Stretchable self-healing hydrogels capable of heavy metal ion scavenging

Self-healing hydrogels were prepared by simply mixing phytic acid (PA) and chitosan (CS) in water. Determined by scanning electron microscopy (SEM), the hydrogels were found to be a three-dimensional (3D) porous network structure. The formation of the network structure was considered to be mainly driven by electrostatic interactions and hydrogen bonding, cooperating with the subtle balance of multiple noncovalent interactions. The rheological data indicated that the hydrogels presented excellent mechanical properties with an elastic modulus of 20 000 Pa and a yield stress exceeding 7000 Pa. The dynamic dissociation and recombination of hydrogen bonding and electrostatic interaction in fractured regions of the gels initiated the self-healable property of PA/CS hydrogels. Since PA had high coordination ability to metal ions, PA/CS hydrogels were shown to exhibit excellent capability for capturing heavy metal ions, for example, Pb²⁺ and Cd²⁺. The PA/CS hydrogels provided a simple, green, and high efficiency strategic approach to scavenging heavy-metal ions from industrial sewage.

Stretchable PA/CS polymer hydrogels with multiresponsiveness presented rapid self-healing behavior, and can be used for metal ions scavenging.     

Dependence of copolymer composition, swelling history, and drug concentration on the loading of diltiazem hydrochloride (DIL.HCl) into poly[(N-isopropylacrylamide)-co-(methacrylic acid)] hydrogels and its release behaviour from hydrogel slabs.

The loading of an antihypertensive cationic drug, diltiazem hydrochloride (DIL.HCl), into poly(N-isopropylacrylamide) [P(N-iPAAm)], poly(methacrylic acid) [P(MAA)], and their poly[(N-isopropylacrylamide)-co-(methacrylic acid)] P[(N-iPAAm)-co-(MAA)] hydrogels as well as their release behaviour have been investigated. For this purpose, two series of hydrogels have been tested, one previously soaked under acidic pH (treated hydrogels) and the other from the synthesis and washed in deionized water (untreated hydrogels). For the drug loading, these two series of hydrogels have been soaked in drug solutions with different concentrations. DIL.HCl amounts loaded by the gels as well as swelling degrees as a function of both hydrogel composition and DL.HCl concentration in the loading solution have been analyzed. Due to the interactions among DIL.HCl and the MAA group, "untreated" enriched MAA copolymer hydrogels present the highest drug load and loading efficiency. A DIL.HCl concentration of 320 microm/mL has been employed to load copolymers for release experiments, because for this concentration, hydrogels reach relative high drug load with a still high efficiency of loading. Release has been tested in three media, namely, fresh water (Milli-Q grade, pH 7.0), 0.1 N hydrogen chloride (pH 1.2), and a phosphate buffer (pH 7.0). In general, release is lower in fresh water and acidic media than in phosphate buffer. To explain these results, the effect of temperature, medium, and composition on the pH and thermo sensitivity of the hydrogels as well as the diltiazem-polymer interactions have been taken into account.     

Synthesis and characterization of photocrosslinkable hydrogels from bovine skin gelatin

Hydrogels that mimic native tissues chemically and structurally have been increasingly sought for a wide variety of tissue engineering applications. Gelatin can be naturally derived from different sources and functionalized to fabricate hydrogels that exhibit high cytocompatibility and favorable biodegradable properties. The amino groups on the gelatin backbone can be substituted by adding varying proportions of methacrylic anhydride (MAA) to create biomimetic hydrogels which can be used as tissue engineering scaffolds. Gelatin from different sources yields hydrogels with distinctive physical, chemical, and biological properties. In this work, gelatin from bovine skin was used to fabricate hydrogels with varying degrees of crosslinking content using 1, 4, 7, and 10 mL MAA. The material properties of these hydrogels were characterized. The cytocompatibility of the gelatin-based hydrogels was studied using L6 rat myoblasts. The hydrogels from bovine skin gelatin exhibit mechanical properties that are conducive for applications which require substrates to propagate cell growth, migration, and proliferation rapidly. These hydrogels exhibit exceptional tunability behavior which makes them useful and applicable to culture different cell types.

Gelatin from bovine skin was chemically modified to synthesize biocompatible photolabile hydrogels for tissue engineering applications.     

Synthesis of highly stable fluorescent poly(methacrylic acid-co-itaconic)-protected silver nanoclusters and sensitive detection of Cu2+

Stable fluorescent silver nanoclusters (AgNCs) were synthesized through one-step UV photoreduction using the multiple carboxyl copolymer poly(methacrylic acid-co-itaconic acid) P(MAA-co-IA) as a novel template. The fluorescence lifetime and the quantum yield of the obtained AgNCs were 1.84 ns and 8.9% in an aqueous solution, respectively. Owing to the multiple carboxyls of the protective P(MAA-co-IA) template, the obtained AgNCs have excellent advantages such as good dispersity, and high stability, which make them suitable for highly sensitive and selective detection of Cu²⁺ by fluorescence quenching. A good linear relationship exists between the degree of fluorescence quenching for silver nanoclusters and Cu²⁺ concentration ranging from 0 to 10 μM. The limit of detection (LOD) is 6.36 nM. The result implies that the as-synthesized AgNCs show great potential in the analysis field.

Silver nanoclusters were synthesized through one-step UV photoreduction using the multiple carboxyl copolymer poly(methacrylic acid-co-itaconic acid) as a novel template, which can be used for highly sensitive and selective detection of Cu²⁺ by fluorescence quenching.     

Preparation and catalytic properties of poly(methyl methacrylate)-supported Pd0 obtained from room-temperature,dark reduction of ionic aggregates of the unstable Pd2+ solution ionomer

A poly(methyl methacrylate)-supported Pd⁰ nanocatalyst was successfully prepared from solution reaction of Pd(CH₃COO)₂ with a copolymer acid, poly(methyl methacrylate-ran-methacrylic acid) (MMA–MAA). The reaction was carried out in a benzene/methanol mixed solvent in the dark at room temperature (∼25 °C) in the absence of a typical chemical reductant. There was coordination between the Pd⁰ nanoclusters and MMA–MAA, resulting in Pd⁰ nanoclusters being stably and uniformly dispersed in the MMA–MAA matrix, with an average particle size of ∼2.5 ± 0.5 nm. Mechanistically, it can tentatively be proposed that PMMA-ionomerization of the Pd²⁺ ions produces intramolecular –2COO⁻–Pd²⁺ aggregate cross-links in the solution. On swelling of the chain-segments that are covalently bound via multiple C–C bonds, the resultant elastic forces cause instantaneous dissociation at the O–Pd coordination bonds to give transient bare (i.e., uncoordinated), highly-oxidative Pd²⁺ ions and H⁺-associative carboxylate groups, both of which rapidly scavenge electrons and protons, respectively, of the active α-H atoms abstracted from the methanol molecules of the solvent to make Pd⁰ nanoclusters supported by the re-formed MMA–MAA. The MMA–MAA acid copolymer, without itself undergoing any permanent chemical change, serves as a mechanical activator or catalyst for the mechanochemical reduction of Pd(CH₃COO)₂ under mild conditions. Compared with traditional Pd/C catalysts, this Pd⁰ nanocatalyst exhibited more excellent catalytic efficiency and reusability in the Heck reaction between iodobenzene and styrene, and it could be easily separated. The supported Pd⁰ nanocatalyst prepared using this novel and simple preparation method may display high-efficiency catalytic properties for other cross coupling reactions.

A polymer-supported Pd⁰ nanocatalyst is prepared by using mechanochemical reduction as the driving force for the reaction.     

Characterization of insulin protection properties of complexation hydrogels in gastric and intestinal enzyme fluids.

The objective of this study was to elucidate the mechanisms contributing to oral bioavailability of insulin by poly(methacrylic acid grafted with poly(ethylene glycol)) (P(MAA-g-EG)) hydrogels using the gastric and intestinal fluids from rats. P(MAA-g-EG) hydrogels successfully protected the incorporated insulin from enzymatic degradation by forming interpolymer complexes in the gastric fluid. The hydrogels also showed the insulin protection ability by itself. In the intestinal fluid, P(MAA-g-EG) hydrogels significantly decreased the insulin degradation rate and calcium ion levels, while protein levels was not changed. Insulin protecting effects were dependent on the fraction of the carboxylic group in the polymer networks. Moreover, the insulin degradation inhibitory effect was significantly correlated with Ca2+ deprivation ability of P(MAA-g-EG) hydrogels in the intestinal fluid, implying that the Ca2+ deprivation ability plays an important role in the inhibition of the intestinal enzyme activities. Insulin-loaded P(MAA-g-EG) (ILPs) hydrogels showed a rapid and almost complete insulin release even in the presence of intestinal proteases. These results suggested that the insulin protection ability of the hydrogels contributed to improve oral insulin absorption and that P(MAA-g-EG) hydrogels can be an excellent carrier for protecting insulin during their transit through the GI tract.     

Comparative study of uranium and thorium metal ion adsorption by gum ghatti grafted poly(acrylamide) copolymer composites

Uranium and thorium ions were selectively removed from aqueous solution using synthesized gum ghatti grafted poly(acrylamide) gum-g-poly(AAm) composite. A gamma radiation induced free radical copolymerization technique was used to synthesize the copolymer composite of gum-g-poly(AAm). Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to characterize the graft copolymer gum-g-poly(AAm). The adsorption of uranium ions and thorium ions using the gum-g-poly(AAm) copolymer composites has been investigated in batch mode. The adsorptive characteristics were investigated by varying the pH, concentration and time for both ions. The adsorption method depends on the pH of each metal ion, and the highest adsorption percentage was achieved at pH 6.0. The adsorption statistics were justified by isotherm, kinetic and thermodynamic models. The Langmuir adsorption model was revealed to be the best fitted monolayer arrangement, with a maximum adsorption capacity of 367.65 mg g⁻¹ for the uranium ions and 125.95 mg g⁻¹ for the thorium ions. The adsorption of metal ions occurred by the ion exchange process, which was specified through the rate controlling step with a best-fitted pseudo-second order kinetic rate model. Thermodynamic analysis shows that the ΔH and ΔS values for the uranium ions and thorium ions were positive. The negative ΔG values decreased with an increase in temperature, suggesting that the metal ion adsorption process was endothermic and spontaneous in behaviour.

Uranium and thorium ions were selectively removed from aqueous solution using synthesized gum ghatti grafted poly(acrylamide) copolymer composite.     

Tough,stretchable and compressive alginate-based hydrogels achieved by non-covalent interactions

In this study, two alginate-based hydrogels with good mechanical strength, toughness and resilience were synthesized by hydrophobic interaction and coordination bonding. Sodium alginate/poly(acrylamide) semi-interpenetrating network (NaAlg/PAM semi-IPN) hydrogels were first synthesized through the micelle copolymerization of acrylamide and stearyl methacrylate in the presence of sodium alginate, then calcium alginate/poly(acrylamide) double network (CaAlg/PAM DN) hydrogels were prepared by immersing the as-prepared NaAlg/PAM semi-IPN hydrogels in a CaCl₂ solution. FT-IR and XPS results revealed NaAlg/PAM semi-IPN hydrogels and CaAlg/PAM DN hydrogels were successfully synthesized through non-covalent interactions. The tensile strength of CaAlg/PAM DN hydrogels could reach 733.6 kPa, and their compressive strengths at 80% strain are significantly higher than those of the corresponding NaAlg/PAM semi-IPN hydrogels, which is attributed to the alginate network crosslinked by Ca²⁺. The dual physically crosslinked CaAlg/PAM DN hydrogels can achieve fast self-recovery, and good fatigue resistance, which is mainly assigned to energy dissipation through dynamic reversible non-covalent interactions in both networks. The self-healing ability, swelling behavior and morphology of the synthesized alginate-based hydrogels were also evaluated. This study offers a new avenue to design and construct hydrogels with high mechanical strength, high toughness and fast self-recovery properties, which broadens the current research and application of hydrogels.

Alginate-based hydrogels based on non-covalent interactions were synthesized, and exhibited good mechanical strength, toughness and resilience.     

POSS-enhanced thermosensitive hybrid hydrogels for cell adhesion and detachment

Thermosensitive poly(N-isopropylacrylamide) (PNIPAM)-based substrates have presented great promise in cell sheet engineering. However, non-functionalized PNIPAM cannot be well applied for cell cultivation, due to the low cell adhesion. Herein, to enhance PNIPAM-based substrates and to promote cell proliferation and detachment, a polyhedral oligomeric silsesquioxane (POSS) nanoscale inorganic enhanced agent has been introduced into PNIPAM matrices to construct POSS-containing hybrid hydrogels. The hydrogels were facilely prepared using POSS as a cross-linker via one-pot crosslinking reaction under UV irradiation. The swelling behavior, thermal stability and the mechanical properties of POSS–PNIPAM hybrid hydrogels have been evaluated and they are all dependent on the content of POSS. The in vitro experiment confirms that human amniotic mesenchymal stem cells (hAMSCs) exhibit clearly enhanced adhesion and proliferation on the substrates of POSS–PNIPAM hybrid hydrogels in comparison to the pure PNIPAM hydrogel without POSS. Based on the thermal-responsiveness of PNIPAM, the proliferated cells are easily released without damage from the surface of hybrid hydrogels. Therefore, POSS-enhanced PNIPAM hybrid hydrogels provide a unique approach for harvesting anchorage dependent stem cells.

Thermosensitive poly(N-isopropylacrylamide) (PNIPAM)-based substrates have presented great promise in cell sheet engineering.     

Fluorescent N-functionalized carbon nanodots from carboxymethylcellulose for sensing of high-valence metal ions and cell imaging

A convenient and sensitive reversible-fluorescence sensing platform for accurate monitoring of high-valence metal ions is still very challenging. As a green kind of fluorescent carbon nanomaterials, carbon dots (CDs) have captured considerable attention because of the stable fluorescence property and low cost. Herein, we fabricated a type of nitrogen-functionalized carbon dots (N-CDs) from CMC as a fluorescent reversible sensing platform for detecting various high-valence metal ions. N-CDs with a mean size of 2.3 nm were obtained and possessed 22.9% quantum yields (QY). A label-free fluorescent probe for detection of high-valence metal ions (Fe³⁺, Cr⁶⁺, Mn⁷⁺) was established via the fluorescence quenching response. Among them, the detection limit (LOD) toward Fe³⁺ ions reached 0.8 µM. We have explored the quenching mechanism of N-CDs to explain the valence state-related electron-transfer fluorescence quenching between high-valence metal ions and N-CDs. Moreover, the valence state-related fluorescence quenching phenomenon of N-CDs in aqueous solution could be effectively recovered by introducing a reducing agent (Ti³⁺). This “turn off-on” fluorescence recovery system of N-CDs could be applied in different applications covering the selective detection of environmental high-valence metal ions and cellular imaging.

N-CDs were synthesized using simple and fast one-pot hydrothermal treatment, and were successfully applied as sensors for the selective detection of environmental high-valence metal ions and cellular imaging.     

Simple,selective detection and efficient removal of toxic lead and silver metal ions using Acid Red 94

Toward the goal of detecting toxic elements and removing them from drinking water, we report herein the utilization of Acid Red 94 (AR94) in sensing the hazardous metal ions in water. Among the various examined metal ions (Ag⁺, Pb²⁺, K⁺, Mn²⁺, Zn²⁺, La³⁺, Hg²⁺, Ca²⁺, Cd²⁺, Co²⁺, and Ni²⁺), the UV-visible absorption spectra showed high selectivity and sensitivity for toxic silver and lead metal ions in an aqueous solution. The observed absorption spectral changes and the rapid color changes confirm complex formation between AR94 and both Ag⁺ and Pb²⁺ metal ions. The emission measurements showed the significant fluorescence quenching of the singlet excited state of AR94 in the presence of Ag⁺ and Pb²⁺ metal ions suggesting the formation of an irradiative dye–metal complex under the prevailing experimental conditions. In order to remove the accumulated complexes of AR94 with silver metal ions, safe and harmless mesoporous titanium dioxide was utilized efficiently in removing the complexes with adsorption capacities of 91% at 30 minutes. These findings suggest a simple, fast and efficient method for both detecting silver in water, and removing the formed AR94–metal complexes in water. In addition, AR94 is shown to be a good sensor for the presence of Ag and Pb nanoparticles, NPs, in aqueous solution. The absorption and emission spectra of AR94 showed significant changes that may be rationalized by the strong electromagnetic coupling induced by NPs plasmonic effects. These findings render AR94 a sensitive and selective sensor and a visual indicator for the qualitative and quantitative detection of silver ions, lead ions and their nanoparticles.

Toward the goal of detecting toxic elements and removing them from drinking water, we report herein the utilization of Acid Red 94 (AR94) in sensing the hazardous metal ions in water.     

Evaluation of two aza-crown ether-based multiple diglycolamide-containing ligands for complexation with the tetravalent actinide ions Np4+ and Pu4+: extraction and DFT studies

Two multiple diglycolamide (DGA)-containing extractants where the DGA arms are tethered to the nitrogen atoms of two aza-crown ether scaffolds, a 9-membered aza-crown ether containing three ‘N’ atoms (L_I) and a 12-membered aza-crown ether containing four ‘N’ atoms (L_II), were evaluated for the extraction of the tetravalent actinide ions Np⁴⁺ and Pu⁴⁺. The tripodal ligand with three DGA arms (L_I) was relatively inferior in its metal ion extraction properties as compared to the tetrapodal ligand with four DGA arms (L_II) and Pu⁴⁺ ion was better extracted than Np⁴⁺ ion with both the ligands. A solvation extraction mechanism, where species of the type ML(NO₃)₄ are extracted, was found to be operative for both the ligands involving both the tetravalent actinide ions. While the extraction of the metal ions increased with the feed nitric acid concentration up to 4 M, a sharp decline in the extraction was seen after that. Quantitative extraction (>99%) of the actinide ions was observed with L_II from 4 M HNO₃, suggesting the possible application of the ligands for actinide partitioning of high-level waste. The structure and the composition of the complexes were optimized by DFT computations.

Two multiple diglycolamide (DGA)-containing aza-crown ether ether-based extractants were evaluated for the extraction of the tetravalent actinide ions Np⁴⁺ and Pu⁴⁺.     

Super rapid removal of copper,cadmium and lead ions from water by NTA-silica gel

Copper (Cu²⁺), cadmium (Cd²⁺) and lead ions (Pb²⁺) are toxic to human beings and other organisms. In this study, a silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple amidation procedure for the removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water. The NTA-silica gels showed rapid removal performances for the three metal ions (Pb²⁺ (<2 min), Cu²⁺ and Cd²⁺ (<20 min)) with relatively high adsorption capacities (63.5, 53.14 and 76.22 mg g⁻¹ for Cu²⁺, Cd²⁺ and Pb²⁺, respectively). At the same concentration of 20 mg L⁻¹, the removal efficiencies of the three metals by the adsorbent ranged from 96% to 99%. The Freundlich and Langmuir models were utilized to fit the adsorption isotherms. The adsorption kinetics for the three metal ions was pseudo-second-order kinetics. The removal performance of the NTA-silica gels increased in a wide pH range (2–9) and maintained in the presence of competitive metal ions (Na⁺, Mg²⁺, Ca²⁺ and Al³⁺) with different concentrations. In addition, the NTA-silica gels were easily regenerated (washed with 1% HNO₃) and reused for 5 cycles with high adsorption capacity. This study indicates that the NTA-silica gel is a reusable adsorbent for the rapid, convenient, and efficient removal of Cu²⁺, Cd²⁺, and Pb²⁺ from contaminated aquatic environments.

A silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple method for the super rapid removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water.     

Post synthetically modified IRMOF-3 for efficient recovery and selective sensing of U(vi) from aqueous medium

A simple and efficient route to develop various novel functionalized MOF materials for rapid and excellent recovery of U(vi) from aqueous medium, along with selective sensing has been demonstrated in the present study. In this connection, a set of four distinct post synthetically modified (PSM) iso-reticular metal organic frameworks were synthesized from IRMOF-3 namely, IRMOF-PC (2-pyridine carboxaldehyde), IRMOF-GA (glutaric anhydride), IRMOF-SMA (sulfamic acid), and IRMOF-DPC (diphenylphosphonic chloride) for the recovery and sensing of U(vi) from aqueous medium. The MOFs were characterized by Fourier transform infrared spectroscopy (FTIR), powder XRD, BET surface area analysis, thermogravimetric analysis (TGA), NMR (¹³C, ¹H and ³¹P), Scanning Electron Microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Among all MOFs, post synthetically modified IRMOF-SMA showed enhanced thermal stability of about 420 °C. The MOFs were investigated for U(vi) sorption studies using a batch technique. All the MOFs exhibit excellent sorption capacity towards U(vi) (>90%) and maximum uptake was observed at pH 6. Sorption capacity of MOFs have the following order; IRMOF-3-DPC (300 mg U g⁻¹) > IRMOF-SMA (292 mg U g⁻¹) > IRMOF-PC (289 mg U g⁻¹) > IRMOF-GA (280 mg U g⁻¹) > IRMOF-3 (273 mg U g⁻¹). IRMOF-DPC shows rapid sorption of uranium within 5 min with excellent uptake of U(vi) (>99%). The desorption of U(vi) was examined with different eluents and 0.01 M HNO₃ was found to be most effective. The fluorescence sensing studies of U(vi) via IRMOF-3 and its PSM MOFs revealed high sensitivity and selectivity towards U(vi) over other competing rare earth metal ions (La³⁺, Ce⁴⁺, Sm³⁺, Nd³⁺, Gd³⁺, and Eu³⁺), wherein IRMOF-GA displayed an impressive detection limit of 0.36 mg L⁻¹ for U(vi).

Four IRMOFs following PSM strategy were prepared. The MOFs were characterized by different techniques and were investigated for U(vi) sorption. PSM MOFs displayed impressive fluorescent sensing and selectivity of U(vi) over competing metal ions.     

Controlled degradation of low-fouling poly(oligo(ethylene glycol)methyl ether methacrylate) hydrogels

Degradable low-fouling hydrogels are ideal vehicles for drug and cell delivery. For each application, hydrogel degradation rate must be re-optimized for maximum therapeutic benefit. We developed a method to rapidly and predictably tune degradation rates of low-fouling poly(oligo(ethylene glycol)methyl ether methacrylate) (P(EG)_xMA) hydrogels by modifying two interdependent variables: (1) base-catalysed crosslink degradation kinetics, dependent on crosslinker electronics (electron withdrawing groups (EWGs)); and, (2) polymer hydration, dependent on the molecular weight (M_W) of poly(ethylene glycol) (PEG) pendant groups. By controlling PEG M_W and EWG strength, P(EG)_xMA hydrogels were tuned to degrade over 6 to 52 d. A 6-member P(EG)_xMA copolymer library yielded slow and fast degrading low-fouling hydrogels suitable for short- and long-term delivery applications. The degradation mechanism was also applied to RGD-functionalized poly(carboxybetaine methacrylamide) (PCBMAA) hydrogels to achieve slow (∼50 d) and fast (∼13 d) degrading low-fouling, bioactive hydrogels.

To tune degradation rates of low-fouling hydrogels, a 6-member P(EG)_xMA copolymer library with different electronics and hydration levels was developed.     

Optimized synthesis of novel hydrogel for the adsorption of copper and cobalt ions in wastewater

Metal ions in wastewater endanger the environment and even human life. In this study, an optimized method was used to synthesize an excellent hydrogel to treat these metal ions. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), and applied to treat the Cu(ii) and Co(ii) ions in wastewater. In the adsorption experiment, the influential factors such as pH, adsorption time, adsorbent dosage and concentration of heavy metal ions and regeneration efficiency were evaluated, and the adsorption kinetics, isotherms and thermodynamics were studied. The orthogonal optimization results show that the best condition for synthesis was when the degree of neutralization of acrylic acid (A) was 70%, the quantity of glucose (B) was 0.2 g, the quantity of chitosan (C) was 0.05 g, and the quantity of initiator (D) was 0.03 g. The influence of the four factors was in the order D > B > C > A. The adsorption performance was optimal under neutral conditions and the dosage of 0.02 g adsorbent was chosen as the best. Experiments show that the composite hydrogels exhibited excellent performance under optimal conditions: at 20 °C and pH = 7, the adsorption capacity of 100 mg L⁻¹ of Cu(ii) by 0.01 g hydrogel was 286 mg g⁻¹. The adsorption process of heavy metal ions by hydrogels conforms to pseudo-second-order kinetics and Langmuir isotherm model, which indicate a spontaneous endothermic reaction. Moreover, after five cycles, the removal rates of Cu(ii) and Co(ii) were 81% and 74.8%, respectively.

Metal ions in wastewater endanger the environment and even human life. In this study, an optimized method was used to synthesize an excellent hydrogel to treat these metal ions.     

Triazole-based cross-linkers in radical polymerization processes: tuning mechanical properties of poly(acrylamide) and poly(N,N-dimethylacrylamide) hydrogels

Triazole-based cross-linkers with different spacer lengths and different functional end groups (acrylamides, methacrylamides, maleimides and vinylsulfonamides) were synthesized, investigated for cytotoxic and antibacterial activity, and incorporated into poly(acrylamide) (PAAm) and poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels by free-radical polymerization. Hydrogels prepared with different cross-linkers and cross-linker contents between 0.2% and 1.0% were compared by gel yields, equilibrium degrees of swelling (S) and storage moduli (G′). Generally with increasing cross-linker content, G′ values of the hydrogels increased, while S values decreased. The different polymerizable cross-linker end groups resulted in a decrease of G′ in the following order for cross-linkers with C₄ spacers: acrylamide > maleimide > methacrylamide > vinylsulfonamide. Longer cross-linker alkyl spacer lengths caused an increase in G′ and a decrease in S. Independent of the cross-linker used, a universal correlation between G′ and equilibrium polymer volume fraction ϕ was found. For PAAm hydrogels, G′ ranged between 4 kPa and 23 kPa and ϕ between 0.07 and 0.14. For PDMAAm hydrogels, G′ ranged between 0.1 kPa and 4.9 kPa and ϕ between 0.02 and 0.06. The collected data were used to establish an empirical model to predict G′ depending on ϕ. G′ of PAAm and PDMAAm hydrogels is given by G′ = 4034 kPa ϕ^2.66 and G′ = 4297 kPa ϕ^2.46, respectively.

Poly(acrylamide) and poly(N,N-dimethylacrylamide) hydrogels were prepared by free-radical polymerization using triazole-based cross-linkers with different spacer lengths and functional end groups and hydrogel properties were assessed.     

Triple network hydrogels (TN gels) prepared by a one-pot,two-step method with high mechanical properties

In this work, poly(vinyl alcohol) (PVA) was incorporated into the networks of polyacrylamide/polyacrylic acid (PAM/PAA) to prepare novel PAM/PAA/PVA Triple-network (TN) hydrogels by an in situ polymerization and repeated freezing–thawing (F–T) process. The TN hydrogels have not only high mechanical strength, but also a moderate swelling ability by varying the weight ratio of calcium chloride (CaCl₂) and PVA and free shaping. The compressive stress of the as-prepared hydrogels could reach 11 MPa, and the highest stretching stress could reach 0.8 MPa. Upon mechanical loading, the coordination network between PAA and CaCl₂ served as sacrificial bonds to efficiently dissipate energy. However, they can reform when the mechanical load is released, resulting from the fast coordination between PAA and Ca²⁺. Therefore, TN hydrogels have potential application in biomaterials.

TN hydrogels with high mechanical properties are prepared and they have potential application in biomaterials.     

MoS42− intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.     

Sensitive electrochemical sensor based on poly(l-glutamic acid)/graphene oxide composite material for simultaneous detection of heavy metal ions

Heavy metal pollution can be toxic to humans and wildlife, thus it is of great significance to develop rapid and sensitive methods to detect heavy metal ions. Here, a novel type of electrochemical sensor for the simultaneous detection of heavy metal ions has been prepared by using poly(l-glutamic acid) (PGA) and graphene oxide (GO) composite materials to modify the glassy carbon electrode (GCE). Due to the good binding properties of poly(l-glutamic acid) (PGA) for the heavy metal ions (such as Cu²⁺, Cd²⁺, and Hg²⁺) as well as good electron conductivity of graphene oxide (GO), the heavy metal ions, Cu²⁺, Cd²⁺, and Hg²⁺ in aqueous solution can be accurately detected by using differential pulse anodic stripping voltammetry method (DPASV). Under the optimized experiment conditions, the modified GCE shows excellent electrochemical performance toward Cu²⁺, Cd²⁺, and Hg²⁺, and the linear range of PG/GCE for Cu²⁺, Cd²⁺, and Hg²⁺ is 0.25–5.5 μM, and the limits of detection (LODs, S/N ≥ 3) Cu²⁺, Cd²⁺, and Hg²⁺ are estimated to be 0.024 μM, 0.015 μM and 0.032 μM, respectively. Moreover, the modified GCE is successfully applied to the determination of Cu²⁺, Cd²⁺, and Hg²⁺ in real samples. All obtained results show that the modified electrode not only has the advantages of simple preparation, high sensitivity, and good stability, but also can be applied in the field of heavy metal ion detection.

A novel electrochemical sensor with high stability and good reproducibility for the simultaneous detection of heavy metal ions was prepared by using PGA/GO to modify the GCE, showing high sensitivity of superior to most of the reported values.