Engineering the photocatalytic performance of B-C₃N₄@Bi₂S₃ hybrid heterostructures for full‐spectrum‐driven Cr(VI) reduction and in-situ H₂O₂ generation: Experimental and DFT studies

Graphitic carbon nitride (g-CN) is a promising metal-free catalyst for environmental remediation. However, its practical applications have been limited due to insufficient solar-light responsivity. Hetero-element doping and the construction of heterostructures, comprised of g-CN and other band-matched semiconductors could be considered to overcome these drawbacks. In the present work, a series of 2D/3D heterostructures comprised of a few layers of boron-doped g-CN (B-CN) anchored on sea urchin-like Bi₂S₃ (BS) particles (B-CN@BS) were successfully synthesized. The catalytic performances of B-CN@BS composites were assessed for the photo-reduction of Cr(VI) and in-situ generation of H₂O₂ under simulated solar-light illumination. A binary composite containing 10 wt% of B-CN (B-CN@BS-10) achieved a photo-reduction of Cr(VI) with a rate of 86.77 % during 150 min, which was 3.41- and 2.04-fold higher than those of pure BS and B-CN, respectively. Interestingly, BS particles not only acted as an excellent co-catalyst to broaden the optical window from UV–vis to near-infrared (NIR), but also provided a large active surface area, enhancing migration of charge-carriers between heterointerface, suppressing charge recombination, and thus improving the photocatalytic activities of B-CN@BS composites. Density functional theory calculations were performed to confirm that N atoms were appropriately replaced with boron atoms in the carbon nitride framework. Replacing nitrogen with boron was found to be beneficial in tuning the energy band levels of B-CN. Moreover, B-CN@BS-10 had greater photocatalytic activity for H₂O₂ generation, which was 4.93 and 2.15 times higher than that of bare BS and B-CN, respectively. The charge-carrier transport pathway and possible photocatalytic mechanisms were systematically studied using ultraviolet photoelectron spectroscopy and electron spin resonance analyses. These findings showed heterostructure strategy could be a breakthrough for developing new photocatalysts with both visible- and NIR-light responsiveness to address the current environmental and energy issues.