Abstract
A novel, lightweight (8 mg/cm3), conjugate sponge of karaya gum (Kg) and chitosan (Ch) has been synthesized with very high porosity (~98%) and chemical stability, as a pH-responsive adsorbent material for the removal of anionic and cationic dyes from aqueous solutions. Experimental results showed that Kg-Ch conjugate sponge has good adsorption capacity for anionic dye methyl orange (MO: 32.81 mg/g) and cationic dye methylene blue (MB: 32.62 mg/g). The optimized Kg:Ch composition grants access to the free and pH-dependent ionizable functional groups on the surface of the sponge for the adsorption of dyes. The studies on the adsorption process as a function of pH, adsorbate concentration, adsorbent dose, and contact time indicated that the adsorption capacity of MB was decreased with increasing pH from 5 to 10 and external mass transfer together with intra-particle diffusion. The adsorption isotherm of the anionic dye MO was found to correlate with the Langmuir model (R2 = 0.99) while the adsorption of the cationic MB onto the sponge was better described by the Freundlich model (R2 = 0.99). Kinetic regression results specified that the adsorption kinetics were well represented by the pseudo-second-order model. The H-bonding, as well as electrostatic interaction between the polymers and the adsorption interactions of dyes onto Kg-Ch sponge from aqueous solutions, were investigated using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and the highly wrinkled porous morphology was visualized in depth by field-emission scanning electron microscopy (FE-SEM) analysis. Moreover, the samples could be reused without loss of contaminant removal capacity over six successive adsorption-desorption cycles. The hierarchical three-dimensional sponge-like structure of Kg has not been reported yet and this novel Kg-Ch sponge functions as a promising candidate for the uninterrupted application of organic pollutant removal from water.
Highlights
Karaya gum (Mw = 1.5 × 106 g/mol), low Molecular weight chitosan (Mw = 9 × 104 g/mol with a degree of deacetylation of 75–85%), acetic acid (CH3 COOH), sodium hydroxide (NaOH), hydrochloric acid (HCl), Methyl orange, and methylene blue were purchased from Sigma Aldrich
(Co − Ce) where, qe is the amount of dye adsorbed at equilibrium, C0 is the initial dye concentration, Ce is the equilibrium dye concentration, m is the weight of adsorbent (g) and V is the volume of the dye solution (L)
Desorption of the Methylene blue (MB) and Methyl orange (MO) dye Molecules was performed in 0.1 M HCl and 0.1 M NaOH, respectively, and the desorbed sponges were washed with distilled water
Summary
Bio-based Materials such as cellulose [13], starch [14], lignin [15], alginate, and chitosan [16] have been used as dye adsorbents for Many reasons These include their affordability, low Manufacturing costs, biocompatibility, biodegradability, hydrophilicity, copiousness, superior physicochemical properties, structural properties, and diversity of chemical functionalities [17]. A significant factor that relies on adsorption is the ability of the chemical functional groups on the adsorbent to interact with the dye Molecules [26] Dyes, based on their chemical structure and application, are classified into different types such as anionic, cationic, and non-ionic dyes. At low pH, the amino groups in chitosan chains get protonated and the Material exhibits a positive charge, while at high pH, the carboxyl groups of karaya gum get deprotonated which brings about a negative charge for the conjugate sponge. The adsorption-desorption of dyes was carried out for several cycles, to establish the reusability potential of the Kg-Ch sponge
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