Facile construction of novel Z-scheme MnWO4/Bi2S3 heterojunction with enhanced photocatalytic degradation of antibiotics

A novel Z-scheme MnWO4/Bi2S3 heterojunction was constructed by a hydrothermal method for the first time. The structure, morphology and optical absorption characterization of photocatalysts were comprehensively identified. The photocatalytic performance of catalysts was investigated by the cephalexin (CFX) and metronidazole (MTZ) degradation under LED irradiation. The degradation efficiency of binary composite was promoted compared to pure MnWO4 and Bi2S3. The enhanced performance was assigned to the Z-scheme construction, leading the broad visible-light adsorption spectrum, superior redox potential as well as impressive separation and reduced recombination of photo-induced charge carriers. The effect of catalyst dose, temperature and light intensity on photodegradation activity was studied. The effect of inorganic ions was investigated in order to simulate the actual situation. The optimal values of catalyst dose, temperature and illumination intensity were found to be 1.2 g/L, 25 °C and 400 W/m2, respectively. The maximum degradation efficiencies of 74.5% and 79.8% were achieved for CFX and MTZ, respectively. TOC removal analysis was applied to measure the mineralization of CFX (46%) and MTZ (65.2%). The degradation intermediates were distinguished by using the gas chromatography/mass spectrometry (GC/MS) analysis. The kinetic investigation of photodegradation followed the first order kinetic for both drugs. The novel binary composite depicted high stability after six cycles. The trapping experiments detected the hydroxyl (OH.) and superoxide (O2.) radicals as the main active species. This research revealed a novel Z-scheme photocatalyst as a promising strategy in order to remove antibiotics.