Simultaneous removal of triclosan and Cd(Ⅱ) by bio-reduced graphene oxide and its mechanism

Abstract

The co-existence of contaminants such as triclosan (TCS) and Cadmium in wastewater is a major public health problem because of their persistence and toxicity. In this study, bio-reduced graphene oxide (B-rGO) synthesized by Lysinibacillus sp. Simultaneously remove TCS and Cd(II), with adsorption capacities of 81.91 and 23.32 mg g−1, for TCS and Cd (Ⅱ), respectively. This was significantly higher than that previously reported for commercially available reduced graphene oxide (C-rGO), which was only 31.94 and 2.01 mg g−1, for TCS and Cd (Ⅱ), respectively. Fourier transform infrared spectroscopy (FTIR) showed that rGO surface-bound extracellular polymeric substances (EPS) played a key role in the observed enhanced contaminant removal, which was verified by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the absorption of both Cd(II) and TCS on B-rGO was confirmed by XPS and high-performance liquid chromatography (HPLC-UV). The adsorption kinetics of both TCS and Cd(II) fitted well to the pseudo-second-order model, while the adsorption isotherms of Cd(II) followed the Langmuir model, and triclosan the Freundlich model. A mechanism of simultaneous removal of TCS was proposed based on π-π interactions and hydrogen bonding, while Cd(II) was removed by a combination of electrostatic and chelation/complexation. Finally, the adsorption of TCS and Cd(II) by B-rGO in real wastewater was shown to be 76.67 and 16.53 mg g−1, respectively, demonstrating that B-rGO has the potential for practical simultaneous removal of TCS and Cd(II) from wastewater.