Spectroscopic investigation of carbon nanotube as nano-filler entrapped in chitosan hydrogel beads

Efficient removal of anionic dye congo red by Chitosan/Poly (dimethyl diallyl ammonium chloride-co-acrylamide) composite hydrogel

Chitosan, as a natural and environmentally friendly material, has attracted significant attention in the field of water treatment. In this study, a Chitosan/poly (dimethyl diallyl ammonium chloride-co-acrylamide) composite hydrogel (CPDA hydrogel) featuring a semi-interpenetrating network structure was synthesized via free radical copolymerization for the removal of the anionic dye Congo Red (CR) from wastewater. SEM-EDS, FTIR, XPS, TG, Zeta potential, and mercury intrusion porosimetry (MIP) were employed to analyze the physical and chemical changes in the hydrogel before and after adsorption. The results revealed that the CPDA hydrogel can selectively adsorb anionic dyes through electrostatic interactions. The study on the adsorption performance of the CPDA hydrogel demonstrated its excellent swelling capacity and stable adsorption of Congo Red over a broad pH range of 4 to 10. Subsequently, the adsorption process of Congo Red followed the Pseudo-Second-Order kinetic model and the Hill isotherm model, suggesting that Congo Red may self-assemble into ribbon-like micelles for cooperative adsorption and achieving a maximum adsorption capacity of 1803.507 mg/g. Furthermore, the CPDA hydrogel exhibited outstanding reusability over six adsorption-desorption cycles. Thus, the prepared CPDA hydrogel shows great potential as a material for the selective removal of Congo Red from mixed dye solutions.

Enhanced methylene blue adsorption using single-walled carbon nanotubes/chitosan-graft-gelatin nanocomposite hydrogels

In the present study, single-walled carbon nanotubes (SWCNTs) incorporating chitosan-graft-gelatin (CS-g-GEL/SWCNTs) hydrogels were fabricated with multiple advantages, including cost-effectiveness, high efficiency, biodegradability, and ease of separation for methylene blue (MB) dye from aqueous solution. To verify the successful formulation of the prepared hydrogels, various characterization methods such as NMR, FTIR, XRD, FE-SEM, TGA, BET, and EDX were employed. The removal efficiency of CS-g-GEL/SWCNTs nanocomposite hydrogel increased significantly to 98.87% when the SWCNTs percentage was increased to 20%. The highest adsorption was observed for pH = 9, an adsorbent dose = 1.5 g L-1, a temperature = 25 °C, a contact time = 60 min, and a contaminant concentration = 20 mg L-1. Based on the thermodynamic results, spontaneous adsorption occurred from a negative Gibbs free energy (ΔG°). In addition, the thermodynamic analysis of the adsorption process revealed an average enthalpy of - 21.869 kJ mol-1 for the adsorption process at a temperature range of 25-45 °C, which indicates its spontaneous and exothermic behavior. The Langmuir isotherm model was successfully used to describe the equilibrium behavior of adsorption. The pseudo-first-order model better described adsorption kinetics compared to the pseudo-second-order, intra-particle, and Elovich models. CS-g-GEL/SWCNTs hydrogels have improved reusability for five consecutive cycles, suggesting that they may be effective for removing anionic dyes from aquatic environments.