Anatase/Rutile homojunction quantum dots anchored on g-C3N4 nanosheets for antibiotics degradation in seawater matrice via coupled adsorption-photocatalysis: Mechanism insight and toxicity evaluation

Abstract

• Anatase/rutile homojunction QDs anchored on g-C 3 N 4 is obtained by template method. • A formation process of A-R QDs/g-C 3 N 4 (TCN-150) is performed. • TCN-150 shows coupled adsorption-photocatalysis activity to OTC removal in seawater. • Toxicity of OTC and its photocatalytic intermediates are evaluated. • Adsorption-photocatalysis synergistic mechanism of TCN-150 is proposed. In this work, a facile two-step approach involving a templated solvothermal reaction and post-pyrolysis was developed for fabrication of ternary heterojunctions of anatase/rutile quantum dots (QDs)/g-C 3 N 4 (TCN-150), which shows well coupled adsorption and photocatalytic activity. The encapsulation of hydrolyzed titanium precursors by P123 polymer on the surface of exfoliated g-C 3 N 4 nanosheets produced anatase/rutile homojunction QDs (7–8 nm)/g-C 3 N 4 heterostructural lamellas, while the subsequent pyrolysis resulted in amorphous carbon layers stacking on g-C 3 N 4 . The adsorption occurs on the carbon layers, while the photocatalysis proceeds on the conduction band of g-C 3 N 4 and valence band of anatase, which gave free radicals of ∙O 2 − and ∙OH for antibiotics decomposition, respectively. Formation of mixed anatase/rutile phases and amorphous carbon in the composite promoted the oxytetracycline (OTC) removal in dynamic flow conditions, with efficiencies about 46.8 and 3.8 times than that of g-C 3 N 4 and TiO 2 respectively, owing to facilitated photogenerated charge separation and transfer, as well as the synergy between adsorption and photocatalysis. The toxicity evaluation of detected final intermediates in the proposed OTC degradation pathways showed decreased acute toxicity of LD 50 and reduced mutagenicity, confirming weaken toxicities of intermediate solutions after visible-light irradiation for 120 min, and this demonstrated a huge potential of TCN-150 as an eco-friendly photocatalyst for practical applications.