Real "zero energy consumption" for efficient antibiotics degradation by floating photocatalysis: modeling, degradation pathway and toxicity assessment.

Floating photocatalysis is a real "zero energy consumption" and practicable green water treatment technology because of no need for reactor and pump, and direct contact with sunlight to produce more free radicals compared to traditional immersion photocatalysts. To realize "green" and "safe" practical application, efficiency for different water quality bodies and toxicity assessment of degradation products are key factors. In this work, an economic and efficient floating photocatalyst Bi doped P25-TiO2 (Bi@P25)/expanded perlite (EP), named BTEP was successfully constructed, exhibiting stronger visible light absorption and faster photogenerated carriers separation ability due to Bi doping and formation of Bi-O-Si bond. Ciprofloxacin (CIP) degradation efficiency (10 mg/L) in deionized water and three types of ambient water reached 97.8 % and 52.9 %-75.2 %, respectively, based on the major active species (h+ and •O2-). Three degradation pathways were determined and the reduced toxicity of most intermediates proved the process is green and safe. BTEP had strong adaptability over a wide pH range (3-9). The degradation efficiency is promoted by higher temperatures, while depressed by humic acid (HA) (still maintain over 65.3 % at 15 mg/L of HA). Moreover, the Random Forest model is the most suitable to achieve degradation efficiency prediction of different water parameters duo to the lowest root mean square error (RMSE) value (9.52) and the highest R2 value (0.9045). The BTEP based floating photocatalysis promotes the practical application of solar photocatalytic technology and realizes zero energy consumption to remove pollutants.