Synthesis and swelling behavior of highly adsorbent hydrogel for the removal of brilliant green from an aqueous solution: Thermodynamic, kinetic, and isotherm models

Abstract

This synthesis aimed to obtain a highly stable, biodegradable, biocompatible, and swellable superabsorbent hydrogel that is ecofriendly. A new method of preparation of hydrogel nanocomposite based on Castor plant leaves within swelling hydrogel networks is developed. Therefore, Sodium Alginate-g-Poly (Itaconic acid-co-Sodium 4-Styrenesulfonate)/Castor plant leaves, (SA-g-P(ITA-co-NaSS)/CPL) was prepared by free radical copolymerization using potassium persulfate (KPS) as an initiator and N,N-methylene bisacrylamide (MBA) as a cross-linker in aqueous solutions. Characterization of the prepared surface nanocomposite has been done by using Fourier-transform infrared spectroscopy (FTIR) shown all functional groups for the surface (SA-g-P(ITA-co-NaSS)/CPL), field emission scanning electron microscopy (FESEM) displayed a smooth, wrinkled nanocomposite surface versus the hydrogel's rough irregular surface. BG-loaded nanocomposite exhibited sheet-like morphology, irregular spherical shapes and nonhomogeneous distribution, transmission electron microscopy (TEM) confirmed CPL interaction with the nanocomposite matrix, evidenced by dark CPL regions, Energy dispersive X-Ray (EDX) analysis was performed to investigate the elemental composition of hydrogel nanocomposite, X-ray diffraction (XRD) pattern of the nanocomposite matrix and CPL is shown to disappear in the matrix of hydrogel., thermogravimetric analysis (TGA) to determine the thermal stability of synthesized nanocomposite, and represented a complete breakdown of the nanocomposite at 600–750 °C, and Brunauer− Emmett−Teller (BET) shows nanocomposite has a specific surface area and total pore volume of 0.019 cm3 g−1. The prepared surface has a highly effect onto Brilliant Green (BG) dye removal, exerted via the adsorbent through electrostatic interactions, and hydrogen bonds. Under the optimal conditions (Co = 700 mg. L−1, pH = 7, t = 1 h, wt. 0.05 g and T = 25 °C), the maximum adsorption efficiency of hydrogel nanocomposite to BG dye was 1260.34 mg. g−1. The higher uptake capacity resulting in efficiencies above 75–95 % across a broad spectrum of initial concentrations, pH of solution, and temperatures. Thus, after 1h of equilibrium time, it was used to obtain saturation of the adsorbate surface. Freundlich isotherm models and pseudo-second order kinetic models were found to be best in fitting the isotherm and kinetics data. Thermodynamic parameters show that the adsorption of BG dye onto nanocomposite (ΔG < 0) is spontaneous and (ΔH < 0) is endothermic. The novelty of this work shows in being of the first report of hydrogel supported on CPL, with a complete investigation of its efficiency carried out in model pollutant molecule, namely BG dye, using adsorption mechanisms. Therefore, nanocomposite is a promising novel absorbance, with proven high stability in up to 6 sequential recycles.

Keywords

• Dyes
• Copolymerization
• Swelling
• Adsorption
• Thermodynamic
• Hydrogel