Mild Acetylation and Solubilization of Ground Whole Plant Cell Walls in EmimAc: A Method for Solution-State NMR in DMSO-d6.

Lignocellulosic biomass is mainly composed of polysaccharides and lignin. The complexity and diversity of the plant cell wall polymers makes it difficult to isolate the components in pure form for characterization. Many current approaches to analyzing the structure of lignocellulose, which involve sequential extraction and characterization of the resulting fractions, are time-consuming and labor-intensive. The present study describes a new and facile system for rationally derivatizing and dissolving coarsely ground plant cell wall materials. Using ionic liquids (EmimAc) and dichloroacetyl chloride as a solvent/reagent produced mildly acetylated whole cell walls without significant degradation. The acetylated products were soluble in DMSO-d6 from which they can be characterized by solution-state two-dimensional nuclear magnetic resonance (2D NMR) spectrometry. A distinct advantage of the procedure is that it realizes the dissolution of whole lignocellulosic materials without requiring harsh ball milling, thereby allowing the acquisition of high-resolution 2D NMR spectra to revealing structural details of the main components (lignin and polysaccharides). The method is therefore beneficial to understanding the composition and structure of biomass aimed at its improved utilization.

Preparation and characterization of cellulose-chitosan/ß-FeOOH composite hydrogels for adsorption and photocatalytic degradation of methyl orange.

Biopolymer-based hydrogels have received great attention in wastewater treatment due to their excellent properties, e.g., high adsorption capacity, fast kinetics, reusability and ease of operation. In the present work, cellulose-chitosan/ß-FeOOH composite hydrogels were prepared via co-dissolution and regeneration process as well as hydrothermal in situ synthesis of ß-FeOOH. Effect of ß-FeOOH loading on the properties of the composite hydrogels and the removal efficiency of methyl orange (MO) was investigated. Results showed that ß-FeOOH was uniformly loaded onto the hydrogel framework, and the nanoporous structure of composite hydrogels could increase not only the effective contact area between ß-FeOOH and the pollutants but also the active sites. Moreover, the increased ß-FeOOH loading led to the enhanced MO removal rate under light conditions. When the loading time was extended from 6 h to 9 h, the MO removal rate increased by 21%, which can be mainly due to the photocatalytic degradation. In addition, MO removal rate reached 97.75% within 40 min under optimal conditions and attained 80.81% after five repetitions. The trapping experiment and EPR results indicated that the main active species were hydrogel radicals and holes. Consequently, this work provides an effective preparation approach for cellulose-chitosan/ß-FeOOH composite hydrogel with high adsorption and photocatalytic degradation, which would hold great promise for wastewater treatment applications.

Synthesis and characterization of polyaniline-based composites using cellulose nanocrystals as biological templates.

Polyaniline (PANI) is considered as an ideal electrode material due to its remarkable Faradaic activity, exceptional conductivity, and ease of processing. However, the agglomeration and poor cycling stability of PANI largely limit its practical utilization in energy storage devices. To address these challenges, PANI was synthesized via a facile one-pot, two-step process using cellulose nanocrystals (CNCs) as bio-templates in this work. Zeta potential and particle size measurements revealed that the CNC template could impart improved dispersion stability to the synthesized PANI, which exhibited a decrease in average particle size from 1100 nm to 300 nm as a function of 10 % CNCs. Furthermore, the effect of CNC loadings on the performance of PANI was systematically investigated. The results showed that the specific capacitance of PANI/CNC increased from 102.52 F·g-1 to 138.12 F·g-1 with the CNC loading increase from 0 to 10 wt%. Particularly, the PANI/CNC composite film with a 1:9 ratio (C-P-10 %) demonstrated a capacity retention of 84.45 % after 6000 cycles and an outstanding conductivity of 526 S·m-1. This work generally offers an effective solution for the preparation of high-performance PANI-based composites, which might hold great promise in energy storage device applications.

Cellulose dissolution and regeneration behavior via DBU-levulinic acid solvents.

Most organic solvents are unable to dissolve carbohydrates due to the lack of hydrogen bonding ability. The development of solvent systems for dissolving cellulose is of great importance for its utilization and conversion. In this study, four new cellulose solvents were designed using inexpensive levulinic acid (LevA) and 1,8-diazabicyclo [5,4,0] undec-7-ene (DBU) as raw materials. The results showed that the prepared DBU-LevA-2 solvent was able to dissolve up to 7 wt% of bamboo cellulose (DP = 860) and 16 wt% of microcrystalline cellulose (DP = 280) at 100 °C and regenerated without derivatization. Also, the molar ratio of each component of this solvent has a significant effect on the dissolution properties of cellulose. The regenerated cellulose had the typical crystalline characteristics of cellulose II. Subsequently, the interactions and microscopic behaviors of solvent and cellulose during the dissolution process were thoroughly investigated by using NMR spectroscopy combined with density functional theory. The systematic study showed that the hydrogen bond-forming ability provided by DBU, a superbase, plays an indispensable role in the overall solvent system.

Highly Stretchable and Stimulus-Free Self-Healing Hydrogels with Multiple Signal Detection Performance for Self-Powered Wearable Temperature Sensors.

A flexible wearable temperature sensor is a novel electronic sensor that can monitor real-time changes in human body temperature in a variety of application scenarios and is regarded as the "crown jewel" of information collection technology. Although flexible strain sensors based on hydrogels have excellent self-healing effects and mechanical durability, their widespread application is still limited by external power sources. Herein, a novel self-energizing hydrogel was developed by embellishing cellulose nanocrystals (CNC) with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The resultant thermoelectrically conductive CNC was then employed as a booster for poly(vinyl alcohol) (PVA)/borax hydrogels. The obtained hydrogels exhibit remarkable self-healing performance (92.57%) and exceptional stretchability (989.60%). Additionally, the hydrogel was capable of accurately and reliably identifying human motion. Most importantly, it exhibits excellent thermoelectric performance, capable of generating stable and reproducible voltages. It shows a large Seebeck coefficient of 1.31 mV k-1 at ambient temperatures. When subjected to a temperature difference of 25 K, the output voltage reaches 31.72 mV. CNC-PEDOT:PSS/PVA conductive hydrogel is multifunctional with self-healing, self-powering, and temperature sensing, which has the potential to be used for the preparation of intelligent wearable temperature-sensing devices.

Cellulose nanofibril as a crosslinker to reinforce the sodium alginate/chitosan hydrogels.

Hydrogels derived from natural polymers have received great attention, but their practical applications are severely hindered by the relatively poor mechanical properties. In this work, cellulose nanofibril (CNF) was used as a crosslinker to reinforce the sodium alginate (SA)/chitosan (CS) hydrogels for drug sustained release. The CNF was prepared via a combined process of ball milling and deep eutectic solvents (DESs) pretreatment and characterized using SEM, FT-IR, and XRD. Furthermore, the microstructure, mechanical/biological properties and swelling performance of SA/CS/CNF hydrogels were investigated. Results showed that 1.0 wt% CNF addition led to the increases of 23.6% in storage modulus and 54.4% in loss modulus for the SA/CS/CNF hydrogels, indicating that CNF addition was effective in reinforcing the three-dimensional entangled networks of the hydrogels. Moreover, the presence of CNF was found to weaken the swelling performance of SA/CS/CNF hydrogels. When the synthesized SA/CS/CNF hydrogel with 1.0 wt% CNF was applied as a carrier for drug release, 50.8% reduction in the release rate in simulated gastric juice was achieved, demonstrating its outstanding sustained release properties. This work suggested that CNF might be conducive to enhancing the properties of SA/CS hydrogels, which can serve as an ideal polymeric carrier for drug release.

Multi-analysis of chemical transformations of lignin macromolecules from waterlogged archaeological wood.

A large number of archaeological wooden building poles have been excavated from the Hai Menkou site (Yunnan province, China). Lignin can be transformed and altered accompanied with significant loss of carbohydrates during this process. Elucidation of chemical and structural transformations of lignin is of primary importance for understanding both the nature of degradation processes and the structure of waterlogged archaeological wood, and crucial for developing proper consolidation technology and restoring artifacts of historical and cultural value. In this study, state-of-the-art analytical techniques, including SEM, FT-IR, XRD, CP-MAS 13C NMR, 2D-HSQC NMR, 31P-NMR, CRM, GPC and TG analysis, were all employed to elucidate the structural characteristics of lignin in waterlogged and reference Pinus wood. The results interpreted by NMR analysis demonstrated the depolymerization of lignin via cleavage of ß-O-4, ß-5, -OCH3 and some LCC linkages, leading to a higher amount of free phenol OH groups in the lignin from the ancient waterlogged wood as compared to that of the reference wood. Microscopically, it was found that extensive degradation of carbohydrates in cell walls was mainly occurred in secondary cell walls, while the lignin concentrations were relatively increased in CCML and S regions in the plant cell wall of the ancient wood.

Amination of biorefinery technical lignins using Mannich reaction synergy with subcritical ethanol depolymerization.

The alcoholic depolymerization and Mannich reaction were conducted to improve the chemical activity of biorefinery technical lignins and introduce amino groups into lignins, respectively. To understand the chemical structural transformations and examine the reaction mechanism, GPC and solution-state NMR techniques were performed. Element analysis was also used to quantify the amount of amine groups. The NMR characterization the depolymerized lignins indicated of the depolymerization, demethoxylation, and bond cleavage of linkages occurred during the depolymerization process. Results showed that the depolymerization temperature instead of the addition of capping reagents was the main factor for improving the reactivity of lignin under the given conditions. The Mannich reaction was very selective, primarily occurred at H3,5 and G5 positions, and the H units present a higher chemical reactivity. It is believed that the understanding of the fundamental chemistry of lignin during depolymerization and Mannich reaction process will contribute to the extension of high value-added applications of biorefinery lignin.

Assessment of integrated process based on autohydrolysis and robust delignification process for enzymatic saccharification of bamboo.

In this study, bamboo (Phyllostachys pubescens) was successfully deconstructed using an integrated process (autohydrolysis and subsequent delignification). Xylooligosaccharides, high-purity lignin, and digestible substrates for producing glucose can be consecutively collected during the integrated process. The structural change and fate of lignin during autohydrolysis process was deeply investigated. Additionally, the structural characteristics and active functional groups of the lignin fractions obtained by these delignification processes were thoroughly investigated by NMR (2D-HSQC and 31P NMR) and GPC techniques. The chemical compositions (S, G, and H) and major linkages (ß-O-4, ß-ß, ß-5, etc.) were thoroughly assigned and the frequencies of the major lignin linkages were quantitatively compared. Considering the structural characteristics and molecular weights of the lignin as well as enzymatic saccharification ratio of the substrate, the combination of autohydrolysis and organic base-catalyzed ethanol pretreatment was deemed as a promising biorefinery mode in the future based on bamboo feedstock.

Structural variations of lignin macromolecule from different growth years of Triploid of Populus tomentosa Carr.

To better understand the variations of structural characteristics of lignin macromolecules during different growth years of Triploid of Populus tomentosa Carr, a novel lignin isolation procedure based on double ball-milling and enzymatic hydrolysis (DEL) was proposed in this study. The morphological distributions of lignin in the plant cell wall of these poplar wood samples were monitored by Confocal Raman Microscopy (CRM). The ultrahigh yields (105.1%-111.2%) of DELs were significantly higher than those (24.4-31.8%) of corresponding cellulolytic enzyme lignins (CELs). DELs and CELs were elaborately characterized by HPAEC, GPC, 2D-HSQC NMR and 31P NMR techniques, and NMR results showed that DEL samples possess similar structural features as compared to CEL counterparts except for the decreased S/G ratio and p-hydroxybenzoate (PB) as well as increased p-hydroxyphenyl units (H). There are no obvious differences in the structural characteristics except for high contents of PB and H units in DEL-1, as well as high S/G ratio and ß-O-4' linkages in DEL-5. It is believed that the DEL proposed in the present study can be used for characterizing the entire structural features of lignin macromolecules in the plant cell wall of different kinds of lignocellulosic biomass.