Rational construction of direct Z-scheme LaMnO3/g-C3N4 hybrid for improved visible-light photocatalytic tetracycline degradation

Abstract

Semiconductor driven photocatalysis has been demonstrated to be one of the promising and effective approaches to resolve the increasing energy and environmental crises by utilizing solar energy. As a typical metal-free semiconductor photocatalyst, graphitic carbon nitride (g-C3N4) has attracted tremendous attention in the photocatalytic water splitting, CO2 reduction and organic pollutants degradation. Unfortunately, the rapid recombination of photoinduced electron-hole pairs of g-C3N4 severely restrained its photocatalytic performance. To this end, lanthanum manganate (LaMnO3) was used to interact with g-C3N4 to rationally construct a direct Z-scheme LaMnO3/g-C3N4 hybrid as an efficient visible-light-driven photocatalyst for the photocatalytic degradation of tetracycline (TC). As expected, the LaMnO3/g-C3N4 product exhibited significant improvement on the performance of photocatalytic TC degradation in aqueous solution under visible light irradiation (λ > 420 nm). Especially, the optimized LaMnO3(9.8 wt%)/g-C3N4 hybrid with 9.8 wt% LaMnO3 achieved the highest apparent first-order rate constant, which was around 10.6 times larger than that of pristine g-C3N4 and 4.0 times greater than that of single LaMnO3. Such an enhanced photocatalytic activity could be ascribed to the formation of unique Z-scheme LaMnO3/g-C3N4 feature, which not just efficiently promoted the separation of the photoinduced electron-hole pairs, but also maintained the strong reducibility of electrons in the conduction band of g-C3N4 and high oxidizability of holes in the valence band of LaMnO3. Furthermore, a probable degradation mechanism was tentatively proposed based on the results of energy band structures, active species trapping experiments, photoluminescence spectroscopy and photoelectrochemical measurements. This work creates a new opportunity for the rational design and construction of highly efficient and stable g-C3N4-based Z-scheme hybrid photocatalysts for applying in environmental remediation and energy conversion.