Theoretical and Experimental Study of the Orientation to the Most Effective Coagulant for Removing Reactive Black-5 Dye from Industrial Effluents

The current research was designed to provide a theoretical approach for the selection of the optimum coagulant to remove Reactive Black-5 dye from industrial waste. Additionally, it seeks to identify the dye's most reactive sites and understand its degradation in water pollution. Theoretically, the study was investigated using the density functional theory (DFT) with a 6-31G (d) basis set. The studied molecules are the reactive Black-5 dye, ferric sulphate (Fe2(SO4)3), ferric chloride (FeCl3), aluminium sulphate (Al2(SO4)3), and aluminium chloride (AlCl3). Based on the electrophilicity index, the results revealed the following classification: Fe2(SO4)3 > FeCl3 > Al2(SO4)3 > AlCl3. Thus, Fe2(SO4)3 acts as an electrophile, and the Reactive (RB5) as a nucleophile. The Parr index analysis of the dye studied indicates that the most vulnerable region for the nucleophilic attack is sited on the C5-9H bonding area with ω_k=2.797 eV. The results of the experiments match well with the reported theoretical data, with the coagulant Fe2(SO4)3 achieving the highest Chemical Oxygen Demand removal rate (84.71% at pH = 4). To support the findings, we provide an experimental investigation using the coagulation-flocculation method for these various coagulants to remove the reactive Black-5 dye from industrial effluents.