Fabrication of Bi1.81MnNbO6.72/sulfite system for efficient degradation of chlortetracycline

Abstract

The design of eco-friendly Bi1.81MnNbO6.72/sulfite system for efficient degradation of chlortetracycline was achieved. The feasibility of synthesizing Bi1.81MnNbO6.72 by hydrothermal method was determined by X-ray diffraction. The magnetic test suggested that Bi1.81MnNbO6.72 possessed paramagnetic properties, indicating unpaired electrons were present. Scanning electron microscope and transmission electron microscopy images revealed that Bi1.81MnNbO6.72 octahedra exhibited exposed [1,1,1] crystal plane containing high density of Bi, Mn and Nb metal atoms. Large numbers of metal atoms will facilitate heterogeneous catalytic process. In a batch system with aeration, Bi1.81MnNbO6.72 could be used as sulfite activator for the disposal of chlortetracycline. The reaction kinetics of the degradation process conformed to the pseudo-second-order kinetic model. In Bi1.81MnNbO6.72/sulfite process, initial pH, Bi1.81MnNbO6.72 dosage, sulfite and chlortetracycline concentrations, as well as inorganic salt ions had great effect on chlortetracycline degradation. Under optimal conditions, the efficiency of Bi1.81MnNbO6.72/sulfite system for degradation of chlortetracycline could reach 76.2%. Moreover, Mn (II) plays a key role in the initiation of the catalytic reaction in Bi1.81MnNbO6.72/sulfite process. Generated SO3●‒ could act as main reactive species in Bi1.81MnNbO6.72/sulfite process, while HO● was also involved. Three new degradation products were detected by UHPLC/MS/MS and the possible degradation pathways in this system were proposed. Based on this, we believe that Bi1.81MnNbO6.72/sulfite is a type of process for degradation of organic contaminants with research significance and application prospects.