Separation/degradation behavior and mechanism for cationic/anionic dyes by Ag-functionalized Fe3O4-PDA core-shell adsorbents

High-performance adsorbents have been well-studied for the removal of organic dye pollutants to promote environment remediation. In this study, an Ag nanoparticle-functionalized Fe3O4-PDA nanocomposite adsorbent (PDA-Fe3O4-Ag) was synthesized, and the adsorption/separation performance of commonly used cationic and anionic organic dyes by the PDA-Fe3O4-Ag adsorbent were assessed. Overall, PDA-Fe3O4-Ag exhibited a significantly higher adsorption capacity for cationic dyes compared to anionic dyes, the highest of which was more than 110.0 mg/g (methylene blue (MB)), which was much higher than not only the adsorption capacities of the anionic dyes in this study but also other dye adsorption capacities reported in the literature. The dye adsorption kinetics data fitted well to both the pseudo second-order kinetics model and the Langmuir isotherm model, suggesting a monolayer-chemisorption-dominated adsorption mode. Thermodynamics analysis indicated that the adsorption process was both endothermic and spontaneous. Furthermore, the PDA-Fe3O4-Ag adsorbent achieved high photodegradation removal rates of the dyes, especially neutral red (NR) and methyl orange (MO), which were 91.2% and 87.5%, respectively. With the addition of PDA-Fe3O4-Ag, the degradation rate constants of NR and MO increased from 0.08 × 10−2 and 0 min−1 to 2.11 × 10−2 and 1.73 × 10−2 min−1, respectively. The high adsorption and photocatalytic degradation performance of the PDA-Fe3O4-Ag adsorbent make it an excellent candidate for removing cationic and anionic dyes from the industrial effluents.