High crosslinked sodium carboxyl methylstarch-g-poly (acrylic acid-co-acrylamide) resin for heavy metal adsorption: its characteristics and mechanisms

Synthesis, characterization, and application of a poly(acrylic acid-co-acrylamide) cation exchanger (ACX) for camel lactoferrin purification

The goal of this study is to develop an optimized poly(acrylic acid-co-acrylamide) cation exchanger (ACX) for protein purification. Cation exchange chromatography is a widely used technique in protein purification. ACX was synthesized and tailored to purify positively charged proteins using batch chromatography. ACX aims to reduce the overall cost of protein purification by integrating cheap monomers, tolerating unclean samples, and without grafting on expensive support materials. ACX was prepared as a copolymer of acrylic acid, acrylamide, and methylene-bis-acrylamide by the inverse emulsion polymerization technique. ACX was characterized by protein binding capacity, ion exchange capacity, elution behavior, pH titration, distribution studies, swelling properties, light microscopy, SEM, FTIR, TGA, and DTA. Then, it was challenged in the purification of lactoferrin -a positively charged protein- from raw camel milk. Microscopic examination of ACX verified the successful synthesis of spherical beads with a mean diameter of 141 ± 63 μm, which exhibited a protein binding capacity of 121.7 ± 0.58 mg/g of dry resin. Furthermore, the purification challenge with camel lactoferrin showed sufficient purity (93 %) with a high purification factor (145). While pH titration studies of ACX revealed its bifunctional nature, distribution studies showed its superior affinity to ferric ions. In conclusion, ACX offers an easy-to-fabricate and cost-effective alternative to commercial cation exchangers for the purification of positively charged proteins by batch chromatography.

PAD resin: An intelligent adsorbent for solving Cr(VI) pollution with real-time feedback and high efficiency

To address the urgent issue of Cr(VI) pollution and protect aquatic ecosystems, we conducted an exhaustive investigation into a Poly(acrylamide-co-methacryloyloxyethyl trimethylammonium chloride) (PAD) resin synthesized through an environmentally friendly aqueous polymerization process. This resin not only boasts a high capacity for Cr(VI) removal but also incorporates a colorimetric sensing mechanism that visually transitions from transparent to yellow upon Cr(VI) adsorption, offering real-time, non-invasive monitoring and optimization of the remediation process. According to the Langmuir model, at a pH of 4.78 and a temperature of 15 ℃, the maximum adsorption capacity of PAD for Cr (VI) is 135.32 mg/g. Its adsorption kinetics conform to a pseudo-first-order model and Langmuir isotherm, indicating uniform adsorption sites and favorable interactions. Thermodynamic analysis further reveals the spontaneous and exothermic nature of the adsorption process, making it suitable for large-scale applications at ambient temperatures.In natural lake water-based Cr(VI) simulated wastewater, PAD resin achieved a remarkable removal efficiency of 99.54 % for 4.82 mg/L Cr(VI) （The filling column had a diameter of 3 cm and a height of 30 cm; The PAD dosage was 1.6 g, with a flow rate of 5 mL/min and an adsorption time of 60 min, at a neutral pH）, effectively reducing residual Cr(VI) concentrations to 0.022 mg/L, well under WHO limits (0.05 mg/L). Additionally, its 93.68 % capacity retention after four HCl regeneration cycles underscores economic feasibility & sustainability.In summary, PAD resin stands out as an innovative, high-performance, and intelligent Cr(VI) adsorbent that transcends the limitations of traditional adsorbents.

The Effect of Silver Nanoparticles/Titanium Dioxide in Poly(acrylic acid-co-acrylamide)-Modified, Deproteinized, Natural Rubber Composites on Dye Removal

This work aims to enhance the dye-removal performance of prepared poly(acrylic acid-co-acrylamide)-modified, deproteinized, natural rubber ((PAA-co-PAM)-DPNR) through incorporation with silver nanoparticles/titanium dioxide. The (PAA-co-PAM)-DPNR was prepared by emulsion-graft copolymerization with a grafting efficiency of 10.20 ± 2.33 to 54.26 ± 1.55%. The composites based on (PAA-co-PAM)-DPNR comprising silver nanoparticles and titanium dioxide ((PAA-co-PAM)-DPNR/Ag-TiO2) were then prepared by latex compounding using the fixed concentration of AgNO3 (0.5 phr) and varying concentrations of TiO2 at 1.0, 2.5, and 5.0 phr. The formation of silver nanoparticles was obtained by heat and applied pressure. The composites had a porous morphology as they allowed water to diffuse in their structure, allowing the high specific area to interact with dye molecules. The incorporation of silver nanoparticles/titanium dioxide improved the compressive modulus from 1.015 ± 0.062 to 2.283 ± 0.043 KPa. The (PAA-co-PAM)-DPNR/Ag-TiO2 composite with 5.0 phr of TiO2 had a maximum adsorption capacity of 206.42 mg/g, which increased by 2.02-fold compared to (PAA-co-PAM)-DPNR. The behavior of dye removal was assessed with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model. These composites can maintain their removal efficiency above 90% for up to five cycles. Thus, these composites could have the potential for dye-removal applications.

Adsorption of Copper and Arsenic from Water Using a Semi-Interpenetrating Polymer Network Based on Alginate and Chitosan

New biobased hydrogels were prepared via a semi-interpenetrating polymer network (semi-IPN) using polyacrylamide/chitosan (PAAM/chitosan) hydrogel for the adsorption of As(V) or poly acrylic acid/alginate (PAA/alginate) hydrogel for the adsorption of Cu(II). Both systems were crosslinked using N,N'-methylenebisacrylamide as the crosslinker and ammonium persulfate as the initiating agent. The hydrogels were characterized by SEM, Z-potential, and FTIR. Their performance was studied under different variables, such as the biopolymer effect, adsorbent dose, pH, contact time, and concentration of metal ions. The characterization of hydrogels revealed the morphology of the material, with and without biopolymers. In both cases, the added biopolymer provided porosity and cavities' formation, which improved the removal capacity. The Z-potential informed the surface charge of hydrogels, and the addition of biopolymers modified it, which explains the further metal removal ability. The FTIR spectra showed the functional groups of the hydrogels, confirming its chemical structure. In addition, the adsorption results showed that PAAM/chitosan can efficiently remove arsenic, reaching a capacity of 17.8 mg/g at pH 5.0, and it can also be regenerated by HNO3 for six cycles. On the other hand, copper-ion absorption was studied on PAA/alginate, which can remove with an adsorption capacity of 63.59 mg/g at pH 4.0, and the results indicate that it can also be regenerated by HNO3 for five cycles.

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.

Single evaluation and selection of functional groups containing N or O atoms to heavy metal adsorption: Law of electric neutrality

Adsorption capacities and characteristics of heavy metal adsorbents have been investigated thoroughly, but the essential functional groups to bind heavy metal pollutants in composites have not been identified and confirmed separately. Previous researches reported that -OH, -NH₂, -CONH₂ or their protonation had binding effects to heavy metals. However, these descriptions were all based on the complex composites. The composites were consisted of different functional groups. Thus, this article aims to evaluate and discuss (1) the adsorption properties of different functional groups containing N or O atoms, (2) the protonation of groups containing N atoms, (3) the basis properties of adsorbents related to adsorption, (4) the physical adsorption by network structure. By a series of single evaluations, the results showed that the hydrophobic ester group (R₁-COO-R₂), non-ionic groups, including -OH, -NH₂, -CONH₂, ether (C-O-C), CO, tertiary amine (R3N), and protonation of -NH₂ and R3N, had no interaction with metals. Only negative groups, such as -COO^-, -SO₃^-, could adsorb cationic heavy metals. And positive -N(CH₃)₃⁺ group could bind with Cr₂O₇^2-. Furthermore, these conclusions have been verified by the law of electric neutrality in the heavy metal solutions and solid adsorbents. This study determined that the combining process between negative functional groups and cationic metals, or between positive groups and anionic metals, can be applied to decrease the heavy metal concentration.

Preparation of Poly(acrylic acid-acrylamide/starch) Composite and Its Adsorption Properties for Mercury (II)

The poly(acrylic acid-acrylamide/starch) composite was synthesized by solution polymerization, aiming to adsorb mercury (II) in water. The resulted copolymer was characterized by particle size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscopy (SEM) and dynamic light scattering particle size analyzer (DLS). It turned out that starch was successfully incorporated with the macromolecular polymer matrix and played a key role for improving the performance of the composites. These characterization results showed that the graft copolymer exhibited narrow molecular weight distribution, rough but uniform morphology, good thermal stability and narrow particle size distribution. The graft copolymer was used to remove Hg(II) ions from aqueous solution. The effects of contact time, pH value, initial mercury (II) concentration and temperature on the adsorption capacity of Hg(II) ions were researched. It was found that after 120 min of interaction, poly(acrylic acid-acrylamide/starch) composite achieved the maximum adsorption capacity of 19.23 mg·g⁻¹ to Hg(II) ions with initial concentration of 15 mg·L⁻¹, pH of 5.5 at 45 °C. Compared with other studies with the same purpose, the composites synthesized in this study present high adsorption properties for Hg(II) ion in dilute solution. The adsorption kinetics of Hg(II) on the poly(acrylic acid-acrylamide/starch) composite fits well with the pseudo second order model.

A Review on the Synthesis, Characterization, and Modeling of Polymer Grafting

A critical review on the synthesis, characterization, and modeling of polymer grafting is presented. Although the motivation stemmed from grafting synthetic polymers onto lignocellulosic biopolymers, a comprehensive overview is also provided on the chemical grafting, characterization, and processing of grafted materials of different types, including synthetic backbones. Although polymer grafting has been studied for many decades—and so has the modeling of polymer branching and crosslinking for that matter, thereby reaching a good level of understanding in order to describe existing branching/crosslinking systems—polymer grafting has remained behind in modeling efforts. Areas of opportunity for further study are suggested within this review.

Recent trends in the application of modified starch in the adsorption of heavy metals from water: A review

The presence of polyfunctional ligands on the bio-macromolecules acts as an efficient adsorbent for heavy metal ions. Starch is one of the most abundant, easily available and cheap biopolymer of plant origin. However, native starch exhibits significantly low adsorption capacity due to the absence of some essential functional groups like carboxyl, amino or ester groups and is thus modified using various reaction routes like grafting, cross-linking, esterification, oxidation and irradiation for addition of functional groups to increase its adsorption capacity. The present review provides a comprehensive discussion on the above mentioned modification schemes of starch over the last 10-15 years highlighting their preparation methods, physico-chemical characteristics along with their adsorption capacities and mechanisms of heavy metal ions from water.