Heterogeneous catalysis on chitosan-based materials: a review

Use of carboxymethyl cellulose as binder for the production of water-soluble catalysts

Bio-based polymers are materials of high interest given the harmful environmental impact that involves the use of non-biodegradable fossil products for industrial applications. These materials are also particularly interesting as bio-based ligands for the preparation of metal nanoparticles (MNPs), employed as catalysts for the synthesis of high value chemicals. In the present study, Ru (0) and Rh(0) Metal Nanoparticles supported on Sodium Carboxymethyl cellulose (MNP(0)s-CMCNa) were prepared by simply mixing RhCl3x3H2O or RuCl3 with an aqueous solution of CMCNa, followed by NaBH4 reduction. The formation of MNP(0)s-CMCNa was confirmed by FT-IR and XRD, and their size estimated to be around 1.5 and 2.2 nm by TEM analysis. MNP(0)s-CMCNa were employed for the hydrogenation of (E)-cinnamic aldehyde, furfural and levulinic acid. Hydrogenation experiments revealed that CMCNa is an excellent ligand for the stabilization of Rh(0) and Ru(0) nanoparticles allowing to obtain high conversions (>90 %) and selectivities (>98 %) with all substrates tested. Easy recovery by liquid/liquid extraction allowed to separate the catalyst from the reaction products, and recycling experiments demonstrated that MNPs-CS were highly efficiency up to three times in best hydrogenation conditions.

Green Biocatalyst for Ultrasound-Assisted Thiazole Derivatives: Synthesis, Antibacterial Evaluation, and Docking Analysis

The catalytic activity of chitosan (Cs) and grafted Cs led to the preparation of terephthalohydrazide Cs Schiff's base hydrogel (TCsSB), which was then investigated as an eco-friendly biocatalyst for synthesizing novel thiazole derivatives. TCsSB exhibited greater surface area and higher thermal stability compared to Cs, making it a promising eco-friendly biocatalyst. We synthesized two novel series of thiazoles via the reaction of 2-(2-oxo-1,2-diphenylethylidene) hydrazine-1-carbothioamide with various hydrazonoyl chlorides and 2-bromo-1-arylethan-1-ones, employing ultrasonic irradiation and using TCsSB as a catalyst. A comparative study between Cs and TCsSB revealed higher yields than TCsSB. The methodology offered advantages such as mild reaction conditions, quick reaction times, and high yields. TCsSB could be reused multiple times without a significant loss of potency. The chemical structures of the newly synthesized compounds were verified through IR, 1H NMR, 13C NMR, and MS analyses. Six synthesized compounds were assessed for their in vitro antibacterial effectiveness by establishing the minimum inhibitory concentration against four distinct bacterial strains. The docking analyses revealed favorable binding scores against several amino acids within the selected protein (PDB Code-1MBT) for these compounds, with compound 4c exhibiting particularly noteworthy binding properties. Additionally, the in silico ADME parameter estimation for all compounds indicated favorable pharmacological properties for these compounds.

Eco-friendly and sustainable basil seed hydrogel-loaded copper hydroxide-based catalyst for the synthesis of propargylamines and tetrazoles

The broad use of propargyl amines and tetrazoles in pharmaceutical applications presents a well-established challenge. Their synthesis relies heavily on catalysis, which, in turn, has been hindered by the scarcity of stable and practical catalysts. In response to this issue, we have developed an environmentally friendly and sustainable catalyst by infusing copper hydroxide into basil seed hydrogel (Cu(OH)2-BSH), creating a 3D nanoreactor support structure. To verify the structural, physical, chemical, and morphological properties of the prepared samples, a comprehensive analysis using various techniques, including FT-IR, EDX, FE-SEM, TEM, XRD, BET, TGA, and XPS, were conducted. The results not only confirmed the presence of Cu(OH)2 but also revealed a porous structure, facilitating faster diffusion and providing a substantial number of active sites. This catalyst boasts a high surface area and can be easily recovered, making it a cost-effective, safe, and readily available option. This catalyst was applied to the synthesis of propargyl amines and tetrazoles through multi-component reactions (MCRs), achieving excellent results under mild conditions and in a remarkably short timeframe. Consequently, this work offers a straightforward and practical approach for designing and synthesizing metal hydroxides and 3D hydrogels for use in heterogeneous catalysis during organic syntheses. This can be achieved using basic and affordable starting materials at the molecular level.

Structural diversity, functional versatility and applications in industrial, environmental and biomedical sciences of polysaccharides and its derivatives - A review

Recent efforts on the expansion of sustainable and commercial primal matters are essential to enhance the knowledge of their hazards and noxiousness to humans and their environments. For example, polysaccharide materials are widely utilized in food, wound dressing, tissue engineering, industry, targeted drug delivery, environmental, and bioremediation due to their attractive degradability, nontoxicity and biocompatibility. There are numerous easy, quick, and efficient ways to manufacture these materials that include cellulose, starch, chitosan, chitin, dextran, pectin, gums, and pullulan. Further, they exhibit distinctive properties when combined favourably with raw materials from other sources. This review discusses the synthesis and novel applications of these carbohydrate polymers in industrial, environmental and biomedical sciences.

Developments and application of chitosan-based adsorbents for wastewater treatments

Water quality is deteriorating continuously as increasing levels of toxic inorganic and organic contaminants mostly discharging into the aquatic environment. Removal of such pollutants from the water system is an emerging research area. During the past few years use of biodegradable and biocompatible natural additives has attracted considerable attention to alleviate pollutants from wastewater. The chitosan and its composites emerged as a promising adsorbents due to their low price, abundance, amino, and hydroxyl groups, as well as their potential to remove various toxins from wastewater. However, a few challenges associated with its practical use include lack of selectivity, low mechanical strength, and solubility in acidic medium. Therefore, several approaches for modification have been explored to improve the physicochemical properties of chitosan for wastewater treatment. Chitosan nanocomposites found effective for the removal of metals, pharmaceuticals, pesticides, microplastics from the wastewaters. Nanoparticle doped with chitosan in the form of nano-biocomposites has recently gained much attention and proven a successful tool for water purification. Hence, applying chitosan-based adsorbents with numerous modifications is a cutting-edge approach to eliminating toxic pollutants from aquatic systems with the global aim of making potable water available worldwide. This review presents an overview of distinct materials and methods for developing novel chitosan-based nanocomposites for wastewater treatment.

Lignin-Based Catalysts for C-C Bond-Forming Reactions

Carbon-carbon (C-C) bond formation is the key reaction in organic synthesis to construct the carbon framework of organic molecules. The continuous shift of science and technology toward eco-friendly and sustainable resources and processes has stimulated the development of catalytic processes for C-C bond formation based on the use of renewable resources. In this context, and among other biopolymer-based materials, lignin has attracted scientific attention in the field of catalysis during the last decade, either through its acid form or as a support for metal ions and metal nanoparticles that drive the catalytic activity. Its heterogeneous nature, as well as its facile preparation and low cost, provide competitive advantages over other homogeneous catalysts. In this review, we have summarized a variety of C-C formation reactions, such as condensations, Michael additions of indoles, and Pd-mediated cross-coupling reactions that were successfully carried out in the presence of lignin-based catalysts. These examples also involve the successful recovery and reuse of the catalyst after the reaction.

Chitosan-supported metal nanocatalysts for the reduction of nitroaromatics

The second most abundant natural polymer in the earth's crust is chitosan (CS). The unique physical, chemical, structural, and mechanical features of this natural polymer have led to its increased application in a variety of fields such as medicine, catalysis, removal of pollutants, etc. To eliminate various pollutants, it is preferable to employ natural compounds as their use aids the removal of contaminants from the environment. Consequently, employing CS to eliminate contaminants is a viable choice. For this aim, CS can be applied as a template and support for metal nanoparticles (MNPs) and prevent the accumulation of MNPs as well as a reducing and stabilizing agent for the fabrication of MNPs. Among the pollutants present in nature, nitro compounds are an important and wide category of biological pollutants. 4-Nitrophenol (4-NP) is one of the nitro pollutants. There are different ways for the removal of 4-NP, but the best and most effective method for this purpose is the application of a metallic catalyst and a reducing agent. In this review, we report the recent developments regarding CS-supported metallic (nano)catalysts for the reduction of nitroaromatics such as nitrophenols, nitroaniline compounds, nitrobenzene, etc. in the presence of reducing agents. The metals investigated in this study include Ag, Au, Ni, Cu, Ru, Pt, Pd, etc.

Enhanced electrocatalytic activity of Pt-SnO2 nanoparticles supported on natural bentonite-functionalized reduced graphene oxide-extracted chitosan from shrimp wastes for methanol electro-oxidation

In this work, tin (IV) oxide (SnO₂) nanoparticles were synthesized based on Amaranthus spinosus plant. The produced graphene oxide by a modified Hummers' method was functionalized with melamine (mRGO) and used accompanied by natural bentonite (Bnt) and extracted chitosan from shrimp wastes to prepare Bnt-mRGO-CH. This was utilized as novel support for anchoring Pt and SnO₂ nanoparticles to prepare the novel Pt-SnO₂/Bnt-mRGO-CH catalyst. The crystalline structure, morphology and uniform dispersion of nanoparticles in the prepared catalyst were determined by TEM images and XRD technique. The electrocatalytic performance of the Pt-SnO₂/Bnt-mRGO-CH catalyst was evaluated for methanol electro-oxidation through electrochemical investigations including cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry techniques. Pt-SnO₂/Bnt-mRGO-CH showed enhanced catalytic activity compared to Pt/Bnt-mRGO-CH and Pt/Bnt-CH catalysts considering its higher electrochemically active surface area, higher mass activity, and better stability for methanol oxidation. SnO₂/Bnt-mRGO and Bnt-mRGO nanocomposites were also synthesized and did not show any significant activity for methanol oxidation. The results showed that Pt-SnO₂/Bnt-mRGO-CH could be a promising catalyst as anode material in direct methanol fuel cells.

Chitosan-Urushiol nanofiber membrane with enhanced acid resistance and broad-spectrum antibacterial activity

Due to the large specific surface area and rich pore structure, chitosan nanofiber membrane has many advantages over conventional gel-like or film-like products. However, the poor stability in acidic solutions and relatively weak antibacterial activity against Gram-negative bacteria severely restrict its use in many industries. Here, we present a chitosan-urushiol composite nanofiber membrane prepared by electrospinning. Chemical and morphology characterization revealed that the formation of chitosan-urushiol composite involved the Schiff base reaction between catechol and amine groups and the self-polymerization of urushiol. The unique crosslinked structure and multiple antibacterial mechanisms endowed the chitosan-urushiol membrane with outstanding acid resistance and antibacterial performance. After immersion in HCl solution at pH 1, the membrane maintained its intact appearance and satisfactory mechanical strength. In addition to its good antibacterial performance against Gram-positive Staphylococcus aureus (S. aureus), the chitosan-urushiol membrane exhibited synergistic antibacterial activity against Gram-negative Escherichia coli (E. coli) that far exceeded that of neat chitosan membrane and urushiol. Moreover, cytotoxicity and hemolysis assays revealed that the composite membrane had good biocompatibility similar to that of neat chitosan. In short, this work provides a convenient, safe, and environmentally friendly method to simultaneously enhance the acid resistance and broad-spectrum antibacterial activity of chitosan nanofiber membranes.

Chitosan bead containing metal-organic framework encapsulated heteropolyacid as an efficient catalyst for cascade condensation reaction

Using cyclodextrin and chitosan that are bio-based compounds, a novel bi-functional catalytic composite is designed, in which metal-organic framework encapsulated phosphomolybdic acid was incorporated in a dual chitosan-cyclodextrin nanosponge bead. The composite was characterized via XRD, TGA, ICP, BET, NH₃-TPD, FTIR, FE-SEM/EDS, elemental mapping analysis and its catalytic activity was examined in alcohol oxidation and cascade alcohol oxidation-Knoevenagel condensation reaction. It was found that the designed catalyst that possess both acidic feature and redox potential could promote both reactions in aqueous media at 55 °C and various substrates with different electronic features could tolerate the aforementioned reactions to furnish the products in 75-95% yield. Furthermore, the catalyst could be readily recovered and recycled for five runs with slight loss of the catalytic activity. Notably, in this composite the synergism between the components led to high catalytic activity, which was superior to each component. In fact, the amino groups on the chitosan served as catalysts, while cyclodextrin nanosponge mainly acted as a phase transfer agent. Moreover, measurement of phosphomolybdic acid leaching showed that its incorporation in metal-organic framework and bead structure could suppress its leaching, which is considered a drawback for this compound. Other merits of this bi-functional catalyst were its simplicity, use of bio-based compounds and true catalysis, which was proved via hot filtration.

Palladium Supported on Bioinspired Materials as Catalysts for C–C Coupling Reactions

In recent years, the immobilization of palladium nanoparticles on solid supports to prepare active and stable catalytic systems has been deeply investigated. Compared to inorganic materials, naturally occurring organic solids are inexpensive, available and abundant. Moreover, the surface of these solids is fully covered by chelating groups which can stabilize the metal nanoparticles. In the present review, we have focused our attention on natural biomaterials-supported metal catalysts applied to the formation of C–C bonds by Mizoroki–Heck, Suzuki–Miyaura and Sonogashira reactions. A systematic approach based on the nature of the organic matrix will be followed: (i) metal catalysts supported on cellulose; (ii) metal catalysts supported on starch; (iii) metal catalysts supported on pectin; (iv) metal catalysts supported on agarose; (v) metal catalysts supported on chitosan; (vi) metal catalysts supported on proteins and enzymes. We will emphasize the effective heterogeneity and recyclability of each catalyst, specifying which studies were carried out to evaluate these aspects.

Sulfamic acid grafted to cross-linked chitosan by dendritic units: a bio-based, highly efficient and heterogeneous organocatalyst for green synthesis of 2,3-dihydroquinazoline derivatives

In this work, novel cross-linked chitosan by the G1 dendrimer from condensation of melamine and toluene-2,4-diisocyante terminated by sulfamic acid groups (CS-TDI-Me-TDI-NHSO₃H), as a bio-based and heterogeneous acidic organocatalyst, was designed and prepared. Also, the structure of the prepared organocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and thermogravimetric analysis/derivative thermogravimetry (TGA/DTA). Subsequently, the catalytic performance of the biobased and dendritic CS-TDI-Me-TDI-NHSO₃H, as a multifunctional solid acid, was evaluated for the preparation of 2,3-dihydroquinazoline derivatives through a three-component reaction by following green chemistry principles. Some of the advantages of this new protocol include high to excellent yields and short reaction times as well as easy preparation and remarkable catalyst stability of the introduced acidic organocatalyst. The CS-TDI-Me-TDI-SO₃H catalyst can be used for up to five cycles for the preparation of quinazoline derivatives with a slight decrease in its catalytic activity.

Metal-Free N-Doped Carbon Catalyst Derived from Chitosan for Aqueous Formic Acid-Mediated Selective Reductive Formylation of Quinoline and Nitroarenes

A chitosan-derived metal-free N-doped carbon catalyst was synthesized and investigated for selective reductive formylation of quinoline to N-formyl-tetrahydroquinoline and nitroarenes to N-formyl anilides via aqueous formic acid (FA)-mediated catalytic transformation. FA dissociated on the catalyst surface and acted as a hydrogenating and formylating source for selective N-formylation of N-heteroarenes. The carbonized catalyst prepared at 700 °C offered the best activity. A 92 % yield of N-formyl-tetrahydroquinoline after 14 h and >99 % yield for N-formyl anilide after 12 h at 160 °C were obtained. The excellent catalytic activity was correlated with the type of "N" species and the basicity of the catalyst. Density functional theory calculations revealed that a water-assisted FA decomposition pathway (deprotonation and dehydroxylation) generated the surface adsorbed -H and -HCOO species, required for the formation of N-formylated products. In addition, the selective formation of N-formyl-tetrahydroquinoline and N-formyl anilides was explained by a comprehensive reaction energetics analysis.

Chitosan-Mediated Environment-Friendly Synthesis of Gold Nanoparticles with Enhanced Photonic Reactivity

We developed a very simple, efficient and environment-friendly synthesis method for the manufacturing of high-performance chitosan-capped gold nanoparticles that could be used for biosensing applications. Gold nanoparticles were prepared through the spontaneous reduction of chloroauric acid by chitosan, which was used as both a reducing and a stabilizing agent. The samples were heated to a temperature of 60 °C under ultrasonic conditions. The composite system made of chitosan as a matrix and gold nanoparticles demonstrated a high stability in an aqueous buffer solution. The nanoparticles displayed an enhancement in photonic performance compared with the same property of individual components as a result of surface plasmon resonance at the interface between the structural phases of the hybrid structure. The enhanced photonic reactivity of the hybrid nanostructure may offer new insights for future possible biosensing applications.

Efficient and Eco-Friendly Perspectives for C-H Arylation of Benzothiazole Utilizing Pd Nanoparticle-Decorated Chitosan

In this contribution, an eco-friendly, sustainable, and efficient palladium nanoparticle-decorated chitosan (Pd@Chitosan) catalyst was synthesized by a simple impregnation method. The synthesized material was utilized as a heterogeneous catalyst for the C-H arylation of benzothiazole under ultrasonic irradiation. The Pd@Chitosan catalyst efficiently catalyzed the conversion of aryl iodides and bromides to 1-(4-(benzothiazol-2-yl)phenyl)ethan-1-one selectively. A single product of 83–93% yield was obtained in N,N-dimethylformamide solvent at 80 °C for 2.5h. This study reveals that Pd@Chitosan is an efficient catalyst, which catalyzes the C-H arylation with good reaction yields. The activity of the Pd@Chitosan is due to the presence of highly dispersed Pd(0) nanoparticles on the surface of the chitosan and Pd2+; a tentative mechanism was proposed based on the XPS results of the fresh catalyst and spent catalyst.

Chitosan Capped Copper Oxide Nanocomposite: Efficient, Recyclable, Heterogeneous Base Catalyst for Synthesis of Nitroolefins

In this article, chitosan copper oxide nanocomposite was synthesized by the solution casting method under microwave irradiation. The nanocomposite solution was microwave irradiated at 300 watt for 3 min under optimal irradiation conditions. By suppressing particle agglomeration, the chitosan matrix was successfully used as a metal oxide stabilizer. The goal of this research was to create, characterize, and test the catalytic potency of these hybrid nanocomposites in a number of well-known organic processes. The prepared CS-CuO nanocomposites were analyzed by different techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, energy-dispersive X-ray spectroscopy (EDS) was used to measure the copper content in the prepared nanocomposite film. The finger-print peaks in the FTIR spectrum at around 632–502 cm−1 confirmed the existence of the CuO phase. The CS-CuO nanocomposite has been shown to be an efficient base promoter for nitroolefin synthesis via the nitroaldol reaction (Henry reaction) in high yields. The reaction variables were studied to improve the catalytic approach. Higher reaction yields, shorter reaction times, and milder reaction conditions are all advantages of the technique, as is the catalyst’s reusability for several uses.

Efficient, Recyclable, and Heterogeneous Base Nanocatalyst for Thiazoles with a Chitosan-Capped Calcium Oxide Nanocomposite

Calcium oxide (CaO) nanoparticles have recently gained much interest in recent research due to their remarkable catalytic activity in various chemical transformations. In this article, a chitosan calcium oxide nanocomposite was created by the solution casting method under microwave irradiation. The microwave power and heating time were adjusted to 400 watts for 3 min. As it suppresses particle aggregation, the chitosan (CS) biopolymer acted as a metal oxide stabilizer. In this study, we aimed to synthesize, characterize, and investigate the catalytic potency of chitosan–calcium oxide hybrid nanocomposites in several organic transformations. The produced CS–CaO nanocomposite was analyzed by applying different analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FESEM). In addition, the calcium content of the nanocomposite film was measured using energy-dispersive X-ray spectroscopy (EDS). Fortunately, the CS–CaO nanocomposite (15 wt%) was demonstrated to be a good heterogeneous base promoter for high-yield thiazole production. Various reaction factors were studied to maximize the conditions of the catalytic technique. High reaction yields, fast reaction times, and mild reaction conditions are all advantages of the used protocol, as is the reusability of the catalyst; it was reused multiple times without a significant loss of potency.

Appealing Renewable Materials in Green Chemistry

In just a few years, chemists have significantly changed their approach to the synthesis of organic molecules in the laboratory and industry. Researchers are encouraged to approach “greener” reagents, solvents, and methodologies, to go hand in hand with the world’s environmental matter, such as water, soil, and air pollution. The employment of plant and animal derivates that are commonly regarded as “waste material” has paved the way for the development of new green strategies. In this review, the most important innovations in this field have been highlighted, paying due attention to those materials that have played a crucial role in organic reactions: wool, silk, and feather. Moreover, we decided to focus on the other most important supports and catalysts in green syntheses, such as proteins and their derivates. Different materials have shown prominent activity in the adsorption of metals and organic dyes, which has constituted a relevant scope in the last two decades. We intend to furnish a complete screening of the application given to these materials and contribute to their potential future utilization.

Efficiency of air-dried and freeze-dried alginate/xanthan beads in batch, recirculating and column adsorption processes

Alginate (Alg) beads are low-cost adsorbents used for wastewater remediation. In this work, alginate (Alg) and alginate/xanthan (Alg/XG) blend beads were synthesized by gelation method into calcium chloride and freeze-dried to improve the porosity. Their adsorption efficiency was tested for methylene blue (MB) dye in batch, recirculating and column adsorption systems. The blend beads were characterized using by SEM, FTIR-ATR and X-ray microcomputer tomography (Micro-CT) analyzes. Freeze-dried Alg and Alg/XG beads presented porosity of 46 ± 5% and 77 ± 3%, respectively. Adsorption isotherms of MB on freeze-dried Alg/XG beads indicated better adsorption capacity in comparison to the air-dried ones. Adsorption kinetics and breakthrough curves based on recirculating and vertical column adsorption processes of MB on freeze dried Alg/XG and air-dried Alg/XG beads indicated higher efficiency for the vertical column system packed with freeze dried Alg/XG beads. The removal efficiency of 91% MB by the freeze-dried Alg/XG beads in vertical column remained even after four consecutive adsorption-desorption cycles, disclosing these beads as potential systems for the wastewater treatment.

Three-Component Synthesis of Some New Coumarin Derivatives as Anticancer Agents

A three-component reaction for the synthesis of novel 3-heteroaryl-coumarin utilizing acetylcoumarin synthon under ultrasonic irradiation was developed using chitosan-grafted poly(vinylpyridine) as an eco-friendly catalyst. The process is a simple, facile, efficient procedure for the preparation of compounds displaying a thiazole ring linked to coumarin moiety. Moreover, all the products were evaluated for their anticancer activities against HEPG2-1. The results revealed that three new compounds showed promising anticancer activities.

Green synthesis of C5–C6-unsubstituted 1,4-DHP scaffolds using an efficient Ni–chitosan nanocatalyst under ultrasonic conditions

A heterogeneous and magnetically recyclable Ni–chitosan nanocatalyst was synthesized and thoroughly characterized by powder Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, etc. It was effectively utilized in the eco-friendly synthesis of new C5–C6-unsubstituted 1,4-DHPs under ultrasonic irradiation. The important focus of the methodology was to develop an environmentally friendly protocol with a short reaction time and a simple reaction procedure. The other advantages of this protocol are a wide substrate scope, a very good product yield, the use of an eco-friendly solvent and a recyclable nanocatalyst, as well as reaction at room temperature.

Bio-Based (Chitosan-ZnO) Nanocomposite: Synthesis, Characterization, and Its Use as Recyclable, Ecofriendly Biocatalyst for Synthesis of Thiazoles Tethered Azo Groups

In recent years, nanotechnology has become a considerable research interest in the area of preparation of nanocatalysts based on naturally occurring polysaccharides. Chitosan (CS), as a naturally occurring biodegradable and biocompatible polysaccharide, is successfully utilized as an ideal template for the immobilization of metal oxide nanoparticles. In this study, zinc oxide nanoparticles have been doped within a chitosan matrix at dissimilar weight percentages (5, 10, 15, 20, and 25 wt.% CS/ZnO) and have been fabricated by using a simple solution casting method. The prepared solutions of the nanocomposites were cast in a Petri-dish and were subsequently shaped as a thin film. After that, the structural features of the nanocomposite film have been studied by measuring the FTIR, SEM, and XRD analytical tools. FTIR spectra showed the presence of some changes in the major characteristic peaks of chitosan due to interaction with ZnO nanoparticles. In addition, SEM graphs exhibited dramatic morphology changes on the chitosan surface, which is attributed to the surface adsorption of ZnO molecules. Based on the results of the investigated organic catalytic reactions, the prepared CS/ZnO nanocomposite film (20 wt.%) could be a viable an effective, recyclable, and heterogeneous base catalyst in the synthesis of thiazoles. The results showed that the nanocomposite film is chemically stable and can be collected and reused in the investigated catalytic reactions more than three times without loss of its catalytic activity.

Recent progress, synthesis, and applications of chitosan-decorated magnetic nanocomposites in remediation of dye-laden wastewaters

Over the past several decades, the disposal of dyes from the industrial manufacturing sector has had an inadvertent impact on water ecology as polluted water bodies with these hazardous dyes...

Fe(II)-phthalocyanine supported on chitosan aerogel as a catalyst for oxidation of alcohols and alkyl arenes

Manipulation of materials is considered as one of the eminent strategies to create desirable catalysts. In this regard, increasing surface area and decreasing dimensions of catalysts have been widely employed on account of effectiveness of these methods. Herein, aerogel form of chitosan as a sustainable, and high aspect ratio compound is employed as a green support for the catalytic purposes. Chitosan aerogel was modified with Fe(II)-phthalocyanine to produce a heterogeneous catalyst for oxidation reactions. The synthesized catalyst promoted the oxidation reactions of alcohols and alkyl arenes to the corresponding aldehydes and ketones using H2O2 as an oxidant in 24 h. The reactions for aliphatic and aromatic alcohols gave turnover numbers of 106-109 at 80 °C and 106-117 at room temperature, respectively. The oxidations of alkyl arenes were carried out with turnover numbers laying in the range of 106-117 at 100 °C. The low toxicity, inexpensive nature, and recycling possibility of the catalyst accompanied by the reaction mild conditions, clean oxidant, and excellent yields offer chitosan aerogel modified with Fe(II)-phthalocyanine as a promising catalyst for oxidation reactions.

Chitosan with Sulfonic Groups: A Catalyst for the Esterification of Caprylic Acid with Methanol

Esterification of caprylic acid with methanol was performed over chitosan with sulfonic acid groups, as a catalyst, at 60 °C. The sulfonic acid groups were introduced into chitosan (CH) by using chlorosulfonic acid. Catalysts were characterized by scanning electron microscopy (SEM), elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and acid–base titration. Catalytic activity increased with the amount of sulfonic acid groups present on chitosan. The 4–CH–SO₃H catalyst (chitosan with sulfonic acid groups—sample 4 prepared) showed the highest activity of all materials. The esterification of caprylic acid with methanol was optimized using a 4–CH–SO₃H catalyst. Under optimized reaction conditions, it was found that, at 60 °C, with 0.2 g of catalyst loading and with a molar ratio methanol to caprylic acid equal 1:95, a caprylic acid conversion of about 83%, after 4 h could be obtained. Catalytic stability of the 4–CH–SO₃H material was evaluated through consecutive batch runs. After the second batch, the catalytic activity stabilized.

Support-Activity Relationship in Heterogeneous Catalysis for Biomass Valorization and Fine-Chemicals Production

Heterogeneous catalysts are progressively expanding their field of application, from high-throughput reactions for traditional industrial chemistry with production volumes reaching millions of tons per year, a sector in which they are key players, to more niche applications for the production of fine chemicals. These novel applications require a progressive utilization reduction of fossil feedstocks, in favor of renewable ones. Biomasses are the most accessible source of organic precursors, having as advantage their low cost and even distribution across the globe. Unfortunately, they are intrinsically inhomogeneous in nature and their efficient exploitation requires novel catalysts. In this process, an accurate design of the active phase performing the reaction is important; nevertheless, we are often neglecting the importance of the support in guaranteeing stable performances and improving catalytic activity. This review has the goal of gathering and highlighting the cases in which the supports (either derived or not from biomass wastes) share the worth of performing the catalysis with the active phase, for those reactions involving the synthesis of fine chemicals starting from biomasses as feedstocks.

Microalgae and bio-polymeric adsorbents: an integrative approach giving new directions to wastewater treatment

This review analyses the account of biological (microalgae) and synthetic (bio-polymeric adsorbents) elements to compass the treatment efficiencies of various water pollutants and mechanisms behind them. While considering pollutant removal, both techniques have their own merits and demerits. Microalgal-based methods have been dominantly used as a biological method for pollutant removal. The main limitations of microalgal methods are capacity, scale, dependence on variables of environment and duration of the process. Biopolymers on the other hand are naturally produced, abundant in nature, environmentally safe and biocompatible with cells and many times biodegradable. Algal immobilization in biopolymers has promoted the reuse of cells for further treatment and protected cells from toxic environment monitoring and controlling the external factors like pH, temperature and salinity can promote the removal process while working with the mentioned technologies. In this review, a mechanistic view of both these techniques along with integrated approaches emphasizing on their loopholes and possibilities of improvement in these techniques is represented. In addition to these, the review also discusses the post-treatment effect on algal cells which are specifically dependent on pollutant type and their concentration. All these insights will aid in developing integrated solutions to improve removal efficiencies in an environmentally safe and cost-effective manner.Novelty statement The main objective of this review is to thoroughly understand the role of micro-algal cells and synthetic adsorbents individually as well as their integrative effect in the removal of pollutants from wastewater. Many reviews have been published containing information related to either removal mechanism by algae or synthetic adsorbents. While in this review we have discussed the agents, algae and synthetic adsorbents along with their limitations and explained how these limitations can be overcome with the integration of both the moieties together in process of immobilization. We have covered both the analytical and mechanistic parts of these technologies. Along with this, the post-treatment effects on algae have been discussed which can give us a critical understanding of algal response to pollutants and by-products obtained after treatment. This review contains three different sections, their importance and also explained how these technologies can be improved in the future aspects.

Microwave-Assisted One Pot Three-Component Synthesis of Novel Bioactive Thiazolyl-Pyridazinediones as Potential Antimicrobial Agents against Antibiotic-Resistant Bacteria

Pyridazine and thiazole derivatives have various biological activities such as antimicrobial, analgesic, anticancer, anticonvulsant, antitubercular and other anticipated biological properties. Chitosan can be used as heterogeneous phase transfer basic biocatalyst in heterocyclic syntheses. Novel 1-thiazolyl-pyridazinedione derivatives were prepared via multicomponent synthesis under microwave irradiation as ecofriendly energy source and using the eco-friendly naturally occurring chitosan basic catalyst with high/efficient yields and short reaction time. All the prepared compounds were fully characterized by spectroscopic methods, and their in vitro biological activities were investigated. The obtained results were compared with those of standard antibacterial/antifungal agents. DFT calculations and molecular docking studies were used to investigate the electronic properties and molecular interactions with specific microbial receptors.

Chitin and chitosan on the nanoscale

In a matter of decades, nanomaterials from biomass, exemplified by nanocellulose, have rapidly transitioned from once being a subject of curiosity to an area of fervent research and development, now reaching the stages of commercialization and industrial relevance. Nanoscale chitin and chitosan, on the other hand, have only recently begun to raise interest. Attractive features such as excellent biocompatibility, antibacterial activity, immunogenicity, as well as the tuneable handles of their acetylamide (chitin) or primary amino (chitosan) functionalities indeed display promise in areas such as biomedical devices, catalysis, therapeutics, and more. Herein, we review recent progress in the fabrication and development of these bio-nanomaterials, describe in detail their properties, and discuss the initial successes in their applications. Comparisons are made to the dominant nanocelluose to highlight some of the inherent advantages that nanochitin and nanochitosan may possess in similar application.

A comprehensive survey upon diverse and prolific applications of chitosan-based catalytic systems in one-pot multi-component synthesis of heterocyclic rings

Heterocyclic compounds are among the most prestigious and valuable chemical molecules with diverse and magnificent applications in various sciences. Due to the remarkable and numerous properties of the heterocyclic frameworks, the development of efficient and convenient synthetic methods for the preparation of such outstanding compounds is of great importance. Undoubtedly, catalysis has a conspicuous role in modern chemical synthesis and green chemistry. Therefore, when designing a chemical reaction, choosing and or preparing powerful and environmentally benign simple catalysts or complicated catalytic systems for an acceleration of the chemical reaction is a pivotal part of work for synthetic chemists. Chitosan, as a biocompatible and biodegradable pseudo-natural polysaccharide is one of the excellent choices for the preparation of suitable catalytic systems due to its unique properties. In this review paper, every effort has been made to cover all research articles in the field of one-pot synthesis of heterocyclic frameworks in the presence of chitosan-based catalytic systems, which were published roughly by the first quarter of 2020. It is hoped that this review paper can be a little help to synthetic scientists, methodologists, and catalyst designers, both on the laboratory and industrial scales.

A sandwich model of Cr(VI) adsorption and detoxification by Fenton modified chitosan

The Fenton reaction has the advantages of short reaction time, low cost, no toxicity, and straightforward application and control. The Fenton reaction generates highly reactive HO•, which has been applied effectively. However, the effect of the generated Fe³⁺ has not been investigated widely. In this study, the Fenton reaction was used to improve the Cr(VI) adsorption and detoxification capacities of chitosan. After the Fenton modification, chitosan efficiently adsorbed Cr(VI) and transformed it into the less toxic Cr(III) in a wide pH range as a result of layer formation, which was described by a sandwich model. The adsorption of Cr(VI) onto the Fenton modified chitosan was in good agreement with the Freundlich adsorption model, and the adsorption capacity exceeded 120 mg/g. During the Fenton reaction, H₂ O₂ and HO• with high oxidative activity broke the hydrogen bonds in the chitosan structure, resulting in the release of free amine groups for Fe³⁺ to form metal-binding biopolymers. The distance between the chitosan polymers increased, and additional adsorption sites were created. HCrO₄ ^- entered the gap between the chitosan polymer and was adsorbed on the newly created adsorption sites. The sandwich adsorption model indicated that the Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification. PRACTITIONER POINTS: Fenton reaction was used to improve the adsorption ability of chitosan. The formed Fe³⁺ in Fenton reaction was utilized. HO· broke the hydrogen bonds and Fe³⁺ ions chelated with chitosan in modification. Cr(VI) could be adsorbed and reduced efficiently by Fenton modified chitosan. The Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification.

ZnFe2O4-chitosan magnetic beads for the removal of chlordimeform by photo-Fenton process under UVC irradiation

A simple protocol was proposed for the preparation of magnetic chitosan beads ZnFe₂O₄-CS via a co-precipitation method. The use of synthesized magnetic ZnFe₂O₄-CS beads as catalyst for the heterogeneous photo-Fenton treatment of chlordimeform insecticide (CDM) was evaluated. The photo-Fenton experiments were carried out with different synthesized catalysts by varying the molar ratio Zn/Fe in chitosan beads, the catalyst concentration and pH. Under optimal conditions using 1 g of ZnFe₂O₄-CS beads with a molar ratio Zn/Fe = 0.35 and at pH_initial = 3, a real wastewater doped with 20 mg L^-1 of CDM was treated and complete removal of the insecticide was achieved after 7 min with a total TOC removal after 2 h of treatment. The generated carboxylic acids and ions during the photo-Fenton process were identified and quantified. The stability of the photocatalytic activity of the best catalyst in terms of pollutant removal, ZnFe₂O₄-CS(0.35) beads with a molar ratio Zn/Fe equal to 0.35, was satisfactory validated by four consecutive cycles. This optimal catalyst was characterized, before and after use, by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy, X-Ray Powder Diffraction and Vibrating Sample Magnetometry analysis.

Chitosan as a chiral ligand and organocatalyst: preparation conditions–property–catalytic performance relationships

Properties of chitosan prepared by alkaline deacetylation of chitin under various conditions were correlated with their performance as ligands or organocatalysts in asymmetric catalytic reactions.

Facile synthesis of chitosan membranes for visible-light-driven photocatalytic degradation of tetracycline hydrochloride

Due to the film-forming ability of polymers, a variety of photocatalytic membranes (PMs) based on polymers easily being separated and reused have been constructed for wastewater contaminant treatment. During their construction processes, chitosan (CS) as a bio-polymer with its distinct merits of abundant resources, low-cost and environmental-friendliness, as well as formability and ease of modification, has attracted great attention. However, the role of CS was mostly believed to be just a support or an adsorbent for fixing or dispersing photocatalysts. Whether CS possessed photocatalytic activity or not still remained vague. Herein, in this work, CS membranes (CSM) were facilely prepared for photocatalytic degradation of tetracycline hydrochloride (TC, a model organic pollutant) in aqueous solution, and its photocatalytic performance was investigated and compared with that of CSP (CS powder) and TiO2-P25 (a commercially used photocatalyst). The results showed that the single-phased CSM exhibited a better visible light photocatalytic activity. After visible light irradiation for 60 minutes, the degradation efficiency of TC can reach above 90% when the CSM was used as a photocatalyst, while with the same irradiation time interval, less TC could be degraded over both CSP and TiO2-P25. Through radical scavenging and EPR experiments, ˙O2 - and h+ were found to be the main active oxygen species generated in the reaction system for TC degradation. After being washed with 2 wt% NaOH solution, the CSM revealed a good recyclability implying its potential for practical applications. This study would provide a certain theoretical and data basis for the future development of CS-based PMs and photocatalysts.

Fabrication of a metal free catalyst for chemical reactions through decoration of chitosan with ionic liquid terminated dendritic moiety

In attempt to develop a biocompatible metal-free catalyst, a dendritic moiety was grown on chitosan through successive reactions with 2,4,6-trichloro-1,3,5-triazine and ethylenediamine. Subsequently, the terminal functional groups of the dendron were decorated with 1-methylimidazolium chloride. The catalyst was characterized with SEM, EDS, TGA, FTIR, XRD and mapping analysis. Then, the catalytic activity of the resultant composite was scrutinized for catalyzing Knoevenagel condensation and synthesis of xanthene derivatives in aqueous media under mild reaction condition. The results confirmed high activity of the catalyst, superior to ionic liquid free counterpart and bare chitosan. This observation was ascribed to the instinct catalytic activity of ionic liquid. Moreover, using control catalysts, it was confirmed that the presence of the dendritic moiety that could increase the content of ionic liquid on the backbone of the catalyst enhanced the catalytic activity.