Lotus pollen-derived hierarchically porous carbons with exceptional adsorption performance toward Reactive Black 5: Isotherms, kinetics and thermodynamics investigations

• A high-efficiency and sustainable adsorbent was developed for RB5 removal. • Lotus pollen-derived hierarchical porous carbons (LPHPCs) show exceptional adsorption capacity. • The maximal equilibrium adsorption capacity reaches 615.6 mg/g on LPHPCs. • The adsorption isotherms, kinetics and thermodynamics were systematically studied. The removal of azo dye from wastewater is urgent due to its massive discharge from various industries and high toxicity. Adsorption is an efficient removal method, but it is limited by the low adsorption capacity of the present adsorbents. Herein, a high-efficiency and sustainable adsorbent for Reactive Black 5 (RB5) was developed, which was obtained using lotus pollen as carbon precursors followed by carbonization and activation with KOH. The as-prepared lotus pollen-derived hierarchically porous carbons (LPHPCs) showed exceptional adsorption performance for RB5, the maximal equilibrium adsorption capacity can reach 615.6 mg/g on LPHPC-2.5, and 269.6 mg/g on LPHPC-1.0, which were far superior to that of commercial activated carbon (CAC) (94.7 mg/g). Their adsorption performance for RB5 under different conditions was examined, such as different initial concentration, adsorbent dosage, inorganic salt concentration, temperature and pH. The adsorption isotherms, kinetics, thermodynamic properties and mechanisms were systematically investigated in depth. The results demonstrated that the adsorption process of RB5 onto LPHPCs involved dominant physical adsorption together with necessary chemical adsorption. The comparative advantages of LPHPCs over CAC for RB5 adsorption were ascribed to the higher specific surface area and larger appropriate pore volume, higher degree of graphitization and better affinity. The findings revealed that LPHPCs are promising adsorbents for the adsorption removal of anionic dyes from wastewater.