Construction of chitosan/polyacrylate/graphene oxide composite physical hydrogel by semi-dissolution/acidification/sol-gel transition method and its simultaneous cationic and anionic dye adsorption properties

Adsorption properties of methylene blue and Cu(II) on magnetically oxidized tannic acid cross-linked carboxymethyl chitosan gels

In this work, tannic acid was selected as a green cross-linking agent to cross-link carboxymethyl chitosan to prepare a magnetic adsorbent (CC-OTA@Fe3O4), which was used to remove methylene blue (MB) and Cu2+. CC-OTA@Fe3O4 was characterized by FTIR, 13C NMR, XRD, VSM, TGA, BET and SEM. The adsorption behavior was studied using various parameters such as pH value, contact time, initial concentration of MB and Cu2+, and temperature. The results showed that adsorption of MB and Cu2+ followed the pseudo-second-order model and the Sips model. The maximum adsorption capacities were determined to be 560.92 and 104.25 mg/g MB and Cu2+ at 298 K, respectively. Thermodynamic analysis showed that the adsorption is spontaneous and endothermic in nature. According to the results of FTIR and XPS analyses, the electrostatic interaction was accompanied by π-π interaction and hydrogen bonding for MB adsorption, while complexation and electrostatic interaction were the predominant mechanism for Cu2+ adsorption. Furthermore, CC-OTA@Fe3O4 displayed remarkable stability in 0.1 M HNO3, exhibited promising recyclability, and could be easily separated from aqueous solutions in the magnetic field. This study demonstrates the potential of CC-OTA@Fe3O4 as an adsorbent for the removal of cationic dyes and heavy metals from wastewater.

Effective removal of Cu(II) from water by three-dimensional composite microspheres based on chitosan/sodium alginate/silicon dioxide: Adsorption performance and mechanism

Chitosan (CS) is commonly used as an adsorbent for removing Cu(II) from water, but it has drawbacks such as solubility in dilute acid, difficulty in recycling in powder form, and short service life. This study utilized sodium alginate (SA) as a gel carrier to encapsulate CS, combined with silicon dioxide (SiO2) to improve mechanical stability. The preparation of CS/SA/SiO2 (SSC1.0) involved physical blending, CaCl2 cross-linking, and freeze-drying. Characterization methods such as SEM-EDS, FTIR, BET, and XRD were used to analyze the structural composition of SSC1.0. The material exhibited a folded surface, porous internal cross-section, nitrogen/oxygen-containing functional groups, and thermal stability in high temperatures and various aqueous environments. The adsorption performance of SSC1.0 on Cu(II) was evaluated under different conditions, showing a maximum adsorption capacity of 47.50 mg/g. The material maintained a removal rate above 70 % after 5 cycles. SSC1.0 also showed the highest removal rate of Cu(II) when applied to mine wastewater treatment. Adsorption modeling indicated that the process was driven by chemical reactions and was spontaneous and heat-absorbing.'

Advances and Applications of Hybrid Graphene-Based Materials as Sorbents for Solid Phase Microextraction Techniques

The advancement of traditional sample preparation techniques has brought about miniaturization systems designed to scale down conventional methods and advocate for environmentally friendly analytical approaches. Although often referred to as green analytical strategies, the effectiveness of these methods is intricately linked to the properties of the sorbent utilized. Moreover, to fully embrace implementing these methods, it is crucial to innovate and develop new sorbent or solid phases that enhance the adaptability of miniaturized techniques across various matrices and analytes. Graphene-based materials exhibit remarkable versatility and modification potential, making them ideal sorbents for miniaturized strategies due to their high surface area and functional groups. Their notable adsorption capability and alignment with green synthesis approaches, such as bio-based graphene materials, enable the use of less sorbent and the creation of biodegradable materials, enhancing their eco-friendly aspects towards green analytical practices. Therefore, this study provides an overview of different types of hybrid graphene-based materials as well as their applications in crucial miniaturized techniques, focusing on offline methodologies such as stir bar sorptive extraction (SBSE), microextraction by packed sorbent (MEPS), pipette-tip solid-phase extraction (PT-SPE), disposable pipette extraction (DPX), dispersive micro-solid-phase extraction (d-µ-SPE), and magnetic solid-phase extraction (MSPE).

Hydrogels comprising oxidized carboxymethyl cellulose and water-soluble chitosan at varied oxidation levels: Synthesis, characterization, and adsorptive toward methylene blue

Chitosan, as a biomaterial, has increasingly garnered attention. However, its limited solubility in water-only dissolving in certain dilute acidic solutions-substantially restricts its broader application. In this investigation, chitosan underwent a solubilization modification to acquire water solubility, facilitating its dissolution in neutral aqueous mediums. Subsequently, this water-soluble chitosan (WSC) was interlinked with oxidized carboxymethyl cellulose (OCMC), characterized by varied oxidation extents, to synthesize hydrogels. Structural characterization verified the formation of imine bonds resulting from crosslinking interactions between the amino groups of water-soluble chitosan and the aldehyde groups of oxidized carboxymethyl cellulose. Employing performance characterization analysis, it was discerned that an increase in the oxidation level of the oxidized carboxymethyl cellulose corresponded to a denser hydrogel network architecture and the hardness increased from 3.01 N to 6.16 N. Moreover, the capacity of these hydrogels to adsorb methylene blue was meticulously examined. Notably, the hydrogel denoted as WSC/66%OCMC manifested an adsorption capability of 28.08 mg/g for methylene blue. Analytical findings from adsorption kinetics and isotherm studies indicate that the adsorption mechanism of the WSC/66%OCMC hydrogel follows the pseudo-second-order kinetic model and corresponds to the Freundlich isotherm model.

One stone, two birds: An eco-friendly aerogel based on waste pomelo peel cellulose for the efficient adsorption of dyes and heavy metal ions

To achieve the objective of "waste control by waste", in this study, a green aerogel adsorbent comprised of pomelo-peel cellulose and sodium alginate (PCC/SA) was prepared through dual-network crosslinking. The resulting 3D hierarchical porous structured PCC/SA aerogel exhibited good structural stability, and kept the morphological integrity during 10 days in a wide pH range (2-10), suggesting its potential for recycling in diverse complex environments. Besides, the superior adsorption capacities for methylene blue (MB) and Cu(II) were observed, with the qm values and adsorption equilibrium times were recorded to be 1299.59 mg/g (300 min) and 287.55 mg/g (120 min), correspondingly. Furthermore, the favorable reusability of the PCC/SA aerogel was also demonstrated, with the removal efficiency for MB remaining almost unchanged (about 94 %) after 10 adsorption-desorption cycles, while there was a slight reduction for Cu(II) from 85.28 % to 72.47 %. XPS and FTIR analysis revealed that electrostatic attraction, hydrogen bonding, cation exchange and coordination were the major adsorption mechanisms. Importantly, the PCC/SA aerogel can be naturally degraded in soil within 10 weeks. Therefore, the as-prepared aerogel bead derived from pomelo peel shows great promise as an adsorbent for wastewater treatment containing dye and heavy metal ions.

Sorption behavior of chitosan nanoparticles for single and binary removal of cationic and anionic dyes from aqueous solution

In this study, chitosan nanoparticles (ChNs) were used as an adsorbent for single and simultaneous uptake of cationic (methylene blue (MB)) and anionic (methyl orange (MO)) dyes. ChNs were prepared based on the ionic gelation method using sodium tripolyphosphate (TPP) and characterized by zetasizer, FTIR, BET, SEM, XRD, and pHPZC. The studied parameters that affect removal efficiency included pH, time, and dyes' concentration. The results showed that in single-adsorption mode, the removal of MB is better in alkaline pH, contrary to MO uptake which presents higher removal efficiency in acidic media. The simultaneous removal of MB and MO from the mixture solution by ChNs could be achieved under neutral conditions. The adsorption kinetic results showed that adsorption of MB and MO for both single-adsorption and binary adsorption systems comply with the pseudo-second-order model. Langmuir, Freundlich, and Redlich-Peterson isotherms were used for the mathematical description of single-adsorption equilibrium, while non-modified Langmuir and extended Freundlich isotherms were used to fit the co-adsorption equilibrium results. The maximum adsorption capacities of MB and MO in a single dye adsorption system were 315.01 and 257.05 mg/g for MB and MO, respectively. On the other hand, and for binary adsorption system, the adsorption capacities were 49.05 and 137.03 mg/g, respectively. The adsorption capacity of MB decreases in solution containing MO and vice versa, suggesting an antagonistic behavior of MB and MO on ChNs. Overall, ChNs could be a candidate for single and binary removal of MB and MO in dye-containing wastewater.

Natural Polysaccharide-Based Hydrogels Used for Dye Removal

Removal of contaminants from discharge water is vital and demands urgent assistance with the goal to keep clean water. Adsorption is one of the most common, efficient, and low-priced methods used in water treatment. Various polysaccharide-based gels have been used as efficient dye adsorbents from wastewater. This review summarizes cutting-edge research of the last decade of different hydrogels based on natural polysaccharides (chitin, chitosan, cellulose, starch, pullulan, and dextran) concerning their dye adsorption efficiency. Beyond their natural abundance, attributes of polysaccharides such as biocompatibility, biodegradability, and low cost make them not only efficient, but also environmentally sustainable candidates for water purification. The synthesis and dye removal performance together with the effect of diverse factors on gels retaining ability, kinetic, and isotherm models encountered in adsorption studies, are introduced. Thermodynamic parameters, sorbent recycling capacity along with conclusions and future prospects are also presented.

Fabrication of maleic anhydride-acrylamide copolymer based sodium alginate hydrogel for elimination of metals ions and dyes contaminants from polluted water

The study explores the synergy of biobased polymers and hydrogels for water purification. Polymer nanomaterial's, synthesized by combining acrylamide copolymer with maleic anhydride, were integrated into sodium alginate biopolymer using an eco-friendly approach. Crosslinking agents, calcium chloride and glutaraladehyde, facilitated seamless integration, ensuring non-toxicity, high adsorption performance, and controlled capacity. This innovative combination presents a promising solution for clean and healthy water supplies, addressing the critical need for sustainable environmental practices in water purification. In addition, the polymer sodium alginate hydrogel (MAH@AA-P/SA/H) underwent characterization via the use of several analytical procedures, such as FTIR, XPS, SEM, EDX and XRD. Adsorption studies were conducted on metals and dyes in water, and pollutant removal methods were explored. We investigated several variables (such as pH, starting concentration, duration, and absorbent quantity) affect a material's capacity to be adsorbed. Moreover, the maximum adsorption towards Cu2+ is 754 mg/g while for Cr6+ metal ions are 738 mg/g, while the adsorption towards Congo Red and Methylene Blue dye are 685 mg/g and 653 mg/g correspondingly, within 240 min. Adsorption results were further analyzed using kinetic and isothermal models, which showed that MAH@AA-P/SA/H adsorption is governed by a chemisorption process. Hence, the polymer prepared from sodium alginate hydrogel (MAH@AA-P/SA/H) has remarkable properties as a versatile material for the significantly elimination of harmful contaminants from dirty water.

Comprehensive review on pH and temperature-responsive polymeric adsorbents: Mechanisms, equilibrium, kinetics, and thermodynamics of adsorption processes for heavy metals and organic dyes

Wastewater treatment technologies have been developed to address the health and environmental risks associated with toxic and cancer-causing dyes and heavy metals found in industrial waste. The most commonly used method to mitigate and treat such effluents is adsorption, which is favored for its high efficiency, low costs, and ease of operation. However, traditional adsorbents have limitations in terms of regeneration and selectivity compared to smart adsorbents. Smart polymeric adsorbents, on the other hand, can undergo physical and chemical changes in response to external factors like temperature and pH, enabling a selective adsorption process. These adsorbents can be easily regenerated and reused with minimal generation of secondary pollutants during desorption. The unique properties acquired by stimuli-responsive adsorbents have encouraged researchers to investigate their potential for the selective and efficient removal of organic dyes and heavy metals. This comprehensive review focuses on two common stimuli, pH and temperature, discussing the fabrication methods and characteristics of smart adsorbents responsive to these factors. It also provides an overview of the mechanisms, isotherms, kinetics, and thermodynamics of the adsorption process for each type of stimuli-responsive adsorbent. Finally, the review concludes with discussions on future perspectives and considerations.

Preparation and application of the thermo-/pH-/ ion-sensitive semi-IPN hydrogel based on chitosan

Chitosan based hydrogels with multiple stimulus responses have broad application prospects in many fields. Considering the advantages of semi interpenetrating network (IPN) technology and the special temperature and ion responsiveness of polymers containing zwitterionic groups, a semi-IPN hydrogel was prepared through in situ free radical polymerization of N,N-dimethyl acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide with polyethylene glycol dimethacrylate as a crosslinker and carboxymethyl chitosan as filler. The gel mass fraction and swelling ratio were measured, and the preparation conditions were optimized. The result indicated that the hydrogel possessed a unique thermo-/pH-/ ion-sensitive behavior. The swelling ratio increased with the increase of temperature and ion concentration, and showed a decreasing trend with the increase in pH. In addition, the hydrogel was stable when the stimuli changed. Adsorption behavior of the hydrogel to Eosin Y (EY) was systematically investigated. The adsorption process can be described well by the pseudo-second-order kinetic model and Langmuir isotherm model, indicating that it was a chemical adsorption. The experiments indicated that the hydrogel exhibited good antifouling and reusability features. Therefore, the semi-IPN hydrogel with antifouling properties and thermo-/pH-/ion-sensitivity can be easily manufactured is expected to find applications in water treatment fields.

Preparation of chitosan-based ternary nanocomposite hydrogel film by loading graphene oxide nanosheets as adsorbent for enhanced methylene blue dye removal

Our objective in this study is to fabricate a novel chitosan-based ternary nanocomposite hydrogel film by incorporating graphene oxide (GO) nanosheets into a chitosan/partially hydrolyzed polyacrylamide (PHPA) network to boost adsorption efficiency through one step self-assembly process in water. Basically, H-bonding interactions drive the formation of a crosslinking network structure. The Batch adsorption experiments evaluated the hydrogel nanocomposite's MB adsorption performance. By loading GO, surface roughness, swelling percentage (from 21,200 % to 35,800 %), elastic modulus of up to 73.7 Pa, and adsorption characteristics (from 282 mg/g to 468 mg/g) were enhanced. The nanocomposite displayed outstanding thermally/pH responsiveness properties. MB adsorption equilibrium was reached after 45 min and the adsorption capacity was 476.19 mg.g-1 when the initial concentration was 100 mg/L. The MB adsorption kinetics and isotherms by the nanocomposite were well correlated by the PSO and the Langmuir models (R2 > 0.99), respectively. The loaded nanocomposite was shown to be regenerative for five cycles through desorption studies. Thermodynamic analysis indicated that MB adsorption occurred spontaneously (ΔG°: -16.47 kJ/mol, 303 K) and exothermically (ΔH°: -79.49 kJ/mol). A plausible adsorption mechanism was proposed for the nanocomposite developed for MB removal. Our results can contribute to the design and fabrication of nanocomposite adsorbents to treat wastewater.

Separation of nutrients and acetate from sewage sludge fermentation liquid in flow-electrode capacitive deionization system: Competitive mechanisms of ions and influence of activated carbon

Effective separation of volatile fatty acids (VFAs), ammonia (NH4+-N) and reactive phosphorous (RP) generated from anaerobic fermentation liquid is critically important for efficient resource recovery. Flow-electrode capacitive deionization (FCDI) is proven to be capable of efficient removal of ions, environmentally friendly and cost-effective in operation. The performances of FCDI system in the separation of NH4+-N, RP, and acetate and mechanism of pHs and activated carbon on their performances were investigated. Results showed that a pH of 5.0 promoted the removal of NH4+-N (53.1 %) and RP (39.5 %), and 72.0 % of acetate was retained in the solution, which revealed that removal of NH4+-N and RP, and retention of acetate were evidently affected by speciation of ions. Furthermore, the recovery of NH4+-N and RP was undermined by the adsorption of ions on activated carbon. This study provides a novel insight of ion selective mechanism during the operation of the FCDI system.

Drying Technique Providing Maximum Benefits on Hydrogelling Ability of Avocado Seed Protein: Spray Drying

The current study focused on creating natural hydrogels consisting of mixtures of avocado seed proteins dried with different techniques and locust bean gum. Proteins were extracted from avocado seed by alkali and isoelectric precipitation methods. Avocado seed proteins were dried by five different drying methods, namely ambient drying, oven drying, vacuum drying, freeze drying, and spray drying. FT-IR spectra were used to analyze the chemical structure of proteins dried using various techniques. Additionally, hydrogel models were constructed in the presence of avocado seed proteins and locust bean gum to clarify the effect of drying techniques on their hydrogelling ability. The impact of drying techniques on the functional behavior of hydrogels was notable. The maximum water holding capacity values were detected in the hydrogel system containing spray-dried proteins (93.79%), followed by freeze-dried (86.83%), vacuum-dried (76.17%), oven-dried (72.29%), and ambient-dried (64.8%) counterparts. The swelling ratio was 34.10, 33.51, 23.05, 18.93, and 14.39% for gels in the presence of freeze-dried, spray-dried, vacuum-dried, oven-dried, and ambient-dried proteins, respectively. Additionally, the desirable values for the amount of protein leaking from the systems prepared using spray-dried (7.99%) and freeze-dried (12.14%) proteins were obtained compared to others (ambient-dried: 24.03%; oven-dried: 17.69%; vacuum-dried: 19.10%). Superior results in terms of textural properties were achieved in hydrogel models containing spray-dried and freeze-dried proteins. In general, hydrogel models exhibited elastic behavior rather than viscous properties; however, the magnitudes of elasticity varied. Furthermore, the success of gels containing hydrogel models containing spray-dried protein and locust bean gum in the bioactive compound delivery system was obvious compared with protein ones alone.

Synchronously construction of hierarchical porous channels and cationic surface charge on lanthanum-hydrogel for rapid phosphorus removal

Phosphorus (P) removal from wastewater is critical for ecosystem operation and resource recovery. To facilitate the recycling of the used absorbents through balancing their adsorption and desorption performance on P, in this work, a novel porous magnetic La(OH)3-loaded MAPTAC/chitosan (CTS)/polyethyleneimine (PEI) ternary composite hydrogel (p-MTCH-La(OH)3) with enhanced bifunctional adsorption sites was synthesized by simultaneous dissolution of pre-embedded CaCO3 and CTS powder, followed by grafting PEI and loading La. Hierarchical porous channels promoted good dispersion of La(OH)3, bringing an excellent P adsorption capacity of 107.23 ± 4.96 mg P/g at neutral condition. PEI grafted with CTS increased the surface charge and enhanced the electrostatic attraction, which facilitated the desorption of P. The porous structure and abundant active sites also facilitated rapid adsorption with an adsorption rate constant of 0.1 g mg-1 h-1. p-MTCH-La(OH)3 maintained effective P adsorption despite co-existence with competing substances and after 5 cycles. Further mechanistic analysis indicated that La-P inner sphere complexation and LaPO4 crystalline transformation were the main pathways for P removal. However, electrostatic interactions contributed 17.5%-46.7% of the adsorption amount during the first 30 min of rapid adsorption, enabling 92.8% of the adsorbed P at this stage to be desorbed by alkaline solution. Based on the variations of adsorption and desorption capacity with adsorption time, a rapid unsaturated adsorption of 1-2 h was proposed to facilitate the recycling of the adsorbent. This study proposed a method to promote P adsorption and desorption by enhancing bifunctional adsorption sites, and proved that p-MTCH-La(OH)3 is a promising phosphate adsorbent.

Double Network Physical Crosslinked Hydrogel for Healing Skin Wounds: New Formulation Based on Polysaccharides and Zn2

Developing convenient, efficient, and natural wound dressings remain the foremost strategy for treating skin wounds. Thus, we innovatively combined the semi-dissolved acidified sol-gel conversion method with the internal gelation method to fabricate SA (sodium alginate)/CS (chitosan)/Zn2+ physically cross-linked double network hydrogel and named it SA/CS/Zn2+ PDH. The characterization results demonstrated that increased Zn2+ content led to hydrogels with improved physical and chemical properties, such as rheology, water retention, and swelling capacity. Moreover, the hydrogels exhibited favorable antibacterial properties and biocompatibility. Notably, the establishment of an in vitro pro-healing wound model further confirmed that the hydrogel had a superior ability to repair wounds and promote skin regeneration. In future, as a natural biomaterial with antimicrobial properties, it has the potential to promote wound healing.

Polymeric hydrogels-based materials for wastewater treatment

Low-cost and reliable wastewater treatment is a relevant issue worldwide to reduce the concentration of environmental pollutants. Industrial effluents containing dyes, heavy metals, and other inorganic and organic compounds can pollute water resources; therefore, novel technologies are required to mitigate and control their release into the environment. Adsorption is one of the simplest methods for treating contaminated water in which a wide spectrum of adsorbents can be used to remove emerging compounds. Hydrogels are interesting materials with high adsorption capacities that can be synthesized via green routes. These adsorbents are promising for large-scale industrial wastewater treatment applications; however, gaps still exist in achieving sustainable commercial implementation. This review focuses on the discussion and analysis of preparation, characterization, and adsorption properties of hydrogels for water purification. The advantages of these polymeric materials for water treatment were analyzed, including their performance in the removal of different organic and inorganic contaminants. Recent advances in the functionalization of hydrogels and the synthesis of novel composites have also been described. The adsorption capacities of hydrogel-based adsorbents are higher than 500 mg/g for different organic and inorganic pollutants, and can reach values of up to >2000 mg/g for organic compounds, significantly outperforming other materials reported for water cleaning. The main interactions involved in the adsorption of water pollutants using hydrogel-based adsorbents were described and explained to allow the interpretation of their removal mechanisms. The current challenges in the implementation of hydrogels for water purification in real-life operations are also highlighted. This review provides an updated picture of hydrogels as interesting materials to address water depollution worldwide.

Facile fabrication of a broad-spectrum starch/poly(α-l-lysine) hydrogel adsorbent with thermal/pH-sensitive IPN structure through simultaneous dual-click strategy

A thermal/pH-sensitive interpenetrating network (IPN) hydrogel was prepared facilely from starch and poly(α-l-lysine) through amino-anhydride and azide-alkyne double-click reactions in one pot. The synthesized polymers and hydrogels were systematically characterized using different analytical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rheometer. The preparation conditions of the IPN hydrogel were optimized via one-factor experiments. Experimental results indicated the IPN hydrogel possessed pH and temperature sensitivity. Effect of different parameters (pH, contact time, adsorbent dosage, initial concentration, ionic strength, and temperature) on adsorption behavior were investigated in monocomponent system with cationic methylene blue (MB) and anionic Eosin Y (EY) as model pollutants. The results indicated that the adsorption process of the IPN hydrogel for MB and EY followed pseudo-second-order kinetics. The adsorption data for MB and EY fitted well with the Langmuir isotherm model, indicating monolayer chemisorption. The good adsorption performance was due to various active functional groups (-COOH, -OH, -NH₂, etc.) in the IPN hydrogel. The strategy described here opens up a new way for preparing IPN hydrogel. The as-prepared hydrogel exhibits potential application and bright prospects as an adsorbent in wastewater treatment.

Simple synthesis of chitosan/alginate/graphene oxide/UiO-67 amphoteric aerogels: Characterization, adsorption mechanism and application for removal of cationic and anionic dyes from complex dye media

A chitosan/alginate/graphene oxide/UiO-67 (CS/SA/GO/UiO-67) amphoteric aerogel was synthesized successfully. A series of characterization experiments of CS/SA/GO/UiO-67 amphoteric aerogel was performed by SEM, EDS, FT-IR, TGA, XRD, BET, and zeta potential. The competitive adsorption properties of different adsorbents for complex dyes wastewater (MB and CR) at room temperature (298 K) were compared. Langmuir isotherm model predicted that the maximum adsorption quantity of CS/SA/GO/UiO-67 for CR and MB was 1091.61 and 1313.95 mg/g, respectively. The optimum pH values of CS/SA/GO/UiO-67 for the adsorption of CR and MB were 5 and 10, respectively. The kinetic analysis showed that the adsorption of MB and CR on CS/SA/GO/UiO-67 was more suitable for the pseudo-second-order and pseudo-first-order kinetic model, respectively. The isotherm study revealed that the adsorption of MB and CR was consistent with the Langmuir isotherm model. The thermodynamic study demonstrated that the adsorption process of MB and CR was exothermic and spontaneous. FT-IR analysis and zeta potential characterization experiments revealed that the adsorption mechanism of MB and CR on CS/SA/GO/UiO-67 depended on π-π bond, hydrogen bond, and electrostatic attraction. Repeatable experiments showed that the removal rates of MB and CR of CS/SA/GO/UiO-67 after six cycles of adsorption were 67.19 and 60.82 %, respectively.

Composite Hydrogel for the Targeted Capture and Photothermal Killing of Bacteria toward Facilitating Wound Healing

Pathogenic infections pose a significant risk to public health and are regarded as one of the most difficult clinical treatment obstacles. A reliable and safe photothermal antibacterial platform is a promising technique for the treatment of bacterial infections. Given the damage that high temperatures cause in normal tissues and cells, a multifunctional hydrogel driven by photothermal energy is created by trapping bacteria to reduce heat transfer loss and conduct low-temperature photothermal sterilization efficiently. The 3-aminobenzene boronic acid (ABA)-modified graphene oxide is combined with carboxymethyl chitosan (CMCS) and cellulose nanocrystalline (CNC) networks to create the ABA-GO/CNC/CMCS composite hydrogel (composite gel). The obtained composite gel displays a uniform three-dimensional network structure, which can be rapidly heated to 48 °C under infrared light irradiation and is beneficial for killing wound infection bacteria and promoting wound healing. The results of animal experiments show that the composite gel significantly reduces inflammation by killing >99.99% of bacteria under near-infrared light irradiation. The result also demonstrates that it increases the granulation tissue thickness and collagen distribution and promotes wound healing. After treatment for 14 days, compared with the remaining 27.73% of the remaining wound area in the control group, the wound area in the composite gel with NIR group is only 0.91%. It significantly accelerates the wound healing process of Staphylococcus aureus infection and shows great potential for clinical application.

Spherical Attapulgite/Silica Aerogels Fabricated via Different Drying Methods with Excellent Adsorption Performance

Dye wastewater has caused great harm to the environment, which is an urgent problem to be solved. As typical three-dimensional porous materials, aerogels have attracted great interest in dye wastewater treatment. In this work, spherical attapulgite/silica (ATP/SiO₂) gels were initially prepared by easily scalable sol-gel dripping methods and then dried to aerogels with three drying techniques, namely, supercritical CO₂ drying (SCD), freeze-drying (FD), and ambient pressure drying (APD). The effect of the drying techniques and heat-treated temperature on the physical characteristic, morphological properties, microstructure, and chemical structure of the spherical ATP/SiO₂ aerogels were investigated. The macroscopic morphology of the spherical ATP/SiO₂ aerogels was homogeneous and integrated without local cracking. The average pore diameter and specific surface area of the spherical ATP/SiO₂ aerogels prepared by the three drying techniques were in the range of 6.8-8.6 nm and 218.5-267.4 m²/g, respectively. The heat treatment temperature had a significant effect on the pore structure and the wetting properties of the aerogels. The 600 °C heat-treated aerogels were subjected to adsorption tests in methylene blue (MB) solution (60 mg/g, 100 mL), which exhibited a great adsorption capacity of 102.50 mg/g. Therefore, the resulting spherical ATP/SiO₂ aerogels possessed multipath preparation and exhibited an efficient adsorption performance, with the potential to be applied as an adsorbent for dye wastewater.

Design of glucono-δ-lactone-induced pinto bean protein isolate/κ-carrageenan mixed gels with various microstructures: fabrication, characterization, and release behavior

BACKGROUND

Protein gels are used for different purposes, such as providing good texture, serving as fat replacers, and enhancing the nutritional and functional characteristics of foods. They can also deliver controlled release agents for sensitive drugs. The objective of this study was to investigate the impact of κ-carrageenan (kcr) concentration (0, 1.5, 3, and 4.5 mg g^-1 ) on the morphological and physicochemical properties and release behavior of glucono-δ-lactone (GDL)-induced pinto bean protein aggregate (PBA) gels.

RESULTS

When κ-carrageenan concentration increased from 0 to 1.5 and 3 mg.g^-1 , the firmness of the samples increased significantly, by 2.04 and 3.7 fold, respectively (P < 0.05). A compact and homogenous network with considerable strength and maximum water-holding capacity (97.52 ± 1.17%) was obtained with the addition of 3 mg g^-1 κ-carrageenan to the gel system. Further increasing the κ-carrageenan concentration to 4.5 mg g^-1 produced a coarse gel structure with higher storage modulus (G'), firmness (6.30-fold), thermal stability, and entrapment efficiency (85.6%). Depending on the κ-carrageenan concentration, various microstructures from protein continuous phase to κ-carrageenan continuous phase were observed. The release test indicated that 70.25% of the loaded curcumin was released in the simulated gastrointestinal tract for pure PBA gels. In contrast, for binary gels containing 4.5 mg g^-1 κ-carrageenan, curcumin was protected in the upper gastrointestinal tract, and 64.45% of loaded curcumin was delivered to the colon.

CONCLUSION

Our study showed that κ-carrageenan/PBA gels had high entrapment efficiency and could protect curcumin in the upper gastrointestinal tract. The hydrogels are therefore very valuable for colon-targeting delivery purposes. © 2022 Society of Chemical Industry.

Contribution Evaluation of Physical Hole Structure, Hydrogen Bond, and Electrostatic Attraction on Dye Adsorption through Individual Experiments

Disagreements over various unanswered questions about contribution of the adsorption process and functional groups on dye adsorption still exist. The main aim of this research was to evaluate the contributions of physical hole structure, hydrogen bond, and electrostatic attraction on dye adsorption. Three ideal representatives, namely, a sponge with porous structure, P(AM) containing -CONH2 groups, and P(AANa/AM) containing -COONa groups, were chosen to evaluate the above contributions. The methylene blue (MB) removal rates of these three products were compared through individual experiments. The results revealed that physical hole structure did not play a role in decreasing dye concentration. Hydrogen bond existed in dye adsorption but did not remarkably reduce dye concentration. The excellent removal results of P(AANa/AM) demonstrated that electrostatic attraction was critical in enriching dye contaminants from the solution into solid adsorbent. The results could provide insights into the dye adsorption mechanisms for further research.

Construction of a polyoxometalate-based magnetic composite MOF for the effective adsorption of cationic dyes

Adsorption and separation of dyes are extremely important as they damage the water environment and human health. ZIF-8 has the benefits of large specific surface area, explicit structure and a good confinement effect on POM, which can better facilitate the synergetic effect of POM and ZIF-8. Therefore, ZIF-8 was chosen as the support material to wrap H₃PW₁₂O₄₀. In the present work, magnetic ZIF-8@H₃PW₁₂O₄₀ composites were prepared by a facile impregnation synthesis strategy and applied to the adsorption of cationic dyes with methylene blue (MB) as a representative. Compared with the other three prepared materials, Fe₃O₄@ZIF-8@H₃PW₁₂O₄₀ exhibited the best adsorption performance. The adsorption process conformed to the pseudo-second-order model and the Langmuir model, and the adsorption reaction was spontaneous with the maximum adsorption capacity of up to 431.03 mg g^-1 within 20 min. The electrostatic attraction has been testified to be the major driving force of the adsorption process, and the material can still hold 90% of the max adsorption capacity after 5 cycles, which serve as the foundation for its further applications in the field of adsorption.

A Novel Low-Cost Bio-Sorbent Prepared from Crisp Persimmon Peel by Low-Temperature Pyrolysis for Adsorption of Organic Dyes

In order to properly reuse food waste and remove various contaminants from wastewater, the development of green, sustainable and clean technologies has demonstrated potential in the efficient inhibition of secondary pollution to the environment. In this study, an economical and green method was used to prepare biochar from crisp persimmon peel (CPP) using flash-vacuum pyrolysis at different temperatures (200–700 °C; referred to as CPP200–CPP700). CPP200 has high polarity, low aromaticity and high oxygen-containing functional groups that exhibit superior MB adsorption capabilities. CPP200 that was prepared at a relatively low temperature of 200 °C exhibited a high adsorption capacity of 59.72 mg/g toward methylene blue (MB), which was relatively higher than that for alizarin yellow R (4.05 mg/g) and neutral red (39.08 mg/g), indicating that CPP200 possesses a higher adsorption selectivity for cationic dyes. Kinetics investigation revealed that the kinetic data of CPP200 for the adsorption of MB was better fitted by a linear pseudo-second-order model. Isothermal studies indicated that the linear Langmuir model was more suitable for describing the adsorption process. The adsorption thermodynamics illustrated that the adsorption of MB onto CPP200 was spontaneous and endothermic. EDS and IR analyses of CPP200 for both pre- and post-adsorption of MB showed that electrostatic interactions between oxygen-containing groups on biochar and target MB dominated the adsorption procedure, in addition to hydrogen bonding interactions. Reusability tests confirmed the excellent regeneration characteristics of CPP200, indicating that CPP200 may be used as a green, sustainable, highly efficient and recyclable adsorbent for the selective removal of cationic organic dyes.

Evaluation of the Adsorption Efficiency of Graphene Oxide Hydrogels in Wastewater Dye Removal: Application of Principal Component Analysis

Industrial dye wastewater is one of the major water pollution problems. Adsorbent materials are promising strategies for the removal of water dye contaminants. Herein, we provide a statistical and artificial intelligence study to evaluate the adsorption efficiency of graphene oxide-based hydrogels in wastewater dye removal by applying Principal Component Analysis (PCA). This study aims to assess the adsorption quality of 35 different hydrogels. We adopted different approaches and showed the pros and cons of each one of them. PCA showed that alginate graphene oxide-based hydrogel (without polyvinyl alcohol) had better tolerance in a basic medium and provided higher adsorption capacity. Polyvinyl alcohol sulfonated graphene oxide-based hydrogels are suitable when higher adsorbent doses are required. In conclusion, PCA represents a robust way to delineate factors affecting hydrogel selection for pollutant removal from aqueous solutions.

Upcycling of blending waste plastics as zwitterionic hydrogel for simultaneous removal of cationic and anionic heavy metals from aqueous system

Upcycling of waste plastics as functional materials is a new approach for synthesizing low-cost and durable adsorbents with zwitterionic property. Herein, a facile process for recycling blending waste plastics to fabricate zwitterionic plastic-g-hydrogel (ZPH) for simultaneous adsorbing cationic and anionic heavy metals was developed. ZPH possessed high affinities for cations and anions in both acid and alkaline conditions owing to its zwitterionic property, and the maximum adsorption capacities of Pb²⁺, Cd²⁺, Ba²⁺, and Cr(VI) (Cr₂O₇^2-) were 132.13, 85.58, 69.92 and 85.15 mg/g, respectively. Mechanism study indicated the incompatibility of blending plastics was skillfully overcome through the crosslinking between sodium alginate (SA)/chitosan (CTS) and plastics. Cations were adsorbed onto ZPH via electrostatic interaction, cation exchange and coordination interactions with Cl/N/O-containing groups. Furthermore, the reduction of Cr(VI) to Cr(III) was another important path for ZPH to capture anionic Cr₂O₇^2-, and subsequently Cr(III) was adsorbed via coordination interaction and cation exchange. Moreover, the regeneration experiment showed ZPH possessed excellent reusability and stable structure. Accordingly, this research provides a profitable approach for recycling blending plastics, and ZPH has potentials for industrial application in wastewater treatment or contaminated site remediation with complex heavy metals pollution.

Optimization of the spontaneous adsorption of food colors from aqueous medium using functionalized Chitosan/Cinnamaldehyde hydrogel

Hydrogels are considered as practical and proficient materials in adsorption and removal of soluble lethal molecules from aqueous system. They are also rapid-decomposable and economical materials besides their diverse preventive claims. In current study, Cinnamaldehyde (C), a natural defensive compound and Chitosan (Ch), natural occurring bio-macromolecule are considered to develop bio-inspired hydrogel (ChC). The structural and surface characteristics of ChC (¹³C solid state NMR, FT-IR, UV-Vis and SEM) are investigated to confirm the successful grafting. The origami of gelation in ChC performs an excellent adsorption activity towards food dyes, Carmoisine (CA) and Tartrazine (TA), which are contaminated by the accumulation during excess release from catering and chemical industries in aqueous system. The adsorption performance is thoroughly screened by varying the pH, ChC dosage, dye concentration, contact time and temperature in aqueous system. Thermodynamic and Kinetics study suggest the natural tendency of adsorption with a good reusability up to 3 cycles. The main mechanism for spontaneous adsorption is initiated by capturing of TA/CA in porous surface followed by the ionic interactions and formation of H-bondings. ChC based adsorption is an excellent and potential approach to control the toxicants for the water-pollution and water-preservation.

Magnetic cross-linked chitosan for efficient removing anionic and cationic dyes from aqueous solution

Herein, a novel magnetic cross-linked chitosan CS-BA@Fe₃O₄ was rationally synthesized by cross-linked with epichlorohydrin and coated with Fe₃O₄ to the acylated chitosan, which was prepared by the reaction of chitosan with benzenetricarboxylic anhydride. The as-obtained absorbent was characterized by FTIR, XRD, VSM, TGA, TEM, BET, SEM and EDS. The results showed that the maximum adsorption capacities of CR and CV were 471.46 ± 16.97 mg/g and 515.91 ± 25.12 mg/g at 318.15 K, respectively. The main adsorption mechanisms were H-bonding and electrostatic interaction. The kinetic data were in good agreement with the pseudo-second-order model and closed to adsorption equilibrium at 30 min. Thermodynamic studies showed that the adsorption on CS-BA@Fe₃O₄ were spontaneous and endothermic. More importantly, the adsorbent exhibited excellent regeneration properties after 6 cycles and remarkable stability under harsh environments including strong acid, strong alkali, multi-salt and mixed dyes conditions. Therefore, abundant efforts revealed a broad application prospect of CS-BA@Fe₃O₄ in water remediation.

Topical Chitosan-Based Thermo-Responsive Scaffold Provides Dexketoprofen Trometamol Controlled Release for 24 h Use

Chronic and non-healing wounds demand personalized and more effective therapies for treating complications and improving patient compliance. Concerning that, this work aims to develop a suitable chitosan-based thermo-responsive scaffold to provide 24 h controlled release of Dexketoprofen trometamol (DKT). Three formulation prototypes were developed using chitosan (F1), 2:1 chitosan: PVA (F2), and 1:1 chitosan:gelatin (F3). Compatibility tests were done by DSC, TG, and FT-IR. SEM was employed to examine the morphology of the surface and inner layers from the scaffolds. In vitro release studies were performed at 32 °C and 38 °C, and the profiles were later adjusted to different kinetic models for the best formulation. F3 showed the most controlled release of DKT at 32 °C for 24 h (77.75 ± 2.72%) and reduced the burst release in the initial 6 h (40.18 ± 1.00%). The formulation exhibited a lower critical solution temperature (LCST) at 34.96 °C, and due to this phase transition, an increased release was observed at 38 °C (88.52 ± 2.07% at 12 h). The release profile for this formulation fits with Hixson-Crowell and Korsmeyer-Peppas kinetic models at both temperatures. Therefore, the developed scaffold for DKT delivery performs adequate controlled release, thereby; it can potentially overcome adherence issues and complications in wound healing applications.

Chitosan-based recyclable composite aerogels for the photocatalytic degradation of rhodamine B

TiO₂ based photocatalyst with sufficient reusability for the degradation of water pollutants remains a challenge. Here, we report a composite chitosan-based aerogel containing TiO₂ nanoparticles, multiwalled carbon nanotubes and layered silicate rectorite with sufficient mechanical strength for Rhodamine B degradation. The aerogels with homogeneous oriented lamellar structure were successfully prepared via a unidirectional freeze-casting technique. As-prepared aerogels showed specific surface area of 84.59 m²/g. The addition of rectorite and carbon nanotubes accelerated the photodegradation and rectorite significantly enhanced the overall mechanical performance. Rapid degradation of rhodamine B (95% in 100 min) was observed on aerogels with 2 wt% and 4 wt% of rectorite. After 3 cycles, 75% degradation of Rhodamine B was achieved with CTCR4, confirming its reusability. Thus, the composite chitosan aerogels show high photocatalytic degradation efficiency towards Rhodamine B during cycle use.