Microscopic Hybrid Membranes Made of Cellulose-Based Materials Tuned for Removing Metal Ions from Industrial Effluents

Most of the polymeric membranes used today in water decentralization are synthesized through complicated and expensive processes, contain unrenewable petrochemical building blocks, and are characterized by untailored surfaces. Besides their significant drawbacks, they do not comply with environmental requirements and regulations and thus should be replaced with more eco-friendly products. The urgent need is to create robust and tunable nano/micro materials for confidently designing efficient and selective polymeric water filters with guaranteed sustainability and biodegradability. Active hybrid membranes made of eco-friendly high-grade microfibrillated cellulose (MFC), appropriately functionalized, have shown superior performance during the separation of metal ions from the industrial effluents, and their separation efficiency has been found to be tunable with a proper selection of type and density of the functional groups. On the basis of these findings and needs, we have developed a chemo-enzymatic functionalization strategy for grafting methyl and phosphate groups on the MFC fibers. This methodology can calibrate the interlayer fiber spacing and control the pore-size distribution of the membranes appropriately. We demonstrate this in the present work by characterizing the impact of Mg2+ and Cr3+ ions and their mixture (Mg2+ and Cr3+) on the membrane separation performance extensively by using various experimental techniques and computational methods. Moreover, we have adapted this sustainable, fully water-based system for upscaling the hybrid membranes in continuous mode by resorting to the phosphate-MFC membranes for the spiral-bound modules in cartridge use. We have developed the flow-through (FTM) and flow-over (FOM) modules and tested them to separate metal ions from the industrial effluent, ensuring regeneration and reusability. Our results indicate that these prototype hybrid MFC membranes represent the most promising type of next-generation high-performance filtration devices for a more sustainable society.