A novel application of HKUST-1 for textile dyes removal in single and binary solutions: Experimental investigation combined with physical modelling

The paper analyzes the single and binary adsorption of textile water pollutants, namely Direct Blue 1 (DB-1) and Direct Yellow-4 (DY-4) dyes, on HKUST-1 at 30 - 50 degrees C and pH 6.8. Experimental adsorption data indicated that the DB-1 and DY-4 adsorption capacities using this MOF decreased from single to binary systems confirming the presence of a competition effect between these dye molecules on the HKUST-1 adsorbent site. This antagonistic adsorption effect was exothermic. A theoretical approach based on the application of two enhanced adsorption models was utilized to understand the mechanisms for the adsorption of both dye molecules. This approach allowed the calculation of the saturation adsorption capacities for these pollutants in single and binary systems, which followed the next sequence: Q(m) (DB-1/HKUST-1) > Q(m) (DY-4/HKUST-1) and Q(mb) (DB-1 (DB-1 + DY-4)/HKUST-1) > Q(mb) (DY-4 (DB-1 + DY-4)/HKUST-1). The binary adsorption of these dyes occurred via the presence of an antagonistic effect that reduced the MOF removal performance. HKUST-1 showed better adsorption performance to remove DB-1 dye. The adsorption orientations of DB-1 and DY-4 on HKUST-1 surface were discussed at different temperatures. The models determined the adsorption energies describing the interactions between both dyes and HKUST-1 surface, with range values from 17 to 21 kJ/mol, 12 to 16.5 kJ/mol in single and binary systems respectively. These calculations indicated that physical interactions may trigger the removal of these water pollutants. Overall, this work reports a cutting-edge application of HKUST-1 as adsorbent to remove toxic pollutants such as dye molecules from water.