Laser-induced fluorescence (LIF) of lignin and lignin model compounds in Raman spectroscopy

Abstract

Raman spectroscopy is a technique that provides structural information on lignin and other components of wood and pulp in situ. However, especially lignin-containing samples may produce laser-induced fluorescence (LIF) that overlaps with Raman bands. In the worst case, this background signal can overwhelm the weaker Raman signal completely. In this study, the LIF of lignin was investigated with the excitation wavelength 532 nm applied in Raman spectroscopy to clarify the correlations between lignin structure and LIF intensity. Raman spectroscopic analyses with lignin model compounds illustrated that the 5-5′ structures induce LIF. It was also shown that the intensity of LIF was significantly less intense when the 5-5′ model compound was structurally rigid (as in dibenzodioxocin) compared with the flexible simple counterpart. The comparison between the free phenolic model compounds with the methylated analogue showed that the presence of the free phenolic structure was not a prerequisite for LIF. It was thus concluded that the conformation of the molecule is the key factor with respect to fluorescence. The role of conformational aspects was further investigated by comparing wood with chemical pulps and isolated lignins.

Infrared and Raman spectra of lignin substructures: Dibenzodioxocin

“…Raman spectra of DBDO show only little fluorescence background, which is in agreement with previous studies where the rotation of individual rings about the coannular bond in 5‐5′ structures was deemed responsible for strong fluorescence observed in lignin spectra . Because this rotation is hindered in DBDO, the fluorescence is expected to be much smaller, as also observed (Figure ).…”

Recent Developments in the Modelling of Heterogeneous Catalysts for CO2 Conversion to Chemicals

“…Most of these catalysts are used and examined in combination with support where mostly metal‐oxides, ‐carbides, ‐sulfides and ‐nitrides are used. Metal oxides are frequently used as supports for the dispersion of metals and reduced oxides have a strong tendency to react with CO 2 .…”

“…Metal oxides are frequently used as supports for the dispersion of metals and reduced oxides have a strong tendency to react with CO 2 . Metal‐carbides due to their bonding between carbon atom and transition metal atom have unique properties such as high melting temperature (>3300 K), high hardness (>2000 kg/mm 2 ) and high tensile strength (>300 GPa) and show catalytic activity similar to activity of noble metals . Metal‐nitrides are characterized by two different effects: ligand effect and ensemble effect .…”

Assembly of metal nanoparticles on regenerated fibers from wood sawdust and de-inked pulp: flexible substrates for surface enhanced Raman scattering (SERS) applications

“…The brown color of the sawdust fibers is due to their high lignin content. As the fluorescence and Raman background of lignin (Lahdetie et al 2013), the saw dust composite substrate were used for moderate concentration Raman analysis, while the fiber regenerated from DIP contains minimal amounts of lignin and has hence a white color. After Ag NPs immobilization, the fibers became dark gray and bright yellow respectively.…”