Green Synthesis of Zinc Oxide Nanoparticles Using Moringa Leaf Extract and Evaluation of Their Efficiency in Removing Methylene Blue from an Aqueous Solution

This study aims to prepare zinc oxide nanoparticles through green synthesis using moringa (Moringa oleifera) leaf extract, characterize the material, and evaluate the removal of methylene blue from an aqueous solution. An initial main experiment was conducted using 0.05 g of the material in 50 mL of dye solution at a concentration of 10 mg/L, with 30 minutes in the dark followed by exposure to light for up to 60 minutes. An additional, independent experimental series and control tests for photolysis and adsorption in the dark were also conducted. The material was characterized using XRD, SEM, and FTIR. In the additional series, the mixture containing the catalyst was kept in the dark for 60 minutes and then exposed to light for up to 60 minutes, and the experiments were performed in three independent replicates. Absorbance was measured at 664 nm, and the calibration equation was used to calculate the concentration and removal percentage. Results from the additional series were reported as the mean ± standard deviation. In the initial experiment, the final concentration reached 0.40 mg/L, and the recorded removal was 96.0%. The additional series yielded a mean final concentration of 0.35 mg/L with a standard deviation of 0.03, and a mean cumulative removal of 96.5% with a standard deviation of 0.8 percentage points. Photolysis without a catalyst was 2.1% with a standard deviation of 0.3 percentage points, while adsorption in the dark was 18.3% with a standard deviation of 1.1 percentage points after 60 minutes. XRD revealed a hexagonal wurtzite structure and a crystallite size of 22.5 nm, while SEM indicated a size range of 20–35 nm, and a Zn–O peak appeared at 435 cm⁻¹ in FTIR. The results of the two experiments were presented separately because their protocols differed.