Photoelectrocatalytic application of palladium decorated zinc oxide-expanded graphite electrode for the removal of 4-nitrophenol: experimental and computational studies

Eseoghene H Umukoro; Moses G Peleyeju; Azeez O Idris; Jane C Ngila; Nonhlangabezo Mabuba; Lydia Rhyman; Ponnadurai Ramasami; Omotayo A Arotiba

doi:10.1039/c8ra00180d

Photoelectrocatalytic application of palladium decorated zinc oxide-expanded graphite electrode for the removal of 4-nitrophenol: experimental and computational studies

RSC Adv. 2018 Mar 13;8(19):10255-10266. doi: 10.1039/c8ra00180d.

Authors

Eseoghene H Umukoro¹, Moses G Peleyeju¹, Azeez O Idris¹, Jane C Ngila^{1

2}, Nonhlangabezo Mabuba^{1

2}, Lydia Rhyman^{1

3}, Ponnadurai Ramasami^{1

3}, Omotayo A Arotiba^{1

2}

Affiliations

¹ Department of Applied Chemistry, University of Johannesburg South Africa oarotiba@uj.ac.za p.ramasami@uom.ac.mu.
² Centre for Nanomaterials Science Research, University of Johannesburg South Africa.
³ Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius Réduit 80837 Mauritius.

Abstract

A novel Pd-ZnO-expanded graphite (EG) photoelectrode was constructed from a Pd-ZnO-EG nanocomposite synthesised by a hydrothermal method and characterised using various techniques such as X-ray diffractometry (XRD), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, nitrogen adsorption-desorption analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Cyclic voltammetry and photocurrent response measurements were also carried out on the electrode. The Pd-ZnO-EG electrode was employed in the photoelectrocatalytic removal of 4-nitrophenol as a target water pollutant at a neutral pH and with a current density of 7 mA cm^-2. Optical studies revealed that the Pd-ZnO-EG absorbed strongly in the visible light region. The Pd-ZnO-EG electrode showed improved photoelectrocatalytic activity in relation to ZnO-EG and EG electrodes for the removal of the 4-nitrophenol. The photocurrent responses showed that the Pd-ZnO-EG nanocomposite electrode could be employed as a good photoelectrode for photoelectrocatalytic processes and environmental remediation such as treatment of industrial waste waters. Density functional theory method was used to model the oxidative degradation of 4-nitrophenol by the hydroxyl radical which generates hydroquinone, benzoquinone, 4-nitrocatechol, 4-nitroresorcinol and the opening of the 4-nitrophenol ring. Furthermore, the hydroxyl radical is regenerated and can further oxidise the ring structure and initiate a new degradation process.