Removal of 17β-estradiol by using highly adsorptive magnetic biochar nanoparticles from aqueous solution

Through biochar nanoparticles (BCNPs) obtained at pyrolysis temperatures of 400 °C, 600 °C and 800 °C, three types of biomass-derived adsorbent, magnetic BCNPs (Mag-BCNP400, Mag-BCNP600 and Mag-BCNP800) were synthesized. The BCNPs possessed large surface area, nearly 14.5 times higher than that of the biochar microparticles, which contributed to enhanced adsorption capacity. Adsorption characteristics of 17β-estradiol (E2) by Mag-BCNPs were investigated and described by a pseudo-second-order model. The thermodynamic study indicated that adsorption was spontaneous and the adsorption isotherms were well described by Langmuir model with the maximum adsorption capacities of 50.24, 41.71 and 34.06 mg/g for Mag-BCNP400, Mag-BCNP600 and Mag-BCNP800, respectively. Fourier transform infrared analysis suggested that hydrophobic interactions and π-π electron donor-acceptor interactions for E2 sorption to Mag-BCNPs may occur simultaneously, whereas the dominating mechanisms may change from hydrophobic interactions to π-π interactions as pyrolysis temperatures increased from 400 °C to 800 °C. Mag-BCNPs can be easily separated using a magnetic force and regenerated by ozonation. Therefore, with the advantageous features of low cost, ease of separation and good reusability, the Mag-BCNPs can be used as potential adsorbents for removing E2 from water.