Enhancement of bifunctional photocatalytic activity of boron-doped g-C3N4/SnO2 heterojunction driven by plasmonic Ag quantum dots

Abstract

Enhancement of photocatalytic charge transfer with reduced electron–hole (e− + h+) recombination toward the targeted chemical reaction is a challenging task. In this study, we utilized boron (B) dopant as impurity levels, and the plasmonic Ag quantum dots (QDs), and g-C3N4/SnO2 heterojunction nanocomposite under visible light (λ = 385–740 nm) as a nanocomposite photocatalytic system for energy and environmental applications. The introduction of B dopant with optimal level (BCN1.0) of 1 wt% resulted in the fast migration of photoexcited electrons from valence band to the conduction band of g-C3N4 and reduced the migration distance of the electrons from valence band to the conduction band and improved surface redox reactions. The heterojunction formed with SnO2 nanorods and nanoparticles enhanced the electron–hole transfer rate across the interface of the heterojunction (BCNS15) with 15 wt% and improved the photocatalytic activity during redox reactions. The introduction of plasmonic Ag QDs (1 wt%) as a co-catalyst improved the H2 generation efficiency (BCNS–Ag1.0). Ultraviolet photoelectron spectroscopy results confirmed that the charge transfer process was initiated via the Z-scheme mechanism. Photoluminescence spectra identified the reduction of electron–hole recombination that was responsible for improved catalytic efficiency in the optimized heterojunction nanocomposite. The synergetic effect of B dopant, the visible light sensitization effect and the co-catalytic effect of the Ag QDs, the formation of a heterojunction of the B-g-C3N4/SnO2/Ag (BCNS–Ag1.0) nanocomposite resulted in 2.5 times higher methyl orange dye degradation efficiency which is 65.6% compared to pristine g-C3N4 (CN) 25.9%. Further, the photocatalysts were tested for photocatalytic H2 generation, the optimized BCNS–Ag1.0 nanocomposite heterojunction showed 3.2 times higher H2 generation activity (10.2 mmol/h/gcat) than pristine CN(3.1 mmol/h/gcat) through Z-scheme mechanism. Finally, the BCNS–Ag1.0 nanocomposite demonstrated excellent stability toward methyl orange degradation as well as H2 generation for at least 4 cycles. Therefore, the BCNS–Ag1.0 nanocomposite is a promising photocatalytic system for scale-up synthesis.