TEMPO-oxidized and carbon dots bound cellulosic nanostructured composite for sustainable fully biobased membranes for separation of nano/micro-sized particles/molecules

Abstract

Membrane separation is a highly energy-efficient method for eliminating pollutants, ranging from micrometer-sized particles to angstrom-sized hydrated ions, from water. Nevertheless, the existing membrane technology, which uses costly synthetic materials, has become unsustainable for the most impoverished populations in the society. Thus, in the present study, a fully biobased sustainable functional membrane was developed for the effective separation of impurities from wastewater. A 2,2,6,6-Tetramethylpiperidin-1-oxyl (TEMPO) oxidation and integration of carbon dots (CDs) to cellulose nanofiber (CNF), resulted in significant improvements in the functional properties of membranes. The effectiveness of this modification resulted in a remarkable augmentation in surface ζ-potential as –68.5 mV for pristine CNF to −102 mV for CDs blended CNF. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies confirmed the existence of essential functional groups that enabled better interactions within the composite membranes. The functionalization of CNF membranes resulted slightly lower in water flux from 1536 L/m²/h for pristine membranes and 1089 L/m²/h for TEMPOoxidized and 1402 L/m²/h for CDs integrated membranes. This hypothesis further confirmed that the tuned membranes were denser with a decreased pore size of 19.96 Å for pristine and 17.49 Å for TEMPO functionalized CNF membranes. We demonstrated that functionalized cellulose nanofiber membranes have high filtration efficiency for heavy metals (Fe³⁺, Cu²⁺), dyes (methylene blue and dyes from garment industry wastewater), and protein (bovine serum albumin). Moreover, such biobased composite membranes can be reused, thereby exerting a significant influence on the circular economy.