N-vinylpyrrolidone/acrylic acid/2-acrylamido-2-methylpropane sulfonic acid based hydrogels: Synthesis,characterization and their application in the removal of heavy metals

In this work, the synthesis of N-vinylpyrrolidone/acrylic acid/2-acrylamido-2-methylpropane sulfonic acid (NVP/AAc/AMPS) based hydrogels by UV-curing technique was studied and their swelling behavior, heavy metal ion recovery capabilities were investigated. The structures of hydrogels were characterized by FT-IR analysis and the results were consistent with the expected structures. Thermal gravimetric analysis of hydrogels showed that the thermal stability of hydrogel decreases slightly with incorporation of AMPS units into the structure. In addition, the morphology of the dry hydrogel sample was examined by SEM. According to swelling experiments, hydrogels with higher AMPS content gave relatively higher swelling ratio compared to neat hydrogel. These hydrogels were used for the separation of Cd(II), Cu(II) and Fe(III) ions from their aqueous solutions. The influence of the uptake conditions such as pH, time and initial feed concentration on the metal ion binding capacity of hydrogel was also tested. The selectivity of the hydrogel towards the different metal ions tested was Cd(II) > Cu(II) > Fe(III). It was observed that the specific interaction between metal ions and ionic co-monomers in the hydrogel affected the metal binding capacity of the hydrogel. The recovery of metal ions was also investigated in acid media.     

Improved mechanical and swelling behavior of the composite hydrogels prepared by ionic monomer and acid-activated Laponite

A composite hydrogel (CH) with much improved mechanical and swelling properties was prepared using an ionic monomer and acid-activated Laponite XLS which was used as a cross-linking agent. Addition of acid-activated clay solved the gelation problem when ionic monomers were added to clay mineral dispersions. Reaction of Laponite XLS with sulfuric acid yielded amorphous silica. A dispersion of the acid-activated Laponite and the monomers was used to synthesize composite hydrogels by in-situ polymerization. The FT-IR spectra and rheological results of the composite hydrogels demonstrated the formation of a network. The equilibrium swelling ratios of composite hydrogels (> 6000 g/g) were more than 18 times larger than traditional organic cross-linked hydrogels. The moduli G′ and G″ in the observed frequency range were about 4 and 10 times larger than those of organic cross-linked hydrogel (OR gel). The improvement in both the equilibrium swelling ratio and mechanical strength was attributed to the homogeneous cross-linked network structure.     

Electrochemically synthesized graphene/polypyrrole composites and their use in supercapacitor

Composite films consisting of polypyrrole (PPy) and graphene oxide (GO) were electrochemically synthesized by electrooxidation of 0.1 M pyrrole in aqueous solution containing appropriate amounts of GO. Simultaneous chronoamperometric growth profiles and frequency changes on a quartz crystal microbalance showed that the anionic GO was incorporated in the growing GO/PPy composite to maintain its electrical neutrality. Subsequently, the GO was reduced electrochemically to form a reduced GO/PPy (RGO/PPy) composite by cyclic voltammetry. Specific capacitances estimated from galvanostatic discharge curves in 1 M H₂SO₄ at a current density of 1 A g^?1 indicated that values for the RGO/PPy composite were larger than those of a pristine PPy film and the GO/PPy composite. In the case of 6 mg mL^?1 GO for the preparation of GO/PPy, a high specific capacitance of 424 F g^?1 obtained at the electrochemically prepared RGO/PPy composite indicated its potential for use as an electrode material for supercapacitors.     

Poly(N,N-dimethylaminoethyl methacrylate)/graphene oxide hybrid hydrogels: pH and temperature sensitivities and Cr(VI) adsorption

Different amounts of graphene oxide (GO) were incorporated to N,N-dimethylaminoethyl methacrylate (DMAEMA), fabricating a series of pH and temperature dual sensitive PDMAEMA/GO hybrid hydrogels by in situ polymerization. Their microscopic network structures as well as swelling properties and Cr(VI) adsorption were characterized. The equilibrium swelling ratios (ESR) of hydrogels increased significantly with 0.5 wt% GO feeding of DMAEMA amount, and then decreased with further GO loading increasing. All hydrogels showed obvious deswelling when pH value of swelling mediums increased from 5 to 10 gradually. At pH 7, hydrogels revealed slight ESR increment with temperature up to 50 °C, above which obvious deswelling occurred. In pH 8 buffer, 0.5 wt% of GO loading triggered lower critical solution temperature (LCST) to decrease by 3 °C, and 2–7 °C increment was observed when 1–6 wt% of GO was loaded, as compared with that of GO-free PDMAEMA hydrogel. Cr(VI) adsorption of hydrogels was also improved by the introduction of GO to some extent, and the maximum Cr(VI) adsorption of 180 mg/g was realized, indicating that the obtained PDMAEMA/GO hybrid hydrogels possess excellent adsorption performance.     

Synthesis,characterization and application of poly(N-isopropylacrylamide-co-itaconic acid) hydrogels as supports for lipase immobilization

Temperature- and pH-sensitive hydrogels based on N-isopropylacrylamide (NiPAAm) and itaconic acid (IA) were applied for immobilization of lipase from Candida rugosa (CRL). The hydrogels were synthesized by free radical crosslinking copolymerization in the presence of lipase. Characterization of samples by swelling studies, at pH 2.20 and 6.80 at a temperature of 37 °C, scanning electron microscopy (SEM) and Fourier transform infrared analysis (FT-IR) confirmed that the degree of crosslinking, the non-ionic/ionic (NiPAAm/IA) ratio and the enzyme content had impacts on the hydrogel structure, mechanical properties, morphology and swelling kinetics. All hydrogels demonstrated protein loading efficiencies as high as 95 wt.%. A specific activity of the immobilized lipase of around 38 IU/g was attained for an enzyme loading of 20.0 wt.%. As a result, improved pH and temperature optima values were obtained for the immobilized systems in relation to those for the free lipase.     

Temperature-sensitive hydrogel modified by polymerizable liquid crystal AAc-Brij-58: Optical and protein adsorption/desorption behaviors

To avoid template-like action of polyoxyethylene 20 cetyl ether (Brij-58) in hydrogel matrix, a polymerizable liquid crystal AAc-Brij-58 based acrylic acid (AAc) and Brij-58, and poly(NIPAm-co-AAc-Brij-58) (ACHX) hydrogels based on N-isopropylacrylamide (NIPAm) and AAc-Brij-58 were synthesized by esterification and free-radical polymerization. The chemical structures of resulting ACHX hydrogels were confirmed by FTIR and ¹H NMR. The optical property of ACHX pre-polymerization solution was monitored by ultraviolet–visible spectrophotometry (UV/Vis). The pore structure was observed by scanning electron microscopy (SEM). The adsorption and desorption behaviors of Bovine Serum Albumin (BSA) were investigated by temperature-oscillating between 37 °C and 25 °C. The result shows that AAc-Brij-58 and ACHX hydrogels have been successfully synthesized. With increasing mass percent of AAc-Brij-58/NIPAm from 0 to 10 wt%, the transparency of ACH01-10 hydrogel decreases to 0 at 20, 17, 14, 12 and 16 min, respectively. The interior of ACHX hydrogels presents honeycomb structure with thick pore wall with pore size from 120 to 600 μm, but shows vent-like structure on the outer surface after copolymerization by AAc-Brij-58. The adsorption and desorption of ACHX hydrogels exhibit reversible temperature oscillation responsibility between 37 °C and 25 °C. As mass percent of AAc-Brij-58/NIPAm is 1 wt%, ACH01 hydrogel presents highest adsorbed BSA amount, about 1090 ± 24 mg/g at 37 °C. After desorption at 25 °C, columniform BSA aggregates on the surface of ACHX hydrogels were not observed.     

Cellulose-graft-polyacrylamide/hydroxyapatite composite hydrogel with possible application in removal of Cu (II) ions

Cellulose-graft-polyacrylamide/hydroxyapatite composite hydrogels of different weight ratios were prepared through a suspension polymerization method. Physical and chemical characteristics of the composite were investigated by Fourier transform infrared spectroscopy and scanning electron microscopy. The swelling behaviors of the composite hydrogels were investigated under varying conditions of time, temperature and pH. The optimized swelling capacity in standard conditions was found to be 5197% per gram of the hydrogel. The prepared hydrogel has the potential to be used for ion adsorption in water treatment. Such a possibility was examined through adsorption of copper (II) ions from an aqueous solution. The effects on adsorption of varying the time, pH, and initial concentration of copper (II) solution as well as some thermodynamic parameters were also investigated. The maximum adsorption capacity was found to be 175 mg per gram of composite hydrogel in dried state. The mechanism of adsorption was well presented using a pseudo-second-order kinetic model. Finally, the mercury-loaded hydrogel was regenerated without losing its original activity and stability.     

Synthesis and properties of biodegradable hydrogels of κ-carrageenan grafted acrylic acid-co-2-acrylamido-2-methylpropanesulfonic acid as candidates for drug delivery systems

Novel types of highly swelling hydrogels were prepared by grafting crosslinked polyacrylic acid-co-poly-2-acrylamido-2-methylpropanesulfonic acid (PAA-co-PAMPS) chains onto κ-carrageenan through a free radical polymerization method. Here, we propose a mechanism for κ-carrageenan-g-PAA-co-PAMPS formation and confirm the hydrogel structure using FTIR spectroscopy. The effect of grafting variables (i.e. concentration of methylenebisacrylamide (MBA), acrylic acid/-2-acrylamido-2-methylpropanesulfonic acid (AA/AMPS) weight ratio, ammonium persulfate (APS), κ-carrageenan, neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with a maximum swelling capacity. The maximum water absorbency of the optimized final product was 1238 g/g, while poly-2-acrylamido-2-methylpropanesulfonic acid-g-κ-carrageenan and polyacrylic acid-g-κ-carrageenan hydrogels swelled to a range of 135–800 g/g. The swelling of superabsorbent hydrogels was measured in various solutions with pH values ranging from 1 to 13. In addition, the pH reversibility, on–off switching behavior and swelling kinetics in distilled water were preliminarily investigated.     

Synthesis and characterization of positively charged interpenetrating double-network hydrogel matrices for biomedical applications

In this study, positively charged interpenetrating double-network (DN) hydrogels of polyvinyl alcohol/polyacrylamide (PVA/PAm) were prepared using bifunctional cationic salt as a crosslinker. The cationic salts were synthesized by the Michael-addition of piperazine (PZ) with butanediol diacrylate (BDDA)/hexanediol diacrylate (HDDA) separately followed by the methylation of the products. The chemical characterization of the quaternary salts was performed using ATR-FTIR and NMR (¹H, ¹³C, DEPT) spectroscopy. The zeta potential of the cationic salts was found to be in the range of 17.6 ± 8.03–20.3 ± 10.1 mV for various monomers. Chemical crosslinking (free radical polymerization) and physical crosslinking (freeze–thaw) techniques were employed to crosslink PAm and PVA, respectively. The quaternized salt of BDDA and PZ was used to crosslink the PAm hydrogel network. The thermal stability and the compression modulus of the hydrogel increased, while the displacement value and the water absorption capacity decreased when crosslinker concentration was increased from 1.0 to 4.0 mol%. The excellent cell viability (?94%) and gel content (?92%) suggest that these matrices can be utilized as future biomaterials for biomedical applications.     

Suprarmolecular hydrogels driven by the dual host–guest interactions between α-cyclodextrin and ferrocene-modified poly(ethylene glycol) with low-molecular-weight

In general, α-cyclodextrin (α-CD) and low-molecular weight poly(ethylene glycol) (low-MW PEG) (M_w = 400–10,000) cannot construct supramolecular hydrogels but easily form crystalline precipitates. In this study, low-MW PEG (M_n = 2000, PEG-2000) was functionalized by ferrocene as mono-end-group. The obtained ferrocene-modified PEG-2000 (FcPEG-2000) further self-assembled into supramolecular hydrogel with α-CD even at low concentration (C_FcPEG-2000 = 17 mg/ml), driven by dual host–guest interaction between α-CD and FcPEG-2000. Interestingly, the hydrogel was still observed even when hydrophobic Fc group was oxidized to hydrophilic ferrocenium (Fc⁺) or included into the cavity of β-CD. In the former case, the existence of Fc⁺ end groups is considered to decrease the probability of PEG de-penetration from α-CD cavity, so that α-CDs have more location and opportunities to aggregate into more channel-type crystalline domains as physical cross-linking points. While in the later case, the synergistic effect of host–guest interaction between β-CD and ferrocenyl groups and host–guest interaction between α-CD and PEG chains are considered to be the main reason. The resultant FcPEG-2000 based hydrogels showed the property of shear-thinning.     

Electrosynthesis of PAni/PPy coatings doped by phosphotungstate on mild steel and their corrosion resistances

Polyaniline/polypyrrole (PAni/PPy), polyaniline-phosphotungstate/polypyrrole (PAni-PW₁₂/PPy) and PAni/PPy-PW₁₂ have been successfully electrodeposited on mild steel (MS) by cyclic voltammetry in aqueous oxalic acid solutions. It was found that the incorporation of PW₁₂ enhanced the corrosion resistance of PAni/PPy coating. Moreover, in comparison to PAni-PW₁₂/PPy, PAni/PPy-PW₁₂ coating exhibited better corrosion resistance for mild steel. After immersion of 36 h in 0.1 M HCl, for instance, the polarization resistance of PAni/PPy-PW₁₂ coating reached 1695 Ω cm², more than those of both PAni/PPy and PAni-PW₁₂/PPy.     

A novel codoping approach for enhancing the performance of polypyrrole cathode in a bioelectric battery

A conducting polymer (CP) based bioelectric battery provides a promising alternative to commercial lithium batteries to drive biomedical devices. However, the low power density limits practical application. Here, we synthesize a polypyrrole (PPy)/anthraquinone sulfonate (AQS)/reduced graphene oxide (r-GO) composite via a facile electrochemical route, and use this as a novel cathode material for bioelectric batteries. The presence of r-GO significantly enhanced the electrochemical properties of PPy and led to greatly improved cell performance compared to that of PPy/AQS. The resultant PPy/AQS/r-GO composite delivered a maximum power density of 6240.5 mW m⁻², 14.2 times higher than that of PPy/p-toluenesulfonate (pTS) as reported previously.     

Quantification of singlet oxygen generation from photodynamic hydrogels

Recently, we described a series of novel porphyrin-impregnated hydrogels capable of producing microbicidal singlet oxygen (¹O₂) on photoactivation. Indirect assessment of the efficacy of ¹O₂ production from such hydrogels has been previously described using microbiological techniques, but here we report a novel, direct method of quantification. Anthracene-9,10-dipropionic acid (ADPA) is known to irreversibly form an endoperoxide on reaction with ¹O₂, causing photobleaching of its absorbance band at approximately 378 nm. Here, the reaction of this probe is exploited in a novel way to provide a simple, inexpensive, and convenient measurement of ¹O₂ generation from the surface of porphyrin-incorporated photosensitising hydrogels, with the ability to account for effects due to hydrogel porosity. Ingress of the probe into the materials was observed, with rates of up to 3.83 × 10³ s⁻¹. This varied by up to 200-fold with material composition and surface modification. Rates of ¹O₂ generation in these porphyrin-incorporated hydrogels, after compensating for ADPA ingress, ranged from 1.86 × 10³ to 5.86 × 10³ s⁻¹. This work demonstrates a simple and straightforward method for direct ¹O₂ quantification from porous materials, with general utility.     

Hydrothermal synthesis of Polypyrrole/MoS2 intercalation composites for supercapacitor electrodes

As a pseudocapacitive electrode materials for supercapacitor, Polypyrrole (PPy) exhibit excellent theoretical specific capacitance. However, it suffers from a poor cycling stability due to structural instability during charge-discharge process. In this work, a novel and facile hydrothermal method has been developed for the intercalation composites of PPy/MoS₂ with multilayer three-dimensional structure. The report result shows that the as-prepared electrode possess a outstanding electrochemical properties with significantly specific capacitance of 895.6 F g⁻¹ at current density of 1 A g⁻¹, higher energy density (3.774 Wh kg⁻¹) at power density of 252.8 kW kg⁻¹, furthermore, it also achieve remarkable cycling stability (~98% capacitance retention after 10,000 cycles) which is attributed to the synergistic effect of PPy and MoS₂. This synthetic strategy integrates performance enables the multilayer PPy/MoS₂ composites to be a promising electrode for energy storage applications.     

The synthesis and electrical conductivity of a polyacrylate/graphite hydrogel

A polyacrylate/graphite composite was synthesized by aqueous solution polymerization. Based on the electrical conductivity of graphite and the water absorbency of polyacrylate, a novel conductive hydrogel with a conductivity of 7.3 mS m⁻¹ was prepared. The influence of crosslinker, initiator, monomer, neutralization degree, graphite, water absorbency and temperature on the electrical conductivity of the hydrogel was investigated. An appended network structure model of the polyacrylate/graphite conductive hydrogel is proposed.     

The synthesis and electrical conductivity of a polyacrylamide/Cu conducting hydrogel

A polyacrylamide/Cu superabsorbent composite was synthesized by aqueous solution polymerization. Based on the electrical conductivity of Cu and the water absorbency of polyacrylamide, a novel conducting hydrogel with a conductivity of 1.08 mS m⁻¹ was prepared. The effect of crosslinker, initiator, monomer, neutralization degree, Cu amount, water absorbency and reaction temperature on the electrical conductivity of the hydrogel was investigated. An appended network structure model of the polyacrylamide/Cu conducting hydrogel is proposed.     

Freezing as a path to build macroporous structures: Superfast responsive polyacrylamide hydrogels

Macroporous polyacrylamide (PAAm) hydrogels were prepared from acrylamide monomer and N,N′-methylene(bis)acrylamide (BAAm) crosslinker in frozen aqueous solutions. It was found that the swelling properties and the elastic behavior of the hydrogels drastically change at a gel preparation temperature of −6 °C. The hydrogels prepared below −6 °C exhibit a heterogeneous morphology consisting of pores of sizes 10–70 μm, while those formed at higher temperatures have a non-porous structure. PAAm networks with largest pores were obtained at −18 °C. The pore size of the networks increased while the thickness of the pore walls decreased by decreasing the monomer concentration. The hydrogels formed below −6 °C exhibit superfast swelling and deswelling properties as well as reversible swelling–deswelling cycles in water and in acetone, respectively.     

Synthesis of PPy/silica nanocomposites with cratered surfaces and their application in heavy metal extraction

A simple fabrication method for a polypyrrole (PPy)/silica nanocomposite with a cratered surface using templated synthesis is described. This nanocomposite was prepared by a modified silica-templated oxidation/polymerization of pyrrole in the presence of FeCl₃ oxidant and was characterized by various methods, including Fourier-transform infrared spectroscopy; BET specific surface area; and transmission electron microscopy (TEM). The PPy/silica nanocomposite with surface craters looked like a golf ball in TEM images. The highest BET surface area of PPy/silica nanocomposite with craters was 306 m²/g at 4 mL silica sol solution (Ludox SM-30) loading through the fabrication process, whereas a PPy/silica nanocomposite without craters had a specific surface area of only 85 m²/g with no Ludox SM-30 introduced. In addition, the material's adsorption capacity for heavy metal ions (Hg²⁺, Ag⁺, and Pb²⁺) and its recycling mechanism were investigated.     

Mechanical and rheological behavior of pNIPAAM crosslinked macrohydrogel

In this study for the first time we investigate the most common reticulated N-isopropylacrylamide (pNIPAAM) macrohydrogel for both its mechanical response and shear rheological behavior in time and frequency domains. Hydrogels are characterized by water content volume and weight measurements, FT-IR spectroscopy, scanning electron microscopy and reflecting index. Compressive uniaxial tests on equilibrated hydrogels individuate a hookean response within a 30% strain range with E_c modulus of 12.2 kPa, and a neo-hookean response within a 79% strain range which upper limit corresponds to material rupture with G_c modulus of 3.8 kPa. Tensile experiments performed for the first time on the pure material evidence a rupture limit for a strain around 30% with hookean modulus E_t of 24.8 kPa and neo-hookean modulus G_t of 7.3 kPa. Rheological studies, carried out in linear response regime around the hydrogel swelling–deswelling transition, report relaxation times of the kinetics towards the equilibrium at different temperatures. The phase transition of pNIPAAM is monitored and the transition temperature is determined following the temperature dependence of the shear modulus. We apply different literature models to the rheological response and to the swelling–deswelling transition of the hydrogel. Finally, we analyze the results providing values for microscopic material parameters such as crosslink density and mesh size.     

Working mechanism of methyl hydroxyethyl cellulose (MHEC) as water retention agent

The working mechanism of methyl hydroxyethyl cellulose, MHEC (M_w = 2.5 · 10⁵ g/mol, DS_methyl = 1.81, MS_hydroxyethyl = 0.15) as water retention agent in cement was investigated. First, the hydrocolloid was characterized and its performance as non-ionic water retention agent was determined employing the filter paper test. Also, water sorption and swelling of individual MHEC fibers under conditions of different humidities were monitored by ESEM imaging. Second, its working mechanism was established. It was found that at low dosages, MHEC achieves water retention by intramolecular sorption of water and concomitant swelling while at higher dosages, MHEC molecules agglomerate into large hydrocolloidal microgel particles (d > 1 μm) which effectively plug the pores in the mortar matrix. MHEC association was evidenced by an exponential increase in solution viscosity as concentration rises, a strong increase in the hydrodynamic diameter of solved MHEC molecules, and a noticeable reduction of surface tension.