Green superabsorbent nanocomposite hydrogels for high-efficiency adsorption and photo-degradation/reduction of toxic pollutants from waste water

A novel and smart biopolymer-based hydrogel was synthesized by graft copolymerization of acrylic acid onto the salep backbones. The new superabsorbent hydrogel was synthesized via simultaneous crosslinking and graft copolymerization of acrylic acid (AA) monomer onto salep backbones using radiochemical methods. In radiochemical methods, γ-rays as initiator, energy source and crosslinker are applied. In our experiments, the effects of reaction variables such as relative contents of salep and AA, as well as γ-rays total dose were examined. According to water absorbency of the entitled network, the best synthesis condition is reported. FTIR spectroscopy, SEM photograph and TGA analysis were used for confirming the structure of the final product and a mechanism for superabsorbent hydrogel formation is also suggested. Furthermore, in this research, several factors affecting the swelling behavior of hydrogel including pH of medium, sensitivity to the salt solution and mixture of solvents were studied.

The amount of water and nutrient material in the soil, decides the yield of the agricultural product .So, there was need of material that act as water as well as nutrient reservoirs .Then, this type of material synthesized, which is known as superabsorbent hydrogel. In this research, superabsorbent hydrogel (GGTPAAFA) made from biodegradable polysaccharide such as gum ghatti and polyacrylamide, so that it does not create any type of pollutant accumulated in environment. Superabsorbent GGTPAAFA hydrogel also contains nutrient material (act as fertilizers because it contains potassium) and it can absorb water in its three dimensional network [1–4]. GGTPAAFA can use in agriculture (as water reservoirs and fertilizers) and dye removal [5]. The structure, morphology, thermal stability and chemical composition of GGTPAAK were investigated, using Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo- gravimetric Analysis (TGA) , Swelling tests at room temperature.

Novel green strategy for CuO–ZnO–C nanocomposites fabrication using marigold (Tagetes spp.) flower petals extract with and without CTAB treatment for adsorption of Cr(VI) and Congo red dye

In this paper, controlled release of diclofenac sodium (DS) from pH-sensitive carrageenan-g-poly( acrylic acid) superabsorbent hydrogels was investigated. The hydrogels were prepared by graft copolymerization of acrylic acid (AA) onto kappa-carrageenan, using ammonium persulfate (APS) as a free radical initiator in the presence of methylene bisacrylamide (MBA) as a crosslinker. Infrared spectroscopy was carried out to confirm the chemical structure of the hydrogel. Moreover, morphology of the samples was examined by scanning electron microscopy (SEM). The synthesized hydrogels were subjected to equilibrium swelling studies in simulated gastric and intestinal fluids (SGF and SIF). Hydrogels containing drug DS, at different drug-to-polymer ratios, were prepared by direct adsorption method. The loading yield was found to depend on both the impregnation time and the amount of encapsulated drug. In vitro drug-release studies in different buffer solutions showed that the most important parameter affecting the drug-release behaviour of hydrogels is the pH of the solution. The mechanism involved in release was Fickian (n ⩽ 0·43, n = 0·348) and Super Case II kinetics (n > 1, n = 1·231) at pH 1·2 and 7·4, respectively.

For several decades, superabsorbent polymer hydrogels had attracted the researchers’ attention due to its afforded unique environmental and commercial advantages. This paper reported the study on the effect of cross linker on the sago starch superabsorbent hydrogel (SSH), prepared via graft co-polymerization method of acrylic acid (AA) onto sago starch (SS). The AA grafted copolymer was obtained via a redox initiator system of ammonium persulfate (APS) and in the presence of N, N’ - methylenebisacrylamide (N-MBA) crosslinker. Fourier Transform infrared spectroscopy (FTIR) spectra proved that AA was grafted onto SS. The thermal stability of SSH is increases with the addition of crosslinker.

The aim of this study was to develop a sugarcane bagasse (SCB)-based biodegradable superabsorbent hydrogels (SAH) with a good swelling. To this end, SCB was firstly mechanically activated by home-made high efficiency stirring mill to enhance its reactivity by breaking the lignin seal and decreasing crystallinity of cellulose in SCB. Then, the SAH were synthesized by graft copolymerization of acrylic acid (AA) onto SCB with different mechanical activation times (t M) by using ammonium persulfate/sodium sulfite redox pair as an initiator in the presence of a crosslinker (N,N′-methylenebisacrylamide, MBAAm). The effect of t M on the equilibrium swelling capacity (Q eq), swelling kinetics of the SAH in deionized water, as well as the influences of pH, electrolytic media, and temperature on Q eq were studied. In addition, the products were characterized by scanning electron microscopy and differential scanning calorimetry. The results showed that mechanical activation promoted the graft copolymerization and thereby altered the Q eq of the SAH. The swelling process of the SAH exhibited anomalous swelling behavior and first-order dynamics, and the Q eq of the SAH was pH, salt, and temperature dependent.

The application of superabsorbent polymer hydrogels is gaining much research attention. Industrial applications include agriculture, environmental engineering, biomedical and tissue engineering, oilfield, construction and electrical products, personal care products, and wastewater treatment. In this study, the swelling performance and adsorption kinetics of two commercial superabsorbent polymer hydrogels were evaluated based upon their stimuli response to pH and salinity at varying temperature and reaction time periods. Characterisation and evaluation of the materials were performed using analytical techniques—optical microscopy, scanning electron microscopy, thermal gravimetric analysis, and the gravimetric method. Experimental results show that reaction conditions strongly influence the swelling performance of the superabsorbent polymer hydrogels considered in this study. Generally, increasing pH and salinity concentration led to a significant decline in the swelling performance of both superabsorbent polymer hydrogels. An optimal temperature range between 50 and 75 °C was considered appropriate based on swell tests performed between 25 c to 100 °C over 2-, 4- and 6-h time periods. These findings serve as a guideline for material technologist and field engineers in the use of superabsorbent polymer hydrogels for a wide range of applications. The study results provide evidence that the two superabsorbent polymer hydrogels can be used for petroleum fraction-saline water emulsions separation, among other applications.Graphic abstractHighlightsThe swelling performance of the two superabsorbent polymer hydrogels experimentally studied showed a maximum absorbency in the range of 270 to 300g/g.Thermal gravimetric analysis curves show that both superabsorbent polymer hydrogels are stable at high temperatures.Commercially available superabsorbent polymer hydrogels can be used in industrial water absorption applications.

Hydrogels Based on Cellulose and its Derivatives: Applications, Synthesis, and Characteristics

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 H2O/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl2, and CaCl2) 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.

Utilization of natural polymer as matrix for preparing hydrogels can improve the performance of the materials and render them environmentally friendly. In this work, the guar gum-g-poly(sodium acrylate) (GG-g-PNaA) superabsorbent hydrogels were prepared by the solution graft copolymerization of natural guar gum (GG) with partially neutralized acrylic acid (NaA) using ammonium persulfate (APS) as initiator and N,N′-methylenebisacrylamide (MBA) as crosslinker. FTIR spectra confirmed that NaA had been grafted on GG chains. The effects of reaction variables including the concentration of APS and MBA, the weight ratio of acrylic acid (AA) to GG and the neutralization degree of AA on water absorption were investigated. The superabsorbent hydrogel prepared under optimal condition gives the best absorption of 1107 g∙g–1 in distilled water and 88 g∙g–1 in 0.9 wt% NaCl solution. Effects of external pH on the swelling properties of hydrogels were investigated, and the practical water retention properties of the hydrogels were also evaluated. Results indicated that the hydrogels exhibited excellent pH-stability in a wide pH range from 4 to 11, and the water-retention capabilities of sand soils were also greatly improved after utilizing the superabsorbent hydrogels. This superabsorbent hydrogels could be used as potential eco-friendly water-saving materials for agricultural or ecological application.

Fast‐swelling highly porous superabsorbent hydrogels were synthesized through a rapid radical polymerization under normal atmospheric conditions. To synthesize a biopolymer‐based superabsorbent hydrogel, 2‐hydroxyethyl acrylate (HEA) and sodium acrylate (AANa) were grafted on the starch backbone in an aqueous solution. The graft copolymerization reaction was carried out in the presence of ammonium persulfate (APS) as an initiator and $\displaystyle N,N'$‐methylenebisacrylamide (MBA) as a crosslinker in a homogeneous medium. The chemical structure of the hydrogels was confirmed by FT‐IR spectroscopy and thermogravimetric analysis (TGA). The morphology of the samples was examined by scanning electron microscopy (SEM). The results indicated that with increasing the amount of sodium acrylate both swelling capacity and swelling under load (AUL) were increased. Preliminary swelling and deswelling behaviors of the hydrogels were also studied. The effects of pH and inorganic salt on the swelling behavior of the hydrogels were investigated as well.

Traditional absorbent hydrogels are based on the copolymerization of petroleum-based synthetic vinyl monomers such as acrylic acid, methacrylic acid, and acrylamide derivatives. Nevertheless, these materials are usually expensive, poorly degradable, and non-environmentally friendly. On the contrary, natural polysaccharides display significant advantages such as availability, low production cost, nontoxicity, biocompatibility, and biodegradability. Accordingly, polysaccharides emerge as an interesting sustainable alternative to traditionally employed polymers. In addition, polysaccharides can easily form hydrogels by chemical or Physical crosslinking physical crosslinking (including hydrogen bonding and ionic interactions) or a combination of both, which makes the crosslinking of natural polysaccharides a versatile and promising approach for superabsorbent hydrogel (SAH) production. Therefore, in the last years, numerous polysaccharides including starch, cellulose, alginate, chitosan, and guar gum, among others, have been employed in SAH fabrication. Polysaccharide-based SAHs have been used in agriculture, hygiene products, waste treatment, crack mitigation in building applications, tissue engineering, and controlled release, for biomedical and soil conditioning applications. Despite of the evident commercial and environmental advantages of polysaccharide-based SAHs, they also display some drawbacks that make them continue appearing as a challenge research field. In this sense, although the biodegradability of polysaccharide-based hydrogels is a key characteristic for some applications because it avoids pollution-related issues and enables enhanced controlled release, at the same time, it could delay the development of longtime sustained release systems. Moreover, polysaccharide crosslinking leads to hydrogels with poor mechanical stability which is another associated disadvantage of these types of materials that needs to be overcome. Therefore an increasing amount of investigations about new synthetic approaches to improve the properties of polysaccharide-based hydrogels have been reported in the last years. In this chapter, the recent progress of this type of hydrogels is reviewed. The synthetic methods employed to obtain SAHs from the most common polysaccharides and the main properties of these materials with a special emphasis on swelling and mechanical properties are studied. Furthermore, the applications of SAHs have been summarized highlighting the most outstanding and promising uses.

Exfoliated graphite (EG), manganese dioxide (MnO2), and EG/MnO2-based electrodes were used in this work for the degradation of organic pollutants in wastewater under visible light irradiation. Methylene blue and Congo red dyes were used for the degradation. The synthesis of the nanocomposite electrodes was carried out through the co-precipitation technique. The electrodes were engaged for degradation of the dyes under electrochemical oxidation, photolysis, and photoelectrochemical methods. The characterization techniques utilized encompass transmission electron microscopy (TEM), ultraviolet-visible (UV) analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The EG/MnO2 photoanode was applied in the photoelectrochemical degradation of 0.1 × 10–4 M methylene blue and Congo red dyes in 0.1 M Na2SO4 under visible light irradiation. The XRD analysis revealed that the MnO2 exist as α-MnO2. SEM morphologies showed a satisfying dispersion of MnO2 on EG. The EG/MnO2 composite absorbed a noticeable amount of light in the visible light region compared with the pure EG and MnO2. The photoelectrochemical degradation process resulted in enhanced degradation efficiency of Congo red (97.6%) and methylene blue (98.7%) within 60 min and was observed to be higher than those of photolysis and electrochemical oxidation processes.

In this work, we synthesize a novel protein-based superabsorbent hydrogel and study its swelling behavior. The crosslinking graft copolymerization of acrylic acid (AA) onto the hydrolyzed collagen as a protein backbone was carried out in a homogeneous medium. Potassium persulfate (KPS) as an initiator and N,N′-methylene bisacrylamide (MBA) as a crosslinker were used. The product’s structure was established using FTIR spectroscopy. We were systematically optimized the certain variables of the graft copolymerization (i.e. the monomer, the initiator, and the crosslinker concentration) to achieve a hydrogel with maximum swelling capacity. Under this condition, maximum capacity of swelling in distilled water was found to be 920 g/g. Morphology of the optimized sample was examined by scanning electron microscopy (SEM). The swelling ratio in various salt solutions was also determined. Additionally, the swelling of superabsorbing hydrogels was measured in solutions with pH ranged from 1 to 13. The synthesized hydrogel exhibited a pH-responsiveness character so that a swelling-collapsing pulsatile behavior was recorded at pH 2 and 8.

A novel superabsorbent hydrogel has been synthesized with the crosslinking graft copolymerization of acrylic acid (AA) and acrylamide onto the chain of silk sericin. Potassium persulfate (KPS)–sodium sulfite (NaHSO3) as redox initiation system and N,N′-methylenebisacrylamide (MBA) as crosslinker were used. The structure of the product characterized by Fourier transform infrared absorption spectroscopy and the surface morphology of the hydrogel were observed by scanning electron microscopy. The certain parameters of the graft copolymerization including the monomer, the initiator, the crosslinker concentration, neutralization degree of AA, reaction temperature, and time were systematically optimized to achieve a hydrogel with maximum swelling capacity (2150 g/g). The optimal conditions were initiator 8 mmol/L, MBA 2.5 mmol/L, neutralization degree of AA 75%, reaction temperature 55 °C, and time 6 h. The swelling ratio in salt solutions was also determined (in 0.9% NaCl aqueous solution: 98 g/g). In addition, the swelling capability of the hydrogel was measured in solutions with pH ranged from 1 to 13. The synthesized hydrogel exhibited a pH-dependent character. Water absorbency of the product in aqueous chloride salt solutions has the Na+ > Ca2+ > Mg2+ > Al3+ order in the investigated concentration.