Cellulose Nanofibrils-Reinforced Pectin Membranes for the Adsorption of Cationic Dyes from a Model Solution

Abstract

In the presented research, a facile, one-step method for the fabrication of cellulose nanofibrils/pectin (CNFs/PC) membranes is described, which were tested further for their ability to remove cationic dyes from the prepared model solutions. For this purpose, ten membranes were prepared with different quantities of CNFs and PC with/without citric acid (CA) or CaCl₂ as mediated crosslinking agents, and they were characterised comprehensively in terms of their physical, chemical, and hydrophilic properties. All the prepared CNFs/PC membranes were hydrophilic with a Water Contact Angle (WCA) from 51.23° (without crosslinker) up to 78.30° (CaCl₂) and swelling of up to 485% (without crosslinker), up to 437% (CaCl₂) and up to 270% (CA). The stability of membranes was decreased with the increase in PC; thus, only four membranes (M1, M2, M3 and M5) were stable enough in water after 24 h, and these were additionally applied in the adsorption trials, using two structurally different cationic dyes, i.e., C.I. Basic Yellow 28 (BY28) and C.I. Basic Blue 22 (BB22), in four concentrations. The highest total surface charge of M3 (2.83 mmol/g) as compared to the other membranes influenced the maximal removal efficiency of both dyes, up to 37% (BY28) and up to 71% (BB22), depending on the initial dye concentration. The final characteristics of the membranes and, consequently, the dye's absorption ability could be tuned easily by changing the ratio between the CNFs and PC, as well as the type and amount of crosslinker.

Keywords: adsorption; cationic dyes; cellulose nanofibrils; dye removal; membrane; pectin.

Figure 1

The chemical structure of the applied dyes: (a) C.I. Basic Yellow 28; and (b) C.I. Basic Blue 22.

Figure 2

ATR-FTIR spectra of (a) the main components (CNF, PC, CA and CaCl₂); and (b) the membranes (M2–M10).

Figure 3

Potentiometric data of the CNF and CNF/PC membranes—total surface charge and pKa.

Figure 4

WCA of CNF and CNF/PC membranes with corresponding photographs.

Figure 5

The percentage of water uptake at different time intervals (primary y-axis) and pH after 360 min (secondary y-axis).

Figure 6

Cationic dye BY28: (a) absorbance (A) in the initial model solutions (initial) and in the solutions after 24 h of a batch experiment at λ_max = 439 nm; (b) on-line absorbance during the batch experiments at a dye concentration of 25 mg/L; (c) percentage of dye reduction after 24 h; and (d) the amount of adsorbed dye on membrane (Q).

Figure 7

Cationic dye BB22: (a) absorbance (A) in the initial model solutions (initial) and in the solutions after 24 h of a batch experiment at λ_max = 588 nm; (b) percentage of reduction after 24 h; (c) on-line absorbance during a batch experiment at a dye concentration of 25 mg/L; and (d) the amount of adsorbed dye on the membrane (Q).

Figure 8

Corresponding smartphone photographs of membranes before and after the adsorption trial employing (a) BY28 and (b) BB22.

Figure 9

Proposed adsorption mechanism of cation dye BB22 removal by a CNF/PC membrane.