Performance Enhancement and Mechanism of Tetracycline Photodegradation in Seawater by Tio2-Based Catalyst-Loaded Floating Photocatalytic Spheres

Abstract

To achieve the effective removal of low-concentration antibiotic pollutants in seawater, floating photocatalytic spheres including Yb-doped TiO2 loaded reduced graphene oxide (Yb-doped TiO2–RGO) as active 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. Yb doping and the reduction reaction during the solvothermal treatment converted a small amount of Ti4+ ions in TiO2 to 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. When ethanol and ethylene glycol were used as solvents, the hydrophilic groups of the Yb-doped TiO2–RGO powder active component were significantly reduced after heat treatment, effectively enhancing their TC adsorption performance in seawater. The eco-friendly PU sponge-filled photocatalytic spheres presented in this study have a promising potential for removing organic pollutants from seawater.

Keywords: Photocatalysis in seawater, Visible-light photocatalysis, Degradation pathway, The floating photocatalytic spheres