Nitrogen-Doped Hollow Mesoporous Carbon Spheres Modified g-C3N4/Bi2O3 Direct Dual Semiconductor Photocatalytic System with Enhanced Antibiotics Degradation under Visible Light

Herein, the nitrogen-doped hollow mesoporous carbon spheres (N-HMCs) modified g-C3N4/Bi2O3 direct dual semiconductor photocatalyst (g-C3N4/Bi2O3@N-HMCs) were synthesized by a facile thermal process. The morphology, structure, elements, and photoelectrochemical properties of the as-prepared samples were characterized by electron microscopy, N2 sorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy, diffuse-reflectance spectra, and photoluminescence spectroscopy, among other technologies. The photocatalytic efficiency was evaluated toward degradation of antibiotics tetracycline hydrochloride (TCH) and ciprofloxacin hydrochloride (CFH) under visible-light irradiation, and the results showed that the g-C3N4/Bi2O3@N-HMCs composite exhibited superior photocatalytic efficiency than other comparison samples, which could be attributed to the synergistic action of g-C3N4/Bi2O3 direct dual semiconductor photocatalytic system and the N-HMCs. The characterization techniques revealed that N-HMCs play three vital roles in improving photocatalytic efficiency. First, N-HMCs could serve as a photosensitizer to enhance visible-light absorption. Second, N-HMCs are an excellent conductive material to transfer the photoexcited electrons quickly to hinder the electron–hole pairs recombination. Third, N-HMCs could provide more active sites in the photocatalytic process. The scavenger experiments and electron-spin-resonance results revealed that the active substances h+, •O2–, and •OH performed together in the photodegradation system. Additionally, the g-C3N4/Bi2O3@N-HMCs composite showed favorable photostability after six rounds of recycling, suggesting the great prospects of the practical application of g-C3N4/Bi2O3@N-HMCs.