Abstract
In this study, cross-linked cationic starch was synthesized with corn starch as a raw material, epichlorohydrin as a cross-linked agent, and 3-chloro-2-hydroxypropyl trimethylammonium chloride as a cationic etherification agent, respectively, and it was characterized by X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, and thermogravimetry. The X-ray photoelectron spectroscopy results showed that cationic N appeared on the surface of cross-linked cationic starch; that is, a quaternary ammonium group was introduced. The X-ray powder diffraction results indicated that although the crystallinity of cross-linked cationic starch was lower than that of corn starch, cross-linked cationic starch still had an A-type crystal structure. The scanning electron microscopy results demonstrated that cross-linked cationic starch maintained a granular structure with small holes on the surface. Finally, the thermogravimetric results illustrated that the thermal stability of cross-linked cationic starch decreased. Before the adsorption experiment, the pHpzc of cross-linked cationic starch was obtained by the pH drift method, and it was 6.8. The optimal removal rate of reactive golden yellow SNE dye obtained by response surface methodology was 99.59%, and the optimal adsorption time, temperature, concentration of dye, and cross-linked cationic starch dosage were 14.3 min, 39°C, 100 mg/L, and 0.7 g/L, respectively. The adsorption of SNE by cross-linked cationic starch conformed to pseudo-second-order kinetics and the Langmuir isothermal adsorption model. The equilibrium adsorption capacity from pseudo-second-order kinetics and the maximum adsorption capacity from Langmuir isotherm model were 123.76 and 208.77 mg/g at 308.15 K, separately. In addition, this adsorption was an endothermic process.
Highlights
In recent years, water pollution from dyes has reached an unprecedented level
The X-ray photoelectron spectroscopy (XPS) results showed that the form of nitrogen changed in cationic starch (CCS) compared with corn starch and quaternary ammonium groups were introduced into the starch molecules
The crystallinity of the starch decreased but did not disappear. This result was due to the introduction of covalent bonds between the starch molecules in the presence of a crosslinking agent whose interaction force was significantly higher than the hydrogen bond force, enhancing the intermolecular binding of starch
Summary
Water pollution from dyes has reached an unprecedented level. Printing and dyeing processes in the textile industry consume large amounts of water and discharge large amounts of wastewater, and approximately 2%–20% of dyes are discharged with wastewater.[1,2] In the dye market, azo dyes are widely used in the printing and dyeing industry for their bright colors and high color fastness, accounting for 60%–70% of synthetic dyes.[3]. The adsorption process of SNE by CCS is affected by the adsorption time, temperature, dosage of adsorbent, initial concentration of dye, pH, and oscillation velocity.
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