Tailoring the electronic properties of g-C3N4 via D-π-A framework for metal-free photocatalytic CO2 conversion and H2 evolution

Abstract

Tuning the optical and electronic properties of graphitic carbon nitride (g-C3N4) is an effective strategy for improving solar-light utilization and charge carrier dynamics. Herein, sulfur self-doping was employed to systematically modulate the optoelectronic characteristics of g-C3N4 yielding sulfur-doped carbon nitride (SCN) using thiosemicarbazide as a sulfur source. Subsequently, 2,6-diaminopyridine (DAP) was molecularly incorporated into SCN to construct a donor-it-acceptor (D- it- A) type architecture. DAP incorporation induces an asymmetric electronic environment, promotes charge separation, and suppresses charge-carrier recombination, as indicated by photoluminescence analysis. It also enhances the it-conjugation and broadens the optical absorption range, facilitating improved solar harvesting. The optimized 7 mg DAP-doped SCN (7 DSCN) achieved a CH4 production rate of 0.13686 & micro;mol center dot g- 1 center dot h- 1, through photocatalytic CO2 reduction, approximately 5-fold and 1.5-fold higher than bulk g-C3N4 (BCN) and the SCN respectively. Under outdoor solar light, 7 DSCN delivers an H2 evolution rate of 9 μmol⋅g 1⋅h 1 representing 8.4- and 5.5-fold enhancements over BCN and SCN, respectively. Moreover, 7 DSCN exhibits exceptional photostability, producing 80922 μmol⋅g 1 of H2 accumulated across 13 consecutive days under mid-day peak-hour solar-light irradiation for 4 h per day. This study demonstrates molecular engineering as a promising strategy for developing stable carbon nitride photocatalysts for solar-driven CO2 conversion and H2 production.