Mechanically recyclable melt-spun fibers from lignin esters and iron oxide nanoparticles: towards circular lignin materials.

The inferior thermoplastic properties have limited production of melt-spun fibers from lignin. Here we report on the controlled esterification of softwood kraft lignin (SKL) to enable scalable, solvent-free melt spinning of microfibers using a cotton candy machine. We found that it is crucial to control the esterification process as melt-spun fibers could be produced from lignin oleate and lignin stearate precursors with degrees of esterification (DE) ranging from 20-50%, but not outside this range. To fabricate a functional hybrid material, we incorporated magnetite nanoparticles (MNPs) into the lignin oleate fibers by melt blending and subsequent melt spinning. Thermogravimetric analysis and X-ray diffraction studies revealed that increasing the weight fraction of MNPs led to improved thermal stability of the fibers. Finally, we demonstrated adsorption of organic dyes, magnetic recovery, and recycling via melt spinning of the regular and magnetic fibers with 95% and 83% retention of the respective adsorption capacities over three adsorption cycles. The mechanical recyclability of the microfibers represents a new paradigm in lignin-based circular materials.

Molecular understanding of the morphology and properties of lignin nanoparticles: unravelling the potential for tailored applications.

Studies have shown that the size of LNP depends on the molecular weight (Mw) of lignin. There is however need for deeper understanding on the role of molecular structure on LNP formation and its properties, in order to build a solid foundation on structure-property relationships. In this study, we show, for similar Mw lignins, that the size and morphology of LNPs depends on the molecular structure of the lignin macromolecule. More specifically, the molecular structure determined the molecular conformations, which in turn affects the inter-molecular assembly to yield size- and morphological-differences between LNPs. This was supported by density functional theory (DFT) modelling of representative structural motifs of three lignins sourced from Kraft and Organosolv processes. The obtained conformational differences are clearly explained by intra-molecular sandwich and/or T-shaped π-π stacking, the stacking type determined by the precise lignin structure. Moreover, the experimentally identified structures were detected in the superficial layer of LNPs in aqueous solution, confirming the theoretically predicted self-assembly patterns. The present work demonstrates that LNP properties can be molecularly tailored, consequently creating an avenue for tailored applications.

LignoPhot: Conversion of hydrolysis lignin into the photoactive hybrid lignin/Bi4O5Br2/BiOBr composite for simultaneous dyes oxidation and Co2+ and Ni2+ recycling.

Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/Bi4O5Br2/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by semiconducting nanosheets. The XPS analysis reveals that growing these nanosheets on lignin instead on cellulose prevents the formation of Bi5+ ions at the surface region, yielding thus a modified heterojunction Bi4O5Br2/BiOBr. The material contains 18.9% of Bi4O5Br2/BiOBr and is effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under light irradiation. Lignin/Bi4O5Br2/BiOBr decreases the dye concentration from 80 mg L-1 to 12.3 mg L-1 for RhB (85%) and from 80 mg L-1 to 4.4 mg L-1 for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for nickel, lead, and cobalt ions. The low cost, stability and ability to simultaneously photo-oxidize organic dyes and adsorb metal ions, make the photoactive lignin/Bi4O5Br2/BiOBr composite a prospective material for textile wastewaters remediation and metal ions recycling.

High-Molecular-Weight Fractions of Spruce and Eucalyptus Lignin as a Perspective Nanoparticle-Based Platform for a Therapy Delivery in Liver Cancer.

The natural polymer, lignin, possesses unique biodegradable and biocompatible properties, making it highly attractive for the generation of nanoparticles for targeted cancer therapy. In this study, we investigated spruce and eucalyptus lignin nanoparticles (designated as S-and E-LNPs, respectively). Both LNP types were generated from high-molecular-weight (M w ) kraft lignin obtained as insoluble residues after a five-step solvent fractionation approach, which included ethyl acetate, ethanol, methanol, and acetone. The resulting S-and E-LNPs ranged in size from 16 to 60 nm with uniform spherical shape regardless of the type of lignin. The preparation of LNPs from an acetone-insoluble lignin fraction is attractive because of the use of high-M w lignin that is otherwise not suitable for most polymeric applications, its potential scalability, and the consistent size of the LNPs, which was independent of increased lignin concentrations. Due to the potential of LNPs to serve as delivery platforms in liver cancer treatment, we tested, for the first time, the efficacy of newly generated E-LNPs and S-LNPs in two types of primary liver cancer, hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), in vitro. Both S-LNPs and E-LNPs inhibited the proliferation of HCC cells in a dose-dependent manner and did not affect CCA cell line growth. The inhibitory effect toward HCC was more pronounced in the E-LNP-treated group and was comparable to the standard therapy, sorafenib. Also, E-LNPs induced late apoptosis and necroptosis while inhibiting the HCC cell line. This study demonstrated that an elevated number of carbohydrates on the surface of the LNPs, as shown by NMR, seem to play an important role in mediating the interaction between LNPs and eukaryotic cells. The latter effect was most pronounced in E-LNPs. The novel S- and E-LNPs generated in this work are promising materials for biomedicine with advantageous properties such as small particle size and tailored surface functionality, making them an attractive and potentially biodegradable delivery tool for combination therapy in liver cancer, which still has to be verified in vivo using HCC and CCA models.

Membrane-Filtered Kraft Lignin-Silica Hybrids as Bio-Based Sorbents for Cobalt(II) Ion Recycling.

Efficient and sustainable recycling of cobalt(II) is of increasing importance to support technological development in energy storage and electric vehicle industries. A composite material based on membrane-filtered lignin deposited on nanoporous silica microparticles was found to be an effective and sustainable sorbent for cobalt(II) removal. This bio-based sorbent exhibited a high sorption capacity, fast kinetics toward cobalt(II) adsorption, and good reusability. The adsorption capacity was 18 mg Co(II) per gram of dry adsorbent at room temperature (22 °C) at near-neutral pH, three times higher than that of the summarized capacity of lignin or silica starting materials. The kinetics study showed that 90 min is sufficient for effective cobalt(II) extraction by the composite sorbent. The pseudo-second-order kinetics and Freundlich isotherm models fitted well with experimentally obtained data and confirmed heterogeneity of adsorption sites. The promising potential of the lignin-silica composites for industrial applications in the cobalt recovering process was confirmed by high values of desorption in mildly acidic solutions.

Removal of Diclofenac, Paracetamol, and Carbamazepine from Model Aqueous Solutions by Magnetic Sol-Gel Encapsulated Horseradish Peroxidase and Lignin Peroxidase Composites.

Sustainable and green synthesis of nanocomposites for degradation of pharmaceuticals was developed via immobilization and stabilization of the biological strong oxidizing agents, peroxidase enzymes, on a solid support. Sol-gel encapsulated enzyme composites were characterized using electron microscopy (TEM, SEM), atomic force microscopy, FTIR spectroscopy, and thermogravimetric analysis. Horseradish peroxidase (HRP) and lignin peroxidase (LiP) were adsorbed onto magnetite nanoparticles and sol-gel encapsulated in a surface silica layer. Encapsulation enhanced the stability of the biocatalysts over time and thermal stability. The biocatalysts showed appreciable selectivity in oxidation of the organic drinking water pollutants diclofenac, carbamazepine, and paracetamol with improved activity being pharmaceutical specific for each enzyme. In particular, sol-gel encapsulated LiP- and HRP-based nanocomposites were active over 20 consecutive cycles for 20 days at 55 °C (24 h/cycle). The stability of the sol-gel encapsulated catalysts in acidic medium was also improved compared to native enzymes. Carbamazepine and diclofenac were degraded to 68% and 64% by sol-gel LiP composites respectively at pH 5 under elevated temperature. Total destruction of carbamazepine and diclofenac was achieved at pH 3 (55 °C) within 3 days, in the case of both immobilized HRP and LiP. Using NMR spectroscopy, characterization of the drug decomposition products, and decomposition pathways by the peroxidase enzymes suggested.

Electrostatic Deposition of the Oxidized Kraft Lignin onto the Surface of Aminosilicas: Thermal and Structural Characteristics of Hybrid Materials.

In recent years, functional polymeric compounds have been widely used to modify the silica surface, which allows one to obtain the corresponding organomineral composites for broad application prospects. In this case, lignin-a cross-linked polyphenolic macromolecule-is of great interest according to its valuable properties and possible surplus as a by-product of pulp and paper industry and various biorefinery processes. Hybrid materials based on kraft softwood lignin and silica were obtained via the electrostatic attraction of oxidized lignin to the aminosilica surface with different porosities, which were prepared by the amination of the commercial silica gel with an average pore diameter of 6 nm, and the silica prepared in the lab with the oxidized kraft lignin and lignin-silica samples with an average pore diameter of 38 nm was investigated by physicochemical methods: two-dimensional nuclear magnetic resonance (NMR), 31P NMR, Fourier transform infrared spectroscopy, thermogravimetric analysis in nitrogen and air atmosphere, scanning electron microscopy, and adsorption methods. After oxidation, the content of carboxylic groups almost doubled in the oxidized lignin, compared to that in the native one (0.74 mmol/g against 0.44 mmol/g, respectively). The lignin content was deposited onto the surface of aminosilica, depending on the porosity of the silica material and on the content of amino groups on its surface, giving lignin-aminosilica with 20% higher lignin content than the lignin-aminosilica gel. Both types of lignin-silica composites demonstrate a high sorptive capacity toward crystal violet dye. The suggested approach is an easy and low-cost way of synthesis of lignin-silica composites with unique properties. Such composites have a great potential for use as adsorbents in wastewater treatment processes.

Peculiarities of Synthesis and Properties of Lignin⁻Silica Nanocomposites Prepared by Sol-Gel Method.

The development of advanced hybrid materials based on polymers from biorenewable sources and mineral nanoparticles is currently of high importance. In this paper, we applied softwood kraft lignins for the synthesis of lignin/SiO2 nanostructured composites. We described the peculiarities of composites formation in the sol-gel process through the incorporation of the lignin into a silica network during the hydrolysis of tetraethoxysilane (TEOS). The initial activation of lignins was achieved by means of a Mannich reaction with 3-aminopropyltriethoxysilane (APTES). In the study, we present a detailed investigation of the physicochemical characteristics of initial kraft lignins and modified lignins on each step of the synthesis. Thus, 2D-NMR, 31P-NMR, size-exclusion chromatography (SEC) and dynamic light scattering (DLS) were applied to analyze the characteristics of pristine lignins and lignins in dioxan:water solutions. X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) were used to confirm the formation of the lignin⁻silica network and characterize the surface and bulk structures of the obtained hybrids. Termogravimetric analysis (TGA) in nitrogen and air atmosphere were applied to a detailed investigation of the thermal properties of pristine lignins and lignins on each step of modification. SEM confirmed the nanostructure of the obtained composites. As was demonstrated, the activation of lignin is crucial for the sol-gel formation of a silica network in order to create novel hybrid materials from lignins and alkoxysilanes (e.g., TEOS). It was concluded that the structure of the lignin had an impact on its reactivity during the activation reaction, and consequently affected the properties of the final hybrid materials.

Development of New Effective Sorbents Based on Nanomagnetite.

Magnetic hybrid nanocomposite material based on the kraft lignin was prepared by the co-precipitating method. Kraft lignin was modified by iron nanooxide in order to enhance its sorption properties towards heavy metal ions. The composite material was characterized by physicochemical methods such as BET N2, ATR-FTIR, TGA, DSC, pHpzc, XRD and SEM. Its adsorption behaviour was studied using the batch mode by varying different parameters like pH, initial concentration of metal ions and shaking time as well as the presence of interfering ions. Adsorption of Cu(II), Cd(II) and Pb(II) ions from the aqueous solutions was studied in comparison with the commercial kraft lignin. The adsorption capacity and kinetic sorption characteristics of the composite material were determined.

Synthesis and adsorption properties of chitosan-silica nanocomposite prepared by sol-gel method.

A hybrid nanocomposite material has been obtained by in situ formation of an inorganic network in the presence of a preformed organic polymer. Chitosan biopolymer and tetraethoxysilane (TEOS), which is the most common silica precursor, were used for the sol-gel reaction. The obtained composite chitosan-silica material has been characterized by physicochemical methods such as differential thermal analyses (DTA); carbon, hydrogen, and nitrogen (CHN) elemental analysis; nitrogen adsorption/desorption isotherms, scanning electron microscopy (SEM); and Fourier transform infrared (FTIR) spectroscopy to determine possible interactions between silica and chitosan macromolecules. Adsorption of microquantities of V(V), Mo(VI), and Cr(VI) oxoanions from the aqueous solutions by the obtained composite has been studied in comparison with the chitosan beads, previously crosslinked with glutaraldehyde. The adsorption capacity and kinetic sorption characteristics of the composite material were estimated.