The competitive adsorption behavior of mixed dye systems—specifically methyl orange (MO), indigo carmine (IC), and methylene blue (MB)—on polystyrene-based adsorbents reveals complex intermolecular interactions that govern selectivity, capacity, and process efficiency. In binary systems involving MO and IC on PsAX, competition is concentration-dependent: at low initial concentrations (0.05–0.2 mM), both dyes mutually influence each other’s uptake due to overlapping ion-exchange sites and limited surface availability. MO strongly inhibits IC adsorption, as its high charge density competes effectively for the quaternary ammonium groups. However, when IC is present at higher concentrations (≥1.0 mM), it forms intermolecular hydrogen bonds between secondary amine and carbonyl groups, creating a self-organized, compact layer that resists displacement by MO, thereby enhancing its own retention.
Conversely, at high MO concentrations, the protonated form of MO engages in end-to-end intermolecular interactions via sulfate and amine groups, increasing molecular aggregation and reducing effective mobility, which indirectly limits IC access. This phenomenon explains why the relative IC/MO adsorption ratio decreases significantly under high-load conditions. At low concentrations, the absence of such aggregation allows more dynamic exchange, leading to stronger mutual interference. These observations confirm that molecular self-assembly plays a critical role in modulating competitive dynamics beyond simple site competition.
In the case of MO and MB on PsAX, a unique synergistic interaction emerges. Although MB is electrostatically repelled by the positively charged quaternary ammonium groups under neutral pH, the presence of MO partially neutralizes these sites through protonation and ion exchange, reducing repulsion and enabling MB adsorption. Simultaneously, MB’s highly polarizable fused-ring structure enhances π–π stacking with the polystyrene matrix, further promoting uptake. As MO concentration increases, MB adsorption rises nonlinearly, suggesting a cooperative mechanism where one dye facilitates the binding of the other.1,2-Hexanediol Epigenetics This effect is not observed in single-solute systems and underscores the importance of multi-component analysis.
On MN200, a nonionic adsorbent, a strong synergistic effect was observed between MO and MB despite their opposite charges.NAD+ Epigenetic Reader Domain The negatively charged sulfonate groups of MO and positively charged nitrogen atoms in MB can form transient ion pairs or dipole-dipole complexes that are stabilized within the microporous structure.PMID:34538025 These complexes exhibit enhanced affinity for the hydrophobic matrix, leading to higher combined adsorption than predicted from individual experiments. The pore size distribution of MN200 favors such molecular clustering, especially at moderate concentrations, resulting in multilayer formation and increased overall capacity.
These findings demonstrate that competitive adsorption in real wastewater is not merely a matter of site competition but involves dynamic interplay between electrostatic forces, molecular self-organization, and pore confinement. Ignoring these interactions can lead to inaccurate predictions and suboptimal treatment design. Therefore, advanced modeling incorporating multi-component equilibria, intermolecular forces, and structural effects is essential for developing efficient, scalable dye removal strategies. This mechanistic understanding enables the rational design of hybrid adsorbents and process configurations tailored for complex industrial effluents.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com