Adsorption of tetracycline hydrochloride on layered double hydroxide loaded carbon nanotubes and site energy distribution analysis

In this study, a novel composite material of growing layered double hydroxides on carbon nanotubes (LDH@CNT) was prepared by in-situ method and possessed a favorable adsorbent structure by the mutual support of LDHs and CNTs. For the removal of antibiotic tetracycline, the adsorption kinetics of LDHs, CNTs, and LDH@CNT composites were well fitted by intraparticle diffusion model and pseudo-second-order model, revealing that the adsorption site was the main factor for the adsorption process. In the isotherm study, Generalized Langmuir model described the adsorption process better than the Langmuir model, indicating that there are multiple interactions between tetracycline and composite material. In addition, site energy distribution theory combined with molecular simulation to explain the adsorption mechanisms, and the removal of tetracycline by LDHs, CNTs, and LDH@CNT composites was calculated. The results showed that the average site energies of LDH@CNT composites were lower than that of LDHs (19.09 kJ /mol) and CNTs (16.41 kJ /mol), but exposed adsorption active sites in LDH@CNT composites were much more than that of LDHs and CNTs, which was beneficial to removal of tetracycline. The innovative growth of LDHs on CNTs overcame the disadvantage of easy aggregation, which exposed more adsorption sites and improved the removal efficiency of TC. In addition, the effects of pH, ion strength, antibiotic competition and reuse tests on LDH@CNT composite samples were also analyzed and showed a good stability of composite. Therefore, the excellent removal performance of LDH@CNT composite suggested a promising strategy for the removal and remediation of antibiotics contaminated environment.

Automated summary

In this study, a novel composite material LDH@CNT was prepared using an in-situ method, which had a favorable adsorbent structure due to the mutual support of LDHs and CNTs. The adsorption kinetics of LDHs, CNTs, and LDH@CNT composites for tetracycline were well described by intraparticle diffusion and pseudo-second-order models, indicating that the adsorption site played a major role. The Generalized Langmuir model was found to better describe the adsorption process than the Langmuir model, suggesting multiple interactions between tetracycline and the composite material. Site energy distribution theory combined with molecular simulation explained the adsorption mechanisms, and the removal of tetracycline by LDHs, CNTs, and LDH@CNT composites was calculated. The results showed that LDH@CNT composites had lower average site energies compared to LDHs and CNTs, but had more exposed adsorption active sites, leading to improved removal efficiency of tetracycline.