Electrochemical Colour Removal of Azo Dyes Using Boron-Doped Diamond Electrodes and Silver Nanoparticles as Electrocatalyst

Abstract

Azo dyes are carcinogenic and if taken would lead to debilitating adverse health effects in animals, man and aquatic organisms. In this study, novel Boron Doped Diamond (BDD) electrodes coated with silver nanoparticles were applied. Iron (11) sulphate was used as a supporting electrolyte and silver nanoparticles as electrocatalyst to enhance the degradation efficiency. Degradation efficiency was monitored by UV-VIS spectrometry while some of the physico-chemical parameters were determined by standard methods for examination of water and wastewater as outlined in the APHA (2000). The absorption spectra for the four dyes were determined and their λ max ranged between 470 to 590 nm in UV-VIS spectrum. Colour removal of 100% was achieved at the end of the electrochemical degradation. The colour levels of the treated textile wastewater were found to be BDL. The final treated wastewater was compared with National Environmental Management Authority (NEMA) and World Health Organization (WHO) effluent discharge standards for the possibility of re-use or direct discharge to a natural water course. From the study findings, it is evident that the concentration of the dyes considered efficient for colour removal was 10 ppm since there was less power consumption thus economical. An increased concentration from 0.1 to 0.5 g/l of FeSO4 was added to act as a supporting electrolyte to enhance quick removal of the dye. As the concentration of silver nanoparticles increased from 0 to 8 ppm lowest power of 0.4536 watts within the group mean value of 0.03±0.0023 time (hours) and 0.63±0.0001 current (amperes) was recorded. Therefore, it was concluded that a greater concentration of AgNPs acted effectively as the electrocatalyst to eliminate the barrier during the dye removal process. In all four experiments using different kinds of textile dyes, it was worth noting that an increase in the inter-electrode distance from 2mm to 8 mm led to a decrease in the current production from 1.23±0.0140 A - 0.58±0.0048 A which resulted to a lot of time taken from 0.025±0.0012 hr -0.723±0.0047 hr. The aspect of temperature was also considered under the above optimal conditions, and at 45ºC the removal was faster as there was an increase in the chemical kinetics of the particles in the reaction system. As the pH increased from 4.0 to 7.0, current production increased from (0.21±0.0005-0.24±0.0014 A). From the group, analyzed pH range of 6.5±¬0.5 was noted to enhance better removal of the studied azo dye from the textile wastewater effluent. The textile azo dye colour was removed to below detectable levels (BDL) and thus could not be detected by human eye after treatment