Effective removal of Pb(II) and Congo red by polyrhodanine-modified sepiolite

Heavy metals and dyes present in industrial wastewater pose a significant threat to both the ecological environment and human health. In this study, we have developed a multifunctional adsorbent, SEP/PR, which is obtained by modifying sepiolite with polyrhodanine. The purpose of this adsorbent is to effectively remove Pb2+ ions and Congo red (CR) dye from contaminated water sources. The adsorbents were systematically characterized using SEM, EDS, XRD, BET, FT-IR and XPS. Compared with raw sepiolite, SEP/PR exhibited better adsorption performance due to its abundant adsorption sites. The adsorption of Pb2+ and CR on SEP/PR can be described by pseudo-second-order and Langmuir models, and the preferential adsorption capacities were still satisfactory even in the presence of interference. The maximum adsorption of Pb2+ and CR was 423.29 mg/g and 894.76 mg/g, respectively, at 298 K. It is noteworthy that the removal rates of both Pb2+ and CR were increased in the binary Pb2+-CR system. These observed increases can be attributed to the introduction of additional adsorption sites, as well as the electrostatic attractions that occur between the adsorbed Pb2+ (+) and CR (−) ions. The adsorption mechanism for Pb2+ primarily involves complexation, while for CR, it involves a combination of electrostatic interactions, hydrogen bonding, and π-π interactions. Finally, SEP/PR has good reusability and practical application capabilities. This study shows that SEP/PR is simple to synthesize and can be used for the synergistic removal of heavy metals and dyes in complex systems.