Kinetic adsorption of humic acid by nitrogen-doped food waste hydrogel biochar

Abstract

Food waste, owing to its high organic content and moisture, offers a more scientifically sound resource utilization method compared to traditional treatment processes. This study presents a method to convert food waste into nitrogen-doped, modified hydrogel biochar modified food waste hydrogel biochar and investigates its effectiveness in adsorbing humic acid (HA). The modified biochar demonstrates superior adsorption capacity for HA compared to unmodified biochar. The adsorption follows the Langmuir isotherm model (R² = 0.999), achieving a maximum adsorption capacity of 49.5 mg/g with R_L = 0.001 3-0.005 1 (0 < R_L < 1). Furthermore, the adsorption process conforms to a pseudo-first-order model. The mechanism underlying HA adsorption involves the successful modification of food waste hydrogel biochar by 3-Aminopropyltriethoxysilane (APTES). This modification forms Si—R—$\mathrm{NH}_{3}^{+}$ on the biochar surface, which interacts with the COOH— groups in HA through hydrogen bonding and coordination bonds. Some unmodified APTES directly adsorbs onto the biochar surface, undergoing condensation and self-assembly to form ladder-like oligomeric siloxane polymers that enhance HA adsorption.

Keywords

food waste / modified biochar / humic acid / adsorption mechanism

Funding

National Natural Science Foundation of China(52470216)

Natural Science Foundation of Jiangsu Province(BK20211175)