1,2,4-Oxadiazolyl phenoxyacetic acid-modified algae-derived biochar for efficient o-nitrophenol removal: adsorption performance and mechanistic insights

Abstract

In this study, a novel efficient adsorbent was engineered by supporting 2-(2-(3-phenyl-1,2,4-oxadiazol-5-yl)phenoxy)acetic acid (POPA) on algae-derived biochar (A-BC). The POPA@A-BC_0.5 composite was inspected using several characterization instruments to determine its chemical structure, surface charge, morphology, structural composition, and crystallographic phase. Furthermore, the adsorption capability of the POPA@A-BC_0.5 composite for o-nitrophenol (o-NP) was evaluated in an equilibrium batch adsorption experiment. The adsorption percentage of o-NP by POPA@A-BC_0.5 was 99.69% at pH 5 and a temperature of 20 °C. In addition, the o-NP adsorption reaction onto POPA@A-BC_0.5 reached equilibrium within 60 minutes. It was deduced from the isotherm analysis that o-NP adsorption onto POPA@A-BC_0.5 occurred via multilayer adsorption interactions, as it was best described by the Freundlich and Langmuir models. In parallel, the kinetic analysis indicated that the chemical interactions between o-NP and POPA@A-BC_0.5 governed the adsorption process because the pseudo-second order model fitted the experimental data. The performed mechanistic investigation suggested the participation of hydrogen bonds, electron donor–acceptor interactions, n → π* interactions, and π–π stacking in the adsorption of o-NP onto the POPA@A-BC_0.5 composite.