Microwave Depolymerization of Lignin via Dynamic Vapor Flow Reaction System: HCOOH as Pretreatment Solvent or Reforming Solvent Vapor.

Different forms of HCOOH in the depolymerization system play an important role in governing the monomeric products from lignin. We reported two strategies for the introduction of HCOOH to enrich the monophenols from kraft lignin by microwave-assisted depolymerization. The reaction of lignin models showed that HCOOH was in favor of the cleavage of C-O bonds (ß-O-4 typically) and partial C-C bonds (Cα-Cß). Subsequently, Microwave-assisted depolymerization of lignin with two strategies was conducted via a designed dynamic vapor flow reaction system. Strategy A with HCOOH as pretreatment solvent showed excellent monophenols enrichment with total mass yields of 193.71 mg/g (lignin basis). Strategy B using HCOOH as reforming solvent vapor significantly increased the monophenols selectivity. It presented unique reforming and upgrading performance by generating catechol (42.59 mg/g, lignin basis) and homovanillic acid (17.58 mg/g, lignin basis). This study provided potential strategies for the efficient conversion of kraft lignin into high-value platform chemicals.

Integrated Preparation of Hollow Lignin Nanoparticles as a Drug Carrier and Levulinic Acid from the Poplar Wood Prehydrolysis Liquor.

Prehydrolysis liquid (PHL) from dissolving pulp and biorefinery industries is rich in saccharides and lignin, being considered as a potential source of value-added materials and platform molecules. This study proposed an environmentally friendly and simple method to prepare morphologically controllable hollow lignin nanoparticles (LNPs) and levulinic acid (LA) from PHL. In the first step, after hydrothermal treatment of PHL with p-toluenesulfonic acid (p-TsOH), lignin with a uniform molecular weight was obtained to prepare LNPs. The prepared LNPs have an obvious hollow structure, with an average size of 490-660 nm, and exhibit good stability during 30 days of storage. When the as-obtained LNPs were used as a sustained-release agent for amikacin sulfate, the encapsulation efficiency reached over 70% and the release efficiency within 40 h reached 69.2% in a pH 5.5 buffer. Subsequently, the remaining PHL that contains saccharides was directly used for LA production under the catalysis of p-TsOH. At 150 °C for 1.5 h, the LA yield reached 58.4% and remained at 56% after 5 cycles of p-TsOH. It is worth noting that only p-TsOH was used as a reactive reagent throughout the entire preparation process. Overall, this study provided a novel pathway for the integrated utilization of PHL and showed the immense potential of the preparation and application of LNPs.

Integrated preparation of functional lignin nanoparticles and levulinic acid directly from the pre-hydrolysis liquor of poplar wood.

The pre-hydrolysis liquor (PHL) produced during pulp dissolution and biomass refining is mainly composed of hemicellulose and lignin, and it is a potential source for production of value-added materials and platform chemicals; however, their utilization has been a serious challenge. In this study, we proposed a green and simple strategy to simultaneously prepare size-controlled functional lignin nanoparticles (LNPs) and levulinic acid (LA) from PHL as the raw material. The as-prepared LNPs exhibited remarkable stability thanks to the presence of saccharides with abundant oxygen-containing groups and surface charges, which prevented aggregation and maintained long-term storage stability. Trace amounts of the LNPs (≤ 0.2 wt%) could stabilize various Pickering emulsions, even with oil-to-water ratios as high as 5:5 (v/v). Subsequently, the remaining PHL was directly used to produce LA without adding a catalyst; under optimal conditions (160 °C and 1 h), the yield of LA was 56.3 % based on the dry saccharide content in the raw PHL. More importantly, p-toluenesulfonic acid (p-TsOH), the only reactive reagent used during the entire preparation process, including the two preparation steps of the LNPs and LA, was reusable, and the recovery rate was >70 % after five cycles. Overall, this green and simple strategy effectively and comprehensively utilized the PHL and showed potential for producing biobased nanomaterials and platform chemicals.

Biodegradable, Strong, and Hydrophobic Regenerated Cellulose Films Enriched with Esterified Lignin Nanoparticles.

The scientific community is pursuing significant efforts worldwide to develop environmentally viable film materials from biomass, particularly transparent, high-performance regenerated cellulose (RC) films, to replace traditional plastics. However, the inferior mechanical performance and hydrophilic nature of RC films are generally not suitable for use as a substitute for plastics in practical applications. Herein, lignin homogenization is used to synthesize high-performance composite films. The esterified lignin nanoparticles (ELNPs) with dispersible and binding advantages are prepared through esterification and nanometrization. In the presence of ELNPs, RC films exhibit a higher tensile strength (110.4 MPa), hydrophobic nature (103.6° water contact angle, 36.6% water absorption at 120 min, and 1.127 × 10-12 g cm cm-2 s-1 Pa-1 water vapor permeability), and exciting optical properties (high visible and low ultraviolet transmittance). The films further display antioxidant activity, oxygen barrier ability, and thermostability. The films completely biodegrade at 12 and 30% soil moisture. Overall, this study offers new insights into lignin valorization and regenerated cellulose composite films as novel bioplastic materials.

Preparation of strong and tough conductive hydrogel based on Grafting, Fe3+-Catechol complexations and salting out for triboelectric nanogenerators.

The development of a strong and tough conductive hydrogel capable of meeting the strict requirements of the electrode of a hydrogel-based triboelectric nanogenerator (H-TENG) remains an enormous challenge. Herein, a robust conductive polyvinyl alcohol (PVA) hydrogel is designed via a three-step method: (1) grafting with 3,4-dihydroxy benzaldehyde, (2) metal complexation using ferric chloride (FeCl3) and (3) salting-out using sodium citrate. The hydrogel contains robust crystalline PVA domains and reversible/high-density non-covalent interactions, such as hydrogen bonding, π-π interactions and Fe3+-catechol complexations. Benefiting from the crystalline domains, the hydrogel can resist external forces to the hydrogel network; meanwhile, the reversible/high-density of non-covalent interactions can impart gradual and persistent energy dissipation during deformation. The hydrogel possesses multiple cross-linked networks, with 6.47 MPa tensile stress, 1000 % strain, 35.24 MJ/m3 toughness and 37.59 kJ/m2 fracture energy. Furthermore, the inter-connected porous hydrogel has an ideal structure for ionic-conducing channels. The hydrogel is assembled into an H-TENG, which can generate open circuit voltage of âˆ¼ 150 V, short-circuit current of âˆ¼ 3.0 µA, with superb damage immunity. Subsequently, road traffic monitoring systems are innovatively developed and demonstrated by using the H-TENG. This study provides a novel strategy to prepare superiorly strong and tough hydrogels that can meet the high demand for H-TENGs.

Tannin-Assisted Synthesis of Nanocomposites Loaded with Silver Nanoparticles and Their Multifunctional Applications.

Nanocomposites have been widely used in many important areas due to their particular physical/chemical properties; however, just though a simple technology, endowing multiple functions into a single nanomaterial for realizing their multifunctional applications is still a challenge. Here, we report a robust method for the facile synthesis of Ag-based multifunctional nanocomposites via using tannin-coated phenol-formaldehyde resin nanospheres (TA-PFRN) as silver nanoparticle (Ag NP) carriers. The thickness of the tannin coating is readily tuned from 50 to 320 nm by regulating the concentration of tannin added. Under the optimal conditions, the TA-PFRN has a 23.8 wt % of Ag NPs loading capacity with only 17.2 nm Ag NP layers. Consequently, the novel TA-PFRN@Ag nanocomposites possess multiple functions and integrated characteristics. As catalysts, the catalytic efficiency of TA-PFRN@Ag is nearly 6 times higher than that of the PFRN@Ag. As highly effective free radical initiators, TA-PFRN@Ag nanocomposites can trigger ultrafast acrylic acid (AA)/acrylamide (AM) polymerization at room temperature (in only a few minutes). As nano-reinforced fillers, the addition of 0.04 wt % nanocomposites can improve the tensile strength of PVA film from 60 to 153.2 MPa. In addition, the nanocomposites can also serve as antibacterial agents, efficiently inhibiting the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus); as antiultraviolet agents, the presence of TA-PFRN@Ag nanocomposites endows the film/hydrogel materials excellent ultraviolet (UV) shielding. This work provides a novel strategy for the green synthesis of Ag-based multifunctional nanocomposites that show promising applications in catalysis, nanomaterials, and biomedicine.

Advances in green materials derived from wood for detecting and removing mercury ions in water.

The issue of mercury pollution in environmental remediation has garnered significant attention due to its severe health hazards to humans. Various strategies have been devised to mitigate the impact of toxic mercury ions, including coagulation, ion exchange, adsorption, membrane technology, and electrochemical treatment. Among these approaches, adsorption has emerged as an efficient and widely employed method for the uptake of low concentrations of mercury ions. It offers convenient operation, high removal efficiency, and facile regeneration of the adsorbent. Wood, being the most abundant renewable and sustainable bioresource, has garnered attention as a promising material for treating heavy metal wastewater. This is attributed to its unique physical and chemical characteristics, encompassing hierarchical pores, aligned channels, active functional groups, biodegradability, and cost-effectiveness. However, a comprehensive examination of the cutting-edge applications of wood and wood-derived biopolymers in the detection and removal of mercury ions from wastewater has yet to be undertaken. Consequently, this article presents a chronological overview of recent advancements in materials and structures derived from bulk wood and its constituents, including cellulose, lignin, hemicellulose, and tannin, with a specific focus on their utility in detecting and eliminating mercury from water sources. Subsequently, the most promising techniques and strategies involving wood and wood-derived biopolymers in addressing the predicament of mercury pollution are explored. Furthermore, this piece offers insights into the existing challenges and future prospects concerning environmentally friendly materials derived from wood, aiming to foster the development of cost-effective mercury adsorbents and detection devices.

Preparation of ultrafine and highly loaded silver nanoparticle composites and their highly efficient applications as reductive catalysts and antibacterial agents.

The size of silver nanoparticles (Ag NPs) and loading amount of Ag NPs onto their substrate/carrier are two key factors for their efficient applications. Herein, we present a facile method for in situ synthesizing ultrafine and highly loaded Ag NPs on the surface of tannin-coated catechol-formaldehyde resin (TA-CFR) nanospheres. TA-CFR nanospheres act as green and highly efficient reducing agents for converting silver ions (Ag+) into Ag NPs, and the size of resultant Ag NPs is only âˆ¼ 7.5 nm, and the Ag NPs loading capacity of TA-CFR is as high as 61.5 wt%, both of which contribute to the very high specific surface area of Ag NPs. Consequently, the as-synthesized TA-CFR@Ag composites show high catalytic performance, and the catalytic rate for the reduction of 4-nitrophenol is almost 10 times higher than that of the control. Meanwhile, TA-CFR@Ag composites also possess high antibacterial activity, efficiently inhibiting the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Furthermore, tannin coating (thickness: ∼ 15 nm) minimizes the aggregation of Ag NPs, and enhances the reusability and stability of resultant Ag NPs, because of their high surface charges (the zeta potential is up to -65.5 ± 1.9 mV) and strong coordination capability with Ag NPs. This work provides a new frontier to develop multifunctional nanomaterials focusing on the green catalyst synthesis and environmental-remedy applications.

Lignin-silver triggered multifunctional conductive hydrogels for skinlike sensor applications.

Conductive hydrogels have attracted tremendous attention as a novel generation of wearable devices and body monitoring due to their great stretchability and high flexibility. Here, a multifunctional cellulose nanocrystal @sodium lignosulfonate-silver-poly(acrylamide) nanocomposite hydrogel was prepared by radical polymerization within only a few minutes. This polymerization rapidly occurred by lignosulfonate-silver (Ls-Ag) dynamic catalysis that efficiently activated ammonium persulfate (APS) to initiate the free-radical polymerization. In particular, the hydrogel exhibited excellent tensile strength (406 kPa), ultrahigh stretchability (1880 %), self-recovery, and fatigue resistance. Furthermore, due to the inclusion of Ls-Ag metal ion nanocomposite in the hydrogels, the composite hydrogel presented repeated adhesion to various objects, excellent conductivity (σ âˆ¼ 9.5 mS cm-1), remarkable UV resistance (100 % shielding of the UV spectral region), and high antibacterial activity (above 98 %), which enabled the hydrogel to be applied to epidermal sensors. In addition, the high-sensitivity (gauge factor of 2.46) sensor constructed of the hydrogel monitored the large and subtle movements of the human body and was used as a biological electrode to collect human electromyography and electrocardiographic signals. This work provided a novel strategy for the high-value utilization of lignin, which had potential application prospects in many fields such as wearable bioelectrodes.

Conductive Hydrogels Based on Industrial Lignin: Opportunities and Challenges.

The development of green materials, especially the preparation of high-performance conductive hydrogels from biodegradable biomass materials, is of great importance and has received worldwide attention. As an aromatic polymer found in many natural biomass resources, lignin has the advantage of being renewable, biodegradable, non-toxic, widely available, and inexpensive. The unique physicochemical properties of lignin, such as the presence of hydroxyl, carboxyl, and sulfonate groups, make it promising for use in composite conductive hydrogels. In this review, the source, structure, and reaction characteristics of industrial lignin are provided. Description of the preparation method (physical and chemical strategies) of lignin-based conductive hydrogel is elaborated along with their several important properties, such as electrical conductivity, mechanical properties, and porous structure. Furthermore, we provide insights into the latest research advances in industrial lignin conductive hydrogels, including biosensors, strain sensors, flexible energy storage devices, and other emerging applications. Finally, the prospects and challenges for the development of lignin-conductive hydrogels are presented.

Co-production of xylose, lignin, and ethanol from eucalyptus through a choline chloride-formic acid pretreatment.

A choline chloride-formic acid (ChCl-FA) pretreatment followed by enzymatic hydrolysis and fermentation were developed in this work for co-produce bioethanol, xylose, and lignin from eucalyptus. Results showed that ChCl-FA pretreatment can simultaneously degrade the xylan (∼95.2%) and lignin (∼74.4%) in eucalyptus, and obtained the pretreated eucalyptus having high glucan content and a numbers of cracks and holes, which was conducive to follow-up cellulase attacking. The hydrolysis experiments showed the maximum yield of glucose of 100 g eucalyptus was 35.3 g, which was equivalent to 90.3% of glucan in eucalyptus feedstock. The fermentation of enzymatic hydrolysate finally achieved the ethanol yield of 16.5 g, which corresponded to 74.5% theoretical ethanol yield from initial glucan in eucalyptus. In addition, 12.1 g xylose and 23.9 g lignin also could be obtained in pretreated liquid or/and hydrolysis residue, which represented for 61.4% xylan and 80.7% lignin in eucalyptus feedstock, respectively.

Lignin Nanoparticles and Alginate Gel Beads: Preparation, Characterization and Removal of Methylene Blue.

A novel and effective green system consisting of deep eutectic solvent (DES) was proposed to prepare lignin nanoparticles (LNPs) without any lignin modification. The LNPs are obtained through the dialysis of the kraft lignin-DES solution. The particle size distribution, Zeta potential and morphology of the LNPs are characterized by using dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average diameter of LNPs is in the range 123.6 to 140.7 nm, and the LNPs show good stability and dispersibility in water. The composite beads composed of LNPs and sodium alginate (SA) are highly efficient (97.1%) at removing methylene blue (MB) from the aqueous solution compared to 82.9% and 77.4% by the SA/bulk kraft lignin composite and pure SA, respectively. Overall, the LNPs-SA bio-nanocomposite with high adsorption capacity (258.5 mg/g) could be useful in improving water quality and other related applications.

High-efficiency synthesis of 5-hydroxymethylfurfural and 2,5-diformylfuran from fructose over magnetic separable catalysts.

In this work, a sulfonic acid-functionalized magnetic separable solid acid (Fe3O4@SiO2-SO3H) was synthesized, characterized, and tested for fructose conversion to 5-hydroxymethylfurfural (HMF). Results indicated that the prepared catalyst had a good efficacy for fructose dehydration to HMF due to its larger specific surface area, appropriate acid amount and homogeneous acid distribution. The maximum HMF yield of this work was 96.1 mol%. It was obtained at 120 °C for 1.5 h with 100 mol% fructose conversion. More importantly, the produced HMF could be further in-situ oxidized into 2,5-diformylfuran (DFF) after the replacing of the Fe3O4@SiO2-SO3H with a ZnFeRuO4 catalyst, and the highest DFF yield of 90.2 mol% (based on initial fructose) was obtained after reaction another 8.5 h. The production of DFF from fructose through the above two consecutive steps avoids the intermediate HMF separation, which saves time and energy. In addition, both Fe3O4@SiO2-SO3H and ZnFeRuO4 catalysts exhibited satisfied stability in the recycling experiments, which can be reused at least for five times with the HMF and DFF yield loss<5.3% and 3.3%, respectively. Finally, the plausible reaction mechanisms for fructose conversion to HMF or DFF over Fe3O4@SiO2-SO3H or/and ZnFeRuO4 catalysts were also proposed in this work.

Pretreatment of willow using the alkaline-catalyzed sulfolane/water solution for high-purity and antioxidative lignin production.

In this study, an alkaline-catalyzed sulfolane/water solvent system was developed for isolating high-purity and antioxidative lignin from willow (Salix matsudana cv. Zhuliu). Optimization of the pretreatment conditions such as temperature, sulfolane/water ratio, and alkaline catalyst (NaOH) dosage were comprehensively investigated for effective lignin extraction from willow. The 44.4% of lignin was recovered from the biomass with 54% of delignification in 50/50 (w/w) sulfolane/water system at 170 °C. As the addition of the alkaline catalyst (NaOH) increased to 4%, the delignification yield was increased up to 94% with about 70% of lignin recovery yield. The recovered lignin was comparatively investigated with its control, milled wood lignin (MWL). The ß-O-4 linkages and phenolic hydroxyl were well preserved in the extracted lignin fractions with the sulfolane/water system. Furthermore, excellent radical scavenging ability was observed with the extracted lignins by sulfolane/water pretreatments owing to rich phenolic hydroxyl groups in the lignins. Hence, systematical investigation on the lignin properties and potential applications under sulfolane organosolv pretreatment would promote the utilization of lignin in biorefinery processes.