Lignin Solution Research Articles

Electrochemical oxidation of lignin at electrochemically reduced TiO2 nanotubes

For this study, the electrochemical oxidation of lignin was investigated at the surfaces of electrochemically (EC) reduced TiO2 nanotube arrays. The effects of nanotube lengths on the lignin oxidation were explored by growing the nanotubes with different lengths through anodization. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and electron paramagnetic resonance (EPR) techniques were employed to characterize the fabricated TiO2 nanotubes. The electrochemical behaviors of the nanotubes before and after the EC treatment were assessed by various electrochemical methods, including cyclic voltammetry (CV), chronopotentiometry (CP), and impedance spectroscopy. The TiO2 nanotubes were treated by applying a cathodic current (5 mA cm−2) for 10 min, which significantly increased its electrocatalytic activity. It was also determined that the nanotube length was linearly increased with the increase of the anodization time, and that the longer the nanotubes and the larger the double layer capacitance. The length of the nanotubes had a significant effect on the level of lignin oxidation, and an optimal TiO2 nanotube length that enabled the most efficient oxidation of lignin was determined. The efficiency of the TiO2 electrodes towards the oxidation of lignin was also compared to a Pt electrode. The TiO2 nanotubes that were grown for 16 h by anodization with ~13.5 μm length exhibited the lowest impedance and the highest lignin oxidation efficacy. The total organic carbon (TOC) of the lignin solution under different oxidation times was also measured to further evaluate the efficiency of the electrochemical degradation of lignin, and 70% TOC removal was achieved in 3 h. The TiO2 electrodes were shown to outperform the Pt electrode in all the lignin oxidation studies. Moreover, the activation energy required for the electrochemical oxidation of lignin was investigated by performing the oxidation under various temperatures and found to be 21.0 kJ mol−1. The EC reduced TiO2 nanotube electrode showed high activity and stability, promising for environmental applications.

Activation of electrospun lignin-based carbon fibers and their performance as self-standing supercapacitor electrodes

The production and activation of self-standing carbon electrodes from electrospun lignin fibers was analyzed in this work. Carbon microfibers were prepared at 900 °C from air-stabilized spun cloths by direct carbonization under inert atmosphere and with diluted O2. The modifications of the porosity and surface chemistry of the carbon fibers was also studied by adding H3PO4 in the lignin solution and using different oxygen partial pressures during activation. The presence of phosphoric acid not only increases the porosity development and the preparation yield, but also enhances the gravimetric capacitance of the electrodes. In addition, the activation in presence of oxygen increases the surface area and the generation of wider micropores. Microporous carbon fibers with surface areas as high as 2340 m2 g−1 were obtained using this method. The direct conformation of carbon fibers into binderless electrodes allows to achieve high-power rate capability supercapacitors. Activation in presence of oxygen can enhance up to 50% the energy storage of supercapacitors without compromising the power of the device (8.4 Wh kg−1 and Pmax of 47 kW kg−1). However, at high activation degrees, no further gain in energy density is observed due to the excessive widening of micropores, and the loss of electrical conductivity that increases the cell resistance, limiting the power capability of the device. The optimal results in terms of energy, power and durability are achieved combining low amounts of H3PO4 and mild activation with O2, confirming that electrospinning of lignin is a promising method for sustainable production of self-standing supercapacitor electrodes.

Pure, stable and highly antioxidant lignin nanoparticles from elephant grass

Finding renewable and green resources for nanomaterial preparation is a compelling topic concerning the sustainability in nanotechnological applications. In particular, lignin-based nanoparticles are pivotal for unlocking the use of lignin in value added products. In this paper, we isolated pure lignin (ca. 98 % of purity) from elephant grass (Pennisetum purpureum) using two simple extractions with diluted acid and alkali solutions and prepared lignin and lignin acetate nanoparticles dispersed in water-basis by anti-solvent addition. Elephant grass in natura contains ca. 25 % of lignin, which could be converted into lignin nanoparticles with a 37 % yield. Spherical lignin and lignin acetate nanoparticles were revealed by electron microscopies (TEM and FESEM) and proved to be stable in a wide pH range (5–11) and ionic strength lower than 0.01. Lignin nanoparticles showed higher antioxidant activity (RSI of ca. 82) as compared to lignin in solution and to the commercial antioxidants (BHT and BHA). These nanoparticles were successfully incorporated in a neutral cream, resulting in a tinted sunscreen formulation with both ultraviolet and visible absorption. Altogether, we present here an effective method to isolate pure lignin from a non-food biomass and to prepare stable and highly antioxidant lignin nanoparticles that can be applied in dermocosmetics and are intrinsically non-toxic to the environment.

Heterogeneous photo-Fenton oxidation of lignin of rice husk alkaline hydrolysates using Fe-impregnated silica catalysts

ABSTRACT Present work shows results of a study on heterogeneous Fenton-like degradation of lignin alkaline hydrolysates formed in the process of obtaining a fibrous mass from rice husk. Fe-impregnate biogenic amorphous silica Fe/RH-SiO2 obtained from rice husk was used as a catalyst. Using IR spectroscopy, X-ray diffraction and EDX analysis it was shown that iron(III) oxide in the form of hematite is present on the catalyst surface. Phenol was used for preliminary assessment of catalytic activity of the catalyst Fe/RH-SiO2. The degree of degradation of phenol by the UV/visible radiation/Fe/RH-SiO2/H2O2 system reaches 90%. The catalytic activity of Fe/RH-SiO2 was studied in the reaction of lignin degradation of rice husk alkaline hydrolysates under ultraviolet and visible irradiation in the presence of hydrogen peroxide. The lignin solutions with COD: Н2О2 ratios from 1:2 to 1:16 were exposure under UV irradiation for 15-minute and the subsequent lightening on sunny days between 9 am and 8 pm in April for 7 days in the presence of a catalyst and without it. The catalyst concentration was 1.0 g L−1. After that, it was found the content of phenolic compounds in the presence of a catalyst is 2–20 times lower than without it. The COD with the COD: Н2О2 = 1:16 ratio in the presence of a catalyst decreases 1.5 times as compared with the initial solution, whereas without a catalyst it increases 13 times.

Self-assembly of colloidal lignin particles in a continuous flow tubular reactor

A scalable tubular flow reactor was designed and developed for the continuous formation of colloidal lignin particles (CLPs). The reactor consists of a series of tubes, inside which many static mixing elements are equipped to aid in the formation of a homogeneous dispersion of CLPs. The colloids were formed instantaneously through self-assembly upon the addition of the lignin solution into water. The effects of flowrate, length of the tubes and static mixing elements on the particle size, stability and CLP yield after drying were determined. It was found that a higher flowrate of lignin solution within the testing range of 32−240 mL/min resulted in smaller sized CLPs. Optimizations of the mixing length and the static mixing elements to 3 m and at least 1 m, respectively, could ensure an efficient mixing, thus resulting in CLP dispersions with smaller size of lignin particles (200 nm–400 nm) and high lignin concentrations (up to 2.8 wt. %) along with yields up to 95 %. The TEM images indicated that the formed colloids are composed of lignin particles of regular sphere shape and with good stability. The tubular reactor offers better control of particle size which ensures the formation of colloidal dispersions with narrower particle size distribution in comparison to a stirred mixer reactor. Furthermore, using a tubular reactor enables the continuous production of CLPs, making it suitable for scale up and industrial applications.

Molecular Orientation and Organization of Technical Lignin-Based Composite Nanofibers and Films.

Natural materials are highly anisotropic, maximizing performance of the polymeric structures while conserving mass and enhancing function. In synthetic materials, nanoscale fibers produced by electrospinning often contain molecular alignment of polymers along the fiber axis achieving some similarity to natural fibers. In this study, isolated softwood kraft lignin (SKL) was electrospun into aligned fibers utilizing a special collector. The molecular organization of lignin within the aligned nanofibers was investigated by polarized light optical microscopy. Furthermore, the functional groups that had preferred alignment along the fiber axis were identified with polarized Fourier transform infrared (FTIR) spectroscopy based on dichroism measurements. In addition, nanocrystalline cellulose (NCC) was added to the lignin solutions in order to create composite nanofibers. Both the orientation of NCC within the nanoscale fibers and the impact this component had on the degree of orientation of SKL within the aligned nanofibers were revealed by utilizing polarized FTIR. Finally, solvent cast lignin films were analyzed for their anisotropic polarizability, demonstrating birefringence with and without nanocrystalline cellulose. The work provided unique insight into both preferred orientation (fibers) and assembly (films) for technical lignin due to processing.

From hollow lignin microsphere preparation to simultaneous preparation of urea encapsulation for controlled release using industrial kraft lignin via slow and exhaustive acetone-water evaporation

AbstractLignin nano/microparticles have recently attracted growing interest for various value-additive applications of lignin, especially encapsulation. In this study, in order to establish a highly efficient and highly productive preparation process to effectively utilize technical lignin, a brand-new, slow and exhaustive solution evaporation process following a simple, self-assembly principle was developed using industrial softwood kraft lignin (SKL) from a starting acetone-water (80/20, v/v) solution to recover 100% of the lignin as homogeneous and well-shaped microspheres. The prepared microspheres had a typical average diameter of 0.81 ± 0.15 μm and were hollow with very thin shells (of nanoscale thickness). Based on this developed technique, encapsulation of urea by these lignin microspheres was directly achieved using the same process as hollow lignin microspheres with urea attached to the outside and entrapped inside of the wall. Two distinct urea release rates were observed for the urea-encapsulated microspheres: a fast release of the urea outside the shell wall and a slow (controlled) release of the urea inside the shell wall. The encapsulation efficiency was as high as 46% of the trapped urea as encapsulated inside the lignin microspheres. The slow and exhaustive solution evaporation procedure reported here is a simple and straightforward method for the valorization of industrial kraft lignin as hollow microspheres with controllable, homogeneous and desired morphologies, and especially for the direct preparation of lignin-based encapsulating fertilizers for controlled release.

Lignin-Based Magnesium Hydroxide Nanocomposite. Synthesis and Application for the Removal of Potentially Toxic Metals from Aqueous Solution

The pollution of water by potentially toxic metals or so-called heavy metals is the most severe form of environmental impact. Nanocomposites are considered promising materials for the removal of potentially toxic metals from aqueous solution through adsorption or ion exchange. To produce high-performance adsorbent for the removal of Ni2+, Cd2+, and Pb2+, lignin–Mg(OH)2 nanocomposite (LH-MH) was developed utilizing hydrolytic lignin waste with possible regeneration after metal uptake. The LH-MH was prepared using hydrolytic lignin, magnesium chloride, and NaOH solution by a thermally assisted method. The structure was studied using X-ray diffraction, transmission electron microscopy, and scanning electron microscopy, while chemical composition was evaluated by Fourier transform infrared spectroscopy, thermogravimetric analysis/differential thermogravimetry, and energy-dispersive X-ray spectroscopy mapping. Adsorption was described by the Langmuir and Sips models, whereas kinetics was elucidated by pseudo-f...

Zinc chloride/acetamide deep eutectic solvent‐mediated fractionation of lignin produces high‐ and low‐molecular‐weight fillers for phenol‐formaldehyde resins

ABSTRACTLignin readily dissolves in a deep eutectic solvent (DES) composed of ZnCl2/acetamide 1:3 M ratio in concentrations up to 16.7 wt %, and upon addition of water, two fractions were obtained; one composed of lignin with low‐molecular weight that remained dissolved in the DES/water mixture, whereas the other fraction of lignin with higher molecular weight (regenerated lignin, RL) was regenerated by precipitation. Both the RL fraction and the whole solution of lignin in DES were used to replace part of phenol (20 wt %) in the condensation of phenol and formaldehyde to introduce biomass in the resulting resins. The lignin treatment that produced the higher yield of RL consisted of lignin/DES ratio of 1:10 (w/w) stirred for 4 h at 100 °C. By using 13C NMR spectroscopy, a preferential cleavage of the S unit of lignin during DES treatment was identified. The modified phenol‐formaldehyde resin (RLPF) containing the RL exhibited higher bonding strength (1.28 ± 0.16 MPa) and shorter Sunshine gel time (557 s) than PF (587 s), showing that the RL helps to improve the polycondensation process. The resin modified with the whole solution of lignin in DES exhibited the shortest Sunshine gel time due to the effect of zinc(II) accelerating the curing process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48385.

A Simple Method to Synthesize Lignin Nanoparticles

The self-assembly of lignin (molecular and supramolecular) is driven mainly by non-covalent interactions, and the nature of the solvents and antisolvents directly affect the driving forces. The lignin particle is usually formed by noncovalently bonded cylindrical subunits. In this paper, we report a simple method which can be used to synthesize lignin nanoparticles by using spray freezing. The method is based on two properties of dimethyl sulfoxide (DMSO) that are excellent lignin solubility and a high melting point. Based on these two properties, kraft lignin solution in DMSO was sprayed onto liquid nitrogen-cooled copper plates using a handheld spray. The high melting point of DMSO caused immediate freezing and particle formation. The obtained particles were characterized for their size and morphology using dynamic light scattering (DLS), as well as scanning electron microscopy (SEM). Nano-range polydispersed particles were obtained by spraying 0.05% of lignin onto DMSO. This method can avoid lignin–solvent–antisolvent interactions, and can also be used to study lignin–lignin (subunits) and lignin–DMSO interactions.

Controlling the Composition, Morphology, Porosity, and Surface Chemistry of Lignin-Based Electrospun Carbon Materials

Electrospinning is a suitable top-down technique for the preparation of polymeric fibers using high voltage electrical fields and solutions of the selected polymer of adequate viscosity and conductivity. The versatility of electrospinning allows accurate control of the morphology and composition of the fibers by a wide combination of operating conditions and small modifications of the spinneret and collector. Alcell lignin, which is extracted from lignocellulosic biomass using organic solvents through Organosolv process, is readily solved in ethanol, producing a solution that matches the requirements of the electrospinning process. This review summarizes the vast collection of carbon materials that can be obtained by processing lignin using electrohydrodynamic forces. The coaxial and triaxial electrospinning setups allow for obtaining fibers with two or more components hierchically arranged, the use of these configurations along with a carefully setting of the operating conditions (distance between needle and collector, voltage, flow rate,…) and the solution properties (conductivity, viscosity,…) facilitates the conformation of lignin into spheres, beaded fibers, straight fibers and fused meshes. All these morphologies can be implemented with solid or hollow bodies (i.e. enabling the production of tubes and hollow spheres) by using a sacrificial templating agent. Phosphoric acid can also be added in small amounts to the lignin solution, shortening the thermostabilization time of the fibers. The porosity of the phosphorus containing carbon fibers can be modified in the last stage of the preparation of carbon fibers by controlled gasification process, owing to the extended oxidation resistance of the P-doped fibers. Fibrillar carbon catalysts can be also obtained by one-pot preparation method, only solving small quantities of metallic salts in the lignin solution. In addition, alumina and silica-coated lignin fibers were produced by feeding a partially gelated solution of the respective alkoxide through the outer needle of the spinneret. The coated fibers can be carbonized without thermostabilization step, decreasing considerably the preparation time. All these carbon materials were successfully tested in different applications such as heterogeneous catalysis, energy storage and environmental protection, confirming that electrospinning is a powerful tool for maximizing the value of lignin as carbon precursor.

Comparative study of solvolysis of technical lignins in flow reactor

The solvolysis of technical lignins was evaluated using water/ethanol solvent mixture with the aim of producing monomeric aromatic compounds in a continuous flow bench reactor. Four lignins issued from various biomasses (softwood, wheat straw) and extracted using different pulping processes (kraft, soda, organosolv) were engaged in the study. Before being converted, these lignins (two kraft, a soda, and an organosolv) were characterized by a multitechnique approach coupling compositional analysis, NMR, IR, GC, and SEC. Data thus obtained allowed us to point out the main differences in terms of structure and chemical composition. Based on its high solubility in water and water/ethanol mixture, alkaline lignin (i.e., from the kraft process) was used to optimize the reaction parameters. Thus, we found out that working at 225 °C under 8 MPa nitrogen using a 1-wt% basic solution of lignin allowed to operate the reactor without difficulties (no foam formation, no char) when a 1/1 water/ethanol mixture was used. Under these conditions, alkaline lignin was converted up to 76%. Other lignins were then evaluated leading to conversions between 46 and 74%. The reaction mixture obtained was fractioned to PM (precipitated matter), OP (organic products), and AP (aqueous phase soluble products) to allow careful analyses of the products. Analytical data obtained showed particularly that the number of β-O-4 linkages in the remaining solid material (PM) decreases significantly (up to − 95%) that correlated with the formation of monomeric organic compounds in OP, however in low amount due to over reactions leading to compounds evolving in the aqueous phase. Generally, whatever the lignin, guaiacol is the main aromatic compound observed under all reaction conditions evaluated.

Acid precipitation of kraft lignin from aqueous solutions: the influence of anionic specificity and concentration level of the salt

Abstract In this study, the formation of particles and evolution of the particle size distribution in the micron range were monitored in situ during acid precipitation of kraft lignin. The objective of this work was to study the influence of anionic specificity and the ion concentration level. The concentrations of ions in the solution were altered both in terms of the concentration of Na+ and the type of anion in the salt added ( SO 4 2 − ${\rm{SO}}_4^{2 - }$ and Cl−). The results indicate that a salting-out phenomenon occurred as NaCl was added (Na+ ≥2 mol kg−1 water) to the kraft lignin solution at high pH, but not when Na2SO4 was added. However, the onset pH of the formation of particles (≥1 μm), triggered by acidification, showed to be virtually non-specific to the anion but strongly dependent on the Na+ concentration. As the pH decreased further to below the onset pH of the formation of particles ≥1 μm, the chord length distributions (particle-size related) indicated that most of the volume of the precipitated kraft lignin (and thus possibly also the mass) may be found among the micron-sized particles, despite the fact that a relatively large number of submicron particles may also be present. The volume-based distributions tended to be wide at relatively low pH and high Na+ concentrations (e.g. pH 9.4 and 2.0 mol kg−1 water).

Biocompatible hydrogels of chitosan-alkali lignin for potential wound healing applications

Biocompatible hydrogels were prepared by mixing aqueous-acidic solution of chitosan with alkali lignin, a major by-product of the paper producing industries, for the first time, by sustainable means. Electrostatic interactions between the phenoxide groups in lignin and the ammonium groups on the chitosan backbone were found to be responsible for the ionotropic cross-linking. These gels were non-toxic to Mesenchymal stem cells, in vitro, and to zebrafish up to 100 μg/ml, in vivo. In addition, these gels provided a conducive surface for cell attachment and proliferation, making it suitable for application as scaffolds in tissue engineering. In presence of the hydrogel, NIH 3T3 mouse fibroblast cells showed good cell migration characteristics suggesting that the gel might be suitable for wound healing application. The chitosan-alkali lignin gelation system was further capable of removing ferric ions from contaminated water by way of complexation and coagulation. Cross-linked films of chitosan and alkali lignin could also be prepared by simply immersing chitosan films into a solution of alkali lignin. Alkali lignin was observed to diffuse into the chitosan “crystal”, forming electrostatic cross-links between the chitosan chains. The choice of lignin, in comparison to the other ionotropic cross-linkers for chitosan, makes the cross-linking system, inexpensive and sustainable.

The effect of pH on the ability of different lignins to stabilize the oil-in-water emulsion

The ability of aspen soda and wheat straw soda lignin to stabilize the “rapeseed oilin-water” (O/W) emulsion, depending on the pH value and concentration of the applied water solutions as well as on the lignin chemical composition and molecular mass, and the sizes and zeta potential of lignin particles was studied. It was shown that the O/W emulsion stabilized with the alkaline water solutions of wheat straw lignin demonstrated the highest stability in alkaline medium, while the ability of aspen soda lignin to prevent the coalescence of oil droplets manifested itself in a whole range of the studied pH values. With decreasing pH values of the wheat straw lignin water solution, the drop in the separation volume of the O/W emulsion was insignificant with the exception for the lignin enhanced concentrations in acidic medium. The aggregative stability of the O/W emulsion, which was stabilized with aspen soda lignin, increased with decreasing pH values and increasing lignin content in the emulsion. The findings indicated that the stabilization of the O/W emulsion with the alkaline lignin solutions proceeded via the electrostatic stabilization mechanism, while in the neutral and acidic medium, this mechanism was more complicated, with a growing role of the ability of lignin to form interfacial polymeric films at the liquid/liquid interface. The comparison of the stability of the O/W emulsion showed that aspen soda lignin was a better stabilizer of the O/W emulsion than wheat straw lignin.

Towards a sustainable technology for H2 production: Direct lignin electrolysis in a continuous-flow Polymer Electrolyte Membrane reactor

We have performed, for the very first time in literature, the production of pure H2 via “electrolysis of lignin solutions in continuous-flow mode in a Polymer Electrolyte Membrane (PEM) reactor”. A Pt-Ru//Fumapem (OH− conductor)//Pt/C (Anode//Anion Exchange membrane//Cathode) electrochemical cell was used. Under the explored conditions, we have demonstrated that lignin can be electrolyzed at much lower electrical potentials (from ~0.45 V) compared to that of water electrolysis (thermodynamically favored from ~1.2 V). In addition, we observed that increasing the reaction temperature gives rise to an enhanced activity towards the electrolysis of lignin, increasing therefore the production of pure H2. Finally, in-situ cyclic voltammetry experiments were performed in the PEM cell to demonstrate that lignin electro-oxidation takes place at potentials lower than that for O2 evolution. These experiments also showed that the whole system did not suffer a significant deactivation during the electrolysis experiments, which pointed out the promising stability and reproducibility of the proposed technology. Further studies should be performed to identify the products of the lignin electro-oxidation at the anode.This study establishes a very important step-forward towards the direct electrochemical valorization of lignin (usually considered as a biomass residue) for a sustainable production of pure H2 using renewable sources.

Continuous production of lignin nanoparticles using a microchannel reactor and its application in UV-shielding films.

With the severe energy and environmental issues, lignin has received increasing attention as a renewable biomass feedstock. The development of lignin-based nanoparticles provides a new route to the valorization of lignin. In this work, we propose a simple continuous method to prepare lignin nanoparticles (LNS) using a microchannel reactor. Polyvinylpyrrolidone (PVP)/sodium dodecyl sulfate (SDS) were selected as stabilizers. Spherical-like lignin nanoparticles with an average size of 13 nm were obtained in a T-shaped microchannel reactor. The effects of solvent species, PVP/SDS mass ratio, and lignin solution flow rate on the size of LNS were investigated. The as-prepared LNS had a good stability during 60 days-storage and were used as an additive to form UV-shielding composite films with poly(vinyl alcohol) (PVA). Compared with raw lignin, the addition of LNS could enhance the UV-shielding efficacy by 13.3% in the ultraviolet spectrum (250 nm). The present work suggests that the microchannel reactor is a promising continuous approach to prepare LNS with versatile applications.

Multiscale Modification of Populus cathayana by Alkali Lignin Combined with Heat Treatment.

Chemical modification of wood with green modifiers is highly desirable for sustainable development. With the aim of enhancing the water resistance and dimensional stability of fast growing wood, modifications were conducted using renewable and toxicity-free industrial lignin combined with heat treatment. Poplar (Populus cathayana) samples first underwent impregnation with alkali lignin solution and were then subjected to heat treatment at 140–180 °C for two hours. The results indicated that the modified wood showed excellent leaching resistance. The alkali lignin treatment improved surface hydrophobicity and compression strength, and decreased moisture and water uptake, thereby reducing the dimensional instability of modified wood. These changes became more pronounced as the heat-treating temperature increased. Scanning electron microscopy, confocal laser scanning microscopy, and Fourier transform infrared spectroscopy evidenced that a multiscale improvement of the alkali lignin occurred in the cell lumen and cell wall of wood fibers and vessels, with small alkali lignin molecules reacting with the wood matrix. This study paves the way for developing an effective modification approach for fast growing wood, as well as promoting the reuse of industrial lignin for high-value applications, and improves the sustainable development of the forestry industry.

Synthesis of lignocellulose-based composite hydrogel as a novel biosorbent for Cu2+ removal

A lignocellulose-based composite hydrogel, as a novel biosorbent, was prepared for Cu2+ removal from wastewater. TEMPO-oxidized cellulose nanofibrils (TOCN) were dispersed in a 7 wt% NaOH/12 wt% urea aqueous solution at room temperature. Meanwhile, the dissolved cellulose was obtained in the same system at subzero temperature. The composite hydrogels were prepared by blending the dissolved cellulose solution, TOCN dispersion, and alkali lignin solution in an NaOH/urea aqueous solution. The composite hydrogel exhibits excellent adsorption capacity for heavy metals, which can be attributed to the synergistic effects of physical adsorption (porous 3D structure) and chemical adsorption (active sites: carboxyl and phenolic groups). The maximum amount of adsorbed Cu2+ onto composite hydrogel can reach 541 mg/g, which was achieved after 45 min. The adsorption behavior is well-described by the pseudo-second-order kinetics and the Freundlich model (R2 > 0.999). Furthermore, the composite hydrogel exhibits high-strength properties, indicating that the presence of TOCN and lignin contributes to mechanical improvements.

Natural Biopolymer-Based Triboelectric Nanogenerators via Fast, Facile, Scalable Solution Blowing.

Here, we fabricated nanofiber (NF)-based triboelectric nanogenerators (TENGs) from natural biopolymers using the industrially scalable solution blowing. This technique eliminates severe restrictions on solutions to be used and allows one to achieve biocompatible devices. Here, solutions of soy protein and lignin were blown into continuous monolithic NFs of hundreds of nanometers in diameter. The technique we employed yields large-area NF mats within tens of minutes and has never been employed to form TENGs. Furthermore, in contrast to electrospun andmeltblownfiber mats, solution-blown NF mats are much fluffier/porous, which is beneficial for achieving higher voltages by means of triboelectricity. In particular, triboelectricity generated by our biopolymer-based TENGs revealed that they hold great promise as sustainable and environmentally friendly self-powered devices for biomedical applications with the highest efficiency in their class. Moreover, these are the first nanotextured plant-derived biopolymer-made TENGs.