Preparation of xylan citrate—A potential adsorbent for industrial wastewater treatment

Synthesis and antitumor activity of bagasse xylan derivatives modified by graft-esterification and cross-linking

A crucial aspect in achieving sustainable development of biomass materials is the modification of renewable polysaccharides to create various high-value functional materials. In this paper, bagasse xylan (BX) was used as a raw material to introduce benzyl methacrylate (BMA) through graft copolymerization reaction to generate the intermediate product BX-g-BMA. Subsequently, the target product (CA-BX-g-BMA) was synthesized by catalytic esterification of BX-g-BMA with citric acid (CA) in AmimCl ionic liquid. Meanwhile, the characterization and bioactivity studies of CA-BX-g-BMA were carried out. The graft copolymerization and esterification reactions induced significant changes in the morphological structure of BX and obviously improved its thermal stability and crystallinity. The application of density functional theory (DFT), molecular electrostatic potential (MEP) and molecular docking has revealed that CA-BX-g-BMA possesses multiple active sites, strong biological activity and a strong binding affinity to 6RCF tumor protein with a binding energy of -32.26 kJ/mol. The in vitro antitumor activity of this novel derivative was tested by MTT assay, and the results showed that CA-BX-g-BMA was non-toxic to normal cells and inhibited MDA-MB-231 (breast cancer cells) by up to 32.16 % ± 4.89 %, which is approximately 11 times higher than that of BX. The exploration of these properties is essential to promote future multidisciplinary applications of BX derivatives.

Magnetic hydrogel based on xylan, poly (acrylic acid), and maghemite as adsorbent material for methylene blue adsorption: experimental design, kinetic, and isotherm

A magnetic hydrogel based on xylan (X), poly (acrylic acid), and maghemite (γ-Fe2O3) named HXA-Fe2O3 was synthesized, characterized, and applied as an alternative material to remove methylene blue (MB) from aqueous media by adsorption. Maghemite was synthesized by coprecipitation method and later incorporated in the hydrogel matrix synthesized by free radical polymerization. The characterization studies included FTIR, DSC, XRD, VSM, Zeta Potential, TGA, SEM, TEM, and N2 adsorption isotherms (BET). The physicochemical characterization results confirmed the intended synthesis and showed the compositional, thermal, structural, morphological, textural, and magnetic profile of the materials. The adsorption studies included experimental design, kinetic, and isotherm. A full factorial design was employed considering the factors adsorbent dosage (g L-1), pH, and ionic strength (mmol L-1 of NaCl) for adsorption capacity and removal percentage responses. As ionic strength was not significant, a Doehlert design was employed with adsorbent dosage and pH, indicating the optimal adsorption conditions. The kinetics was well described by the PSO model, while the isotherm obeyed the Sips model. Equilibrium was attained at 60 min, and the maximum experimental adsorption capacity was up to 250.26 mg g-1 at pH 8.5, adsorbent dosage of 0.2 g L-1, and 298 K. These findings show that the magnetic hydrogel produced has great potential to be applied in the adsorption of basic molecules, such as MB.

Molecular scale behavior of xylan during solvent-controlled extraction and precipitation

Solvent-controlled extraction and precipitation are the most fundamental methods for obtaining hemicellulose from lignocellulosic biomass and purification processes. However, the dissolution and precipitation mechanisms involved have scarcely been mentioned. In this study, the molecular scale behavior of xylan-type hemicellulose during solvent-controlled extraction and precipitation is investigated using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. To bring the model closer to the real extracted xylan, a high degree of polymerization (DP100) of xylan is established, and hemicelluloses with low DP (DP15 and DP50) are also investigated. Four phenomena are explained at the molecular level, including the influence of the polymerization degree and side chain on the solubility of xylan in water, the improvement of the xylan's solubility in NaOH, the precipitation of xylan in ethanol, and the acetyl group preservation of xylan in DMSO. This study contributes to an increased understanding of the dissolution and precipitation mechanisms of hemicellulose and provides a resource for the simulation of high DP hemicellulose, which gives a theoretical basis for the efficient extraction of high-purity hemicellulose as well as economic biorefining.

Development of hydrogels based on xylan and poly (acrylic acid) for melamine adsorption in batch and continuous mode: experimental design, kinetics, isotherms, recyclability, and fixed-bed column

Two hydrogels were synthesized, characterized, and applied as alternative materials to remove melamine (MEL) from aqueous media by adsorption. For the first time, a complete study of MEL adsorption is presented, including optimization, kinetics, isotherm, reuse, and column studies with these new materials. One hydrogel is based on xylan and poly (acrylic acid) and was named HXy, and the other is based on the same components functionalized with activated carbon and was named HXy-AC. The materials were synthesized by free radical polymerization and characterized by FTIR, XRD, TGA, DSC, SEM, zeta potential, point of zero charge, N2 adsorption isotherms (BET), helium gas pycnometry, Archimedes method, swelling analysis, and stability tests. The characterization results confirmed the intended synthesis and showed the thermal, morphological, textural, structural, and compositional profile, as well as the adsorption characteristics of the materials. The adsorption studies in batch process included experimental design, kinetics, isotherms, and recyclability, and in continuous mode, the studies included fixed-bed column experiments. The full factorial design showed that adsorbent dosage, pH, and ionic strength are significant for adsorption capacity and removal percentage responses. Doehlert design enabled the definition of the values of adsorbent dosage and pH that were most suitable for MEL adsorption into the materials, indicating the optimal adsorption conditions. The kinetics were well described by the pseudo-first-order model, with R2 above 0.9920 for both materials at all concentrations tested. The isotherm obeyed the Langmuir model, with R2 above 0.9939 for both materials at all temperatures tested. Equilibrium was attained at 180 min, and the maximum experimental adsorption capacity was up to 132.46 and 118.96 mg g-1 at pH 7, with adsorbent dosage of 0.5 g L-1, and 298 K for HXy and HXy-AC, respectively. Furthermore, HXy and HXy-AC materials maintained about 58 and 70% of their initial adsorption capacity at the end of five adsorption/desorption cycles, respectively. Breakthrough curves were described by the Yan model and presented a maximum adsorption capacity of 30.2 and 30.4 mg g-1, treating 3.4 and 6.1 L of influent until the breakthrough point of 0.5 mg L-1 with HXy-AC using 2.0 and 4.0 g of material, respectively. These findings show that the hydrogels produced present the potential to be applied in the adsorption of basic molecules, such as MEL.

Sustainable hemp-based bioplastics with tunable properties via reversible thermal crosslinking of cellulose

Modern bioplastics and biocomposites frequently contain non-biodegradable or non-sustainable components and require complex recycling routes. Sustainable materials require integrating bio-based, cheap, widely available, recycled, or waste components. In order to incorporate these concepts, we selected hemp stalk waste, the industrial byproducts glycerol and xylan (hemicellulose), and citric acid as key components. Hemp stalks were processed into cast papers using only mechanical processes and no chemical modifications or pre-treatments. Cast papers were impregnated with a crosslinking mixture of glycerol, xylan, citric acid, and the plasticizer polyethylene glycol (PEG). Thermal crosslinking was performed as a single-step reaction by curing materials at 140 °C. All prepared bioplastics were washed in water for 48 h and extensively tested for water resistance and water absorption. A recycling route with depolymerization (for pulp recovery) in sodium hydroxide is demonstrated. A comprehensive analysis of crosslinking reaction is provided via FTIR and rheology, supplemented by structure analysis via SEM. A 7-fold reduction in water uptake was achieved compared to cast hemp paper. Obtained bioplastics, after washing in water, show elastic modulus up to 2.9 GPa, tensile strength up to 70 MPa, and elongation up to 4.3 %. As a result of component ratio variation, bioplastics achieve a high tuneability of properties ranging from brittle to ductile. Dielectric analysis indicates that bioplastics have the potential for application in electric insulation. A three-layer laminate is demonstrated as a concept for potential application as an adhesive for bio-based composites.

Fabrications and applications of hemicellulose-based bio-adsorbents

Super adsorbents exhibit great potential to remove pollutants from media or store considerable amounts of water, which may undermine the pressure triggered by environmental pollution and shortage of water resources. Super adsorbents made from biopolymers have been an attractive topic because of biodegradability, renewability and outstanding adsorption capacity. Hemicelluloses are a type of biopolymers very abundant in agricultural, forestry and pulping industrial wastes. Hemicellulose-based bio-adsorbents are thriving because the inherent chemical structures and physical properties of hemicelluloses make themselves easy to be processed into matrix materials applicable in super adsorbents. This review summarizes recent studies in hemicellulose-based bio-adsorbents, i.e. hydrogels and activated carbons, from the perspectives of types, applications, fabrication methods, the elements affecting the adsorption performance and the kinetics of adsorption process, which thus helps to further improve the properties of hemicellulose-based bio-adsorbents and to promote the industrial production and utilization of hemicelluloses and hemicellulose-based bio-adsorbents.

Polarity of Cationic Lignin Polymers: Physicochemical Behavior in Aqueous Solutions and Suspensions

The structure of cationic monomers can significantly impact the polarity of lignin after polymerization. Cationic hydrolysis lignin (CHL) polymers were produced by polymerizing hydrolysis lignin (HL) with [3-(methacryloylamino)propyl] trimethylammonium chloride (MAPTAC) or [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (METAC). The METAC monomer has an oxygen atom, with larger electronegativity, in its molecular structure, whereas the MAPTAC monomer contains a nitrogen atom, as well as an extra nonpolar CH₂ group, facilitating investigation into the effects of the polarity of CHLs on their physicochemical performance in an aqueous system. CHL polymers are analyzed and their interactions with clay particles are determined in colloidal systems. CHLs are designed to have similar charge densities (2.1-2.2 mmol g^-1) and molecular weights (55000-60000 g mol^-1 ). The hydrodynamic radius (H_y) and radius of gyration, (R_g) of HL-METAC are larger than those of HL-MAPTAC, implying a more 3-dimensional structure of HL-METAC in aqueous solution. The stability ratio of kaolin particles affirms the better performance of HL-METAC in comparison to HL-MAPTAC, which reflects the better flocculation efficiency of HL-METAC. The results also reveal that salt and urea aqueous solutions affect the H_y, R_g, and configuration of CHL polymers, which alters the flocculation efficiency of HL-METAC and HL-MAPTAC polymers in kaolin suspensions.

Chemically crosslinked xylan-β-Cyclodextrin hydrogel for the in vitro delivery of curcumin and 5-Fluorouracil

Novel hydrogels were synthesized from xylan and β-Cyclodextrin using Ethylene Glycol Diglycidyl Ether as a crosslinker in alkaline medium at different molar ratio. The physical characterization of hydrogels was carried out by the swelling study whereas the chemical characterization was performed in Fourier Transform Infrared Spectroscopy. The morphological analysis revealed the porous structure of hydrogel and the rheological study summarised the flow behavior and gelation characteristics of the hydrogels. Curcumin and 5-Fluorouracil (5-FU) were used as the model drugs to be loaded in hydrogel and subsequent studies involving the in vitro release in phosphate buffer saline (PBS, pH = 7.4). The hydrogels showed drug loading of 98% of 5-FU and 26% of curcumin. Furthermore, the gels showed the highest cumulative release of 56% 5-FU and 37% curcumin after 24 h. The kinetics of drug release was then analyzed by various kinetic models.

How Fine Structural Differences of Xylooligosaccharides and Arabinoxylooligosaccharides Regulate Differential Growth of Bacteroides Species

Xylooligosaccharides (XOS) and arabinoxylooligosaccharides (AXOS) could be used to selectively favor growth of certain gut bacterial groups. The objective of this research was to understand how the structural differences of XOS and AXOS influenced the growth of Bacteroides species commonly found in the intestine. We report that the specific structural details of XOS and AXOS dictate the differential growth of Bacteroides species in the intestine. We also investigated the expression of two polysaccharide utilization loci (PULs) in a strain of Bacteroides ovatus upon growth on AXOS using three different susC transcripts as sentinel reporter genes. 2³-α-l-Arabinofuranosyl-xylotriose (A4) was shown to upregulate small xylan PUL gene expression, while 2³,3³-di-α-l-arabinofuranosyl-xylotriose (A6) decreased expression of this PUL. These results reveal new details about the potentially very specific structure-function relationship of XOS and AXOS that could be used in targeted alteration of the microbial population in the gut through dietary interventions to maintain health.

Preparation and Application of Phosphorylated Xylan as a Flocculant for Cationic Ethyl Violet Dye

In this study, phosphorylated birchwood xylan was produced under alkali conditions using trisodium trimetaphosphate. Three single-factor experiments were used to explore the influences of time, temperature, and the molar ratio of trisodium trimetaphosphate to xylan on the degree of substitution (DS) and charge density of xylan. The response surface methodology was used to explore the interaction of these three factors. Phosphorylated xylan with a maximum DS of 0.79 and a charge density of -3.40 mmol/g was produced under the optimal conditions of 80 °C, 4 h, and a molar ratio of xylan/sodium trimetaphosphate (STMP) of 1/3. Fourier transform infrared (FTIR), ascorbic acid method analyses, and inductively coupled plasma⁻atomic emission spectrometer (ICP-AES) analyses confirmed that the phosphate groups were successfully attached to xylan. Thermogravimetric analysis confirmed that phosphorylated xylan was less stable than birchwood xylan. Furthermore, the phosphorylated xylan was applied as a flocculant for removing ethyl violet dye from a simulated dye solution. The results indicated that more than 95% of the dye was removed from the solution. The theoretical and experimental values of charge neutralization for the dye removal were close to one another, confirming that charge neutralization was the main mechanism for the interaction of dye and phosphorylated xylan. The impacts of salts on the flocculation efficiency of phosphorylated xylan were also analyzed.

Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial

In this work, three-dimensional (3D) aerogels and hydrogels based on lignin-containing arabinoxylan (AX) and cellulose nanofibers (CNF) were prepared. The effects of the CNF and the crosslinking with citric acid (CA) of various contents (1, 3, 5 wt%) were evaluated. All the aerogels possessed highly porous (above 98%) and lightweight structures. The AX-CNF hydrogel with a CA content of 1 wt% revealed a favorable network structure with respect to the swelling ratio; nanofiber addition resulted in a five-fold increase in the degree of swelling (68 g of water per g). The compressive properties were improved when the higher CA content (5 wt%) was used; when combined with CNF, there was a seven-fold enhancement in the compressive strength. The AX-CNF hydrogels were prepared using a green and straightforward method that utilizes sustainable resources efficiently. Therefore, such natural hydrogels could find application potential, for example in the field of soft tissue engineering.

Plant biomimicking assembly: the use of cellulose nanofibers as a functional biomaterial for promoted hydrogel formation from lignin-containing arabinoxylan-based aerogels.

Synthesis of Acylated Xylan-Based Magnetic Fe₃O₄ Hydrogels and Their Application for H₂O₂ Detection

Acylated xylan-based magnetic Fe₃O₄ nanocomposite hydrogels (ACX-MNP-gels) were prepared by fabricating Fe₃O₄ nanoctahedra in situ within a hydrogel matrix which was synthesized by the copolymerization of acylated xylan (ACX) with acrylamide and N-isopropylacrylamide under ultraviolet irradiation. The size of the Fe₃O₄ fabricated within the hydrogel matrix could be adjusted through controlling the crosslinking concentrations (C). The magnetic hydrogels showed desirable magnetic and mechanical properties, which were confirmed by XRD, Raman spectroscopy, physical property measurement system, SEM, TGA, and compression test. Moreover, the catalytic performance of the magnetic hydrogels was explored. The magnetic hydrogels (C = 7.5 wt %) presented excellent catalytic activity and provided a sensitive response to H₂O₂ detection even at a concentration level of 5 × 10^-6 mol·L^-1. This approach to preparing magnetic hydrogels loaded with Fe₃O₄ nanoparticles endows xylan-based hydrogels with new promising applications in biotechnology and environmental chemistry.

Production of cationic xylan-METAC copolymer as a flocculant for textile industry

Xylan is a part of hemicelluloses of woody materials and can be converted to value-added products such as flocculants for the textile industry. To assess the production of flocculants from hemicelluloses of woody materials, xylan was selected as a model and rendered cationic via copolymerization. In this study, the copolymerization reaction of xylan and [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC) was optimized. The optimum parameters were 3mol/mol METAC/xylose, 3h reaction time, 80°C reaction temperature, pH 7 and 25g/L xylan concentration. The copolymer was characterized by a charge density analyzer, viscometer, gel permeation chromatography (GPC), light scattering instrument, Fourier transform infrared spectroscopy (FTIR) and an elemental analyzer. The application of the cationic xylan copolymer as a flocculant to decolorize the simulated reactive orange 16 azo-dye wastewater was evaluated. The results confirmed that, by having 160mg/L xylan-METAC concentration in the dye solution with the concentration of 100mg/L, 97.8% of dye could be removed.

Quantitative analysis of citric acid/sodium hypophosphite modified cotton by HPLC and conductometric titration

Isocratic HPLC was used in conjunction with conductometric titration to quantitatively examine the modification of cotton cellulose by citric acid (CA)/sodium hypophosphite (SHP). CA/SHP had been extensively used as a green crosslinking agent for enhancement of cellulose and other carbohydrate polymers without in-depth understanding of the mechanisms. The current study investigated all identifiable secondary polycarboxylic acids from CA decomposition in the CA/SHP-cellulose system under various curing conditions. It was found that CA decomposition was more sensitive to temperature compared with the desirable esterification reaction. Two crosslinking mechanisms, namely ester crosslinking and SHP crosslinking were responsible for the observed improvement in crease resistance of CA/SHP treated cotton fabrics. An oligomer of citraconic acid (CCA) and/or itaconic acid (IA) was identified as a possible contributor to fabric yellowing. Finally, the crease resistance of fabrics correlated strongly with CA preservation in polyol-added CA/SHP crosslinking systems. The dosage of polyol should be held below an inflexion point to keep the undesirable competition against cellulose minimum. The combination of HPLC and conductometric titration was demonstrated to be useful in studying the CA/SHP-cellulose crosslinking system. The findings have implications for better application of CA/SHP in polysaccharide modifications in general.

Modified β-cyclodextrin inclusion complex to improve the physicochemical properties of albendazole. complete in vitro evaluation and characterization

The potential use of natural cyclodextrins and their synthetic derivatives have been studied extensively in pharmaceutical research and development to modify certain properties of hydrophobic drugs. The ability of these host molecules of including guest molecules within their cavities improves notably the physicochemical properties of poorly soluble drugs, such as albendazole, the first chosen drug to treat gastrointestinal helminthic infections. Thus, the aim of this work was to synthesize a beta cyclodextrin citrate derivative, to analyze its ability to form complexes with albendazole and to evaluate its solubility and dissolution rate. The synthesis progress of the cyclodextrin derivative was followed by electrospray mass spectrometry and the acid-base titration of the product. The derivative exhibited an important drug affinity. Nuclear magnetic resonance experiments demonstrated that the tail and the aromatic ring of the drug were inside the cavity of the cyclodextrin derivative. The inclusion complex was prepared by spray drying and full characterized. The drug dissolution rate displayed exceptional results, achieving 100% drug release after 20 minutes. The studies indicated that the inclusion complex with the cyclodextrin derivative improved remarkably the physicochemical properties of albendazole, being a suitable excipient to design oral dosage forms.