Development of mesoporous Bi2WO6/g-C3N4 heterojunctions via soft- and hard-template-assisted procedures for accelerated and reinforced photocatalytic reduction of mercuric cations under vis light irradiation

Abstract

In this study, mesoporous Bi2WO6/g-C3N4 heterojunctions were developed using soft and hard templates [triblock copolymer surfactant (F127) and mesoporous silica (MCM-41), respectively]. The performance of the developed heterojunctions was assessed through the photocatalytic reduction of mercuric cations under Vis light illumination, with HCOOH being adopted to provide sacrificial holes agent. Surface measurements demonstrated that the fabricated specimens acquired large specific surface areas when compared with the neat ingredient. Furthermore, a transmission electron microscopy (TEM) analysis of the developed heterojunctions showed the homogeneous distribution of the spherical Bi2WO6 nanoparticles (NPs) on the surface of g-C3N4 nanosheets. Meanwhile, an accelerated rate (700 μ·mol·g−1·h−1) of photocatalytic mercuric cation reduction with improved efficiency (approximately 100%), compared with those of the pure ingredients [rate of 55 μ·mol·g−1·h−1 and efficiency of 13% for g-C3N4 nanosheets; rate of 95 μ·mol·g−1·h−1 and efficiency of 20% for mesoporous Bi2WO6 NPs], was accomplished via testing of the Bi2WO6/g-C3N4 heterojunction comprising 4 wt% Bi2WO6 after 40 min of illumination. Evidently, the efficiency of the photocatalytic reduction of mercuric cations endorsing the Bi2WO6/g-C3N4 heterojunction comprising 4 wt% Bi2WO6 NPs is 7.7 and 5 times more when compared with those of the neat g-C3N4 nanosheets and mesoporous Bi2WO6 NPs, respectively. The improved performance of the fabricated heterojunctions in the photocatalytic reduction of mercuric cations could be ascribed to i) fast diffusion of the mercuric cations through the mesoporous texture to the active ensembles, ii) greater specific surface area, iii) limited bandgap magnitude, iv) homogenous dispersion of the Bi2WO6 NPs on the surface of the nanosheets, and v) finite particle dimension of the mesoporous Bi2WO6 NPs. The durability and stability of the Bi2WO6/g-C3N4 heterojunctions were confirmed via their recyclability, which was maintained for up to five runs without pronounced activity loss.