Nanocellulose from Spinifex as an Effective Adsorbent to Remove Cadmium(II) from Water

Abstract

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.

Cross‐Linked Nanocellulosic Materials and Their Applications

“…Moreover, heavy metal ions behaved as an effective cross‐linking agent to bind negatively charged NC particles by ionic interactions in aqueous media. At high concentrations, the adsorption was dominated by the mineralization of heavy metal hydroxide crystals within the NC scaffold . The interactions between NC and metal ions can be elucidated by visual examination.…”

“…The adsorption capacity also significantly depends on the pH of the aqueous solution which affects both the speciation of metal ions and the surface charge of the adsorbent. High adsorption of Cr VI was observed at acidic pH of 1–3, however, the highest adsorption of Pb II , Cu II , Cd II , and Hg II appeared around neutral pH, while carboxylic groups are difficult to dissociate at a lower pH value . This might be ascribed to different adsorption steps for various metal ions .…”

“…Nanoscale materials have shown great potential for wastewater treatment as higher specific surface areas result in higher adsorption capacities compared to the same materials in their micro‐ or macro‐ structural scales . Negatively charged NC particles can bind heavy metal ions by ionic interactions in aqueous media, which shows a sustainable and cost‐effective path to tackle heavy metal contamination in wastewater …”

“…[12] In addition, cross-linked NCs have been considered as candidates for removing heavy metal contaminants, such as copper, cadmium, lead, andm ercury,f rom wastewater due to their uniquep roperties. [23] Heavy metal contamination caused by discharge of industriale ffluents in water poses serious health and environmental hazards. Adsorption is considered as an effectivea nd relativelye conomical methodf or removing heavy metal ions from wastewater.…”

Surface modification for nano‐lignocellulose fiber through vapor‐phase‐assisted surface polymerization

“…The modification of hydrophilic surface on nanofibers to enhance the reinforcement effect has been reported in many works . Covalent grafting or physical adsorptions is among the commonly used methods to modify the surface of the nanofibers . Polymers can be covalently grafted onto nanofiber surfaces by means of various polymerization techniques .…”