Adsorption behavior of tannic acid on polyethylenimine-modified montmorillonite with different morphologies

In this work, montmorillonite clay mineral (Mt) was modified with different amounts of polyethyleneimine (PEI) to obtain two new adsorbents that were used to remove tannic acid (TA) from aqueous solutions. Raw Mt and PEI-modified Mt particles, named MtPEI1 (Mt modified with 0.2% w/w PEI solution) and MtPEI4 (Mt modified with 0.8% w/w PEI solution), were characterized by infrared spectroscopy (FTIR), X-ray diffractometry (XRD), thermogravimetric analysis coupled spectroscopy mass (TG/MS), scanning electron microscopy (SEM), surface area analyses (BET), and zeta potential (ZP). Several parameters such as composition and morphology of PEI-modified Mt particles, pH, temperature, kinetic, isotherms and thermodynamic properties were used to investigate the TA adsorption process. The experimental results showed that MtPEI4 possesses higher PEI content and crystallite size than MtPEI1. The maximum adsorption capacity of MtPEI1 and MtPEI4 was found to 426.3 and 790.7 mg g(-1), respectively. Adsorption kinetics showed that the TA adsorption behavior followed the pseudo-second-order model. The adsorption isotherms were better fitted by Sips model. The obtained thermodynamic parameters indicated that the TA adsorption process is spontaneous and entropy-driven.