Glucose-based carbon coated MnOx hierarchical architectures with enhanced photostability and photocatalytic activity

• Carbon coated MnOx hierarchical architectures with controllable size and morphologies were prepared.
• Carbon layer displayed multifunction: chemical protection and enhancement of the visible light absorption.
• Carbon coated MnOx products exhibit semiconductors feature with enhanced photocatalytic activities.

Carbon coated MnOx (MnOx@C) with various novel and complex 3D hierarchical architectures self-assembled from different building blocks were successfully synthesized by a hydrothermal method in glucose-mediated processes. The morphology modulation of MnOx@C could be easily realized simply by adjusting the amount of glucose added into the reaction system. The formation mechanisms for different hierarchical architectures were proposed on the basis of time-dependent experiments. An investigation on UV–visible absorption spectroscopy revealed that the as-synthesized MnOx@C expanded the light absorption from UV region to visible light region. Specifically, when 0.45 g of glucose was used, the samples (ε-MnO2-C-0.45 and MnO-C-0.45) obtained from different calcination process exhibited the semiconductor feature with a band gap of 1.9 eV and 1.84 eV, respectively. In addition, the carbon coating on MnOx provided good chemical protection for MnOx and greatly improved its photostability. The laser heating effect for ε-MnO2@C structures were also studied. The ε-MnO2@C structures could be stable at a high laser power of 1200 μW, which suggested significantly enhanced photostability. When used for decolorization of methyl orange under visible light (λ ⩾ 420 nm), the MnOx@C structures exhibited much higher activities than pure MnOx. The decolorization rate for the optimum catalyst ε-MnO2-C-0.45 could reach above 90% within 10 min.

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