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Using Pearson's hard and soft acids and bases (HSAB) principle as the design guideline, a novel chitosan/poly(ethylene glycol)/poly(acrylic acid) (CS/PEG/PAA) hydrogel adsorbent containing hard Lewis base adsorption site (i.e., amino group, hydroxyl group, ether linkage, carboxylate ions) was prepared by glow-discharge electrolysis plasma (GDEP) technique and then applied for the selective adsorption of Pb. A copolymerization mechanism initiated by GDEP was proposed. The structure, thermal stability, and morphology of CS/PEG/PAA adsorbent were characterized by FT-IR, thermogravimetry/differential thermogravimetry (TG/DTG), and SEM. The effects of the solution pH and contact time on the single-component adsorption were examined by batch experiments. Competitive adsorptions of Pb and Cd were carried out under equal mass concentration and equal molar concentration. In addition, regeneration and reusability of adsorbent were also investigated in detail. The results showed that the maximum adsorption capacities for Pb and Cd are 431.7 and 265.0 mg g, respectively. The kinetic behaviors of the adsorption and the fourth desorption for single component and the competitive adsorption for Pb follow the pseudo-second-order model with pH = 4.8. The CS/PEG/PAA adsorbent has good adsorption selectivity for Pb with the coexistence of Cd. The adsorbent displays excellent regeneration and reusability in the EDTA-4Na solution. [ABSTRACT FROM AUTHOR]

A palygorskite/poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylamide) (PGS/P(AMPS-co-AM)) superabsorbent hydrogel was prepared in aqueous solution using glow-discharge electrolysis plasma (GDEP) as an initiator and N, N′-methylene-bis-acrylamide as a cross-linker. A possible copolymerization mechanism initiated by GDEP was proposed. The structure, thermal stability, and morphology of PGS/P(AMPS-co-AM) were characterized by FT-IR, XRD, TG-DTG, and SEM. The swelling kinetics, pH-reversibility, and influence of various pH and salt solutions on the swelling were investigated. Adsorption kinetics and adsorption mechanism of hydrogel for dyes were studied in detail. The results indicated that the equilibrium swelling of hydrogel is 652.6 g g in distilled water. The swelling of the hydrogel in salt solutions from highest to lowest is Na > Mg > Fe. The hydrogel has pH-reversibility responsive to the pH and salts solutions. The adsorption process of dyes follows the pseudo-second-order kinetic model with multi-step diffusion process. In addition, PGS/P(AMPS-co-AM) hydrogel can be regenerated and reused. [ABSTRACT FROM AUTHOR]

Highly swelling P(2-acrylamido-2-methyl-1-propanesulfonic acid- co-acrylic acid) (P(AMPS- co-AAc)) superabsorbent hydrogel was synthesized in aqueous solution by a simple one-step using glow-discharge electrolysis plasma technique, in which N,N'-methylenebisacrylamide was used as a crosslinking agent. The structure, thermal stability and morphology of P(AMPS- co-AAc) superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. A mechanism for synthesis of P(AMPS- co-AAc) superabsorbent hydrogel was proposed. The reaction parameters affecting the equilibrium swelling (i.e., discharge voltage, discharge time, macroscopic temperature of the liquid phase, mass ratio of AMPS to AAc, and content of crosslinker) were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The hydrogel formed which absorbed about 1,685 g HO/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl, and CaCl) on the equilibrium swelling. In addition, swelling kinetics in distilled water and on-off switching behavior were preliminarily investigated. The results showed that superabsorbent hydrogel was responsive to the pH and salts. [ABSTRACT FROM AUTHOR]

A highly absorptive resin was prepared by glow-discharge electrolysis plasma initiated suspension copolymerization, in which methyl methacrylate and butyl acrylate were used as monomers, N, N′-methylenebis(acrylamide) as crosslinking agent, polyvinyl alcohol as dispersant, and NaSO solution as supporting electrolyte. To optimize the synthesis conditions, the discharge voltage, discharge time, polymerization temperature, the ratio of monomers, the amounts of crosslinking agent and supporting electrolyte, as well as the ratio of water to oil, were examined in detail. The structure and properties of the obtained resin were characterized by means of attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), respectively. The oil absorbency, absorption rate, absorption selectivity, and network parameters of the resin were also examined. Results showed that under the optimal conditions, the oil absorbency was about 28.5 g/g for benzene, 25.4 g/g for toluene, 28.0 g/g for xylene, 38.1 g/g for chloroform, and 37.0 g/g for carbon tetrachloride. [ABSTRACT FROM AUTHOR]

Crosslinking graft polymerization of poly acrylic/montmorillonite superabsorbent composite in aqueous solution was prepared by using glow-discharge electrolysis plasma, in which acrylic acid and acid-activated montmorillonite were used as starting materials, N, N-methylenebisacrylamide as a crosslinking agent. To optimize the synthetic conditions, seven important parameters of the graft-polymerization were examined in detail, such as the discharge voltage, discharge time, the neutralization of acrylic acid, post polymerization temperature, amounts of crosslinking agent, montmorillonite and acrylic acid used in this study. The structure, thermal stability and morphology of product were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, respectively. The absorbency of poly acrylic/montmorillonite superabsorbent was examined to yield the following results: 1,834 g/g for distilled water, 116 g/g for 0.05 mol/L and 75 g/g for 0.15 mol/L sodium chloride solution. Such excellent character could be important to use in many fields, for example, in agricultural and horticultural applications. [ABSTRACT FROM AUTHOR]