Recovery of cobalt from spent lithium-ion batteries as the dopant of TiO2 photocatalysts for boosting ciprofloxacin degradation

Recovery of valuable metal of cobalt (Co) from spent lithium-ion batteries is an important way to make sustainable use of Co resource, while the directly obtained Co2+ solution often contains impurities, such as some trace elements and organic reagents, which have limited its high standard application due to the high cost in further purification. The Co2+ doped TiO2 photocatalysts by using pure Co resources have attracted intensive attention for degradation of the residues of antibiotics in waste water, but by comparison, the economical Co2+ solution recovered from spent lithium-ion batteries is suitable to be used as the Co precursor, because the fabrication process of photocatalysts is tolerant and flexible, and the resultant photocatalytic performance is not influenced or even improved. Herein, the Co2+ (8.773 g/L) solution recovered from spent lithium-ion batteries through the treatment procedures of pre-saponification, extraction, and stripping is first used to prepare the Co2+ doped TiO2 (TC) photocatalysts. The doping effect of Co2+ greatly enhances the visible light responsive ability, physical adsorption property, and electron-hole pair separation efficiency of the TC samples. Under 60 min ultraviolet–visible–near-infrared (UV–Vis–NIR) light irradiation, the degradation rates of the antibiotic ciprofloxacin over the optimum TC samples reach 95%, and within 180 min Vis-NIR light irradiation, the degradation rates also exceed 88%, which are much higher than those of pure TiO2 and comparable with that of the Co2+ doped TiO2 sample with pure Co source, because more oxidative holes and superoxide radicals are generated on the TC samples. The excellent photocatalytic performance of the TC samples for the degradation of antibiotics proves that it is feasible to use the Co components from spent lithium-ion batteries as the metal dopants of photocatalysts.