Dye adsorption revisited: application of the cationic dye adsorption method for the quantitative determination of the acidic surface groups of nanocellulose materials

Jun Araki

doi:10.1007/s10570-021-04035-x

Abstract

The surface carboxyl and sulfate groups on cellulose nanowhiskers were quantified via the adsorption of toluidine blue O (TBO), a cationic dye. Here, simple and rapid protocols, such as mixing the nanowhisker suspensions with a dye solution, separating the supernatants via centrifugation, and determining the excess dye concentration via visible light absorbance techniques, were used to obtain reproducible results comparable with those obtained via titration. In addition to facilitating the discrete quantification of the sulfate and carboxyl groups, the TBO adsorption method enabled carboxyl quantification in the presence of mercapto groups, which was difficult to achieve via titration. The adsorption of TBO onto the carboxyl groups was completed within 30 min, enabling the rapid treatment of many samples within a short period.

Highlights

The surface carboxyl and sulfate groups on cellulose nanowhiskers were quantified via the adsorption of toluidine blue O (TBO), a cationic dye
In addition to facilitating the discrete quantification of the sulfate and carboxyl groups, the TBO adsorption method enabled carboxyl quantification in the presence of mercapto groups, which was difficult to achieve via titration
Various nanocellulose materials, including cellulose nanowhiskers (CNWs) (Araki 2013; de Souza Lima and Borsali 2004; Eichhorn 2011), cellulose nanofibers (CNFs) (Isogai et al 2011), and cellulose nanocrystals (CNCs) (Habibi et al 2010), contain different types of surface functional groups, especially ionic groups. These ionic surface functional groups include sulfates which are introduced onto the surface of CNWs (Araki 2013; Araki et al 1998; de Souza Lima and Borsali 2004; Eichhorn 2011) or CNCs (Habibi et al 2010) during sulfuric acid-mediated hydrolysis

Summary

Introduction

Various nanocellulose materials, including cellulose nanowhiskers (CNWs) (Araki 2013; de Souza Lima and Borsali 2004; Eichhorn 2011), cellulose nanofibers (CNFs) (Isogai et al 2011), and cellulose nanocrystals (CNCs) (Habibi et al 2010), contain different types of surface functional groups, especially ionic groups. In addition to facilitating the discrete quantification of the sulfate and carboxyl groups, the TBO adsorption method enabled carboxyl quantification in the presence of mercapto groups, which was difficult to achieve via titration.

Results

Conclusion