Atomic Fe sites embedded within carbon nanotubes for the efficient photodegradation of multiple tetracyclines

Abstract

We have constructed a series of mesoporous carbon nanotube (CNT) networks loaded with trace atomic Fe sites (denoted as Fe-CNTs) by calcining a melamine–cyanuric acid complex and glucose absorbed with Fe3+ (denoted as MCA/G–Fe3+) at different high temperatures (800 °C, 900 °C, and 1000 °C) under N2 atmosphere. The series of Fe-CNT hybrids were then utilized as efficient catalysts for the photodegradation of different types of tetracyclines (TCs), including tetracycline hydrochloride (TCH), chlortetracycline (CTC), and oxytetracycline (OTC), under visible-light irradiation. The mesoporous multiple-layered structure of CNTs not only efficiently inhibited the aggregation of active Fe species but also afforded the hybrids with fast electron transfer and charge separation abilities. Among the three catalysts obtained, Fe-CNT-900, which was synthesized by annealing the MCA/G–Fe3+ complex at 900 °C, demonstrated multifunctionality and intertwined carbon rings. As compared with other catalysts, Fe-CNT-900 showed higher porosity, larger specific surface area, and superior magnetic performance. Thereby, Fe-CNT-900 exhibited significantly improved photocatalytic efficiency toward TCH, CTC, and OTC, showing high photodegradation rates of 93.2%, 99.4% and 94.3%, respectively, under optimal conditions. Trapping experiments and electron spin resonance analysis confirmed that superoxide (•O2−) and hydroxyl (•OH) radicals played essentials roles during photocatalysis. Moreover, the degradation mechanisms and pathways of diverse antibiotics were proposed, while the toxicities of the degradation products of TCs were assessed via the growth of Escherichia coli. The present work provides novel insights into the design of highly efficient Fe-N-C-based photocatalysts for the treatment of harmful pharmaceutical pollutants.