Photocatalytic degradation of methyl red using seaweed mediated zinc oxide nanoparticles.

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. • Zinc oxide nano photocatalysts fabricated using two different seaweeds, Stoechospermum marginatum and Ulva lactuca were used to degrade methyl red dye under sunlight. • Stoechospermum marginatum based ZnO nano catalyst exhibited better efficacy than Ulva lactuca based ZnO nanoparticles for degradation of methyl red dye under sunlight. • The feasibility of treated dye solution for irrigation purposes has been studied by analyzing the growth of green gram plants. • The parameters such as chlorophyll content, protein and carbohydrate content of the leaves of green gram plants have been evaluated as a measure of quality of treated water. [ABSTRACT FROM AUTHOR]