Abstract:
Water pollution caused by toxic dyes from the textile industry has become a major concern
nowadays. Specifically, rhodamine B (RhB) dyes found in textile wastewater have harmful and
toxic impacts on the surroundings and human health. To address these problems, photocatalytic
wastewater treatment using metal-organic frameworks (MOFs) and MOF-on-MOF
heterojunctions has emerged as a promising and dynamic research area. This is due to the
unthinkable properties of MOFs. However, pristine MOFs often have low photocatalytic
efficiency due to their wide band gaps and high electron-hole recombination rates, which limits
their practical application. Coupling two different MOFs into MOF-on-MOF heterojunctions
can help overcome these limitations. The heterojunction structure facilitates precise charge
transfer interfaces, thereby increasing the photocatalytic activity of the MOFs. Additionally, the
heterojunction can preserve the porous framework of the MOF materials, supporting both
adsorption and photocatalytic behaviors. This study describes the sustainable synthesis of
pristine MIL-100(Fe) and NH2-MIL-53(Al) MOFs, as well as the NH2-MIL-53(Al)/MIL-100(Fe)
heterojunctions. Characterization techniques such as X-ray diffraction (XRD), Fourier transform
infrared (FT-IR) spectroscopy, Scanning electron microscopy (SEM), DRS-UV-vis spectroscopy
(DRS-UV-vis) and so on were used to confirm the successful synthesis of the materials under
environmentally friendly, energy-efficient, and economical (3E) conditions. The formation of the
NH2-MIL-53(Al)/MIL-100(Fe) heterojunctions significantly enhanced the photo-responsive
range and charge separation efficiency, leading to improved photocatalytic activity in the
degradation of RhB dye. Under visible light irradiation, the NH2-MIL-53(Al)/MIL-100(Fe)-1wt%
catalyst showed the highest performance, achieving 95.28% degradation efficiency within 140
minutes, outperforming the individual components. The active site trapping study revealed that
superoxide radicals (•O2
-
) and holes (h+
) play crucial roles in the photodegradation of RhB.
Moreover, the selected photocatalyst revealed remarkable recyclability, retaining a high
photocatalytic degradation efficency of 83.0% even after four cycles of activity.
