Microwave enhanced sorption of methylene blue dye onto bio-synthesized iron oxide nanoparticles: kinetics, isotherms, and thermodynamics studies.

To adequately address the grave human health risks and environmental damage caused by the uncontrolled utilization of organic dyes, we greenly synthesized iron oxide nanoparticles (IONPs) using micro-algae for sequestration of cationic methylene blue (MB) dye from an aqueous solution. The nano-engineered sorbent was thoroughly scrutinized by different spectral analyses of; FT-IR, SEM, EDX, BET surface area, TEM, VSM, UV/Vis spectroscopy, and PH measurement. The adsorption of MB was methodically carried out in a batch process to investigate the effects of initial pH (2.2-10.4), adsorbent concentration (0.5-5.0 g L), initial dye concentration (10-1000 mg L), contact time (0-230 min), and adsorption temperature (298 K, 308 K, 318 K, and 328 K). The outlined results inferred that the maximum adsorption capacity of MB dye by IONPs (surface area of 134.003 m/g, a total pore volume of 0.3715 cc/g, and average pore size of 5.54 nm) was 312.5 mg g under the optimized pH value (i.e., pH = 10.4). Collectively, the adsorption kinetics profile showed that the experimental data were in good agreement with the PSORE model, and the equilibrium adsorption isotherm data were quantitatively dominated by the Langmuir model. The thermodynamic findings conformed to the endothermic nature of the adsorption process. Interestingly, the proposed microwave scenario enhanced the adsorption rate and the equilibrium was attained in a very short time (only 1 min), compared with the normal sorption conditions (∼70 min). Repeatability of the spent sorbent was successfully emphasized for 5 times of adsorption/desorption cycles using 0.5 M of HCl. The productive adsorbent admirably sequestered MB dye from spiked real specimens (>83%). These results demonstrated that IONPs can be considered as a cost-efficient adsorbent in practical applications such as wastewater purification.