Realization of thorough photodegradation of the A-ring of tetracycline over urail-doped g-C3N4/Bi2WO6/chitosan using the synergistic effect of nonmetal dopants, the Z-scheme heterojunction and chitosan modification

Abstract

It is well known that the toxicity of the widely used tetracycline (TC) mainly originates from the intermediates of its A-ring, which are difficult to thoroughly degrade. Therefore, it is critical to exploit an efficient method for fast and thorough degradation of the A-ring of TC. Herein, an urail-doped g-C3N4/Bi2WO6/chitosan (10UB-CS) composite was fabricated for the abovementioned purpose. Over 10UB-CS, A-ring and B, C, D- rings could be thoroughly decomposed into small molecules without toxicity after 100-min photodegradation for the first time owing to the following synergistic effects: (1) the substitution of diazine organic groups of uracil by partial tris-triazine units in g-C3N4 leads to a new channel beneficial to the transfer of photogenerated carriers and leads to a negative shift in ECB, resulting in the production of more •O2–. (2) The formed Z-scheme urail-doped g-C3N4/Bi2WO6 not only improves the separation of photoactivated electrons and holes but also causes a high redox potential. (3) Chitosan possesses superior surface-electron mobility so that the photoactivated electrons can easily migrate to the surface of the as-prepared composite particles, preventing the recombination of photoactivated electrons and hole pairs. Hence, more high-energy electrons react with O2 to produce more •O2–. This work has identified the roles of •O2– and h+ in photodegrading the A-ring of TC by comparing the active-species-trapping-experiments results for the first time. This work also finds for the first time that the fracture of A-ring in TC by h+ could realize through breaking the bonds which bridges B-ring and A-ring. This work is of great significance for rapidly and completely (100%) photodegrading the A ring of TC. This work has laid a solid foundation to effectively address the toxic issues of TC.