Sustainable Route for Molecularly Thin Cellulose Nanoribbons and Derived Nitrogen-Doped Carbon Electrocatalysts

Ultrathin cellulose nanoribbons were extracted from earth-abundant biomass using 2,2,6,6-tetramethylpiperidine-1-oxyl-catalyzed (TEMPO-catalyzed) oxidation and sonication processes. By two TEMPO-oxide systems with different processing times, TEM and AFM observations indicate the obtained cellulose nanoribbons (Cel-NRs) with dimensions of 400–800 nm in length, 1.72–2.54 nm in width, and 0.78–2.67 nm in thickness. The dimension data indicate that the Cel-NRs from the TEMPO/NaBr/NaClO system are much shorter but contain more cellulose chains than those from the TEMPO/NaClO/NaClO₂ system. Moreover, these abundant biomass nanoribbons were fabricated from direct pyrolysis with NH₃ activation. The obtained highly active nitrogen-doped carbon nanoribbons (N-CNRs) and metal-free oxygen reduction reaction (ORR) electrocatalysts show superb ORR activity (half-wave potential of 0.71 and 0.73 V versus reversible hydrogen electrode) and high selectivity (electron-transfer number of 3.26 and 3.74 at 0.8 V), comparable current density and onset potential (0.906 and 0.926 V), excellent electrochemical stability (higher than 89.5% and 91.6% after 20 000 potential cycles) in alkaline media, and better resistance to crossover effects in the ORR. More importantly, when used as a cathode catalyst for constructing the air electrode of the Zn–air battery, the N-CNRs exhibit super long-term stability and a capacity of 587 and 583 mAh g^–1 at the discharge current densities of 5 and 20 mA cm^–2, respectively, which are highly comparable with those of the state-of-the-art Pt/C catalyst (20 wt % Pt, Hispec 3000). This indicates that our present work is the first example of using atomically thin carbon nanoribbons as the metal-free electrocatalyst substitution to Pt for developing high-performance metal–air batteries from earth-abundant terrestrial plants

Preparation and Formation Mechanism of Renewable Lignin Hollow Nanospheres with a Single Hole by Self-Assembly

Lignin hollow nanospheres with a single hole were prepared through a straightforward self-assembly method, which included dissolving enzymatic hydrolysis lignin, a byproduct derived from biorefinery, in tetrahydrofuran and afterward dropping deionized water to the lignin/tetrahydrofuran solution. The formation mechanism and structural characteristics of the lignin hollow nanospheres were explored. The results indicated that the nanospheres exhibited hollow structure due to the effect of tetrahydrofuran on the self-assembly behavior. Hydrophobic outside surface and hydrophilic internal surface were formed via layer-by-layer self-assembly method from outside to inside based on π–π interactions. The chemical structure of lignin did not produce a significant change in the preparation process of lignin hollow nanospheres. With increasing of initial lignin concentration, the diameter of the nanospheres and the thickness of shell wall increased, while the diameter of the single hole, the surface area, and the pore volume of the nanospheres decreased. The surface area reached the maximum value (25.4 m² g^–1) at an initial lignin concentration of 0.5 mg/mL in setting concentration range. Increasing the stirring speed or dropping speed of water resulted in a decrease of the diameter of the hollow nanospheres. Moreover, an apparent change of the average diameter of the nanospheres was not observed after 15 days, and the nanosphere dispersions were stable at pH values between 3.5 and 12. The lignin hollow nanospheres with a single hole offer a novel route for a value-added utilization of lignin and would improve the biorefinery viability

Coherent-Interface-Assembled Ag₂O‑Anchored Nanofibrillated Cellulose Porous Aerogels for Radioactive Iodine Capture

Nanofibrillated cellulose (NFC) has received increasing attention in science and technology because of not only the availability of large amounts of cellulose in nature but also its unique structural and physical features. These high-aspect-ratio nanofibers have potential applications in water remediation and as a reinforcing scaffold in composites, coatings, and porous materials because of their fascinating properties. In this work, highly porous NFC aerogels were prepared based on <i>tert</i>-butanol freeze-drying of ultrasonically isolated bamboo NFC with 20–80 nm diameters. Then nonagglomerated 2–20-nm-diameter silver oxide (Ag₂O) nanoparticles (NPs) were grown firmly onto the NFC scaffold with a high loading content of ∼500 wt % to fabricate Ag₂O@NFC organic–inorganic composite aerogels (Ag₂O@NFC). For the first time, the coherent interface and interaction mechanism between the cellulose I_β nanofiber and Ag₂O NPs are explored by high-resolution transmission electron microscopy and 3D electron tomography. Specifically, a strong hydrogen between Ag₂O and NFC makes them grow together firmly along a coherent interface, where good lattice matching between specific crystal planes of Ag₂O and NFC results in very small interfacial straining. The resulting Ag₂O@NFC aerogels take full advantage of the properties of the 3D organic aerogel framework and inorganic NPs, such as large surface area, interconnected porous structures, and supreme mechanical properties. They open up a wide horizon for functional practical usage, for example, as a flexible superefficient adsorbent to capture I^– ions from contaminated water and trap I₂ vapor for safe disposal, as presented in this work. The viable binding mode between many types of inorganic NPs and organic NFC established here highlights new ways to investigate cellulose-based functional nanocomposites

Coherent-Interface-Assembled Ag₂O‑Anchored Nanofibrillated Cellulose Porous Aerogels for Radioactive Iodine Capture

Nanofibrillated cellulose (NFC) has received increasing attention in science and technology because of not only the availability of large amounts of cellulose in nature but also its unique structural and physical features. These high-aspect-ratio nanofibers have potential applications in water remediation and as a reinforcing scaffold in composites, coatings, and porous materials because of their fascinating properties. In this work, highly porous NFC aerogels were prepared based on <i>tert</i>-butanol freeze-drying of ultrasonically isolated bamboo NFC with 20–80 nm diameters. Then nonagglomerated 2–20-nm-diameter silver oxide (Ag₂O) nanoparticles (NPs) were grown firmly onto the NFC scaffold with a high loading content of ∼500 wt % to fabricate Ag₂O@NFC organic–inorganic composite aerogels (Ag₂O@NFC). For the first time, the coherent interface and interaction mechanism between the cellulose I_β nanofiber and Ag₂O NPs are explored by high-resolution transmission electron microscopy and 3D electron tomography. Specifically, a strong hydrogen between Ag₂O and NFC makes them grow together firmly along a coherent interface, where good lattice matching between specific crystal planes of Ag₂O and NFC results in very small interfacial straining. The resulting Ag₂O@NFC aerogels take full advantage of the properties of the 3D organic aerogel framework and inorganic NPs, such as large surface area, interconnected porous structures, and supreme mechanical properties. They open up a wide horizon for functional practical usage, for example, as a flexible superefficient adsorbent to capture I^– ions from contaminated water and trap I₂ vapor for safe disposal, as presented in this work. The viable binding mode between many types of inorganic NPs and organic NFC established here highlights new ways to investigate cellulose-based functional nanocomposites