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Room temperature ionic liquids (RTILs) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) is used as the solvent for the first time to prepare multi-walled carbon nanotubes (MWCNTs) supported nanocomposite catalysts of PdxNiy (atomic ratios of Pd to Ni are 1:1, 1:1.5, 1:2, and 1:2.5) nanoparticles (denoted as PdxNiy/MWCNTs) by using a simple pyrolysis process. The PdxNiy/MWCNTs catalysts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that the PdxNiy nanoparticles (NPs) are quite uniformly dispersed on the surface of MWCNTs with an average crystallite size of ∼7.0 nm. The electro-catalytic activity of the PdxNiy/MWCNTs catalysts for ethanol oxidation reaction (EOR) is examined by cyclic voltammetry (CV). It is revealed that the onset potential is ∼80 mV lower and the peak current is about three times higher for ethanol oxidation for MWCNT catalysts with Pd1Ni1.5 compared to those of Pd/MWCNTs. The catalytic mechanisms of the Pd1Ni1.5/MWCNTs towards EOR are also proposed and discussed.

Multi-walled carbon nanotubes (MWCNTs) decorated with PdxCoy (the nominal atomic ratios of Pd to Co were 3:1, 3:1.5, 3:2, 3:3, respectively) nanoparticles (denoted as PdxCoy/MWCNTs ) were fabricated by a simple pyrolysis process, in which room temperature ionic liquids (RTILs) of butyl-3-methylimidazolium hexafluorophosphate (denoted as [BMIM]PF6) was used as the solvent. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were all used to characterize the PdxCoy/MWCNTs catalysts, showing that the PdxCoy particles were dispersed on the surface of the MWCNTs with an average particle size of ~25.0 nm. The electro-catalytic activity of the PdxCoy/MWCNTs catalysts toward ethanol oxidation reaction (EOR) was examined by cyclic voltammetry (CV). It was revealed that the onset potential was ~90 mV lower and the peak current was about four times higher for ethanol oxidation for Pd3Co1.5/MWCNTs compared to those of Pd3Co1/MWCNTs. The possible catalysis mechanisms of the Pd3Co1.5/MWCNTs toward EOR were also discussed.

This article provides an overview of current research activities on the synthesis and applications of magnetic nanocomposites, especially highlights their potential environmental remediations such as heavy metal (Cr, As, Pd, Hg) removal. After a brief introduction of the emergency situation of heavy metal pollution all over the world and current techniques designed to deal with these situations, different synthetic methods to fabricate various types of magnetic nanocomposites will be reviewed. The focus is to reveal the advantages of magnetic nanocomposites as an efficient adsorbent which is able to reduce the heavy metal concentrations well below the EPA requirement. At the same time, the conventional process can be redesigned to be an economic and energetic one without using extra energy to recycle the adsorbent, which is desired for future. This review mainly deals with the heavy metal removal using magnetic nanocomposites, the adsorption behaviors of heavy metal ions on the surface of novel adsorbents are well investigated including the concentration effect of both contaminants and adsorbents, adsorption kinetics, solution pH effect with regards to real application.

A facile thermodecomposition process to synthesize magnetic graphene nanocomposites (MGNCs) is reported. High-resolution transmission electron microscopy and energy filtered elemental mapping revealed a core@double-shell structure of the nanoparticles with crystalline iron as the core, iron oxide as the inner shell and amorphous Si-S-O compound as the outer shell. The MGNCs demonstrate an extremely fast Cr(VI) removal from the wastewater with a high removal efficiency and with an almost complete removal of Cr(VI) within 5 min. The adsorption kinetics follows the pseudo-second-order model and the novel MGNC adsorbent exhibits better Cr(VI) removal efficiency in solutions with low pH. The large saturation magnetization (96.3 emu/g) of the synthesized nanoparticles allows fast separation of the MGNCs from liquid suspension. By using a permanent magnet, the recycling process of both the MGNC adsorbents and the adsorbed Cr(VI) is more energetically and economically sustainable. The significantly reduced treatment time required to remove the Cr(VI) and the applicability in treating the solutions with low pH make MGNCs promising for the efficient removal of heavy metals from the wastewater.

The removal of toxic hexavalent chromium (Cr(VI)) from polluted water by magnetic polyaniline (PANI) polymer nanocomposites (PNCs) was investigated. The PNCs were synthesized using a facile surface initiated polymerization (SIP) method and demonstrated unique capability to remove Cr(VI) from polluted solutions with a wide pH range. Complete Cr(VI) removal from a 20.0 mL neutral solution with an initial Cr(VI) concentration of 1.0–3.0 mg L−1 was observed after a 5 min treatment period with a PNC load of 10 mg. The PNC dose of 0.6 g L−1 was found to be sufficient for complete Cr(VI) removal from 20.0 mL of 9.0 mg L−1 Cr(VI) solution. The saturation magnetization was observed to have no obvious decrease after treatment with Cr(VI) solution, and these PNCs could be easily recovered using a permanent magnet and recycled. The Cr(VI) removal kinetics were determined to follow pseudo-first-order behavior with calculated room temperature pseudo-first-order rate constants of 0.185, 0.095 and 0.156 min−1 for the solutions with pH values of 1.0, 7.0 and 11.0, respectively. The Cr(VI) removal mechanism was investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and energy-filter transmission electron microscopy (EFTEM). The results showed that PANI was partially oxidized after treatment with Cr(VI) solution, with Cr(VI) being reduced to Cr(III). The EFTEM observation indicated that the adsorbed Cr(III) had penetrated into the interior of the PNCs instead of simply adsorbing on the PNC surface. This synthesized material was found to be easily regenerated by 1.0 mol L−1p-toluene sulfonic acid (PTSA) or 1.0 mol L−1 hydrochloric acid (HCl) and efficiently reused for further Cr(VI) 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.

Lithium titanate (Li4Ti5O12) was prepared by a quasi solid-state method using water and ethanol as the solvents, in which Li2CO3 and TiO2 were used as the starting materials. In this work, the calcination temperature, molar ratio of Li to Ti, and sintering time were all well investigated. The obtained samples were thoroughly characterized by XRD and SEM, revealing that the above three factors not only affected the crystal structure, but also the morphologies of the resultant samples. Galvanostatic charge discharge curves were also employed to evaluate the electrochemical performance of the samples. The best electrochemical performance of the samples was observed when the molar ratio of Li to Ti, sintering temperature and time are 6:5, 850 oC and 12 hours, respectively. It was revealed that the smaller particle size and the higher crystallinity of the resultant samples were favorable to enhance the electrochemical performance.