Bisphenol-A-diglycidyl ether modified chitosan/nano-SiO2 via hydrothermal process: A statistical modeling and adsorption mechanism for reactive orange 16 dye removal

Preparation and characterization of oat hulls-filled-sodium alginate biocomposite microbeads for the effective adsorption of toxic methylene blue dye

In this work, the performance of oat hull-filled sodium alginate (SA-O) biocomposite microbeads in the adsorptive removal of methylene blue (MB) dye was examined. First, oat hulls were pulverized and biocomposite gels containing different weight ratios of oat hulls (10 %, 20 %, and 30 %, concerning the SA amount) were prepared by dispersing them in SA solution by ultrasonic homogenization method. Finally, gels were cross-linked by dropping into a 2 % CaCl2 solution. The study revealed that the optimal adsorbent dosage was 0.025 g/50 mL, pH was roughly 6-8, and the contact time was 120 min. According to isotherm models, the non-linear Sips and Langmuir model was more appropriate compare to other isotherms from error analysis, with a maximum adsorption capacity of 687.65 mg/g and 757.57 mg/g at 298 K, respectively. Furthermore, the non-linear kinetic data and error analyzes demonstrated that the process followed the pseudo-second-order kinetic. The adsorption process was exothermic (∆H°=-17.71 kJ/mol) and spontaneous (∆G°=-26.23 kJ/mol) at 298 K, based on thermodynamic characteristics. Furthermore, reusability investigations demonstrated that the adsorbent retained its performance with no major changes in characteristics. This work reveals that highly efficient, low-cost, sustainable, and eco-friendly SA-O composites with properties might be useful adsorbents for cationic dye adsorption.

One-step functionalization of chitosan with rich sulfur and nitrogen adsorption sites for efficient recovery of silver ions from actual wastewater

The recovery of silver ions from wastewater is of great importance due to their adverse environmental impact and significant economic value. This paper introduces a novel adsorbent (CS-AHMT) that can be easily synthesized via a one-step functionalization of chitosan with 4-Amino-3-hydrazino-1,2,4-triazol-5-thiol to efficiently recover silver ions from actual wastewater. CS-AHMT demonstrated superior adsorption performance, achieving an adsorption capacity of 241.4 mg·g-1 at pH 5 and 318 K, and the adsorption equilibrium was rapidly attained within 60 to 120 min. Kinetic and isotherm studies indicate that the adsorption process conforms to the pseudo-nth-order (PNO) and Sips models, suggesting a monolayer adsorption that incorporates both physical and chemical processes, with internal mass transfer being the primary rate-limiting step. Electrostatic and coordination interactions are primarily involved in the adsorption mechanism of silver ions on CS-AHMT, as further validated by density functional theory (DFT) calculations. The selectivity and practical applicability of CS-AHMT were confirmed in real wastewater containing high concentrations of competing ions. The findings underscore the potential of CS-AHMT as an effective adsorbent for silver ion recovery in wastewater treatment applications.

A novel sponge composite of chitosan-sodium tripolyphosphate-melamine for anionic dye Orange II removal

Since the potential carcinogenic, toxic and non-degradable dyes trigger serious environmental contamination by improper treatment, developing novel adsorbents remains a major challenge. A novel high efficiency and biopolymer-based environmental-friendly adsorbent, chitosan‑sodium tripolyphosphate-melamine sponge (CTS-STPP-MS) composite, was prepared for Orange II removing with chitosan as raw material, sodium tripolyphosphate as cross-linking agent. The composite was carefully characterized by SEM, EDS, FT-IR and XPS. The influence of crosslinking conditions, dosage, pH, initial concentration, contacting time and temperature on adsorption were tested through batch adsorption experiments. CTS-STPP-MS adsorption process was exothermic, spontaneous and agreed with Sips isotherm model accompanying the maximum adsorption capacity as 948 mg∙g-1 (pH = 3). Notably, the adsorption performance was outstanding for high concentration solutions, with a removal rate of 97 % in up to 2000 mg∙L-1 OII solution (100 mg sorbent dosage, 50 mL OII solution, pH = 3, 289.15 K). In addition, the adsorption efficiency yet remained 97.85 % after 5 repeated adsorption-desorption cycles. The driving force of adsorption was attributed to electrostatic attraction and hydrogen bonds which was proved by adsorption results coupled with XPS. Owing to the excellent properties of high-effective, environmental-friendly, easy to separate and regenerable, CTS-STPP-MS composite turned out to be a promising adsorbent in contamination treatment.

Crosslinked chitosan-montmorillonite composite and its magnetized counterpart for the removal of basic fuchsin from wastewater: Parametric optimization using Box-Behnken design

Treating wastewater polluted with organic dyestuffs is still a challenge. In that vein, facile synthesis of a structurally simple composite of chitosan with montmorillonite (CS-MMT) using glutaraldehyde as a crosslinker and the magnetized analogue (MAG@CS-MMT) was proposed as versatile adsorbents for the cationic dye, basic Fuchsin (FUS). Statistical modeling of the adsorption process was mediated using Box-Behnken (BB) design and by varying the composite dose, pH, [FUS], and contact time. Characterization of both composites showed an enhancement of surface features upon magnetization, substantiating a better FUS removal of the MAG@CS-MMT (%R = 98.43 %) compared to CS-MMT (%R = 68.02 %). The surface area analysis demonstrates that MAG@CS-MMT possesses a higher surface area, measuring 41.54 m2/g, and the surface analysis of the magnetized nanocomposite, conducted using FT-IR and Raman spectroscopies, proved the presence of FeO peaks. In the same context, adsorption of FUS onto MAG@CS-MMT fitted-well to the Langmuir isotherm model and the maximum adsorption capacities (qm) were 53.11 mg/g for CS-MMT and 88.34 mg/g for MAG@CS-MMT. Kinetics investigation shows that experimental data fitted well to the pseudo-second order (PSO) model. Regeneration study reveals that MAG@CS-MMT can be recovered effectively for repeated use with a high adsorption efficiency for FUS.

Facile synthesis of new metal-organic framework/chitosan composite sponge for Hg(II) removal: Characterization, adsorption efficiency, and optimization using Box-Behnken design

The objective of this research was to develop a novel adsorbent to eliminate mercury (Hg(II)) from water. A unique citrate-crosslinked La-MOF/citrate crosslinked chitosan composite sponge (La-MOF@CSC composite sponge) was successfully synthesized in an acidic environment using a one-step technique. Modifying the composition of adsorbent materials is a commonly employed strategy to enhance adsorption capacity, particularly for materials composed of metal-organic frameworks. The study investigated the impact of the composite sponge on the adsorption and removal of Hg(II). The composite sponge exhibited a maximum adsorption capacity (qmax) for Hg(II) at 765.22 mg/g and an impressive high surface area of 1208 m2/g. Various factors influencing the adsorption capacity were taken into account in this study. The adsorption isotherm and kinetics were modeled using Langmuir and pseudo-second-order equations, respectively. Consistent with thermodynamics, the adsorption process was identified as spontaneous and endothermic. The quantities of adsorbed substances increased with rising temperature. The La-MOF@CSC composite sponge demonstrated the ability to be reused up to five times with satisfactory efficiency, retaining its chemical composition and exhibiting similar XRD and XPS data before and after each reuse. The interaction between heavy metals and the La-MOF/CSC composite sponge was examined. Optimization of the adsorption outcomes was conducted using the Box-Behnken design (BBD).