Phenol removal from aqueous solutions using rice stalk-derived activated carbon: Equilibrium, kinetics, and thermodynamics study

The conventional disposal practices of rice stalks (RS) such as burning in situ or incorporating in the soil, contribute to climate change and endanger the long-term soil fertility. This study investigated the production of activated carbon (AC) using rice stalks as a sustainable recycling solution. The rice stalks (RS) were carbonized in a tube furnace at 500 °C and heating rate of 10 °C/min for 2 h. The rice stalks-based activated carbon (RSA) properties were analyzed based on Brunauer-Emmett-Teller (BET) technique to measure the surface area and transform infrared spectroscopy (FTIR) measurements to identify the surface functional groups. RSA was also characterized using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-Ray spectroscopy (SEM-EDX). Batch experiments were conducted to examine the efficiency of RSA in removing phenol, with varying operation parameters comprising pH (2–9), initial phenol concentration (IPC) (50–200 mg/L), reaction time (5–300 min), and RSA dose (0.2–2 g/100 ml). The surface area (SBET) of RSA was 488.26 m2/g with a total micropore volume of 0.165 cm³/g, and a pore diameter of 6.99 nm. The highest phenol uptake of RSA was 80.37 mg/g. The kinetics of phenol adsorption was found to be accurately described by the pseudo-second-order reaction, while the Langmuir model provided a better match for the isotherm process than the Freundlich model. The thermodynamic study indicated that the adsorption process was exothermic and spontaneous. These results confirm that the adsorption process occurred due to physical forces, rather than involving chemical bonding, providing further insight into the underlying mechanisms.