Effect of framework metal ions of analogous magnetic porous coordination polymers on adsorption of cationic and anionic dyes from aqueous solution

The present study demonstrated the synthesis of porous coordination polymers (CPs), which built from piperazine (P) and benzen-1,2,4,5 tetracarboxylic acid (BTCA) with different metal ions, copper and cadmium. CPs were magnetized with iron oxide nanoparticles and were successfully synthesized BTCA-P-Cu-MCP and BTCA-P-Cd-MCP. The influence of framework metal ions on the adsorption behaviour of cationic methylene blue (MB) and anionic Chicago Sky Blue (CSB) textile dyes towards both magnetized CPs was investigated. Fourier transform infrared, X-ray diffraction, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, CHN, and Brunauer–Emmett–Teller analysis were used to characterize the synthesized adsorbents. The surface area and the pore size of BTCA-P-Cu-MCP and BTCA-P-Cd-MCP were 10.68 and 5.45 m 2 g −1 , 174.00 and 291.97 Å, respectively. BTCA-P-Cd-MCP more selective towards anionic CSB than cationic MB, while BTCA-P-Cu-MCP has the same selectivity for both dyes. The effect of adsorbent dosage, pH and contact time on the adsorption experiment was investigated. Adsorption isotherm, kinetic, and thermodynamic studies were applied for evaluation of the adsorption process. BTCA-P-Cu-MCP exhibited higher adsorption capacity of 130.0 and 64.6 mg g −1 compared to BTCA-P-Cd-MCP with adsorption capacity of 29.7 and 3.6 mg g −1 for CSB and MB adsorption, respectively. The adsorption kinetic of both dyes followed pseudo-second-order reaction kinetic. The adsorption of dyes on MCPs was spontaneous, feasible, and exothermic, as shown in the thermodynamic results study. Most significantly, the results prove the influence of framework metal ion (Cu 2+ and Cd 2+ ) on the adsorbent surface charge and properties that critically affects the dye removal properties including capacity and adsorption rate.