Mesoporous Sulfonated Hydrochar from Garcinia Mangostana L Peel for Fast and Effective Methylene Blue Dye Removal: Hydrothermal Activation and Adsorption Statistical Optimization

In this work, a feasible conversion of mangosteen peel (MP) waste into mesoporous sulfonated hydrochar (SMP-HC) via hydrothermal assisted sulfuric acid (H2SO4) activation was carried out. The hydrothermal activation process was assisted by 1M H2SO4 for 14 h at 100 0C to produce SMP-HC. The specific surface area (BET SA) analysis shows a mesoporous structure of SMP-HC with remarkable increase of ca. 576 folds (BET SA = 14,4 (m2/g) as compared to the raw MP (0.025 m2/g). Thus, SMP-HC was utilized to be a promising adsorbent for removal of toxic cationic dye namely methylene blue (MB) dye from aqueous environment. Box-Behnken design (BBD) with desirability function was applied to optimize and validate the adsorption working parameters including SMP-HC dosage (coded A:0.02–01 g/0.1L), solution pH (coded B: 4–10), and contact time (coded C:2–8 min). The optimal desirability function conditions for MB dye removal (97.5%) by SMP-HC were found to be SMP-HC dose = 0.07 g/0.1L, solution pH = 9.9, and contact time = 8 min. The maximum adsorption capacity (qm) of SMP-HC for MB dye was found to be 203.5 mg/g at 25 0C. The loading of MB dye onto SMP-HC surface can be attributed to the several possible attractions including electrostatic attraction, π-π interaction, pore filling, and hydrogen bonding. This research shows the possibility of MP waste conversion into functionalized hydrochar with preferable adsorptive performance towards MB dye removal from the contaminated water.