obtained from the adsorption kinetics model were found to correspond to the pseudo-second-order model. Also, the thermodynamic parameters including enthalpy change (ΔH°), entropy change (ΔS°), and Gibbs free energy change (ΔG°) indicated that MG dye adsorption by the meso-CaAl2O4 was feasible, endothermic, and occurred spontaneously. Furthermore, the meso-CaAl2O4 was regenerated by microwave irradiation under 900 W at 6 min, and the MG dye removal efficiency was remained over 90% after the five cycles of microwave regeneration.