Rapid adsorption of sulfamethazine on mesoporous graphene produced from plastic waste: optimization, mechanism, isotherms, kinetics, and thermodynamics

Abstract

Sulfonamide antibiotics like sulfamethazine (SMZ) can threaten aquatic and terrestrial life even in small concentrations (≤ 1 mg/L); hence, their removal from wastewater is indispensable. However, the need to explore new promising adsorbents that are cheap, effective, and reusable also remains crucial to developing adsorption technology. This work presents a one-pot solvent-free conversion of the current most ubiquitous anthropogenic bio-resistant solid waste (plastics) into valuable carbon materials to remove SMZ from aqueous solution. High-density polyethylene waste was pyrolyzed at 500–1000 °C in an enclosed stainless-steel reactor to produce mesoporous graphene. The graphene products were characterized via microscopic and spectroscopic analyses. The effect of temperature on the graphene yield and properties was investigated. The optimum sulfamethazine (SMZ) adsorption was achieved with 600 °C carbon product (CP-600) due to its high porosity and aromatic structure. The adsorption parameters (pH, catalyst dose, and SMZ concentration) were optimized by response surface methodology (RSM) with a central composite design. 99.99% SMZ removal was achieved at 0.9 g/L adsorbent dose, 12.4 mg/L SMZ concentration, and pH 3 at 25 °C. FTIR analysis revealed that the SMZ adsorption occurred mainly via π–π/π+–π electron interactions between the aromatic and pyrimidine rings of SMZ and the benzene ring of graphitic CP-600. The SMZ adsorption followed the pseudo-second-order kinetics, Langmuir, and Freundlich isotherm models. The adsorption was controlled by film and intraparticle diffusion and was spontaneous and endothermic. The carbon synthesized in this work is reusable and can rapidly remove more SMZ than other SMZ adsorbents.