In a review recently published in the open access journal EnergiesResearchers discussed recent advances in the development of metallic organostructure (MOF)-derived adsorbents and their usefulness for the removal of dyes from the aquatic environment.
Study: Recent advances in MOF-based adsorbents for the removal of dyes from the aquatic environment. Image Credit: Kanghophoto/Shutterstock.com
Water is the most important element for life on the planet. Pollution and water scarcity are major environmental problems all over the world. Dyes are one of the most dangerous pollutants in water resources. Therefore, wastewater contaminated with dyes must be treated before being discharged into the environment.
For the treatment of dyeing wastewater, adsorption technology has been presented as a popular, inexpensive, efficient, simple and fast solution. Finding new adsorbents or modifying current adsorbents to achieve better adsorption conditions and higher adsorption capacity has long been a priority in this field. For dye removal applications, MOFs have been touted as high performance adsorbents.
MOFs have outstanding characteristics that can improve separation performance over current commercial adsorbents, and thus these materials represent a significant advance in improving dye removal from water treatment systems.
About the study
In the present study, the authors discussed recent advances made in customizing MOF structures for dye removal from the aquatic environment. This review presents the synthetic methodologies used to improve the efficiency of adsorption, as well as the main adsorption mechanisms and the most important parameters in the removal of dyes by adsorption using MOFs. Improved separation performance of MOF-based adsorbents has also been described.
The team determined the impact of adding different functional groups and nanomaterials to MOFs, such as amine functional groups, carbon-based materials, and magnetic nanoparticles like CNT and graphene oxide, on the dispersion in water, water stability, interactions between contaminant and MOF structure, and adsorption capacity. The problems faced by MOF-based materials when it comes to removing dyes from water, as well as potential future research directions were also discussed.
The properties of optimized and bare MOFs in the removal of dyes by adsorption were illustrated, and the properties and performance of MOFs as adsorbents, as well as recent advances in the removal of dyes from aquatic environments at the frameworks using zeolitic imidazolate (ZIF), zirconium-based MOFs, amine-functionalized MOFs, magnetic MOFs, and nanocomposites of carbon nanotubes (CNTs)-MOFs and graphene oxide (GO) -MOFs have been demonstrated. Additionally, the effects of pH, adsorbent dose, contact time, and initial dye concentration on dye removal using MOFs were explored.
The maximum adsorption capacities of methylene blue (MB), basic blue (BB) 41 and BB46 were 862, 1257 and 1296 mg/g, respectively. The equilibrium adsorption capacity (qand) of MB per Fe3O4@MIL-100(Fe) increased from 28 mg/g to 42 mg/g when pH was increased from 2 to 9.
For AO7 adsorption, the highest capacity found for UiO-66, NH2-UiO-66, CNT/UiO-66 and GO/UiO-66, respectively, were 42.6, 55, 80.6 and 66.198 mg/g. For AY17 adsorption, the highest capacity obtained for UiO-66, NH2-UiO-66, CNT/UiO-66 and GO/UiO-66, respectively, were 22.3, 81.8, 86.4 and 63.2 mg/g, respectively. Addition of 5% (w/w) GO to MOF increased the adsorption capacity from 1019 mg/g to 1231 mg/g for MB and from 667 to 1189 mg/g for methyl orange (MO) .
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Due to the increase in active adsorption sites, the removal efficiency of MB and malachite green (MG) was increased by 94.6% and 93.8%, respectively, when the dose of adsorbent was increased. MB removal efficiency using UiO-66 increased from 30% to 70% when the initial dose of UiO-66 was increased from 0.1 to 0.5 g/L. When the dose of MIL-100(Fe) was increased from 1 to 50 mg, the adsorption percentage of methyl blue and MB was increased by 65-80% and 75-99%, respectively.
MOF-based absorbents have been used to remove dyes such as Methyl Orange, MB, Acid Orange 7, Congo Red, MG, Acid Red 1, Acid Chromium Blue K, methyl, orange G, BB 41, neutral red, rhodamine B, safranin T, eosin, basic fuchsin, acid fuchsin, alizarin red S, xylene orange, reactive black 5, etc.
In conclusion, this review found that the most studied structures in dye removal applications are Institut Lavoisier (MIL)-type MOF structures with customizable features for selective adsorption, zirconium-based MOFs with a exceptional stability in acidic and aqueous acidic conditions, and ZIF structures. with large adsorption capacity and large surface area.
Amine-functionalized MOF structures can enhance electrostatic interactions and hydrogen bonds between adsorbent structure and dye molecules to increase adsorption capacity. The use of graphene-MOF composites could enhance electrostatic and π-π interactions, which can increase adsorption capacity. The authors pointed out that due to their sandwich-like architectures and the inclusion of graphene in the structure, these composites have high thermal stability.
Beydaghdari, M., Saboor, FH, Babapoor, A., et al. Recent advances in MOF-based adsorbents for the removal of dyes from the aquatic environment. Energies 15(6), 2023 (2022). https://www.mdpi.com/1996-1073/15/6/2023