Amine-Functionalized Crystalline Carbon Nanodots Decorated on Bi<sub>2</sub>WO<sub>6</sub> Nanoplates as Solar Photocatalysts for Efficient Degradation of Tetracycline and Ciprofloxacin
Krishanan Bisht, Gandharve Kumar, Raj Kumar Dutta
Abstract
A bismuth tungstate (Bi2WO6) nanoplate surface decorated with amine-functionalized crystalline carbon nanodots (ACCN) is developed as a sunlight responsive photocatalyst for degradation of tetracycline and ciprofloxacin antibiotics. The photocatalyst, named ACCN/Bi2WO6, has been thoroughly characterized to elucidate its structural, morphological, textural, and compositional aspects. The crystalline carbon nanodots are synthesized by hydrothermal treatment of ortho-phenylenediamine with a zwitterionic l-alanine, which offered doping of a large number of nitrogen atoms. Because of these features, compared to pristine Bi2WO6, the optimized batch of the photocatalyst prepared with 2 wt % ACCN (named 2-ACCN/Bi2WO6) exhibited significantly enhanced degradation of tetracycline (96%) and ciprofloxacin (95%) within 75 min of sunlight exposure. The corresponding photocatalytic degradation rates are 0.030 and 0.027 min–1, respectively. The mechanism involved in photocatalytic degradation is addressed in the light of (a) enhanced absorption of sunlight by 2-ACCN/Bi2WO6, (b) favorable Z-scheme-like band positions of Bi2WO6 and the HOMO–LUMO levels of ACCN, (c) large photocurrent density, (d) inhibition of charge carrier recombination and formation of reactive oxygen species (ROS), (e) in situ generation of a superoxide radical anion (O2–•), confirmed by specific ROS scavenging studies, and (f) identification of intermediate products by ultraperformance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry.