BACKGROUND The remnants of antibiotics in aquatic environments have emerged as hazardous pollutants. To eliminate these remnants, new methods have been proposed, including photocatalysis. Powdery photocatalysis has been widely studied, yet its several disadvantages such as light-harvesting and recyclability in suspension systems have remained as bottlenecks for practical applications. A recent report on a floating photocatalyst provided an alternative method to solve the above problems. In the present paper, TiO2 nanoparticles were co-doped by copper (Cu) and nitrogen (N), and then immobilized onto substrate diatomite. The composite powder was granulated to produce a self-floating granule catalyst (Cu/N co-doped TiO2/diatomite hybrid granules), denoted as CN-TDHG. The photoactivity of CN-TDHG was investigated via the degradation of antibiotic oxytetracycline (OTC) under visible light. RESULTS The characterization results indicated that Cu/N co-doped TiO2 nanoparticles were successfully dispersed onto the surface of diatomite. Compared to powdery composite, the granule catalyst presented enhanced photodegradation efficiency. Optimal values of both doping amount and granule dosage were determined. The optimal granule catalyst removed 92.5% OTC within 150 min reaction time. Based on the experimental results, the corresponding photodegradation mechanism was proposed. CONCLUSION The self-floating granule catalyst presented enhanced photodegradation capability, thanks to the synergy between Cu- and N-dopants, as well as the adsorption and degradation dual processes between TiO2 and diatomite. Moreover, CN-TDHG could simply be filtered from the surface of the water matrix, and presented good stability and reusability after five repetitions, proving itself as a promising candidate for the remediation of water environment. (c) 2018 Society of Chemical Industry