Mo-modified band structure and enhanced photocatalytic properties of tin oxide quantum dots for visible-light driven degradation of antibiotic contaminants

Functional nanomaterials are desirable in the sustainable photocatalytic degradation of antibiotic contaminants, but the development of nanostructured photocatalysts is facing fatal challenges not only in synthesis strategies but also in property control. Herein, a facile synthesis strategy is accomplished by the green synthesis of SnO2 quantum dots (QDs) engineered by Mo modification. The effects of Mo incorporation on the microstructural, compositional, electrical and optical properties are discussed. The electronic band structure of SnO2 QDs is modified by Mo dopants, which reduce the band gap by changing the position of the conduction band edge. The Mo-modified band structure provides the SnO2 QDs with visible-light driven photocatalytic abilities in the removal of antibiotics as emerging organic contaminants. The nanostructured photocatalysts exhibit proficient performances in the degradation of tetracycline hydrochloride. The degradation efficiency is up to 96.5% when the antibiotic concentration is 25 mg/L and the rate constant is 0.033 min(-1). The hydroxyl radicals, produced by the oxidation of water, are determined to be the main active species in the photocatalytic process. The valence band edge over 3 eV guarantees the strong oxidizing abilities of photogenerated holes to create highly active hydroxyl radicals for the efficient photocatalytic degradation. First principle calculations based on the density functional theory reveal the mechanism of Mo modification, illustrating that Mo 4d electrons extend the conduction band edge to the Fermi level. The present work provides a green synthesis strategy and mechanism insights for band structure modification of SnO2 QDs as proficient visible-light driven photocatalysts for environmental remediation.