Simultaneous destruction of Nickel (II)-EDTA with TiO2/Ti film anode and electrodeposition of nickel ions on the cathode

Abstract

a b s t r a c tEthylenediaminetetraacetic acid (EDTA) forms stable complexes with toxic metals such as nickel. A combined photocatalytic-electrochemical system using TiO 2 /Ti plate as anode and stainless steel as cathode achieves the simultaneous decomplexation of Ni-EDTA and recovery of nickel. Ni-EDTA was efficiently destroyed in photoelectrocatalytic process in comparison with individual photocatalytic and electrooxidation process. At 60 min, removal efficiencies of Ni-EDTA were 75%, 12%, and 5%, respectively. At 180 min, the removal efficiency of Ni-EDTA in the photocatalysis and electrolysis processes is only 21% and 18%, respectively. By contrast, nearly 90% Ni-EDTA is removed in the photoelectrocatalytic process. The recovery percentage of nickel was determined to be 45%, 21%, and 5% in the photoelectrocatalysis, electrolysis, and photocatalysis process, respectively. The deposition of nickel ions at the cathode was confirmed by scanning electron microscopy analysis and the nickel species were identified via X-ray photoelectron spectra as nickel with zero value. The removal of Ni-EDTA and recovery of nickel ions increased with the current density and favored at acid conditions. Intermediates detected using a capillary electrophoresis and a high performance liquid chromatography includes Ni-NTA, glycine, maleic acid, glycolic acid, formic acid, acetic acid, oxalic acid, and oxamic acid were identified. The decomplexation pathway of Ni-EDTA was proposed.

Achievements and Trends in Photoelectrocatalysis: from Environmental to Energy Applications

“…Table 1 displays the main results obtained when this kind of electrode is applied in the treatment of textile dyes, pesticides, and pharmaceutical and other emerging contaminants. The results indicate high decolorization and the maximum total organic carbon of 50 % removal [26,32,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50].…”

“…The PEC technique reduced around 98-100 % of Cr(VI) and reached 95 % of TOC removal. Simultaneous degradation of EDTA and the respective Ni-EDTA complex has been published [50], where 45 % has been recovered in the form of Ni 0 on the cathode during degradation.…”

Enhancement of Photoelectrocatalysis Efficiency by Using Nanostructured Electrodes

“…In this case, the reduction takes place at a p-type semiconductor [12]. The reduction of toxic metals (Cr 6+ to Cr 3+ ) has also been described [61] in a photoelectrocatalytic process where the cathode is Pt but is conjugated in a system where the organic molecules are oxidized simultaneously in a photocathode such as Ti/TiO 2 and the electrons are forwarded to the counter electrode, where the reduction of Cr (VI) takes place [167]. Solar conversion of CO 2 to hydrocarbon fuels seems promising to reduce global warming for improved sustainability.…”

“…They obtained contaminant and nickel recovery on the cathode. The deposition of TiO 2 film was performed by dip-coating [167]. Paschoal and colleagues promoted the photoelectrochemical reduction of bromate under Ti/TiO 2 coated as a photocathode.…”

Photoelectrocatalytic oxidation of metal-EDTA and recovery of metals by electrodeposition with a rotating cathode

“…Photoelectrocatalytic (PEC) oxidation process in which a diminutive positive potential is applied on the semiconductor photoanode has proven to be more efficient than single photocatalytic (PC) process [6]. In PEC systems, the application of a small external bias decreases the recombination rate of photogenerated electronhole pairs and thus increasing the photocatalytic activity of the semiconductor photocatalyst [7].…”