Understanding Photocatalytic Degradation of RB5 Dye under Salts Using Nickel Sulfide Nanoparticles: Insights from Dynamic Light Scattering and Theoretical Investigations.

This study reports the photocatalytic degradation of the RB5 dye by nickel sulfide nanoparticles (NiS NPs) in the presence of salts. Dynamic light scattering has rarely been used to study dye photocatalytic degradation. However, hydrodynamic size ( ) and zeta potential measurements offer insights into RB5 photocatalytic degradation. The hydrodynamic radius of NiS increased from 244.97 ± 31 to 1325.43 ± 531 nm upon interaction with NaCl, with 99% degradation efficiency for RB5 via OH, O , and Cl radical mechanisms, which further increased to 1882 ± 385 nm, indicating deposition of dye degraded and mineralized products on the catalyst surface. Least interaction of AgNO increased the hydrodynamic radius to 672.6 ± 339 nm with only 40% RB5 degradation. Zeta potential studies confirmed that NiS NPs are negatively charged and stable for RB5 photocatalytic degradation in NaCl, although their overall stability decreased upon interaction with salts. Trapping studies verify the radicals' generation, and the Langmuir-Hinshelwood model attests adsorption as an active process followed by the RB5 photocatalytic degradation. XRD analysis confirmed an average crystallite size of 7.08 nm with a rhombohedral crystal system. Scanning electron microscopy exhibits agglomerated nanoclusters, and BET analysis demonstrates the mesoporous nature of NiS with a surface area of 161 m/g. Optical analysis (UV-vis and PL) confirms the interaction of NiS NPs with RB5 and the salts, respectively. HPLC and TOC analyses demonstrate the degradation and mineralization of RB5, respectively. Theoretical investigation reveals that the N-N position is the preferred site for RB5 interaction with NiS NPs, whereas the cage-like structure was found suitable for photocatalysis with a bandgap energy of 2.11 eV. FTIR analysis confirmed the structural stability of NiS NPs up to the 10th cycle, maintaining over 85% RB5 degradation efficiency. These findings highlight the potential of NiS NPs for the elimination of toxic dyes from wastewater and their applicability to practical applications.