Highly porous hydrophobic chitin-based carbon foam spheres for gaseous para-xylene removal: Preparation, adsorption mechanisms, and optimization

Reports on shaped porous biochar adsorbents prepared with waste biomass by co-regulation of hydrophobicity, physical structure, and chemical properties to capture air pollutants are limited. This study utilized chitin, the main component of shrimp shell waste, as the raw material to explore the formation mechanism of carbonized porous hydrochars (CPHCs), adsorption performance, and mechanisms of para-xylene (PX) onto CPHCs. The optimal preparation conditions were determined as follows: 1.68 mL of H 2 SO 4 , 0.84 mL of H 3 PO 4 (H 3 PO 4 :H 2 SO 4 = 1:2, with a total acid volume of 2.50 mL), 12.50 g of phenol, liquefaction temperature of 150 °C, liquefaction time of 2 h, 5.20 g of NaOH, hydrothermal time of 12 h, hydrothermal temperature of 130 °C, a mixture ratio of 1:2.4 for chitin powder and ZnCl 2 , and a calcination temperature of 500 °C. The resulting CPHCs exhibited uniform size, high mechanical strength, and abundant micropores. The BET specific surface area, total pore volume, micropore volume, and water contact angle of CPHCs were 751.81 m 2 /g, 0.32 cm 3 /g, 0.16 cm 3 /g, and 120°, respectively. The adsorption of PX followed pseudo-first-order kinetics and Langmuir isotherm model, with a maximum adsorption capacity of 302.11 mg/g. The adsorption process was endothermic and spontaneous. The main mechanisms of PX adsorption on CPHCs involved hydrogen bonding, π-π interactions, and micro-pore filling. The preparation of shaped hydrophobic biomass materials using chitin powder is feasible, and CPHCs exhibited excellent capture performance for PX.