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

Abstract

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.