Photocatalytic degradation of methyl red using seaweed mediated zinc oxide nanoparticles

Abstract

In the present work, the photocatalytic potential of zinc oxide nanoparticles, prepared using extracts of Ulva lactuca (U. lactuca) and Stoechospermum marginatum (S. marginatum), has been evaluated. The effect of catalyst dosage, pH of the solution, and initial dye concentration on the degradation of methyl red under sunlight has been studied. After 180 min of solar irradiation, the S. marginatum based zinc oxide nanoparticles (Sm-ZnO) exhibited the highest degradation efficiency, 92%, at pH 7, 5 mg/L dye concentration, and 2.5 mg/mL catalyst load. Under the same conditions, U. lactuca based ZnO NP (Ul-ZnO) recorded 90% degradation. The zinc oxide nanoparticles displayed notable performance during the three degradation cycles, and the stability of the catalyst is confirmed by X-ray diffraction analysis. The dye degradation reaction followed pseudo-first-order kinetics with a rate constant of 0.0167 min−1 for Sm-ZnO NPs and 0.0155 min−1 for Ul-ZnO NPs. The treated dye solution at pH 7, 2.5 mg/mL catalyst, and 10 mg/L dye concentration has been further utilized for watering green gram plants, and the growth parameters were, with a maximum shoot and root lengths of 13.5 cm and 1.8 cm, respectively. The total chlorophyll content was 72.9 μg/mL, protein content was 62 mg/g and the carbohydrate content 446 mg/g.