Dissolution Mechanism of Cellulose in <i><i>N,N</i></i>-Dimethylacetamide/Lithium Chloride: Revisiting through Molecular Interactions

Understanding the interactions between solvent molecules and cellulose at a molecular level is still not fully achieved in cellulose/<i><i>N,N</i></i>-dimethylacetamide (DMAc)/LiCl system. In this paper, cellobiose was used as the model compound of cellulose to investigate the interactions in cellulose/DMAc/LiCl solution by using Fourier transform infrared spectroscopy (FTIR), ¹³C, ³⁵Cl, and ⁷Li nuclear magnetic resonance (NMR) spectroscopy and conductivity measurements. It was found that when cellulose is dissolved in DMAc/LiCl cosolvent system, the hydroxyl protons of cellulose form strong hydrogen bonds with the Cl^–, during which the intermolecular hydrogen bonding networks of cellulose is broken with simultaneous splitting of the Li⁺–Cl^– ion pairs. Simultaneously, the Li⁺ cations are further solvated by free DMAc molecules, which accompany the hydrogen-bonded Cl^– to meet electric balance. Thereafter, the cellulose chains are dispersed in molecular level in the solvent system to form homogeneous solution. This work clarifies the interactions in the cellulose/DMAc/LiCl solution at molecular level and the dissolution mechanism of cellulose in DMAc/LiCl, which is important for understanding the principle for selecting and designing new cellulose solvent systems

Osmium Bipyridine-Containing Redox Polymers Based on Cellulose and Their Reversible Redox Activity

Thermo-, pH-, and electrochemical-sensitive cellulose graft copolymers, hydroxypropyl cellulose-<i>g</i>-poly(4-vinylpyridine)-Os(bipyridine) (HPC-<i>g</i>-P4VP-Os(bpy)), were synthesized and characterized. The electrochemical properties of the resulting material were investigated via cyclic voltammetry by coating the graft copolymers on the platinized carbon electrode. The results indicated that the electrochemical properties of the graft copolymer modified electrode were responsive to the pH values of the electrolyte solution. The reversible transformation between the active and inactive state originated from the changes in the architecture of the HPC-<i>g</i>-P4VP-Os(bpy) graft copolymer at different pH values. At high pH (e.g., above the p<i>K</i>_a of P4VP), the chains of P4VP collapsed, and the electrochemical activity of the electrode was reduced. With immobilization of glucose oxidase (GOx) on the graft copolymer decorated electrode, a biosensor for glucose detection was prepared. The current of the biosensor depended on the glucose concentration in the detected solution and increased with the successive addition of glucose

Bacterial Cellulose Supported Gold Nanoparticles with Excellent Catalytic Properties

Amidoxime surface functionalized bacterial cellulose (AOBC) has been successfully prepared by a simple two-step method without obviously changing the morphology of bacterial cellulose. AOBC has been used as the reducing agent and carrier for the synthesis of gold nanoparticles (AuNPs) that distributed homogeneously on bacterial cellulose surface. Higher content in amidoxime groups in AOBC is beneficial for the synthesis of AuNPs with smaller and more uniform size. The AuNPs/AOBC nanohybrids have excellent catalytic activity for reduction of 4-nitrophenol (4-NP) by using NaBH₄. It was found that catalytic activity of AuNPs/AOBC first increases with increasing NaBH₄ concentration and temperature, and then leveled off at NaBH₄ concentration above 238 mM and temperature above 50 °C. Moreover, AuNPs with smaller size have higher catalytic activity. The highest apparent turnover frequency of AuNPs/AOBC is 1190 h^–1. The high catalytic activity is due to the high affinity of 4-NP with AuNPs/AOBC and the reduced product 4-aminophenol has good solubility in water in the presence of AuNPs/AOBC. The catalytic stability of the AuNPs/AOBC was estimated by filling a fluid column contained AuNPs/AOBC and used for continuously catalysis of the reduction of 4-NP by using NaBH₄. The column works well without detection of 4-NP in the eluent after running for more than two months, and it is still running. This work provides an excellent catalyst based on bacterial cellulose stabilized AuNPs and has promising applications in industry

Dissolution and Metastable Solution of Cellulose in NaOH/Thiourea at 8 °C for Construction of Nanofibers

To develop a facile approach for the dissolution of cellulose, a novel solvent (9.3 wt % NaOH/7.4 wt % thiourea aqueous solution) was used, for the first time, to dissolve cellulose within 5 min at 8 °C. The results of NMR and Raman spectra demonstrated that stable thiourea···OH^– complexes were formed through strong hydrogen bonds in NaOH/thiourea at room temperature. Moreover, the strength of the hydrogen bonds in thiourea···OH^– complexes was much higher than that in urea···OH^– complexes, and the number of thiourea···OH^– complexes increased significantly in 9.3 wt % NaOH/7.4 wt % thiourea compared to that in 9.5 wt % NaOH/4.5 wt % thiourea, which dissolved cellulose at −5 °C, leading to the dissolution of cellulose at a relatively high temperature (8 °C). The cellulose that dissolved at such a high temperature was metastable. The results of dynamic light scattering and transmission electron microscope experiments confirmed that the extended cellulose chains and their aggregates coexisted in the dilute cellulose solution. Interestingly, stiff cellulose chains could be self-assembled in parallel to form nanofibers in the metastable cellulose solution, from which cellulose microspheres consisting of nanofibers could be easily produced by inducing heating. This work not only proposed a novel method for the dissolution of cellulose in aqueous system at temperatures over 0 °C but also opened up a new pathway for the construction of nanofibrous cellulose materials

Intermolecular Interactions and 3D Structure in Cellulose–NaOH–Urea Aqueous System

The dissolution of cellulose in NaOH/urea aqueous solution at low temperature is a key finding in cellulose science and technology. In this paper, ¹⁵N and ²³Na NMR experiments were carried out to clarify the intermolecular interactions in cellulose/NaOH/urea aqueous solution. It was found that there are direct interactions between OH^– anions and amino groups of urea through hydrogen bonds and no direct interaction between urea and cellulose. Moreover, Na⁺ ions can interact with both cellulose and urea in an aqueous system. These interactions lead to the formation of cellulose–NaOH–urea–H₂O inclusion complexes (ICs). ²³Na relaxation results confirmed that the formation of urea–OH^– clusters can effectively enhance the stability of Na⁺ ions that attracted to cellulose chains. Low temperature can enhance the hydrogen bonding interaction between OH^– ions and urea and improve the binding ability of the NaOH/urea/H₂O clusters that attached to cellulose chains. Cryo-TEM observation confirmed the formation of cellulose–NaOH–urea–H₂O ICs, which is in extended conformation with mean diameter of about 3.6 nm and mean length of about 300 nm. Possible 3D structure of the ICs was proposed by the M06-2X/6-31+G­(d) theoretical calculation, revealing the O3H···O5 intramolecular hydrogen bonds could remain in the ICs. This work clarified the interactions in cellulose/NaOH/urea aqueous solution and the 3D structure of the cellulose chain in dilute cellulose/NaOH/urea aqueous solution