Microwave-assisted DES fabrication of lignin-containing cellulose nanofibrils and its derived composite conductive hydrogel.

Deep eutectic solvents (DES) have been regarded as green solvents in the biorefinery of lignocellulosic biomass, but long duration time has severely limited efficiency. The microwave-assisted DES pretreatment along with enzymatic hydrolysis and high-pressure homogenization process was proposed to produce lignin-containing cellulose nanofibrils (LCNF) from corncob. Benefiting from microwave-assisted DES pretreatment, the duration time was greatly shortened; meanwhile the effects of different kinds of DES on the resultant LCNF were investigated. The results showed that, the microwave-assisted DES fabricated LCNF (M-LCNF) was successfully obtained, exhibiting good nano size, thermal stability, colloidal stability, and fluorescence. M-LCNF was further introduced into phytic acid (PA) enhanced poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) network and constructed composite conductive hydrogels (PLP). The obtained hydrogels exhibited good mechanical strength, UV blocking ability, fluorescence, and conductivity. A simple battery assembled with the resultant PLP as electrolyte had an out voltage of 2.41 V. The composite conductive hydrogel showed good sensing performance towards different stimuli (e.g., stretching and compression) and human motions in real time. It is expected that this research would provide an alternative way for green fabrication of LCNF and potential application of LCNF in flexible sensors.

Enhancing photocatalytic destruction of lignin via cellulose derived carbon quantum dots/g-C3N4 heterojunctions.

Lignocellulosic biomass exhibits a promising potential for production of carbon materials. Nitrogen and phosphorus co-doped carbon quantum dots (N,P-CQDs) were fabricated via (NH4)2HPO4 assisted hydrothermal treatment of cellulose pulp fibers. The as-prepared N,P-CQDs were characterized by HRTEM, FTIR, fluorescence and UV-vis, and then incorporated into g-C3N4 (CN) through sonication and liquid deposition, forming N,P-CQDs/sonication treated g-C3N4 (C-SCN) composites, which were then explored as photocatalysts. The photocatalytic ability of C-SCN towards model lignin was further analyzed. The results showed that, the fluorescence intensity and photoluminescence performance of N,P-CQDs were much higher than that of CQDs; the heterojunction was successfully constructed between the composites of N,P-CQDs and SCN; the incorporation of N,P-CQDs enhanced the visible light absorption, but reduced the band gap of the composite heterojunction; the resultant photocatalysts exhibited a good photocatalytic ability of model lignin via catalyze the fracture of ß-O-4' ether bond and CC bond, i.e., the photocatalytic degradation ratio reached up to 95.5 %; and the photocatalytic reaction generated some valuable organics such as phenyl formate, benzaldehyde, and benzoic acid. This study would promote the high value-added utilization of lignocellulosic resources especially in the transformation of lignin, conforming the concept of sustainable development.

Upgrading lignin macromolecular by green and recyclable ternary deep eutectic solvents.

Lignin is the most abundant natural aromatic macromolecule in the nature, but its high value-added utilization has been seriously hindered by the highly random and branched structures and the high difficulty in separation and purification. A microwave-assisted ternary deep eutectic solvent (DES) composed by formic acid, lactic acid and choline chloride was developed for lignin pretreatment. The effects of three types of DES on main characteristics of lignin were investigated, and the corresponding dissolution mechanism was proposed. The results showed that, the microwave-assisted ternary DES pretreatment showed an obvious improvement on main characteristics of regenerated lignin, e.g., a higher purity, lower molecular weight with reduced dispersity, improved thermal stability, higher phenolic hydroxyl content, and increased antioxidative activity in comparison with control. It is expected that the lignin macromolecular can be facile regulated and upgraded by the proposed ternary DES.

Enhancing sludge methanogenesis with changed micro-environment of anaerobic microorganisms by Fenton iron mud.

Conductive materials have been demonstrated to enhance sludge methanogenesis, but few researches have concentrated on the interaction among conductive materials, microorganisms and their immediate living environment. In this study, Fenton iron mud with a high abundance of Fe(III) was recycled and applied in anaerobic reactors to promote anaerobic digestion (AD) process. The results show that the primary content of extracellular polymeric substances (EPS) such as polysaccharides and proteins increased significantly, possibly promoting microbial aggregation. Furthermore, with the increment of redox mediators including humic substances in EPS and Fe(III) introduced by Fenton iron mud, the direct interspecies electron transfer (DIET) between methanogens and interacting bacteria could be accelerated, which enhanced the rate of methanogenesis in anaerobic digestion (35.21 ± 4.53% increase compared to the control). The further analysis of the anaerobic microbial community confirmed the fact that Fenton iron mud enriched functional microorganisms, such as the abundance of CO2-reducing (e.g. Chloroflexi) and Fe(III)-reducing bacteria (e.g., Tepidimicrobium), thereby expediting the electron transfer reaction in the AD process via microbial DIET and dissimilatory iron reduction (DIR). This work will make it possible for using the recycled hazardous material - Fenton iron mud to improve the performance of anaerobic granular sludge during methanogenesis.

Structure regulated 3D flower-like lignin-based anode material for lithium-ion batteries and its storage kinetics.

As a green sustainable material, lignin-derived porous carbon (LPC) exhibits great application potential when used as the anode material in lithium-ion batteries (LIBs), but the applications are limited by the heterogeneity of the lignin precursor. Therefore, it is crucial to reveal the relationship among lignin properties, porous carbon structure and the kinetics of lithium-ion storage. Herein, LPCs from fractionated lignin have been prepared by an eco-friendly and recyclable activator. The structure of the LPCs was regulated by adjusting the molecular weight, linkage abundance and glass transition temperature (Tg) of lignin macromolecules. As the anode material of LIBs, the prepared 3D flower-like LPCE70 could achieve a reversible capacity of 528 mAh g-1 at a current density of 0.2 A g-1 after 200 cycles, 63 % higher than that of commercial graphite. Furthermore, kinetic calculations of lithium-ion storage behavior of LPCs were firstly used to confirm the contribution ratio of diffusion-controlled behavior and capacitive effect. Lignin with a high linkage abundance could yield LPCE70 with the largest interlayer spacing and specific surface area to maximize lithium-ion storage from both diffusion-controlled and capacitive contributions of specific capacities. This work provides a green, facile and effective pathway for value-added utilization of lignin in LIBs.

Fabrication of a Carbonized Cellulose Nanofibrils/Ti3C2Tx MXene/g-C3N4 Heterojunction for Visible-Light-Driven Photocatalysis.

Photocatalytic degrading pollutants driven by visible-light irradiation has attracted tremendous attention. One strategy of preparing carbonized cellulose nanofibrils/Ti3C2Tx MXene/g-C3N4 (CMCN) as a photocatalyst was developed. The as-prepared CMCN was comprehensively characterized in terms of the chemical composition, chemical and crystal structure, morphology, and photoelectrochemical properties. The CMCN was explored as a photocatalyst and exhibited good photocatalytic performance in degrading MB (96.5%), RhB (95.4%), and TC (86.5%) under visible-light conditions. In addition, the CMCN as a photocatalyst exhibited good reusability and stability. It is found that the incorporation of cellulose nanofibrils provided a high carbon content, a high porosity, and a large specific surface area, enhanced the electron transfer, improved the photocatalytic performance, and ensured a semiconductor with a high stability. It is believed that this study would provide an effective approach to preparing a photocatalyst and broaden the potential application of cellulose nanofibrils in photocatalysis.

Spider-web-inspired cellulose nanofibrils networking polyaniline-encapsulated silica nanoparticles as anode material of lithium-ion batteries.

As the promising anode material of lithium-ion batteries (LIBs), SiO2 has high theoretical capacity, but the volume expansion severely hinders its application. To address the challenge, inspired by the highly flexible spider-web architecture, the SiO2@carbonized polyaniline/carbonized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (SiO2@cPANI/cTOCNFs) composite was designed, and fabricated via carbonizing the freeze-dried SiO2@PANI/TOCNFs. The resultant SiO2@cPANI/cTOCNFs composite exhibited unique spider-web-like nanostructures, providing a double-layer carbon network to protect SiO2 anode material. The results showed that, the SiO2@cPANI/cTOCNFs composite as anode material of LIBs offered a reversible capacity of 1103 mAh g-1 at a current density of 0.1 A g-1 after 200 cycles, and gave a capacity of 302 mAh g-1 after 1000 cycles at a current density of 1 A g-1, exhibiting excellent cycling stability. This study provides a strategy of spider-web-inspired cellulose nanofibrils networking polyaniline-encapsulated silica nanoparticles as anode material of LIBs.

Combination of hydrothermal and chemi-mechanical pretreatments to enhance enzymatic hydrolysis of poplar branches and insights on cellulase adsorption.

An integration of different pretreatments is important to overcome recalcitrance and realize efficient bioconversion of lignocellulosic biomass. This study aims at the effects of combination of hydrothermal pretreatment and different chemi-mechanical pretreatments on enzymatic hydrolysis, and understanding the enzymes adsorption mechanism. The combination of hydrothermal and chemi-mechanical pretreatments effectively improved the enzymatic hydrolysis of poplar substrates, in which the enzymatic hydrolysis of substrates pretreated by hydrothermal pretreatment + Fenton pretreatment + mechanical refining (HFM) was the highest (92.39% of glucose conversion yield, and 20.88 g/L of glucose concentration). The substrates' main characteristics were obviously changed after combined pretreatments, such as swelling ability and specific surface area of substrates were increased. The Langmuir adsorption model (R2 > 0.98) and pseudo second-order adsorption kinetic model (R2≈1) were well suitable to describe the adsorption of enzymes on substrates, meanwhile the adsorption mechanism was summarized.

Fabricating lignin-containing cellulose nanofibrils with unique properties from agricultural residues with assistance of deep eutectic solvents.

Lignocellulosic biomass-derived nanocellulose has been attracting more and more attentions due to its distinguished advantages and various applications, but its development has been restricted by the preparation especially with environmental friendly approach. Herein, lignin-containing cellulose nanofibrils (LCNF) was prepared from corncob via the combined pretreatment of choline chloride-based DES (ChCl-DES) and enzymatic hydrolysis followed by high-pressure homogenization. The effects of different types of ChCl-DES on the properties of LCNF were investigated and compared. The results showed that LCNF can be successfully fabricated through the combined pretreatments; the LCNF had an average diameter of 60-90 nm, exhibited good fluorescence, high thermal stability (up to 353 °C of Tmax), hydrophobicity, stability, and redispersibility in organic solvent; AC-LCNF showed well oriented arrangement, the highest hydrophobicity and fluorescence, and distinguished redispersibility especially in DMSO. ChCl-DES as one green and sustainable approach would realize efficient separation and high value-added utilization of agricultural residues.

Facile preparation of cellulose nanofibrils (CNFs) with a high yield and excellent dispersibility via succinic acid hydrolysis and NaClO2 oxidation.

An efficient and low-cost approach to preparing CNFs with succinic acid hydrolysis and NaClO2 oxidation is explored. High-temperature-short-time hydrolysis can depolymerize the cellulose, whereas the dispersibility of the CNFs is hugely enhanced by NaClO2 oxidation under alkaline condition. The degradation of cellulose in succinic acid hydrolysis follows first-order reaction kinetics and is severely influenced by the hydrolysis temperature, moreover, the molecular chains of the cellulose are seriously cracked under the optimized condition. The NaClO2 oxidation greatly improves the zeta potential (-36.2 mV) and the dispersibility of the CNFs. The obtained CNFs have an ultimate yield of 94.6%, and the diameter distribution is mainly within 20-40 nm. In addition, some amount of carboxyl groups in the cellulose will be instead of the hydroxyl groups, and the crystallinity of the CNFs is significantly increased.