Abstract:

The g-C₃N₄/PANI composite was prepared by coupling the photocatalytic material graphite carbon nitride（g-C₃N₄） and the conductive polymer polyaniline（PANI） by constructing a heterojunction strategy.The morphology，elemental composition and photoelectrochemical properties of the composites were characterized and evaluated by X-ray diffraction（XRD），Fourier transform infrared spectroscopy（FT-IR），X-ray photoelectron spectroscopy（XPS），scanning electron microscopy（SEM），UV-vis diffuse reflectance spectroscopy（UV-vis DRS），steady-state/transient photoluminescence spectroscopy（PL and TRPL），transient photocurrent spectroscopy（TPC） and electrochemical impedance spectroscopy（EIS）.The results showed that the structure of g-C₃N₄/PANI composites was PANI uniformly covered on the surface of g-C₃N₄，and there was a heterojunction structure between g-C₃N₄ and PANI.After coated by PANI，the specific surface area of g-C₃N₄ was significantly increased from 21.31 to 66.13 m²/g，an increase of about 2.10 times，which effectively improved the photocatalytic performance.By optimizing the amount of PANI，the g-C₃N₄/PANI（3%） composite exhibited the best visible light photocatalytic reduction of CO₂ performance，and the space-time yield of CH₃OH reached 3.12 μmol/（g·h），which was 4.27 times that of pure g-C₃N₄.The construction of heterojunction broadened the spectral response range of g-C₃N₄/PANI（3%） composites in the visible light region，effectively promoted the separation of photogenerated carriers，significantly reduced the AC impedance，and significantly improved the charge transfer rate，thereby significantly improving the photocatalytic reduction of CO₂ performance.Gas chromatography analysis showed that the main product of the reaction was CH₃OH，accompanied by a small amount of CO formation，which confirmed that the g-C₃N₄/PANI（3%） composite had good selectivity as a catalyst.After 5 cycles，the space-time yield of CH₃OH was still higher than 2.97 μmol/（g·h），and the activity was maintained above 95%.Finally，the spuce-time energy band structure was obtained by valence band-X-ray photoelectron spectroscopy（VB-XPS） characterization and Mott-Schottky curve analysis.The visible light photocatalytic reduction of CO₂ by g-C₃N₄/PANI composites followed the Type-Ⅱ mechanism.

Key words: photocatalysis, CO₂ reduction, heterojunction, composite materials, carbon nitride