ABSTRACT
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°C to 1200°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 (SBET) and total pore volumes (Vtotal) of biochar increased with the increasing pyrolysis temperatures. The highest SBET and Vtotal were obtained at a pyrolysis temperature of 900°C for GB (775 m2/g and 0.392 cm3/g), 500°C for SB (410 m2/g and 0.212 cm3/g), and 600°C for XB (426 m2/g and 0.225 cm3/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°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 (2.332 mmol/g) > Pb2+ (1.052 mmol/g) > Cu2+ (0.825 mmol/g) > methylene green 5 (0.426 mmol/g) > acid red 1 (0.076 mmol/g). This study provides a simple method to prepare spherical biochar – a new and potential adsorbent for adsorbing heavy metals and aromatic contaminants.
Acknowledgements
The first author would like to thank Chung Yuan Christian University for the Distinguished International Graduate Students (DIGS) scholarship to pursue his doctoral studies.
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCID
Hai Nguyen Tran http://orcid.org/0000-0001-8361-2616
Tien Vinh Nguyen http://orcid.org/0000-0003-3893-1217