Dispersive evaluation and surface chemistry of advanced, multifunctional silica/lignin hybrid biomaterials

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.

Preparation, characterization and the adsorption characteristics of lignin/silica nanocomposites from cellulosic ethanol residue

The synthesis lignin/silica nanocomposites by in situ co-precipitation method.