Preparation of modified-biochar from Laminaria japonica: Simultaneous optimization of aluminum electrode-based electro-modification and pyrolysis processes and its application for phosphate removal

The preparation conditions of electro-modification (current density) and pyrolysis (pyrolysis temperature and heating rate) processes were simultaneously optimized using response surface methodology with the quadratic regression model associated with Box-Behnken design. By numerical optimization, the phosphate adsorption capacity of 245.06 mg/g was achieved, corresponding to 99.9% of the predicted values under statistically optimized conditions (current density: 38.78 mA/cm², pyrolysis temperature: 584.1 °C, heating rate: 6.91 °C/min). By considering R² and three error functions values, the experimental results of adsorption kinetics, and the equilibrium isotherms at different temperatures (10-30 °C) showed that predictive pseudo-second-order and Sips isotherm models could adequately interpret the phosphate adsorption process for 'statistically optimized electrically modified'-biochar (SOEM-biochar). The maximum phosphate adsorption capacities of SOEM-biochar were found to be 273.9, 345.1, and 460.3 mg/g at 10, 20, and 30 °C, respectively, which are higher than that of other adsorbents reported in the literature.