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The broad utility of cellulose nanocrystals (CNCs) as green, vivid, and long-term photonic films is restricted by their coloration instability and limited gamut. Herein, four polyols, two monosaccharides, two organic acids, and four amino acids were doped into a CNC for a detailed structure and color hue investigation. The results show that polyols and saccharides bearing neural multihydroxyl groups promoted a doping-amount-dependent red-shift reflection. Polyols were also found to improve the flexibility of CNCs as effective plasticizers. Organic tartaric or malic acid showed effects on the overall blue shift although a switch from blue shift to red shift happened at a doping amount of 8 wt %. Nevertheless, amphoteric amino acids with multifunctional groups show limited regulating effects due to their poor compatibility and complicated interactions with CNCs. Therefore, acidic or alkaline functional groups, the isoelectric point, a compatible saccharide ring, the molecular weight, and crystallization of dopants are crucial factors for tuning the structure and properties of CNCs.

Highly surface-charged rigid bionanofibrils are difficult to be processed into integrated foams or aerogels owing to lack of good interfibrillar adhesion. An alternative solution is to involve flexible hydrophilic polymers for gluing fibril bundles, allowing a perfect alignment under ice induction in the lyophilized foams. In this work, we incorporated the defibrillated chitin/chitosan nanofibrils (CTF/CSF) into gelatinized starch foams and investigated the effects of surface charge, solid content, nanofibril loading, and directional orientation on the dimensional stability, morphology, crystallinity, compressive stress, and flame-retardant properties of lyophilized composite foams. Results show that CTF with low positive surface charges presents stable electroattractions to negatively charged starch and also exhibits sustainable reinforcement effects on the composite foam. What is more, compact, small porous, and lamellar CTF-supported foams exhibit relatively high resistance to flammable combustion. In the case of high loading of polycationic CSF, directional freeze-drying successfully induced the channel orientation along the vertical, horizontal, spiral, or bi/triphase junctional direction in the anisotropic foams, which revealed variable compression properties according to the fibril alignment.

A mechanical disintegration of waste wood biomass and freeze-induced assembly of colloidal nanowood were effectively deployed to explore ion-associated cellular foams (NWFs) with unidirectional channels. Under the assistance of inorganic ions, the as-fabricated foams were significantly enhanced in physical stability, compressive strength, flame retardancy, and thermal barrier, accounting for the tuning effects of pores and channels, surface charges, and microphase interaction by ion effects and freeze orientation. As a result, the vascular-like ion-doped channels benefited from quick capillary liquid transport. Under 1 sun illumination, NWF-V as a 3-D evaporator exhibited a high evaporation rate of 1.50 kg m −2 h −1 and a conversion efficiency of up to 88.9% for seawater desalination. Dramatically, an average of 12.5 kg m −2 of fresh water could be generated on each sunny day by outdoor NWFs for durability beyond 15 days. Under the drive of fuel combustion, an efficient conveying of ethanol or pump oil could be at rates of 0.44 and 0.26 mL min −1 , respectively. Moreover, combustion flame with variable color was generated according to the doping cations in NWFs. Therefore, sustainable, green, facile, and multifunctional wood-based cellular foams could be tailored, scaled-up, and applied as color flame burners or desalination evaporators under combustion or solar drive in the energy and environment fields.

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