Synthesis of Ionic Liquid-Assisted Nanoparticles: High Activity, Fast Removal for Photodegradation of Methylene Blue in Water

Abstract The discharge of dye residues from the textile industry is a major contributor to water pollution, highlighting the urgent need for effective wastewater treatment solutions. This study investigates the synthesis of ZnO and Bi₂O₃ nanoparticles using ionic liquid-assisted methods for enhanced photocatalytic degradation of methylene blue. Three ionic liquids were employed: 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]-BF₄), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]-PF₆), and 1-butyl-3-methylimidazolium chloride ([BMIM]-Cl). The synthesized nanoparticles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Results showed that ionic liquid incorporation led to improved crystallinity, uniform morphology, and reduced particle sizes. ZnO-[BMIM]-BF₄ (1%) and Bi₂O₃-[BMIM]-BF₄ (1%) exhibited the lowest band gap energies of 2.50 eV and 2.20 eV respectively, indicating enhanced light absorption. These catalysts also demonstrated superior photocatalytic activity, achieving complete degradation of methylene blue within 40 and 35 min under UV-B irradiation, and 60 min under sunlight. The enhanced performance was attributed to improved light absorption, reduced electron–hole recombination, and efficient charge transfer facilitated by the ionic liquids. The catalysts showed excellent stability over multiple degradation cycles. This study highlights the potential of ionic liquid-assisted synthesis in developing highly efficient and stable photocatalysts for environmental remediation applications. Graphical Abstract