Performance enhancement and mechanism of tetracycline photodegradation in seawater by TiO2-based catalyst-loaded floating photocatalytic spheres

To achieve the effective removal of low-concentration antibiotic pollutants present in seawater, floating photocatalytic spheres loaded with ytterbium-doped titania-loaded reduced graphene oxide (Yb-doped TiO₂/RGO) as active catalytic components were prepared and tested for the degradation of tetracycline (TC) in simulated seawater. Three solvothermal reduction processes were employed to promote TiO₂ crystallization in the Yb-doped TiO₂/RGO powder catalyst prepared via adsorption-layer nanoreactor synthesis, while simultaneously achieving the surface modification of the GO carrier in the active component. Doping with Yb and reduction reaction during solvothermal treatment converted a small amount of Ti⁴⁺ ions in TiO₂ into Ti³⁺ and introduced a low content of lattice oxygen vacancies, which extended the visible light response region of Yb-doped TiO₂/RGO. Under weak visible light excitation, the three Yb-doped TiO₂/RGO samples and their corresponding polyurethane (PU) sponge-filled photocatalytic spheres could effectively degrade TC in simulated seawater, with the highest degradation rates of 92 % (within 5 h) for the powder active component and 81 % (within 15 h) for the photocatalytic floating spheres. Use of ethanol and ethylene glycol as solvents led to the significant reduction in the hydrophilic groups of the Yb-doped TiO₂/RGO powder active component after heat treatment, effectively enhancing their TC adsorption performance in seawater. The eco-friendly PU sponge-filled photocatalytic spheres presented in this study exhibit a promising potential for effective removal of organic pollutants from seawater.