Phase-controllable synthesis of maghemite–carbonaceous composites


The deterioration of the environment by human activities, specifically the use of fossil fuels, has recently reached alarming levels. The need for alternative source of energy is now as high as it has ever been. Photocatalytic water splitting to gaseous oxygen and hydrogen provides a renewable green energy source alternative that could reduce over-dependence on fossil fuels and reduce the emission of greenhouse gasses. Unfortunately, the development of low-cost catalysts of a high efficiency remains a bottleneck and the main shortcoming. In pursuit of a suitable catalysts, researchers have discovered that the use of stable, earth-abundant, environmentally-benign and inexpensive features of transition metal oxides make them uniquely attractive. Subsequent studies have helped reveal that some of these transition metals have narrow band gaps and can therefore absorb visible light. Consequently, tremendous efforts have been put in place including the construction of nanocomposites containing those metal oxides as components with graphene being the most successful. However, little has been done regarding the use of the various species of iron oxide/graphene composites in the direct photocatalytic water reduction reaction to produce hydrogen gas.

Recently, a team of researchers from South China University of Technology: Juan Yao, Junying Chen, Kui Shen and Yingwei Li demonstrated that those inherent limitations could be overcome by the incorporation of small amounts of graphene oxide in the metal–organic framework (MOF)-templated synthesis of iron oxide, thereby affording a uniform and highly ordered ferrite octahedral nanostructure embedded on graphene nanosheets. Moreover, they focused on delivering a potential solution for the facile, inexpensive and phase-controllable synthesis of iron oxide–carbonaceous composites, using an iron-metal–organic framework and graphene oxide to tune the constitution of the phase and the photochemical and optical properties under the designed thermolysis conditions. Their work is currently published in the research journal, Journal of Materials Chemistry A.

The research technique employed commenced by conducting powder X-ray diffraction spectral measurements on the purchased materials. Next, the researchers obtained the BET surface areas and pore volumes from the nitrogen gas adsorption/desorption isotherms. Afterwards, they proceeded to perform the photocatalytic water splitting experiments. Lastly, photo-electrochemical measurements were acquired.

The authors mainly observed that the resulting maghemite–carbonaceous composite exhibited a high photocatalytic hydrogen gas evolution rate in the absence of noble metal cocatalysts and external bias. Additionally, they noted that different phases of iron oxide, including maghemite, hematite and magnetite, and their carbonaceous composites could be obtained through the cautiously selected thermolysis of iron-MOF and MOF/graphene composites.

In conclusion, the South China University of Technology study demonstrated that the various phases of iron oxides and their carbonaceous composites could be synthesized by cautiously selecting thermolysis of iron-MOF and MOF/graphene oxide composites. Generally, they observed that their noble procedure had potential to pave a facile way in the finely controlled synthesis of iron oxide species-containing photocatalysts, combining several essential requirements for efficient water splitting using earth abundant and non-toxic elements. Altogether, the high ferromagnetism and thermally stable features could endow the maghemite–carbonaceous composite with great potential in magnetism and biomedicine-related research fields.

Phase-controllable synthesis of maghemite–carbonaceous composites for efficient photocatalytic hydrogen production. - Advance in Engineering


Juan Yao, Junying Chen, Kui Shen and Yingwei Li. Phase-controllable synthesis of MOF-templated maghemite–carbonaceous composites for efficient photocatalytic hydrogen production. Journal of Materials Chemistry A, 2018, volume 6, Page 3571

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