Sulfite activation and tetracycline removal by rectangular copper oxide nanosheets with dominantly exposed (0 0 1) reactive facets: Performance, degradation pathway and mechanism

Copper(II) oxide with (0   0   1) facet-exposed nanosheets was prepared via a hydrothermal method. Due to exposure of the (0   0   1) facet, the CuO nanosheets exhibited remarkable catalytic activity towards sulfite activation and tetracycline (TC) degradation across a wide pH range (pH 3.00–9.00), with the degradation rate of TC at pH 4.51–9.00 reaching 87% in the first 5 min. This rapid degradation reaction followed the BMG kinetic model. The Cu II OH groups on the (0   0   1) facet of CuO adsorbed negative SO 3 2− to form a Cu II SO 3 − complex and generate SO 3 − radicals. Sulfite radicals were oxidized by dissolved oxygen to form SO 5 − , and then, SO 5 − transformed to SO 4 − and then HO . Both SO 4 − and HO were the main species involved in TC degradation. The utilization efficiency of sulfite reached almost 100%. After normalization of the degradation rate to the specific surface area, the degradation rate of TC in the current system was 4.84 times that obtained using a CuO nanosphere system. The potential degradation pathways of TC and the catalytic mechanism of the CuO catalyst are proposed.