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Biomass resource lignin was used to construct a large-scale and ordered lignin graphitization structure in a two-dimensional space through the catalytic graphitization process, forming a lignin-based graphene-like film with conductivity.

Lignosulfonate (LS), a biomass by-product from sulfite pulping and the paper-making industry, which has many excellent characteristics, such as renewable, environmentally friendly, amphiphilic nature, and especially the abundant content of hydrophilic functional groups in its architecture, making it highly reactive and can be used as a sensitive material in sensors to show changes in electrical signals. Herein, we report a one-step

The high value-added conversion of biomass lignin has been paramount in the field of lignin utilization, especially for high performance energy conversion and storage devices. A majority of lignin-based supercapacitors generally exhibit inferior electrochemical performance with low capacitance and slow diffusion kinetics due to the poor interfacial compatibility, low conductivity, and uncontrollable morphology. Herein, we designed all-lignin converted graphene quantum dot and graphene sheet (GQD/Gr) hetero-junction for simultaneous fast charging and boosted specific capacitance. The conversion from lignin to GQDs and then refusion into graphene allows the in situ growth of GQDs on graphene, endowing good interfacial compatibility with the GQD/Gr hetero-junction. Furthermore, both GQDs and graphene sheets exhibit highly crystalline structure with obvious graphene lattice, giving GQDs/Gr good conductivity. GQDs play an additive role for avoiding stacks and agglomerates between graphene layers, which endow the assembled GQDs/Gr with massive electron capacitive sites and more hierarchical channels. Therefore, the GQD/Gr hetero-junction gives rise to a high specific capacitance of 404.6 F g−1 and a short charging time constant (τ0) of 0.3 s, 2.5 times higher and 7.5 times faster than that of the unmodified lignin electrode with 162 F g−1 and 2.3 s, respectively. This proposed strategy could offer the opportunity to unblock the critical roadblocks for a superior electrochemical performance lignin-based supercapacitor by composing a 0D/2D GQD/Gr hetero-junction system and also paves a bright way for the high-value industrial lignin conversion into cheap, scalable, and high-performance electrochemical energy devices.

The present chemical converted graphene sheets are mostly dependent on the exfoliation of graphite with strong oxidants, which suffer from heavy burden of environmental pollution. Here, we report a simple, green and scalable method to synthesize graphene sheets by one-pot activation-synthesis method derived from black liquor, a biomass waste resource in pulping industry. The pulping black liquor consisting of alkali lignin as main components with phenyl skeletons and condensed aromatic segments was successively transferred from heterogeneous chemical states into micron-sized graphene sheets. The proposed conversion mechanism mainly consists of aromatic rebonding, refusion and deoxygenation reaction, in which alkaline species acting as situ-activation agent. The graphene sheets obtained from pulping black liquor (BL-G) show typical hexagonal honeycomb lattice in thickness of 1–3 atomic carbon layers with controllable lateral size ranging from 0.36 to 2.5 μm. After spin-coating single- or few-layer of BL-G sheets onto flexible substrate, it could produce transparent and conductive thin films (TCFs) with sheet resistance as low as 2.1 kΩ sq−1 and 85% transmittance for 550 nm light, suggesting its great potentials using as flexible electrode materials. This green synthesis route may pave a bright way in large-scale production of chemically converted graphene sheets.

Direct transformation of bioethanol fermentation residues to valuable products is a challenge for current bioethanol fermentation processes. Traditionally, the addition of carbohydrate will reduce the performance of lignin-based resin, which greatly limits the transformation of fermentation residues (lignin-rich component) into resin. In this study, we overcame this challenge by the simple and novel strategy of producing high-quality co-condensed fermentation residue-based resins (FRs) over inexpensive sodium hydroxide and sodium carbonate as catalysts. Herein, thorough characterization of the physical properties, chemical structures, and curing behavior was performed to acquire additional data for the prepared resins obtained from two different types of fermentation residues. The current study is the first to meticulously investigate the synergistic effect of lignin and carbohydrates on resins. The mechanism results indicate that numerous co-condensed linkages were formed to produce resins with a firm structure. More importantly, when carbohydrate-rich solid residues were used instead of wheat flour, successful adjustment of viscosity, prevention of excessive osmosis, and increased bonding strength of the FRs occurred. Under the synergistic effect, the produced green FRs were utilized to manufacture plywood with a satisfactory bonding strength (1.07 MPa). The emission of formaldehyde, a harmful volatile organic compound, was also reduced by 94%. This work developed a promising sustainable technology with no waste production for direct transformation of bioethanol fermentation residues from bioethanol manufacturing. The technique reported here vastly broadens the application of fermentation waste and advances the bioethanol industry.

The natural lignin macromolecule is structurally complex and heterogeneous polymers. Herein, to comprehend the dynamic structural characteristics of poplar (Populus tomentosa) lignin during the gro...

Facile and controllable synthesis of graphene or graphene-like 2D nanosheets from plentiful and biocompatible materials still remains a great challenge. Herein, a bottom-up and controllable approach was firstly reported to transform earth-abundant lignosulfonate into graphene-like materials, in which lignosulfonate-based 2D nanosheets were fabricated via self-assembly in water/acetone dual solvent system, and then the nanosheets materials were transformed into graphene-like materials by carbonization. The physical properties of obtained lignosulfonate-based nanosheets were characterized, and the formation mechanism of these nanosheets was also elucidated. The thickness of the nanosheets was in the range of 5–20 nm depending on the concentration of lignosulfonate in water. Directed by π − π interactions and hydrogen bonds, the evolution of layered nanosheets seemed to experience from nano-sized rodlikes, a flake with defect holes, and smooth lignosulfonate-based nanosheets. Because of the relatively lower resistance, nano-sized structures and good cytocompatibility, the lignosulfonate-based graphene-like materials exhibited great potential in biomedical energy-related applications.

Lignosulfonate (LS), an aromatic polymer with massive hydrophilic groups from biomass, has been firstly developed as sensitive material for detecting environmental humidity. Using LS as moisture sensing layers and additive reduced graphene oxide (rGO) as resistant transduction layers, an rGO/LS composite thin-film has been prepared as humidity sensor through a cost-effective approach. Here we demonstrate that the three-dimensional molecular structure and amphiphilic behavior of LS enable ultrahigh sensitivity to the degree of moisture. The maximum response of 3 wt% rGO/LS thin-film reaches up to 298% for 97% relative humidity, which is nearly 4 orders of magnitude than that of pure rGO thin-film. Moreover, the rGO/LS thin-film can be used as a humidity sensor with large response, low hysteresis and stable repeatability in broad relative humidity ranging from 22% to 97%. This opens the door to various applications, such as flexible touchless interfaces, which we presented with a respiratory frequency transducer. The low cost, simple designed and portable used humidity sensor highlights the potential application of lignin as high-valued materials.

Renewable, cheap and green biomass resources could meet the urgent need for producing graphene quantum dots (GQDs) on a large scale if high quality can be obtained. Here we report the gram-scale synthesis of single-crystalline GQDs derived from lignin biomass via a two-step method. The synthetic processes involve the oxidized cleavage step followed by the aromatic refusion step of alkali lignin molecules. Notably, this approach successively converts the biomass commonly considered as waste into a high-valued nanoscale product. The as-prepared single-crystalline GQDs, presenting a hexagonal honeycomb graphene network, are 1–3 atomic layers thick. Due to the bright fluorescence, up-conversion properties, long-term photostability, water solubility and biocompatibility, these high quality GQDs have potential to be excellent nanoprobes for multicolour bioimaging. The utilization of renewable biomass resources paves the way for green, low-cost and large-scale production of high quality GQDs and allows for the development of sustainable applications.

Graphene quantum dots (GQD), including carbon quantum dots (CQD), as one class of novel fluorescent carbon nanomaterials, have gained numerous interests owning to its excellent photoluminescence, good biocompatibility, and unique physiochemical structure over conventional toxic semiconductors quantum dots and organic dyes, exhibiting great potentials in the optical, displaying, biological, electrocatalysis, and photoelectric fields. There is a factor that GQDs synthesis with large scale still stays relatively complex, expensive, and low efficient. Large-scale synthesis of GQD by utilizing a facile, green, and low-cost method is highly desirable especially with high-quality and large quantum yield. This chapter summarizes GQDs’ synthesis method based on the “top-down” and “bottom-up” approaches, highlighting the ongoing raw materials strategies of large-scale GQDs synthesis, and also reviews recent emerging novel synthetic methods and remaining challenges.

Technical lignin from pulping, an aromatic polymer with ~59% carbon content, was employed to develop novel lignin-based nano carbon thin film (LCF)-copper foil composite films for thermal management applications. A highly graphitized, nanoscale LCF (~80&ndash, 100 nm in thickness) was successfully deposited on both sides of copper foil by spin coating followed by annealing treatment at 1000 &deg, C in an argon atmosphere. The conditions of annealing significantly impacted the morphology and graphitization of LCF and the thermal conductivity of LCF-copper foil composite films. The LCF-modified copper foil exhibited an enhanced thermal conductivity of 478 W m&minus, 1 K&minus, 1 at 333 K, which was 43% higher than the copper foil counterpart. The enhanced thermal conductivity of the composite films compared with that of the copper foil was characterized by thermal infrared imaging. The thermal properties of the copper foil enhanced by LCF reveals its potential applications in the thermal management of advanced electronic products and highlights the potential high-value utility of lignin, the waste of pulping.

Low cost fabrication of water treatment polymer materials directly from biomass resources is urgently needed in recent days. Herein, a compressive alginate sponge (AS) is prepared from seaweed biomass resources through a green two-step lyophilization method. This material is much different from conventional oven-, air-, vacuum-dried alginate-based adsorbents, which show limitations of shrinkage, rigidness, tight nonporous structure and restricted ions diffusion, hindering its practical applications, and was used to efficiently remove methylene blue (MB), a main colorful contaminant in dye manufacturing, from wastewater. The batch adsorption studies are carried out to determine the impact of pH, contact time and concentration of dye on the adsorption process. The maximum adsorption capacity can be obtained at 1279 mg g&minus, 1, and the shape-moldable AS can be facilely utilized as a fixed-bed absorption column, providing an efficient approach for continuous removal of MB within a short time. It is also important that such a compressive AS can be regenerated by a simple squeezing method while retaining about 70% capacity for more than ten cycles, which is convenient to be reused in practical water treatment. Compressive AS demonstrates its merits of high capability, large efficiency and easy to recycle as well as low cost resources, indicating widespread potentials for application in dye contaminant control regarding environmental protection.

Nanocomposite materials with uniform microstructure and high permittivity have attracted extensive interest in modern electronics. The compatibility between the filler phase and the polymer matrix is crucial in preparing high-performance composites. As an alternative to conventional surface modification treatment methodologies, hydroxylated colloidal BaTiO3 (BT) nanoparticles synthesized via a green and scalable process were directly used to fabricate high-permittivity nanocomposites. Interfacial interaction analyses between the BT nanoparticles and polymer matrix reveals that due to strong hydrogen bonding at the interface, transparent composite sols with excellent flow behavior can be observed. The sols are ideal formulations for the preparation of BT/PVDF–hfp 0–3 nanocomposite films. Owing to the unique interface structure, the composite films show a dense and uniform microstructure and superior dielectric properties. Parallel plate capacitor devices and the co-development of a sandwich architecture leads to the ability to prepare dielectric films with favorable performance characteristics. This method provides a novel and greatly simplified strategy for the fabrication of high-permittivity dielectric nanocomposites.

Emerging flexible supercapacitors have motivated tremendous research interest in portable energy devices. However, challenges still exist in the pursuit of cheap and renewable electrode materials. Herein, a metal-free and flexible supercapacitor was fabricated based on lignosulfonate functionalized graphene hydrogels (LS-GHs). The supercapacitor shows comparable or even higher performance than reported transition metal based pseudocapacitive supercapacitors, which can be attributed to the reversible redox charge transfer of quinone groups in lignin. It presents an impressive specific capacitance of 432 F g−1 in an aqueous electrolyte, which is nearly 2 times higher than that of a pure graphene hydrogel (238 F g−1). Moreover, the device exhibits high rate capability (81.0% capacitance retention at 20 A g−1) and cycling stability (90.0% capacitance retention over 10 000 cycles). The resulting LS-GH electrodes are further fabricated into a flexible solid-state supercapacitor using H2SO4–polyvinyl alcohol (PVA) gel as the electrolyte. The integrated flexible device not only maintains high capacitive performances (408 F g−1 at 1 A g−1, 75.4% capacitance retention at 20 A g−1 and 84.0% capacitance retention over 10 000 cycles), but also exhibits excellent mechanical flexibility. This work paves the way to develop flexible energy devices based on metal-free, renewable and low-cost biomass resources.

Environmental issues and constantly diminishing petroleum resources are considerable barriers inhibiting modernization, and vast efforts have been exerted to address these problems. Carbon fibers (CFs) are carbon materials with high mechanical strength and functionality for applications in construction, electronics, transportation, and aviation. Currently, most CFs are produced from polyacrylonitrile, a petroleum-based, unsustainable, and non-renewable chemical of relatively high price. Interestingly, lignin is an inexpensive, highly accessible, and renewable resource. It has been utilized to fabricate lignin-based carbon fibers (LCFs), which have met rapid development during the past two decades. In this review, LCFs are generalized by focusing on their steps of manufacture. Resource types and corresponding pretreatments ensure the processability of spinning and thermal treatments. Fibers are formed via spinning methods, including melt-spinning, wet-spinning, dry-spinning, and electrospinning. The next step is the most significant process of stabilization, in which fibers are oxidized, crosslinked, and thermally stabilized for pyrolysis. Subsequent to carbonization and/or additional processes (activation and graphitization), LCFs are obtained. Each step can influence the terminal performance of LCFs, which is discussed in detail. Recently produced LCFs of sub-micron size, also known as lignin-based carbon nanofibers (LCNFs), are detailed. Furthermore, attributed to the excellent performance and low cost of LCFs and LCNFs, they have been applied in various fields, predominantly for electronic devices such as batteries and supercapacitors. Our review is concluded with opinions on the potential for further advancement of this promising material.

Developing an effective and efficient biorefinery process is crucial for the utilization of biomass. In this work, corn stalk was treated in a methyl isobutyl ketone (MIBK)/water biphasic system to produce furfural and treated-corn stalk residues. The results showed that Al(NO3)3·9H2O owned the best property to convert hemicelluloses into furfural in the MIBK/water system. Under the optimal conditions (0.1 M Al(NO3)3·9H2O, 160 °C and 60 min), the furfural yield could reach 52.0%, while only 2.3% hemicelluloses remained in the treated-corn stalk residues. The cellulose largely remained in the residues, and the glucose yield had an apparent increment by the subsequent enzymatic hydrolysis process (85.5%). Additionally, lignin was the main component of the residues obtained after enzymatic hydrolysis process, which has been degraded to some extent. Moreover, in the morphological aspect, the cell walls swelled evidently and the vascular bundles were broken down. The result of confocal Raman microscopy indicated that there was a severe cleavage of ether and ester linkages between hydroxycinnamic acids and hemicelluloses or lignin, and lignin largely remained during the treatment. In short, the MIBK/water/Al(NO3)3·9H2O treatment process provided an efficient integrated utilization of corn stalk to produce furfural and fermentable glucose for the bioethanol production, and the feasible biorefinery process is beneficial for the environment protection and sustainable development.

A lignosulfonate-modified graphene hydrogel (LS-GH) for Pb(II) adsorption was synthesized through a one-step method. The three-dimensional (3D) porous architecture of the graphene hydrogel was functionalized by using lignosulfonate with diverse oxygen containing groups. Benefiting from a large specific surface area, multiple porosity and sufficient active sites, the LS-GH adsorbent exhibited ultrahigh adsorption capacity (1210 mg g−1) for Pb(II) removal, which was among the highest of previously reported Pb(II) adsorbents. Importantly, the free-standing and flexible LS-GH can be used as a column-packed device, providing an efficient pathway for the fast removal of Pb(II) with an ultrahigh adsorption capacity of 1308 mg g−1 within 40 min. The high capacity LS-GH adsorbent is low cost, eco-friendly and recyclable, which could be an attractive adsorbent for the purification of wastewater on a large scale.

Graphene is a unique and attractive energy material because of its atom-thick two-dimensional structure and excellent properties. Graphene sheets are also mechanically strong and flexible. Thus, graphene materials are expected to have wide and practical applications in bendable, foldable and/or stretchable devices related to energy conversion and storage. We present a review on the recent advancements in flexible graphene energy devices including photovoltaic devices, fuel cells, nanogenerators (NGs), supercapacitors (SCs) and batteries, and the devices related to energy conversion such as organic light-emitting diodes (OLEDs), photodetectors and actuators. The strategies for synthesizing flexible graphene materials will be summarized and the challenges facing the design and construction of the devices will be discussed.

Lignin is a renewable source of aromatics, and the conversion of lignin to chemicals, fuels and materials is very attractive. Herein, a novel lignin-based cation exchange resin (LBR) was easily synthesized through an economical one-pot method. Results demonstrated that the sulfonic acid groups were successfully introduced into the skeleton of the resins, and the S contents and swelling capacity of the prepared LBRs gradually increased with the increment of the sulfonation reagents dosage. A maximum ion-exchange capacity of 2.26 mmol/g was achieved for the LBR obtained at 120 °C for 4 h with a molar ratio of phenol to formaldehyde (P:F) of 1:5 (SSPL-0.50), which was comparable to the commercial phenol type cation exchange resin. Furthermore, the SSPL-0.50 exhibited a high adsorption capacity (167.2 mg/g) for Pb (II) removal. The LBR can be considered as a promising substitute for the petroleum-based ion exchange resin in the purification of wastewater.

Pristine graphene and chemically modified graphenes (CMGs, e.g., graphene oxide, reduced graphene oxide and their derivatives) can react with a variety of chemical substances. These reactions have been applied to modulate the structures and properties of graphene materials, and to extend their functions and practical applications. This perspective outlines the chemistry of graphene, including functionalization, doping, photochemistry, catalytic chemistry, and supramolecular chemistry. The mechanisms of graphene related reactions will be introduced, and the challenges in controlling the chemical reactions of graphene will be discussed.

Graphene nanomeshes (GNMs) which can be cheaply produced on a large scale and processed through wet approaches are important materials for various applications, including catalysis, composites, sensors and energy related systems. Here, we report a method for large scale preparation of GNMs by refluxing reduced graphene oxide sheets in concentrated nitric acid solution (e.g., 8 moles per liter). The diameters of nanopores in GNM sheets can be readily modulated from several to hundreds nanometers by varying the time of acid treatment. The porous structure increased the specific surface areas of GNMs and the transmittances of GNM-based thin films. Furthermore, GNMs have large number of carboxyl groups at the edges of their nanopores, leading to good dispersibility in aqueous media and strong peroxidase-like catalytic activity.

Graphene oxide (GO) sheets prepared by Hummers' method have been separated into two portions with large (f1) or small (f2) lateral dimensions from their aqueous dispersion. This method is based on the selective precipitation of GO sheets with lateral dimensions mostly (90%) larger than 40 μm(2) at a pH value of 4.0 because of their larger hydrophobic planes and fewer hydrophilic oxygenated groups. The hydrazine reduced Langmuir-Blodgett (LB) films of f1 showed much higher conductivities than those of f2. Furthermore, the thin film of f1 prepared by filtration exhibited a smaller d-space and much higher tensile strength and modulus than those of f2 films. The one-step size fractionation method reported here is simple, cheap, efficient, and environmentally friendly, which can be used for the size fractionation of GO sheets in large scale.

Platinum (Pt)-based catalysts used in direct methanol fuel cells (DMFCs) usually suffer from low catalytic activity, slow kinetics of methanol oxidation and poor electrochemical stability. This is mainly due to the toxic effect of carbon monoxide and inefficient use of the Pt catalysts. To address these problems, we immobilized Pt nanoparticles with diameters of 4-6 nm onto the three-dimensional (3D) interpenetrating graphene networks (graphene hydrogel or G-Gel) deposited in the micropores of nickel foam (NF). In this Pt/G-Gel/NF composite catalyst, nearly all the Pt nanoparticles are accessible to methanol and can be efficiently used for electrocatalyzation. It showed excellent electrochemical stability and an activity 2.6 times that of a conventional Pt/reduced graphene oxide (Pt/rGO) composite catalyst. Furthermore, the rate of methanol electro-oxidation at the Pt/G-Gel/NF catalyst can be about 27 times that at the Pt/rGO catalyst, making it applicable for fabricating DMFCs with high current and/or power outputs.

Composite crystals of calcium carbonate (CaCO3) and graphene with hexagonal plate or ring, dendritic and rhombohedral shapes were synthesized by the hydrothermal reaction of calcium acetate and urea in the presence of graphene oxide (GO) sheets. Their crystal structures were characterized to be vaterite, aragonite and calcite, respectively. In this case, the hydrothermally reduced graphene oxide (rGO) acted as an atom-thick, two-dimensional template for controlling the nucleation and growth of the CaCO3 crystals. The vaterite CaCO3 composite crystals (VCCs) were used as a filler of poly(vinyl alcohol) (PVA) to form a composite with a nacre-like structure. The Young's modulus and tensile strength of PVA/45 wt% VCC were tested to be 34.1 ± 2.5 GPa and 165 ± 6 MPa, respectively.

Composite films of chitosan and reduced graphene oxide (RGO) sheets with nacre-like layered structure have been prepared by vacuum filtration of the stable aqueous mixture of both components. The film containing 6 wt% RGO is electrically conductive with a conductivity of 1.2 S m−1. Furthermore, it is mechanically strong and ductile; its Young's modulus, tensile strength and elongation at break were measured to be 6.3 ± 0.2 GPa, 206 ± 6 MPa and 6.5 ± 0.6%, respectively. These values partly exceed those of nacre. The high mechanical and electrical properties of chitosan/RGO composite films are mainly attributed to the uniform dispersion of RGO nanofillers in the polymer matrices to form a compact layered structure.