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.
Reinforcement of natural rubber (NR) using nanofillers often results in an enhancement of the tensile strength, but at the expense of elongation at break and toughness. In this study, with the objective of strengthening NR without compromising its compliance, we investigate the reinforcement efficiency of a series of cellulose nanofibers (CNF) with variations in residual hemicellulose, lignin and therefore surface chemistry. Different types of high aspect ratio CNF isolated from Triodia pungens (T. pungens), an Australian arid grass commonly known as spinifex, were added at 0.1-2 wt% loadings into a pre-vulcanized NR latex. CNF/NR nanocomposites then were benchmarked against NR nanocomposites incorporating a well-known wood-derived CNF. It was found that the presence of residual lignin and hemicellulose, and the pretreatment with a deep eutectic solvent, a mixture of choline chloride and urea (CCU), could increase the compatibility of CNF with the NR matrix, while still enabling stability and handling of the colloidal latex mixture. Incorporation of 0.5 and 0.1 wt% of the sodium hydroxide treated CNF and choline chloride/urea treated CNF into the NR latex showed respectively 11 and 17% enhancement in tensile stress, and importantly without compromising viscoelastic properties; while addition of 0.1 wt% wood-derived CNF resulted in 18% decrease in both tensile stress and strain coupled with more pronounced latex stiffening.
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