Multifaceted Applications of Nanocellulose-based Materials for Water Remediation

During the last decades, water pollution has become a severe environmental and health crisis in many countries due to rapid industrialization and urbanization, attracting increasing attention worldwide. As one of the most common sources of natural polymers, wood-derived materials have caused much attention in water treatment for attributes such as enewability, abundance, non-toxicity, environmentally friendly, and accessibility for derivatization. Therefore, this thesis aimed to develop functional wood-derived materials for wastewater treatment, which is of great significance for both the environment and future biorefinery concepts.

In this thesis, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) - oxidized cellulose nanofibers (CNFs) were prepared. Then the CNFs were used to fabricate composite aerogel by combining with poly(ethylene imine) (PEI) and silver nanoparticles (Ag NPs). The obtained aerogel with a microporous structure presented excellent catalytic discoloration properties towards organic dyes. Notably, the catalytic activity was very stable, and the discoloration efficiency remained over 98% after 10 times cycles, and the water transportation could reach 5×104 L m−2 h−1. In addition, the composites also exhibited rapid water-activated shape memory, and the structure kept its integrity over an extended period of time.

Then the TEMPO-CNFs were also used to prepare porous and ultralight aerogel with PEI via physical and chemical cross-linking with epichlorohydrin (ECH). The results revealed that the dual cross-linked composite aerogel exhibited superior water resistance in different water environments, fast water-activated shape memory, and rapid water transportation. Most impressively, the CNF/PEI aerogel with a weight ratio at 1:2 showed excellent performance for removing methyl orange (MO) in batch (1226 mg g−1, pH 6). Moreover, the aerogel presented outstanding selective separation performance.

Furthermore, we firstly produced a novel type of nanocellulose through exfoliation of amidoximated cellulose nanofibers (AO-CNF) from commercial softwood pulp. Both morphology and the abundant active adsorption sites endow excellent performance for extracting uranium ions. The obtained AO-CNF exhibited excellent uranium uptake in batch (1327 mg g−1) at pH 8. Moreover, AO-CNF can also be used to construct nanofibrous membranes via vacuum filtration. In the case of a 2.5 μm thick membrane it could afford an ultra-high flux of ~48 L m−2 h−1 with high treatment efficiency (99.9%).

Lastly, natural wood was directly used to fabricate highly mesoporous wood aerogels through cyanoethylation and amidoximation. The obtained amidoximated wood (AO-wood) exhibited excellent mechanical performance and high surface area. The adsorption capacity towards uranium was high over a wide pH value, and the highest uptake ability was as high as 1375 mg g−1. More importantly, the AO-wood's unique structure can make it a filter to remove uranium ions efficiently by filtration.

Therefore, the studied wood-derived functional materials exhibit great potential for wastewater treatment.