Research Progress in Lignin-Based Slow/Controlled Release Fertilizer

Valorization of lignin from aqueous-based lignocellulosic biorefineries

An additional 100 million tons/year of lignin coproduct will result when lignocellulosic biomass is processed in biorefineries to fiber, sugars, biofuels, and bioproducts. This will double the amount of lignin already generated from pulping and paper production. Unlike pulping that results in lignosulphonate (88% of total) or Kraft lignin (9%), aqueous-based biorefining leaves behind non-sulfonated lignin and aromatic molecules. This new type of lignin provides opportunities for large volume agricultural uses such as controlled-release carriers and soil amendments as well as feedstocks for new chemistries that lead to molecular building blocks for the chemical industry and to precursors for sustainable aviation biofuels.

Unlocking the potential: Evolving role of technical lignin in diverse applications and overcoming challenges

Recent advancements have transformed lignin from a byproduct into a valuable raw material for polymers, dyes, adhesives, and fertilizers. However, its structural heterogeneity, variable reactive group content, impurities, and high extraction costs pose challenges to industrial-scale adoption. Efficient separation technologies and selective bond cleavage are crucial. Advanced pretreatment methods have enhanced lignin purity and reduced contamination, while novel catalytic techniques have improved depolymerization efficiency and selectivity. This review compares catalytic depolymerization methodologies, highlighting their advantages and disadvantages, and noting challenges in comparing yield values due to variations in isolation methods and lignin sources. Recognizing "technical lignin" from pulping processes, the review emphasizes its diverse applications and the necessity of understanding its structural characteristics. Emerging trends focus on bio-based functional additives and nanostructured lignin materials, promising enhanced properties and functionalities. Innovations open possibilities in sustainable agriculture, high-performance foams and composites, and advanced medical applications like drug delivery and wound healing. Leveraging lignin's biocompatibility, abundance, and potential for high-value applications, it can significantly contribute to sustainable material development across various industries. Continuous research in bio-based additives and nanostructured materials underscores lignin's potential to revolutionize material science and promote environmentally friendly industrial applications.

Release and Degradation Mechanism of Modified Polyvinyl Alcohol-Based Double-Layer Coated Controlled-Release Phosphate Fertilizer

This study aims to improve the slow-release performance of a film material for a controlled-release fertilizer (CRF) while enhancing its biodegradability. A water-based biodegradable polymer material doped with biochar (BC) was prepared from modified polyvinyl alcohol (PVA) with polyvinylpyrrolidone (PVP) and chitosan (CTS), hereinafter referred to as PVA/PVP-CTSaBCb. An environmentally friendly novel controlled-release phosphate fertilizer (CRPF) was developed using PVA/PVP-CTS8%BC7% as the film. The effect of the PVA/PVP-CTS8%BC7% coating on the service life of the CRPF was investigated. The film was characterized via stress-strain testing, SEM, FTIR, XRD, and TGA analyses. The addition of the CTS modifier increased the stress of PVA/PVP-CTS8% by 7.6% compared with that of PVA/PVP owing to the decrease in the crystallinity of PVP/PVP-CTS8%. The hydrophilic -OH groups were reduced due to the mixing of CTS and PVA/PVP. Meanwhile, the water resistance of the PVA/PVP-CTS8%BC7% was improved. And the controlled-release service life of the CRPF was prolonged. Moreover, the addition of BC increased the crystallinity of the PVA/PVP-CTS8% by 10%, reduced the fracture elongation of the material, and further improved the biodegradability of the PVA/PVP-CTS8%BC7%. When the amount of BC added was 7%, the phosphorus release rate of the CRPF was 30% on the 28th day. Moreover, the degradation rate of the PVA/PVP-CTS8%BC7% polymer film was 35% after 120 days. This study provides basic data for applying water-based degradable polymer materials in CRFs.

CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi-Hydrogenation/Reduction Strategy

Due to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi-hydrogenation/reduction strategy utilizing CsPbBr3 quantum dots (CPB-QDs) and Hantzsch ester (HEH2 ) as a synergistic catalytic system was introduced to reduce the BDE of Cβ -O-Ar, achieving effective cleavage of the Cβ -O-Ar bond. This strategy offers a wide substrate scope encompassing various β-O-4 model lignin dimers, preoxidized β-O-4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir-catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH2 can be activated by CPB-QDs via single electron transfer (SET), generating HEH2 ⋅+ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH2 ⋅+ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton-coupled electron transfer (PCET) from HEH2 ⋅+ to the carbonyl group of the substrate generates a Cα ⋅ intermediate.

A facile strategy to fabricate lignocellulose-based slow-release fertilizers via a high-performance treatment of rice straw using deep eutectic solvents

Lignin-based slow-release fertilizers (SRFs) have attracted widespread attention due to their ability to enhance nutrient utilization efficiency and reduce environmental pollution in agricultural production. However, the extraction and separation processes of lignin from biomass sources are intricate, involving substantial quantities of non-reusable toxic reagents. Here, a sustainable and eco-friendly approach using deep eutectic solvents (DES) was employed to treat rice straw, effectively dissolving the lignin present. Subsequently, the in-situ lignin regeneration was facilitated through the addition of a zinc chloride solution. The regenerated lignin was tightly wrapped around and connected to cellulose micro/nanofibers, forming a homogeneous slurry. A simple coating technique was employed to uniformly coat urea particles with the lignocellulosic slurry, yielding lignocellulose-based SRFs. Results revealed that the nutrient release of the lignocellulose-based coated fertilizers in water exceeded 56 days. A pot trial demonstrated that the application of lignocellulose-based SRFs significantly promoted the growth of rice and improved grain yield (by 10.7 %) and nitrogen use efficiency (by 34.4 %) compared to the urea treatment in rice production. Furthermore, the DES demonstrated consistently high efficiency in biomass processing even after four cycles of reuse. This green strategy offers a novel approach for the preparation of SRFs coating materials, promoting agricultural sustainability.

Recent developments in lignin-based fluorescent materials

Biomass-based fluorescent materials are an alternative to plastic-based materials for their multifunctional applications. Lignin, an inexpensive and easily available raw material, demonstrates outstanding environment-responsive properties such as pH, metal ions, dyes sensing, bioimaging and so on. To date, only a little work has been reported on the synthesis of lignin-based fluorescent materials. In this review report, synthetic approaches and light-responsive applications of lignin-based fluorescent carbon dots and other materials are summarized. The results reveal that lignin-based fluorescent carbon dots are prepared by hydrothermal method, exhibit small size <10 nm, reveal significant quantum yield, biocompatibility, non-toxicity, photostability and display substantial tunable emission and can be efficiently employed for sensing, bioimaging and energy storage applications. Finally, the forthcoming challenges, investigations, and options open for the chemical and/or physical modification of lignin into fluorescent materials for future applications are well-addressed. To our knowledge, this is the first comprehensive review report on lignin-based fluorescent materials and their light-responsive applications. In addition, this review will attract remarkable consideration and thrust for the researchers and biochemical technologists working with the preparation of lignin-based fluorescent materials for broad applications.

Microbial cell factories using Paenibacillus: status and perspectives

Considered a "Generally Recognized As Safe" (GRAS) bacterium, the plant growth-promoting rhizobacterium Paenibacillus has been widely applied in: agriculture, medicine, industry, and environmental remediation. Paenibacillus species not only accelerate plant growth and degrade toxic substances in wastewater and soil but also produce industrially-relevant enzymes and antimicrobial peptides. Due to a lack of genetic manipulation tools and methods, exploitation of the bioresources of naturally isolated Paenibacillus species has long been limited. Genetic manipulation tools and methods continue to improve in Paenibacillus, such as shuttle plasmids, promoters, and genetic tools of CRISPR. Furthermore, genetic transformation systems develop gradually, including: penicillin-mediated transformation, electroporation, and magnesium amino acid-mediated transformation. As genetic manipulation methods of homologous recombination and CRISPR-mediated editing system have developed gradually, Paenibacillus has come to be regarded as a promising microbial chassis for biomanufacturing, expanding its application scope, such as: industrial enzymes, bioremediation and bioadsorption, surfactants, and antibacterial agents. In this review, we describe the applications of Paenibacillus bioproducts, and then discuss recent advances and future challenges in the development of genetic manipulation systems in this genus. This work highlights the potential of Paenibacillus as a new microbial chassis for mining bioresources.

A lignin-derived material improves plant nutrient bioavailability and growth through its metal chelating capacity

The lignocellulosic biorefinery industry can be an important contributor to achieving global carbon net zero goals. However, low valorization of the waste lignin severely limits the sustainability of biorefineries. Using a hydrothermal reaction, we have converted sulfuric acid lignin (SAL) into a water-soluble hydrothermal SAL (HSAL). Here, we show the improvement of HSAL on plant nutrient bioavailability and growth through its metal chelating capacity. We characterize HSAL's high ratio of phenolic hydroxyl groups to methoxy groups and its capacity to chelate metal ions. Application of HSAL significantly promotes root length and plant growth of both monocot and dicot plant species due to improving nutrient bioavailability. The HSAL-mediated increase in iron bioavailability is comparable to the well-known metal chelator ethylenediaminetetraacetic acid. Therefore, HSAL promises to be a sustainable nutrient chelator to provide an attractive avenue for sustainable utilization of the waste lignin from the biorefinery industry.

Lignins as Promising Renewable Biopolymers and Bioactive Compounds for High-Performance Materials

The recycling of biomass into high-value-added materials requires important developments in research and technology to create a sustainable circular economy. Lignin, as a component of biomass, is a multipurpose aromatic polymer with a significant potential to be used as a renewable bioresource in many fields in which it acts both as promising biopolymer and bioactive compound. This comprehensive review gives brief insights into the recent research and technological trends on the potential of lignin development and utilization. It is divided into ten main sections, starting with an outlook on its diversity; main properties and possibilities to be used as a raw material for fuels, aromatic chemicals, plastics, or thermoset substitutes; and new developments in the use of lignin as a bioactive compound and in nanoparticles, hydrogels, 3D-printing-based lignin biomaterials, new sustainable biomaterials, and energy production and storage. In each section are presented recent developments in the preparation of lignin-based biomaterials, especially the green approaches to obtaining nanoparticles, hydrogels, and multifunctional materials as blends and bio(nano)composites; most suitable lignin type for each category of the envisaged products; main properties of the obtained lignin-based materials, etc. Different application categories of lignin within various sectors, which could provide completely sustainable energy conversion, such as in agriculture and environment protection, food packaging, biomedicine, and cosmetics, are also described. The medical and therapeutic potential of lignin-derived materials is evidenced in applications such as antimicrobial, antiviral, and antitumor agents; carriers for drug delivery systems with controlled/targeting drug release; tissue engineering and wound healing; and coatings, natural sunscreen, and surfactants. Lignin is mainly used for fuel, and, recently, studies highlighted more sustainable bioenergy production technologies, such as the supercapacitor electrode, photocatalysts, and photovoltaics.

Green construction and release mechanism of lignin-based double-layer coated urea

BACKGROUND

Lignin played an important role in the establishment of coated fertilizers coating material as a substitute for petrochemical raw materials. However, so far, the lignin-based coated fertilizers was limited in only the poor slow-release performance. To achieve good slow-release performance of lignin-based coated fertilizers, hydrophilic of lignin need to be resolved to establish an green and better controllable lignin-based coated fertilizers.

RESULTS

In the study, a novel green double layer coating with lignin-based polyurethane (LPU) as the inner coating and epoxy resin (EP) as the outer coating was effectively constructed for coated urea. Fourier transform infrared spectra confirmed that lignin and polycaprolactone diol successfully reacted with Hexamethylene diisocyanate. The loss weight and water contact angle (WCA, 75.6-63.6°) of the LPUs decreased with the increased lignin content. The average particle hardness of the lignin-based double-layer coated urea (LDCU) first increased from 58.1 N (lignin of 30%) to 67.0 N (lignin of 60%), but then decreased to 62.3 N (lignin of 70%). The release longevity of the coated urea was closely related to the preparation parameters of the coating material. The optimal cumulative nutrient release rate (79.4%) of LDCU was obtained (lignin of 50%, -CNO/-OH molar ratios of 1.15, EP of 35%, and coating ratio of 5%). The aggregates of hydrone on the LDCU caused the dissolution and swelling of nutrients, and then the diffusion of nutrients through the concentration gradient.

CONCLUSIONS

A though the nutrient release of the LDCUs was affected by many factors, the successful development of the LDCUs will help improve the rapid development of the coated fertilizer industry.

Understanding the cadmium passivation and nitrogen mineralization of aminated lignin in soil

Aminated lignin (AL) was prepared and first applied to remediation of cadmium (Cd) pollution in soil. Meanwhile, the nitrogen mineralization characteristics of AL in soil and its effect on soil physicochemical properties were elucidated by soil incubation experiment. The results showed that the Cd availability was dramatically lowered in soil by adding the AL. The DTPA-extractable Cd content of AL treatments was considerably reduced by 40.7-71.4 %. The soil pH (5.77-7.01) and absolute value of zeta potential (30.7-34.7 mV) enhanced simultaneously as the AL additions increased. The content of soil organic matter (SOM) (99.0-264.0 %) and total nitrogen (95.9-301.3 %) were gradually enhanced due to high C (63.31 %) and N (9.69 %) content in AL. Moreover, AL significantly elevated the content of mineral nitrogen (77.2-142.4 %) and available nitrogen (95.5-301.7 %). The first-order kinetic equation of soil nitrogen mineralization revealed that AL greatly enhanced nitrogen mineralization potential (84.7-143.9 %) and reduced environmental pollution by lowering the loss of soil inorganic nitrogen. AL could effectively reduce the availability of Cd through direct (self-adsorption) and indirect effects (improvement of soil pH, SOM and reduction of soil zeta potential), thereby achieving passivation of Cd in soil. In short, this work will develop a novel approach and technical support for soil heavy metal remediation, which is of great significance for improving the sustainable development of agricultural production.

Wood-derived bio-coating materials incorporating hydrophobic lignin and hierarchically porous biochar for high-efficiency coating slow-release fertilizers

Coating slow-release fertilizers (CSRFs) have gained significant attention for their potential to improve nutrient utilization efficiency and prevent environmental pollution through mitigating soil and water contamination. This study developed a novel wood waste-derived composition as a bio-coating material for urea slow-release by integrating modified lignin (PCL) and activated biochar (ABC). PCL was prepared by grafting palmitoyl chloride (PC) with hydrophobic groups to the lignin via an esterification reaction. ABC with a high surface area and hierarchically porous structure created rich channels for ion transportation. These results increased the water-retention ability with a reduced absorbing/expelling rate and confer an excellent Cr(VI) adsorption capacity to the PCL and ABC hybrid coating material (PCL/ABC). The as-prepared PCL/ABC-based CSRF (PCL/ABC-CSRF) showed improving fertilizer slow-release properties for real application (nitrogen release persistence for 40 days at soil). The rice (Oryza sativa L.) hydroponics study suggested that such novel PCL/ABC was conducive to the rice growth in micro metallic contaminated hydroponics by eliminating the accumulation of chromium metal in rice roots. Overall, this study provides an attractive platform for developing biodegradable, heavy-metal adsorbable, and high-efficient CSRFs and a feasible and effective way for functionalized utilization of wood waste.

Significantly enhanced enzymatic hydrolysis of waste rice hull through a novel surfactant-based deep eutectic solvent pretreatment

The potential of green solvents, specifically deep eutectic solvents (DESs), has piqued the interest of researchers in the field of lignocellulose pretreatment. To enhance the enzymatic digestion efficiency of waste rice hull (RCH), an effective pretreatment approach was developed using the DES [AA][CATB], which was made with acetic acid (AA) and cetyltrimethylammonium bromide (CTAB). The results showed that [AA][CATB] improved enzymatic saccharification by 3.7 times compared to raw RCH and efficiently eliminated lignin (38.7%) and removed xylan (42.9%). The improvement in enzymatic hydrolysis efficiency was then interpreted by a series of characterizations that showed a great morphological changed RCH with an obvious accessibility increase and a lignin surface area and hydrophobicity reduction. This work demonstrates that functional, and easily recoverable DESs have potential for improving the efficiency of lignocellulose pretreatment in biorefineries, providing a promising approach for developing green solvents and achieving more sustainable and efficient biorefinery processes.

Current roles of lignin for the agroindustry: Applications, challenges, and opportunities

Lignin has the potential to be used as an additive, coating agent, fertilizer, plant growth stimulator, and packaging material in the agroindustry due to its functional aromatic structure. The quantitative measurement of functional groups is a significant element of the research for lignin structure since they directly impact their optical, dispersion, and chemical properties. These physical and chemical properties of lignin strongly depend on its type and source and its isolation procedure. Thus, lignin provides numerous opportunities for the circular economy in the agroindustry; however, studying and resolving the challenges associated with its separation, purification, and modification is required. This review discusses the most recent findings on lignin use in agroindustry and historical facts about lignin. The properties of lignin and its roles as coating agents, pesticide carriers, plant growth stimulators, and soil-improving agents have been summarized. The emerging challenges in the field of lignin-based agroindustry are considered, and potential future steps to overcome these challenges are discussed.

The Biomodified Lignin Platform: A Review

A reliance on fossil fuel has led to the increased emission of greenhouse gases (GHGs). The excessive consumption of raw materials today makes the search for sustainable resources more pressing than ever. Technical lignins are mainly used in low-value applications such as heat and electricity generation. Green enzyme-based modifications of technical lignin have generated a number of functional lignin-based polymers, fillers, coatings, and many other applications and materials. These bio-modified technical lignins often display similar properties in terms of their durability and elasticity as fossil-based materials while also being biodegradable. Therefore, it is possible to replace a wide range of environmentally damaging materials with lignin-based ones. By researching publications from the last 20 years focusing on the latest findings utilizing databases, a comprehensive collection on this topic was crafted. This review summarizes the recent progress made in enzymatically modifying technical lignins utilizing laccases, peroxidases, and lipases. The underlying enzymatic reaction mechanisms and processes are being elucidated and the application possibilities discussed. In addition, the environmental assessment of novel technical lignin-based products as well as the developments, opportunities, and challenges are highlighted.

Reduced nutrient release and greenhouse gas emissions of lignin-based coated urea by synergy of carbon black and polysiloxane

An advanced hydrophobic lignin-based polyurethane coated urea (HLPCU) was successfully developed by synergy of carbon black (CB) and polysiloxane. In this work, CB and polysiloxane were employed to modify the liquefied lignin-based polyurethane (LLPU) and improve it's the hydrophobicity. The effects of polysiloxane contents and coating rates on the nutrient release of HLPCU were thoroughly investigated. The lignin was degraded into polyol with a low molecular weight. FT-IR, XPS and EDX results confirmed that polysiloxane was grafted to the LLPU. The water contact angle (WCA) of the HLPUs (89.39°-98.68°) gradually increased as the polysiloxane content rose (5 %-15 %). However, when the polysiloxane content further increased to 20 %, the WCA of the HLPUs rapidly declined (90.82°). A proper amount of polysiloxane molecules could increase thermo-physical properties of LLPU. The almost no pores were observed on the section micrograph of the HLPCU obtained by synergy of CB and polysiloxane. Synergy between CB and polysiloxane could significantly improve hydrophobicity and then enhance N release longevity of HLPCU (polysiloxane content of 15 %, coating rates of 7 %) up to 44 days. Compared to traditional urea, HLPCU could improve total N use efficiency the cabbage. The HLPCU and HLPCU85 treatments (15 % weight loss with fertilization) reduced the greenhouse effect of N₂O, CO₂ and CH₄ and finally reduced GWP, especially for HLPCU85 treatment. This work will supply an advanced approach and process technology for progress of HLPCU and sustainable agriculture.

Opportunities and Challenges for Lignin Valorization in Food Packaging, Antimicrobial, and Agricultural Applications

The exploration of renewable resources is essential to help transition toward a more sustainable materials economy. The valorization of lignin can be a key component of this transition. Lignin is an aromatic polymer that constitutes approximately one-third of the total lignocellulosic biomass and is isolated in huge quantities as a waste material of biofuel and paper production. About 98% of the 100 million tons of lignin produced each year is simply burned as low-value fuel, so this renewable polymer is widely available at very low cost. Lignin has valuable properties that make it a promising material for numerous applications, but it is far from being fully exploited. The aim of this Perspective is to highlight opportunities and challenges for the use of lignin-based materials in food packaging, antimicrobial, and agricultural applications. In the first part, the ongoing research and the possible future developments for the use of lignin as an additive to improve mechanical, gas and UV barrier, and antioxidant properties of food packaging items will be treated. Second, the application of lignin as an antimicrobial agent will be discussed to elaborate on the activity of lignin against bacteria, fungi, and viruses. Finally, the use of lignin in agriculture will be presented by focusing on the application of lignin as fertilizer.

Effects of the Structure and Molecular Weight of Alkali-Oxygen Lignin Isolated from Rice Straw on the Growth of Maize Seedlings

The abundant and low-cost features of lignin in combination with its natural activities make it a fascinating biopolymer for valorization, especially, in agriculture as an active plant growth regulator. However, the structure-activity relationship of lignin in regulating plant growth and metabolism remains unclear. In this work, rice-straw-based low-molecular-weight (LWM, 1860 Da) and high-molecular-weight (HMW, 6840 Da) alkali-oxygen lignins are structurally and comparatively investigated to understand their effects on the growth and metabolism of maize seedlings. The results indicate that LMW lignin at 150 mg·L^-1 displays early growth stimulation in maize. Under the optimal concentration of LMW lignin (25 mg·L^-1), the growth of maize shoot is ∼83% higher than that of the control one. Furthermore, LMW lignin also has a positive effect on the upregulation of photosynthetic pigment, carbohydrate, and protein synthesis. In contrast, HMW lignin shows an overall inhibitory effect on the above-mentioned biochemical parameters. Based on the structural characterization, LMW lignin contains a higher syringyl/guaiacyl ratio (0.78) and carboxyl content (1.64 mmol·g^-1) than HMW lignin (0.43 and 1.27 mmol·g^-1, respectively), which demonstrates that methoxyl and carboxyl content of lignin may play a decisive role in seedling growth.

Dual-functional lignin-based hydrogels for sustained release of agrochemicals and heavy metal ion complexation

An effective way of improving the efficiency of agrochemicals and improving crop yield and quality is by slow or sustained release, which is conducive to environmental protection. Meanwhile, the excessive amount of heavy metal ions in soil can create toxicity in plants. Here, we prepared lignin-based dual-functional hydrogels containing conjugated agrochemical and heavy metal ligands through free-radical copolymerization. The content of the agrochemicals (including plant growth regulator 3-indoleacetic acid (IAC) and herbicide 2,4-dichlorophenoxyacetic acid (DCP)) in the hydrogels were tuned by changing the hydrogel composition. The conjugated agrochemicals could slowly release through the gradual cleavage of the ester bond. As a result of the release of the DCP herbicide, the growth of lettuce was effectively regulated, thus confirming the feasibility and effectiveness of this system in application. At the same time, due to the presence of metal chelating groups (such as COOH, phenolic OH, and tertiary amine) the hydrogels could act as adsorbents or stabilizers towards heavy metal ions for improving the soil remediation and preventing the adsorption of these toxic metals by plant roots. Specifically, Cu(II) and Pb(II) could be adsorbed >380 and 60 mg/g, respectively.

Bio-based Polyurethane Based on a Dynamic Covalent Network with Damage Tolerance for Controlled Release of Fertilizers

Bio-based polyurethanes are promising for the controlled release of nutrients and fertilizers, but their toughness and plasticity need to be improved. We developed a smooth, dense, elastic, and indestructible bio-based polyurethane (BPU) coating with a nutrient controlled release ∼150% superior, a tensile strength ∼300% higher, and a toughness ∼1200% higher than those for the original BPU coating. Through a one-step reaction of soybean oil polyols (accounting for more than 60%), isocyanate, and benzil dioxime, the dynamic covalent network based on oxime-carbamate replaces part of irreversible covalent cross-linking. The dynamic fracture-bonding reaction in the modified coating BPU can effectively promote the hydrogen bond recombination and oxime-carbamate chain migration in the coating process, which avoids the structural defects caused by coating tear and fertilizer collision. This work provides a simple and versatile strategy for building controlled-release fertilizer coatings.

Overexpression of PtoMYB115 improves lignocellulose recalcitrance to enhance biomass digestibility and bioethanol yield by specifically regulating lignin biosynthesis in transgenic poplar

Background

Woody plants provide the most abundant biomass resource that is convertible for biofuels. Since lignin is a crucial recalcitrant factor against lignocellulose hydrolysis, genetic engineering of lignin biosynthesis is considered as a promising solution. Many MYB transcription factors have been identified to involve in the regulation of cell wall formation or phenylpropanoid pathway. In a previous study, we identified that PtoMYB115 contributes to the regulation of proanthocyanidin pathway, however, little is known about its role in lignocellulose biosynthesis and biomass saccharification in poplar.

Results

Here, we detected the changes of cell wall features and examined biomass enzymatic saccharification for bioethanol production under various chemical pretreatments in PtoMYB115 transgenic plants. We reported that PtoMYB115 might specifically regulate lignin biosynthesis to affect xylem development. Overexpression of PtoMYB115 altered lignin biosynthetic gene expression, resulting in reduced lignin deposition, raised S/G and beta-O-4 linkage, resulting in a significant reduction in cellulase adsorption with lignin and an increment in cellulose accessibility. These alterations consequently improved lignocellulose recalcitrance for significantly enhanced biomass saccharification and bioethanol yield in the PtoMYB115-OE transgenic lines. In contrast, the knockout of PtoMYB115 by CRISPR/Cas9 showed reduced woody utilization under various chemical pretreatments.

Conclusions

This study shows that PtoMYB115 plays an important role in specifically regulating lignin biosynthesis and improving lignocellulose features. The enhanced biomass saccharification and bioethanol yield in the PtoMYB115-OE lines suggests that PtoMYB115 is a candidate gene for genetic modification to facilitate the utilization of biomass.

Efficient utilization of waste wheat straw through humic acid and ferric chloride co-assisted hydrothermal pretreatment for fermentation to produce bioethanol

The adsorbed ash and lignin contained in waste wheat straw (WWS) have been the essential factors restricting its high-value utilization in biorefinery. Hence, humic acid (HA) and FeCl3 as the additives of hydrothermal pretreatment were applied to simultaneously enhance the removal of lignin and eliminate the acid buffering of ash in WWS, respectively. The results showed that the xylan and lignin removal of WWS pretreated with 10 g/L HA and 20 mM FeCl3 could be efficiently increased from 61.4% to 72.9% and from 14.7% to 38.7%, respectively. The enzymatic hydrolysis efficiency and ethanol yield of WWS were increased this way from 44.4% to 82.7% and from 20.55% to 36.86%, respectively. According to the characterization of WWS, the synergistic interaction between HA and FeCl3 was beneficial to the cellulose accessibility and surface lignin area of WWS changed in positive directions, leading to the improvement of hydrolysis efficiency.

Effects of nitrogen reduction combined with organic fertilizer on growth and nitrogen fate in banana at seedling stage

Nitrogen reduction combined with organic fertilizer is of considerable significance for the sustainable development of agriculture. A pot experiment using nitrogen reduction combined with organic fertilizer was conducted to explore the effects of different treatments on matter accumulation, physiological resistance, and fertilizer nitrogen fate in banana seedlings. Compared with conventional fertilization, a 20% reduction of nitrogen did not affect the dry weight, chlorophyll content, physiological resistance, and fertilizer utilization rate of banana seedlings, but significantly reduced the nitrogen leaching loss and increased the nitrogen soil residue. Compared with conventional fertilization, organic nitrogen substituting 20% or 30% of the nitrogen reduced by 20% significantly promoted dry matter accumulation and physiological resistance. Organic nitrogen substituting 30% of the 20% reduction of nitrogen increased the dry matter of the whole plant by 24.94%, the nitrogen uptake in the root by 30.87%, the chlorophyll content by 6.05%, the soluble sugar content by 16.88%, Peroxidase (POD) activity by 26.35%, Catalase (CAT) activity by 27.48%, and Super Oxide Dismutase (SOD) activity by 22.97%. Compared with conventional fertilization, all organic substitution treatments significantly reduced fertilizer nitrogen leaching loss, apparent loss, and increased nitrogen soil residue. Compared with the 20% reduction of nitrogen, organic nitrogen substituting 30% of the 20% reduction of nitrogen significantly increased nitrogen utilization by 16.34% and soil residue rate by 13.26%, and reduced nitrogen leaching loss by 35.46%. The results of the present study revealed that a 20% reduction of nitrogen fertilizer with a 30% organic substitution application promoted matter accumulation, enhanced the physiological resistance of banana seedlings, increased the utilization and residue of nitrogen fertilizer, and reduced nitrogen pollution.

Development of Biodegradable PLA/PBAT-Based Filaments for Fertilizer Release for Agricultural Applications

The aim of this work was to produce filaments of PLA/PBAT and NPK fertilizer adsorbed on organophilized bentonite intended for application in the prototyping of biodegradable agricultural artifacts in 3D printing, using the Fused Deposition Modeling (FDM) technique. This is the first time that we have reported this composite for a 3D printing approach. Systems containing PLA/PBAT, organobentonite and NPK were initially processed in an internal mixer and later extruded as filaments in a single-screw extruder. The prototypes were printed by FDM. Structural, morphological and thermal properties, as well as NPK releasing, were investigated. The results suggest that exfoliated and/or intercalated nanocomposites were obtained by the organoclay addition to the PLA/PBAT blend. The morphological analysis revealed a good surface quality of the impressions. Systems containing organobentonite released approximately 22% less fertilizer in 24 h compared to the systems without organobentonite. This difference is due to the higher concentration of nanoparticles that generate more barriers to the diffusion of NPK. The release data for these systems had a better fit to the kinetic model of Korsmeyer-Peppas. Thus, studied filaments have the potential to retard the release of fertilizer and are suitable for further development of structures for agricultural applications by FDM.

Improvement of bio-based polyurethane and its optimal application in controlled release fertilizer

In the past decades, polyurethane has emerged as a new material that has been widely developed and applied in coated controlled release fertilizers (CRFs). Particularly in recent years, the excessive consumption of petroleum resources and increasing demand for sustainable development have resulted in considerable interest in bio-based polyurethane coated controlled-release fertilizers. This review article focuses on the application and progress of environmentally friendly bio-based materials in the polyurethane-coated CRF industry. We also explore prospects for the green and sustainable development of coated CRFs. Using animal and plant oils, starch, lignin, and cellulose as raw materials, polyols can be produced by physical, chemical, and biological means to replace petroleum-based materials and polyurethane film coating for CRFs can be prepared. Various modifications can also improve the hydrophobicity and degradability of polyurethane film. A growing body of research on bio-based polyurethane has revealed its great potential in the production and application of coated CRFs. The purpose of this review is to highlight the practicality of bio-based materials in the application of polyurethane-coated CRFs and to clarify their current limitations.

Preparation of lignin modified hyper-cross-linked nanoporous resins and their efficient adsorption for p-nitrophenol in aqueous solution and CO2 capture

A series of lignin modified hyper-cross-linked nanoporous resins (LMHCRs) had been synthesized from lignin, 4-vinylbenzyl chloride, and divinylbenzene by free radical polymerization reaction and following Friedel-Crafts reaction. The results indicated that Brunauer-Emmett-Teller surface area (S_BET) of LMHCRs decreased with different degrees compared with polymeric microspheres (HCRs) without adding lignin. With increasing the feeding amount of lignin, the S_BET of LMHCRs first increased and then decreased, and LMHCR-2 had larger S_BET (968.52 m²/g) and average pore size (D_A: 2.51 nm). Meanwhile, their contact angle continuously decreased from 92.1⁰ to 71.3⁰, indicating the enhanced polarity. Interestingly, the adsorption capacity of p-nitrophenol (PNP) on all LMHCRs were obviously higher than rhodamine B, and LMHCR-2 had the largest capacity ratio (3.780) of PNP to rhodamine B or other organic dyes at 298 K. Specifically, the Q_m of PNP on LMHCR-2 reached the largest value (492.1 mg/g) due to its suitable porosity and favorable surface polarity. LMHCR-2 also displayed excellent CO₂ capture (86.5 mg/g) at 273 K and 1 bar and good reusability. This study provided an efficient route to modify hyper-cross-linked resin by using the residual lignin, and showed the enhanced adsorption performance.

A Study on the Impact of Low-Carbon Technology Application in Agriculture on the Returns of Large-Scale Farmers

The relationship and mechanism between agricultural low-carbon technology application and farm household returns are not yet clear, especially the lack of evidence from developing countries. This paper takes large-scale farming households in Jiangxi Province, China, from 2019 to 2020 as the research object, and obtains relevant data from field research to explore the intrinsic impact of agricultural low-carbon technology application on the returns of large-scale farming households. Based on the relevant theoretical analysis, the division dimensions of agricultural low-carbon technologies were proposed, and agricultural low-carbon technologies were subdivided into ten specific low-carbon technologies according to six dimensions: tillage system, breeding, fertilization, irrigation, medicine application, and waste treatment. Relevant questions were designed and researched to obtain data on the application status of low-carbon technologies in agriculture and the income cost status of large-scale farmers. Based on the theoretical analysis, the research hypotheses were proposed, and an empirical analysis was conducted based on the obtained data from large-scale farmers. The application of seven low-carbon technologies in agriculture: conservation tillage system, direct sowing technology, selection of compound fertilizer/organic fertilizer/controlled-release fertilizer, soil formula fertilization technology, deep fertilization/irrigation fertilization, sprinkler/drip irrigation/wet irrigation/intermittent irrigation, and straw resourceization significantly improved the income level of large-scale farmers. Furthermore, the application of biodegradable agricultural membranes, biopesticides, and new pesticide-controlled release technologies did not have significant effects on the income level of large-scale farmers, due to their low application and penetration rate. Based on the findings of the paper, the government should strengthen the promotion and subsidies of agricultural low-carbon technologies, especially those technologies that have no significant impact on large-scale farmers' income, such as biodegradable agricultural membranes, biopesticides, and new pesticide controlled-release technologies, so as to achieve a win-win situation of reducing carbon emissions and increasing farmers' income.

Biopolymeric Nanocarriers for Nutrient Delivery and Crop Biofortification

Driven by the possibility of precise transformational change in nutrient-enrichment technology to meet global food demand, advanced nutrient delivery strategies have emerged to pave the path toward success for nutrient enrichment in edible parts of crops through bioderived nanocarriers with increased productivity. Slow and controlled release of nutrient carrier materials influences the nutrient delivery rate in soil and in the edible parts of crops with a sluggish nutrient delivery to enhance their availability in roots by minimizing nutrient loss. With a limited understanding of the nutrient delivery mechanism in soil and the edible parts of crops, it is envisaged to introduce nutrient-enrichment technology for nutrient delivery that minimizes environmental impact due to its biodegradable nature. This article attempts to analyze the possible role of the cellulose matrix for nutrient release and the role of cellulose nanocomposites and nanofibers. We have proposed a few cellulose derived biofortificant materials as nutrient carriers, such as (1) nanofibers, (2) polymer-nanocellulose-clay composites, (3) silk-fibroin derived nanocarriers, and (4) carboxymethyl cellulose. An effort is undertaken to describe the research need by linking a biopolymer derived nanocarrier for crop growth regulation and experimental nitrogen release analysis. We have finally provided a perspective on cellulose nanofibers (CNFs) for microcage based nutrient loading ability. This article aims to explain why biopolymer derived nutrient carriers are the alternative candidate for alleviating nutrient deficiency challenges which are involved in focusing the nutrient delivery profile of biopolymers and promising biofortification of crops.

Controlled release fertilizers (CRFs) for climate-smart agriculture practices: a comprehensive review on release mechanism, materials, methods of preparation, and effect on environmental parameters

Fertilizers play an essential role in increasing crop yield, maintaining soil fertility, and provide a steady supply of nutrients for plant requirements. The excessive use of conventional fertilizers can cause environmental problems associated with nutrient loss through volatilization in the atmosphere, leaching to groundwater, surface run-off, and denitrification. To mitigate environmental issues and improve the longevity of fertilizer in soil, controlled release fertilizers (CRFs) have been developed. The application of CRFs can reduce the loss of nutrients, provide higher nutrient use efficiency, and improve soil health simultaneously to achieve the goals of climate-smart agricultural (CSA) practices. The major findings of this review paper are (1) CRFs can prevent direct exposure of fertilizer granule to soil and prevent loss of nutrients such as nitrate and nitrous oxide emissions; (2) CRFs are less affected by the change in environmental parameters, and that can increase longevity in soil compared to conventional fertilizers; and (3) CRFs can maintain required soil nitrogen levels, increase water retention, reduce GHG emissions, lead to optimum pH for plant growth, and increase soil organic matter content. This paper could give good insights into the ongoing development and future perspectives of CRFs for CSA practices.

Synthesization and Characterization of Lignin-graft-Poly (Lauryl Methacrylate) via ARGET ATRP

Lignin as an abundant biological macromolecule isolated from the plant cell wall, and it cannot be efficiently utilized until suitable modifications to its structures were made. Therefore, we proposed a strategy to prepare an all biomass-based Lignin-graft-poly(Lauryl methacrylate, LMA) by grafting LMA monomers on the organosolv lignin through ARGET ATRP. The results of FT-IR and ¹H NMR analysis demonstrated that PLMA molecular chains were successfully grafted on the lignin. Lignin improved copolymer's thermal stability and had a negligible effect on crystallization of PLMA molecular chains, according to our findings in the test of TGA and DSC. The rheological properties of the copolymer were found depending on the length of molecular chains of copolymer and lignin inside it. Both height and phase images of AFM suggest that lignin constituted a nanoscale aciculas and embedded in the microscale spheral dot composed by grafted PLMA molecular chains. Furthermore, the integrated consideration of results of all characterizations suggests a relative independent micro-component, which was composed by central lignin and peripheral PLMA, aggregates with each other to build the OL-g-PLMA copolymers. It hopes that the copolymer will be used as an additive for improving mechanical performance and UV blocking of other biopolymers.

Machine learning prediction of lignin content in poplar with Raman spectroscopy

Based on features extracted from Raman spectra, regularization algorithms, SVR, DT, RF, LightGBM, CatBoost, and XGBoost were used to develop prediction models for lignin content in poplar. Firstly, Raman features extracted from FT-Raman spectra after data processing were used as input of models and determined lignin contents were output. Secondly, grid-search combined with cross-validation was used to adjust the hyper-parameters of models. Finally, the predictive models were built by aforementioned algorithms. The results indicated regularization algorithms, SVR, DT held test R² were >0.80 which means the predictive values from model still deviate from measured ones. Meanwhile, RF, LightGBM, CatBoost, and XGBoost were better than above algorithms, and their test R² were >0.91 which suggesting the predictive values was nearly close to measured ones. Therefore, fast and accurate methods for predicting lignin content were obtained and will be useful for screening suitable lignocellulosic resource with expected lignin content.

Next generation applications of lignin derived commodity products, their life cycle, techno-economics and societal analysis

The pulp and biorefining industries produce their waste as lignin, which is one of the most abundant renewable resources. So far, lignin has been remained severely underutilized and generally burnt in a boiler as a low-value fuel. To demonstrate lignin's potential as a value-added product, we will review market opportunities for lignin related applications by utilizing the thermo-chemical/biological depolymerization strategies (with or without catalysts) and their comparative evaluation. The application of lignin and its derived aromatics in various sectors such as cement industry, bitumen modifier, energy materials, agriculture, nanocomposite, biomedical, H2 source, biosensor and bioimaging have been summarized. This comprehensive review article also highlights the technical, economic, environmental, and socio-economic variable that affect the market value of lignin-derived by-products. The review shows the importance of lignin, and its derived products are a platform for future bioeconomy and sustainability.

Catalytic Hydrogenolysis of Lignin: The Influence of Minor Units and Saccharides

The precise elucidation of native lignin structures plays a vital role for the development of "lignin first" strategies such as reductive catalytic fractionation. The structure of lignin and composition of the starting material has a major impact on the product yield and distribution. Here, the differences in structure of lignin from birch, pine, reed, and walnut shell were investigated by combining detailed analysis of the whole cell wall material, residual enzyme lignin, and milled wood lignin. The results of the 2D heteronuclear single quantum coherence NMR analysis could be correlated to the product from Ru/C-catalyzed hydrogenolysis if monomeric products from ferulate and p-coumaryl and its analogous units were also appropriately considered. Notably, residual polysaccharide constituents seemed to influence the selectivity towards hydroxy-containing monomers. The results reinforced the importance of adequate structural characterization and compositional analysis of the starting materials as well as distinct (dis)advantages of specific types of structural characterization and isolation methods for guiding valorization potential of different biomass feedstocks.

Synergistic effects of hydrothermal and deep eutectic solvent pretreatment on co-production of xylo-oligosaccharides and enzymatic hydrolysis of poplar

Full utilization of lignocellulose is critical for its biorefinery development. In this study, a sustainable biorefinery process based upon poplar sawdust was established using sequential hydrothermal and deep eutectic solvent treatment (HP-DES). Results showed that single hydrothermal pretreatment (HP) could produce 53.2% xylo-oligosaccharides (XOS) (based on raw xylan), while the enzymatic digestibility was low. Conversely, single DES treatment achieved effective enzymatic digestibility but low XOS yields. As compared to HP, both DES treatment and HP-DES showed high selectivity for lignin removal and high glucose yield. Surprisingly, most of HP-DES residues had obviously lower enzymatic digestibilities than those of single DES residues. This was mainly explained by the differences of the surface lignin contents between DES and HP-DES residues. Moreover, nearly complete enzymatic hydrolysis of HP-DES residues was achieved with the addition of bovine serum albumin. This work demonstrated this HP-DES yielded XOS, fermentable sugar, and pure lignin with high processibility.

Structural characterization of poplar lignin based on the microwave-assisted hydrothermal pretreatment

Increasing application for lignin due to its unique aromatic structures has encouraged the development of pretreatment techniques for lignin separation and recovery. In this work, the integration of microwave-assisted hydrothermal pretreatment (MW-HTP) and alkaline post-treatment was proposed for separating lignin from poplar wood and revealing its structural characteristics. Results showed that the yields of the lignins fractionated via the integrated treatment based on MW-HTP were increased up to 52.6%, and their associated sugars contents were clearly decreased to 0.19-0.09%, as compared to the fractionated lignins without the microwave pretreatment (29.8% and 0.29%). Interestingly, the integrated treatment based on MW-HTP promoted the cracking of β-O-4 ethers in the lignin macromolecules of poplar wood, resulting in the raise of their phenol OH groups up to 2.36 mmol/g. Overall, the fulfillment of this work will be conducive to improve the fractionation and efficient utilization of lignin in biorefinery industry.

Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

Enzymatic hydrolysis of lignocellulose for bioethanol production shows a great potential to remit the rapid consumption of fossil fuels, given the fact that lignocellulose feedstocks are abundant, cost-efficient, and renewable. Lignin results in low enzymatic saccharification by forming the steric hindrance, non-productive adsorption of cellulase onto lignin, and deactivating the cellulase. In general, the non-productive binding of cellulase on lignin is widely known as the major cause for inhibiting the enzymatic hydrolysis. Pretreatment is an effective way to remove lignin and improve the enzymatic digestibility of lignocellulose. Along with removing lignin, the pretreatment can modify the lignin structure, which significantly affects the non-productive adsorption of cellulase onto lignin. To relieve the inhibitory effect of lignin on enzymatic hydrolysis, enormous efforts have been made to elucidate the correlation of lignin structure with lignin-enzyme interactions but with different views. In addition, contrary to the traditional belief that lignin inhibits enzymatic hydrolysis, in recent years, the addition of water-soluble lignin such as lignosulfonate or low molecular-weight lignin exerts a positive effect on enzymatic hydrolysis, which gives a new insight into the lignin-enzyme interactions. For throwing light on their structure-interaction relationship during enzymatic hydrolysis, the effect of residual lignin in substrate and introduced lignin in hydrolysate on enzymatic hydrolysis are critically reviewed, aiming at realizing the targeted regulation of lignin structure for improving the saccharification of lignocellulose. The review is also focused on exploring the lignin-enzyme interactions to mitigate the negative impact of lignin and reducing the cost of enzymatic hydrolysis of lignocellulose.

Revalorization of sunflower stalk pith as feedstock for the coproduction of pectin and glucose using a two-step dilute acid pretreatment process

BACKGROUND

Sunflower stalk pith, residue from the processing of sunflower, is rich in pectin and cellulose, thereby acting as an economic raw material for the acquisition of these compounds. In order to increase the commercial value of sunflower processing industry, a two-step dilute sulfuric acid treatment process was conducted on spent sunflower stalk pith to obtain the value-added products, pectin and glucose.

RESULTS

In this study, pectin was firstly extracted under mild acid condition to avoid pectin degradation, which was conducted at 90 °C with a pH of 2.0 for 2 h, and ~0.14 g/g of pectin could be recovered. Then the remaining solids after pectin extraction were subjected to the reinforced treatment process with 0.75% H₂SO₄ at 150 °C for 30 min to further improve enzymatic hydrolysis efficiency. Moreover, by combining a fed-batch enzymatic hydrolysis strategy, a solid loading content of 16% was successfully achieved and the glucose titer reached 103.1 g/L with a yield of 83.6%.

CONCLUSION

Finally, ~140 g pectin and 260 g glucose were produced from 1 kg of raw sunflower stalk pith using the integrated biorefinery process. This work puts forward a two-step dilute acid pretreatment combined with enzymatic hydrolysis method to produce pectin and glucose from sunflower spent waste.

Benzenesulfonic acid-based hydrotropic system for achieving lignocellulose separation and utilization under mild conditions

Developing low-cost and sustainable fractionation technology is the key to achieve the maximal utilization of lignocellulosic biomass. This study reported benzenesulfonic acid (BA) as a green hydrotrope for efficient lignocellulose conversion into two fractions at atmospheric pressure: (1) a primarily cellulosic solid residue that can be utilized to produce high-value building blocks (lignocellulosic nanomaterials or sugars), and (2) the collected spent acid liquor that can be diluted with anti-solvent to easily obtain lignin nanoparticles. BA hydrotropic method exhibited greater reaction selectivity to solubilize lignin, where approximately 80% lignin were removed at only 80 °C in 20 min. The lower lignin content substrates resulted in relatively higher enzymatic hydrolysis efficiency of 80% and less entangled lignocellulosic nanofibrils (LCNF). Furthermore, the separated lignin particles size can be easily adjusted by the initial acid concentration. Overall, this work presented a promising and simple technology in achieving lignocellulose separation and utilization under mild conditions.

Multifunctional lignin-based nanocomposites and nanohybrids

Significant progress in lignins valorization and development of high-performance sustainable materials have been achieved in recent years. Reports related to lignin utilization indicate excellent prospects considering green chemistry, chemical engineering, energy, materials and polymer science, physical chemistry, biochemistry, among others. To fully realize such potential, one of the most promising routes involves lignin uses in nanocomposites and nanohybrid assemblies, where synergistic interactions are highly beneficial. This review first discusses the interfacial assembly of lignins with polysaccharides, proteins and other biopolymers, for instance, in the synthesis of nanocomposites. To give a wide perspective, we consider the subject of hybridization with metal and metal oxide nanoparticles, as well as uses as precursor of carbon materials and the assembly with other biobased nanoparticles, for instance to form nanohybrids. We provide cues to understand the fundamental aspects related to lignins, their self-assembly and supramolecular organization, all of which are critical in nanocomposites and nanohybrids. We highlight the possibilities of lignin in the fields of flame retardancy, food packaging, plant protection, electroactive materials, energy storage and health sciences. The most recent outcomes are evaluated given the importance of lignin extraction, within established and emerging biorefineries. We consider the benefit of lignin compared to synthetic counterparts. Bridging the gap between fundamental and application-driven research, this account offers critical insights as far as the potential of lignin as one of the frontrunners in the uptake of bioeconomy concepts and its application in value-added products.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

Lignin Nanoparticles: Promising Sustainable Building Blocks of Photoluminescent and Haze Films for Improving Efficiency of Solar Cells

Films with the capacity for photoluminescence and haze, which can convert UV to visible light and enhance light management, are of great importance for optoelectronic devices. Here, taking advantage of the inherent fluorescence and self-assembly properties of lignin, we have developed a sustainable lignin-derived multifunctional dopant (L-MS-NPs) for fabricating optical films with haze, fluorescence, and room-temperature phosphorescence (RTP) together with poly(vinyl alcohol) (PVA). The optical films are used to improve the light-harvesting efficiency of solar cells. Specifically, attributed to the robust morphology in the film matrix, L-MS-NPs cause a rough morphology in the surface of an L-MS-NPs/PVA composite film, which eventually triggers the great optical haze. Additionally, L-MS-NPs inherit fluorescence properties from lignin and show fluorescence emission when embed in the film matrix. Moreover, the PVA film matrix can stabilize the excited triplet state, which finally induces RTP of L-MS-NPs. The combined haze, fluorescence, and RTP properties of the L-MS-NPs/PVA composite film enhances the power conversion efficiency (PCE) of dye-sensitized solar cells from ∼3.9 to ∼4.1%.

Tandem Character of Liquid Hot Water and Deep Eutectic Solvent to Enhance Lignocellulose Deconstruction

Pretreatment with efficient fractionation, eco-friendliness, and low-cost brings high security to future biorefinery systems. Synergistic pretreatment is a compelling blueprint to tackle the compact structure of lignocellulose towards a high-level valorization. Here, a stepwise approach was designed using hydrothermal and deep eutectic solvent (DES) pretreatments to hierarchically extract hemicelluloses and lignin from poplar, while delivering a cellulose-rich substrate that could easily undergo enzymatic hydrolysis to obtain fermentable glucose and residual lignin. The lifetime of recyclable DES showed that the pretreatment efficiency was still largely maintained after the fourth recycling. An enhancement of enzymatic digestibility from 13.9 to 90.4 % was initiated by the deconstruction of amorphous portions and robust cell wall. 23.7 % Xylooligosaccharides (degree of polymerization 2-6), 47.5 % DES-isolated lignin, and 19.2 % cellulose enzymatic lignin were harvested via this coupled process. This study could promote the precise design of sustainable tandem pretreatment that can boost the frontier of highly available biorefinery.

Isolating High Antimicrobial Ability Lignin From Bamboo Kraft Lignin by Organosolv Fractionation

Lignin from different biomasses possess biological antioxidation and antimicrobial activities, which depend on the number of functional groups and the molecular weight of lignin. In this work, organosolv fractionation was carried out to prepare the lignin fraction with a suitable structure to tailor excellent biological activities. Gel permeation chromatography (GPC) analysis showed that decreased molecular weight lignin fractions were obtained by sequentially organosolv fractionation with anhydrous acetone, 50% acetone and 37.5% hexanes. Nuclear magnetic resonance (NMR) results indicated that the lignin fractions with lower molecular weight had fewer substructures and a higher phenolic hydroxyl content, which was positively correlated with their antioxidation ability. Both of the original lignin and fractionated lignins possessed the ability to inhibit the growth of Gram-negative bacteria (Escherichia coli and Salmonella) and Gram-positive bacteria (Streptococcus and Staphylococcus aureus) by destroying the cell wall of bacteria in vitro, in which the lignin fraction with the lowest molecular weight and highest phenolic hydroxyl content (L3) showed the best performance. Besides, the L3 lignin showed the ability to ameliorate Escherichia coli-induced diarrhea damages of mice to improve the formation of intestinal contents in vivo. These results imply that a lignin fraction with a tailored structure from bamboo lignin can be used as a novel antimicrobial agent in the biomedical field.

Natural surfactant-aided dilute sulfuric acid pretreatment of waste wheat straw to enhance enzymatic hydrolysis efficiency

Traditional surfactants have been reported to enhance enzymatic saccharification of lignocellulose, however, it is important to transfer these findings to a system that uses a high-efficiency and low-toxicity natural surfactant instead. In this work, a novel hybrid method involving use of the natural surfactant (humic acid, HA) during mild acid (H₂SO₄) pretreatment was developed for waste wheat straw (WWS) biorefinery. The HA was found to help remove lignin up to 40.6%, and hemicellulose up to 96.2%. As a result of these changes, the enzymatic hydrolysis efficiency reached as high as 92.9%. The success of enzymatic digestion was partly attributed to the improved accessibility of cellulose to cellulase and changes in lignocellulose structures. We anticipate that these findings will be used to further evaluate HA as a beneficial surfactant in biorefinery pretreatment processes, and perhaps spur others to identify other natural surfactants that may prove even more effective.

Revealing the structural characteristics of lignin macromolecules from perennial ryegrass during different integrated treatments

To reveal the structural characteristics and physicochemical properties of perennial ryegrass lignin, sequential alkali extractions or double ball-milling and enzymatic hydrolysis on the basis of ultrasonic and hydrothermal pretreatments were proposed in this study. Results revealed that sequential alkali extractions released 89.4% of original lignin from the ryegrass cell walls and 0.75-4.16% of associated carbohydrates as compared to the double ball-milling and enzymatic hydrolysis (96.0% and 18.39%). It was observed that the two types of lignin prepared were SGH-type and had different amounts of p-coumarates and ferulates, and primarily consisted of β-O-4' linkages combined with minor amounts of β-β' and β-5' linkages. Besides, alkali-soluble lignins exhibited relatively fewer β-O-4' linkages, higher S/G ratios and H-type units, and abundant phenolic OH groups as compared to the double enzymatic lignin. Overall, the deeper investigation of the lignin structure of ryegrass will provide useful information for the efficient utilization of lignin macromolecules in biorefineries.

A novel recyclable furoic acid-assisted pretreatment for sugarcane bagasse biorefinery in co-production of xylooligosaccharides and glucose

BACKGROUND

Pretreatment is the key step for utilizing lignocellulosic biomass, which can extract cellulose from lignin and disrupt its recalcitrant crystalline structure to allow much more effective enzymatic hydrolysis; and organic acids pretreatment with dual benefic for generating xylooligosaccharides and boosting enzymatic hydrolysis has been widely used in adding values to lignocellulose materials. In this work, furoic acid, a novel recyclable organic acid as catalyst, was employed to pretreat sugarcane bagasse to recover the xylooligosaccharides fraction from hemicellulose and boost the subsequent cellulose saccharification.

RESULTS

The FA-assisted hydrolysis of sugarcane bagasse using 3% furoic acid at 170 °C for 15 min resulted in the highest xylooligosaccharides yield of 45.6%; subsequently, 83.1 g/L of glucose was harvested by a fed-batch operation with a solid loading of 15%. Overall, a total of 120 g of xylooligosaccharides and 335 g glucose could be collected from 1000 g sugarcane bagasse starting from the furoic acid pretreatment. Furthermore, furoic acid can be easily recovered by cooling crystallization.

CONCLUSION

This work put forward a novel furoic acid pretreatment method to convert sugarcane bagasse into xylooligosaccharides and glucose, which provides a strategy that the sugar and nutraceutical industries can be used to reduce the production cost. The developed process showed that the yields of xylooligosaccharides and byproducts were controllable by shortening the reaction time; meanwhile, the recyclability of furoic acid also can potentially reduce the pretreatment cost and potentially replace the traditional mineral acids pretreatment.