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In this study, we synthesized hybrid systems based on manganese oxide@zinc oxide (Mn 3 O 4 @ZnO), using sol gel and hydrothermal methods. The hybrid materials exhibited hierarchical morphologies and structures characterized by the hexagonal phase of ZnO and the tetragonal phase of Mn 3 O 4 . The hybrid materials were tested for degradation of methylene blue (MB), methyl orange (MO), and malachite green (MG) under ultraviolet (UV) light illumination. The aim of this work was to observe the effect of various amounts of Mn 3 O 4 in enhancing the photocatalytic properties of ZnO-based hybrid structures towards the degradation of MB, MO and MG. The ZnO photocatalyst showed better performance with an increasing amount of Mn 3 O 4 , and the degradation efficiency for the hybrid material containing the maximum amount of Mn 3 O 4 was found to be 94.59%, 89.99%, and 97.40% for MB, MO and MG, respectively. The improvement in the performance of hybrid materials can be attributed to the high charge separation rate of electron-hole pairs, the co-catalytic role, the large number of catalytic sites, and the synergy for the production of high quantities of oxidizing radicals. The performance obtained from the various Mn 3 O 4 @ZnO hybrid materials suggest that Mn 3 O 4 can be considered an effective co-catalyst for a wide range of photocatalytic materials such as titanium dioxide, tin oxide, and carbon-based materials, in developing practical hybrid photocatalysts for the degradation of dyes and for wastewater treatment.

Activation is commonly used to improve the surface and porosity of different kinds of carbon nanomaterials: activated carbon, carbon nanotubes, graphene, and carbon black. In this study, both physical and chemical activations are applied to graphene oxide by using CO 2 and KOH-based approaches, respectively. The structural and the chemical properties of the prepared activated graphene are deeply characterized by means of scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and nitrogen adsorption. Temperature activation is shown to be a key parameter leading to enhanced CO 2 adsorption capacity of the graphene oxide-based materials. The specific surface area is increased from 219.3 m 2 g -1 for starting graphene oxide to 762.5 and 1060.5 m 2 g -1 after physical and chemical activation, respectively. The performance of CO 2 adsorption is gradually enhanced with the activation temperature for both approaches: for the best performances of a factor of 6.5 and 9 for physical and chemical activation, respectively. The measured CO 2 capacities are of 27.2 mg g -1 and 38.9 mg g -1 for the physically and chemically activated graphene, respectively, at 25 °C and 1 bar.

High-quality graphene is an especially promising carbon nanomaterial for developing nanofluids for enhancing heat transfer in fluid circulation systems. We report a complete study on few layer graphene (FLG) based nanofluids, including FLG synthesis, FLG-based nanofluid preparation, and their thermal conductivity. The FLG sample is synthesized by an original mechanical exfoliation method. The morphological and structural characterization are investigated by both scanning and transmission electron microscopy and Raman spectroscopy. The chosen two-step method involves the use of thee nonionic surfactants (Triton X-100, Pluronic ® P123, and Gum Arabic), a commercial mixture of water and propylene glycol and a mass content in FLG from 0.05 to 0.5%. The thermal conductivity measurements of the three FLG-based nanofluid series are carried out in the temperature range 283.15-323.15 K by the transient hot-wire method. From a modeling analysis of the nanofluid thermal conductivity behavior, it is finally shown that synergetic effects of FLG nanosheet size and thermal resistance at the FLG interface both have significant impact on the evidenced thermal conductivity enhancement., Competing Interests: The authors declare no conflict of interest.