Facile synthesis and characterization of γ-AlOOH/PVA composite granules for Cr(VI) adsorption

ZIF-67 grafted-boehmite-PVA composite membranes with enhanced removal efficiency towards Cr(VI) from aqueous solutions

In this work, we developed a thin membrane of boehmite-polyvinyl alcohol composite (BOPOM) (diameter ∼ 5 cm) grafted ZIF-67 combing sol-gel and in-situ growth methods. The fabricated materials were characterized using FT-IR, SEM, XRD, TGA, XPS, and N2 sorption techniques. Results indicate that ZIF-67 nanocrystals were well-grafted into the AlOOH-PVA matrix with reduced crystallite size. Furthermore, the decorated ZIF-67 offered additional porous structures and adsorption sites onto the membrane, enhancing their removal efficiency towards Cr6+ compared to the undecorated and pristine ZIF-67. At pH ∼5.5, the harvested ZIF-67/BOPOM exhibited the highest Cr6+ uptake capacity of ∼56.4 mg g-1. Kinetic studies showed that the chromium adsorption on the prepared materials obeyed the pseudo-second-order model, and the kinetic parameters followed the order ZIFF-67/BOPOM (0.020 mg g-1 min-1) > BOPOM (0.011 mg g-1 min-1) > ZIF-67 (0.006 mg g-1 min-1). Notably, the adsorption mechanism study revealed that adsorbed Cr6+ was reduced to Cr3+, and the reduction yield was boosted owing to grafting ZIF-67 into the BOPOM. In addition, the fabricated ZIF-67/BOPOM can simultaneously remove Cr6+ and methyl orange dye (MO) in the solution due to their synergetic effects on each other. Furthermore, the hybrid membrane ZIF-67/BOPOM showed a chromium removal efficiency of ∼78.2% after four successive adsorption-desorption cycles. This study indicates that grafting nanocrystals ZIF-67 onto the super-platform boehmite-PVA is a promising strategy to harvest an adsorbent with a high adsorption ability, cost-effectiveness, and reduced secondary pollution risks.

3D-Printed Chitosan-Based Hydrogels Loaded with Levofloxacin for Tissue Engineering Applications

Herein, we demonstrate the feasibility of a three-dimensional printed chitosan (CS)-poly(vinyl alcohol) (PVA)-gelatin (Gel) hydrogel incorporating the antimicrobial drug levofloxacin (LEV) as a potential tissue engineering scaffold. Hydrogels were prepared by physically cross-linking the polymers, and the printability of the prepared hydrogels was determined. The hydrogel with 3% w/v of CS, 3% w/v of PVA, and 2% w/v of Gel presented the best printability, producing smooth and uniform scaffolds. The integrity of 3D-printed scaffolds was improved via a neutralization process since after testing three different neutralized agents, i.e., NH3 vapors, EtOH/NaOH, and KOH solutions. It was proved that the CS/PVA/Gel hydrogel was formed by hydrogen bonds and remained amorphous in the 3D-printed structures. Drug loading studies confirmed the successful incorporation of LEV, and its in vitro release continued for 48 h. The cytotoxicity/cytocompatibility tests showed that all prepared scaffolds were cytocompatible.

Sustainable Microbial and Heavy Metal Reduction in Water Purification Systems Based on PVA/IC Nanofiber Membrane Doped with PANI/GO

Effective and efficient removal of both heavy metal pollutants and bacterial contamination from fresh water is an open issue, especially in developing countries. In this work, a novel eco-friendly functional composite for water treatment application was investigated. The composite consisted of electrospun nanofiber membrane from blended polyvinyl alcohol (PVA)/iota carrageenan (IC) polymers doped with equal concentrations of graphene oxide (GO) nanoparticles and polyaniline (PANI). The effectiveness of this composite as a water purification fixed-bed filter was optimized in a batch system for the removal of cadmium (Cd⁺²) and lead (Pb⁺²) ions, and additionally characterized for its antimicrobial and antifungal properties and cytotoxicity effect. The fiber nanocomposite exhibited efficient antibacterial activity, with maximum adsorption capacity of about 459 mg g⁻¹ after 120 min for Cd⁺² and of about 486 mg g⁻¹ after 90 min for Pb⁺². The optimized conditions for removal of both metals were assessed by using a response surface methodology model. The resulting scores at 25 °C were 91.4% (Cd⁺²) removal at 117 min contact time for 89.5 mg L⁻¹ of initial concentration and 29.6 cm² membrane area, and 97.19% (Pb⁺²) removal at contact time 105 min for 83.2 mg L⁻¹ of initial concentration and 30.9 cm² nanofiber composite membrane. Adsorption kinetics and isotherm followed a pseudo-second-order model and Langmuir and Freundlich isotherm model, respectively. The prepared membrane appears to be promising for possible use in domestic water purification systems.

Fabrication of nanofibers using sodium alginate and Poly(Vinyl alcohol) for the removal of Cd2+ ions from aqueous solutions: adsorption mechanism, kinetics and thermodynamics

Nowadays, separation of heavy metals from polluted wastewater is one of the most important environmental issues, and various methods have been investigated for treating polluted water and industrial wastewater. Surface adsorption using an inexpensive, biodegradable and environmentally consistent adsorbent can be considered an efficient and cost-effective method. One of these adsorbents is sodium alginate (SA). The purpose of this study was to fabricate composite nanofibers using poly (vinyl alcohol) (PVA) and sodium alginate to remove cadmium metal ion from aqueous solutions. For this purpose, polymer solutions consisting of poly (vinyl alcohol) (10% wt)/sodium alginate (2% wt) with three volume ratios of 0/100, 20/80 and 40/60 were first made, and then nanofibers were produced from the resulting solutions by electro-spinning process. The prepared nanofibers were examined by scanning electron microscopy (SEM) and the synthetic poly (vinyl alcohol)/sodium alginate nanofibers at a ratio of 40/60 were selected as adsorbent. The obtained nanofibers were characterized by Fourier-transform infrared spectroscopy (FTIR). The synthesized adsorbent was used to remove the aqueous solution of cadmium metal; the effect of various parameters such as changes in initial metal ion concentration, pH, temperature, contact time and stirring speed on the adsorption process were investigated, and optimum values of the parameters were obtained. The maximum amount of equilibrium adsorption under optimum experimental conditions was 67.05 mg/gr. The Taguchi experiment design method was used to optimize the three effective factors in the cadmium ion adsorption process. The results of the adsorption process were adapted to different adsorption isotherms such as Langmuir and Freundlich isotherms. The fit of the laboratory data to the Langmuir model was better, and the maximum adsorption capacity through this model was obtained equal to 93.163 mg/g of the adsorbent. Since the performance of an adsorbent depends on the duration of the adsorption process, the kinetics of the adsorption process were investigated by pseudo-first-order equation and pseudo-second-order equation. Moreover, the results indicated that the laboratory data showed a better fit to the pseudo-second-order model. Finally, the thermodynamic perspective was examined, and the process was found to be endothermic and spontaneous. The results showed the optimum values for maximum cadmium uptake.

High dispersions of nano zero valent iron supported on biochar by one-step carbothermal synthesis and its application in chromate removal

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution. High dispersions of nanoscale zero-valent iron supported on biochar were successfully synthesized by the pyrolysis of an iron-impregnated biomass (corn stover) as the carbon and iron source under nitrogen atmosphere. The effects of the pyrolytic temperature on the Fe mineralogies formed on the biochar are discussed. In general, the effects of the treatment time, initial solution pH, and nZVI/BC dosage on the Cr(vi) removal are presented. The results showed high crystallinity and purity, and nZVI/BC was obtained at a pyrolytic temperature of 800 °C. The batch experimental results determined that the adsorption capacity of Cr(vi) decreases with the increase in the initial pH value from 4.0 to 10.0. The Cr(vi) adsorption kinetics data effectively followed a pseudo-second-order kinetics with a calculated rate constant of 0.0.3396 g mg⁻¹ min⁻¹. The calculated thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were evaluated, and the results indicated that the Cr(vi) reduction on nZVI/BC was a spontaneous and endothermic process. The adsorption mechanism of Cr(vi) was investigated by XRD and XPS analyses and the results demonstrated that Cr(vi) was reduced to Cr(iii) and the oxidation of nZVI occurred during the reaction process. These results prove that nZVI/BC synthesized by a one-step carbothermal method can be considered as a potential candidate for the removal of Cr(vi) from aqueous solutions.

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution.

Adsorption of Cu(II) and Zn(II) Ions from Aqueous Solution by Gel/PVA-Modified Super-Paramagnetic Iron Oxide Nanoparticles

Super-paramagnetic iron oxide nanoparticles (SPIONs)/gelatin (gel)/polyvinyl alcohol (PVA) nanoparticles were designed and synthesized by the co-precipitation method and further modified with gel and PVA. These nanoparticles were used for the removal of Cu(II) and Zn(II) from aqueous solutions. The adsorbents were rich in different functional groups for chemisorption and showed effective adsorption properties. The adsorption of Cu(II) and Zn(II) on the SPIONs/gel and SPIONs/gel/PVA materials were investigated with respect to pH, adsorption kinetics, and adsorption isotherms. The adsorption data was fitted to the Langmuir, Freundlich, and Sips models at the optimum pH 5.2 (±0.2) over 60 min; SPIONs/gel showed maximum adsorption capacities of 47.594 mg/g and 40.559 mg/g for Cu(II) and Zn(II); SPIONs/gel/PVA showed those of 56.051 mg/g and 40.865 mg/g, respectively. The experimental data fitted the pseudo-second-order model, indicating that the process followed chemical monolayer adsorption. In addition, the SPIONs/gel/PVA showed better stability and Cu(II) adsorption efficiency than SPIONs/gel.

Silica based inorganic–organic hybrid materials for the adsorptive removal of chromium

We employed polymer functionalized silica gel as an adsorbent for the removal of Cr(vi) from water. The chains of 2-aminoethyl methacrylate hydrochloride (AEMA·HCl) polymer were grown from the surface of silica gel via surface-initiated conventional radical polymerization and the resulting hybrid material exhibited high affinity for chromium(vi). To investigate the adsorption behavior of Cr(vi) on diverse polymer based hybrid materials, the removal capacity of (SG-AEMH) was compared with our previously reported branched polyamine functionalized mesoporous silica (MS-PEI). The adsorption capacities of polymer based materials were also compared with their respective monolayer based platforms comprising a 3-aminopropyltriethoxysilane (APTES) functionalized silica gel (SG-APTES) and mesoporous silica (MS-APTES). The polymer based systems showed excellent Cr(vi) adsorption efficiencies compared to monolayer counterparts. The structural characteristics and surface modification of these adsorbents were examined by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The experimental data were analyzed using the Langmuir and Freundlich models. Correlation coefficients were determined by analyzing each isotherm. The kinetic data of adsorption reactions were described by pseudo-first-order and pseudo-second-order equations. Thermodynamic parameters, i.e., change in the free energy (ΔG°), the enthalpy (ΔH°), and the entropy (ΔS°), were also evaluated. The synthesized hybrid materials exhibited a high adsorption capacity for chromium ions. Furthermore, they could be regenerated and recycled effectively.

We employed and compared polymer functionalized silica gel and mesoporous silica as adsorbents for the removal of Cr(vi) from water.