Nanocellulose-Based Hollow Fibers for Advanced Water and Moisture Management

Natural plant fibers such as cotton have favorable performance in water and moisture management; however, they suffer from inferior processing ability due to limited diameter and length, as well as natural defects. Although commercially available regenerated cellulose fibers such as lyocell fibers can have tunable structures, they rely on the complete dissolution of cellulose molecules, including the highly crystalline parts, leading to inferior mechanical properties. Through a specially designed coaxial wet-spinning process, we prepare a type of hollow fiber using only cellulose nanofibrils (CNFs) as building blocks. It mimics cotton fibers with a lumen structure but with a tunable diameter and a long length. Moreover, such hollow fibers have superior mechanical properties with a Young’s modulus of 24.7 GPa and tensile strength of 341 MPa, surpassing lyocell fibers and most wet-spun CNF-based fibers. Importantly, they have 10 times higher wicking ability, wetting rate, drying rate, and maximum wetting ratio compared to lyocell fibers. Together with a superior long-term performance after 500 rounds of wetting–drying tests, such CNF-based hollow fibers are sustainable choices for advanced textile applications. And this study provides a greater understanding of nanoscale building blocks and their assembled macromaterials, which may help to reveal the magic hierarchical design of natural materials, in this case, plant fibers

High Thermoelectric Performance in Crystallographically Textured n‑Type Bi₂Te_3–<i>x</i>Se_<i>x</i> Produced from Asymmetric Colloidal Nanocrystals

In the present work, we demonstrate crystallographically textured n-type Bi₂Te_3–<i>x</i>Se_<i>x</i> nanomaterials with exceptional thermoelectric figures of merit produced by consolidating disk-shaped Bi₂Te_3–<i>x</i>Se_<i>x</i> colloidal nanocrystals (NCs). Crystallographic texture was achieved by hot pressing the asymmetric NCs in the presence of an excess of tellurium. During the hot press, tellurium acted both as lubricant to facilitate the rotation of NCs lying close to normal to the pressure axis and as solvent to dissolve the NCs approximately aligned with the pressing direction, which afterward recrystallize with a preferential orientation. NC-based Bi₂Te_3–<i>x</i>Se_<i>x</i> nanomaterials showed very high electrical conductivities associated with large charge carrier concentrations, <i>n</i>. We hypothesize that such large <i>n</i> resulted from the presence of an excess of tellurium during processing, which introduced a high density of donor Te_Bi antisites. Additionally, the presence in between grains of traces of elemental Te, a narrow band gap semiconductor with a work function well below Bi₂Te_3–<i>x</i>Se_<i>x</i>, might further contribute to increase <i>n</i> through spillover of electrons, while at the same time blocking phonon propagation and hole transport through the nanomaterial. NC-based Bi₂Te_3–<i>x</i>Se_<i>x</i> nanomaterials were characterized by very low thermal conductivities in the pressing direction, which resulted in <i>ZT</i> values up to 1.31 at 438 K in this direction. This corresponds to a <i>ca</i>. 40% <i>ZT</i> enhancement from commercial ingots. Additionally, high <i>ZT</i> values were extended over wider temperature ranges due to reduced bipolar contribution to the Seebeck coefficient and the thermal conductivity. Average <i>ZT</i> values up to 1.15 over a wide temperature range, 320 to 500 K, were measured, which corresponds to a <i>ca</i>. 50% increase over commercial materials in the same temperature range. Contrary to most previous works, highest <i>ZT</i> values were obtained in the pressing direction, corresponding to the <i>c</i> crystallographic axis, due to the predominance of the thermal conductivity reduction over the electrical conductivity difference when comparing the two crystal directions

Thermoelectric Performance of Surface-Engineered Cu_{1.5–<i>x</i>}Te–Cu₂Se Nanocomposites

Cu2–xS and Cu2–xSe have recently been reported as promising thermoelectric (TE) materials for medium-temperature applications. In contrast, Cu2–xTe, another member of the copper chalcogenide family, typically exhibits low Seebeck coefficients that limit its potential to achieve a superior thermoelectric figure of merit, zT, particularly in the low-temperature range where this material could be effective. To address this, we investigated the TE performance of Cu1.5–xTe–Cu2Se nanocomposites by consolidating surface-engineered Cu1.5Te nanocrystals. This surface engineering strategy allows for precise adjustment of Cu/Te ratios and results in a reversible phase transition at around 600 K in Cu1.5–xTe–Cu2Se nanocomposites, as systematically confirmed by in situ high-temperature X-ray diffraction combined with differential scanning calorimetry analysis. The phase transition leads to a conversion from metallic-like to semiconducting-like TE properties. Additionally, a layer of Cu2Se generated around Cu1.5–xTe nanoparticles effectively inhibits Cu1.5–xTe grain growth, minimizing thermal conductivity and decreasing hole concentration. These properties indicate that copper telluride based compounds have a promising thermoelectric potential, translated into a high dimensionless zT of 1.3 at 560 K