Adsorption performance and mechanism of cationic and anionic dyes by KOH activated biochar derived from medical waste pyrolysis

The massive generation of medical waste (MW) results in a series of environmental, social, and ecological problems. Pyrolysis is one such approach that has attracted more attention because of the production of value-added products with lesser environmental risk. In this study, the activated biochar (ABC600) was obtained from MW pyrolysis and activated with KOH. The adsorption mechanism of activated biochar on cationic (methylene blue) and anionic (reactive yellow) dyes were studied. The physicochemical characterization of biochar showed that increasing pyrolysis temperature and KOH activation resulted in increased surface area, a rough surface with a clear porous structure, and sufficient functional groups. MB and RYD-145 adsorption on ABC600 was more consistent with Langmuir isotherm (R-2 >= 0.996) and pseudo-second-order kinetics (R-2 >= 0.998), indicating chemisorption with monolayer characteristics. The Langmuir model fitting demonstrated that MB and RYD-145 had maximum uptake capacities of 922.2 and 343.4 mg.g-1. The thermodynamics study of both dyes showed a positive change in enthalpy (delta H degrees) and entropy (delta S degrees), revealing the endothermic adsorption behavior and randomness in dye molecule arrangement on activated-biochar/solution surface. The activated biochar has excellent adsorption potential for cationic and anionic dyes; hence, it can be considered an economical and efficient adsorbent.

Automated summary

The massive generation of medical waste leads to various environmental, social, and ecological problems. This study focuses on the use of pyrolysis and activation to obtain activated biochar from medical waste and investigates its adsorption mechanism and properties for dyes. The results show that activated biochar has excellent potential for adsorbing both cationic and anionic dyes, making it an economical and efficient adsorbent.