Quaternization of Porous Cellulose Beads and Their Use for Removal of Humic Acid from Aqueous Medium

Abstract

Porous cellulose beads were quaternized with glycidyltrimethylammonium chloride (GTMAC) to explore a potential use of them as an adsorbent for removal of humic acid (HA) from aqueous medium. The introduction of quaternary ammonium groups was confirmed by FT-IR and XPS analysis. The content of introduced quaternary ammonium groups increased with an increase in the GTMAC concentration. The adsorption capacity increased with a decrease in the initial pH value and attained the maximum value at pH 3 and increased with an increase in the content of quaternary ammonium groups. The removal % increased with the dose of quaternized cellulose beads at both pH 3.0 and 6.0. The adsorption process obeyed the pseudo-second order kinetic model and exhibited a better fit to the Langmuir isotherm model, suggesting that the adsorption of HA is accomplished through the electrostatic interaction between a quaternary ammonium group introduced and a dissociated carboxy group of a HA molecule. The maximum adsorption capacity obtained in this study is comparable to or higher than those published by other articles. HA loaded was completely released to NaOH solutions at higher than 100 mM to regenerate the quaternized cellulose beads. The above-mentioned results clearly show that the quaternized cellulose beads prepared in this study can be used as a regenerable adsorbent with high capacity for removal of HA from aqueous medium.

Kinetic, Isothermal, and Thermodynamic Analyses of Adsorption of Humic Acid on Quaternized Porous Cellulose Beads

“…First, about 5.0 g of cellulose beads were dispersed in a NaOH solution at 5 w/v% for 24 h. Then, to this mixture, GTMAC in a NaOH solution at 5 w/v% was added [21,22] to give a GTMAC concentration of 0.10-1.0 M. The mixtures were stirred for 2 h at 65 • C. After separation by decantation, the cellulose beads were washed with ion exchange water and acetone (each several times), followed by drying under reduced pressure for 24 h [21].…”

“…After 0.05-1.0 g of the quaternized cellulose beads were mildly stirred in 20.0 mL of a HCl solution at 10.0 mM for at least 18 h under nitrogen atmosphere, the supernatants were titrated against a NaOH solution at 10.0 mM with bromothymol blue as a pH indicator. The content of quaternary ammonium groups per 1 g of the quaternary cellulose beads was calculated from the difference in the HCl concentration using Equation (1) [21]:…”

“…The photographs (magnification of 150 times) of the untreated and quaternized cellulose beads were taken in the dry and water-swollen states using a Keyence VH-5500 microscope (Osaka, Japan) [21]. The diameters of 200 pieces of the untreated and quaternized cellulose beads were measured and the average particle size was calculated from the particle size distribution on the supposition that they were regarded as a sphere.…”

“…The HA solutions were prepared according to the procedure reported in our previous article [21]. About 0.125 g of HA was dissolved in about 450 mL of water.…”

“…The HA adsorption experiments were performed by varying the experimental conditions, such as the initial pH, temperature, dose of quaternized cellulose beads, and content of quaternary ammonium groups in the batch method. Unless otherwise described, 10 mg of quaternized cellulose beads were added to 50 mL of a HA solution at 100 mg/L, the pH value of which was adjusted to 3.0 or 6.0 beforehand at 25 • C. The absorbance was measured until equilibrium and the adsorbed amount was calculated using Equation (4) [21,22]:…”