Construction of porous-hydrangea BiOBr/BiOI n-n heterojunction with enhanced photodegradation of tetracycline hydrochloride under visible light

Porous-hydrangea x%BiOBr/BiOI n-n heterojunction with ordered morphology was successfully prepared through a simple solvothermal process using Bi(NO₃)₃·5H₂O, KBr, BiOI, and ethylene glycol as the precursors. The prepared x%BiOBr/BiOI (x = 2, 5, 10, 15 mol ratio) n-n heterojunctions exhibit enhanced photodegradation properties during treatment of tetracycline hydrochloride (TC-HCl) under visible light irradiation. The highest efficiency at optimized x = 5 is 1.3-, 1.7- and 1.3-fold higher than that of the pristine BiOI, BiOBr, and commercial titanium dioxide (P25), respectively. The improved photocatalytic performance was assigned to the optimized charge-separation properties of n-n heterojunction. However, over-loading of BiOBr upon BiOI may restrain the access of light to BiOI, which could limit the light absorption. The active species have been investigated by trapping experiments and it was found that holes (h⁺) and superoxide radicals (∙O₂^-) were mainly responsible for the photodegradation of TC-HCl. Additionally, the structure and activity relationship were systemically investigated, and the formation of n-n heterojunction is discussed accordingly. The photodegradation of TC-HCl is proved to be a complete mineralization process and the reaction mechanism is also proposed.