Peanut shells-derived biochars prepared from different carbonization processes: Comparison of characterization and mechanism of naproxen adsorption in water.

The ubiquitous appearance of nonsteroidal anti-inflammatory drugs (i.e., naproxen) in water bodies has raised enormous concerns among general public. Development of promising materials for eliminating such contaminants from water environment has attracted much attention in the scientific community. In this study, three (direct, post-treated and pre-treated) methods were developed to prepare biochars (800-PSB, 800-800-PSB, and 190-800-PSB, respectively) derived from the wastes of peanut shells (PS). They were thoroughly characterized by various important properties (i.e., porosity and superficial functional group) and applied to remove naproxen drug from water. Results indicated that although the pre- and post-treatments had a slight effect on the surface area of biochars (i.e., 571 m/g for 800-PSB, 596 m/g for 800-800-PSB, and 496 m/g for 190-800-PSB), such treatments remarkably improved the adsorption capacity of biochar. The maximum adsorption capacity of biochar (obtained from the Langmuir model) towards naproxen in solution at 25 decreased in the following order: 800-800-PSB (324 mg/g) > 190-800-PSB (215 mg/g) > 800-PSB (105 mg/g). The thermodynamic study demonstrated that the adsorption was spontaneous and exothermic. Depending the preparation process, the contribution of each mechanism in the adsorption process was dissimilar. The overall adsorption mechanism was regarded as pore filling, π-π interaction, hydrogen bonding formations, n-π interaction, van der Waals force, and electrostatic attraction. Two methods used to identify the important role of π-π interaction were proposed herein. The possible desorption and reuse of laden-biochars were investigated by the chemical and thermal methods. The prepared biochar samples can serve as potential carbonaceous porous adsorbents for effectively removing naproxen from water media.