Oxygen vacancies and phosphorus codoped black titania coated carbon nanotube composite photocatalyst with efficient photocatalytic performance for the degradation of acetaminophen under visible light irradiation

In the past two decades, carbon-titania composite photocatalysts had attracted extensive attention for high photocatalytic performance. However, their visible light driven activity was still limited. Therefore, it was urgent to find a way to improve its visible light responsive photocatalytic activity. In the present work, a novel efficient visible light driven photocatalysts, oxygen vacancies and phosphorus (P) codoped titania coated carbon nanotube composites (OVPTCN), were prepared by a facile two step solvothermal and phosphorization method for the first time. The obtained sample exhibited significantly enhanced photocatalytic performance for acetaminophen (ACE) degradation under visible light irradiation. The effects of carbon nanotube (CNT) amount and phosphorization content on the photocatalytic efficiency for ACE degradation were also investigated deeply. Results showed that the optimal sample exhibited a high rate constant of 0.025 min-1 for ACE degradation in contrast to that of pure TiO2 (0.00053 min-1) and titania-carbon nanotube (TCN) composite (0.0036 min-1). The characterization results suggested that phosphorization could produce oxygen vacancies and P dopants in TiO2, thus narrowing the band gap of TiO2, increasing the transfer and separation efficiency of photogenerated charges. Moreover, it was revealed by EIS Nyquist plots that CNT got better conductivity after the solvothermal reaction and phosphorization, which also increased the transfer efficiency of charges. Therefore, the synergistic effect of P doping, oxygen vacancies and better conductivity of CNT resulted in the significantly enhanced visible light responsive photocatalytic performance. The transformation products and degradation pathway were analyzed based on the results of liquid chromatography-mass spectrometry (LC/MS). Our work provided a new way to prepare efficient visible light driven composite photocatalysts for drugs removal.