One-Pot Synthesis of Magnetic Graphene Nanocomposites Decorated with Core@Double-shell Nanoparticles for Fast Chromium Removal

A waste-free process to recycle Fe@Fe2O3/polypropylene (PP) polymer nanocomposites (PNCs) is introduced to synthesize magnetic carbon nanocomposites (MCNCs) and simultaneously produce useful chemical species which can be utilized as a feedstock in petrochemical industry. The magnetic nanoparticles (NPs) are found to have an effective catalytic activity on the pyrolysis of PP. The PNCs (with a NP loading of 20.0 wt%) undergo a complete degradation with 2 h pyrolysis at 500 °C in a H2/Ar atmosphere and the degradation components exhibit a distribution of species with different numbers of carbon, while only 40% of pure PP is decomposed after applying the same pyrolytic conditions. The coked solid waste from the conventional process has been utilized as a carbon source to form a protective carbon shell surrounding the magnetic NPs. The magnetic carbon nanocomposites (MCNCs) pyrolyzed from PNCs containing 20.0 wt% NPs demonstrate extremely fast Cr(VI) removal from wastewater with the almost complete removal of Cr(VI) within 10 min. The pH effect on the Cr(VI) removal efficiency is investigated with a preferable value of 1–3. The adsorbent exhibits much higher adsorption capacity in acidic solutions than that in alkali solutions. The large saturation magnetization (32.5 emu g−1) of these novel magnetic carbon nanocomposites allows fast recycling of both the adsorbents and the adsorbed Cr(VI) from the liquid suspension in a more energetically and economically sustainable way by simply applying a permanent magnet. The significantly reduced treatment time required to remove the Cr(VI) makes these MCNCs promising for the efficient removal of the heavy metals from wastewater. Kinetic investigation reveals the pseudo-second-order adsorption of Cr(VI) on these novel magnetic carbon nanocomposite adsorbents.

Covalent bonding synthesis of magnetic graphene oxide nanocomposites for Cr(III) removal

Magnetic graphene nanocomposites (MGNCs) with surface-adhered magnetic nanoparticles (NPs) are synthesized by a facile thermal-decomposition method. Two different sized graphenes (Gra-10 and Gra-40) are used. The stacking of a few layers of NPs is revealed by the AFM observation in the nanocomposites, especially with a higher particle loading. The TEM observations show that the average particle size increases from 12.1 to 17.4 nm with increasing particle loading from 2 to 10% on Gra-10 substrate. The NPs exhibit a core@shell structure with an iron core and iron oxide shell, confirmed by high resolution TEM, selected area electron diffraction and X-ray diffraction analysis. The graphene size and particle loading dependent behavior such as dielectric permittivity, electrical conductivity, magnetization and giant magnetoresistance (GMR) are observed. The electrical conductivity has been significantly changed in the different sized graphenes after coating with NPs (conductivity: Gra-10 > NPs/Gra-10; Gra-40 < NPs/Gra-40). The MR is observed to vary from 38 to 64% at 130 K, and even higher MR of about 46–72% is observed at 290 K. More interestingly, the dielectric permittivity can be tuned from negative to positive at high frequency with increasing particle loading. All the results indicate that graphene with smaller size obtains superior properties than the one with larger size.

The ever-increasing disposal of municipal solid waste (MSW) has caused serious environmental problems in the past few decades. Landfilling, incineration, and recycling are currently the major options for MSW treatment. However, landfilling poses environmental risks due to the chemical inertness of plastics and limited available space, a serious drawback of this method. Incineration, not widely used primarily because of the potential generation of toxic gaseous products and ash, only shifts a solid waste issue to an air pollution problem. Recycling plastic waste yields great benefits in terms of environmental concerns and economic feasibility, which include reducing the need for landfilling and incineration, preventing the pollution caused by the manufacturing of products from raw materials, decreasing greenhouse gas emissions, and conserving natural resources such as timber, water, and minerals. Much more effort is still required to recycle plastics due to the very low recycling rate for some types of plastic wastes. For instance, polypropylene accounted for 13.6% of the total plastic waste in the United States in 2000, but only about 0.3% was recycled. Being aware of the current challenges in recycling plastic wastes, how to efficiently recycle polymer nanocomposites (PNCs) becomes even more challenging due to complex components and unpredictable degradation species with the existence of nanofillers. In this chapter, a comprehensive and sustainable waste-free process of PNC recycling will be discussed in which magnetic carbon nanocomposites (MCNCs) decompose and produce useful chemical species that can be utilized as feedstock in the petrochemical industry. Moreover, these MCNCs can serve as novel adsorbents with large adsorption capacity and high removal efficiency to remove heavy metals such as Cr(VI) from wastewater. Large saturation magnetization (32.5 emu/g) of these novel MCNCs allows fast recycling of both the adsorbents and the adsorbed Cr(VI) from liquid suspension in a more energetically and economically sustainable way by simply applying a permanent magnet. The high kinetics of the treatment to remove Cr(VI) makes these MCNCs promising for efficient removal of heavy metals from wastewater. In addition to the aforementioned MCNCs, other multifunctional nanocomposites, including conducting polymers and graphene nanoplatelets, will also be discussed as nanocomposite matrix choices, especially with regard to their application to the remediation of heavy metals and arsenic species from water resources. Kinetics and related mechanisms will be elaborated as well. In summary, the synergistic process and advantages of applying multifunctional nanocomposites to environmental remediation including solid wastes, heavy metals, arsenic, and organic dyes are backed and confirmed by the sound research work published by our team and others in this chapter.

High specific surface area of graphene (GR) has gained special scientific attention in devel- oping magnetic GR nanocomposite aiming to apply for the remediation of diverse environmental problems like point-of-use water purification and simultaneous separation of contaminants applying low external magnetic field (\1.0 T) from ground water. Fabrica- tion of magnetic manganese-incorporated iron(III) oxide (Mnx 2? Fe2-x 3? O4 2- ) (IMBO)-GR nanocom- posite is reported by exfoliating the GR layers. Latest microscopic, spectroscopic, powder X-ray diffraction, BET surface area, and superconducting quantum interference device characterizations showed that the material is a magnetic nanocomposite with high specific surface area (280 m 2 g -1 ) and pore volume (0.3362 cm 3 g -1 ). Use of this composite for the immobilization of carcinogenic As(III) from water at 300 K and pH *7.0 showed that the nanocomposite has higher binding efficiency with As(III) than the IMBO owing to its high specific surface area. The composite showed almost complete ((99.9 %) As(III) removal (B10 l gL -1 ) from water. External magnetic field of 0.3 T efficiently separated the water dispersed composite (0.01 g/10 mL) at room temperature (300 K). Thus, this composite is a promising material which can be used effectively as a potent As(III) immobilizer from the contaminated groundwater ((10 l gL -1 ) to improve drinking water quality.

Magnetic graphene nanocomposites (MGNCs) synthesized by a facile thermal decomposition method have been introduced. TEM observations reveal a uniform distribution of the Fe2O3 nanoparticle size and preferential nuclei growth along the edge defects. Both graphene and its Fe2O3 nanocomposites are prepared as electrochemical electrodes to evaluate their capacitor performances. Under normal conditions (without a magnetic field), the MGNCs show lower capacitance than graphene due to the large particle loading (52.5 wt%), which brings larger internal resistance and thus prevents efficient electron transportation within the electrodes. However, in the presence of an external magnetic field, both graphene and MGNC electrodes exhibit significantly enhanced capacitance as compared to the results obtained under normal conditions. Specifically, the capacitance of graphene is increased by 67.1 and 26.8% at the sweeping rates of 2 and 10 mV s−1, respectively. Even larger enhancements of 154.6 and 98.2% were observed in MGNCs at the same sweeping rates of 2 and 10 mV s−1, respectively. The energy density and power density of the electroactive materials are also dramatically enhanced in the presence of a magnetic field. Equivalent circuit modeling of impedance spectra revealed that the magnetic field played a critical role in restricting the interfacial relaxation process and thus enhanced the electrode capacitance. These findings present a potential revolution of traditional electrochemical capacitors by simply applying an external magnetic field to enhance the capacitance dramatically (even doubling it depending on the electroactive materials) without material replacement and structural modification.

In this work, magnetic graphene nanocomposites were synthesized via hydrothermal reaction and used as an effective adsorbent to extract and concentrate nitrobenzene in water samples, followed by analysis using gas chromatography-mass spectrometry. The properties of the magnetic nanocomposites were characterized by Fourier transform infrared analysis, transmission electron microscopy, and scanning electron microscopy. The nanocomposites have a distinct structure with the magnetite particles scattered over the surface of the graphene. Due to the unique structure, they not only adsorb the target compound strongly, but also have excellent magnetic response that allows fast separation from water. All the experimental parameters affecting the extraction efficiency, including the amounts of sorbents, eluting solvents and volume, adsorption and desorption time were investigated and optimized. Under the optimum conditions, validation experiments showed a good linearity (r 2 = 0.9999) at the range of 5–1,000 μg/L, satisfactory precision (RSD of intra-day = 3.3 % and RSD of inter-day = 3.9 %), high recovery of 77.3 % for 500 μg/L and 82.5 % for 100 μg/L and 84.7 % for 50 μg/L, respectively, and low detection limit of 0.01 μg/L for nitrobenzene in aqueous solutions. Finally, the magnetic graphene nanocomposites were successfully applied to detect nitrobenzene in real-world water samples and showed promising results.

Enhanced removal of Cr(VI) from aqueous solution using polypyrrole/Fe 3O 4 magnetic nanocomposite

A magnetic graphene nanocomposite for efficient removal of methylene blue from wastewater

ABSTRACTA magnetic graphene nanocomposite (Fe3O4-GNC) was prepared and used for the solid phase extraction (SPE) and removal of 2,4-dichlorophenol from aqueous solutions. The physicochemical properties were investigated using SEM, EDX, FTIR, and TGA. Different factors affecting sorption capacity were studied systematically. Results for kinetics studies revealed that 2,4-dichlorophenol sorption followed pseudo-second-order kinetics and the qe value (987.45 mg/g) was in close agreement with experimental value (1000 mg/g). Thermodynamic study showed that the sorption is endothermic (∆Hº = +56.116 kJ/mol) and spontaneous. The desorption studies were carried out for the reusability and extraction of 2,4-dichlorophenol from aqueous samples and 94% recoveries were obtained. The method was found feasible for the removal and preconcentration of trace analysis of 2,4-dichlorophenol in environmental water samples.

In this study, magnetic graphene nanocomposite Fe3O4/rGO was synthesized by facile one-pot solvothermal method. The nanocomposite was successfully used as magnetic solid phase extraction (MSPE) adsorbents for the determination of aflatoxins in edible vegetable oils through the π–π stacking interactions. MSPE parameters including the amount of adsorbents, extraction and desorption time, washing conditions, and the type and volume of desorption solvent were optimized. Under optimal conditions, good linear relationships were achieved. Limits of detection of this method were as low as 0.02 µg/kg and 0.01 µg/kg for aflatoxin B1 and B2, respectively. Finally, the magnetic graphene nanocomposite was successfully applied to aflatoxin analysis in vegetable oils. The results indicated that the recoveries of the B-group aflatoxins ranged from 80.4% to 106.0%, whereas the relative standard deviations (RSDs) were less than 8.1%. Owing to the simplicity, rapidity and efficiency, Fe3O4/rGO magnetic solid phase extraction coupled with high-performance liquid chromatography fluorescence with post-column photochemical derivatization (Fe3O4/rGO MSPE-HPLC-PCD-FLD) is a promising analytical method for routine and accurate determination of aflatoxins in lipid matrices.

In this study, Ni nanoparticle supported by graphene oxide (GO) (Ni-GO) is successfully synthesized through hydrothermal synthesis and calcination, and Cr(VI) is extracted from aqueous solution. The morphology and structure of Ni- GO composites are characterized by scanning electron microscopy (SEM), trans mission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HRTEM) and XRD confirms the high dispersion of Ni nanoparticle after support by GO. Loading Ni on GO can obviously enhance the stability of Ni-GO composites. It can be calculated from TGA that the mass percentage of Ni is about 60.67%. The effects of initial pH and reaction time on Cr(VI) removal ability of Ni-GO are investigated. The results indicate that the removal efficiency of Cr(VI) is greater than that of bared GO. Ni-GO shows fast removal capacity for Cr(VI) (<25 min) with high removal efficiency. Dynamic experiments show that the removal process conforms to the quasi-second order model of adsorption, which indicates that the rate control step of the removal process is chemical adsorption. The removal capacity increases with the increase of temperature, indicating that the reaction of Cr(VI) on Ni-GO composites is endothermic and spontaneous. Combined with tests and characterization, the mechanism of Cr(VI) removal by rapidly adsorption on the surface of Ni-GO and reduction by Ni nanoparticle is investigated. The above results show that Ni-GO can be used as a potential remediation agent for Cr(VI)-contaminated groundwater.

Magnetic cyclodextrin/graphene oxide (MCGO) materials were fabricated through a facile chemical route and their application as excellent adsorbents for methylene blue (MB) was also demonstrated. The results from FTIR, SEM, TEM, VSM and XRD showed that MCGO was prepared. The large saturation magnetization (51.13 emu g−1) of the synthesized nanoparticles allows fast separation of the MCGO from liquid suspension. The MCGO demonstrate extremely fast MB-removal from wastewater with a high removal efficiency within 50 min. The adsorption kinetics, isotherms and thermodynamics were investigated and indicate that the kinetics and equilibrium adsorption are well-described by pseudo-second-order kinetics and the Langmuir isotherm model, respectively. The results showed that, benefiting from the surface properties of graphene oxide, the hydrophobicity of cyclodextrin, and from the magnetic properties of Fe3O4, the adsorbent possesses quite a good and versatile adsorption capacity towards the dye under investigation. Most importantly, the adsorbent can be easily and efficiently regenerated for reuse with hardly any compromise of the adsorption capacity. The inherent advantages of the nano-structured adsorbent, such as high adsorption capacity, easy operation, rapid extraction, and regeneration, may pave a new, efficient and sustainable way towards highly-efficient dye pollutant removal in water and wastewater treatment.

Dumbbell-like Pt/Pd-Fe3O4 nanoparticles (NPs) for the effective and simultaneous removal of Humic Acids and Cr (VI) have been prepared by a one-step synthetic approach. The NPs after a ligand exchange process result suitable to be dispersed in water, electrochemical tests were carried out in a batch electrochemical cell. The NPs show excellent removal efficiency for total Cr. In particular ~ 64% of total Cr was removed in 30 min, while ~ 95 % of total Cr was removed in 9 h. Moreover, the complete removal of Cr (VI) was achieved in 1.5 h. Furthermore, they result able to remove ~ 95% of TOC after 9 h electrolysis, indicating a quite complete mineralization to CO2 of HAs.

Enhanced removal of phosphate and nitrate ions from aqueous media using nanosized lanthanum hydrous doped on magnetic graphene nanocomposite