A sulfoxide-functionalized graphitic carbon nitride–cobalt dialkyl phosphate bipyridine heterojunction for photocatalytic hydrogen production

Abstract

Suitable solar-active photocatalysts are presently being sought for green hydrogen generation. Graphitic carbon nitride (gCN) has emerged as one of the best photocatalysts due to its suitable band gap and its economic and scalable production in a facile manner. Unfortunately, it suffers from a serious drawback of fast electron–hole recombination, which significantly affects its performance in photocatalysis. To prevent fast exciton recombination, we herein report the synthesis of nanohybrids of sulfoxide functionalized gCN with different amounts of cobalt organophosphate (CP) 2D grid (SCN–CP-1 (1.3%), SCN–CP-2 (2.6%), SCN–CP-3 (3.6%)) for band gap engineering as well as for possible synergy in photocatalytic HER performance. While HRTEM atomistic imaging revealed crystallographic modulations due to hybridization, UV-Vis and ultraviolet photoelectron spectroscopy hinted at band alignment at the interface. Co–N and Co–P binding and SO functionalization in the nanohybrid were confirmed by XPS and FT-IR spectroscopy, respectively, further revealing interlayer coupling. Among the nanohybrids prepared, SCN–CP-2 (2.6% CP in the SCN matrix) in sulfoxide functionalized gCN was found to be the optimized sample, exhibiting the visible light photocatalytic hydrogen production of 3740 µmol g⁻¹ in 5 hours, which was much better than that of SCN (1668 µmol g⁻¹ in 5 hours) and gCN as well as the other compositions of gCN hybrids with CP. The optimized nanohybrid also exhibited an enhanced photocurrent (∼7 times) with superior current density (13.18 µA cm⁻²), outpacing both gCN and sulfoxide functionalized gCN. The results presented in this study will pave the way for further development of a novel class of nanohybrids for photocatalysis, offering a new platform with improved charge transfer and surface active sites.