Spectroscopic Studies of the Intermolecular Interactions of Congo Red and Tinopal CBS with Modified Cellulose Fibers

Abstract

The adsorption of Congo red and tinopal CBS dyes on cellulose fibers was investigated using electronic absorption and fluorescence spectroscopies. Hydrogen bonds appear to be relevant for the dye-fiber interactions as indicated by the solvatochromism of Congo red in water, methanol, and dimethyl sulfoxide solutions, and when adsorbed on cellulose fibers. We also demonstrate that electrostatic interactions play an important role in the dye-medium interaction, through the analysis of absorption spectra of Congo red and fluorescence spectra of tinopal in aqueous solutions containing salt and in layer-by-layer nanostructured films with poly(allylamine hydrochloride). For instance, dye adsorption was enhanced when salt was added to the dipping solution, which was explained by the synergistic effect between the conformational changes of the cellulose and changes in the solvation layer around the cellulose chains and around dye molecules. On the basis of the fluorescence results for tinopal CBS, we inferred that dye aggregation is not relevant for adsorption on the fibers. In addition, fluorescence spectroscopy is proven very sensitive for studying the organization of dye molecules in layer-by-layer films, particularly those undergoing irreversible structural changes.

Study of assembly of arachidic acid/LDHs hybrid films containing photoactive dyes

“…The red-shift of λ max due to the CR aggregation has also been widely reported [42][43][44]. For example, Yamaki et al [45] have reported the λ max of the CR red-shift to 504 nm upon forming aggregates in a layer-by-layer nanostructured film under a given condition.…”

Behaviors and mechanism of acid dyes sorption onto diethylenetriamine-modified native and enzymatic hydrolysis starch

“…Spectrum of AG25 absorbed on CAES is very different: the band is largely broadened toward the short wavelength and no obvious peak position can be seen. For the pH and ion strength are insensitive to the max of dyes, this shift indicates strong hydrogen bonding between dyes and adsorbent [41]. The trend is also apparent for AR18 ( max = 517 nm in DMSO, max = 508 nm in methanol, max = 506 nm in water and a broad band for the AR18 adsorbed onto CAES), implied strong hydrogen bonding between AR18 and CAES.…”

Modelling of Congo red adsorption on the hydrophobic surface of cellulose using molecular dynamics

“…In order to address such question, the present paper describes an attempt to model the adsorption of the direct Congo red (CR) dye on model cellulose crystals. Even if the staining of cellulose with CR is not used industrially for toxicological and colour stability reasons, its adsorption on cellulose and other polysaccharides, which is used for analytical purpose, is well documented (Wood 1980(Wood , 1982Yamaki et al 2005). In a molecular mechanics modelling study, Woodcock et al (1995), have investigated the docking of CR molecules on the hydrophilic faces of crystalline cellulose.…”