[Coadsorption of Heavy Metal and Antibiotic onto Humic Acid from Polder River Sediment].

To clarify the interactions between heavy metals, antibiotics, and humic acid, copper (Cu2+), oxytetracycline (OTC), norfloxacin (NOR), and humic acid samples from river sediment in the Polder area were selected to build single and coexisting systems. Groups of experiments were designed to investigate the kinetics, thermodynamics, and isotherms of Cu2+, OTC, and NOR adsorption onto humic acid in single and Cu2++OTC and Cu2++NOR coexisting systems (concentration ratio=1:1). The physicochemical properties of humic acid were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), BET tests, and IR spectroscopy, and the possible adsorption mechanisms are discussed. The results showed that the humic acid was a typical amorphous material with a negative charge and non-uniform porous structure, and the pore size was at the mesoporous scale. In the single systems, the saturated adsorption capacity (qm) of Cu2+, OTC, and NOR onto humic acid was 33.043, 19.512, and 26.676 mg·g-1, respectively. In the Cu2++OTC system, the qm of Cu2+ and OTC was 38.053 and 25.965 mg·g-1, respectively. In the Cu2++NOR system, the qm of Cu2+ and NOR was 39.187 and 32.728 mg·g-1, respectively. The adsorption behaviors in the single and coexisting systems were similar and the adsorption processes were well fitted by the pseudo-second-order kinetic equation; the Sips model provided good descriptions for the isothermal adsorption equilibrium. Moreover, adsorption thermodynamics were characterized by spontaneous endothermic reactions with the reduction of free energy and the increase of enthalpy and entropy. It can be concluded that Cu2+ combines with OTC and NOR to form complexes, which increases the number of species available for adsorption by humic acid. Also, adsorbed Cu2+ can combine with free OTC and NOR in a bridging manner. Thus, a more favorable adsorption situation occurred in the coexisting systems. The IR characteristics of the carboxyl, phenolic hydroxyl, ketone, and aldehyde groups of humic acid changed by different degrees after adsorption, indicating that oxygen-containing functional groups generally participated in the adsorption reactions.

Adsorption behaviors of the pristine and aged thermoplastic polyurethane microplastics in Cu(II)-OTC coexisting system.

In this work, the hypothesis that thermoplastic polyurethane (TPU) microplastics (MPs) could form complex toxic pollution by absorbing both antibiotics and heavy metals simultaneously was proposed. The unique features of the adsorption of Cu(II) and oxytetracycline (OTC) on the pristine TPU and photo-aged (aged) TPU MPs in single and coexisting system were investigated, which included the kinetics, isothermal equilibrium and thermodynamics. The possibly synergistic or competitive effects between Cu(II) and OTC were also evaluated. The results showed that the adsorption process of Cu(II) and OTC could be described well by pseudo-second-order kinetic equation. The entire process could be divided into two stages: internal diffusion and external diffusion. The Sips model could give good fitting for the isothermal adsorption equilibrium. The thermodynamic parameters depicted the endothermic nature of adsorptions and the process was spontaneous. In the coexisting system, synergistic or competitive effects depended critically on the ratio of concentrations (Cu(II) vs OTC). When the ratio was 1:1, Cu(II) significantly enhanced the adsorption of OTC, while OTC showed a weak effect on Cu(II) adsorption. The synergies could be attributed to the formation of Cu(II)-OTC complex and the bridging effect of Cu(II). Overall, the adsorption capacity of aged TPU was higher than that of pristine TPU, which was due to the differences in morphological characteristics and functional groups. FTIR studies revealed that ester carbonyl and acylamino groups in the TPU may be involved in the adsorption of Cu(II) and OTC.

[Sorption Behaviors of Copper Ions and Tetracycline on Microplastics in Aqueous Solution].

The interaction between microplastics, heavy metals, and antibiotics can lead to combined pollution, which could result in greater environmental damage. The pathway and mechanism of the interaction between microplastics, heavy metals, and antibiotics are the preconditions for evaluating the associated environmental risk; however, these are not well understood. As probe sorbates, the sorption behaviors of copper ions (Cu2+) and tetracycline (TC) on two microplastics [high density polyethylene (HPDE) and general-purpose polystyrene (GPPS)] in aqueous solution were investigated and the welding theory with relevant experimental results were discussed. The adsorption capacity of HDPE was greater than that of GPPS in a single Cu solution, whereas the reverse situation occurred in a single TC solution. Moreover, the adsorption capacity of the microplastics in a Cu2+-TC binary solution was larger than that in the single solutions. The pseudo-second-order kinetic models to describe the adsorption process were reasonable and the entire process could be divided into two phases:surface adsorption and internal diffusion. The Langmuir model provided a better fit of the data than did the Freundlich model. In the single solutions, the saturated adsorption amounts of Cu2+ and TC were 0.178 µmol·g-1 and 0.257 µmol·g-1, respectively, for GPPS, and 0.334 µmol·g-1 and 0.194 µmol·g-1, respectively, for HDPE. In the binary solution, the corresponding numerical values were 0.529 µmol·g-1 and 0.411 µmol·g-1, respectively, for GPPS and 0.471 µmol·g-1 and 0.341 µmol·g-1, respectively, for HDPE. The variations in the surface morphological characteristics and chemical functional groups were the main reasons for the difference in the adsorption behavior of microplastics. The variation of the pH of the adsorption system could change the existing forms and surface electrical properties of microplastics and adsorbed objects, and subsequently affected the equilibrium adsorption capacity. When the ambient temperature was in the range of 15 to 35℃, increasing the temperature was unfavorable for the adsorption process. Cu2+ and TC could produce a synergistic effect under the conditions of coexistence. The formation of complexes and bridging make Cu2+ and TC more easily adsorbed by microplastics.