Expanded graphite supported p-n MoS₂-SnO₂ heterojunction nanocomposite electrode for enhanced photo-electrocatalytic degradation of a pharmaceutical pollutant

Wastewater treatment challenges by conventional methods have necessitated the need for alternative/complementary methods that are environmentally benign and efficient especially toward recalcitrant organic pollutants. In this regard, a novel photoanode consisting of a p-n MoS₂-SnO₂ heterojunction anchored on expanded graphite (EG) was fabricated and employed in the photo-electrocatalytic degradation of ciprofloxacin, a pharmaceutical pollutant, in water using a current density of 0.010 A cm⁻². The photoanode material was characterised with transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Raman spectroscopy and X-ray diffraction (XRD) to confirm that the nanocomposite was successfully prepared. Photoelectrochemical studies were carried out with cyclic/linear sweep voltammetry and chronoamperometry. The removal efficiency of the photo-electrocatalytic cell was determined on a UV–Visible spectrophotometer and the extent of mineralisation was measured by a total organic carbon analyser. The results obtained revealed that the SnO₂ particles are nanosheets while the MoS₂ particles are hierarchical microspheres having nanosheets of MoS₂, and they were anchored on the interlayers of the EG sheets. Also, the p-n MoS₂-SnO₂ heterojunction anchored on expanded graphite (EG) was found to be photoactive and displayed a better removal efficiency and mineralisation in comparison to EG, SnO₂-EG and MoS₂-EG electrodes. This may be due to the formation of the MoS₂-SnO₂ p-n heterojunction in the MoS₂-SnO₂/EG nanocomposite which enhanced the light harvesting ability of the material resulting in its improved photo-electrocatalytic performance. Hence the MoS₂-SnO₂/EG is potentially a good photoelectrode which may be beneficial for a photo-electrocatalytic treatment of industrial wastewaters and other photo-electrocatalytic applications.