Studies on chitin. IX. Crosslinking of water-soluble chitin and evaluation of the products as adsorbents for cupric ion

Recent Advances in Chitosan-Based Applications-A Review

Chitosan derived from chitin gas gathered much interest as a biopolymer due to its known and possible broad applications. Chitin is a nitrogen-enriched polymer abundantly present in the exoskeletons of arthropods, cell walls of fungi, green algae, and microorganisms, radulae and beaks of molluscs and cephalopods, etc. Chitosan is a promising candidate for a wide variety of applications due to its macromolecular structure and its unique biological and physiological properties, including solubility, biocompatibility, biodegradability, and reactivity. Chitosan and its derivatives have been known to be applicable in medicine, pharmaceuticals, food, cosmetics, agriculture, the textile and paper industries, the energy industry, and industrial sustainability. More specifically, their use in drug delivery, dentistry, ophthalmology, wound dressing, cell encapsulation, bioimaging, tissue engineering, food packaging, gelling and coating, food additives and preservatives, active biopolymeric nanofilms, nutraceuticals, skin and hair care, preventing abiotic stress in flora, increasing water availability in plants, controlled release fertilizers, dye-sensitised solar cells, wastewater and sludge treatment, and metal extraction. The merits and demerits associated with the use of chitosan derivatives in the above applications are elucidated, and finally, the key challenges and future perspectives are discussed in detail.

A Review of Adsorbents for Heavy Metal Decontamination: Growing Approach to Wastewater Treatment

Heavy metal is released from many industries into water. Before the industrial wastewater is discharged, the contamination level should be reduced to meet the recommended level as prescribed by the local laws of a country. They may be poisonous or cancerous in origin. Their presence does not only damage people, but also animals and vegetation because of their mobility, toxicity, and non-biodegradability into aquatic ecosystems. The review comprehensively discusses the progress made by various adsorbents such as natural materials, synthetic, agricultural, biopolymers, and commercial for extraction of the metal ions such as Ni2+, Cu2+, Pb2+, Cd2+, As2+ and Zn2+ along with their adsorption mechanisms. The adsorption isotherm indicates the relation between the amount adsorbed by the adsorbent and the concentration. The Freundlich isotherm explains the effective physical adsorption of the solute particle from the solution on the adsorbent and Langmuir isotherm gives an idea about the effect of various factors on the adsorption process. The adsorption kinetics data provide valuable insights into the reaction pathways, the mechanism of the sorption reaction, and solute uptake. The pseudo-first-order and pseudo-second-order models were applied to describe the sorption kinetics. The presented information can be used for the development of bio-based water treatment strategies.

Chitosan derivatives as green corrosion inhibitors for P110 steel in a carbon dioxide environment

Two chitosan derivatives were synthesized for the first time as green corrosion inhibitors for the carbon dioxide corrosion of P110 steel. The structures of the synthesized products were characterized by infrared spectroscopy. Electrochemical and weight-loss experiments were used to test the effect of corrosion inhibitors, while SEM-EDS, AFM and other analysis methods were used to study the protection mechanism of corrosion inhibitors. The experimental results show that synthetic corrosion inhibitors CHC and CAHC are all good corrosion inhibitors for carbon dioxide corrosion inhibition. Both chitosan derivatives can form hydrophobic protective films on the metal surface. For inhibition performance, CAHC is better than CHC, which is the same conclusion drawn from practical experiments and quantum chemical calculations. Investigation into chitosan inhibitors has opened up a new area of research of environmentally friendly corrosion inhibitors, which is of great significance for metal protection without toxicity and side effects.

Synthesis and characterisation of chitin from periwinkle (Tympanotonus fusatus (L.)) and snail (Lissachatina fulica (Bowdich)) shells

This study characterizes chitin extracted from bio-sources of snail and periwinkle using varied combinations of acid and alkali concentrations. A three level factorial design of experiment with alkali and acid concentrations was used. FTIR, XRD and SEM were used to investigate the structural changes after treatments. Results reveal that both alkali and acid concentrations significantly affect the development of the functional groups and their intensities in the extracted chitin. A certain combination of concentration of acid and alkali can be used to obtain chitin with high degree of order (Crystallinity Index (CrI)>0.9) and a degree of de-acetylation (DD>50%). This results in combined high crystallinity and degree of de-acetylation. The study also established that certain combination of acid and alkali concentrations could lead to alpha to beta transformation in chitin structure.

Improving the integrity of natural biopolymer films used in food packaging by crosslinking approach: A review

Currently used approaches for biopolymer modification are either expensive, poisonous or do not lead into the well-desired characteristics to the final film materials. Development of crosslinking procedure is an innovative strategy to improve mechanical, physical and thermal properties of biopolymer films. This review provides a brief description of film-forming biopolymers (e.g. chitosan, whey protein, alginate and starch) followed by a detailed introduction to definition and classification of various crosslinkers, the effect of crosslinking on emerging attributes of biopolymer films including physical, mechanical and thermal properties, identification of crosslinking occurrence, and cytotoxicity status of commonly used crosslinkers in the field of food and food-related packaging materials.

Synthesis of Novel Crosslinked Chitosans with a Higher Fatty Diacid Diglycidyl and Their Adsorption Abilities towards Acid Dyes

Novel chitosan-based adsorbent materials with a higher fatty diacid diglycidyl as the crosslinking agent were synthesized and the adsorption abilities of the resulting polymers evaluated towards typical acid dyes. The successful formation of a crosslinked structure was confirmed via infrared spectroscopic measurements and the solubility of the polymer towards 10% aqueous solutions of acetic and formic acids determined. At higher dye concentrations, the adsorption abilities of the crosslinked chitosan towards hydrophilic CI Acid Orange 7 and CI Acid Red 1 increased with decreasing degree of substitution. However, at lower dye concentrations, the crosslinked chitosan with the lowest degree of substitution exhibited the lowest adsorption capability. With such hydrophilic acid dyes, the extent of adsorption decreased significantly as the pH of the solution increased. On the other hand, CI Acid Red 138, which contains a dodecyl group in the chemical structure, was adsorbed to a considerable extent even at higher pH values, suggesting hydrophobic interaction between the alkyl group in the dye molecule and the hydrophobic crosslinker.

Applications and Properties of Chitosan

Chitosan, a polycationic polymer and waste product from the sea food processing industry, is an abundant natural resource that has, as yet, not been fully utilized. Advantages of this polymer include availability, low cost, high biocompatibility, biodegradability and ease of chemical modification. In this paper, the physicochemical properties of chitosan, as well as its numerous applications, are reviewed with particular emphasis on its use in water treat ment, pharmaceutics, agriculture and membrane formation.

Chitosan-based nanomaterials: a state-of-the-art review

This manuscript briefly reviews the extensive research as well as new developments on chitosan based nanomaterials for various applications. Chitosan is a biocompatible and biodegradable polymer having immense structural possibilities for chemical and mechanical modification to generate novel properties and functions in different fields especially in the biomedical field. Over the last era, research in functional biomaterials such as chitosan has led to the development of new drug delivery system and superior regenerative medicine, currently one of the most quickly growing fields in the area of health science. Chitosan is known as a biomaterial due to its biocompatibility, biodegradability, and non-toxic properties. These properties clearly point out that chitosan has greater potential for future development in different fields of science namely drug delivery, gene delivery, cell imaging, sensors and also in the treatment as well as diagnosis of some diseases like cancer. Chitosan based nanomaterials have superior physical and chemical properties such as high surface area, porosity, tensile strength, conductivity, photo-luminescent as well as increased mechanical properties as comparison to pure chitosan. This review highlights the recent research on different aspect of chitosan based nanomaterials, including their preparation and application.

Adsorption of Copper(II) and Mercury(II) Ions onto Chemically-Modified Chitosan Membranes: Equilibrium and Kinetic Properties

Cross-linked chitosan was synthesized with glutaraldehyde (chitosan–GLA) and epichlorohydrin (chitosan–ECH). The structures of these matrices were characterized by elemental analysis, Fourier-transform infrared spectrometry (FT-IR), the degree of de-acetylation and the surface topography as determined via scanning electron microscopy (SEM). After promoting interaction with the metal ion, the adsorbent was also studied using FT-IR and energy dispersive X-ray spectroscopy (EDXS). Adsorption studies for Cu(II) and Hg(II) ions were carried out in a batch process. The adsorption kinetics were tested using three models, viz. pseudo-first-order, pseudo-second-order and intra-particle diffusion. The experimental kinetic data were best fitted by the pseudo-second-order model for Cu(II) ions (R2 ≥ 0.98) and for Hg(II) ions (R2 = 0.99). Higher rate constants (k2) were obtained for the adsorption of Cu(II) ions onto chitosan–GLA [1.40 g/(mmol h)] and for Hg(II) ions onto raw chitosan [5.65 g/(mmol h)]. The adsorption rate depended on the concentration of Cu(II) and Hg(II) ions on the adsorbent surface and on the quantity of ions adsorbed at equilibrium. At 293 K, the Langmuir–Freundlich model provided a better fit to the adsorption isotherms on both raw and cross-linked chitosan membranes. The maximum adsorption capacity for Cu(II) ions was obtained with the chitosan–GLA matrix (2.7 mmol/g). A maximum adsorption capacity of 3.1 mmol/g was attained for Hg(II) ions onto the chitosan–ECH matrix.

Adsorption of copper-citrate complexes on chitosan: equilibrium modeling

The effects of complexes on the adsorption of copper from citrate solutions using chitosan were investigated. Various copper to citrate ratios and solution pHs were used to determine the copper adsorption capacity on the chitosan and a mathematical model was developed to simulate the copper adsorption process. According to the model, the three parameters influencing the copper adsorption capacity are the fraction of protonated amine groups (RNH(3)(+)), the fraction of anionic copper-citrate complexes (CuL(-) and CuL(2)(4-)), and the fraction of anionic citrate complexes (HL(2-), H(2)L(-), and L(3-)). The copper adsorption capacities onto chitosan at varying copper-citrate ratios and solution pHs can be predicted by the mathematical model. With such a model to facilitate understand the copper adsorption mechanisms at varying copper-citrate ratios and solution pHs, the copper adsorption efficiency can be increased by the adjustment of the copper-citrate ratio and solution pH.

Dynamic and static adsorption and desorption of Hg(II) ions on chitosan membranes and spheres

The adsorption and desorption of Hg(II) ions was studied using static and dynamic methods, employing membranes and spheres of chitosan as the adsorbent. The quantity of adsorption was influenced by chitosan crosslinking and by the adsorbent shape. The Langmuir model was applied to fit the experimental equilibrium data. Glutaraldehyde-crosslinked membranes presented a lower desorption capacity, when compared to natural membranes, but could be regenerated for use in successive cycles. Dynamic adsorption experiments suggested that the adsorption capacity depended mainly on adsorbent geometry, due to differences between surface area to mass ratio and initial concentration of Hg(II) ions. The adsorption capacity determined by the dynamic method was 65% and 77% for membranes and spheres, respectively of the value obtained static method results. A process combining dynamic adsorption and static desorption can be used to concentrate the Hg(II) ions by a factor of nearly seven (7x), when compared to the initially treated volume.

Crosslinked chitosan—preparation and characterization

Chitosan undergoes radical-induced depolymerization in the presence of potassium persulfate at 60 degrees C, leading to extensive crosslinking of the fragmented chains on subsequent cooling at 4 degrees C. As a result, a possible conformational change leading to higher crystallinity, as evidenced by IR, X-ray and 13C NMR was observed.

Chemical modification of chitosan and equilibrium study for mercury ion removal

To increase the uptake capacity of mercury ions, several chemical modifications of chitosan beads which are cross-linked with glutaraldehyde were performed. Among them, aminated chitosan bead prepared through chemical reaction with ethylenediamine had a high uptake capacity of about 2.3 mmol g(-1) dry mass at pH 7. The increased number of amine groups was confirmed by IR analysis and measuring the saturation capacities for adsorption of HCl. The surface condition and existence of mercury ions on the beads was confirmed by the environmental scanning electron microscope and energy dispersive X-ray spectroscopy instrumental analyses. The beads showed the characteristic of competitive sorption between mercury and hydrogen ions and it was successfully modelled by an equilibrium model.

Adsorption behavior of mercury and precious metals on cross-linked chitosan and the removal of ultratrace amounts of mercury in concentrated hydrochloric acid by a column treatment with cross-linked chitosan

Cross-linked chitosan was synthesized with chitosan and ethylene glycol diglycidyl ether. The adsorption behavior of trace amounts of metal ions on the cross-linked chitosan was systematically examined by packing it in a mini-column, passing a metal solution through it and measuring metal ions in the effluent by ICP-MS. The cross-linked chitosan adsorbed mercury and precious metals (Pd, Pt, and Au) at pH values from acidic to neutral. Especially, mercury in concentrated hydrochloric acids could be adsorbed on cross-linked chitosan quantitatively by an anion-exchange mechanism in the form of a stable chloride complex. This method was applied to the removal of mercury from commercially available hydrochloric acid; more than 97% of mercury was removed, and the residual mercury in the hydrochloric acid (Grade: for trace analysis) was found to be 0.15 ppb. Mercury adsorbed on the cross-linked chitosan could be easily desorbed with an eluent containing I M hydrochloric acid and 0.05 M thiourea. The thus-refreshed cross-linked chitosan could be repeatedly used for the removal of mercury in hydrochloric acid.

Interaction between chitosan and uranyl ions. Part 2. Mechanism of interaction

In this part of the study--understanding the mechanism of interaction between chitosan and uranyl ions, we confirmed the restrictive role of polymer crystallinity on uranyl sorption capacity. The saturation of the polymer by uranyl ions showed that approximately 1 mol of uranyl ions was sorbed for 2 mol of amino groups contained in the amorphous domain. This result can be related to the intrinsic properties of chitosan. Desorption experiments are in favour of strong interaction, in fact, no desorption was observed whatever the experimental conditions. Spectroscopic characterization was performed on complexes in solution and in the solid state. U.V.-visible spectrophotometric experiments showed that a unique type of complex was formed. FT-IR spectroscopy allowed us to observe the appearance of a new band at 1525 cm of amide II type and led us to conclude the formation of a unique complex by the coordination with chitosan amino groups.

Interaction between chitosan and uranyl ions. Part 1. Role of physicochemical parameters

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5-7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.