Simple and low-cost synthesis of g-CN for efficient sunlight photocatalytic degradation of antibiotics in biogas slurry.

Applying biogas slurry containing antibiotics as organic fertilizer to farmland can lead to the accumulation of antibiotics in the soil and access the water environment further through surface runoff and leachate, posing a potential risk to the regional water environment. In this study, photocatalysis was performed to degrade the antibiotics in biogas slurry employing g-CN as a catalyst under visible light and sunlight. g-CN was prepared by simple thermal polymerization at different temperatures and times with cheap urea and melamine, respectively, and the yield, structural characterization, and photocatalytic performance were analyzed. The results showed that the yield of g-CN prepared by melamine (MCN) was 31.5 times higher than that of g-CN prepared by urea (UCN), and decreasing the calcination temperature and time could effectively increase the yield of UCN. The TEM images indicated that UCN possessed a porous nanosheet structure with a specific surface area (74.91 m/g) that was 4.41 times higher than that of MCN (16.99 m/g). The UCN550 showed favorable photocatalytic properties under visible light and sunlight, especially the removal of tetracyclines (TCs) from biogas slurry reached 94.43% after 30 min of photocatalysis under sunlight. The comparative study revealed that UCN550-1 exhibited favorable catalytic performance for antibiotics in real wastewater, and it showed great promise in terms of synthesis, efficiency, cost, and engineering applications. This study can provide a reference for the harmless treatment of biogas slurry and the engineering application of sunlight photocatalytic degradation of antibiotics in real complex water quality systems.