A chitosan-based composite for adsorption of uranyl ions; mechanism, isothems, kinetics and thermodynamics

The present paper describes a green and cost-effective approach to investigate chitosan-sepiolite (Ch-Sep) composite as an adsorbent for removal of UO₂²⁺ ions in aqueous solution. The Ch-Sep composite was prepared as a beads using with two cross-linking agents: tripolyphosphate (TPP) and epichlorohydrin (ECH). Their adsorption properties for the removal of UO₂²⁺ ions in aqueous solution by batch experimental conditions were studied. The adsorptive removal processes of UO₂²⁺ ions from aqueous solution were evaluated by Langmuir, Freundlich and Dubinin-Radushkevich isotherm models, and was found to be perfectly fit to the Langmuir model (R² = 0.971). The maximum adsorption capacity was 0.220 mol kg^-1 at 25 °C from Langmuir isotherm model. Adsorption energy was 12.1 kJ mol^-1 indicating that the adsorption process was chemical. The adsorption kinetics followed the pseudo second order and intra particle diffusion models. The thermodynamics parameters of UO₂²⁺ ions removal from aqueous solution was confirmed spontaneous, endothermic and possible at higher temperatures behavior of adsorption process. The adsorption mechanism of UO₂²⁺ ions onto Ch-Sep composite beads was investigated by FT-IR and SEM analysis. These findings revealed the effectiveness and potential of the newly synthesized Ch-Sep composite beads for the removal of UO₂²⁺ ions.

Probing the Molecular Interactions of Chitosan Films in Acidic Solutions with Different Salt Ions

Understanding the interaction mechanisms of chitosan films plays a central role in a wide range of its applications, such as bioadhesive, drug delivery, wound healing, tissue engineering, and wastewater treatment for heavy metal ions. Here, we investigated the molecular interactions between chitosan films in acidic solutions with different salt ions using a surface forces apparatus (SFA). The results showed that chitosan can be adsorbed to mica surfaces by electrostatic interaction under acidic conditions. The force measurements demonstrated that the interactions depend on the salt types, concentrations, and contact time. With the addition of 1 mM LaCl3 and NaCl into the acetic acid (HAc) buffer solution, the cohesion between chitosan films enhanced by about 45% and 20%, respectively, after a contact time of 60 min. The enhanced cohesion induced by the combination of partly intermolecular complexation formation in a bridge model and conformation adjustment of chitosan under contact time in 1 mM LaCl3 solution. However, the cohesion reduced rapidly and even disappeared when the salt concentration increased to 10 mM and 100 mM. We proposed that the cross-linked structures of chitosan mainly contribute to the significant reduction of chitosan cohesion in LaCl3 solution. In comparison, the decrease in cohesion capacity in NaCl solution mainly results from the enhanced hydration effect. Our findings may provide insights into the interaction mechanisms of chitosan films under nanoconfinement in acidic conditions and suggestions for the development of chitosan-based materials.

Chemical synthesis of chitosan-mimetic polymers via ring-opening metathesis polymerization and their applications in Cu2+ adsorption and catalytic decomposition

Aiming at solving the uncontrollability in the properties of chitosan, we synthesized two chitosan-mimetic polymers, the homopolymer mimic PHNI and the copolymer mimic PHNI-PHNIA, by ring-opening metathesis polymerization (ROMP).

The stability of magnetic chitosan beads in the adsorption of Cu2+

MCBs were synthesized through an embedding method. The adsorption capacity and saturated magnetization stability of MCBs were investigated in various conditions.

New gel-like polymers as selective weak-base anion exchangers

A group of new anion exchangers, based on polyamine podands and of excellent ion-binding capacity, were synthesized. The materials were obtained in reactions between various poly(ethyleneamines) with glycidyl derivatives of cyclotetrasiloxane. The final polymeric, strongly cross-linked materials form gel-like solids. Their structures and interactions with anions adsorbed were studied by spectroscopic methods (CP-MAS NMR, FR-IR, UV-Vis). The sorption isotherms and kinetic parameters were determined for 29 anions. Materials studied show high ion capacity and selectivity towards some important anions, e.g., selenate(VI) or perrhenate.

Technological options for the removal of arsenic with special reference to South East Asia

Arsenic contamination in ground water, used for drinking purpose, has been envisaged as a problem of global concern. However, arsenic contamination of ground water in parts of South East Asia is assuming greater proportions and posing a serious threat to the health of millions of people. A variety of treatment technologies based on oxidation, co-precipitation, adsorption, ion exchange and membrane process are available for the removal of arsenic from ground water. However, question remains regarding the efficiency and applicability/appropriateness of the technologies, particularly because of low influent arsenic concentration and differences in source water composition. Some of these methods are quite simple, but the disadvantage associated with them is that they produce large amounts of toxic sludge, which needs further treatment before disposal into the environment. Besides, the system must be economically viable and socially acceptable. In this paper an attempt has been made to review and update the recent advances made in the technological development in arsenic removal technologies to explore the potential of those advances to address the problem of arsenic contamination in South East Asia.

Use of chitosan and chitosan-derivatives to remove arsenic from aqueous solutions--a mini review

Arsenic removal has become a relevant concern due to the final confirmation of its behaviour as chronic human carcinogen, corresponding to an ever-increasing contamination of water, soil and crops in many parts of the world. Developing easily accessible removal strategies is therefore a primary environmental matter. Chitosan and chitosan derivatives show good adsorption performances against arsenic removal and are considered low cost products, easily obtainable. This review provides a summary of recent advances of the application of these compounds in the area of sorption sciences for arsenate and arsenite removal from water, focusing on equilibrium and kinetic mechanisms.

Thermal stability and degradation of chitosan modified by benzophenone

N-(biphenylmethylidenyl) chitosan polymer was prepared, characterized and thermal stability was compared with chitosan. Thermal degradation products of the modified polymer were identified by GC-MS technique. It seems that the mechanism of degradation of the prepared polymer is characterized by formation of low molecular weight radicals, followed by random scission mechanism along the backbond chain.

Biosorption of Cu(II), Zn(II), Ni(II) and Pb(II) ions by cross-linked metal-imprinted chitosans with epichlorohydrin

Cross-linked metal-imprinted chitosan microparticles were prepared from chitosan, using four metals (Cu(II), Zn(II), Ni(II), and Pb(II)) as templates, and epichlorohydrin as the cross-linker. The microparticles were characterized by Fourier transform infrared spectroscopy, solid state (13)C nuclear magnetic resonance spectroscopy, and energy-dispersive X-ray spectroscopy. They were used for comparative biosorption of Cu(II), Zn(II), Ni(II) and Pb(II) ions in an aqueous solution. The results showed that the sorption capacities of Cu(II), Zn(II), Ni(II), and Pb(II) on the templated microparticles increased from 25 to 74%, 13 to 46%, 41 to 57%, and 12 to 43%, respectively, as compared to the microparticles without metal ion templates. The dynamic study showed that the sorption process followed the second-order kinetic equation. Three sorption models, Langmuir, Freundlich, and Dubinin-Radushkevich, were applied to the equilibrium isotherm data. The result showed that the Langmuir isotherm equation best fitted for monolayer sorption processes. Furthermore, the microparticles can be regenerated and reused for the metal removal.

Competitive biosorption of azo dyes from aqueous solution on the templated crosslinked-chitosan nanoparticles

The nanoparticles of templated crosslinked chitosan, ECH-RB5 and ECH-3R, were prepared through the imprinting process using Remazol Black 5 (RB5) and Remazol Brilliant Orange 3R (3R) dyes, respectively, as templates and ECH as a crosslinker. The nanoparticles exhibited significantly higher adsorption capacities of the dyes than other nanoparticles formed without a dye template and with three crosslinkers (ECH, GLA, and EGDE). The adsorption of the dyes on the nanoparticles was affected by the initial pH, dye concentration, and temperature. The results were in accordance with the second-order and the Langmuir adsorption models. Meanwhile, the E values of the dyes calculated using the Dubinnin-Radushkevich model revealed that the adsorption process may be due to the dual nature of the process, physisorption and chemisorption, and that adsorption was predominant in the chemisorption process. The adsorption processes in the nanoparticles were spontaneous and exothermic. Moreover, competition adsorption through analysis of the intraparticle diffusion model apparently favored the 3R dye more than the RB5 dye on the nanoparticles in mixture solution B. The nanoparticles for the adsorption of the dyes were regenerated efficiently through the alkaline solution and were then reused for dye removal.

Adsorption characterization of Pb(II) and Cu(II) ions onto chitosan-tripolyphosphate beads: Kinetic, equilibrium and thermodynamic studies

Chitosan-tripolyphosphate (CTPP) beads were synthesized, characterized and were used for the adsorption of Pb(II) and Cu(II) ions from aqueous solution. The effects of initial pH, agitation period, adsorbent dosage, different initial concentrations of heavy metal ions and temperature were studied. The experimental data were correlated with the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. The maximum adsorption capacities of Pb(II) and Cu(II) ions in a single metal system based on the Langmuir isotherm model were 57.33 and 26.06 mg/g, respectively. However, the beads showed higher selectivity towards Cu(II) over Pb(II) ions in the binary metal system. Various thermodynamic parameters such as enthalpy (DeltaH degrees), Gibbs free energy (DeltaG degrees) and entropy (DeltaS degrees) changes were computed and the results showed that the adsorption of both heavy metal ions onto CTPP beads was spontaneous and endothermic in nature. The kinetic data were evaluated based on the pseudo-first and -second order kinetic and intraparticle diffusion models. Infrared spectra were used to elucidate the mechanism of Pb(II) and Cu(II) ions adsorption onto CTPP beads.

Biosorption of azo dyes from aqueous solution by glutaraldehyde-crosslinked chitosans

The crosslinked chitosan microparticles prepared through homogeneous coupling reaction and microparticle formation using a sodium hydroxide solution showed the largest adsorbed amounts toward the RB5 and 3R dyes than those from the three other methods through heterogeneous coupling reaction and microparticle formation using sodium hydroxide or sodium tripolyphosphate solutions. The dynamical experimental study showed that the dye adsorption accurately followed the second-order adsorption process. The experimental isotherm data were analyzed using three isotherm models, namely, Langmuir, Freundlich, and Dubinin-Radushkevich. The results revealed that the adsorption behavior of the RB5 and 3R dyes on the microparticles fitted well with the Langmuir model. In addition, the mean adsorption energy (E) from the Dubinin-Radushkevich isotherm and the activation energy (E(a)) from Arrhenius equation indicated that the adsorption process might be the dual nature of the process, physisorption and chemisorption, and was predominant on the chemisorption process The competitive adsorption showed that the adsorption of the 3R dye on the microparticles in the mixture solution was much more affected by the existence of the RB5 dye than the other way around. Furthermore, it was also found that the crosslinked chitosan microparticles can be regenerated and reused for dye adsorption.

The chemically crosslinked metal-complexed chitosans for comparative adsorptions of Cu(II), Zn(II), Ni(II) and Pb(II) ions in aqueous medium

The chemically crosslinked metal-complexed chitosans were synthesized by using the ion-imprinting method from a chitosan with four metals (Cu(II), Zn(II), Ni(II) and Pb(II)) as templates and glutaraldehyde as a crosslinker. The influences of adsorption conditions, including molar ratios of crosslinker/chitosan and pH changes, were studied. They were used to investigate for comparative adsorptions of Cu(II), Zn(II), Ni(II) and Pb(II) ions in an aqueous medium. They were demonstrated the comparative adsorptions of Cu(II), Zn(II), Ni(II) and Pb(II) ions in the orders of the adsorbed amounts with templates: Cu(II) approximately Pb(II)>Zn(II) approximately Ni(II), Zn(II)>Cu(II) approximately Pb(II)>Ni(II), Ni(II)>Pb(II)>Zn(II)>Cu(II) and Pb(II) approximately Cu(II)>Zn(II)>Ni(II), respectively. In addition, the dynamical study showed to be well followed the second-order kinetic equation in the adsorption process. At the same time, the equilibrium adsorption data were fitted in three adsorption isotherm models, namely, Langmuir, Freundlich, and Dubinin-Radushkevich to show very good fits in the Langmuir isotherm equation for the monolayer adsorption process. The most important aspect of the chemically crosslinked metal-complexed chitosans with glutaraldehyde demonstrated to afford a higher adsorption capacity, and a more efficient adsorption toward metals in an aqueous medium.

Comparative adsorption of Cu(II), Zn(II), and Pb(II) ions in aqueous solution on the crosslinked chitosan with epichlorohydrin

The crosslinked chitosans synthesized by the homogeneous reaction of chitosan in aqueous acetic acid solution with epichlorohydrin were used to investigate the adsorptions of three metals of Cu(II), Zn(II), and Pb(II) ions in an aqueous solution. The crosslinked chitosan characterized by 13CNMR, SEM, and elemental analysis, and the effects of pH and anion on the adsorption capacity were carried out. The dynamical study demonstrated that the adsorption process was followed the second-order kinetic equation. The results obtained from the equilibrium isotherms adsorption studies of three metals of Cu(II), Zn(II), and Pb(II) ions by being analyzed in three adsorption models, namely, Langmuir, Freundlich, and Dubinnin-Radushkevich isotherm equations, indicated to be well fitted to the Langmuir isotherm equation under the concentration range studied, by comparing the linear correlation coefficients. The order of the adsorption capacity (Qm) for three metal ions was as follows: Cu2+>Pb2+>Zn2+. This technique for syntheses of the crosslinked chitosans with epichlorohydrin via the homogeneous reaction in aqueous acetic acid solution showed that the adsorptions of three metal ions in aqueous solution were followed the monolayer coverage of the adsorbents through physical adsorption phenomena.

Removal of arsenic (III) and arsenic (V) from aqueous medium using chitosan-coated biosorbent

A biosorbent was prepared by coating ceramic alumina with the natural biopolymer, chitosan, using a dip-coating process. Removal of arsenic (III) (As(III)) and arsenic (V) (As(V)) was studied through adsorption on the biosorbent at pH 4.0 under equilibrium and dynamic conditions. The equilibrium adsorption data were fitted to Langmuir, Freundlich, and Redlich-Peterson adsorption models, and the model parameters were evaluated. All three models represented the experimental data well. The monolayer adsorption capacity of the sorbent, as obtained from the Langmuir isotherm, is 56.50 and 96.46 mg/g of chitosan for As(III) and As(V), respectively. The difference in adsorption capacity for As(III) and As(V) was explained on the basis of speciation of arsenic at pH 4.0. Column adsorption results indicated that no arsenic was found in the effluent solution up to about 40 and 120 bed volumes of As(III) and As(V), respectively. Sodium hydroxide solution (0.1M) was found to be capable of regenerating the column bed.

Dielectric analysis of chitosan gel beads suspensions: Influence of low crosslinking agent concentration on the dielectric behavior

Dielectric measurements were carried out for the suspensions of chitosan gel beads (CGB) crosslinked with glutaraldehyde (GA), ranging in crosslinking time from 1 to 180 min at six fixed low GA concentrations over a frequency range from 40 to 110 MHz. The distinct dielectric relaxations observed in the frequency range of 10(4)-10(5) Hz were explained by the effects of the interfacial polarization. By fitting the experimental data with Cole-Cole equation the dielectric parameters of the suspensions were obtained, and the phase parameters were calculated using Hanai's method. The influence of crosslinking on the dielectric spectra of CGB was investigated by viewing the crosslinking time dependencies of conductivity increment (Deltakappa), relaxation frequency (f(0)), permittivity of CGB (epsilon(i)), conductivity of CGB (kappa(i)) and conductivity of continuous media (kappa(a)) at six fixed GA concentrations. Some information were gained, such as, thinner electric double layer, particle with rougher surface and more compact gel backbone with increasing crosslinking time. The basic information obtained can provide valuable references for the preparation of CGB and the application to more extensive fields such as controlled-release technology of medicament.

Characteristics of equilibrium, kinetics studies for adsorption of fluoride on magnetic-chitosan particle

The magnetic-chitosan particle was prepared and characterized by the SEM, XRD, FT-IR and employed as an adsorbent for removal fluoride from the water solution in the batch system. The Langmuir isotherms, Bradley's isotherm, Freundlich isotherm and Dubinin-Kaganer-Radushkevich (DKR) isotherm were used to describe adsorption equilibrium. The kinetic process was investigated using the pseudo-first-order model, pseudo-second-order model and intra-particle diffusion model, respectively. The results show that the magnetic-chitosan particle is amorphous of irregular clumps in the surface with groups of RNH(2), RNH(3), Fe-O, etc. Bradley's equation and two-sites Langmuir isotherms were fitted well with the adsorption equilibrium data; the maximal amount of adsorption of 20.96-23.98 mg/l and free energy of 2.48 kJ/mol were obtained from the Bradley's equation, two-sites Langmuir isotherm and DKR modeling, respectively. The pseudo-second-order with the initial adsorption rate 2.08 mg/g min was suitable to describe the kinetic process of fluoride adsorption onto the adsorbent. In overall, the major mechanism of fluoride adsorption onto the heterogeneous surface of magnetic-chitosan particle was proposed in the study.

Synthesis of novel chitosan resin derivatized with serine diacetic acid moiety and its application to on-line collection/concentration of trace elements and their determination using inductively coupled plasma-atomic emission spectrometry

A novel chelating resin functionalized with serine diacetic acid moiety was synthesized by using chitosan as base material, and applied to the collection/concentration of trace elements in environmental water samples, followed by the determination using inductively coupled plasma-atomic emission spectrometer (ICP-AES). The synthesized resin, crosslinked chitosan serine diacetic acid (CCTS-SDA), showed good adsorption behavior toward trace amounts of Cd, Pb, Cu, Ni, V, Ga, Sc, In, and Th in a wide pH range. Additionally, rare earth elements also can be retained on the resin at neutral pH region. The adsorbed elements can be easily eluted with 1 mol L(-1) of nitric acid, and their recoveries were found to be 90-100%. The CCTS-SDA was packed in a mini-column, which was then installed in a computer-controlled auto-pretreatment system (Auto-Pret System) for on-line trace elements collection and determination with ICP-AES. Experimental parameters which related to the improvement of sensitivity and reproducibility were optimized. The limits of detection (LOD) for 13 elements were found to be in sub-ppb level. The proposed method with CCTS-SDA resin was successfully applied to the determination of trace elements in river water samples. The method was validated by determining a certified reference material of river water, SLRS-4.

Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads

A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.

Equilibrium and kinetics studies of adsorption of copper (II) on chitosan and chitosan/PVA beads

The adsorption of Cu(II) ions from aqueous solution by chitosan and chitosan/PVA beads was studied in a batch adsorption system. Chitosan solution was blended with poly(vinyl alcohol) (PVA) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. The adsorption capacities and rates of Cu(II) ions onto chitosan and chitosan/PVA beads were evaluated. The Langmuir, Freundlich and BET adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isothermal data could be well interpreted by the Langmuir model. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step. The Cu(II) ions can be removed from the chitosan and chitosan/PVA beads rapidly by treatment with an aqueous EDTA solution. Results also showed that chitosan and chitosan/PVA beads are favourable adsorbers.

Encapsulation of isotope on novel beta-emitting poly(ethylene terephthalate) surfaces

Recent data indicate that intravascular betaa-irradiation from centrally located sources at the time of balloon angioplasty or stenting reduces proliferation of smooth muscle cells, neointima formation, and restenosis. In an effort to simplify radiation delivery, a novel beta-radiation source was developed based on the adsorption of 32P (phosphoric acid) by pH-sensitive chitosan hydrogel on a poly(ethylene terephthalate) balloon surface. To prevent the 32P-isotope desorption in the patient's blood, the adsorbed phosphoric acid was precipitated as CaHPO4 on the surface by a saturated Ca(OH)2/5% CaCl2 solution. Various polyurethanes were applied to seal the radioactive surface by the dip-coating method. The isotope off-rate results were determined. Optimal results were obtained by serially coating with two polyurethane solutions. This approach holds promise for simplifying and improving the safety, and minimizing the cost of intravascular brachytherapy.