We have recently demonstrated a revolutionary membrane design based on hierarchical assembly of fibrous materials with different fiber diameters (nm to μm). This design has led to breakthrough filtration performance from microfiltration to reverse osmosis, i.e., high flux, low energy and small system footprint. The key components of this technology are electrospun nanofibers (dia. ~100 nm) and carboxylate cellulose nanofibrils (dia. ~5 nm) extracted from biomass using a combined TEMPO-oxidation/defibrillation method. These nanofibers have large surface-to-volume ratio and high capacity for surface modification/charge, making them ideal materials for fabrication of highly permeable separation media, e.g., microfiltration filter that can simultaneously remove bacteria, viruses and toxic metal ions at gravity pressure. We further discovered that a simple two-chemical process can produce carboxylate nanocelluloses of different dimensions fusing biomass from different source. This ‘green’ method can bypass both electrospinning and conventional nanocellulose fabrication steps (extraction/pretreatment, bleaching and TEMPO oxidation) and generate inexpensive new nanostructured materials for water purification in a very sustainable manner.