Removal of Pb(II) ions from aqueous solutions using functionalized cryogels

Surface functionalized cryogels - characterization methods, recent progress in preparation and application

Cryogels are polymeric materials with a sponge-like microstructure and have attracted significant attention in recent decades. Research has focused on their composition, fabrication techniques, characterization methods as well as potential or existing fields of applications. The use of functional precursors or functionalizing ligands enables the preparation of cryogels with desired properties such as biocompatibility or responsivity. They can also exhibit adsorptive properties or can be used for catalytical purposes. Although a very brief overview about several functional (macro-)monomers and functionalizing ligands has been provided by previous reviewers for certain cryogel applications, so far there has been no particular focus on the evaluation of the functionalization success and the characterization methods used. This review will provide a comprehensive overview of different characterization methods most recently used for the evaluation of cryogel functionalization. Furthermore, new functional (macro-)monomers and subsequent cryogel functionalization strategies are discussed, based on synthetic polymers, biopolymers and a combination of both. This review highlights the importance of the functionalization aspect in cryogel research in order to produce materials with tailored properties for certain applications.

Environmentally Benign Freeze-dried Biopolymer-Based Cryogels for Textile Wastewater Treatments: A review

Motivated by sustainability and environmental protection, great efforts have been paid towards water purification and attaining complete decolorization and detoxification of polluted water effluent. Textile effluent, the main participant in water pollution, is a complicated mixture of toxic pollutants which seriously impact human health and the entire ecosystem. Developing effective materials for potential removal of the water contaminants is urgent. Recently, cryogels have been applied in wastewater sectors due to their unique physiochemical attributes(e.g. high surface area, lightweight, porosity, swelling-deswelling, and high permeability). These features robustly affected the cryogel's performance, as adsorbent material, particularly in wastewater sectors. This review serves as a detailed reference to the cryogels derived from biopolymers and applied as adsorbents for the purification of textile drainage. We displayed an overview of: the existing contaminants in textile effluents (dyes and heavy metals), their sources, and toxicity; advantages and disadvantages of the most common treatment techniques (biodegradation, advanced chemical oxidation, membrane filtration, coagulation/flocculation, adsorption). A simple background about cryogels (definition, cryogelation technique, significant features as adsorbents, and the adsorption mechanisms) is also discussed. Finally, the bio-based cryogels dependent on biopolymers such as chitosan, xanthan, cellulose, PVA, and PVP, are fully discussed with evaluating their maximum adsorption capacity.

Highly efficient removal of trace heavy metals by high surface area ordered dithiocarbamate-functionalized magnetic mesoporous silica

The study describes synthesizing and characterizing a novel dithiocarbamate-functionalized magnetic nanocomposite. This nanocomposite exhibits several desirable properties, including a large pore diameter of 2.55 nm, a high surface area of 1149 m2/g, and excellent capturing capabilities. The synthesis process involves the preparation of highly porous magnetic nanocomposites, followed by functionalization with dithiocarbamate functional groups through a reaction with carbon disulfide and amine. The synthesized nanocomposite was thoroughly characterized using various techniques, including X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The performance of the mesoporous nanocomposite as an adsorbent for removing Pb(II), Cd(II), and Cu(II) cations from contaminated water was evaluated. The study finds that the maximum removal efficiency for Pb(II), Cd(II), and Cu(II) cations is achieved at pH values above 4. The optimal contact time for achieving 100% removal efficiency of the mentioned cations ranged between 60 and 120 min. Within this time range, the adsorbent exhibited efficient capture of the heavy metal cations from contaminated water. Additionally, the appropriate amount of adsorbent required for complete elimination of the heavy metal cations is determined. For Cd(II), the optimal dosage was found to be 50 mg of the adsorbent. For Cu(II), the optimal dosage was determined to be 40 mg. Finally, for Pb(II), the optimal dosage was 30 mg. The adsorbent's regeneration capability was demonstrated, showing that it could be reused for five consecutive runs.

Optimized Peppermint Essential Oil Microcapsules Loaded into Gelatin-Based Cryogels with Enhanced Antimicrobial Activity

In this study, chitosan (Chi) was used to microencapsulate peppermint essential oil (PEO). A novel gelatin-based cryogel loaded with PEO microcapsules was further developed and characterized for potential applications. Four different cryogel systems were designed, and the morphological, molecular, physical and antibacterial properties were investigated. Additionally, the antimicrobial properties of PEO, alone and microcapsulated, incorporated into the cryogel network were evaluated. The observed gel structure of cryogels exhibited a highly porous morphology in the microcapsules. The highest values of the equilibrium swelling ratio were acquired for the GelCryo-ChiCap and GelCryo-PEO@ChiCap samples. The contact angle GelCryo-PEO@ChiCap sample was lower than the control (GelCryo) due to the water repelling of the essential oil. It has been found that the incorporation of encapsulated PEO into the cryogels would be more advantageous compared to its direct addition. Moreover, GelCryo-PEO@ChiCap cryogels showed the strongest antibacterial activities, especially against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria). The system that was developed showed promising results, indicating an improved antibacterial efficacy and enhanced structural properties due to the presence of microcapsules. These findings suggest that the system may be an appropriate candidate for various applications, including, but not limited to, drug release, tissue engineering, and food packaging. Finally, this system demonstrates a strategy to stabilize the releasing of the volatile compounds for creating successful results.

Hyaluronic Acid Methacrylate Hydrogel-Modified Electrochemical Device for Adsorptive Removal of Lead(II)

This paper presents the development of a compact, three-electrode electrochemical device functionalized by a biocompatible layer of hyaluronic acid methacrylate (HAMA) hydrogel for the adsorptive removal of detrimental lead (Pb(II)) ions in aqueous solutions. An adsorption mechanism pertaining to the observed analytical performance of the device is proposed and further experimentally corroborated. It is demonstrated that both the molecular interactions originating from the HAMA hydrogel and electrochemical accumulation originating from the electrode beneath contribute to the adsorption capability of the device. Infrared spectral analysis reveals that the molecular interaction is mainly induced by the amide functional group of the HAMA hydrogel, which is capable of forming the Pb(II)–amide complex. In addition, inductively coupled plasma mass spectrometric (ICP-MS) analysis indicates that the electrochemical accumulation is particularly valuable in facilitating the adsorption rate of the device by maintaining a high ion-concentration gradient between the solution and the hydrogel layer. ICP-MS measurements show that 94.08% of Pb(II) ions present in the test solution can be adsorbed by the device within 30 min. The HAMA hydrogel-modified electrochemical devices exhibit reproducible performance in the aspect of Pb(II) removal from tap water, with a relative standard deviation (RSD) of 1.28% (for n = 8). The experimental results suggest that the HAMA hydrogel-modified electrochemical device can potentially be used for the rapid, on-field remediation of Pb(II) contamination.

A Multifunctional Microspheric Soil Conditioner Based on Chitosan-Grafted Poly(acrylamide-co-acrylic acid)/Biochar

A multifunctional microspheric soil conditioner based on chitosan-grafted poly(acrylamide-co-acrylic acid)/biochar [CS-g-P(AM-co-AA)/BC] was prepared. First, the P(AM-co-AA) was synthesized and successfully grafted onto CS, and the three-dimensional network structure of microspheres was formed with N,N-methylenebis(acrylamide) as the cross-linking agent according to the inverse suspension polymerization method. Meanwhile, BC and urea were encapsulated into the body of microspheres during the polymerization. The structure of the microspheres was analyzed by Fourier transform infrared spectroscopy, polarized optical microscopy, and scanning electron microscopy, and the mechanism of adsorption of Cu²⁺ on the microspheres was investigated by X-ray photoelectron spectroscopy. Furthermore, the experimental results demonstrated the excellent water absorption and retention capabilities of microspheres, and the release rate of urea was dramatically reduced. Importantly, the introduction of BC significantly enhanced the adsorption performance of the microspheres with respect to heavy metal ions. Consequently, the multifunctional soil conditioner held promise for use in soil improvement and agricultural production.

Hydrous manganese dioxide modified poly(sodium acrylate) hydrogel composite as a novel adsorbent for enhanced removal of tetracycline and lead from water

In this study, hydrous manganese dioxide (HMO) modified poly(sodium acrylate) (PSA) hydrogel was produced for the first time to remove tetracycline(TC) and lead(Pb(II)) from water. The as-prepared composite was characterized using various techniques, such as SEM-EDS, FTIR, XRD, BET, and XPS, to elucidate the successful loading of HMO and analyze subsequent sorption mechanisms. Different influencing parameters such as adsorbent dose, initial concentration of adsorbates, reaction time, solution pH, and temperature were also investigated. The adsorption kinetic studies of both TC and Pb(II) removal indicated that equilibrium was achieved within 12 h, with respective removal rates of 91.9 and 99.5%, and the corresponding adsorption data were fitted to the second-order kinetics model. According to the adsorption isotherm studies, the sorption data of TC best fitted to the Langmuir isotherm model while the adsorption data of Pb(II) were explained by the Freundlich isotherm model. The maximum adsorption capacities of both TC and Pb(II) were found to be 475.8 and 288.7 mg/g, respectively, demonstrating excellent performances of the adsorbent. The uptake capacity of PSA-HMO was significantly influenced by the level of solution pH, in which optimum adsorption amount was realized at pH 4.0 in the TC and Pb(II) systems, respectively. Thermodynamic studies showed the process of TC and Pb(II) adsorptions were endothermic and spontaneous. Overall this study elucidated that PSA-HMO composite can be a promising candidate for antibiotics and heavy metal removal in water treatment applications.

Reducing lactose content of milk from livestock and humans via lactose imprinted poly(2-hydroxyethyl methacrylate-N-methacryloyl-i-aspartic acid) cryogels

Lactase, which can cause lactose intolerance in its deficiency, is a vital enzyme concerning digestion. To overcome lactose intolerance for patients with digestion problem depending of this kind of issue, lactose in food should be removed. In this study, lactose imprinted poly(2-hydroxyethyl methacrylate-N-methacryloyl-l-aspartic acid), poly(HEMA-MAsp), cryogels were synthesized to reduce the amount of lactose content of milk samples. Occurrence of desired bounds, structural integrity, and surface characteristics were analyzed via Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), micro computed tomography (CT), and confocal microscope methods. Water retention characteristic were tested in solution with different electrolytic nature. Adsorption parameters were optimized in an aqueous medium. The adsorption performance of imprinted cryogels was studied in milk samples obtained from cow, sheep, goat, buffalo, and from human volunteers at different intervals after birth. Amount of lactose adsorbed in aqueous media and milk sample from humans were 322 (56.7%) and 179.5 (5.94%) mg lactose/g polymer, respectively. Selectivity studies revealed an approximately 8-fold increase in adsorption rate of molecularly imprinted cryogels as compared to that of nonimprinted cryogels. In addition, competitive adsorption was conducted using lactose-imprinted cryogels in aqueous media containing lactose, glucose, and galactose molecules resulting in adsorption rates of 220.56, 57.87, and 61.65 mg biomolecule/g polymer, respectively.

Evaluation of adsorption ability of cyclodextrin-calixarene nanosponges towards Pb2+ ion in aqueous solution

Different cyclodextrin-calixarene nanosponges (CyCaNSs) have been characterized by means of FFC-NMR relaxometry, and used as sorbents to remove Pb²⁺ ions from aqueous solutions. Considering that the removal treatments may involve polluted waters with different characteristics, the adsorption experiments were performed on solutions without and with the addition of background salts, under different operational conditions. The adsorption abilities and affinities of the nanosponges towards Pb²⁺ ions were investigated by measuring the metal ion concentration by means of Inductively Coupled Plasma Emission Spectroscopy (ICP-OES) and Differential Pulse Anodic Stripping Voltammetry (DP-ASV). The acid-base properties of nanosponges and of metal ion as well as their interactions with the other interacting components of the systems have been considered in the evaluation of adsorption mechanism. Recycling and reuse experiments on the most efficient adsorbents were also performed. On the grounds of the results obtained, post-modified CyCaNSs appear promising materials for designing environmental remediation devices.

PAMPS-graft-Ni3Si2O5(OH)4 multiwalled nanotubes as a novel nano-sorbent for the effective removal of Pb(ii) ions

The existence of Pb(ii) ions in water systems poses significant potential hazards to public health and the environment. In the present study, poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) brush-modified Ni3Si2O5(OH)4 nanotubes were prepared, and their adsorption efficiency against the Pb(ii) ions was investigated. The characterization results of FTIR spectroscopy, TGA, TEM, and XPS indicated the successful grafting of PAMPS on the surface of free Ni3Si2O5(OH)4 NTs, and the prepared PAMPS-g-Ni3Si2O5(OH)4 NTs exhibited a 6-8 nm grafting layer, which could provide abundant binding sites for metal adsorption. During the Pb(ii) removal process, a pH-dependent adsorption behavior was observed, and the adsorption processes fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm model. Compared with unmodified Ni3Si2O5(OH)4, the PAMPS-g-Ni3Si2O5(OH)4 NTs exhibited obviously faster adsorption of Pb(ii) and higher equilibrium adsorption capacity for the removal of Pb(ii). The maximum adsorption capacity calculated via the Langmuir isotherm model was 0.653 mmol g-1 (135.3 mg g-1) at 298 K. In a metal coexisting system, the total adsorption capacity of the NTs was increased; this indicated the potential of the proposed NTs in the removal of Pb(ii) from metal coexisting wastewater. This study showed the significant potential of PAMPS-g-Ni3Si2O5(OH)4 NTs in the effective removal of Pb(ii).

A review of cryogels synthesis, characterization and applications on the removal of heavy metals from aqueous solutions

The physical and chemical attributes of cryogels, such as the macroporosity, elasticity, water permeability and ease of chemical modification have attracted strong research interest in a variety of areas, such as water purification, catalysis, regenerative medicine, biotechnology, bioremediation and biosensors. Cryogels have shown high removal efficiency and selectivity for heavy metals, nutrients, and toxic dyes from aqueous solutions but there are challenges when scaling up from lab to commercial scale applications. This paper represents an overview of the most recent advances in the use of cryogels for the removal of heavy metals from water and attempts to fill the gap in the literature by deepening the understanding on the mechanisms involved, which strongly depend on the initial monomer composition and post-modification agent precursors used in synthesis. The review also describes the advantages of cryogels over other adsorbents and covers synthesis and characterization methods such as SEM/EDS, TEM, FTIR, zeta potential measurements, porosimetry, swelling and mechanical properties.