Adsorption, kinetics and thermodynamics of phenol removal by ultrasound-assisted sulfuric acid-treated pea (Pisum sativum) shells

Abstract

In the present study, waste pea shells were used to synthesize an efficient adsorbent (ultrasound-assisted sulphuric acid-treated pea shells, USAPS) and was applied for phenol removal. The USAPS characterization was done by SEM-EDS, FT-IR, XRD, optical profilometry, BET, and PZC techniques. The use of ultrasound during the chemical activation significantly enhanced the adsorption properties. The adsorption of phenol was probed by varying pH (2–9), temperature (25–45°C), the USAPS dose (0.1–0.6 g/100ml), phenol concentration (50–500 mg/L), and inorganic salt addition (0.1 M KCl and 0.1 M CaCl2). The maximum phenol uptake was found to be 125.77 mg/g for 500 mg/L of phenol concentration at pH 7 and 25°C with 0.1 g/100ml of the USAPS dose. Adsorption was negatively affected by an increase in temperature and the USAPS dose while 0.1 M KCl and 0.1 M CaCl2 addition decreased the maximum phenol uptake from 125.77 mg/g to 103.45 mg/g and 84.11 mg/g, respectively. The time-dependent phenol removal was best explained by the pseudo-second-order kinetic model while equilibrium data were best explained by the Langmuir model. The thermodynamic study revealed the physical nature of adsorption with no structural alteration at the adsorbent-adsorbate interface.