High adsorption capacities for dyes by a pH-responsive sodium alginate/sodium lignosulfonate/carboxylated chitosan/polyethyleneimine adsorbent

Dyes are indispensable for the rapid development of society, but untreated dye wastewater can threaten human health. In this study, an adsorbent (SA/SL/CCS/PEI@MNPs) was synthesized by one-pot method using magnetic nanoparticles (MNPs), sodium alginate (SA), sodium lignosulfonate (SL), carboxylated chitosan (CCS) and polyethyleneimine (PEI). The adsorbent was mesoporous micrometer-sized particles with pore size of 34.92 nm, which was favorable for dynamic column experiments. SA/SL/CCS/PEI@MNPs possessed pH-responsive performance. Under acidic condition, the maximum adsorption capacities for anionic dyes (tartrazine, reactive black-5, indigo carmine) reached >550 mg/g. Under alkaline condition, those for cationic dyes (methylene blue, methyl violet, neutral red) exceeded 1900 mg/g. The function of the various modifiers was investigated. The results indicated that the incorporation of SL, CCS and PEI was able to provide plenty of sulfonate, carboxylate and amino/imine reactive groups so that adsorption capacities of dyes were improved. The adsorption mechanism was explored by FTIR and XPS. At the same time, the adsorption mechanism was more deeply analyzed using molecular dynamics simulations and radial distribution function. It was demonstrated that the dyes adsorption on the SA/SL/CCS/PEI@MNPs was mainly due to electrostatic attraction and π-π interaction. In addition, the adsorbent had good reusability, and the removal still reached over 90 % after five cycles. In conclusion, the adsorbent displayed a broad prospect for the adsorption of organic dyes. [Display omitted] •Magnetic micron-sized adsorbent was prepared by one-step method.•Adsorption of MB and E102 with pH sensitive.•Had maximum adsorption capacity of 2010.15 mg/g for MB and 637.68 mg/g for E102.•Electrostatic attraction and π-π interaction were verified using MD simulation and RDF.•Micron-sized hard particles that could be easily loaded on the column.