Mixed Redox-Couple-Involved Bornite Phase Cu5FeS4 as Efficient and Robust Cocatalysts for Greatly Enhanced Visible-Light Photocatalytic Activities

Design and conception of a competent photocatalyst for water splitting and photodegradation are critical for energy transformation and environmental remediation. Herein, for the first time, we demonstrated that mixed redox-couple-involved bornite phase Cu5FeS4 could act as an efficient and robust cocatalyst for graphitic C3N4 (g-C3N4), which enables the achievement of considerably boosted visible-light photocatalytic activities in both H2 evolution and pollutant degradation reactions. Under visible-light irradiation, the optimized g-C3N4/Cu5FeS4 heterojunction presented a remarkably increased H2 production rate of 27.92 μmol g–1 h–1 (without involving any noble metals) and methyl orange (MO) photodegradation rate of 2.18 min–1 g–1 compared with those of g-C3N4 and Cu5FeS4. To be more specific, these rates are ∼15 and 3 times higher than those of pure g-C3N4 in these two reactions, where the pure Cu5FeS4 did not show any activities. The enhanced photocatalytic performance was identified to be due to the presence of a "mixed redox-couple" of Cu(I)–S–Fe(III), which enhanced charge separation efficiency between g-C3N4 and Cu5FeS4, consequently facilitating the overall reaction kinetics. Overall, our work not only demonstrates the immense potential of using mixed redox-couple-involved bornite phase Cu5FeS4 as the cocatalyst in photocatalysis but also expedites the designing and discovering of novel photocatalytic systems based on the proposed concept of the mixed redox-couple.