Metal-Organic Frameworks (MOFs) Incorporated Polymeric Membranes for the Removal of Hazardous Materials from Wastewater

Abstract

Rapid industrial development, urbanization, and population growth have given rise to an immense responsibility to address increasing water scarcity and environmental pollution issues. Currently, the volume of textile wastewater discharged into the aquatic environment is rising enormously. The purification of harmful textile dyeing wastewater has unveiled several challenges since it comprises a complex mixture, counting dyestuff, additives, microplastics, salts, etc. Moreover, these large quantities of textile wastewater with colored chemicals are non-biodegradable and highly harm humans and creatures living in aqueous environments. Therefore, it is essential to remove the contaminants from textile wastewater. Many conventional techniques, including adsorption, advanced oxidation processing, distillation, flocculation, and membrane separation, have been extensively used for textile wastewater treatment. Recently, membrane separation has attracted extensive interest for wastewater treatment owing to its excellent benefits of low energy consumption yet higher separation efficiency combined with a convenient operating procedure. Several membrane separation techniques were established, such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Specifically, nanofiltration (NF) technologies offer the highest potential as the most potent candidate for separating organic molecules and inorganic salts. However, developing an innovative NF membrane capable of rejecting almost 100 % of contaminants with high water flux is highly desirable. Numerous studies have focused on fabricating novel composite NF membranes composed of nanofillers and a polymer matrix for selective contaminant removal from wastewater. More recently, synthetic and natural polymers have become the dominant raw materials for fabricating separation membranes. However, polymeric membranes facing several disadvantages, including lack of hydrophilicity, low anti-fouling ability, limited mechanical stability, and insufficient chemical stability. Therefore, they significantly restrict their use in wide-reaching applications. Membrane modification is a superior technique to overcome these obstacles. Incorporating novel nanomaterials into polymers has impressively contributed to developing renewable composite membranes for wastewater treatment. Metal-organic frameworks (MOFs) have been widely utilized as novel candidates to fabricate futuristic composite membranes due to their high porosity, superior surface area, tunable pore structure, suitable polymers affinity, an abundance of functional groups, and high adsorption capacity. Consequently, in this work, the fabricated PES/MOF-5 membrane was primarily studied to remove hazardous indigo carmine (IC) and methylene blue (MB) dyes. MOF-5 incorporation enhances the permeability and hydrophilicity of the PES membrane with the values of pure water flux (PWF) of 20.5 to 77.1 L/m2 h and contact angle of 73.1 to 60.3°, respectively, even though PES/MOF-5 membrane sustained 97% and 89% rejection of MB and IC, respectively. Likewise, an Eco-friendly MOF membrane was fabricated with hazardous free MOFs (MIL-100 (Fe)) incorporated into the chitosan (CS) biopolymer. MIL-100 (Fe) incorporation enhances the CS membrane properties, including pore size, surface charge, structural morphology, and hydrophilicity. The CS/MIL-100 (Fe) membrane exhibited the improved pure water flux from 5 to 52 L/m2 h and 99% rejection of cationic methylene blue and anionic methyl orange. The CS/MIL-100 (Fe) membrane rejects the salts in the following trend of MgSO4 (Rreal - 67% and Ractual - 64.2%) > Na2SO4 (Rreal - 59.4% and Ractual - 58.1%) > CaCl2 (Rreal - 49.1% and Ractual - 48.3%) > NaCl (Rreal - 32.6% and Ractual - 32.1%). The CS/MIL-100 (Fe) membrane exhibited excellent rejection and anti-fouling performances with outstanding recycling stability. Moreover, the removal of harmful dye adsorbed microplastics (MPs) was studied by the PSF/MIL-100 (Fe) membrane. Compared to the pristine PSF membrane (M0), incorporation of the hydrophilic MIL-100 (Fe) nanoparticles significantly modified the morphology, hydrophilicity (water contact angle reduced to 63.2º ±1.2 from 83.6º ±1), porosity, and pore size. Incorporating a 0.5 wt% loading of MIL-100 (Fe) particles into the PSF matrix (M0.5) was initiated to deliver the highest performance relative to the membranes with other loadings. M0.5 membrane includes superior pure water flux (10.3 times higher than M0) with a high methylene blue (MB) rejection rate of more than 99% and excellent anti-fouling properties of MB dye, microplastics (MPs)+MB dye feed solutions. Besides, the M0.5 membrane was sustained with outstanding performances at various concentrations of MB dye, MPs, and a range of transmembrane pressures (TMPs). Furthermore, the membrane exhibited good salt rejection capability and reusability for as many as six cycles of MB dye rejection without compromising the permeability and anti-fouling performance. This study highlights MOFs incorporated polymeric composite membrane offers excellent potential for efficiently removing contaminants from the actual textile wastewater.