Synthesis by Sol-Gel and Coprecipitation of Zn_1−xFe_xO Nanoparticles for the Adsorption of Congo Red Dye

The influence of the synthesis method on the properties of Zn₁₋ₓFeₓO nanoparticles with different Fe doping levels (x = 0, 0.01, 0.03, and 0.05) for Congo Red (CR) adsorption was investigated. Nanoparticles were prepared by sol-gel and coprecipitation, and characterized using XRD, SEM, and FTIR. Sol-gel synthesis produced smaller (~13 nm) particles, exhibiting high CR adsorption efficiency (~90%) at 10 ppm and room temperature. In contrast, coprecipitation generated larger (~35 nm) nanostructures, with lower adsorption capacity (~24%). Both the synthesis method and calcination temperature significantly influenced the nanocrystallite size. Fe doping enhanced adsorption in all cases, particularly by maintaining high adsorption percentages at elevated temperatures. Fe³⁺ incorporation into ZnO nanoparticles modifies the crystal structure, possibly creating defects and vacancies that serve as preferential adsorption sites for anionic dyes. Efficient removal of organic dyes such as Congo Red is critical due to their toxicity and environmental persistence in industrial wastewater. These findings suggest that careful selection of synthesis parameters can yield highly effective adsorbents, providing a promising strategy for environmental remediation and sustainable water treatment applications.