Instantaneous photocatalytic degradation of malachite green dye under visible light using novel green Co–ZnO/algae composites

Abstract

Nano-ZnO and Co–ZnO supported algae (Sargassum species) were synthesized as a novel composite of promising photocatalytic activities in decolorization of malachite green dye under a visible light source. The composites were characterized by different analytical techniques, and the results confirmed the loading process and the formation of composites of low band gap energies for ZnO/algae composite (2.45 eV) and Co–ZnO/algae composite (2.32 eV). The composites were used as photocatalysts for the rapid degradation of malachite green dye (MG) within the visible light zone. The synthetic catalysts showed stunning photocatalytic activities reflected in the complete degradation of 5 mg/L of MG after 10 min using 0.06 g of ZnO/algae and 0.05 g of Co–ZnO/algae at pH 7. Also, the studied composites showed high efficiency in the degradation of higher MG concentration (10 mg/L and 15 mg/L). The photocatalytic performances were enhanced by 58% for ZnO/algae and about 75% for Co–ZnO/algae as compared to pure ZnO without support. Moreover, they have high reusability properties and are applied effectively in seven cycles of MG degradation reusing tests. The active species trapping tests reflected the dominance of the electron–hole pairs in the visible light degradation of MG by ZnO/algae. For Co–ZnO/algae composite, the degradation mechanism appears to be controlled by both the electron–hole pairs and hydroxyl radicals with a similar effect.