Porosity enhancement of spherical activated carbon: Influence and optimization of hydrothermal synthesis conditions using response surface methodology

Abstract In this work, spherical activated carbons (SACs) were synthesized from spherical carbons (SCs) obtained by hydrothermal carbonization treatment of sucrose and subsequent CO2 activation. The effects of SC synthesis conditions (temperature, time and sucrose concentration) on the BET surface area (SBET) values of obtained SACs were investigated and optimized by response surface methodology (RSM) based on central composite rotatable (CCR) design. The optimum conditions were found to be: temperature of 194 °C, hydrothermal carbonization time of 1197 min and 0.85 mol L−1 sucrose concentration. The optimization performed by CCR in conjunction with RSM allowed obtaining SAC with high surface area by performing only one experiment, saving time, energy and precursor. We have demonstrated that it is not necessary to perform the hydrothermal carbonization above 24 h, often adopted in similar studies, since the temperature and sucrose concentration have greater influence in the SAC area. The characterization of spherical activated carbon obtained in the optimized conditions (SACop) was carried out by scanning electron microscopy, N2 physisorption, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The SACop showed spheres with an average diameter of 3.0 μm, SBET of 1012 m2 g−1, hydrophilic surface, amorphous structure and good thermal stability.