Synthesis of MWNTs/g-C3N4 composite photocatalysts with efficient visible light photocatalytic hydrogen evolution activity

Novel multi-walled carbon nanotubes (MWNTs) and graphitic carbon nitride (g-C3N4) composite photocatalysts were synthesized via a facile heating method. The resulting MWNTs/g-C3N4 composite photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The photoelectrochemical I–t curves were tested using several on–off cycles of visible light irradiation. The visible light photocatalytic hydrogen evolution was investigated for MWNTs/g-C3N4 in methanol aqueous solutions. The optimal MWNTs content is determined to be 2.0 wt%; and corresponding H2 evolution rate is 7.58 μmol h−1, about 3.7 folds that of pure g-C3N4. A possible mechanism of MWNTs on the enhancement of visible light performance is proposed. It suggests that MWNTs play key roles, which may lead to efficiently separation of the photo-generated charge carriers and, consequently, enhance the visible light photocatalytic H2 production activity.

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► Novel MWNTs/g-C3N4 composite photocatalysts were prepared for the first time.
► The MWNTs/g-C3N4 shows significantly enhanced H2 evolution activity.
► Photocatalytic mechanism is proposed based on the experimental results.
► The mechanism is confirmed by PL spectra and transient photocurrent curves.