Characterization of potassium hydroxide modified anthracite particles and enhanced removal of 17α-ethinylestradiol and bisphenol A

Abstract

Anthracite is a natural inorganic-organic hybrid environmentally friendly material, which often is used as a filter medium in water treatment. In this study, we processed anthracite particles using potassium hydroxide (KOH) with different concentrations. The anthracites, before and after treatments, were characterized by Brunauer-Emmett-Teller analysis, scanning electron microscopy, Fourier transform infrared spectrometer, X-ray diffraction, X-ray photoelectron spectroscopy, and Boehm titration. The specific surface area and the amount of total alkalinity of anthracite were 23.73 m² g⁻¹ and 0.38 mmol g⁻¹ (increased by 101 and 217%, respectively) for 4 M KOH treatments, but decreased to 10.09 m² g⁻¹ and 0.12 mmol g⁻¹ for 10 M KOH treatments. We selected 4 M KOH-modified anthracite particles to remove 17α-ethinylestradiol (EE2) and bisphenol A (BPA) from water with unmodified anthracite used in control experiments. The pseudo-second-order model fitted well for the whole adsorption process, and intraparticle diffusion was not the unique rate-controlling step. The equilibrium adsorption data fitted well with the Langmuir-Freundlich model, and the adsorption capacities of EE2 and BPA on anthracite particles after 4 M KOH treatments were 0.7914 and 0.4327 mg g⁻¹ (increased by 138 and 97%, respectively), because the active sites markedly increased. The ligand exchange, hydrogen bonds, and π-π electron donor-acceptor interactions were the main adsorption mechanisms. The 4 M KOH-modified anthracite could be promising in large-scale applications, both as filter medium and adsorbent for organic contaminants.