Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption

Abstract

A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materials as adsorbents. Adsorption isotherms of Azure B on wheat straw (WS), sugarcane bagasse (SGB), oat husk, and isolated lignin materials were determined. The maximum adsorption capacities predicted by the Langmuir isotherms were used to calculate the amounts of surface-accessible acidic hydroxyl groups. WS contained 1.7-times more acidic hydroxyls (0.21 mmol/g) and higher surface area of lignin (84 m 2 /g) than SGB or oat husk materials.Equations for determining the amount of surface-accessible acidic hydroxyls in solid fractions of the three plant materials by a single point measurement were developed. A method for high-throughput characterization of lignocellulosic materials is now available.

Reduction of surface area of lignin improves enzymatic hydrolysis of cellulose from hydrothermally pretreated wheat straw

“…13 Briey, solid residues (100 mg) were agitated in 0.1 g L À1 Azure B solution at pH 7 at 25 C, and aer 24 h the absorbance was measured from the liquid phase passed through 0.45 mm PTFE lters. Lignin surface area (SA) and specic surface area (SSA) were calculated based on the amount of surface-accessible acidic hydroxyls:…”

A novel film–pore–surface diffusion model to explain the enhanced enzyme adsorption of corn stover pretreated by ultrafine grinding

“…This is further corroborated by surface composition measurement for the two substrates. The surface areas of cellulose and lignin, which are two dominant components in the cellulase adsorption [20, 21], were measured by determining the maximum adsorption capacity of the dyes Congo Red [22] and Azure B [23] on the substrates, respectively (Table 1). The cellulose surface area of the UGCS (290.76 m 2 /g) was almost twofold higher than that of SGCS (168.69 m 2 /g).…”

“…The surface areas of cellulose and lignin on the SGCS and UGCS were analyzed by determining the monolayer adsorption maximum of Congo Red (Direct Red 28) [22] and Azure B [23], respectively. Of each adsorption, 100 mg dry material was weighed in 25 mL conical flask; 10 mL of the dye (Congo Red in 30 mM phosphate buffer at pH 6 and Azure B in 50 mM Na-phosphate buffer at pH 7) was added to the conical flasks and incubated for 24 h on a shaker at 200 rpm.…”

“…Then, the cellulose surface area was calculated per dry material from the adsorption maximum with 1 g of the adsorbed dye representing 1055 m 2 surface [22]. And the surface area of the lignin was obtained from the maximum adsorption capacity and the area (1.297 m 2 /mg) covered by Azure B [23]. …”

Effects of Catalysts and pH on Lignin in Partial Wet Oxidation of Wood and Straw Black Liquors

“…The column was eluted with deionized water at 0.7 mL/min, and the column effluent was monitored using a RID-10A refractive index (RI) detector (Shimadzu). 20 Glucose, xylose, galactose, arabinose, and mannose in the injected sample (10 μL) were identified and quantified relative to the authentic standards used for external calibration in the linear concentration range of 0.25−4.0 g/L. The composition results were corrected with the amount of sulfate originating from the neutralization step.…”