Removal of heavy metals by homolytically functionalized poly(acrylic acid) with hydroquinone

Design and synthesis of a new recyclable nanohydrogel based on chitosan for Deltamethrin removal from aqueous solutions: Optimization and modeling by RSM-ANN

In this study, a new magnetic biocompatible hydrogel was synthesized as an adsorbent for Deltamethrin pesticide removal. The optimal conditions and adsorption process of Deltamethrin by chitosan/polyacrylic acid/Fe3O4 nanocomposite hydrogel was studied by Response Surface Methodology by Central Composite Design (RSM-CCD) and Artificial Neural Network (ANN). This adsorbents were synthesized, and then characterized and investigated using FT-IR, XRD, FE-SEM, EDX, Map, VSM, and TGA methods. The results of these analyses showed that the nanocomposite hydrogel was well synthesized and has the ability to adsorb the Deltamethrin pesticide. The results obtained through analysis using response surface methodology showed that the maximum amount of adsorption was 99.79 % at 26 °C, while pH, initial concentration, contact time, and adsorbent dose were 7, 22 ppm, 90 min, and 1.3 g/L respectively. Comparison between results obtained from CCD modeling and artificial neural network proved that both methods had high ability to predict the adsorption process but the CCD method had higher coefficient of determination and lower error. The equilibrium and kinetic study of the process showed that the Toth isotherm model, pseudo-second-order is all suitable for expressing the adsorption process. In addition, the adsorption mechanism followed double-exponential model that combines external and internal diffusions. Results of Thermodynamic study suggested that the Deltamethrin adsorption on CS/PAA/Fe3O4 was a spontaneous and exothermic process. The results of the equilibrium process study revealed that the adsorption process was physical and desirable, therefore, the adsorption-desorption process was performed which showed that the composite was reusable up to 10 cycles.

Magnetic cobalt nanoparticles embedded in a carbonaceous hydrogel for the activation of peroxymonosulfate to degrade azo dyes and organic pollutants

Heterogeneous cobalt-based catalysts have recently gained attention as persulfate activators to degrade dyes and organic pollutants in sulfate radical-based advanced oxidation processes (SR-AOPs). This study fabricated magnetic cobalt nanoparticles embedded in a carbonaceous hydrogel (Co@C) using high-temperature pyrolysis of the Co2+-embedded chitosan-graft-poly(acrylic acid) (Co2+-embedded CTS-g-PAA) hydrogel. Subsequently, the prepared Co@C was evaluated as a peroxymonosulfate (PMS) activator for degrading azo dyes. The catalyst showed the highest performance toward reactive red 141 (RR141) than Congo red, methyl orange, direct yellow 50, and reactive black 5. RR141 was completely degraded within 10 min, with a 3.20 min-1 pseudo-first-order rate constant. The degradation rate increased with higher catalyst dosage, PMS dosage, and temperature. The pH of the solution had a minimal effect on the degradation of RR141, indicating that the catalyst could be effective across a wide pH range. Moreover, the quenching experiment and the electron paramagnetic resonance analysis indicated that the catalytic system generated SO4•-, HO•, O2•-, and 1O2. The RR141 degradation was slightly affected by Cl-, NO3-, and SO42-. The catalyst demonstrated high efficiencies in real water samples. The catalyst could be easily recovered using a magnet and reused for ten cycles with only a 10% degradation efficiency loss. Furthermore, the catalyst could effectively degrade other organic pollutants, including tetracycline and 4-nitrophenol. This study demonstrates that the Co@C catalyst can effectively purify wastewater via SR-AOPs.

Hyperconfined bio-inspired Polymers in Integrative Flow-Through Systems for Highly Selective Removal of Heavy Metal Ions

Access to clean water, hygiene, and sanitation is becoming an increasingly pressing global demand, particularly owing to rapid population growth and urbanization. Phytoremediation utilizes a highly conserved phytochelatin in plants, which captures hazardous heavy metal ions from aquatic environments and sequesters them in vacuoles. Herein, we report the design of phytochelatin-inspired copolymers containing carboxylate and thiolate moieties. Titration calorimetry results indicate that the coexistence of both moieties is essential for the excellent Cd2+ ion-capturing capacity of the copolymers. The obtained dissociation constant, KD ~ 1 nM for Cd2+ ion, is four-to-five orders of magnitude higher than that for peptides mimicking the sequence of endogenous phytochelatin. Furthermore, infrared and nuclear magnetic resonance spectroscopy results unravel the mechanism underlying complex formation at the molecular level. The grafting of 0.1 g bio-inspired copolymers onto silica microparticles and cellulose membranes helps concentrate the copolymer-coated microparticles in ≈3 mL volume to remove Cd2+ ions from 0.3 L of water within 1 h to the drinking water level (<0.03 µM). The obtained results suggest that hyperconfinement of bio-inspired polymers in flow-through systems can be applied for the highly selective removal of harmful contaminants from the environmental water.

Co2+-adsorbed chitosan-grafted-poly(acrylic acid) hydrogel as peroxymonosulfate activator for effective dye degradation

In this work, chitosan-grafted-poly(acrylic acid) (CS-g-PAA) was synthesized for use as a Co2+ adsorbent and circularly utilized as a peroxymonosulfate (PMS) activator in the degradation of rhodamine B (RhB) dye. CS-g-PAA demonstrated 3.7 times higher adsorption capacity toward Co2+ than pristine chitosan. The impact of the adsorption conditions was evaluated. The pseudo-second-order kinetic model and the Langmuir isotherm model best described the adsorption process. Under optimum conditions, the adsorption capacity of CS-g-PAA for Co2+ was 212 mg/g. The Co2+-adsorbed CS-g-PAA hydrogel was further utilized in the RhB degradation process. The effects of catalyst dosage, initial RhB concentration, pH, and the coexistence of anions on the degradation of RhB were studied. The hydrogel catalyst could remove 98 % of RhB within 5 min, at a degradation rate of 0.624 per min. Electron paramagnetic resonance (EPR) analysis and the radical scavenger experiment suggested that SO4•-, HO•, 1O2, and O2•- were involved in the degradation. Furthermore, when tested in various water systems, high degradation efficiencies of 98 % were attained after 20 min. The hydrogel catalyst performed excellent degradation over ten cycles without any chemical recovery processes. Moreover, high degradation efficiencies were observed between 95 % and 98 % when tested with other dyes.

Determination of breast cancer biomarkers with poly acrylic acid/ MIL-88(Fe)-NH2 hydrogel as a coating for stir bar sorptive extraction

The Poly acrylic acid/MIL-88(Fe)-NH2 composite material, carefully prepared, is employed as a sorbent for the stir bar. The best formula of the composite was selected by investigation of two parameters including the cross-linker of PAA and MIL-88(Fe)-NH2 content. The prepared stir bar was used for extraction of 2-pentanone, 2-heptanone, ethyl propionate, para-xylene, 1,2,4-trimethylbenzene, o-cresol, m-cresol in urine samples as breast cancer biomarkers with gas chromatography-flame ionization detector. The prepared Poly acrylic acid / MIL-88(Fe)-NH2 as sorbent for the stir bar demonstrate good repeatability of one bar (relative standard deviation (RSD%) < 4.61 %) and satisfactory reproducibility between two bars (RSD% < 6.85 %). The central composite design method was applied for the optimization of extraction parameters. Under the optimum conditions, linear dynamic ranges for compounds were in the acceptable range with correlation coefficients higher than 0.99. Detection limits of them were less than 1.71 µg L-1.

Poly(acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-grafted chitosan hydrogels for effective adsorption and photocatalytic degradation of dyes

As a result of the growth of industrialization and urbanization, the water ecosystem is contaminated by various pollutants, including heavy metal ions and dyes. The use of low-cost and environmentally friendly dye adsorbents has been investigated. A hydrogel was fabricated via graft polymerization of acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto chitosan. The hydrogel was used as a dye adsorbent and support for a zinc oxide (ZnO) powder photocatalyst. The adsorption capacity of the bare hydrogel was greater towards cationic dyes than anionic dyes. Grafting P(AA-co-AMPS) exhibited a 23-time increase in adsorption capacity towards crystal violet (CV) compared to pristine chitosan. The effect of the AA-AMPS molar ratio on CV adsorption was studied. A hydrogel with an AA-AMPS ratio of 10 : 1 had the highest adsorption capacity towards CV in water, removing 91% of the dye in 12 h. The maximum adsorption capacity was 2023 mg g-1. The adsorption kinetics and isotherm were described by the pseudo-second-order model and the Langmuir model, respectively. ZnO particles were in situ synthesized within the 10 : 1 hydrogel to facilitate the recovery of the photocatalyst. The ZnO hydrogel composite could remove 95% and 92% of CV from solutions on the 1st and 2nd cycle, respectively. In addition, the hydrogel composite containing only 8.7 wt% of ZnO particles effectively degraded adsorbed CV under sunlight and could be reused without requiring a chemical regeneration or photocatalyst recovery procedure. This hydrogel composite is an effective dual-functional material for the adsorption and photodegradation of dye pollutants in wastewater.

Benchmarking the Effect of Particle Size on Silicon Anode Materials for Lithium-Ion Batteries

High-capacity silicon has been regarded as one of the most promising anodes for high-energy lithium-ion batteries. However, it suffers from severe volume expansion, particle pulverization, and repeated solid electrolyte interphase (SEI) growth, which leads to rapid electrochemical failure, while the particle size also plays key role here and its effects remain elusive. In this paper, through multiple-physical, chemical, and synchrotron-based characterizations, the evolutions of the composition, structure, morphology, and surface chemistry of silicon anodes with the particle size ranging from 50 to 5 µm upon cycling are benchmarked, which greatly link to their electrochemical failure discrepancies. It is found that the nano- and micro-silicon anodes undergo similar crystal to amorphous phase transition, but quite different composition transition upon de-/lithiation; at the same time, the nano- and 1 µm-silicon samples present obviously different mechanochemical behaviors from the 5 µm-silicon sample, such as electrode crack, particle pulverization/crack as well as volume expansion; in addition, the micro-silicon samples possess much thinner SEI layer than the nano-silicon samples upon cycling, and also differences in SEI compositions. It is hoped this comprehensive study and understanding should offer critical insights into the exclusive and customized modification strategies to diverse silicon anodes ranging from nano to microscale.

A green approach for preparation of polyacrylic acid/starch incorporated with titanium dioxide nanocomposite as a biocompatible platform for curcumin delivery to breast cancer cells

Curcumin (Cur) is a polyphenolic hydrophobic molecule with several biological uses, including cancer therapy. However, its widespread use in cancer treatment faces limitations due to its low solubility in acidic and neutral conditions, rapid removal from the circulatory system, and poor bioavailability. In order to overcome these challenges, a biocompatible and pH-sensitive carrier nanoplatform was designed for the specific delivery of curcumin to breast cancer cells. This nanocomposite containing polyacrylic acid (PAA), starch, and titanium dioxide (TiO₂) was synthesized with a specific morphology through the water-in-oil-in-water green emulsification strategy. The nanocomposite structure was confirmed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential, and field-emission scanning electrom microscopy (FE-SEM) imaging tests. The mean particle size of 151 nm for the PAA-Starch-TiO₂ nanocomposite ensures specific entry into cancer cells and minimal damage to healthy cells. Loading efficiency (LE) and encapsulation efficiency (EE) for curcumin obtained 49.50 % and 87.25 %, which are desirable for a carrier nanoplatform. Compared to the physiological medium, the in-vitro release of curcumin was higher in the acidic conditions in all time intervals, which indicates the possibility of targeted drug release from the PAA-Starch-TiO₂ nanocomposite around the tumor tissue. Furthermore, for better understanding of the release mechanism, the cumulative release data in both media were fitted with common mathematical kinetic models. Cytotoxicity tests against the MCF-7 cell line were performed using in vitro MTT and flow cytometry tests. The results showed that the PAA-Starch-TiO₂ carrying Cur was more effective through increasing the bioavailability and controlled release of the drug compared to the free Cur. Also, the death of cancer cells in the presence of this nanocomposite compared to free Cur occurred mainly through the induction of apoptosis, which indicates the programmed death of cancer cells and the high efficiency of the designed nanocarrier.

Synthesis and Post-Processing of Chemically Homogeneous Nanothreads from 2,5-Furandicarboxylic Acid

Compared with conventional, solution-phase approaches, solid-state reaction methods can provide unique access to novel synthetic targets. Nanothreads-one-dimensional diamondoid polymers formed through the compression of small molecules-represent a new class of materials produced via solid-state reactions, however, the formation of chemically homogeneous products with targeted functionalization represents a persistent challenge. Through careful consideration of molecular precursor stacking geometry and functionalization, we report here the scalable synthesis of chemically homogeneous, functionalized nanothreads through the solid-state polymerization of 2,5-furandicarboxylic acid. The resulting product possesses high-density, pendant carboxyl functionalization along both sides of the backbone, enabling new opportunities for the post-synthetic processing and chemical modification of nanothread materials applicable to a broad range of potential applications.

Fabrication of a new SPME fiber based on Polyacrylic acid/ MIL-88(Fe)-NH2 composite as a self-healing coating for the analysis of breast cancer biomarkers in the urine sample

Analysis of cancer biomarkers in the body fluids is a new method for early detection of illness. However, due to the complex matrices of samples, the application of a pre-treatment method is unavoidable before the final analysis by gas chromatography (GC). Solid-phase microextraction (SPME) is a simple and, promising pre-concentration and separation method that its coatings are modified with different materials on the fibers. A new innovative self-healing polyacrylic acid PAA/MIL-88(Fe)-NH₂ composite was synthesized as an SPME coating. The parameters including pH, crosslinker, and MIL-88(Fe)-NH₂ content were optimized to formulate the composite. The prepared fiber was used to extract 2-pentanone, 2-heptanone, ethyl propionate, p-xylene, 1,2,4-trimethylbenzene, and o-cresol as a biomarker in breast cancer from urine samples. The prepared PAA/MIL-88(Fe)-NH₂ SPME fibers demonstrate excellent repeatability (relative standard deviation (RSD%)< 3.4%) and satisfactory reproducibility (RSD%<6.9%). The central composite design method was applied for the optimization of extraction parameters. Under the optimum conditions, linear dynamic ranges for biomarkers were in the acceptable range with correlation coefficients higher than 0.98. The detection limits of them were less down 0.0016 µg L^-1. Self-healing ability of fiber coating increased useful lifetime (about 120 times extraction with one fiber) as well as accuracy, reproducibility, and recovery of fibers.

Thermally Conductive and Superhydrophobic Polyurethane Sponge for Solar-Assisted Separation of High-Viscosity Crude Oil from Water

The rapid and effective separation of high-viscosity heavy crude oil from seawater is a worldwide challenge. Herein, an ultralow density, photothermal, superhydrophobic, and thermally conductive polyurethane/polyaniline/hexagonal boron nitride@Fe₃O₄/polyacrylic-oleic acid resin sponge (PU/PANI/h-BN@Fe₃O₄/AR) was fabricated with a water contact angle (WCA) of 158°, thermal conductivity of 0.76 W m^-1 K^-1, density of 0.038 g cm^-3, limited oxygen index (LOI) of 28.82%, and porosity of 97.97% and used for solar-assisted separation of high-viscosity crude oil from water. Photothermal components were composed of PANI and Fe₃O₄, while h-BN particles were used as thermally conductive and flame retardant fillers. Therefore, the illuminated sunlight irradiation on the modified sponge was converted to heat due to the activity of photothermal components. The produced heat was rapidly transferred to the environment due to the presence of h-BN for increasing the temperature of the high-viscosity crude oil and reducing oil viscosity that helped to promote its fluidity and effective absorption. The crude oil absorption capacity of this sponge increased from 4 to 57 g g^-1 under irradiation of a sunlight simulator (power: 1 sun: 1 kW m^-2) for 17 min due to oil viscosity reduction from 2.46 × 10⁴ to below 100 mPa s followed by an increase in the surface temperature from 26 to 89 °C. Also, the oil absorption capacity was evaluated in a static state (172 g g^-1 for chloroform), under different external magnetic fields (140.7 g g^-1 for gasoline), and in a continuous state, which was 65,100 times of its own weight in the gasoline filtration process. The PU/PANI/h-BN@Fe₃O₄/AR sponge exhibited excellent stability against 20 times of reusing, mechanical compression, abrasion, immersing in various pH solutions, seawater, and high temperature. In all, the results confirmed that the prepared sponge is an excellent absorbent for organic solvents and highly viscous crude oil in the absence and presence of sunlight irradiation.

Functionalization of PET Track-Etched Membranes by UV-Induced Graft (co)Polymerization for Detection of Heavy Metal Ions in Water

Nowadays, water quality monitoring is an essential task since environmental contamination and human exposure to heavy metals increased. Sensors that are able to detect ever lower concentrations of heavy metal ions with greater accuracy and speed are needed to effectively monitor water quality and prevent poisoning. This article shows studies of the modification of flexible track-etched membranes as the basis for the sensor with various polymers and their influence on the accuracy of detection of copper, cadmium, and lead ions in water. We report the UV-induced graft (co)polymerization of acrylic acid (AA) and 4-vinylpyridine (4-VPy) on poly(ethylene terephthalate) track-etched membrane (PET TeMs) and use them after platinum layer sputtering in square wave anodic stripping voltammetry (SW-ASV) for detection of Cu²⁺, Cd²⁺, and Pb²⁺. Optimal conditions leading to functionalization of the surface and retention of the pore structure were found. Modified membranes were characterized by SEM, FTIR, X-ray photoelectron spectroscopy (XPS) and colorimetric analysis. The dependence of the modification method on the sensitivity of the sensor was shown. Membrane modified with polyacrylic acid (PET TeMs-g-PAA), poly(4-vinylpyridine) (PET TeMs-g-P4VPy), and their copolymer (PET TeMs-g-P4VPy/PAA) with average grafting yield of 3% have been found to be sensitive to µg/L concentration of copper, lead, and cadmium ions. Limits of detection (LOD) for sensors based on PET TeMs-g-PAA are 2.22, 1.05, and 2.53 µg/L for Cu²⁺, Pb²⁺, and Cd²⁺, respectively. LODs for sensors based on PET TeMs-g-P4VPy are 5.23 µg/L (Cu²⁺), 1.78 µg/L (Pb²⁺), and 3.64 µg/L (Cd²⁺) µg/L. PET TeMs-g-P4VPy/PAA electrodes are found to be sensitive with LODs of 0.74 µg/L(Cu²⁺), 1.13 µg/L (Pb²⁺), and 2.07 µg/L(Cd²⁺). Thus, it was shown that the modification of membranes by copolymers with carboxylic and amino groups leads to more accurate detection of heavy metal ions, associated with the formation of more stable complexes.