Comparative Evaluation of Dichromate Adsorption Parameters Using Colorimetry on Glutaraldehyde-Crosslinked Polyethylene Imine (PEI) and Polyaniline (PANI)

Environmental pollution caused by hexavalent chromium [Cr(IV)] is a critical global concern due to its carcinogenic and acute toxicity. This study describes the synthesis of crosslinked polyethylene imine (PEI) and polyaniline (salt and base forms) and their effectiveness at removing dichromate ion (Cr2O72−) from aqueous solutions. The synthetized polymer adsorbents were comprehensively characterized using IR, TGA, and SEM-EDX methods. The adsorption processes were monitored via colorimetry and UV–Vis spectroscopy using the 1,5-diphenylcarbazide method under acidic conditions. Kinetic modeling revealed that the adsorption data fitted well to the pseudo-second-order model, confirming a chemisorption-controlled process. Equilibrium data followed the Langmuir isotherm at room temperature, predicting maximum adsorption capacities of 161 mg/g for PEI and exceeding 285 mg/g for the PANI salt. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were all negative, confirming the spontaneous and exothermic nature of the adsorption process. In selective competitive studies, the PANI salt demonstrated exceptional robustness, maintaining a Cr(VI) removal efficiency of 93% to 99% in the concurrent presence of KH2PO4, NaNO3, and CuSO4 interferents, which is highly comparable to the control. Conversely, the removal efficiency of PEI was sensitive to the matrix, dropping to 52–53% in the presence of NaNO3 and CuSO4 while remaining unaffected (65%) by KH2PO4. Furthermore, regeneration studies using 5% HNO3 demonstrated stable reusability, with both polymers maintaining high adsorption efficiencies (88–99%) over four consecutive cycles. These findings highlight the significant potential of these accessible polymeric materials for functional integration into real-world industrial wastewater treatment facilities.