Upcycled PET carbon dots build an S-scheme Fe2O3 heterojunction photocatalyst for visible-light degradation of tetracycline

초록

Polyethylene terephthalate-derived carbon dots (PET-CDs) were interfaced with iron oxide (Fe2O3) to develop a visible-light PET-CDs/Fe2O3 photocatalyst for tetracycline (TC) removal. Waste PET bottles were upcycled via a peroxide-free route, enabling oxidant-free operation. The photocatalyst forms a defect-rich, mesoporous carbon-dot network with uniformly dispersed Fe2O3 nanoparticles, enhancing adsorption and interfacial charge transport. This study demonstrates efficient TC removal at a relatively high initial concentration (C-0 = 100 mg L-1) under visible-light (lambda > 420 nm) without added oxidants. The optimized PET-CDs/Fe2O3 (0.4) reaches 98.2% TC removal. Kinetics follow a pseudo-first-order model, and blank tests confirm negligible photolysis and dark adsorption. The TOC and LC-MS results show rapid degradation followed by slower oxidation. Mineralization is substantial, with TOC decreasing from 100 to 34 mg L-1 at 4 h and reaching 89.6% removal at 10 h. The PET-CDs/Fe2O3 photocatalyst operates across pH 3-11. Phosphate reduces activity by competitive site blocking. At least 80% efficiency is retained over repeated cycles. Convergent evidence supports an S-scheme pathway rather than a type-II junction. DRS-Tauc analysis and band alignment indicate favorable energetic offsets and interfacial band bending. Steady-state PL shows selective quenching of PET-CDs emission with enhanced red Fe2O3 or interfacial emission. Transient photocurrent and EIS Nyquist plots reveal enhanced charge separation and reduced charge-transfer resistance. Scavenger tests and ESR identify h(+) and center dot O-2(-) as dominant species, with center dot OH secondary. LC-MS tracking shows early functional-group loss products at m/z 417 and 402, followed by lower-mass fragments (m/z 301-231 and 189-72), confirming stepwise oxidation toward mineralization.

키워드