Cobalt(II) phenylphenoxides as effective photocatalyst in the degradation of some organic dyes

Abstract

Removal of toxic dyes by physical, biological and chemical methods have been carried out extensively, of which photochemical degradation, by coordination complexes in particular, has been found to be an effective treatment method owing to the use of natural sunlight as source of energy, resulting in no sludge formation along with the release of less toxic substances in the environment. In this study, synthesis and evaluation of photocatalytic activity of new cobalt(II) phenylphenoxides, 1–4, against some organic dyes viz. Malachite green, methyl orange, crystal violet, methylene blue and fuchsin basic have been studied. The complexes were characterized by physicochemical, 1H NMR, FTIR, high resolution mass spectra (HRMS), powder X-ray diffraction (PXRD) and electrochemical techniques. An attempt has been made to study the effect of varying experimental conditions like concentration of catalyst, nature of ligand, presence of initiator, on the degradation of dyes. Results have shown that the rate of degradation increases with increase in the concentration of catalyst in the presence of environment friendly initiator, hydrogen peroxide. Furthermore, the complexes were found to be more photo-catalytically active towards degradation of malachite green and methyl orange showing degradation of 89.7 % and 95 %, respectively, in the presence of initiator. The photocatalytic degradation of the dyes displayed pseudo first-order kinetics wherein the physical concept of dye degradation i.e. physiosorption governed the adsorption rate of particles onto the adsorbent. The complexes were found to act as effective photocatalyst as well as strong oxidant generator, HO·, carried out by photochemical decomposition of H2O2 under the effect of sunlight. Scavenging studies unveiled the active involvement of hydroxyl radicals (HO·) and electron vacancies (h+) in facilitating the degradation process. Notably, the complexes exhibited remarkable reusability, enduring up to 6 repeat cycles for methyl orange and 5 cycles for malachite green with significant degradation percentages which have revealed their potential role in the degradation of these dyes.