Insights into the synergistic removal of rhodamine B dye through photocatalysis over Zn(II)-based complex: A structural and mechanistic insights

A Zn(II) containing complex formulated; [Zn(2-MeImi)₂(Cl)(3-NBA)] (where, 2-MeImi = 2-methylimidazole; 3-NBA = 3-nitrobenzoic acid) (1) has been prepared and characterized. Single crystal X-ray diffraction shows that the central Zn(II) metal ion exhibits four coordination numbers with distorted tetrahedral geometry. The complex illustrates the supramolecular architecture which is consolidated by short-range, directional intermolecular interactions comprising the nitro (–NO₂) moieties of the 3-nitrobenzoate ligands. Although individual nitro-nitro interactions are energetically weak, their collective action, along with hydrogen bonding interactions, contributes to the lattice cohesion and structural rigidity and this phenomenon resembles collective weak interactions, analogous to pnicogen bonding. In photoluminescence study, the two types of peaks were observed; broad peaks show an instruct defect state of Zn²⁺ while weak peaks show the de-excitation of electrons from a higher energy to a lower one. Under optimized conditions, the photodegradation efficiency of 89.8% has been obtained for Rhodamine B (RhB) dye. The photocatalytic degradation of RhB was caused by the production of hydroxyl radicals and superoxide anions which are sufficient for the degradation of RhB into simpler non-toxic molecules like CO₂ and H₂O. The pseudo-first order (PFO) kinetic was followed by the photocatalytic reaction with high-rate constant of 0.0272 min⁻¹ and the recyclability test showed good stability of the catalyst with negligible loss of degradation efficiency over four successive photocatalytic runs. The key findings indicate that the reported material is efficient for degradation of RhB and useful towards environmental remediation.