One-pot fabrication of a double Z-scheme CeCO3OH/g-C3N4/CeO2 photocatalyst for nitrogen fixation under solar irradiation

Abstract

A CeCO₃OH/g-C₃N₄/CeO₂ ternary photocatalyst (abbreviated as 2Ce-CN) was synthesized by a facile in situ self-sacrificing hydrothermal method, using CeCl₃ and graphitic carbon nitride (g-C₃N₄) as precursors. 2Ce-CN exhibited an enhanced nitrogen photofixation activity of approximately 1.16 mM g⁻¹ h⁻¹ without adding any sacrificial agent, which was four times higher than that of pristine g-C₃N₄. The nitrogen photofixation performance was attributed to a combination of the following reasons. First, the chemical adsorption of nitrogen at Ce³⁺ sites activated the NN bond. Second, photogenerated electrons in the conduction band (CB) of CeO₂ transferred to the valence band (VB) of g-C₃N₄, while electrons in the CB of g-C₃N₄ transferred to the VB of CeCO₃OH, as a result of the intimate-contact chemically-bound interface. This electron transfer is shown to be a double Z-scheme mechanism. The rate of charge carrier recombination was reduced, leaving more electrons in the CB of CeCO₃OH to reduce the adsorbed nitrogen to ammonia. Third, the valence change between Ce⁴⁺ and Ce³⁺ in CeO₂ further promoted the nitrogen hydrogenation reaction. This simple self-sacrificing method provides an alternative perspective for designing functional g-C₃N₄ with excellent photocatalytic activity.