The Preparation and Characterization of MnFe2O4-Decorated Expanded Graphite for Removal of Heavy Oils from Water

Removal of organic pollutants in shale gas fracturing flowback and produced water: A review

Shale gas has been developed as an alternative to conventional energy worldwide, resulting in a large amount of shale gas fracturing flowback and produced water (FPW). Previous studies focus on total dissolved solids reduction using membrane desalination. However, there is a lack of efficient and stable techniques to remove organic pollutants, resulting in severe membrane fouling in downstream processes. This review focuses on the concentration and chemical composition of organic matter in shale gas FPW in China, as well as the hazards of organic pollutants. Organic removal techniques, including advanced oxidation processes, coagulation, sorption, microbial degradation, and membrane treatment are systematically reviewed. In particular, the influences of high salt on each technique are highlighted. Finally, different treatment techniques are evaluated in terms of energy consumption, cost, and organic removal efficiency. It is concluded that integrated coagulation-sorption-Fenton-membrane filtration represents a promising treatment process for FPW. This review provides valuable information for the feasible design, practical operation, and optimization of FPW treatment.

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.

Magnetic CuNiFe2O4 nanoparticles loaded on multi-walled carbon nanotubes as a novel catalyst for peroxymonosulfate activation and degradation of reactive black 5

Novel copper-nickel ferrite nanocatalyst loaded on multi-walled carbon nanotube (MWCNTs-CuNiFe₂O₄) was synthesized and applied to activate peroxymonosulfate (PMS) in the degradation of the reactive black 5 (RB5). The structure of the catalyst was well characterized by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The MWCNTs-CuNiFe₂O₄/PMS system showed a high performance in the degradation of RB5 with a kinetic rate of 1.5-2.5 times higher than homogeneous and heterogeneous systems. Maximum degradation efficiency (99.60%) was obtained at an initial pH of 7, catalyst dosage of 250 mg/L, PMS dosage of 4 mM, the temperature of 25 °C, and reaction time of 15 min. Anion experiments emphasized that the presence of nitrate, carbonate, and phosphate in the solution reduced the degradation efficiency by producing reactive species with low oxidation potential. The RB5 degradation rate evolved with temperature, and the activation energy was obtained to be 44.48 kJ/mol. The mechanism of PMS activation and production of free radicals was proposed based on tert-butyl alcohol (TBA), ethanol (EtOH), and potassium iodide (KI) scavengers. Trapping experiments showed that both sulfate (SO₄^•-) and hydroxyl (^•OH) radicals are involved in the catalytic degradation of RB5. The effective treatment of real wastewater and tap water by the MWCNTs-CuNiFe₂O₄/PMS system requires a long reaction time. Gas chromatography-mass spectrometry (GC-MS) analysis indicated that RB5 can be degraded via methylation, decarboxylation, hydroxylation, and ring/chain cleavage pathways. The stable catalytic activity after three consecutive cycles suggested that MWCNTs-CuFe₂O₄ is a novel reusability catalyst in PMS activation.

Expandable Graphite as a Fire Retardant for Cellulosic Materials—A Review

A diversity of chemicals is used to produce fire retardants (FRs); some of the main group of chemicals are hazardous to the environment as well as to human life; however, expandable graphite (EG) can be a gateway to a more environmentally friendly FRs or intumescent fire retardants (IFRs). Researchers define intumescent as the swelling of a particular substance placed between a heat source and an underlying substrate when they are heated. EG is a material with extraordinary thermophysical and mechanical properties. The referred EG properties are unparalleled. EG is a low-density carbon material having a series of unique properties: developed specific surface, binder-free pressing capacity, stability to aggressive media, and low thermal conductivity. Therefore, EG is a promising material both for research work and for industrial applications. The primary goal of this literature review was to report current knowledge on the use of EG as a fire retardant for cellulose and cellulose-modified materials. EG is produced, among other methods, by thermal shock of graphite oxide under forming gas. When exposed to heat, EG will expand. The expansion mechanism was presented in this review. Equally important to this review is the knowledge related to cellulose thermal degradation and cellulose impact on the development of science and technology.

Removal of Reactive Dyes in Textile Effluents by Catalytic Ozonation Pursuing on-Site Effluent Recycling

The textile wash-off process consumes substantial amounts of water, which generates large volumes of wastewater that pose potential pollution issues for the environment. In the present study, catalytic ozonation was applied to degrade residual dyes present in rinsing effluents from wash-off processes towards the aim of recycling the waste effluents. A magnetic catalyst was prepared for promoting dye degradation by catalytic ozonation. Via a hydrothermal reaction, highly magnetic manganese ferrite (MnFe₂O₄) particles were successfully loaded on carbon aerogel (CA) materials (MnFe₂O₄@CA). The results showed that the developed catalyst strikingly promoted the degradation of dye contaminants by catalytic ozonation, in terms of color removal and reduction of chemical oxidation demand (COD) in rinsing effluents. COD removal efficiency in catalytic ozonation was enhanced by 25% when compared with that achieved by ozonation alone under the same treatment conditions. Moreover, we confirmed that after catalytic ozonation, the rinsing effluents could be recycled to replace fresh water without any evident compromise in the color quality of fabrics. The color difference (ΔE_cmc(2:1)) between fabrics treated with recycled effluents and water was not more than 1.0, suggesting that the fabrics treated with recycled effluents displayed acceptable color reproducibility. Although colorfastness and color evenness of fabrics treated with recycled effluents were slightly poorer than those of fabrics treated with water, they were still within the acceptable tolerance. Therefore, the present study validated that catalytic ozonation was a promising technology for saving water and wastewater elimination in textile dyeing. It provides a feasibility assessment of catalytic ozonation for recycling waste effluents to reduce water dependence in textile production. Furthermore, we show a new perspective in on-site recycling waste effluents by catalytic ozonation and enrich the knowledge on feasible approaches for water management in textile production.