Biosorbent Based on Poly(vinyl alcohol)-Tricarboxi-Cellulose Designed to Retain Organic Dyes from Aqueous Media

Abstract

Methylene Blue, a cationic dye, was retained from aqueous solutions using a novel biosorbent made of poly(vinyl alcohol) reticulated with tricarboxi-cellulose produced via TEMPO oxidation (OxC25). The study of the Methylene Blue biosorption process was performed with an emphasis on operational parameters that may have an impact on it (such as biosorbent concentration, pH of the aqueous media, and temperature). The current study focused on three areas: (i) the physic-chemical characterization of the biosorbent (scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX)); (ii) biosorption data modeling to determine the quantitative characteristic parameters employing three equilibrium isotherms (Langmuir, Freundlich, and Dubinin-Radushkevich-DR); and (iii) the study of temperature influence. The results of the study showed that the Langmuir model provided a good fit for the experimental data of biosorption, realizing a maximum capacity of 806.45 mg/g at 20 °C. The free energy of biosorption (E) evaluated by the DR equation was in the range of 6.48-10.86 KJ/mol. The values of the thermodynamic parameters indicated an endothermic process because the free Gibbs energy ranged from -9.286 KJ/mol to -2.208 KJ/mol and the enthalpy was approximately -71.686 KJ/mol. The results obtained encourage and motivate the further study of this biosorption process by focusing on its kinetic aspects, establishing the biosorption's controlled steps, identifying the mechanism responsible for the retention of textile dyes presented in moderate concentration in aqueous media, and studying the biosorption process in a dynamic regime with a view to applying it to real systems.

Keywords: aqueous medium; biosorption; cationic organic dye; cellulose; hydrogel as biosorbent.

Figure 1

Chemical structure of cationic dye, Methylene Blue—C.I. 52015.

Figure 2

Chemical structure of the compound used to obtain OxC25 hydrogel: (a) 2,3,6 tricarboxy-cellulose; (b) poly(vinyl alcohol).

Figure 3

Scanning electron microscopy (SEM) of the biosorbent after (a) and before (b) Methylene Blue cationic dye biosorption.

Figure 4

Energy-dispersive X-ray (EDX) spectra of the biosorbent OxC25 after (a) and before (b) Methylene Blue cationic dye biosorption.

Figure 5

The influence of pH on the retention of the MB cationic dye on the OxC25 hydrogel. Operational conditions: C₀ = 38.4 mg/L; 0.4 g/L biosorbent; T = 20 °C.

Figure 6

The influence of biosorbent dose on the retention of the MB cationic dye on the OxC25 hydrogel. Operational conditions: C₀ = 38.4 mg/L; pH = 11; T = 20 °C.

Figure 7

The biosorption isotherms of Methylene Blue dye on hydrogel OxC25. Conditions: pH = 11, contact time = 24 h, amount of biosorbent = 0.44 g/L.

Figure 8

The biosorption isotherms (Langmuir I and Freundlich) of Methylene Blue dye on the hydrogel OxC25 biosorbent. Conditions: pH = 11, contact time = 24 h, amount of biosorbent = 0.4 g/L.

Figure 9

Graphical representation used to determine the ΔH and ΔS characteristic values of the biosorption process of Methylene Blue dye on OxC25 hydrogel as a biosorbent. Conditions: pH = 11, contact time = 24 h, amount of biosorbent = 0.4 g/L.