Search

This document is a contents list for the journal "Green Chemistry," published by the Royal Society of Chemistry. It features research papers on various topics related to sustainable chemistry, including photocatalytic upgrading of hydroxymethylfurfural, lignin extraction and nanodispersion, selenium-doped carbon materials, and the valorization of bio-renewable glycerol. The journal also includes tutorial reviews on topics such as Pickering emulsion-derived nano/microreactors and the iron ligand-to-metal charge transfer chemistry in water. Additionally, there are perspective papers, communications, and other research papers covering a range of subjects in green chemistry. The papers provide valuable insights into the development of greener and more sustainable chemical processes. [Extracted from the article]

This study shows a functional deep eutectic solvent (DES) employing choline chloride (ChCl) and glyoxylic acid (GA) for lignocellulose fractionation. This DES exhibited a higher pretreatment efficiency (92.15%) than that composed of ChCl and lactic acid (10.36%). Molecular dynamic (MD) simulations indicated that the ChCl : GA DES showed a higher total binding energy (ΔE) with lignin than the ChCl : LA DES, resulting in a higher dissolution of lignin. GA prevented lignin condensation during pretreatment. The stabilized lignin containing 69.39% β-O-4 linkages can be used for phenolic monomer production with a bio-oil yield of 59.60% and lignin-based sunscreen preparation with a SPF of 58.46. The cellulose residues with a mild pretreatment severity exhibited a high enzymatic saccharification yield of 91.99%. Meanwhile, an esterification reaction occurred between cellulose and GA during pretreatment. The inhibition of enzymatic hydrolysis and microbial growth enables the use of functional cellulose to produce antibacterial paper. Furthermore, 96.80% of the DES could be easily recycled and reused for biorefinery purposes. [ABSTRACT FROM AUTHOR]

The electrochemical reductive cleavage of the C–O bond in the lignin α-O-4 model compound benzyl phenyl ether (BPE) at room temperature was investigated using earth-abundant nickel as a catalyst in methanol. Experiments using a divided cell setup using either NiCl2·6H2O salt or pre-deposited Ni on a carbon paper cathode (Ni/CP) under an inert atmosphere revealed the essential role of freshly and uniformly deposited Ni0 on the electrode surface for the reductive, catalytic cleavage to yield phenol and toluene. To better understand the reaction mechanism, the surface morphology and composition of the Ni/CP electrode were investigated by SEM, XRD, and XPS. Additionally, the role of methanol as a proton donor was established, and electrochemical hydrogenation/hydrogenolysis (ECH) experiments of BPE with sterically hindered substituents revealed that the reaction mechanism shares similarities with Pd/C hydrogenation/hydrogenolysis chemistry. DFT calculations further supported this mechanistic route and were consistent with the experimental observations. Based on both experimental and calculation results, a mechanism including (1) the interaction of the benzylic side of BPE with the catalyst surface, (2) adsorbed hydrogen interacting with the benzylic carbon to induce C–O bond scission, and (3) proton transfer to the phenoxy anion from the methanol was proposed. [ABSTRACT FROM AUTHOR]

Current catalytic hydrogenolysis of lignin C–O bonds, which is crucial for lignin valorization, often requires a noble metal catalyst or/and harsh conditions such as elevated temperatures and high pressures. Herein, we report a highly selective electrochemical protocol to reductively cleave the benzylic C–O bond of the α-O-4 lignin model compound benzyl phenyl ether (BPE) at room temperature and ambient pressure. Nearly complete conversion of BPE to toluene and phenol in methanol was achieved in an undivided cell using Ni foam at both the anode and cathode, with yields of 97% and 30%, respectively. Using a divided cell, yields of 90% (toluene) and 84% (phenol) could be achieved using inexpensive carbon paper as the cathode when Ni(II) salts were added to the cathode chamber. Notably, other divalent metal salts did not lead to any product formation, suggesting a unique role of Ni ions in benzylic C–O bond cleavage. Further, a substrate scope study revealed the suitability of the method for a variety of substituted BPEs. This work provides an economical and environmentally friendly method for selective cleavage of C–O bonds in benzylic ethers as model compounds for lignin. [ABSTRACT FROM AUTHOR]

In this paper, we describe an approach for producing both high quality and high quantity of lignin through studying the structural change of lignin during treatment of poplar wood in γ-valerolactone (GVL) for a range of temperatures (from 80 to 120 °C) and reaction time at temperature (from 1 to 24 h). Various techniques, including nuclear magnetic resonance (NMR) spectroscopies (solution- and gel-state 1H–13C 2D HSQC and 31P) and gel-permeation chromatography (GPC) were applied to characterize the lignin structures. As the GVL-extracted lignin yield increases, the level of β-ether units decreases and the level of condensation products increases. The β-ether content, the aliphatic hydroxyl group content, and the molecular weight of the GVL-extracted lignin fractions were close to the poplar lignin from other preparation methods (e.g., enzyme lignin). A two-step hydrolytic process (120 °C, 2 × 15 min) gave a higher lignin yield (56.5% vs. 54.8%) with three times higher β-ether content (31.9% vs. 10.6%) than lignin extracted from a single-step process at 120 °C for 1 h. The results demonstrate that multiple-step cycling of cosolvent-assisted hydrolysis can help preserve more of the virgin ether-bond structures of GVL-extracted poplar lignin. Such a strategy can also be applied to a fully continuous-flow reactor system in future research to further improve both the productivity and quality of GVL-extracted lignin. [ABSTRACT FROM AUTHOR]

Pretreatment facilitates cost-effective operations on lignocellulosic biomass ranging from densification to deconstruction and bioproduct development. However, determining molecular-level mechanisms behind pretreatment and their effects has remained elusive. Here, we combine computational simulation and experiment to investigate the effects on wheat straw agricultural residue densification of an emerging pretreatment solvent, namely, a deep eutectic solvent (DES) consisting of choline chloride (ChCl) and oxalic acid (OA). Ab initio molecular dynamics indicates that dissociation of lignin from cellulose in lignin–carbohydrate complexes, which does not occur to a significant extent in aqueous solution, is favorable in the DES and occurs via cleavage of the guaiacyl : xylose ether bond linkage by OA. The ensuing hemicellulose removal exposes lignin to the DES which, molecular dynamics simulation indicates, leads to lignin expansion. The resulting changes in wheat straw fiber structure, lignin distribution, and functional group modifications upon DES treatment by scanning electron and fluorescence microscopy along with Fourier-transform infrared spectroscopy. The molecular expansion of lignin enhances inter-particle binding in wheat straw, leading to denser structures under pelletization. The resulting high mechanical stability and combustion properties make the wheat straw a suitable precursor of high-quality densified solids (e.g., solid biofuel). Overall, we shed light on the molecular-level mechanisms involved in DES pretreatment for biomass densification, demonstrated here in the development of a solid biofuel. The approach here illuminates the rational design from first chemical principles of methods to convert lignocellulosic resources into advanced materials. [ABSTRACT FROM AUTHOR]

Kraft lignin (KL), an abundant and underutilized biobased aromatic resource, was valorized into polyester vitrimers showing enhanced recyclability. KL was first modified with ethylene carbonate, to expose only highly reactive primary aliphatic OH groups, allowing the direct synthesis of polyester networks by polycondensation with PEG-based dicarboxylic acid. In addition to avoiding the use of toxic acyl halides or coupling agents, this fast synthetic process yields networks in which the amount of free OH groups can be easily controlled by adjusting the stoichiometry between COOH and OH groups. The presence of free OH groups allows transesterification reactions resulting in a vitrimer behavior. Increasing the number of free OH groups promotes the stress relaxation process, but does not affect the activation energy, which is relatively low compared to typical transesterification vitrimers, owing to the specific network topology. High performance materials with improved mechanical and chemical recyclability were clearly demonstrated. Besides, the modified lignin can be recovered and isolated in high yields with only minor changes in its chemical structure, offering further upcycling opportunities. This makes lignin, the first aromatic and biobased resource, a raw material that can also be recycled, in line with the concept of a circular bioeconomy. [ABSTRACT FROM AUTHOR]

Electrochemical catalysis emerges as a promising method for lignin depolymerization due to its environmental friendliness and mild reaction condition. Metal oxyhydroxides have displayed appealing electrochemical activity for the oxidation for various biomass substrates. In this study, we prepared different metal (Ni, Co, Mn, Fe, and Cu) oxyhydroxides on nickel foam electrodes through electrodeposition. Their electrochemical properties were characterized and the reactivity towards lignin oxidative cleavage was investigated using lignin model compounds. NiOOH exhibited significantly higher activity for oxidative cleavage of the β-O-4 linkage compared to other metal oxyhydroxides, resulting in a 93% yield of aromatic monomers with 99% selectivity towards benzoic acids. Furthermore, the reconstruction process of the active site NiOOH was revealed by in-situ testing, and the reaction mechanism was explored. The non-phenolic structure underwent Cβ–Cγ/Cβ–O or Cα–Cβ cleavage, predominantly producing benzoic acids, while the phenolic structure was rapidly oxidized into dicarboxylic acids over NiOOH. [ABSTRACT FROM AUTHOR]

Derived from lignocellulosic biomass, sustainable hard carbon has emerged as a promising low-cost anode material for sodium-ion batteries (SIBs). However, the intricate formation process of the hard carbon microstructure remains unclear. This study investigates the structural differences and pyrolysis behaviors of pine lignin and its graded variants obtained through a lignin molecular sieving engineering strategy. Moreover, it delves into the relationship between the microstructure of lignin-derived hard carbon and its sodium-ion storage characteristics. Pristine pine lignin, along with ethanol-isolated lignin, acetone-isolated lignin, and residual lignin, serves as a precursor for synthesizing hard carbon materials. Quantitative analysis via31P NMR spectroscopy reveals the highest content of polar functional groups in ethanol-isolated lignin. Interestingly, hard carbon derived from ethanol-isolated lignin exhibits the smallest closed pore volume, leading to the lowest plateau capacity of sodium-ion storage. Conversely, hard carbon derived from acetone-dissolved lignin displays the highest plateau capacity owing to its largest closed pore volume formed in the carbonization process. The origin of open and closed pore structures of hard carbons is thoroughly analyzed. [ABSTRACT FROM AUTHOR]

Deep eutectic solvent (DES) pulping is a promising alternative to conventional pulping techniques, mainly owing to the favourable solvent properties and reduced environmental impact. DES lignin, however, still awaits complete structural characterisation, especially in terms of the potential incorporation of DES constituents. Here, we describe the structural modification of lignin during lactic acid : choline chloride DES pulping of Miscanthus biomass in unprecedented detail. We show that DES pulping induces β-O-4 aryl ether cleavage and extensive substitution by DES incorporation. The covalent incorporation of both lactic acid and choline was confirmed through saponification of the precipitated lignin and lignin model compound studies. Detailed multidimensional NMR analysis allowed us to validate aliphatic and benzylic lactic acid esterification as well as benzylic choline and lactic acid etherification of β-O-4 aryl ethers. We demonstrate that these reactions occur in all process phases by comprehensive analysis of the precipitated, residual and solubilised lignin fractions, together comprising 93% w/w of the initial lignin in Miscanthus. Covalent lactic acid and choline incorporation occurs independently of biomass type (grass, hardwood and softwood) and can be modulated by water content, reaction duration and temperature. Going forward, these new insights will offer ample opportunities for producing lignins with unique structural features and ultimately will open up new avenues for specific functional ingredient applications. Our work thus clearly advances the DES biorefinery concept and contributes to the valorisation of lignin in general. [ABSTRACT FROM AUTHOR]

Lignin, a crucial component of lignocellulosic biomass, holds immense promise for advancing biorefineries and producing sustainable energy alternatives. This study engineered a CN/rGO/BMO (2 : 1) heterojunction photocatalyst with varying Pd NP loading to selectively target the hydrogenolysis of challenging C–O ether bonds in lignin model compounds. Specific focus was on β-O-4, α-O-4, and the formidable 4-O-5 linkages. The 4-O-5 linkage, due to its high dissociation energy, poses a significant challenge. Electrochemical and spectral analyses unveiled improvements in charge separation, leading to delayed recombination of charge carriers in the heterojunction photocatalyst. Decorating the heterojunction with Pd NPs exhibited an elevated work function and a low Fermi energy level, facilitating the accommodation of photogenerated electrons and enabling efficient H2 dissociation. Such enhancement facilitated the cleavage of all three linkages, including the resistant 4-O-5 bonds under ambient conditions. The photocatalyst exhibited effective cleavage, yielding aromatic (toluene, phenol, ethylbenzene) and aliphatic (cyclohexane, ethylcyclohexane) products. Selectivity modulation was achieved by adjusting the time, hydrogen pressure, and Pd loading. Furthermore, this photocatalytic approach successfully transformed simulated lignin bio-oil containing all three linkages into valuable monomers. The alcoholic solvents efficiently harnessed photogenerated holes and prevented electron–hole recombination. The photocatalyst also demonstrated the capability to produce monomers from the native lignin extracted from teak wood sawdust. Emphasizing the focus on the reaction pathway and mechanism, scavenging studies and analyses were conducted, including UPS and VBXPS, to establish the Z-scheme charge transfer mechanism within the heterojunction. These findings provide a sustainable and efficient pathway for lignin valorisation in biorefineries, significantly contributing to the advancement of green fuels and aligning with the principles of green chemistry. [ABSTRACT FROM AUTHOR]

Recently, the ambient drying method for the preparation of xerogels has attracted great attention due to its low cost and high drying efficiency. However, the strong capillary forces existing during ambient drying cause severe shrinkage or even collapse of the aerogels (called xerogels). Although chemical crosslinking or displacement of water by organic solvents have been tried to solve the problem, extensive usage of chemicals and time-consuming displacement processes seem to be environmentally unfriendly and complex. Herein, we reported a green and efficient method for the preparation of a lignocellulosic xerogel. The xerogel was fabricated by alkali freezing of unbleached eucalyptus fibers followed by water washing and ambient drying. The alkali freezing promoted fiber swelling and enhanced the hydrogen bonds among the fibers, resulting in the gelation of lignocellulosic fibers. In particular, the residual lignin in the fibers reduced the capillary force during the drying process. The resulting lignocellulosic xerogel achieved a low shrinkage rate (27.50%), low density (0.039 g cm−3 ), high porosity (97.57%), and excellent mechanical strength (782.23 kPa) as well as environmental stability, and low thermal conductivity (44.76 mW m−1 K−1 ). Similarly structured xerogels could be generated using recycled NaOH solution. This technique was suitable for production using various kinds of plant fibers, which shows its great scalable production prospects. [ABSTRACT FROM AUTHOR]

Lignocellulose biorefining has great potential to replace the use of petrochemical resources in the production of fuels and chemicals. However, the full use of lignocellulose, which is depolymerized to yield mainly glucose, xylose, and lignin-derived phenolics, remains challenging. Here, we developed a glucose–xylose–phenolics (GXP) system to fully use lignocellulose for the production of L-tyrosine and its analogues in minimal medium. First, we engineered an Escherichia coli–Escherichia coli consortium carrying a CRISPR/dCas9 interference system to simultaneously use glucose and xylose to support cell growth and produce pyruvate, obtaining 34.3 g L−1 pyruvate with a yield of 0.68 g g−1 sugar. Then, we introduced tyrosine phenol lyase and other biocatalytic enzymes into this consortium to generate the GXP system, which could convert pyruvate and lignin-derived phenolics to L-tyrosine and its analogues. Using this GXP system, 20.8 g L−1L-tyrosine was produced from 12.5 g L−1 phenol with a yield of 86.4%. Using the hydrolysate of the raw material sorghum pith, 0.94 g L−1L-tyrosine was produced from 0.96 g L−1p-coumaric acid with a yield of 88.7%, and 8.1 g L−1 pyruvate remained, corresponding to an overall yield of 0.163 g product g−1 sorghum pith. The development of this GXP system illustrates a strategy for fully utilizing lignocellulosic biomass for the synthesis of value-added chemicals. [ABSTRACT FROM AUTHOR]

Reductive catalytic fractionation (RCF) is a lignin-first biorefining technique that produces a polysaccharide-rich pulp and a lignin oil that is rich in aromatic monomers from aryl–ether bond cleavage and carbon–carbon linked aromatic oligomers. Separations of the lignin-derived monomers, both from one another and from the oligomers, out of these lignin oils could potentially yield high value co-products. To that end, we demonstrate that counter-current chromatography (CCC) is an effective means for simultaneous lignin monomer–monomer and monomer–oligomer separations using oils from RCF reactions with hardwood, softwood, and herbaceous feedstocks. Partition coefficient measurements of aromatic monomers from RCF of poplar, pine, and corn stover were first used to inform CCC solvent selection. We subsequently demonstrated CCC separations of those lignin oils using the HEMWat −3 solvent system and refined the measured partition coefficients using solute retention times and the cell utilized partitioning model to account for matrix effects in the following optimization experiments. Furthermore, the carbon–carbon linked oligomers in the lignin oil substrates elute together and separately from the aromatic monomers in lignin oil, resulting in an oligomer-rich product stream. Case studies of optimization of poplar RCF-derived lignin oil separations exhibited non-polar monomer yields of 95–99% with purities of 72–96%. Additionally, the same separation using a propyl-rich lignin oil produced from a H2-free RCF process showed a nearly 46% increase in normalized productivity, exhibiting the importance of tuning feed composition to improve separation performance. Taken together, this work shows that CCC is a promising method for simultaneous lignin monomer–monomer and monomer–oligomer separations. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) and ionic liquids (ILs) are potential solvents for lignocellulosic biomass fractionation. In this study, the rice straw pretreatment efficiency of four cholinium-based solvents (DESs and ILs) prepared from the same sources (lactic acid and lysine) were comparatively investigated at 110 °C for 4 h. The lignin removal rate correlated well with the saccharification efficiency of the pulps. Quantum chemical (QC) calculations and molecular dynamics (MD) simulations focused on the microscopic structure and non-covalent interactions of the solvents and lignin model molecules (guaiacylglycerol-β-guaiacyl ether, GG) were carried out, and the results indicate that anions of the solvent systems play a leading role (through strong hydrogen bonds or electrostatic interactions) in establishing interactions with GG, supported by cations (via van der Waals interactions). There were clear positive relationships between the total interaction energies (IEs) and lignin removal, cellulose digestibility and glucose yields. In particular, [Ch][Lys] with a low self-interaction energy is able to free some active sites to form strong hydrogen bonds and electrostatic interactions with lignin, thus resulting in lignin dissolution and excellent delignification. For cholinium cations, an ideal partner system provides low self-IEs for solvent molecules and strong IEs between solvents and lignin, which are determined by the type and number of functional groups and the alkyl chain length of the partner components. This work provides ideas about tailoring suitable partner systems for cholinium cations to build solvents for efficient biomass deconstruction. [ABSTRACT FROM AUTHOR]

Laser-induced graphene (LIG) is a versatile form of graphene materials synthesized through direct laser writing (DLW) onto a carbon-rich precursor. Lignin is a promising natural precursor for LIG. However, the lack of understanding of the relationship between lignin chemistry and LIG properties limits the effective utilization of lignin. Herein, we aimed to understand the structural evolution of lignin into few-layer graphene during direct laser writing via the combined experimental investigation and reactive force field molecular dynamics (MD) simulation. Strong correlations were found between structural features of lignin and LIG characteristics, especially the sheet resistance (electrical conductivity) and defects in graphene domains. Specifically, higher molecular weight lignin demonstrated a superior propensity for generating the graphitic structure in the turbostratic matrix of LIG. This phenomenon led to better graphene quality in terms of morphological continuity, conductivity, and graphene domains. The glass transition temperature (Tg) of fractionated lignin was identified to have the strongest linear correlation with both sheet resistance and defect density in LIG. Additionally, the MD simulations shed light on the role of closely positioned carbon atoms in the initial substrate, highlighting their facilitative effect on the formation of large graphene domains. The proposed LIG formation pathway offers a new avenue for lignin biorefinery, facilitating efficient production of graphene materials from renewable resources. [ABSTRACT FROM AUTHOR]

Lignin-containing cellulose nanofibrils are successfully produced after enzymatic treatment of curlinduced, unbleached kraft pulps. An enzyme cocktail composed predominantly of endoglucases but also containing xylanases, laccases, and lytic polysaccharide monooxygenases (LPMO's) results in significant enzyme-mediated fiber modification. A substantial (70%) reduction in pulp viscosity can be achieved while enzyme treatment of curl-induced fibers results in improved fibrillation and increased colloidal stability. This is likely due to the higher negative charge density (-57.5 mV) of the fibers. The enzymetreated, curl-derived cellulose nanofibrils show improved characteristics such as higher transmittance, lower viscosity, and thinner nanofibrils, resulting in enhanced nano-fibrillation. Superior mechanical properties, such as increasing the tensile strength of cellulose nanopapers to 150 MPa, are obtained as a result of the improved fibril network. The pre-curled fibers appear more accessible to enzyme treatment, resulting in cellulose nanofibrils with improved properties with less chemical treatments and mechanical refining energy required. [ABSTRACT FROM AUTHOR]

Research on zinc-ion hybrid supercapacitors has been gaining much attention due to the combination of their high energy and power density. However, the cost of preparation and poor rate performance of porous carbon cathode materials are two major issues limiting their large-scale utilization. In this study, we used nano calcium carbonate as the hard template agent and economical lignin as the carbon source to synthesize lignin-derived porous carbon with high specific surface areas and high mesopore ratios. Through a double decomposition reaction, calcium chloride produced by acid pickling is combined with sodium carbonate to create nano-calcium carbonate, thus enabling the regeneration of nano-calcium carbonate. More importantly, carbon dioxide resulting from the pyrolysis of calcium carbonate causes an internal activation effect on carbon materials, thus causing the formation of micropores and expanding the pore size of some micropores and small mesopores. Through this strategy, the specific surface area of lignin-derived porous carbon is up to 860.5 m² g-1, and the mesopore volume accounts for more than 90% of the total pore volume. The zinc-ion hybrid supercapacitor with lignin-derived porous carbon as the cathode displays an impressive capacity retention rate of 64% when the current density is increased from 0.1 to 20 A g-1. This work provides a green and sustainable route for the development of low-cost, high-rate performance porous carbon materials. [ABSTRACT FROM AUTHOR]

A sustainable lignin bioconversion depends on the exploitation of the inherent aromaticity of lignin for high-value aromatic products. However, the microbial valorization of lignin is hindered by the lack of established bioconversion routes or the inefficient heterologous expression of key enzymes. Here, an efficient biological lignin conversion route was constructed in a microbial cell factory by tapping the inherent aromaticity of lignin to produce aromatic natural compounds such as homoeriodictyol. The heterologous biosynthesis pathways were successfully constructed to convert lignin-derived monomers to homoeriodictyol in Saccharomyces cerevisiae. The implementation of combinatorial regulating strategies resulted in enhanced CoA supply, suppression of branch pathways, and upregulation of the rate-liming enzymes, which increased the titer of homoeriodictyol by a remarkable 22.5-fold. After that, engineering cofactor supply and recycling led to a substantial 95% increase in homoeriodictyol production. The rational design and modification of the heterologous rate-limiting enzymes helped achieve substantial improvement in the homoeriodictyol yield. All these strategies together enabled the record homoeriodictyol titer of 3.2 mmol l-1 from lignin derivatives by S. cerevisiae. Overall, such an innovative conversion route meets the atom-economy concept by converting lignin derivatives into valuable flavonoids, paving a green, sustainable way for both the valorization of lignin and the production of aromatic natural products. [ABSTRACT FROM AUTHOR]

Rigid lignin foam is prepared by a baking method using kraft lignin as the sole source. The eco-forming process involved cold-pressing kraft lignin powder into a solid block, heating the solid block to form lignin foam, and finally curing and cooling the lignin foam to obtain an open-cell, rigid foam. Both adsorbed water and water generated from the dehydration of hydroxyl groups in the lignin served as the blowing agent in this baking method. It was found that as the moisture content of lignin decreased, the foam densities increased, the mean bubble sizes decreased, and the bubble size distributions became narrower. Foam morphology showed an open cell structure and a wide cell volume distribution. The results suggest that controlling the moisture content in raw lignin allows for the control of the pore structure of the lignin foam. Based on their unique properties, lignin foam materials hold great promise in many applications especially as core insulation materials for structural insulated panels (SIPs). [ABSTRACT FROM AUTHOR]

Phenolic resins (PRs) are being widely used in many fields such as molding plastics, foams, coatings, and semiconductor packaging owing to their good properties including corrosion resistance, heat resistance, flame resistance, and electrical insulation properties. However, the traditional phenolic resins industry depends very heavily on petroleum as a source of phenol raw material, which is under the influence of petroleum reserves. In recent years, many studies have been conducted to develop cheap, abundant, renewable, and high-performance alternatives to phenol for the production of PR. Lignin, as the most abundant natural polyphenol, has similar chemical structures to that of phenol. Lignin has received increasing attention as a potential feedstock for renewable fuels and chemical production. The substitution of lignin for phenol can not only reduce the costs of PRs but also increase their performance, such as low-toxicity residues and environmental friendliness. This paper reviews the recent progress in lignin activation and modification for lignin-based phenolic resin (LPR) synthesis, highlights the different lignin modification methods, compares the performance of different LPR products, and summarizes their applications in adhesives, foams, molding powders, micro/nano-spheres, and other advanced materials. Finally, this review puts forward the current challenges and potential future prospects for LPR materials. [ABSTRACT FROM AUTHOR]

Lignocellulose flow fuel cells are promising technologies for large scale generation of renewable electricity at low temperature. However, most of them have low electron transfer kinetics and require pre-reaction and redox mediators in anolytes for a liquid-phase catalytic reaction, which leads to low power density, energy consumption and resource waste. Herein, we develop a new low temperature and high-power density lignin flow fuel cell (LFFC) catalyzed by CoMn-LDH electrocatalysts with superhydrophilic intercalation on the anode to efficiently degrade lignin and transfer electrons rapidly. The experiments and DFT calculations show that CoMn-LDH exhibits high adsorption capacity for lignin due to its superhydrophilic intercalation, and has good electrical conductivity due to the greater overlap of antibonding orbitals and high continuity at the Fermi level. Moreover, the abundant oxygen defects of CoMn-LDH can depolymerize lignin effectively. Thus, the prepared CoMn-LDH electrocatalyst enables fast charge transfer and high catalytic efficiency. The power density of the designed LFFC reached 269.3 mW cm−2, and the generated electrical energy is 294.7 mW h based on 1.0 g of lignin, which are obviously higher than those of the reported LFFCs. Furthermore, it can work stably for more than 9 h at 0.3 V and 413.5 mA cm−2, and successfully power a 1.5 V LED pattern with only a 1 cm2 active membrane. It presents a promising approach for developing high-power density LFFCs towards a sustainable society. [ABSTRACT FROM AUTHOR]

The use of HZSM-5 and modified catalysts for the pyrolysis of lignin to produce aromatics has been extensively investigated. But certain limitations including catalyst deactivation and high-cost modifications still exist. A magnetic field (MF) was used to assist Fe and HZSM-5 catalytic lignin pyrolysis for aromatics production in this study. Product composition analysis revealed that the monocyclic aromatic hydrocarbon (MAH) and benzene, toluene, ethylbenzene, and xylene (BTEX) contents exhibited an upward trend in correlation with the MF intensity. The introduction of a MF significantly affects the improvement of the BTEX yield. Under the conditions of 80 mT MF intensity, 500 °C temperature and 50 mL min−1 carrier gas flow rate, the MAH and BTEX contents reach 32.94% and 27.19%, while the BTEX yield reaches roughly 19.55 mg g−1. Compared to no MF, these values rose by about 1.28, 1.36, and 1.94 times, respectively. Characterization results from XRD, XPS, TPO, N2 adsorption–desorption, and NH3–TPD tests showed that the MF facilitated the deoxidation and fragmentation of macromolecular oxygenates on the surface of Fe, promoting the ingress of smaller molecular compounds into the pores of HZSM-5 and boosting MAH production. Simultaneously, the MF impeded pore blockage in HZSM-5 and kept acidic sites from deactivating due to carbon deposition. This study lays a crucial groundwork for improving advanced technologies aimed at optimizing the utilization of organic solid waste. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) are widely used as recyclable green solvents for the separation of lignin from lignocellulosic biomass. However, the poor permeability of DES solution limits the green advancement of separation systems. In addition, lignin fragment molecules are susceptible to repolymerization reactions during separation, resulting in reduced lignin reactivity. In this study, a DES consisting of choline chloride (ChCl) as a hydrogen acceptor, 5-sulfosalicylic acid (5Saa) as a hydrogen donor, and a certain amount of γ-valerolactone (GVL) as an additive was designed. The system not only efficiently fractionated lignin from poplar (71.35%), but also selectively retained almost complete cellulose (retention 92.87%) under the optimal fractionation (ChCl/5Saa/GVL molar ratio 1/4/15, temperature 120 °C, time 3.0 h). Pre-crushing processing of raw materials was avoided as the new DES solution has stronger permeability compared to the previous DES solution. Selective deconstruction of lignocellulose was achieved due to a strong hydrogen network structure. The lignin fragments were effectively dissolved. The results showed that the stability of the carbo-positive active intermediates was enhanced by ChCl–5Saa/GVL. Lignin with a low molecular weight (2305 g mol−1), high purity (98.77%) and high total phenolic hydroxyl content (6.92 mmol g−1) was obtained. Homogeneous lignin nanoparticles (LNPs) were prepared with an average particle size of 23 nm. LNPs had high dispersion stability and excellent UV shielding properties. The green advancement of the new DES has been significantly improved and the efficient fractionation of high-value lignin was realized. [ABSTRACT FROM AUTHOR]

Lignin is composed of phenylpropyl alcohol through the C–O and C–C bonds, where β-O-4 accounts for the majority. Self-transfer hydrogenolysis (STH) is a promising method to produce valuable chemicals and fuels from lignin by cleaving the β-O-4 bond without exogenous hydrogen, but all the reported work used noble metal-based catalysts. In this work, a highly efficient Ni/C catalyst was derived from a Ni-containing metal–organic framework (Ni-MOF), and its self-transfer hydrogenolysis performance towards ether bonds in lignin model compounds was evaluated using 2-phenoxy-1-phenylethanol as a model compound in detail. It was found that the catalyst pyrolyzed under a nitrogen atmosphere at 500 °C (Ni-NDC-500) was very efficient for the reaction. Moreover, it could also catalyze the reaction of native lignin into monomers effectively without exogenous hydrogen. In addition, Ni-NDC-500 was recycled three times without an obvious reduction of the activity. [ABSTRACT FROM AUTHOR]

The electrochemical selective oxidative transformation of lignin feedstocks into valuable oxygenated aromatics is essential to establish a sustainable biorefinery. In this study, we used a rhombohedral ZnIn2S4 (R-ZIS) electrocatalyst to realise the efficient anodic cleavage of C-O bonds in benzyl phenyl ether (BPE), an a-O-4 lignin model compound, to a series of industrially relevant oxygenated mono-aromatics. The reaction occurred at +2 VAg/AgCl, 65 °C, and atmospheric pressure. In optimised conditions, the reaction achieved over 99% conversion rate with a Faraday efficiency of 51.6% at 91.3% conversion of BPE, that is greater than most known electrocatalytic oxidative cleavage examples. The ZnIn2S4 electrocatalyst was deposited on a carbon cloth support, and its structural properties and surface morphology were extensively investigated. Systematic potential controlled electrolysis coupled with 18O isotopic labelling confirmed that C-O scission occurred exclusively between the benzylic carbon and phenolic oxygen. Furthermore, substrate competition studies were conducted to compare the electrocatalytic performance of the R-ZIS catalyst with that of its structural analogue, hexagonal ZnIn2S4, in terms of BPE and monoaromatics conversion. The experimental results were supported by density functional theory calculations. The substrate scoping study revealed the suitability of the R-ZIS induced electrocatalytic system for a variety of substituted a-O-4/ß-O-4 model dimers. Overall, this work demonstrates an efficient anodic process that can enable the atom-efficient valorisation of lignin to produce oxygenated aromatics. The proposed approach can complement the numerous existing reductive lignin cleavage methods. [ABSTRACT FROM AUTHOR]

Solvents with integrated functions enable directional lignin valorization for producing value-added chemicals or lignin polyols. In this study, a solvent-triggered directional lignin valorization process was developed based on the design of a biphasic deep eutectic solvent/dichloromethane (DES/DCM) system. The designed solvents exhibit a combined feature of chemical stabilization from ethylene glycol-based-DES and physical stabilization from a biphasic system. By establishing the DES/DCM, lignin was effectively functionalized into lignin polyols with high yield. Furthermore, by implementing a simple recycling procedure of the DCM phase, the reaction pathway was switched, leading to depolymerization and stabilization of the stabilized lignin polyols. This process resulted in an almost threefold increase in monomeric acetal yields. The effect of biphasic DES on functionalization or switched depolymerization of lignin was confirmed through model compound studies. Our findings demonstrate a directional lignin valorization route using the designed biphasic DES system, which offers potential applications in the production of value-added aromatic chemicals or potential intermediates for polymers. [ABSTRACT FROM AUTHOR]

The global forest industry is focused on developing waste valorization technologies. Regional resources use in biorefineries could be a strategy to improve profitability and mitigate the environmental impact of the involved industrial sectors, adding a new value chain to the forest industry. This study develops the mass and energy balance for bioethylene and lignin production from industrial pine sawdust (IS), a primary wood processing in Argentina. The proposed production process is composed of: (i) sodaethanol pretreatment to remove the lignin; (ii) simultaneous saccharification and fermentation (SSF) to convert the cellulose to glucose and then to ethanol; (iii) ethanol recovery (95%); (iv) ethanol dehydration to bioethylene and; (v) bioethylene recovery through an ethylene tower and stripper. In the proposed process, 107 kg of bioethylene per ton of dry sawdust could be obtained, recovering 208 kg of lignin. Energy consumption is about 1885 MW h t-1 of dry sawdust. The highest consumption is in pretreatment and ethanol recovery processes, which can be reduced by 42%. Regarding economic assessment, the internal rate of return (IRR) and net present value (NPV) were 10.08% and 5.21 MM USD, respectively. Sensitivity analysis shows that the most influential parameters are lignin and bioethylene market prices and energy and enzyme costs. [ABSTRACT FROM AUTHOR]

It is generally believed that the formation of lignin-based carbon quantum dots (L-CQDs) includes lignin depolymerization and repolymerization. However, the detailed mechanism has not been well understood. In this study, the effect of lignin molecular weight on the properties of L-CQDs is studied to elucidate the formation mechanism of L-CQDs. Firstly, alkaline lignin is sequentially fractionated into five lignin samples with a molecular weight range of 7100–2000 using a continuous organic solvent precipitation method. Then, the five lignin fractions are used to prepare five L-CQDs numbered from 1 to 5, corresponding to the lignin fractions from high to low, respectively. L-CQDs-3 that was prepared from the lignin fraction with an intermediate molecular weight of 5042 g mol−1 has a 1.86-fold increase in fluorescence intensity compared to the L-CQDs-0 prepared from pristine alkaline lignin. It is found that this lignin fraction with a molecular weight of 5042 g mol−1 can depolymerize into a large number of vanillin and benzaldehyde (2,4-dihydroxy-6-methyl) units. These low molecular weight units can easily form highly conjugated carbon core structures, thus improving the fluorescence performance of L-CQDs-3. In addition, the present study confirms the excellent imaging ability of L-CQDs-3 in the L02, HepG2 and Escherichia coli cells. This study not only supplements the existing L-CQD formation mechanism, but also provides a simple method for the preparation of L-CQDs with high fluorescence performance. [ABSTRACT FROM AUTHOR]

Producing green carbon fiber from lignin is not only attractive to biorefineries for valorizing lignin but also contributes to the decarbonization of multiple industries. However, the difficulty of obtaining high-quality lignin-based carbon fibers at low cost remains the bottleneck and barrier to its commercial application. Previous approaches for chemically modifying lignin or blending with co-precursors were ineffective in delivering the carbon fiber with the desired quality. We discovered that introducing thermo-mechanochemistry of lignin to carbon fiber processing is a facile and green approach to overcome this challenge. Thermo-mechanochemistry can be introduced by properly integrating thermal heating and mechanical tension force applied to the spun fiber, which can manipulate the ordinary lignin chemistry to control the microstructure evolution from lignin. Under the influence of this newly known chemistry, lignin can transform into an oriented structure that can easily be graphitized at low temperatures. In this work, three precursors consisting of lignin or lignin blends were used to produce the carbon fibers with average tensile strength and modulus of 2.45 GPa and 236 GPa, 2.11 GPa and 215 GPa, 2.2 GPa and 225 GPa, respectively, using a surprisingly low carbonization temperature of only 700 °C. The preliminary techno-economic analysis suggests a low production cost. The discovery of the thermo-mechanochemistry of lignin will alter perceptions of lignin-based carbon fibers and provide opportunities to produce commercially viable low-cost green carbon fibers, advancing lignin valorization. [ABSTRACT FROM AUTHOR]

The utilization of lignin in material fabrication has garnered significant attention despite its complex structure that greatly limits its applications. This study reports a green method for grading and modifying lignin to prepare stable hydrophobic coatings via the solvent/anti-solvent (ethanol/water) self-assembly method. First, the formic acid lignin particle (FLP) is prepared and the underlying mechanism is primarily ascribed to the hydrogen bonding, π–π interactions among aromatic groups within and between molecules, and hydrophobic interactions. The lignin nanoparticles were utilized to chelate with metal ions (iron) in order to obtain the stable hydrophobic coatings using the special nanostructures of FLP. This hydrophobic coating could be applied to different substrates (blocks, straw, and fabric). The cotton fabric exhibited an initial water contact angle (WCA) that increased from 73.4° to 129.6°, and excellent chemical and physical hydrophobic performance. Moreover, this coating has strong self-cleaning ability and could be used for oil–water separation. In this newly proposed fabrication, ethanol can be recovered in the preparation of lignin nanoparticles, which makes the green and facile preparation of a stable hydrophobic coating possible. Additionally, this work is important in upgrading formic acid lignin by controlling the polarity into value-added hydrophobic materials via green classification. [ABSTRACT FROM AUTHOR]

Biomass-derived solvents have been proposed as a novel pathway in biorefining for the realization of biofuels and bioproducts derived from lignocellulosic biomass. Cyrene derived from cellulose has recently been shown to have a high potential as a green organic solvent for pretreating poplar biomass. However, due to its high dynamic viscosity nature, high Cyrene concentration could cause negative effects on the sugar release of the pretreated biomass as well as driving up the operational cost of the lignin recovery. In this study, we combine experimental and computational approaches to examine the impact of Cyrene pretreatment with reduced Cyrene concentration under mild conditions on switchgrass lignin. Our experimental studies indicated correlation between pretreatment condition and recovery and structure modification of lignin. Switchgrass lignin extracted by Cyrene pretreatment possessed high preservation of β-O-4 ether inter-unit linkage, which could provide versatility in the integration of downstream lignin valorization into the modern biorefinery industries. Molecular modeling examining the solvation of switchgrass lignin polymer and the disaggregation of low-molecular weight lignin aggregates under pretreatment conditions indicated that a preferential interaction exists between Cyrene and lignin, which likely drives lignin release, and that the disruption of inter-lignin contacts can be modulated as a non-monotonic function of Cyrene : water ratio. Further, while Cyrene–lignin interactions permit the solubilization of lignin, simulations with proxy reactive-species reveal that changes to the diffusion of these reactive proxies and their localization near linkage sites under Cyrene conditions may inhibit chemical processes. The results indicated that loss of pretreatment efficacy caused by low Cyrene concentration could be compensated by prolonged pretreatment time and high catalyst dosage. [ABSTRACT FROM AUTHOR]

The conversion of lignin into carbon dots is an emerging technology to make use of this renewable and abundant material. The low yield and low quantum yield of carbon dots from lignin remain key challenges of this technique. Here, prior amino modification of lignin using the Mannich reaction was proposed to improve carbon dot production from lignin by the hydrothermal method. Accordingly, the yield and quantum yield of carbon dots were synchronously improved from 9.8 wt% and 5.36% to 68 wt% and to 42.7%, respectively, because modified lignin suppresses hydrochar formation. A survey of the impact of the lignin structure on carbon dot production, and the structure and property relationship of the as-prepared carbon dots showed that the process could make use of condensed lignin to produce carbon dots with high performance. Techno-economic analysis suggested that this process noticeably reduced the product selling price because of the improved yield. This study provides a strategy to reduce the production cost of carbon dots from lignin, which may inspire the community to extract money out of lignin. [ABSTRACT FROM AUTHOR]

The biomass flow fuel cell (BFFC) is a promising technology for realizing a sustainable society. However, BFFCs generally require electron mediators and complex pretreatment, resulting in miscellaneous ion pollution and energy consumption. Herein, we develop a lignin flow fuel cell (LFFC) for self-generating electricity via the privileged structure and redox chemistry of lignin without any electron mediators and pre-reaction. The experiments and theoretical simulations reveal that lignin can automatically release electrons by its oxidation and cleavage under a high voltage difference to achieve high cell performance. Interestingly, phenolic lignin model compounds with more methoxy groups exhibit higher cell performance because the methoxy groups can significantly reduce their HOMO–LUMO energy gaps and oxidation potentials, which is beneficial for releasing electrons. When industrial lignin was utilized as the fuel, the LFFC achieved a high power density of 159.9 mW cm−2 and worked stably for more than 8 h with 5.0 g lignin. Moreover, the LFFC fueled by 1.0 g lignin can output 219.9 mW h electrical energy, which is significantly higher than that of the reported BFFCs. Furthermore, the scale-up of the LFFC can power several electrical devices simultaneously at room temperature. This work provides a promising approach for next-generation LFFCs with low cost and high performance towards a sustainable future. [ABSTRACT FROM AUTHOR]

As a new type of green photothermal material, lignin exhibits an excellent photothermal effect due to its abundant aromatic rings and π–π conjugated structure. To develop value-added applications of lignin in the photothermal field, it is important to explore strategies for regulating the photothermal conversion of lignin. In this work, the photothermal effect of lignin was improved significantly through modification with an electron-withdrawing group. The introduction of acetyl resulted in the formation of an electron donor–acceptor (D–A) structure in lignin and enhanced the light absorption ability. The intermolecular interaction among lignin molecules also decreased after modification with acetyl groups, leading to enhanced non-radiative decay induced by molecular motion. Under 808 nm laser irradiation at 0.51 W cm−2, the photothermal conversion efficiency of acetylated lignin (ACAL) reached as high as 73.2%, which was 37% higher than that of unmodified lignin. This study provides a new strategy to enhance the photothermal effect of lignin and deepens the understanding of the lignin photothermal mechanism. [ABSTRACT FROM AUTHOR]

Green and efficient biorefinery strategies are essential for sustainable biomass utilization. This study reported a novel fractionation strategy using deep eutectic solvent–sodium bicarbonate (DES–SB) for full-component utilization of corn stover (CS). The results showed that the addition of SB significantly improved the delignification efficiency (90.03%) compared to that of the neat DES pretreatment (34.64%). As a result, excellent carbohydrate digestibility was achieved (glucose yield, 97.47%; xylose yield, 92.93%). Moreover, the regenerated lignin exhibited high purity (94.31%), excellent thermal stability, a low molecular weight (1593 g mol−1), and good uniformity (1.76), indicating great potential for further value enhancement. NMR analysis indicated the retention of major interunit linkages (45.6% of β-O-4), and the recovered lignin presented a greater number of carboxyl groups and a lower number of p-hydroxyphenyl OH groups as the pretreatment severity increased. Finally, mass balance analysis demonstrated that 1 kg of dry CS could produce 367.03 g of glucose, 171.70 g of xylose, and 143.52 g of lignin. Overall, this study provides a green, high-efficiency, and synergistic DES–SB pretreatment strategy that has great potential for full-component biomass utilization and sustainable industrial biorefinery application. [ABSTRACT FROM AUTHOR]

The photocatalytic depolymerization of lignin is a sustainable strategy to produce high-value aromatic chemicals. The selective and efficient cleavage of β-O-4 bonds under mild conditions remains one of the challenges in lignin valorization. Herein, an efficient and mild strategy was employed for one-step photocatalytic depolymerization of lignin and β-O-4 model compounds over novel Z-scheme heterojunction g-C3N4/carbon quantum dot/CdZnS (CN/CQD/CZS) under simulated solar light. The total yield of vanillin and vanillic acid from lignin depolymerization was 36.3 mg g−1 lignin when the volume ratio of SDS-8 (sodium dodecyl sulfate solution with a mass fraction of 0.08%) to HCOOH was 4 : 1 within 2 h. The depolymerization mechanism of lignin was investigated using β-O-4 model compounds. The β-O-4 model compounds were converted into phenolic monomers over optimized CN/CQD/CZS, yielding 84% substrate conversion and ∼100% C–O bond cleavage selectivity. Three extractive natural lignin samples were applied to this system and successfully depolymerized. A combination of experimental results and theoretical calculations illustrated that CQDs played a crucial role in accelerating photogenerated electron transfer at the CN/CZS interface via the Z-scheme electron pathway, which effectively promoted the separation and transfer of photoexcited hole–electron pairs. Mechanistic studies demonstrated that the selective cleavage of the β-O-4 bond mainly involved a photogenerated electron–hole coupled redox mechanism. The construction of the Z-scheme CN/CQD/CZS heterojunction is essential to enhance the kinetics of electron transport and maintain strong redox ability. The approach in this work offers a useful guidance for the construction of Z-scheme heterojunction photocatalysts with a carbon-based electron mediator and the selective breakage of C–O bonds in lignin. [ABSTRACT FROM AUTHOR]

This study presented for the first time a continuous flow microreactor system for efficient dealkaline lignin depolymerization applying an electrochemical advanced oxidation process (EAOP). The insolubility of dealkaline lignin in water poses a challenge for its chemical depolymerization via EAOP. To address this limitation, several co-solvent systems were developed and investigated to achieve efficient dealkaline lignin depolymerization. Five water-miscible organic solvents, namely methanol (MeOH), ethanol (EtOH), acetonitrile (MeCN), tetrahydrofuran (THF), and N,N-dimethylformamide (DMF), were used as co-solvents. With the co-solvent fraction of 1% in water, the solubility of dealkaline lignin followed the order of THF > DMF > MeCN > MeOH > EtOH. The electron spin resonance (EPR) of various co-solvents revealed that different co-solvents affected the concentration of in situ OH radical generation, leading to the difference in dealkaline lignin conversions. For dealkaline lignin in water–MeCN system, 72% conversion was observed within 100 s of residence time under ambient conditions with a 1 mA current. Moreover, the two main lignin model compounds (2-phenoxy-1-phenyl ethanol (PPE) containing β-O-4 and benzyl phenyl ether (BPE) containing α-O-4) were used to understand the kinetic analysis and degradation of dealkaline lignin. High conversions of 75% and 92% were achieved for the β-O-4 (PPE) and α-O-4 (BPE) lignin model compounds, respectively. All the products were confirmed using GC-MS analysis. Additionally, mechanistic insights for lignin depolymerization were provided using lignin model compounds. [ABSTRACT FROM AUTHOR]

As global interest in carbon-neutrality policies grows, the demand for sustainable alternatives to fossil fuels intensifies. Herein, we demonstrate functionalized lignin-based n- and p-dopants for nanocarbon materials, providing promising eco-friendly alternatives to chemical dopants derived from fossil fuels. A simple microwave-assisted phenolation of organosolv lignin introduces phenol groups, offering additional reaction sites and enhancing solvent solubility for uniform, reliable and efficient carbon nanotube (CNT) doping. To create effective n- and p-dopants, the phenolated lignin is further functionalized with amine and hexafluoropropyl groups, respectively. The aminated and fluorinated lignin-doped CNTs present the Seebeck coefficients of −48.0 and 53.9 μV K−1, respectively, confirming an efficient and eco-friendly conversion between n- and p-type CNT. Notably, this n-doping performance is of particular significance since stable and reliable n-doping is challenging due to the inherent p-type semiconducting properties of CNTs. As a proof of concept, we demonstrate a flexible thermoelectric generator using 10 p–n pairs of the CNT films. The output voltage (7.86 mV) and output power (247 nW) of the flexible generator at ΔT = 15 K confirm that the aminated- and fluorinated lignin-doped CNT films exhibit n- and p-type characteristics, respectively. This study paves the way for sustainable, lignin-based doping of carbon nanomaterials, offering a green alternative to traditional fossil fuel-derived dopants and contributing to the transition towards carbon-neutral technologies. [ABSTRACT FROM AUTHOR]

An effective method of grafting functionalities onto lignin based on glycerol carbonate has been developed. This biobased grafting reagent reacts with lignin without generating co-products. Alkenyl groups were added to the glycerol carbonate moiety from 1,3-butadiene chemistry using the nickel-catalysed hydroalkoxylation reaction and the newly developed nickel-catalysed telomerisation reaction under solvent-free conditions. The high-atom economical reactions lead to three different sets of glycerol carbonate ethers with various chain lengths that can be separated from the catalyst to avoid lignin contamination with metals. Kraft, organosolv and soda lignins, without prior purification, were grafted via ether functions using these linkers in a clean and efficient procedure. The technical and modified lignins were characterised by NMR, IR and SEC, and their thermal properties were determined by DSC. The glass transition temperatures of the modified lignins are significantly reduced, opening up possibilities of shaping, for example, on hot presses. In addition, these modifications offer the possibility of inserting new reactive functions within the lignin, including unsaturations and alcohols, allowing a new range of lignin-based resins to be developed. [ABSTRACT FROM AUTHOR]

Condensation, dark color and low extraction yield of lignin have hindered the full valorization of biomass during lignocellulosic fractionation. Herein, we introduce a novel biomass fractionation concept that addresses the issue of lignin's spatial confinement. Building upon this concept, we have devised an environmentally friendly and straightforward strategy. This approach involves a combination of selective carboxylation at the Cγ-OH position using citric acid and etherification at the Cα-OH position using butanol. The objective is to mitigate the spatial confinement of lignin and stabilize its active intermediates for lignin extraction. Consequently, up to 91.4 ± 0.2% lignin with a light color can be separated from the recalcitrant softwoods, as a UV blocker to improve the performance of sunscreen cream. The cellulosic residue can be enzymatically digested to glucose with a yield of 80%. The initiated biomass fractionation theory and strategy in this study provide a new concept for the isolation of lignin and full valorization of lignocellulose, promoting the development of a sustainable economy. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) and Fenton pretreatment (FP) are effective methods currently being used to treat lignin. However, there are few reports of combining the two techniques and applying them in the treatment of lignin. Additionally, the synergistic effect of the two techniques on the physicochemical properties of lignin has not been widely investigated. Therefore, this study innovatively combined Fenton pretreatment with hydrothermal carbonization to investigate the synergistic effect on two types of structurally different lignans, and to reveal the changes in physicochemical properties of lignin under the synergistic effect. In this work, 13C NMR, XPS, FTIR, XRD, Raman spectroscopy, and automated calorimetry were used to determine the physicochemical properties and characterize the chemical structure of lignin. The results showed that the synergistic effect of FP–HTC increased the carbon fixation rate of herbal lignin (HL) and de-alkalized lignin (DAL) by 46.07 and 59.27%, respectively, and heating value of HL and DAL by 45.53 and 46.07%, respectively. The synergistic action of FP–HTC broke the stubborn and complex chemical barrier of lignin, and effectively enhanced the degree of aromatization and demethoxylation of lignin. It is notable that the synergistic effect of FP–HTC induced the formation of more stable 4-O-5 bonds and C–C bonds in the lignin structure, resulting in a moderate enhancement of the lignin chemical structure and material properties. In this study, the synergistic effect of Fenton pretreatment and hydrothermal carbonization is utilized to convert lignin into sustainable carbon materials, and the effect of the synergistic effect on the physicochemical properties of lignin is analyzed in detail, which provides valuable references for the subsequent research on the conversion of waste lignin into carbon materials. [ABSTRACT FROM AUTHOR]

The conventional fractionation of lignocellulose into cellulose, hemicellulose, and lignin was generally carried out at high temperatures and under highly acidic conditions owing to the rigid matrix of lignocellulose and crystallinity of cellulose, causing the degradation of carbohydrates and condensation of lignin, thus hindering their value-added utilization. In this study, a stepwise fractionation method was proposed in which microwave-assisted fractionation of hemicellulose under mild conditions contributed to 81.9% of xylose yield; then, the cellulose part solid was rapidly dissolved in LiBr molten salt hydrate (LiBr-MSH) solution, followed by a filtration process to isolate lignin solid. It was found that the removal of hemicellulose provided more pores for the next dissolution of cellulose, and LiBr-MSH caused the cleavage of the hydrogen bonds of cellulose. Consequently, the cellulose part solid was rapidly dissolved in LiBr-MSH. The results showed that under the optimal fractionation conditions, 78.0% yield of glucan oligomers and 89.7% purity of noncondensed lignin were obtained from cellulose fractionation and filtration, respectively. A high β-O-4 bond content close to 87.3% of the theoretical maximum yield was detected in the obtained lignin, indicating that most β-O-4 bond structure of lignin was well preserved. Additionally, the isolated lignin can be selectively depolymerized into aromatic monomers with a high yield of 20.4%, which is 74.2% of the theoretical maximum yield. [ABSTRACT FROM AUTHOR]

Lignin nanoparticles (LNPs) have gained great interest as a promising renewable nanomaterial toward value-added applications. This work investigated solution chemistry and particle–particle interaction force in the LNP formation aiming at a facile technique to balance amphiphilic properties of lignin for size-controlled synthesis. By facilely tuning solution chemistry, lignin with different amphiphilic properties can form the nanoparticles with 57–262 nm and dispersity index (Đ) less than 0.2 at an initial lignin concentration of 10–80 g L−1. A numerical estimation of particle size was established with Derjaguin–Landau–Verwey–Overbeek's (DLVO) theory and population balance equation (PBE) to evaluate the interaction energy of particles as the function of solution chemistry and lignin properties. In the developed DLVO–PBE model, lignin properties such as molecular weights and content of functional groups are closely related to the repulsive energy calculation in the particle collision and further determine the assembly patterns. The model can be applied to lignin with varied properties with high prediction accuracy, especially in the DLVO forces-driven aggregation. It also suggests that solvated lignin chains can involve the uneven electrostatic force field and non-DLVO forces leading to a broad/multi-modal size distribution. Overall, the combination of experimental and theoretical investigations provides new insights into assembly mechanisms of lignin molecules involved in the formation of nano-/submicron particles. [ABSTRACT FROM AUTHOR]

Kraft lignin (KL) was treated by employing mild oxidation conditions enhanced by ultrasound irradiation (US) for obtaining more functionalized particles, avoiding the undesired side reactions of degradation and depolymerization. The aim was to obtain products with plausible value for applications with a greater potential market, enabling the introduction of low-cost bio-based materials for technically advanced applications. In the present work, KL was oxidized in alkaline media, applying low temperatures (30–60 °C), short times (15 to 60 min), and US waves (20 kHz). The influence of incorporating hydrogen peroxide (H2O2) as an oxidizing agent was also studied, as well as the chemical composition, physicochemical, thermal, and morphological properties of the final lignin particles. It was observed from Quantitative Acid Hydrolysis (QAH), Elemental Analysis (EA), and molecular weights (Mw) that oxidized lignin particles (OxL) did not suffer any major degradation. Other techniques used to determine physicochemical properties, such as Fourier Transformed Infrared (FTIR), 31 Phosphorous Nuclear Magnetic Resonance (31P NMR), or Ultraviolet–visible (UV-vis) methods, corroborated oxidation reactions, evident by the increment of carboxylic groups. The most noticeable difference, however, was observed when the stability and morphology of the particles were observed by Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). Some conditions greatly promoted the formation of more stable and nanosized particles. The best conditions were the mildest but with the highest reaction times (no addition of H2O2, 30 °C and 60 minutes). Moreover, all reactions had good recovery yields, above 70% of the original lignin. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) are intriguing for biomass fractionation, but high DES dosage and low biomass loading make them challenging to be used in industry. In this study, a DES was integrated into a novel pretreatment technology, namely "Densifying Lignocellulosic biomass with Chemicals followed by Autoclave (DLCA)", to realize lignocellulose fractionation and valorization with low DES dosage and high fractionation efficiency. Remarkably, a total DES dosage of 2 g g−1 biomass, which is substantially low compared to traditional DES pretreatments, achieved a high delignification ratio of 75% with over 95% cellulose preserved at 50% solid loading. Moreover, DLCA(DES)-CS exhibited superior bioconversion efficiency even at high solid loadings, with the maximum total fermentable sugar concentration exceeding 300 g L−1 and the ethanol concentration as high as 110 g L−1. Comprehensive characterization methods such as SEM, XRD, FTIR and Simons' staining were used to disclose the properties of cellulose-rich solids, and the chemical structure of the extracted lignin was characterized by GPC and 2D-HSQC NMR spectroscopy, revealing that DLCA(DES) pretreatment not only ensured complete exposure of cellulose, but also remarkably protected the native structures of lignin. Without recondensation, lignin extracted by DLCA(DES) preserved more than 98% of native β-O-4 linkages. In brief, this study demonstrates great potential for lignocellulose valorization initiated by DLCA(DES) pretreatment, including polysaccharide conversion to bioethanol and selective lignin depolymerization to aromatic monomers. [ABSTRACT FROM AUTHOR]

Catalytic depolymerisation of naturally occurring catechyl lignins (C-lignins) with benzodioxane linkages represents a direct and sustainable protocol for producing catechols, but the configuration of this process typically involves operation at high temperature, high H2 pressure, and high solvent-to-biomass ratios. Here, for the first time, we demonstrate that tris(pentafluorophenyl)borane (B(C6F5)3) can efficiently catalyse reductive cleavage of vicinal C–O bonds in benzodioxane structures with Et3SiH as a hydrogen donor. This homogeneous catalytic system can be generalized to C-lignin biopolymer derived from castor seed coats at room temperature and ambient pressure in highly concentrated form, thus giving silylated catechol derivatives in 85% yield. The as-depolymerized product is readily purified from the reaction mixture owing to high monomer selectivity. Reactivity screening of various C-lignin mimics, together with DFT calculations, offer an insight into the mechanistic understanding of the current depolymerisation of benzodioxane C-lignin. Overall, our results pave an economic and environmental pathway for producing catechols from biomass waste products. [ABSTRACT FROM AUTHOR]

The development of novel catalysts to regulate product selectivity and insight into the mechanism of lignin hydrogenolysis are important for the comprehensive utilization of lignocellulose. Herein, we present a non-precious bimetallic catalyst Ni5Fe5/Al2O3 with improved catalytic performance relative to commercial Pd/C and Ni10/Al2O3 for hydrogenolysis of woody sawdust. In particular, the selectivity of propylguaiacol and propylsyringol is 79.1%. We developed kinetic experimental studies on β-O-4 model compounds and directly monitored the coniferyl alcohol or sinapyl alcohol intermediates in the reaction system for the first time. This directly demonstrates the lignin hydrolysis reaction pathway with simultaneous breakage of Cα-OH and Cβ-O. In the catalytic system, the reason for the difference in selectivity between Ni5Fe5/Al2O3 and other catalysts is their different hydrogenation pathways for intermediates coniferyl alcohol or sinapyl alcohol. Our work provides both an efficient catalyst and insight into understanding and regulating the mechanism of lignin hydrogenolysis. [ABSTRACT FROM AUTHOR]

DLC pretreatment is a novel and efficient pretreatment method for lignocellulosic biomass, but its mechanism of action has not been illustrated yet. In this study, a systematic investigation was conducted to find that the synergy of acidic chemical and mechanical actions during DLC pretreatment played an important role to ensure excellent performance. Mechanical actions likely exposed the internal polysaccharides of biomass by disrupting the cell wall structure, and the exposed polysaccharides reacted with concentrated acid until they were partially deconstructed, thereby significantly reducing the severity of subsequent dilute acid treatment. This synergism increased the accessible breakpoints of crystalline cellulose to cellulase by reducing the cellulose crystallinity and polymerization degree, as well as by digesting amorphous cellulose. Additionally, the large removal (about 60%) of hemicellulose increased biomass porosity. The native lignin structure was well preserved without the generation of pseudo-lignin and large amounts of toxic degradation products. These properties contribute to the high sugar recovery (97.2%), great digestibility (83.4% total yield of monosaccharides), and outstanding fermentability of DLC biomass; these results are not achievable for traditional dilute acid pretreatment. Simultaneous saccharification and co-fermentation of DLC-pretreated rice straw resulted in an ethanol titer as high as 82.9 g L−1 without detoxification. Detailed structural analysis revealed that the well-preserved inter-unit linkages (>80%) and non-condensed subunits remained in the DLC lignin. This study revealed the mechanism of DLC technology in promoting biomass conversion, and thus, provides guidance to potentially realize efficient and economical biorefinery. [ABSTRACT FROM AUTHOR]

Numerous deep eutectic solvents (DESs) have been studied for effective saccharification of cellulose by removing hemicellulose and/or lignin. However, the removed fractions, including lignin and hemicellulose, have not been sufficiently characterized. For a successful biorefinery strategy, valorization of these fractionated portions is as important as cellulose utilization. In this study, a novel biphasic solvent process using DES and γ-valerolactone (GVL) was investigated for efficient glucan saccharification, furfural production, and high-quality lignin recovery. This process dramatically enhanced the enzymatic saccharification of cellulose by significantly removing lignin (88.61%) and xylan (98.67%). Remarkably, the recovered lignin exhibited a well-preserved lignin structure, and the furfural output reached a satisfactory yield of 50.90%. The fractionation mechanism of the biphasic system was comprehensively investigated. This study emphasized that the biphasic DES/GVL system is an ideal solvent to maximize the use of biomass components with high enzymatic saccharification yield, furfural yield, and high-quality lignin as co-products. [ABSTRACT FROM AUTHOR]