Charge Redistribution in Nise2/Mos2 n–n Heterojunction towards the Photoelectrocatalytic Degradation of Ciprofloxacin

This study reports the photoelectrocatalytic (PEC) activity of a n–n heterojunction comprising MoS₂ and NiSe₂. The synthesis of the composite was achieved through a facile solvothermal method, yielding an exfoliated MoS₂ layered sheet loaded with NiSe₂ nanoparticles. Under visible light radiation and an external electric field, the obtained composite NiSe₂/MoS₂ exhibited enhanced catalytic activity for ciprofloxacin (CIP) degradation. The NiSe₂/MoS₂ heterojunction achieved about 78 % degradation efficiency with a first-order kinetic rate of 0.0111 min⁻¹, compared to 38 % efficiency and a first-order kinetic rate of 0.0044 min⁻¹ observed for MoS₂. The NiSe₂/MoS₂ heterojunction was more advantageous due to the synergy of charge carrier induction by visible light radiation and improved charge carrier separation induced by the external electric field. The formation of n–n heterojunction at the interface of the two materials resulted in charge redistribution in the materials, with a simultaneous realignment of the band structure to achieve Fermi energy equilibration. The primary reactive species responsible for CIP degradation was identified as the photo-induced h⁺. Furthermore, the catalyst exhibited high stability and reusability, with no significant reduction in activity observed after five experimental cycles. This study reveals the potential of exploring the synergy between the photocatalytic and electrocatalytic processes in removing harmful pharmaceutical compounds from water.