Applied Chemistry and Chemical Engineering

Ashraful Bari Anik

Job Holder

Thesis Title: Green Synthesis of ZnO Nanoparticles from Justicia adhatoda Leaves Extract for Enhanced Photocatalytic Degradation of Methylene Blue Dye & Antibacterial Activity

Overview: Enter Project/Thesis OverviewThe newly developed eco-friendly green synthesis method for producing zinc oxide nanoparticles shows great potential due to its sustainable nature, lack of harmful effects, ecologically benign behavior and non-toxicity. This study aimed to synthesize ZnO nanoparticles (ZnO NPs) via green method & chemical co-precipitation method to compare photocatalytic efficiency for dye removal. The antibacterial activities of the synthesized green ZnO NPs were also assessed. Nano scaled ZnO NPs were synthesized from zinc nitrate hexahydrate (Zn(NO3)2.6H2O) salt with the addition of Justicia adhatoda leaf extracts which acts as reducing agents during the formation of NPs under room temperature. The characterization of synthesized nanoparticles was performed using UV–Vis spectrophotometry, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) Analysis. The optical absorption plot and direct band gap energy of the synthesized green ZnO NPs exhibited absorption band 371 nm and 3.04 eV whereas for chemically synthesized ZnO NPs exhibited band 382 nm and 3.44eV. The hexagonal wurtzite crystal structure size, as determined by XRD pattern analysis, was 13.62 nm & 27.95 nm for green synthesized and chemical synthesized ZnO NPs respectively. Biomolecules were found in the green-mediated catalyst, as shown by the FTIR spectra. SEM analysis demonstrated that the uniform and spherical shaped morphology was observed in green ZnO NPs with average particle size of 75 nm and chemically synthesized ZnO NPs exhibit irregular and flake-shaped surface morphology with an average particles size of 140 nm. The photocatalytic degradation of Methylene Blue (MB), a cationic dye was investigated using the ZnO NPs as a photocatalyst under sunlight irradiation. The capacity of methylene blue dye degradation was assessed under different parameters, including variations in catalyst dosage, initial dye concentration, and pH levels. Maximum removal efficacy was obtained with 50 mg green ZnO catalyst, 10ppm MB Dye solution, basic pH 11, and irradiation time 60 minutes for the green synthesized ZnO NPs. Green ZnO NPs exhibits high performance adhering to pseudo-first-order reaction kinetics, with a rate constant of 0.064 min-1. Chemically synthesized nanoparticles were utilized to compare with the green synthesized ZnO NPs for effectivity. Antibacterial activity against S. aureus, Bacillus spp., E. coli, Salmonella Typhi bacterial strains were performed by the synthesized nanoparticles and showed no significant action which indicates its biocompatibility. This photocatalyst is cost-effective and environmentally safe, making it suitable for removing organic pollutants from wastewater using solar irradiation light.