Synthetically engineered chitosan-based materials and their sorption properties with methylene blue in aqueous solution

Hemp fibers modified with graphite oxide as green and efficient solution for water remediation: Application to methylene blue

In this paper, the use of hemp fibers modified with graphite oxide for the removal of methylene blue (MB) from aqueous solutions was investigated. Parameters such as contact time, pH, temperature, initial concentration of dye and ionic strength were varied and their effects on the adsorption recovery were evaluated. The adsorption process attained the equilibrium within 30 min while the adsorption capacity was found to increase with increasing contact time. The experimental data were fitted through a pseudo-second order model. Maximum adsorption capacity slightly increases with temperature changing from 54 mg/g to 58 mg/g at pH = 7.5, from 37 mg/g to 45 mg/g at pH = 3 and from 44 mg/g to 49 mg/g at pH = 12, by increasing the temperature from 20 °C to 80 °C indicating that the process is slightly endothermic (ΔH = 3.43 kJ/mol). The thermodynamic parameters were even calculated demonstrating that the process is spontaneous (ΔG ≈ -4.4 J/mol K and ΔS = 3.16 J/mol K)). Finally, a mathematical algorithm was applied to forecast the response surface model. A second order model was chosen to fit the experimental data and the statistical effect of the process parameters were estimated. A numerical optimization was even performed to individuate the optimal set of process parameters (pH = 9.25, T = 53.8 °C and C₀ = 13.2 mg/L) which maximizes the removal capacity. A possible adsorption mechanism was even presented. So, it was proved the efficiency of the adsorption of a novel, inexpensive and sustainable composite material obtained from agro-waste resources by performing reusability cycles.

Preparation and characterization of salicylic acid grafted chitosan electrospun fibers

Chitosan (chi) and its modified forms as electrospun nanofibers have potential applications in advanced water treatment and biomedicine. Polyethylene oxide (PEO) is an additive commonly used to facilitate the formation of chitosan electrospun fibers because PEO (Mw ≥ 400 kDa) affords chain entanglement that stabilize the electrospinning jet, leading to enhanced formation of chi-based electrospun fibers. Herein, we report on the preparation of chitosan grafted with salicylic acid and its utility to afford improved electrospun fibers with low molecular weight (LMw) PEO (Mw » 100 kDa). A comparison of the interactions between original and grafted chitosan with PEO reveals that stable supramolecular assemblies are established between grafted chitosan and PEO, which provides support that such supramolecular interactions favor formation of chitosan electrospun fibers. Moreover, a porous chitosan electrospun nanofiber was prepared through physical treatment that reveals notably higher (ca. 4-fold) dye uptake than the pristine (unmodified) chitosan electrospun nanofibers.

Chitosan-Poly(Acrylic Acid) Nanoparticles Loaded with R848 and MnCl2 Inhibit Melanoma via Regulating Macrophage Polarization and Dendritic Cell Maturation

Purpose

Since immune cells in the tumor microenvironment (TME) can affect the development and progression of tumors, strategies modulating immune cells are considered to have an important therapeutic effect. As a TLR7/8 agonist, R848 effectively activates the innate immune cells to exert an anti-tumor effect. Mn²⁺ has been reported to strongly promote the maturation of antigen-presenting cells (APCs), thereby enhancing the cytotoxicity of CD8⁺ T cells. Thus, we tried to investigate whether chitosan-poly(acrylic acid) nanoparticles (CS-PAA NPs) loaded with R848 and MnCl₂ (R-M@CS-PAA NPs) could exert an anti-tumor effect by regulating the function of immune cells.

Methods

R-M@CS-PAA NPs were prepared, and their basic characteristics, anti-tumor effect, and potential mechanisms were explored both in vitro and in vivo.

Results

R-M@CS-PAA NPs easily released MnCl₂ and R848 at low pH. In B16F10 mouse melanoma model, R-M@CS-PAA NPs exerted the most significant anti-melanoma effect compared with the control group and CS-PAA NPs loaded with R848 or MnCl₂ alone. FITC-labeled R-M@CS-PAA NPs were displayed to be accumulated at the tumor site. R-M@CS-PAA NPs significantly increased the infiltration of M1 macrophages and CD8⁺ T cells but reduced the number of suppressive immune cells in the TME. Moreover, in vitro experiments showed that R-M@CS-PAA NPs polarized macrophages into the M1 phenotype to inhibit the proliferation of B16F10 cells. R-M@CS-PAA NPs also enhanced the killing function of CD8⁺ T cells to B16F10 cells. Of note, R-M@CS-PAA NPs not only promoted the maturation of APCs such as dendritic cells and macrophages by STING and NF-кB pathways, but also enhanced the ability of dendritic cells to present ovalbumin to OT-I CD8⁺ T cells to enhance the cytotoxicity of OT-I CD8⁺ T cells to ovalbumin-expressing B16F10 cells.

Conclusion

These data indicate that the administration of R-M@CS-PAA NPs is an effective therapeutic strategy against melanoma.

Adsorption Studies of Waterborne Trihalomethanes Using Modified Polysaccharide Adsorbents

The adsorptive removal of trihalomethanes (THMs) from spiked water samples was evaluated with a series of modified polysaccharide adsorbents that contain β-cylodextrin or chitosan. The uptake properties of these biodegradable polymer adsorbents were evaluated with a mixture of THMs in aqueous solution. Gas chromatography employing a direct aqueous injection (DAI) method with electrolytic conductivity detection enabled quantification of THMs in water at 295 K and at pH 6.5. The adsorption isotherms for the polymer-THMs was evaluated using the Sips model, where the monolayer adsorption capacities ranged between 0.04 and 1.07 mmol THMs/g for respective component THMs. Unique adsorption characteristics were observed that vary according to the polymer structure, composition, and surface chemical properties. The modified polysaccharide adsorbents display variable molecular recognition and selectivity toward component THMs in the mixed systems according to the molecular size and polarizability of the adsorbates.

Facile fabrication of chitosan-based adsorbents for effective removal of cationic and anionic dyes from aqueous solutions

To develop chitosan-based adsorbents for the treatment of dye wastewater, poly acrylic acid (PAA) and poly acrylamide (PAM) were simultaneously grafted onto the chitosan (CTS) chain to obtain a grafted-crosslinked material g-CCTS, and then, Fe-g-CCTS was prepared via coordination of Fe(III) onto the prepared g-CCTS. Two adsorbents g-CCTS and Fe-g-CCTS were fully characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Nitrogen adsorption and desorption, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis. In adsorption experiment, g-CCTS exhibited effective adsorption towards cationic dye methylene blue (MB), and Fe-g-CCTS showed effective adsorption towards anionic dye reactive brilliant red (RBR). The effects of solution pH, salt concentration and temperature on the adsorption process were investigated. The maximum adsorption capacity of g-CCTS for MB was up to 79.09 mg/g at pH 12, and that of Fe-g-CCTS for RBR reached 918.53 mg/g at pH 2. It was observed that both adsorption processes were monolayer adsorption, and conformed to the pseudo-second-order model and the Langmuir isotherm model. This research provided a facile and accurate method for effective dyes removal from wastewater.

Uptake of Methylene Blue from Aqueous Solution by Pectin–Chitosan Binary Composites

To address the need to develop improved hybrid biopolymer composites, we report on the preparation of composites that contain chitosan and pectin biopolymers with tunable adsorption properties. Binary biopolymer composites were prepared at variable pectin–chitosan composition in a solvent directed synthesis, dimethyl sulfoxide (DMSO) versus water. The materials were characterized using complementary methods (infrared spectroscopy, thermal gravimetric analysis, pH at the point-of-zero charge, and dye-based adsorption isotherms). Pectin and chitosan composites prepared in DMSO yielded a covalent biopolymer framework (CBF), whereas a polyelectrolyte complex (PEC) was formed in water. The materials characterization provided support that cross-linking occurs between amine groups of chitosan and the –COOH groups of pectin. CBF-based composites had a greater uptake of methylene blue (MB) dye over the PEC-based composites. Composites prepared in DMSO were inferred to have secondary adsorption sites for enhanced MB uptake, as evidenced by a monolayer uptake capacity that exceeded the pectin–chitosan PECs by 1.5-fold. This work provides insight on the role of solvent-dependent cross-linking of pectin and chitosan biopolymers. Sonication-assisted reactions in DMSO favor CBFs, while cross-linking in water yields PECs. Herein, composites with tunable structures and variable physicochemical properties are demonstrated by their unique dye adsorption properties in aqueous media.

Graphene Oxide-Chitosan Composite Material for Treatment of a Model Dye Effluent

Graphene oxide (GO) was cross-linked with chitosan to yield a composite (GO-LCTS) with variable morphology, enhanced surface area, and notably high methylene blue (MB) adsorption capacity. The materials were structurally characterized using thermogravimetric analysis and spectroscopic methods (X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and 13C solid-state NMR) to support that cross-linking occurs between the amine groups of chitosan and the -COOH groups of GO. Equilibrium swelling studies provide support for the enhanced structural stability of GO-cross-linked materials over the synthetic precursors. Scanning electron microscopy studies reveal the enhanced surface area and variable morphology of the cross-linked GO materials, along with equilibrium and kinetic uptake results with MB dye in aqueous media, revealing greater uptake of GO-LCTS composites over pristine GO. The monolayer uptake capacity (Q m; mg g-1) with MB reveals twofold variation for Q m, where GO-LCTS (402.6 mg g-1) > GO (286.9 mg g-1). The kinetic uptake profiles of MB follow a pseudo-second-order trend, where the GO composite shows more rapid uptake over GO. This study reveals that the sorption properties of GO are markedly improved upon formation of a GO-chitosan composite. The facile cross-linking strategy of GO reveals that its physicochemical properties are tunable and versatile for a wider field of application for contaminant removal, especially over multiple adsorption-desorption cycles when compared against pristine GO in its highly dispersed nanoparticle form.

Characterization and differentiation of the adsorption behavior of crystal violet and methylene blue at the silica/water interface using near field evanescent wave

Different molecular structures lead to different adsorption performances. In this work, the adsorption behavior of two organic dyes, namely, crystal violet (CV, triphenylmethane dye of symmetric structure) and methylene blue (MB, azo dye of linear structure), were investigated, characterized and differentiated at the silica/water interface using the total internal reflection induced near field evanescent wave (TIR-NFEW) platform. According to the change in the evanescent wave intensity and following Beer's law, the adsorption behaviors of CV and MB can be monitored real time and sensitively. On one hand, the Langmuir adsorption model was applied to obtain the related thermodynamic data (including adsorption equilibrium constant (Kads) and adsorption free energy (ΔG)). With ΔG(MB) = -25.7 ± 1.7 kJ mol-1 < ΔG(CV) = -21.5 ± 0.6 kJ mol-1 < 0, the linear MB showed a higher spontaneous adsorption ability than the symmetric CV at the silica/water interface. On the other hand, a two-step adsorption kinetic model was applied to obtain the dynamics data including the linear adsorption rate constant (k1) and the exponential adsorption rate constant (k2). With k1(CV) < k1(MB) and k2(CV) ≈ k2(MB), MB diffused faster than CV at the first diffusion step but had nearly the same interaction speed as CV in the second adsorption step. A molecular-aligned-mechanism was successfully proposed to describe the interfacial interaction process for both CV and MB that includes molecular reactions involving electrostatic attraction of type I SiO- and H-bonds of type II SiOH. This work provides new insights into the molecular-level interpretation of the adsorption of the azo and triphenylmethane dyes at the silica-water interface.

Real-Time Monitoring of Azo Dye Interfacial Adsorption at Silica-Water Interface by Total Internal Reflection-Induced Surface Evanescent Wave

An interface research method based on total internal reflection induced evanescent wave (TIR-EW) is developed to monitor the adsorption behavior of azo dye at the silica-water interface. The monitoring system is constructed by employing silica optical fiber (SOF) as both charged substrate for dye adsorption and light transmission waveguide for evanescent wave production. According to the change of evanescent wave intensity and followed by Beer's law, the methylene blue (MB) adsorption behavior can be real-time monitored at the silica-water interface. Langmuir adsorption model and pseudo-first-order model are applied to obtain the related thermodynamic and kinetic data. The adsorption equilibrium constant ( K_ads) and adsorption free energy (Δ G) of MB at the silica-water interface are determined to be (3.3 ± 0.5) × 10⁴ M^-1 and -25.7 ± 1.7 kJ mol^-1. Meanwhile, this method is highlighted to isolate elementary processes of adsorption and desorption under steady-state conditions, and gives adsorption rate constant ( k_a) and desorption rate constant ( k_d) of 8585 ± 19.8 min^-1 and 0.26 ± 0.0006 min^-1 for 15 r/min flow rate. The surface interaction process is revealed and adsorption mechanism is proposed, indicating MB first adsorbed on Si-O^- sites through electrostatic attraction and then on Si-OH sites through hydrogen bond with increasing MB concentrations. Our findings from this study provided molecular-level interpretation of azo dye adsorption at silica-water interface, and the results provide important insight into how MB adsorption can be controlled at the interface.

Fast microwave-assisted green synthesis of xanthan gum grafted acrylic acid for enhanced methylene blue dye removal from aqueous solution

In the present project, graft polymerization was employed to synthesis a novel adsorbent using acrylic acid (AA) and xanthan gum (XG) for cationic methylene dye (MB⁺) removal from aqueous solution. The XG was rapidly grafted with acrylic acid (CH₂=CHCOOH) under microwave heating. Fourier-transform infrared spectroscopy (FTIR), Proton Nuclear magnetic resonance spectroscopy (¹H NMR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Thermal gravimetric analysis (TGA) techniques were used to verify the adsorbent formed under optimized reaction conditions. Optimum reaction conditions [AA (0.4M), APS (0.05M), XG (2gL^-1), MW power (100%), MW time (80s)] offer maximum %G and %GE of 484 and 78.3, respectively. The removal ratio of adsorbent to MB⁺ reached to 92.8% at 100mgL^-1. Equilibrium and kinetic adsorptions of dyes were better explained by the Langmuir isotherm and pseudo second-order kinetic model respectively. The results demonstrate xanthan gum grafted polyacrylic acid (mw XG-g-PAA) absorbent had the universality for removal of dyes through the chemical adsorption mechanism.

A recyclable and regenerable magnetic chitosan absorbent for dye uptake

A recyclable and regenerable magnetic polysaccharide absorbent for methylene blue (MB) removal was prepared by coating magnetic polyethyleneimine nanoparticles (PEI@MNPs) with sulfonated chitosan (SCS) and further cross-linked with glutaraldehyde. The driving force for coating is the electrostactic interaction between positively charged PEI and negatively charged SCS. Infrared spectra, zeta potential, thermal gravimetric analysis and X-ray diffraction demonstrated the successful synthesis of magnetic polysaccharide absorbent. The self-assembly of polysaccharide with magnetic nanopartices did not alter the saturation magnetization value of the absorbent confirmed by vibrating sample magnetometer. The nanoparticles showed fast removal (about 30min reached equilibrium) of MB. In particular, the removal ability of MB after desorption did not reduce, demonstrating an excellent regeneration ability. Our study provides new insights into utilizing polysaccharides for environmental remediation and creating advanced magnetic materials for various promising applications.

Biodegradable poly(butylene succinate-co-terephthalate) nanofibrous membranes functionalized with cyclodextrin polymer for effective methylene blue adsorption

PBST and PBST/CDP nanofibrous membranes were prepared for the first time. PBST/CDP membranes were fabricated by means of in situ polymerization. The morphologies of membranes were dependent on the CDP content. PBST/CDP membranes exhibited excellent adsorption capacity.

Design and characterization of chitosan-based composite particles with tunable interfacial properties

Composite nano-microparticles were prepared in aqueous solution that contain chitosan or modified (carboxymethyl) chitosan with polyanion species such as alginate or tripolyphosphate, respectively. Several types of particles were prepared and characterized by (1)H/(31)P NMR spectroscopy, IR spectroscopy, and DLS. According to DLS, the particle size was observed to increase as the concentration of the aqueous urea solution increased. The average size and polydispersity index (in parentheses) vary and are reported for the chitosan-based particles from 243.0 ± 1 nm (0.28) to 424 ± 14 nm (0.33), according to DLS measurements at ambient conditions. Thus, the particles are herein referred to as nano-microparticles (NMPs) due to the relative size range. The stability of the NMPs is related to the particle composition and the aqueous solution conditions, as evidenced by variable NMP stability on the order of two weeks or more at different ionic strength.

Synthesis of magnetic ZnO/ZnFe2O4 by a microwave combustion method, and its high rate of adsorption of methylene blue

The magnetic ZnO/ZnFe2O4 particles have been synthesized by a microwave combustion method using NaAc as fuel. The as-obtained ZnO/ZnFe2O4 was characterized and applied for the removal of methylene blue (MB) from aqueous solution in the batch system. The ZnO/ZnFe2O4 particles display larger S(BET) and smaller size with increase of NaAc dosage. Because a certain amount of gas is generated during NaAc decomposing and the gas prevent the particles from growing larger. More interestingly, even at neutral pH value, the ZnO/ZnFe2O4 obtained with 24 mL NaAc shows high-rate adsorption properties with the MB removal efficiency up to 90% in 0.5 min and a maximum adsorption capacity of 37.27 mg/g.

Sorptive Uptake Studies of an Aryl-Arsenical with Iron Oxide Composites on an Activated Carbon Support

Sorption uptake kinetics and equilibrium studies for 4-hydroxy-3-nitrobenzene arsonic acid (roxarsone) was evaluated with synthetic magnetite (Mag-P), commercial magnetite (Mag-C), magnetite 10%, 19%, and 32% composite material (CM-10, -19, -32) that contains granular activated carbon (GAC), and synthetic goethite at pH 7.00 in water at 21 °C for 24 h. GAC showed the highest sorptive removal of roxarsone and the relative uptake for each sorbent material with roxarsone are listed in descending order as follows: GAC (471 mg/g) > goethite (418 mg/g) > CM-10 (377 mg/g) CM-19 (254 mg/g) > CM-32 (227 mg/g) > Mag-P (132 mg/g) > Mag-C (29.5 mg/g). The As (V) moiety of roxarsone is adsorbed onto the surface of the iron oxide/oxyhydrate and is inferred as inner-sphere surface complexes; monodentate-mononuclear, bidentate-mononuclear, and bidentate-binuclear depending on the protolytic speciation of roxarsone. The phenyl ring of roxarsone provides the primary driving force for the sorptive interaction with the graphene surface of GAC and its composites. Thus, magnetite composites are proposed as multi-purpose adsorbents for the co-removal of inorganic and organic arsenicals due to the presence of graphenic and iron oxide active adsorption sites.