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

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-C3N4 (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-C3N4 nanosheets produced anatase/rutile homojunction QDs (7–8 nm)/g-C3N4 heterostructural lamellas, while the subsequent pyrolysis resulted in amorphous carbon layers stacking on g-C3N4. The adsorption occurs on the carbon layers, while the photocatalysis proceeds on the conduction band of g-C3N4 and valence band of anatase, which gave free radicals of ∙O2− 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-C3N4 and TiO2 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 LD50 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.