Rice Straw-Derived Cellulose Nanocrystal-based Adsorptive Filtration Nanocomposite Membranes for Efficient Removal of Methylene Blue

Abstract

Industrial wastewater, particularly from textile, paper, and dye industries, often contains methylene blue (MB), a hazardous synthetic dye and causes health hazards. Cellulose nanocrystals (CNCs), especially when modified with polydopamine (PDA), offer a sustainable and efficient adsorbent due to their high surface area, abundant functional groups, and natural availability. Furthermore, their ordered self-assembled structure can create a porous and tortuous path in the composite membranes, desirable for efficient filtration. Herein, PDA-modified rice straw-derived cellulose nanocrystals (RSDCNCs)-based biocompatible adsorption filtration nanocomposite membranes were fabricated to efficiently remove MB dye from water. A certain feed ratio of polyvinyl alcohol (PVA) as a binder and glutaraldehyde (GA) as a crosslinker were added with RSDCNC and the mixture was deposited onto a Whatman filter paper substrate via vacuum filtration to fabricate the adsorptive membranes. The addition of a binder and a crosslinker in a requisite ratio enhanced the flexibility and strength of the membranes and provided mechanical stability against filtration. The as-prepared adsorptive filtration membranes having an optimized adsorbent area density of 1.44 mg.cm-² have demonstrated higher removal efficiency, repeatability, and reusability for the treatment of MB contaminated water. Reusability analysis using 20 mL of initial 10 ppm dye solution showed that the PVA/RSDCNC-50-50 membrane displayed the highest removal efficiency up to the 5th cycle of filtration. The removal efficiency of 99.6, 99.3, 98.3, 97.7, and 89.0% were obtained after 1st, 2nd, 3rd, 4th, and 5th filtration cycle, respectively, with MB removal time 8-15 min per filtration cycle. Furthermore, the optimized PVA/RSDCNC-50-50 membranes exhibited an MB dye removal efficiency of approximately 94% at 50 ppm and 69% at 100 ppm initial dye concentrations. The catechol groups, imine and amine functionality, and aromatic moieties of PDA, porous morphology of the modified substrate, and abundant surface hydroxyl groups and the tortuosity created by CNCs in the membrane are responsible factors for the efficient dye removal. Therefore, all these features and properties make the bio-based PVA/RSDCNC adsorptive filtration membrane a potential material for diversified dye contaminated wastewater remediation, heavy metal ions, and oil-water separation.