Saccharide-derived microporous spherical biochar prepared from hydrothermal carbonization and different pyrolysis temperatures: synthesis, characterization, and application in water treatment

Three saccharides (glucose, sucrose, and xylose) were used as pure precursors for synthesizing spherical biochars (GB, SB, and XB), respectively. The two-stage synthesis process comprised: (1) the hydrothermal carbonization of saccharides to produce spherical hydrochar' and (2) pyrolysis of the hydrochar at different temperatures from 300 degrees C to 1200 degrees C. The results demonstrated that the pyrolysis temperatures insignificantly affected the spherical morphology and surface chemistry of biochar. The biochar' isoelectric point ranged from 2.64 to 3.90 (abundant oxygen-containing functionalities). The Brunauer-Emmett-Teller (BET)-specific surface areas (S-BET) and total pore volumes (V-total) of biochar increased with the increasing pyrolysis temperatures. The highest S-BET and V-total were obtained at a pyrolysis temperature of 900 degrees C for GB (775m(2)/g and 0.392cm(3)/g), 500 degrees C for SB (410m(2)/g and 0.212cm(3)/g), and 600 degrees C for XB (426m(2)/g and 0.225cm(3)/g), respectively. The spherical biochar was a microporous material with approximately 71-98% micropore volume. X-ray diffraction results indicated that the biochar' structure was predominantly amorphous. The spherical biochar possessed the graphite structure when the pyrolysis temperature was higher than 600 degrees C. The adsorption capacity of GB depended strongly on the pyrolysis temperature. The maximum Langmuir adsorption capacities () of 900GB exhibited the following selective order: phenol (2.332mmol/g)>Pb2+ (1.052mmol/g)>Cu2+ (0.825mmol/g)>methylene green 5 (0.426mmol/g)>acid red 1 (0.076mmol/g). This study provides a simple method to prepare spherical biochar - a new and potential adsorbent for adsorbing heavy metals and aromatic contaminants. [GRAPHICS] .