Evaluation of thermodynamic parameters via reaction stoichiometry and the corrected Langmuir parameter for sorption of Cu(II) on chitosan and chitosan blended PVA films

Advances in sustainable food packaging applications of chitosan/polyvinyl alcohol blend films

Researchers are addressing environmental concerns related to petroleum-based plastic packaging by exploring biopolymers from natural sources, chemical synthesis, and microbial fermentation. Despite the potential of individual biopolymers, they often exhibit limitations like low water resistance and poor mechanical properties. Blending polymers emerges as a promising strategy to overcome these challenges, creating films with enhanced performance. This review focuses on recent advancements in chitosan/polyvinyl alcohol (PVA) blend food packaging films. It covers molecular structure, properties, strategies for performance improvement, and applications in food preservation. The blend's excellent compatibility and intermolecular interactions make it a promising candidate for biodegradable films. Future research should explore large-scale thermoplastic technologies and investigate the incorporation of additives like natural extracts and nanoparticles to enhance film properties. Chitosan/PVA blend films offer a sustainable alternative to petroleum-based plastic packaging, with potential applications in practical food preservation.

Facile Separation of Cu2+ from Water by Novel Sandwich NaY Zeolite Adsorptive Membrane

Polyethersulfone-sulfonated polyethersulfone (PES-SPES)/NaY zeolite/nylon sandwich structure membranes were prepared and used to adsorb Cu2+ from water. The adsorption kinetics, adsorption isotherm, dynamic adsorption experiment, and reusability were discussed. The experimental data showed that the Langmuir isotherm model, Dubinin–Radushkevich (D-R) isotherm model, and the pseudo-first-order kinetic model can well represent the adsorption of Cu2+ on the membrane, indicating an ion exchange mechanism, with the maximum adsorption capacity of 111.25 mg·g−1. Repeatability experiments show that the sandwich film still has good adsorption performance after five times of adsorption and desorption. The as-prepared membrane showed considerable separation performance in removing Cu2+ from aspirin solution, providing a feasible method to remove heavy metals from drugs.

Immobile Iron-Rich Particles Promote Arsenic Retention and Regulate Arsenic Biotransformation in Treatment Wetlands

Remediation of arsenic (As)-contaminated wastewater by treatment wetlands (TWs) remains a technological challenge due to the low As adsorption capacity of wetland substrates and the release of adsorbed As to pore water. This study investigated the feasibility of using immobile iron-rich particles (IIRP) to promote As retention and to regulate As biotransformation in TWs. Iron-rich particles prepared were immobilized in the interspace of a gravel substrate. TWs with IIRP amendment (IIRP-TWs) achieved a stable As removal efficiency of 63 ± 4% over 300 days, while no As removal or release was observed in TWs without IIRP after 180 days of continuous operation. IIRP amendment provided additional adsorption sites and increased the stability of adsorbed As due to the strong binding affinity between As and Fe oxides. Microbially mediated As(III) oxidation was intensified by iron-rich particles in the anaerobic bottom layer of IIRP-TWs. Myxococcus and Fimbriimonadaceae were identified as As(III) oxidizers. Further, metagenomic binning suggested that these two bacterial taxa may have the capability for anaerobic As(III) oxidation. Overall, this study demonstrated that abiotic and biotic effects of IIRP contribute to As retention in TWs and provided insights into the role of IIRP for the remediation of As contamination.

Elucidating the adsorption mechanism of Rhodamine B on mesoporous coconut coir-based biosorbents through a non-linear modeling and recycling approach

The search for renewable adsorbent materials has increased continuously, being the agro-wastes an interesting alternative. This work aimed to elucidate the mechanism of adsorption of Rhodamine B on crude and modified coconut fibers from aqueous systems and the feasibility of reusing the biosorbents. The chemical modification of crude coconut fiber was carried out by the organosolv process. The biosorbents were characterized by lignocellulosic composition, FTIR, TGA, WCA, SEM, nitrogen adsorption/desorption (BET-BJH), and pH of zero point of charge (pHPZC) analyses. The batch adsorption tests evaluated the effects of the adsorbent and adsorbate dosages, contact time, and temperature on Rhodamine B adsorption. For elucidating the adsorption mechanisms involved in the process, the non-linear forms of kinetic and isotherm models were used. The regeneration of the biosorbents was evaluated by carrying out the desorption experiments. Modified coconut fiber had an increase in the amount of α-cellulose, which influenced its structural, morphological, surface, and porous properties. The removal efficiency of Rhodamine B was about 90% for modified coconut fiber and 36% for crude coconut fiber. The dye adsorption was spontaneous and endothermic for both biosorbents, showing higher spontaneity and affinity with the adsorbate for biosorbent modified. Therefore, the coconut fiber can be considered an alternative to the traditional adsorbent materials that allows the reuse by four times without performance loss, in which its adsorptive capacity has increased through its chemical modification by a biorefinery process.

Synthesis of hybrid biosorbent based on 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and organo-functionalized calcium alginate for adsorptive removal of Cu(II)

The present study is based on the synthesis of a novel hybrid biosorbent using 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and amino-thiocarbamate moiety functionalized sodium alginate (CDTA-CS/TSC-CA). The fabricated sorbent was employed to investigate the efficient recovery of Cu(II) from aqueous media. CDTA-CS/TSC-CA was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Analysis confirmed the successful modification of both biopolymers and subsequent loading of Cu(II) ions. CDTA-CS/TSC-CA was casted in the form of hydrogel beads having different CDTA-CS to TSC-CA mass ratios i.e., 10.0-40.0% by mass. The hydrogel beads 4CDTA-CS/TSC-CA with CDTA-CS/TSC-CA mass ratio of 40.0% was found most effective for copper sorption. Equilibrium sorption results showed that initial concentration of copper, medium pH, contact time, sorbent dosage and temperature influenced the sorption capacity (q_e). Rate of sorption data was interpreted using different kinetic models and found best fitted with pseudo second order rate expression (R² ≈ 0.99), illustrating that the rate determining step includes the electron density transfer from sorbent coordination sites to central copper ions. Crank's RIDE equation and Elovich chemisorption model (ECM) revealed the presence of two sorption phases, initially rapid sorption followed by comparatively a slow uptake. Equilibrium sorption data was well depicted by Langmuir model and maximum monolayer adsorption capacity (q_m) was computed as 276.53 mg·g^-1 at 298 K. Standard Gibbs free energy change, ∆G° (-19.99, -20.18 and -20.36 kJ/ mol), standard enthalpy change, ∆H° (-8.95 kJmol) and standard entropy change, ∆S° (0.04 kJ/mol K^-1) values suggested that the adsorption process is spontaneous and exothermic. Hence, 4CDTA-CS/TSC-CA was found efficient biosorbent for copper removal from its dilute effluents.