Electrochemical and photocatalytic oxidation of organic pollutants from waste water using efficient nano-catalytic coatings prepared by electrodeposition

Abstract

Wastewater from the textile industry is considered to be one of the most pollutant effluents due to its toxic organic colourants content being strongly resistant to oxidation. When these substances are directly discharged into rivers and sea they persist for long periods causing environmental and aesthetic problems together with high health risks to living organisms. The main goal of this research is to study the oxidation of different textile dyes and organic pollutants, in particular reactive black-5 (RB-5) and methylene blue (MB) dyes using different nano catalytic coatings. A 3D flexible titanium felt electrode was anodized for growing TiO2 nanotubes and further decorated with PbO2 subsequently employed for anodic electrochemical and photochemical treatment of wastewater containing RB-5 dye. Similarly, reticulated vitreous carbon (RVC)surfaces were decorated with a layer of PbO2 and titanate nanosheets by anodic electrophoretic deposition, with subsequent structural and morphological characterization using FESEM and Raman spectroscopy. The TiNS/PbO2/RVC electrode has titanium anatase phase which was obtained by annealing at 450°C for 60 min in air. The structure revealed a well-specified, microporous structure with hydrophilic properties along the length and thickness of the RVC struts. Electrochemical and photocatalytic behaviour of the composite assisted the decolourisation of organic RB-5 dye in aqueous solution; on one hand • OH radicals were electrochemically produced via TiNS/PbO2/RVC anode composite coating and the photocatalytic decolourisation use the synergetic photocatalytic activity associated with the holes and free electron acceptors generated during UV irradiation experiments. Another objective of this thesis is the synthesis of efficient nanotubular titanates (TiNTs) coatings over the surface of the RVC substrate to make the organic oxidation more efficient. Titanate nanotubes (TiNTs) were deposited over the surface of a 100 pores per inch (ppi) RVC by anodic electrophoresis. The photocatalytic characteristics of the coating were enhanced by annealing at 450 °C for 60 min in air. A preliminary evaluation of novel TiNT/RVC coatings demonstrated to be useful for the photocatalytic colour removal of MB dye. In addition, a zinc metal plate was electrochemically anodised to produce ZnO nanowires. The selected operational conditions together a subsequent dip-coating process of the anodised ZnO surface in a TiO2 containing solution, produced a core-shell coating. A further electrochemical deposition of PbO2 over the core-shell produced a hybrid core (ZnO-TiO2)-shell (PbO2) coatings. The electrochemical and photocatalytic behaviour of the coatings were analysed by employing them to remove RB-5 dye (1 × 10-5 mol dm-3 ). The nano-coatings are low cost option for the oxidation of textile dyes and improved removal of RB-5 and MB dyes at a removal efficiency of ≈99 %.

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Identifiers

ORCID for Carlos Ponce De Leon Albarran: orcid.org/0000-0002-1907-5913

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