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In this work, two different reduced graphene oxide/iron oxide (rGO-IO) nanocomposites with different iron oxide loadings were fabricated using a one-step solvothermal method. The structure, properties and applications of the synthesized nanocomposites were evaluated with Raman spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, electron microscopy, and energy-dispersive X-ray spectroscopy. The iron oxide is in the form of magnetite (Fe 3 O 4 ), so that the resultant adsorbent can readily be separated from the treated water using a magnetic field. The ability of the nanocomposites to remove methylene blue (MB) from water by adsorption was investigated. The highest adsorptive capacity observed was 39 mg g -1 , for the composite containing 60 wt% iron oxide. The adsorptive capacity of the rGO-IO decreased to 26 mg g -1 when the mass fraction of iron oxide was increased to 75 wt%. Electrochemical regeneration of MB loaded rGO-IO was also investigated. The electrochemical regeneration was found to be rapid and with low electrical energy consumption relative to conventional adsorbents, due to the high electrical conductivity and nonporous surface of the rGO. A regeneration efficiency of 100% was obtained after 30 min of electrochemical treatment using a 2 mm thick bed of rGO-IO loaded with 39 mg g -1  MB, using a current density of 10 mA cm -2 . Multiple adsorption-electrochemical regeneration cycles demonstrated that the surface of the rGO was modified leading to increase in the adsorptive capacity to around 80 mg g -1 after the second regeneration cycle. The morphology of the rGO was observed to change significantly after electrochemical regeneration, suggesting that the rGO based adsorbent materials could only be used for a few cycles., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A nanocomposite of graphene and titanium dioxide (G/TiO 2) was prepared using the sol-gel method for use in an electrochemical adsorption/regeneration process. The effect of annealing temperature on electrochemical characteristics of the nanocomposites was investigated by cyclic voltammetry and constant current electrochemical regeneration, using methylene blue (MB) as the adsorbate. The G/TiO 2 could be regenerated more rapidly and with less corrosion than the bare graphene. The G/TiO 2 annealed at 400 °C had a higher proportion of anatase phase TiO 2 (ca. 7% rutile TiO 2) compared to that annealed at 500 °C (ca. 40% rutile TiO 2). Cyclic voltammetry indicated that the G/TiO 2 annealed at 400 °C had a higher activity for MB oxidation than the nanocomposite annealed at 500 °C. Similarly, the regeneration of MB loaded G/TiO 2 annealed at 400 °C was much faster than for the nanocomposite annealed at 500 °C. Complete regeneration of the G/TiO 2 annealed at 400 °C was obtained after an electrochemical charge of 21 C per mg of adsorbate. The G/TiO 2 annealed at 400 °C was regenerated in half the time required for the bare graphene. TEM studies showed that the bare graphene was rapidly corroded, while corrosion was not observed for the G/TiO 2 nanocomposites. Image 1 • Graphene TiO 2 nanocomposite was an effective adsorbent for methylene blue. • Graphene/anatase TiO 2 adsorbent rapidly regenerated by anodic treatment. • Charge required for regeneration of G/TiO 2 adsorbent was around half that of graphene. • Graphene/TiO 2 nanocomposites were stable over 5 cycles of adsorption and regeneration. [ABSTRACT FROM AUTHOR]