Microwave‐Assisted Soft Method for Synthesis of Poly (Acrylic Acid)/Organo‐clay Composites: Application As Superabsorbent For Phenol and Cr (VI)

Abstract

A series of superabsorbent composites (PAA/HDTMA‐MMT) based on poly (acrylic acid) (PAA) and different content of organo‐modified natural clay HDTMA‐MMT (1,3 and 5 wt.%) were synthesized via in‐situ radical polymerization using microwave method. This eco‐friendly route was chosen to avoid the use of toxic solvents and reduce polymerization time. In addition, it can be considered an efficient approach for industrial‐scale polymer synthesis. The microstructure of the obtained hydrogels was evidenced by Fourier transformation infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). Thermal stability was examined according to nano‐filler content on the matrix. The composite (PAA/HDTMA‐MMT) at 3 wt % exhibits an important swelling capacity value (833.33 g g−1). The efficiency of the synthesized hydrogel composites for phenol and Cr (VI) uptakes from aqueous solutions was studied in batch experiments. The main reason for their selection is their remarkable industrial use, despite their high toxicity and persistence in the environment. In order to underline the mechanism of the phenol and Cr (VI) adsorptions on the (PAA/HDTMA‐MMT), respectively, the zeta potential of the hydrogel was evaluated. Maximum adsorption capacity values of 170.7 mg g−1 and 197.3 mg g−1 were screened for phenol and Cr(VI), respectively. The adsorption process concurs with pseudo‐second‐order kinetics and with the Langmuir isotherm equation. A very high adsorption capacity (qmax=225.2 mg g−1) and a correlation coefficient of 0.998 calculated from isotherm equations show the high efficiency of the adsorbent and thus expected to be a good adsorbent candidate for wastewater treatment. The thermodynamic studies evidenced the exothermic character of the adsorption reactions of the studied pollutants.

Swelling behaviors of superabsorbent composites based on acrylic acid/acrylamide copolymer and acid-modified attapulgite

“…This may be because attapulgite is combined with the polymer monomer via a chemical bond, and attapulgite serves as a crosslinking point in the resin, which is favorable for the formation of a porous three-dimensional network structure of the resin. 21,24 The gelation reaction between the attapulgite nanoparticles and monomers changes the network structure of the polymer materials, 13,30,36 further improving water absorption. The proportion was relatively low, or excess attapulgite only plays a role in filling the pores, which results in a decrease in the water absorption ratio.…”

“…27–29 Ultrasonic treatment can effectively improve the stability and water absorption of the composite materials. 30 Adding a certain amount of attapulgite to the composite material increases the number of hydrophilic functional groups, such as –COOH and –COOH, resulting in a higher percentage of bound and half-bound water in the composite superabsorbent than free water, which significantly enhances the water retention ability of the formed polymer. 31–35 Higher ultrasonic power (400 W and 500 W) could cause liquid splashes.…”

“…Ultrasonication has a strong stirring effect on the liquid, where the localized high-temperature and high-pressure microenvironment that was formed via cavitation could lead to breaking and decomposition of polymer chains, and free radicals have an important effect on the solution polymerization. 30 However, the excessive cavitation that was generated by the excessive ultrasonic power would cause polymer chain breakage and hinder the formation of the three-dimensional network structure. In addition, high cavitation produced high temperatures and led to an increase in the reaction speed.…”

Swelling properties of sand-fixing materials prepared with acrylic acid/acrylamide copolymer and palygorskite

“…Due to their unique characteristics, such as swell-ability, insolubility, hydrophilicity and stimuli-responsiveness, applications of superabsorbent materials have been expanded to diverse elds, such as agriculture, horticulture, environmental protection and deserti cation control, these materials have attracted considerable attention. However, most superabsorbent are expensive and environmentally toxic [2,5,6]. Hence, in order to reduce their cost of production, as well as to improve their biocompatibility, renewable, eco-friendly, non-toxic and biodegradable natural polysaccharides and inorganic clay have often been incorporated into superabsorbent, for instance, have been prepared with natural materials, such as starch, sodium alginate, chitosan, guar gum and clay [7][8][9][10][11][12][13].…”