Activated carbon embedded alginate beads for removing nonsteroidal anti-inflammatory drug naproxen from wastewater: equilibrium, kinetics, thermodynamics, desorption, and reusability

Green magnetic carbon/alginate biocomposite beads from iron scrap waste for efficient removal of textile dye and heavy metal

The circular economy can help enhance the value of industrial waste and remediate the environment. This study considers the application of iron scrap from steel production as a free resource to produce magnetic adsorbent beads to remove methylene blue dye and lead (II) ions from wastewater. Composite beads were prepared by incorporating iron scrap and activated carbon into a calcium alginate gel using a simple 'mix and drop' synthesis. The optimized magnetic beads were stable and offered a large specific surface area. The maximum adsorption capacity of the adsorbent, calculated from the Langmuir isotherm model, was 476.19 mg g-1 for methylene blue and 163.93 mg g-1 for lead (II) ions. This study places emphasis upon the zero-waste principle and employs a scalable synthetic approach for the conversion of waste iron scrap into an adsorbent material capable of delivering significant environmental benefits.

Chitosan-Supported ZnO Nanoparticles: Their Green Synthesis, Characterization, and Application for the Removal of Pyridoxine HCl (Vitamin B6) from Aqueous Media

A composite of chitosan-supported ZnO nanoparticles (ZnO/CS) was green-synthesized via an easy and cost-effective method using Chicory (Cichorium intybus) plant extract. The synthesis was confirmed using uv-vis spectrometry at a λmax of 380 nm, and the surface of the material was characterized via FT-IR spectroscopy, and finally via SEM, which confirmed the distribution of ZnO nanoparticles on the surface of chitosan biopolymer (CS). The synthesized material was applied in the adsorptive removal of residues of the pyridoxine hydrochloride (vitamin B6) pharmaceutical drug from aqueous media using the batch technique. The material's removal capacity was studied through several adjustable parameters including pH, contact time, the dose of the adsorbent, and the capacity for drug adsorption under the optimal conditions. Langmuir and Freundlich isotherms were applied to describe the adsorption process. The removal was found to obey the Freundlich model, which refers to a chemisorption process. Different kinetic models were also studied for the removal process and showed that the pseudo-second-order model was more fitted, which indicates that the removal was a chemisorption process. Thermodynamic studies were also carried out. The maximum removal of vitamin B6 by the nano-ZnO/CS composite was found to be 75% at optimal conditions. The results were compared to other reported adsorbents. Reusability tests showed that the nano-ZnO/CS composite can be efficiently reused up to seven times for the removal of PDX drugs from aqueous media.

Reswellable alginate/activated carbon/carboxymethyl cellulose hydrogel beads for ibuprofen adsorption from aqueous solutions

In this study, alginate (Alg) composite beads were prepared by blending with activated carbon (AC) to enhance adsorption capacity for ibuprofen and carboxymethyl cellulose (CMC) to create a reswellable hydrogel. The dried Alg/AC/CMC composite beads could be recovered to sizes and morphologies similar to the initial hydrogel states via a simple reswelling process; however, the dried Alg/AC composite beads without CMC could not be recovered to the initial hydrogel state. Following the reswelling process, the dried Alg/AC/CMC beads demonstrated an 86 % recovery (qe = 34.0 mg/g) in the adsorption capacity for ibuprofen compared to the initial hydrogel beads (qe = 39.6). In contrast, the reswelled Alg/AC beads exhibited only 18 % (qe = 8.6) of the initial adsorption capacity (qe = 48.1). We elucidated the effects of the substitution degree of CMC, AC content, and solution pH on the reswelling property and ibuprofen adsorption capacity of the Alg/AC/CMC composite beads. The adsorption kinetics and isotherms of the prepared composite beads in the hydrogel and reswelled states fit the pseudo-second-order and Langmuir models, respectively. Furthermore, the reswelled Alg composite beads exhibited high adsorption capacity (>93 %) after 10 cycles. Taken together, our findings indicate that the Alg/AC/CMC composite beads can be used as adsorbents without a considerable decrease in adsorption performance by reswelling the beads with distilled water after long-term storage in a dry state.

Removal of pharmaceuticals from aqueous medium by alginate/polypyrrole/ZnFe2O4 beads via magnetic field enhanced adsorption

The physicochemical and structural characteristics of the magnetic materials can be modulable due to exposition to a magnetic field, which allows, for example, to enhance its adsorption performance. In this sense, this study describes the preparation of magnetic beads of alginate/polypyrrole/ZnFe₂O₄ (Alg/PPy/ZnFe₂O₄) and investigates the effect of an external magnetic field (EMF) on their adsorption performance towards two overconsumed drugs, acetaminophen (ACT) and ibuprofen (IBU). Characterization analyses confirmed the composite formation and magnetic nature of Alg/PPy/ZnFe₂O₄. Conversely to the pristine beads (Alg/PPy), the presence of an EMF altered the swelling and pH_PZC behavior of the magnetic beads, indicating that these properties are affected by this external stimulus. Batch experiments revealed that the amount of ACT and IBU adsorbed by Alg/PPy/ZnFe₂O₄ in 60-70 min is appreciably high (106.7 ad 108.2 mg/g). The presence of an EMF modulated the structure of Alg/PPy/ZnFe₂O₄ beads enhancing their adsorption capacity towards ACT and IBU by 14% and 12% compared to Alg/PPy. Kinetic analysis revealed that the adsorption of both drugs on Alg/PPy/ZnFe2O4 followed a pseudo-second-order. Besides, the adsorption mechanism was fitted by the Freundlich isotherm. Reuse experiments showed that the magnetic beads keep a high adsorption capacity for both drugs even after ten consecutive reuse cycles. The results presented here suggest that magnetic-responsive materials like Alg/PPy/ZnFe₂O₄ are prominent and modulable tools for improving the treatment of water/wastewater containing this class of contaminants.

Removal of naproxen from wastewater using chitosan-aerogel-activated carbon biocomposites: Theory, equilibrium, kinetics, thermodynamics, and process optimization

This study investigated the performance of chitosan-aerogel-activated carbon (CHT:AEO:AC) biocomposite as an adsorbent for the removal of naproxen from wastewater. Naproxen removal in % was 99, 33, 62, and 90 using 300 mg of raw AC, raw CHT, CHT:AEO, and CHT:AEO:AC, respectively. Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Temkin isotherm models were used to obtain adsorption isotherms. Chi-squared (χ2) and correlation coefficients (R2) values showed that the parameters of the Freundlich, Temkin, and D-R models were more suitable for naproxen adsorption than the Langmuir model for raw CHT, CHT:AEO, and CHT:AEO:AC, whereas the Langmuir model fitted well for raw AC. The adsorption of naproxen onto biocomposites was defined by pseudo-second-order kinetic model, and adsorption rate constants were 0.245, 0.036, 0.075, and 0.147 mg g-1 min-1 for raw AC, raw CHT, CHT:AEO, and CHT:AEO:AC, respectively. The impact of optimum process conditions on naproxen adsorption was explored using response surface methodology. The optimum independent variables were 288.94 mg, 29.64°C, and 372.5 min, leading to a rate of naproxen removal onto CHT:AEO:AC of 90.29%. PRACTITIONER POINTS: Naproxen adsorption from wastewater using chitosan-aerogel-activated carbon biocomposite (CHT:AEO:AC) was investigated. The effects of the amount of biocomposite, temperature, and time on the adsorption were investigated. Optimization of the process conditions was carried out using the response surface methodology.