Coadsorption, desorption hysteresis and sorption thermodynamics of sulfamethoxazole and carbamazepine on graphene oxide and graphite

Although the simultaneous presence of multiple pollutants is common, the behaviors of the pollutants as affected by other chemicals are still unclear. Graphite (GP) and graphene oxide were applied as model adsorbents to study the coadsorption of sulfamethoxazole (SMX) and carbamazepine (CBZ). For the first time, desorption hysteresis and thermodynamic analysis were incorporated in studying the coadsorption. Competitive sorption was observed as indicated by the decreased adsorption of the primary adsorbates with adding competing adsorbate. The absolute sorption inhibition of the primary sorbate (ΔQpri) was compared with the amount (Qsec) of competitor sorbed. Complementary sorption was evidenced as the generally observed ΔQpri < Qsec. Stronger interactions between CBZ and adsorbents resulted in stronger competition of CBZ to SMX than that of SMX to CBZ, lower release ratio of the adsorbed CBZ, more energy released and higher orderliness during CBZ sorption than SMX sorption. CBZ does not have any preference of sorption sites on GP as suggested by Langmuir-type sorption and insignificant change of SMX sorption nonlinearity and SMX release ratio after CBZ addition. Competitive sorption was observed at a wide pH range and in the presence of DOM, suggesting ubiquitous presence of this phenomenon in the environment.