Influence of fuel nature on dye adsorption efficiency of solution combustion derived zinc oxide nanoparticles: A comparative study

The present work demonstrates the use of coffee husk extract as a fuel (otherwise an agro waste) for the synthesis of nano zinc oxide (ZnO) by one step solution combustion synthesis. We also show the comparative studies of coffee husk extract (green fuel) derived nano ZnO (CHZnO) and sugar (chemical fuel) derived nano ZnO (SZnO) as an adsorbent for Congo red dye removal. Synthesized ZnO nanoparticles were characterized using XRD, SEM, TEM, FTIR, and BET. The adsorption characteristics were investigated with respect to changes in pH, temperature, initial dye concentration, adsorbent dose and contact time. CHZnO exhibited higher adsorption capacity (76 mg g⁻¹) compared to SZnO (56 mg g⁻¹). The equilibrium adsorption data were analyzed using various isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevith) and thermodynamic parameters. Among the models studied, Langmuir isotherm fitted well with experimental equilibrium data (R² > 0.99). Adsorption kinetics was found to follow pseudo-second order with the highest R² value. Intraparticle or pore diffusion was the major rate controlling step in the adsorption process. The present study demonstrates the potential application of agro-based bio-waste as a novel fuel in the synthesis of nanomaterials for use as efficient adsorbents in water treatment. (paper)