Z-Scheme g-C3N4-Au-MoO3-x heterojunction for boosted photocatalytic H2O2 production and enhanced selective oxidation of cyclohexane

Abstract

Rational design of Z-Scheme photocatalyst with outstanding charge separation and robust redox capabilities for photocatalytic H₂O₂ generation and cyclohexane oxidation under mild conditions still poses a significant hurdle. In response to this challenge, ternary g-C₃N₄-Au-MoO_3-x composite catalyst was developed though combining in-situ reduced MoO_3-x-Au composite and exfoliated g-C₃N₄ nanosheets using an ultrasonic liquid-phase approach. In addition, variations in the synthesis procedures led to the preparation of g-C₃N₄₋MoO_3-x, g-C₃N₄-Au, and Au-g-C₃N₄₋MoO_3-x composites, aimed at exploring their effectiveness in both H₂O₂ production and catalyzing cyclohexane oxidation. Notably, the g-C₃N₄-Au-MoO_3-x composite exhibited an impressive optical rate of H₂O₂ generation at 723.18 µmol·L⁻¹·h⁻¹, achieving a 11.94-fold enhancement compared to Au-g-C₃N₄₋MoO_3-x. Meanwhile, the conversion rate of cyclohexane reached 11.59 %, with a high selectivity of 97.43 % towards KA oil (cyclohexanol and cyclohexanone), and a KA oil production rate of 1166.86 µmol·L⁻¹·g⁻¹. Through analyzing the photoelectrochemical properties and band energy structures, it has been established that the involvement of an Au mediator was essential and vital for the Z-Scheme electron transfer in g-C₃N₄-Au-MoO_3-x. The incorporation of a Z-scheme heterojunction has resulted in increased light absorption, reduced charge recombination rates, and a substantial elevation in the levels of ·O₂⁻ and ·OH radicals, leading to a significant enhancement in photocatalytic efficiency for both H₂O₂ generation and cyclohexane oxidation. This study opens the door to on-site immediate production of hydrogen peroxide to boost the oxidation efficiency in the photocatalytic cyclohexane oxidation process.