A Nickel (II) Complex of Naphthaldehyde Derived Bis-Imine Ligand for Sunlight Driven Dye Remediation: Mechanistic study, Intermediate identification and Recyclability

Abstract

Dye are proven to act as persistent organic pollutants for fresh water bodies as well as marine environment. Thus, suitable dye remediation measures become obligatory to save the aquatic biosystems as well as human health. This work presents a study on the photoactalytic remediation of cationic dye using a Nickel (II) complex (NiL 1 Et). The NiL 1 Et complex was synthesized using the ONS donor ligand (L 1 ) as the ligand and confirmed with spectroscopic techniques and elemental analysis. The Ni(II) complex, NiL 1 Et adopts a square planar geometry which was envisioned through computational study. The direct band gap of 2.19 eV estimated experimentally agreed well to the HOMO-LUMO energy which was computationally predicted through computational study.This establishes the semiconductor like property of the NiL 1 Et complex. Morevoer, the slower electron-hole recombination rate in the excited complex predicted from the emission intensities, further establishes the potential of NiL 1 Et as photocatalyst. Methylene Blue (MB) was employed as the model dye and a maximum degradation efficiency of 80.15% was achieved using NiL 1 Et just within 60 min under natural sunlight without any artificial light source. The effect of different parameters like catalyst amount, concentration of the dye used, reaction time, pH, and H 2 O 2 dose were analyzed. It was observed that the complex could be efficiently used as photocatalysts for five catalytic cycles. Furthermore, insights into the mechanistic route of the MB degradation was analyzed. The pathway of MB degradation was predicted by determining the intermediates species generated during the degradation process using LCMS.