Mesoporous BiVO4/2D-g-C3N4 heterostructures for superior visible light-driven photocatalytic reduction of Hg(II) ions

Abstract

In this contribution, a Z-scheme mesoporous BiVO4/g-C3N4 nanocomposite heterojunction with a considerable surface area and high crystallinity was synthesized by a simple soft and hard template-assisted approach. This material demonstrates superior visible light-driven photocatalysis for the photoreduction of Hg(II) ions. TEM and XRD results show that the mesoporous BiVO4 NPs, with a monoclinic phase and an ellipsoid-like shape, are highly dispersed onto the porous 2D surfaces of g-C3N4 nanosheets with a particle size of 5–10 nm. The obtained BiVO4/g-C3N4 nanocomposites with a p-n heterojunction show significantly enhanced Hg(II) photoreduction efficiency compared to the mesoporous BiVO4 NPs and pristine g-C3N4. Among all synthesized photocatalysts, the 1.2% BiVO4/g-C3N4 nanocomposite indicated the highest photoreduction of Hg(II) performance, reaching ~ 100% within 60 min; this result is 3.9 and 4.5 –fold larger than that of the BiVO4 NPs and pristine g-C3N4. The Hg(II) photoreduction rates highly increase to 208.90, 314.95, 411.23 and 418.68 μmol g−1min−1 for the mesoporous 0.4, 0.8, 1.2 and 1.6% BiVO4/g-C3N4 nanocomposites, respectively. The reduction rate of the mesoporous 1.2% BiVO4/g-C3N4 nanocomposite demonstrated a 5.2 and 3.8 times larger increase than that of the pristine g-C3N4 nanosheets and pure BiVO4 NPs. The superior Hg(II) photoreduction efficiency was ascribed to decreased carrier recombination and the improved utilization of visible light by constructing BiVO4/g-C3N4 nanocomposites with a p-n junction. Transient photocurrent measurement and photoluminescence spectra were employed to confirm the possible Hg(II) photoreduction mechanism over these BiVO4/g-C3N4 photocatalysts. This research provides an accessible route for the nanoengineered design of mesoporous BiVO4/g-C3N4 heterostructures that demonstrated unique photocatalytic performance.