Fabrication of Hydrogels via Host–Guest Polymers as Highly Efficient Organic Dye Adsorbents for Wastewater Treatment

Abstract

New self-assembled hydrogel materials of poly(vinyl alcohol)/cyclodextrinmodified poly(acrylic acid)/azobenzene-modified poly(acrylic acid) (PVA/PAA-CD/PAA-Azo) were successfully prepared via host−guest interactions and hydrogen bonds. The asprepared hydrogel materials were characterized by various techniques, including Fourier transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, ultraviolet spectroscopy, and specific surface area tests. The prepared hydrogels with different concentrations of PVA exhibited different network structures. In addition, ultraviolet (UV) light irradiation and temperature change induce a gel−sol phase transition in the hydrogel materials. The obtained hydrogel materials could be used as good adsorbents for two model organic dye molecules, which was mainly due to electrostatic interactions between methylene blue/rhodamine B (MB/RhB) and the gels in the adsorption process. In particular, the adsorption processes of the as-prepared hydrogel materials conformed to the pseudo-firstorder model with a high correlation coefficient, which indicates that gel has a potential application in the field of wastewater purification.

A Review on the Design and Hydration Properties of Natural Polymer-Based Hydrogels

“…These processes can induce changes in polarity, steric hindrance, and polymer/crosslinking densities to affect the sol-gel transition (desolvated vs swollen or rod-to-coil conformations) of materials, and subsequent release of the guest payload (e.g., drugs and proteins). It is well known that azobenzene-based compounds exhibit typical trans → cis isomerization under UV irradiation and show an unfavorable cis→trans transition under visible light [ 90 , 91 ]. Peng and coworkers [ 92 ] have reported a photoresponsive hydrogel composed of trans azobenzene-modified dextran and CD-modified dextran for release of protein (cf.…”

Environmentally Friendly Polyvinyl alcohol−alginate/bentonite Nanocomposite Hydrogel Beads as Efficient Adsorbents for Removal of Toxic Methylene Blue from Aqueous Solution

“…Maximum percentage of dye removal (94.64%) was achieved at pH 8. As mentioned above, the pH of the dye solution may affect the ionization of functional groups on the designed nanocomposite hydrogel adsorbent, which worked as the active sites of the hydrogel adsorbent, in turn, governing the electrostatic attraction between the anions on the hydrogel matrix and the cation on the MB dye [51,53,58]. At acid conditions, the negative surface charges of the nanocomposite hydrogel adsorbent were reduced, which were undesirable for the removal of positively charged MB dye.…”

“…Above pH 8, the surface of the hydrogel exhibited negative electricity, which lessening the electrostatic attraction between MB and the hydrogel, consequently, causing smaller removal values [55,58].…”

“…These may be attributed to the filling of the all surface binding sites and diffusion of the MB molecules into pores of the designed beads. At the starting of adsorption process, there were plentiful active sites on the surface of the beads, which could combined with the MO molecules once they were added into dye solution [57,58]. Moreover, the high MB concentration in the solution provided the apparent driving force for MB adsorption supported by concentration gradient.…”

“…This indicated that at a lower concentration of MB, nanocomposite hydrogel beads had an abundance adsorption active sites leading to a high adsorption for the majority of MB molecules [60]. However, saturation of adsorption sites would be established with further increasing MB concentration, and adsorption became difficult since the increased numbers of MO molecules attached to the surface of the beads would repel free MO molecules [58,59,60].…”