In situ construction of green ZnFe2O4/sub-5nm N, Cu dual-doped SnO2 S-scheme heterostructure with the boosted spatial charge separation towards decontamination of tetracycline: Mechanistic perspectives and aquatic hazard assessment.

The extensive consumption of pharmaceuticals has exacerbated environmental threats to living organisms globally. Herein, designing a green and magnetically separable S-scheme heterostructure with boosted visible light photocatalytic activity is imperative for the disintegration of these contaminants. In this study, ultra-fine (<5 nm) high surface area (118 m2 g-1) SnO2 nanoparticles (NPs) were constructed, exhibiting a remarkably reduced bandgap of 2.9 eV compared to the conventional value of 3.6 eV for SnO2. Concurrently, N and Cu impurities were incorporated into the SnO2 lattice framework (denoted as NCS) to facilitate efficient charge carrier separation and augment visible light absorption capability through the introduction of acceptor and donor energy levels into the band structure. Furthermore, the magnetically separable ZnFe2O4/sub-5nm NCS (denoted as NCSZ) S-scheme heterostructure was constructed via an environmentally friendly and chemical free bio-hydrothermal approach. The incorporation of merely 4 % dopants and 10 % ZnFe2O4 into SnO2 resulted in a superior rate constant of 7.9 min-1, which was 39.5 times higher than that of pristine SnO2. Complete removal of tetracycline (TTC) was attained at a rate constant of 85.8 min-1 within 60 min of visible light illumination. The mechanistic aspects of N and Cu doping, along with the S-scheme charge migration pathway, were scrutinized through trapping experiments and band structure analysis. A new approach was introduced to evaluate the photo-decomposition behavior of TTC across a broad pH range using density functional theory (DFT) calculations. Eventually, the aquatic hazards of both untreated and treated TTC solutions were assessed utilizing hazard quotient (HQ) method.