A simple approach was developed to prepare carboxycellulose nanofibers directly from untreated biomass using nitric acid or nitric acid-sodium nitrite mixtures. Experiments indicated that this approach greatly reduced the need for multichemicals, and offered significant benefits in lowering the consumption of water and electric energy, when compared with conventional multiple-step processes at bench scale (e.g., TEMPO oxidation). Additionally, the effluent produced by this approach could be efficaciously neutralized using base to produce nitrogen-rich salts as fertilizers. TEM measurements of resulting nanofibers from different biomasses, possessed dimensions in the range of 190-370 and 4-5 nm, having PDI = 0.29-0.38. These nanofibers exhibited lower crystallinity than untreated jute fibers as determined by TEM diffraction, WAXD and C CPMAS NMR (e.g., WAXD crystallinity index was ∼35% for nanofibers vs 62% for jute). Nanofibers with low crystallinity were found to be effective for removal of heavy metal ions for drinking water purification.

Mechanistic behavior and flow properties of cellulose nanofibers (CNFs) in aqueous systems can be described by the crowding factor and the concept of contact points, which are functions of the aspect ratio and concentration of CNF in the suspension. In this study, CNFs with a range of aspect ratio and surface charge density (380–1360 μmol/g) were used to demonstrate this methodology. It was shown that the critical networking point of the CNF suspension, determined by rheological measurements, was consistent with the gel crowding factor, which was 16. Correlated to the crowding factor, both viscosity and modulus of the systems were found to decrease by increasing the charge density of CNF, which also affected the flocculation behavior. Interestingly, an anomalous rheological behavior was observed near the overlap concentration (0.05 wt %) of CNF, at which the crowding factor was below the gel crowding factor, and the storage modulus (G′) decreased dramatically at a given frequency threshold. This behavior is discussed in relation to the breakup of the entangled flocs and network in the suspension. The analysis of the mechanistic behavior of CNF aqueous suspensions by the crowding factor provides useful insight for fabricating high-performance nanocellulose-based materials.

Membrane technology remains the most energy‐efficient process for removing contaminants (micrometer‐size particles to angstrom‐size hydrated ions) from water. However, the current membrane technology, involving relatively expensive synthetic materials, is often nonsustainable for the poorest communities in the society. In this article, perspectives are provided on the emerging nanocellulose‐enabled membrane technology based on nanoscale cellulose fibers that can be extracted from almost any biomass. It is conceivable that nanocellulose membranes developed from inexpensive, abundant, and sustainable resources (such as agriculture residues and underutilized biomass waste) can lower the cost of membrane separation, as these membranes offer the ability to remove a range of pollutants in one step, via size exclusion and/or adsorption. The nanocellulose‐enabled membrane technology not only may be suitable for tackling global drinking water challenges, but it can also provide a new low‐cost platform for various pressure‐driven filtration techniques, such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Some relevant parameters that can control the filtration performance of nanocellulose‐enabled membranes are comprehensively discussed. A short review of the current state of development for nanocellulose membranes is also provided.

Nanocelluloses, in the form of carboxycellulose nanofibers, with low crystallinity (CI ∼ 50%), high surface charge (−68 mV), and hydrophilicity (static contact angle 38°), were prepared from an untreated (raw) Australian spinifex grass using a nitro-oxidation method employing nitric acid and sodium nitrite. The resulting nanofibers (NOCNF) were found to be an effective medium to remove Cd2+ ions (cadmium­(II)) from water. For example, a low concentration of NOCNF suspension (0.20 wt %) could remove Cd2+ ions over a large concentration range (50–5000 ppm) in a relatively short time period (≤5 min). The results showed that at low Cd2+ concentrations (below 500 ppm), the remediation mechanism was dominated by interactions between carboxylate groups on the NOCNF surface and Cd2+ ions, which also acted as a cross-linking agent to gel the NOCNF suspension. At high Cd2+ concentrations (above 1000 ppm), the remediation mechanism was dominated by the mineralization process of forming Cd­(OH)2 nanocrystals, which was verified by TEM and WAXD. Based on the Langmuir isotherm model, the maximum Cd2+ removal capacity of NOCNF was around 2550 mg/g, significantly higher than those of any adsorbents reported in the literature. NOCNF exhibited the highest removal efficiency of 84%, when the Cd2+ concentration was 250 ppm. This study demonstrated a simple pathway to convert underutilized biomass into valuable absorbent nanomaterials that can effectively remove cadmium­(II) ions from water.

Carboxycellulose nanofibers (NOCNF) were extracted from untreated jute fibers using a simple nitro-oxidation method, employing nitric acid and sodium nitrite. The resulting NOCNF possessed high surface charge (−70 mV) and large carboxylate content (1.15 mmol/g), allowing them to be used as an effective medium to remove UO2 2+ ions from water. The UO2 2+ (or U­(VI)) removal mechanism was found to include two stages: the initial stage of ionic adsorption on the NOCNF surface following by the later stage of uranyl hydroxide mineralization, as evidenced by the Fourier transform infrared, scanning electron microscopy with energy dispersive spectroscopy capabilities, transmission electron miscroscopy, and wide-angle X-ray diffraction results. Using the Langmuir isotherm model, the extracted NOCNF exhibited a very high maximum adsorption capacity (1470 mg/g), about several times higher than the most efficient adsorbent reported (poly­(acrylic acid) hydrogel). It was also found that the remediation of UO2 2+ ions by NOCNF was pH dependent and possessed the maximum adsorption at pH = 7. The removal efficiency of NOCNF was between 80 and 87% when the UO2 2+ concentration was below 1000 ppm, while it decreased to 60% when the UO2 2+ concentration was around 1250 ppm.

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Regenerated microfibrillated cellulose (R-MFC) fibers were prepared successfully by a combined dissolution and regeneration approach using phosphoric acid/ethanol treatment on jute cellulose. The prepared R-MFC fibers possessed high surface area (10.74 m2/g), good aspect ratio (L/D = 30), and excellent thermal stability (T max = 352 °C). In addition, the fibers exhibited 3.84 wt % of phosphate groups (PO4 2–) with a ζ-potential of −8.4 mV and low crystallinity index (CI) of 47.5%. These R-MFC fibers were in the cellulose II polymorph, confirmed by 13C CPMAS NMR and WAXD measurements, and they were effective to anchor the growth of ZnO nanocrystals. WAXD and TEM examinations on the imbedded ZnO nanocrystals indicated that they possessed the hexagonal wurtzite crystal structure and could assemble into a flower-like morphology in the R-MFC scaffold. A R-MFC composite containing 41 wt % of ZnO nanocrystals was found to be very efficient to remove arsenic (As­(V)) ions from water with the maximum capacity of 4,421 mg/g at neutral pH (7), based on the Langmuir isotherm analysis. The binding stability study between ZnO nanocrystals and R-MFC confirmed that the composite scaffold only had negligible release of ZnO at neutral pH, indicating the viability of this system for practical water purification applications. This is the first study on preparation of R-MFC from nonwood cellulose (jute), while most of the earlier studies were on microcrystalline wood-based cellulose.