UV‐Induced Oxidation Preparation of Multi‐Functional Lignin‐Based AgNPs and its Application for Conductive Coating, Antibacterial Enhancement, and Product Separation
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Abstract This study presents a novel approach for regulating the properties of lignin‐based silver nanoparticles (AgNPs), which was UV‐induced Tetrahydrofuran (THF) to form peroxide for the etching of these nanoparticles. The lignin coating was first degraded by oxidation, and the properties of the exposed AgNPs changed under etching. Notably, water can greatly regulate the oxidation capacity of the THF medium, thereby controlling the degradation degree of lignin coating and obtaining dissolution, aggregation, precipitation, and color‐variable phenomena of AgNPs under the synergistic effect of UV irradiation and peroxide etching. By adjusting UV irradiation time, various functional products of silver nanowires (AgNWs), color‐variable AgNPs, lignin‐based AgNPs aggregates, and composite solution of Ag particles and Ag + were obtained. The transformation of these product properties is closely related to the oxidation capacity of H 2 O/THF medium. In addition, Multi‐functional Lignin‐based AgNPs show excellent application potential in conductive coating, antibacterial enhancement, and product separation, providing a promising avenue for the targeted utilization of lignin‐based AgNPs.Keywords:
Silver nanoparticle
Residue (chemistry)
Chemical modification
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Hemicellulose
Enzymatic Hydrolysis
Depolymerization
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Hemicellulose
Gel permeation chromatography
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The temperature dependence of the pyrolysis products of two types of lignin (Alcell lignin and Asian lignin) was investigated using pyrolysis−gas chromatography−mass spectrometry (PyGC−MS). About 50 compounds were identified and quantified for each type of lignin over a temperature range of 400−800 °C. The maximum yield of phenolic compounds was obtained at 600 °C for both lignins, which was 17.2% for Alcell lignin and 15.5% for Asian lignin. Most of the phenolic compounds had an individual yield of less than 1%; however, for Alcell lignin, 5-hydroxyvanillin was the highest yield at 4.29 wt % on dry ash-free lignin, and for Asian lignin, 2-methoxy-4-vinylphenol was the highest yield at 4.15 wt % on dry ash-free lignin.
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The objective of this chapter is to provide a concise overview of lignin composition and structure in different species and materials (wood, barks and nonwood plants). It includes a brief review on the lignin precursors and their polymerization as well as of the analytical tools used for lignin characterization from wet chemical to spectroscopic methods. Wood of gymnosperms is characterized by high lignin content (25–35%) and a HG-type of lignin with more guaiacyl (G) units and a small portion of p-hydroxyphenyl (H) units. Wood of angiosperms has a lignin content of 15–28%, with a GS-lignin having different proportions of syringyl (S) units. Nonwoody monocotyledon species have different lignin content (9–20%) and a HGS type of lignin, characterized by a high proportion of H units. Bark lignin content ranges from 13 to 43% and is of HGS-type with species-specific composition and different in the bark components, phloem and cork. Lignin composition and macromolecular structure are key issues to understand the properties of lignocellulosic materials and to design a lignin-based pathway within biomass biorefineries. The available information on lignin composition is still limited to a few species and plant components. This is certainly an area where more research is needed.
Lignocellulosic Biomass
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The dissolution of minerals in water is typically studied on macroscopic length- and time-scales, by detecting dissolution products in bulk solution and deducing reaction rates from model assumptions. Here, we report a direct, real-time measurement of silica dissolution, by monitoring how dissolution changes the first few interfacial layers of water in contact with silica, using surface-specific spectroscopy. We obtain direct information on the dissolution kinetics of this geochemically relevant mineral. The interfacial concentration of dissolution products saturates at the level of the solubility limit of silica (~millimolar) on the surprisingly short timescale of tens of hours. The observed kinetics reveal that the dissolution rate increases substantially with progressing dissolution, suggesting that dissolution is an auto-catalytic process.
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In this investigation the lignin, the total of membrane substances, the crude protein and the methoxyl in lignin were determined in different materials. Some observations on the properties of lignin have been made. The lignin content, as calculated from the dry matter or from the total of the membrane substances, varies greatly in different materials, as can be seen in Table 1. This is the case even if one leaves out of consideration such materials as the bark of woods, sea-weeds, and mosses, the »lignin» of which scarcely is real lignin. In grasses and clover the content of lignin in the cell walls increases with the successive stages of development. The methoxyl content of lignin varies in different plants, in the same plant at successive stages of growth, and in the different tissues of the same plant. The solubility of lignin in hot diluted alkali solutions varies in different materials. Of the lignin in Gramineae plants even in an 0.1 N natrium hydroxide solution about 50 % dissolves, but of the lignin of softwoods only negligible amounts in a 2 N solution. The lignin preparations isolated by the usual acid methods contain, besides the real hydrolysis residue, also substances dissolved by the strong acid but precipitated by the succeeding dilution. The nitrogen content of the precipitated fraction is high. The high methoxyl content of its nitrogen free portion points to real lignin.
Sodium hydroxide
Softwood
Black liquor
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Lignin, a complicated organic polymer, plays a significant structural function in the support tissues of vascular plants. It is particularly prevalent in woody plants and is highly polymerized. Lignin is one of the three crucial elements of wood, along with extractives and carbohydrates. Lignin, a three-dimensional amorphous polymer made of methoxylated phenylpropane structures, is important for the survival of vascular plants. In nature, lignin polymer generally forms ether or ester linkages with hemicellulose which is also connected with cellulose. The structural and chemical composition of lignin; representative linkages in lignin molecules and types of lignin are presented in this chapter.
Hemicellulose
Synthetic polymer
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There are several methods to isolate near-native lignins, including milled-wood lignin, enzymatic lignin, cellulolytic enzyme lignin, and enzymatic mild-acidolysis lignin. Which one is the most representative of the native lignin? Herein, near-native lignins were isolated from different plant groups and structurally analyzed to determine how well these lignins represented their native lignin counterparts. Analytical methods were applied to understand the molecular weight, monomer composition, and distribution of interunit linkages in the structure of the lignins. The results indicated that either enzymatic lignin or cellulolytic enzyme lignin may be used to represent native lignin in softwoods and hardwoods. None of the lignins, however, appeared to represent native lignins in grasses (monocot plants) because of substantial syringyl/guaiacyl differences. Complicating the understanding of grass lignin structure, large amounts of hydroxycinnamates acylate their polysaccharides and, when released, are often conflated with actual lignin monomers.
Softwood
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