Network Structure and Congo Red Dye Removal Characteristics of New Temperature-Responsive Hydrogels

Abstract

New temperature-responsive hydrogels containing various composition of N-acryloyl morpholine (AM) and N-isopropyl acrylamide (NIPAM) were prepared by free-radical solution polymerization using poly(ethyleneglycol) diacrylate (PEGDA) as the chemical crosslinker. The gels were responsive to changes in external temperature, and exhibited the volume phase transition phenomenon. The gels swelled extensively in water at 23 °C, with water-uptake of more than 90 % at swelling equilibrium. The influence of molecular heterogeneity of the gels in terms of comonomer and crosslinker composition on the swelling capacity and equilibrium water uptake was evaluated. The dye adsorption capacity of the gels at room temperature was studied using Congo red as a model dye. The gels displayed significant adsorption capacity of the dye, and the adsorption capacity was found to be dependent on the hydrophilic character of the gel.The characteristic adsorption parameters were determined using the Langmuir isotherm model.The value of equilibrium binding constant was below 1 which indicated favorable adsorption of dye by the hydrogels. The dye release behavior was studied below and above the volume phase transition temperature of the gels. The dye release from the gels was about 95 % at temperatures above the volume phase transition temperature of the gels. These gels can be used as reversible sorbents in the efficient removal of Congo red from waste water.A c c e p t e d M a n u s c r i p t 2 INTRODUCTION Hydrogels are cross-linked three-dimensional polymer networks that can absorb large amounts of water and remain insoluble. Depending on the nature of chemical units along the polymer chain, these materials can be made to respond to changes in certain external stimuli such as pH, temperature, ionic strength, illumination, and magnetic field (1-5), and are called stimuliresponsive, intelligent, smart, or environmentally sensitive polymers. The potential response to these stimuli is changes in phase, shape, volume or optical properties. Due to their excellent properties such as biocompatibility, elasticity, and water-uptake capacity, hydrogels have found applications in skin care products, targeted drug delivery systems, enzyme immobilizations, dye sorbents and chemical sensors (5-10). In many of these applications, the swelling property and strength of the hydrogel plays an important role which has been the subject of research interest in recent years.The development of new sorbents to remove organic or heavy metal pollutants from organic effluents produced in textile, paper, leather, and plastic industries represents an intensive and popular area of research. The main source of water and land pollution is by effluents from textile and leather industries. As a result of dying process, these industrial effluents are colored and contain synthetic organic dyes which are hazardous to the environment and biological activities in water bodies.These organic dyes are also mutagenic and carcinogenic in nature and hence very hazardous to human health...

Target-Specific Superparamagnetic Hydrogel with Excellent pH Sensitivity and Reversibility: A Promising Platform for Biomedical Applications

“…The morphology of the swelled PAAVSA/Fe 3 O 4 magnetic hydrogel at different pH values (after the swollen hydrogels were freeze-dried 32 ) was further investigated by field emission scanning electron microscopy (FESEM), as shown in Figure 9 a–d. The corresponding elemental mapping (Fe), through energy-dispersive X-ray analysis (EDX), has been displayed in Figure 9 e–h.…”

“…The swollen hydrogel, PAAVSA/Fe 3 O 4 , after reaching the equilibrium swelling state for a given pH solution, was lyophilized to preserve the structure of the hydrogel 32 for the FESEM/EDX study. The study shows that there was no anisotropy in surface morphology of the PAAVSA/Fe 3 O 4 hydrogel for a given pH value, as shown in Figure 9 , indicating the homogeneous swelling nature of the hydrogel.…”

“…The surface morphology, energy-dispersive X-ray (EDX) analysis, and elemental mapping of the as-prepared PAAVSA/Fe 3 O 4 hydrogel and the hydrogel in different pH solutions were studied (after the swollen hydrogels were freeze-dried 32 ) by field emission scanning electron microscopy (FESEM, Supra55 Zeiss and JSM 7610F, JEOL).…”

“…Distinct pH reversibility of the system was also demonstrated through swelling/deswelling analysis. Furthermore, a pH-responsive significant change in the morphology and packing fraction of iron oxide nanoparticles in PAAVSA/Fe 3 O 4 was explored by energy-dispersive X-ray (EDX) elemental mapping with the field emission scanning electron microscopy (FESEM) study (for freeze-dried 32 PAAVSA/Fe 3 O 4 , swelled at different pH values), which signifies the stimulus-responsive drastic change in susceptibility and induced saturation magnetization of the magnetic hydrogel, which could be easily detectable using a magnetic probe or an impedance analysis technique.…”

One-pot Synthesis of IPN Hydrogels with Enhanced Mechanical Strength for Synergistic Adsorption of Basic Dyes

“…Hydrogels are chemically or physically cross-linked polymers that can absorb large amounts of water without dissolving and without losing their shape (4). Many publications concentrated on the use of hydrogels as the adsorbent to remove dyes due to the high adsorption capacity and the ease of operation (5)(6)(7)(8)(9). Additionally, this type of sorbent can be easily and completely regenerated with no significant decrease in sorption capacity (7)(8)(9).…”