Green synthesis of Quercus coccifera hydrochar in subcritical water medium and evaluation of its adsorption performance in BR18 dye
Abstract In this study, we investigated the production conditions of hydrochar produced from Quercus coccifera, which is an inexpensive and easy available adsorbent, for the adsorption of Basic Red 18 (BR18) azo dye. Hydrochar was produced in the eco-friendly subcritical water medium (SWM). The effects of the pH (2–10), adsorbent size (45–106 μm), adsorbent dose (0.5–1.5 g/L), dyes concentrations (40–455 mg/L), and contact time (5–120 min) were studied through the optimization experiments. The optimum condition was obtained at pH 10, particle size of 45 μm, particle amount of 1.5 g/L, dyes concentration of 455 mg/L, and 60 minutes. The removal efficiency increased sharply for the first 5 min after that the removal efficiency reached a steady state at the 60 min with maximum removal of 88.7%. The kinetic studies for the adsorption of BR18 dye in aqueous solution using hydrochar showed the second-order kinetics. Langmuir and Freundlich isotherm models were used to explain the relationship between adsorbent and adsorbate and Freundlich isotherm was the most suitable model because of its high regression coefficient (R2) value. The intraparticle diffusion model was used to determine the adsorption mechanism of the BR18 onto Q. coccifera fruit. Desorption studies were also carried out using different type acids and different molarity.