Functional elastic hydrogel as recyclable membrane for the adsorption and degradation of methylene blue

Non-Invasive Assessment of PVA-Borax Hydrogel Effectiveness in Removing Metal Corrosion Products on Stones by Portable NMR

The cleaning of buildings, statues, and artworks composed of stone materials from metal corrosion is an important topic in the cultural heritage field. In this work the cleaning effectiveness of a PVA-PEO-borax hydrogel in removing metal corrosion products from different porosity stones has been assessed by using a multidisciplinary and non-destructive approach based on relaxation times measurement by single-sided portable Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy—Energy Dispersive Spectroscopy (SEM-EDS), and Raman Spectroscopy. To this end, samples of two lithotypes, Travertine and Carrara marble, have been soiled by triggering acidic corrosion of some copper coins in contact with the stone surface. Then, a PVA-PEO-borax hydrogel was used to clean the stone surface. NMR data were collected in untreated, soiled with corrosion products, and hydrogel-cleaned samples. Raman spectroscopy was performed on PVA-PEO-borax hydrogel before and after cleaning of metal corrosion. Furthermore, the characterization of the dirty gel was obtained by SEM-EDS. The combination of NMR, SEM-EDS and Raman results suggests that the mechanism behind the hydrogel cleaning action is to trap heavy metal corrosion products, such as Cu²⁺ between adjacent boron ions cross-linked with PVA. Moreover, the PVA-PEO-borax hydrogel cleaning effectiveness depends on the stone porosity, being better in Carrara marble compared to Travertine.

A Short Review on the N,N-Dimethylacrylamide-Based Hydrogels

Scientists have been encouraged to find different methods for removing harmful heavy metal ions and dyes from bodies of water. The adsorption technique offers promising outcomes for heavy metal ion removal and is simple to run on a large scale, making it appropriate for practical applications. Many adsorbent hydrogels have been developed and reported, comprising N,N-dimethylacrylamide (DMAA)-based hydrogels, which have attracted a lot of interest due to their reusability, simplicity of synthesis, and processing. DMAA hydrogels are also a suitable choice for self-healing materials and materials with good mechanical properties. This review work discusses the recent studies of DMAA-based hydrogels such as hydrogels for dye removal and the removal of hazardous heavy metal ions from water. Furthermore, there are also references about their conduct for self-healing materials and for enhancing mechanical properties.

Highly Porous Hydroxyapatite/Graphene Oxide/Chitosan Beads as an Efficient Adsorbent for Dyes and Heavy Metal Ions Removal

Dye and heavy metal contaminants are mainly aquatic pollutants. Although many materials and methods have been developed to remove these pollutants from water, effective and cheap materials and methods are still challenging. In this study, highly porous hydroxyapatite/graphene oxide/chitosan beads (HGC) were prepared by a facile one-step method and investigated as efficient adsorbents. The prepared beads showed a high porosity and low bulk density. SEM images indicated that the hydroxyapatite (HA) nanoparticles and graphene oxide (GO) nanosheets were well dispersed on the CTS matrix. FT-IR spectra confirmed good incorporation of the three components. The adsorption behavior of the obtained beads to methylene blue (MB) and copper ions was investigated, including the effect of the contact time, pH medium, dye/metal ion initial concentration, and recycle ability. The HGC beads showed rapid adsorption, high capacity, and easy separation and reused due to the porous characteristics of GO sheets and HA nanoparticles as well as the rich negative charges of the chitosan (CTS) matrix. The maximum sorption capacities of the HGC beads were 99.00 and 256.41 mg g⁻¹ for MB and copper ions removal, respectively.

Design and construction of a novel measurement device for mechanical characterization of hydrogels: A case study

Natural biopolymer-based hydrogels especially agarose and collagen gels, considering their biocompatibility with cells and their capacity to mimic biological tissues, have widely been used for in-vitro experiments and tissue engineering applications in recent years; nevertheless their mechanical properties are not always optimal for these purposes. Regarding the importance of the mechanical properties of hydrogels, many mechanical characterization studies have been carried out for such biopolymers. In this work, we have focused on understanding the mechanical role of agarose and collagen concentration on the hydrogel strength and elastic behavior. In this direction, Amirkabir Magnetic Bead Rheometry (AMBR) characterization device equipped with an optimized electromagnet, was designed and constructed for the measurement of hydrogel mechanical properties. The operation of AMBR set-up is based on applying a magnetic field to actuate magnetic beads in contact with the gel surface in order to actuate the gel itself. In simple terms the magnetic beads leads give rise to mechanical shear stress on the gel surface when under magnetic influence and together with the associated bead-gel displacement it is possible to calculate the hydrogel shear modulus. Agarose and Collagen gels with respectively 0.2-0.6 wt % and 0.2-0.5 wt % percent concentrations were prepared for mechanical characterization in terms of their shear modulus. The shear modulus values for the different percent concentrations of the agarose gel were obtained in the range 250-650 Pa, indicating the shear modulus increases by increasing in the agar gel concentration. In addition to this, the values of shear modulus for the collagen gel increase as function of concentration in the range 240-520 Pa in accordance with an approximately linear relationship between collagen concentration and gel strength.

Carbon dot cross-linked polyvinylpyrrolidone hybrid hydrogel for simultaneous dye adsorption, photodegradation and bacterial elimination from waste water

The creation of a polymeric hydrogel from polyvinylpyrrolidone (PVP) cross-linked by Carbon Quantum Dots (CD) for the adsorption and photocatalytic degradation of both cationic and anionic dyes. PVP, an important biocompatible constituent and often surplus in cosmetic industry, was carboxylated through NaOH refluxing and covalently conjugated to surface amine functionality of CD derived from lemon juice and Cysteamine. The hybrid hydrogel was obtained from PVP-CD covalent conjugate by careful manipulation of pH and found to possess better rheological properties than only carboxylate-PVP. The monolayer physisorption of the dyes on the hydrogel was affected by hydrogen bonding, dispersion or inductive effect, and π-π interaction with the polymer backbone as well as the CD that followed pseudo-second-order kinetics. Degradation of the adsorbed dyes was instated by the unique Reactive Oxygen Species (ROS) generating ability of the CD embedded in the hydrogel matrix upon exposure to sunlight, the mechanism of which is also unveiled. The same CD-induced ROS was found to effectively annihilate both gram-positive and gram-negative bacteria in real polluted water in less than 10 min of photoexcitation of the hydrogel. The hydrogel was restored by mild acid wash that is able to perform dye adsorption and photo-degradation upto four cycles.

Hydrogel-clay Nanocomposites as Carriers for Controlled Release

The present review aims to summarize the research efforts undertaken in the last few years in the development and testing of hydrogel-clay nanocomposites proposed as carriers for controlled release of diverse drugs. Their advantages, disadvantages and different compositions of polymers/biopolymers with diverse types of clays, as well as their interactions are discussed. Illustrative examples of studies regarding hydrogel-clay nanocomposites are detailed in order to underline the progressive researches on hydrogel-clay-drug pharmaceutical formulations able to respond to a series of demands for the most diverse applications. Brief descriptions of the different techniques used for the characterization of the obtained complex hybrid materials such as: swelling, TGA, DSC, FTIR, XRD, mechanical, SEM, TEM and biology tests, are also included. Enlightened by the presented data, we can suppose that hydrogel-clay nanocomposites will still be a challenging subject of global assiduous researches. We can dare to dream to an efficient drug delivery platform for the treatment of multiple affection concomitantly, these being undoubtedly like "a tree of life" bearing different kinds of fruits and leaves proper for human healing.

Efficient Removal of Pb(II) from Aqueous Solutions by Using Oil Palm Bio-Waste/MWCNTs Reinforced PVA Hydrogel Composites: Kinetic, Isotherm and Thermodynamic Modeling

Polyvinyl alcohol (PVA) hydrogel are still restricted for some applications because their lower mechanical strength and thermal stability. The PVA-based composites are drawing attention for the removal of heavy metals based on their specific functionality in adsorption process. The main objective of this work is to synthesize oil palm bio-waste (OPB)/multiwalled carbon nanotubes (MWCNTs) reinforced PVA hydrogels in the presence of N,N′-methylenebisacrylamide (NMBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator via simple in-situ polymerization technique. The as-prepared reinforced nanocomposites were characterized by FESEM, BET surface area, differential scanning calorimetry (DSC), TGA and FTIR analysis. The possible influence of OPB and MWCNTs on the tensile strength, elongation at break and elastic modulus of the samples were investigated. It was found that reinforced nanocomposites exhibited enhanced mechanical properties as compared to non-reinforced material. The evaluation of reinforced nanocomposites was tested by the removal of Pb(II) aqueous solutions in a batch adsorption system. The pseudo-second-order kinetic model was used to illustrate the adsorption kinetic results and Langmuir isotherm was more suitable to fit the equilibrium results providing maximum adsorption capacities. The evaluation of thermodynamic parameters describes the spontaneous, endothermic and chemisorption adsorption process while activation energy reveals the physical adsorption mechanism. Therefore, the coordination effects among OPB, MWCNTs and PVA polymer hydrogels can produce a promising adsorbent material for wastewater treatment applications.

A review on cellulose nanocrystals as promising biocompounds for the synthesis of nanocomposite hydrogels

Hydrogels are hydrophilic cross-linked polymer networks formed via the simple reaction of one or more monomers with the ability to retain a significant extent of water. Owing to an increased demand for environmentally friendly, biodegradable, and biocompatible products, cellulose nanocrystals (CNCs) with high hydrophilicity have emerged as a promising sustainable material for the formation of hydrogels. The cytocompatibility, swellability, and non-toxicity make CNC hydrogels of great interest in biomedical, biosensing, and wastewater treatment applications. There has been a considerable progress in the research of CNC hydrogels, as the number of scientific publications has exponentially increased (>600%) in the last five years. In this paper, recent progress in CNC hydrogels with particular emphasis on design, materials, and fabrication techniques to control hydrogel architecture, and advanced applications are discussed.

Removal of methylene blue from aqueous solution using porous starch-g-poly(acrylic acid) superadsorbents

Porous starch-g-poly(acrylic acid) superadsorbents were prepared, which can be used for effective removal of methylene blue in water.

Magnetic nanocomposite hydrogel prepared by ZnO-initiated photopolymerization for La (III) adsorption

Here, we provide an effective method to fabricate magnetic ZnO clay nanocomposite hydrogel via the photopolymerization. The inorganic components endow the hydrogel with high mechanical strength, while the organic copolymers exhibit good adsorption capacity and separation selectivity to La (III) ions. An optimized hydrogel has the maximum compressive stress of 316.60±15.83 kPa, which still exhibits 138.98±7.32 kPa compressive strength after swelling. The maximum adsorption capacity of La ion is 58.8 mg/g. The adsorption matches the pseudo-second-order kinetics model. La (III) ions can be effectively separated from the mixtures of La/Ni, La/Co, La/Cu, and La/Nd in a broad pH range (2.0 to 8.0). After six adsorption-desorption cycles, the hydrogel can maintain its adsorption capacity. This work not only provides a new approach to the synthesis of tough hydrogels under irradiation, but also opens up enormous opportunities to make full use of magnetic nanocomposite hydrogels in environmental fields.