Utilization of prepared activated biochar from water lily (Nymphaea lotus) stem for adsorption of malachite green dye from aqueous solution

Activated biochar was prepared from water lily through combination of physical and chemical technique. The prepared adsorbent was characterized by thermogravimetric analysis (TGA), elemental analysis (CHN/O), Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Brunauer-Emmett-Teller model (BET). Batch technique was used for adsorption of 99.25% of MG dye onto prepared adsorbent with 102.35 mg/g maximum monolayer adsorption capacity ( Q max ) at optimum conditions of initial dye concentration (100 mg/L), adsorbent dose (0.1 g/100 mL), contact time (30 min), temperature (301 K), and stirring speed (200 rpm). Kinetic and equilibrium models were best fit with pseudo-first order kinetic and Langmuir isotherm, respectively. Thermodynamic parameters showed∆ H o , ∆ S o , and ∆ G o to be 1.154 kJ/mol, 3.139 kJ/mol K, and −943.685 kJ/mol, respectively. Positive value of ∆ H o and large value of ∆ S o indicated that adsorption process was endothermic and that there was high collision rate at adsorbent–dye interface. The negative value of ∆ G o confirmed that adsorption process was spontaneous and feasible. Comparison of water lily stem-derived activated biochar (WLSAB) Q max with those reported for other plant-derived activated carbons affirmed WLSAB as a better potential alternative adsorbent for treatment of dye-contaminated wastewater.