Eco-Friendly and Economic, Adsorptive Removal of Cationic and Anionic Dyes by Bio-Based Karaya Gum-Chitosan Sponge

Rapid eco-friendly selective dye removal using modified chitosan-based sponges: Synthesis, characterization, and application

The ongoing challenge of water scarcity persists alongside a concerning rise in water pollution driven by population expansion and industrial development. As a result, urgent measures are imperative to address the pressing need for a clean and sustainable water supply. In this study, a sustainable and green approach was utilized to prepare four chitosan-based sponges from a chemically modified chitosan with different alkyl chains in aqueous medium and at room temperature. The resulting sponges displayed excellent stability in water with outstanding dye removal efficiency. The adsorption capacity was associated with the alkyl chain length incorporated to the polymer backbone. All sponges displayed a high adsorption capacity of methyl orange (MO) ranges between 238 and 380 mg g-1, while a low capacity were obtained for methylene blue (MB) and Rhodamine B (RB). Competitive adsorption experiments were conducted on binary and ternary mixtures to assess the selective removal of MO from a mixture of dyes in which the separation factor was found to be ranging between 1.6 and 32. The adsorption kinetics isotherms of all sponges followed the pseudo-second-order, and the Langmuir model was found to be more suitable than the Freundlich for the adsorption of MO on the sponges. The chitosan-based sponges showed stable performance, robustness and reusability over 5 adsorption-desorption cycles, indicating their great potential for water treatment applications.

Surface activity, kinetics, thermodynamics and comparative study of adsorption of selected cationic and anionic dyes onto H3PO4-functionalized bagasse from aqueous stream

The discharge of dyes into the water body creates toxicity to aquatic organisms because of their aromatic structure and difficult degradation. So, the treatment of dye-contaminated wastewater is required before releasing it. In the present study, thermally treated (600 °C) and H3PO4 (55%)-functionalized bagasse, henceforth called thermochemically activated bagasse (TCAB), was synthesized as potential adsorbent for the effective removal of selected cationic and anionic dyes from their aqueous stream. TCAB characterization was done employing FT-IR, SEM, XRD, zeta potential, BET, and PZC techniques. The comparative study shows that the relative adsorption on TCAB followed the sequence, methyl red (185 mg/g) > safranin (178 mg/g) > congo red (146 mg/g) > brilliant green (139 mg/g) > malachite green (130 mg/g) > bromocresol green (94 mg/g). The adsorption efficiency was investigated concerning the effect of change in TCAB dose (0.05-0.3 g/100 mL), initial dye concentration (20-200 mg/L), pH (4.0-10.0), ionic strength (0.1-0.5 M KCl), urea concentration (0.1-0.5 M) and temperature (25-45 °C). The representative adsorption isotherms belong to typical L-type. The time-dependent dye removal was best explained by the pseudo-second-order (PSO) kinetic model (R2 = 0.9859-0.9991), while equilibrium data were best explained by the Freundlich model (R2 = 0.9881-0.9961). Thermodynamic study showed the spontaneous (ΔG0 <0) and exothermic nature (ΔH0 <0) of the adsorption of different cationic and anionic dyes. The cyclic adsorption ability of TCAB for different dyes was checked up to three cycles (185 to 168 mg/L for MR, 178 to 165 mg/L for SF, 146 to 130 mg/L for CR, 139 to 127 mg/L for BG, 130 to 114 mg/L for MG and 94 to 80 mg/L for BCG), and no significant decrease in the adsorption capacity was noticed. So, the present study provides valuable insights into the adsorption of cationic and anionic dyes onto H3PO4-functionalized bagasse. Addressing the adsorptive aspects enhances the clarity, reliability and applicability of the study's findings and contributes to its overall scientific impact.

Synthesis and Design of a Synthetic-Living Material Composed of Chitosan, Calendula officinalis Hydroalcoholic Extract, and Yeast with Applications as a Biocatalyst

Design and development of materials that couple synthetic and living components allow taking advantage of the complexity of biological systems within a controlled environment. However, their design and fabrication represent a challenge for material scientists since it is necessary to synthesize synthetic materials with highly specialized biocompatible and physicochemical properties. The design of synthetic-living materials (vita materials) requires materials capable of hosting cell ingrowth and maintaining cell viability for extended periods. Vita materials offer various advantages, from simplifying product purification steps to controlling cell metabolic activity and improving the resistance of biological systems to external stress factors, translating into reducing bioprocess costs and diversifying their industrial applications. Here, chitosan sponges, functionalized with Calendula officinalis hydroalcoholic extract, were synthesized using the freeze-drying method; they showed small pore sizes (7.58 μm), high porosity (97.95%), high water absorption (1695%), and thermal stability, which allows the material to withstand sterilization conditions. The sponges allowed integration of 58.34% of viable Saccharomyces cerevisiae cells, and the cell viability was conserved 12 h post-process (57.14%) under storage conditions [refrigerating temperature (4 °C) and without a nutrient supply]. In addition, the synthesized vita materials conserved their biocatalytic activity after 7 days of the integration process, which was evaluated through glucose consumption and ethanol production. The results in this paper describe the synthesis of complex vita materials and demonstrate that biochemically modified chitosan sponges can be used as a platform material to host living and metabolically active yeast with diverse applications as biocatalysts.

Black-wattle tannin/kraft lignin H3PO4-activated carbon xerogels as excellent and sustainable adsorbents

This work proposed new black-wattle tannin/kraft lignin H₃PO₄-activated carbon xerogels as sustainable and efficient adsorbents. The precursors were chosen based on their eco-friendly and cost-effective nature, aiming to achieve adsorbents with high adsorption capacities. Carbon xerogels were synthesized through polycondensation with formaldehyde and alkaline catalyst in a simple one-pot procedure. Activation was performed using H₃PO₄ in a tubular furnace (500 °C), under a nitrogen atmosphere. Results show that the inclusion of the kraft lignin led to changes in the morphology of the materials, facilitating the development of their porous structure and increasing specific surface area and pore volume. The best adsorbent (XLT 50 %) was synthesized using a 1:1 tannin/kraft lignin mass ratio. This material presented an adsorption capacity of nearly 1150 mg g^-1 of methylene blue (pH = 5 and T = 298 K), which was linked to its high specific surface area of 1348 m² g^-1. The adsorption process followed the pseudo-second-order kinetic model, whereas the adsorption isotherms were best fitted by the Sips model. The XLT 50 % presented good reusability properties, maintaining its adsorption capacity for 3 cycles. Finally, the XLT 50 % presented good adsorptive properties toward other pollutants (methyl orange, 4-chlorophenol, and hexavalent chromium), indicating its versatility for adsorption processes.

Blood-Coagulation-Inspired Dynamic Bridging Strategy for the Fabrication of Multiscale-Assembled Hierarchical Porous Material

Porous materials, from macroscopic bulk materials (MBs) with (sub-)millimeter-scale pores to tiny particles (TPs) with (sub-)nanometer-scale pores, have attracted ever-growing interest in various fields. However, the integration of multi-scale pores in one composite is promising but challenging, owing to the considerable gap in the scale of the pores. Inspired by blood coagulation, a fibrin-based dynamic bridging strategy is developed to fabricate a multiscale-assembled hierarchical porous material (MHPM), in which fibrin formed as the sub-framework for the weaving-narrow of MBs and the enwinding-load of TPs. The bio-polymerization nature makes the fabrication rapid, facile, and universal for the customizable integration of seven kinds of TPs and four kinds of MBs. Besides, the integration is controllable with high load capacity of TPs and is stable against external shock forces. The unique multi-level structure endows the MHPM with large and accessible surface area, and efficient mass transfer pathways, synergistically leading to high adsorption capacity and rapid kinetics in multiple adsorption models. This work suggests a strategy for the rational multi-level design and fabrication of hierarchical porous architectures.

Chitin-Based Magnesium Oxide Biocomposite for the Removal of Methyl Orange from Water

In this work, a cost-effective chitin-based magnesium oxide (CHt@MgO) biocomposite with excellent anionic methyl orange (MO) dye removal efficiency from water was developed. The CHt@MgO biocomposite was characterized by FT-IR, XRD, SEM-EDX, and TGA/DTG. Results proved the successful synthesis of CHt@MgO biocomposite. Adsorption of MO on the CHt@MgO biocomposite was optimized by varying experimental conditions such as pH, amount of adsorbent (m), contact time (t), temperature (T), and initial MO concentration (C_o). The optimized parameters for MO removal by CHt@MgO biocomposite were as follows: pH, 6; m, 2 g/L; t, 120 min. Two common isotherm models (Langmuir and Freundlich) and three kinetic models (pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD)) were tested for experimental data fitting. Results showed that Langmuir and PFO were the most suitable to respectively describe equilibrium and kinetic results on the adsorption of MO adsorption on CHt@MgO biocomposite. The maximum Langmuir monolayer adsorption capacity (q_m) on CHt@MgO biocomposite toward MO dye was 252 mg/g at 60 °C. The reusability tests revealed that CHt@MgO biocomposite possessed high (90.7%) removal efficiency after the fifth regeneration cycle.

Green and Superior Adsorbents Derived from Natural Plant Gums for Removal of Contaminants: A Review

The ubiquitous presence of contaminants in water poses a major threat to the safety of ecosystems and human health, and so more materials or technologies are urgently needed to eliminate pollutants. Polymer materials have shown significant advantages over most other adsorption materials in the decontamination of wastewater by virtue of their relatively high adsorption capacity and fast adsorption rate. In recent years, "green development" has become the focus of global attention, and the environmental friendliness of materials themselves has been concerned. Therefore, natural polymers-derived materials are favored in the purification of wastewater due to their unique advantages of being renewable, low cost and environmentally friendly. Among them, natural plant gums show great potential in the synthesis of environmentally friendly polymer adsorption materials due to their rich sources, diverse structures and properties, as well as their renewable, non-toxic and biocompatible advantages. Natural plant gums can be easily modified by facile derivatization or a graft polymerization reaction to enhance the inherent properties or introduce new functions, thus obtaining new adsorption materials for the efficient purification of wastewater. This paper summarized the research progress on the fabrication of various gums-based adsorbents and their application in the decontamination of different types of pollutants. The general synthesis mechanism of gums-based adsorbents, and the adsorption mechanism of the adsorbent for different types of pollutants were also discussed. This paper was aimed at providing a reference for the design and development of more cost-effective and environmentally friendly water purification materials.

Chitosan-Functionalized-Graphene Oxide (GO@CS) Beads as an Effective Adsorbent to Remove Cationic Dye from Wastewater

In this study, the preparation of graphene oxide@chitosan (GO@CS) composite beads was investigated via continuous dropping techniques to remove methylene blue (MB)-dye from an aqueous media. The prepared beads were characterized using various techniques before and after the adsorption of MB. The experimental results showed that the adsorption processes fit the kinetic pseudo-second-order and Langmuir isotherm models. Moreover, the GO@CS beads achieve maximum adsorption capacities of 23.26 mg g⁻¹, which was comparable with other adsorbents in the literature. An important advantage of our adsorbent is that the GO@CS can remove 82.1% of the real sample color within 135 min.

Magnetite Metal-Organic Frameworks: Applications in Environmental Remediation of Heavy Metals, Organic Contaminants, and Other Pollutants

Due to the increasing environmental pollution caused by human activities, environmental remediation has become an important subject for humans and environmental safety. The quest for beneficial pathways to remove organic and inorganic contaminants has been the theme of considerable investigations in the past decade. The easy and quick separation made magnetic solid-phase extraction (MSPE) a popular method for the removal of different pollutants from the environment. Metal-organic frameworks (MOFs) are a class of porous materials best known for their ultrahigh porosity. Moreover, these materials can be easily modified with useful ligands and form various composites with varying characteristics, thus rendering them an ideal candidate as adsorbing agents for MSPE. Herein, research on MSPE, encompassing MOFs as sorbents and Fe₃O₄ as a magnetic component, is surveyed for environmental applications. Initially, assorted pollutants and their threats to human and environmental safety are introduced with a brief introduction to MOFs and MSPE. Subsequently, the deployment of magnetic MOFs (MMOFs) as sorbents for the removal of various organic and inorganic pollutants from the environment is deliberated, encompassing the outlooks and perspectives of this field.

Biobased hydrogels and their composite containing MgMOF74 for the removal of textile dyes and wastewater treatment

In this work, we report the synthesis of a biobased hydrogel comprised of collagen, chitosan, and polyurethane for the removal of textile dyes. The adsorption capacity of this hydrogel was improved by adding a magnesium metal-organic framework to the semi-interpenetrating polymer matrix yielding a composite hydrogel. Removal of Bismarck Brown and Congo red was studied, and the experimental results fit Freundlich's model. Both hydrogel formulations were tested for the removal of textiles dyes from wastewaters. The magnesium-metal organic framework improved the efficiency of the biobased hydrogel for the removal of direct and mordant dyes reaching up to 89 ± 2%. The composite hydrogel was tested for the removal of Congo Red in a fixed bed column observing the breakthrough point after 168 min. Also, a flocculant material was prepared from collagen and chitosan and was tested for the removal of direct red dye from wastewater removing up to 80 ± 1%. The pretreated wastewater by coagulation-flocculation was treated by adsorption yielding a global removal efficiency of 99%. Finally, the studied hydrogels are potentially biodegradable being completely degraded by the proteolytic action after 22 days. PRACTITIONER POINTS: Composite hydrogels of collagen, chitosan, and MgMOF74 removed efficiently textile dyes from wastewater in batch systems and fixed bed columns. A biobased flocculant of collagen and chitosan significantly improved water quality after coagulation flocculation. Hydrogels were reusable for four cycles, and they can be proteolytically degraded after 22 days.

Optimized hydration dynamics in mucoadhesive xanthan-based trilayer vaginal films for the controlled release of tenofovir

Karaya gum, pectin and xanthan gum have been tested as candidates for manufacturing mucoadhesive trilayer films containing ethylcellulose and chitosan for the vaginal administration of the antiviral Tenofovir (TFV). The swelling profile correlated with the amount of mobile dipoles determined by impedance spectroscopy allows the determination of the hydration dynamics of these films. The fast water penetration has been demonstrated to favor the formation of polyelectrolyte complexes (PEC) via hydrogen or ionic bonds which would favor a controlled release. The incorporation of an inorganic drug release regulator induces the weakness of the polymeric chains thus enhancing the ionic mobility via the formation of low molecular weight PECs in films manufactured with karaya gum. Due to the different mechanical properties of the individual components, pectin-based films failed for a potential pharmaceutical formulation. However, mucoadhesive trilayer films produced with xanthan gum have demonstrated a moderate swelling, improved wettability and a controlled release of TFV.

Surface engineering of silica based materials with Ni-Fe layered double hydroxide for the efficient removal of methyl orange: Isotherms, kinetics, mechanism and high selectivity studies

Herein, low-cost diatomite (DE) and bentonite (BE) materials were surface modified with Ni-Fe layered double hydroxide (LDHs) (represented as NFD and NFB respectively), using a simple co-precipitation procedure for the removal of methyl orange (MO) dye from water. The adsorbents of both before and after MO adsorption have been studied by XRD, N₂ adsorption-desorption isotherm, FTIR, FESEM-EDX and XPS characterization. The zeta potential analysis was used to observe the surface charge of adsorbents within the pH ranges of 4-10. The MO removal efficiency was significantly improved after LDHs modification, showing a 94.7% and 92.6% efficiency for NFD and NFB at pH 6, respectively. Whereas bare DE and BE have shown removal efficiency of 15.5% and 4.9% respectively. The maximum adsorption capacities of NFD and NFB using the Langmuir isotherm model were found to be 246.9 mgg^-1 and 215.9 mgg^-1 respectively. The designed NFD showed high selectivity towards anionic-based dyes from water and also the effect of salts shows the dye removal percentage was increased and decreased for the addition of Na₂SO₄ and NaCl, respectively. The reusability of NFD and NFB have been studied for a maximum of five cycles and they can remove MO up to four cycles. Therefore, the designed adsorbents can be very effective towards the removal of MO from water and they may be useful for dye-based wastewater treatment.

An Overview on Composite Sorbents Based on Polyelectrolytes Used in Advanced Wastewater Treatment

Advanced wastewater treatment processes are required to implement wastewater reuse in agriculture or industry, the efficient removal of targeted priority and emerging organic & inorganic pollutants being compulsory (due to their eco-toxicological and human health effects, bio-accumulative, and degradation characteristics). Various processes such as membrane separations, adsorption, advanced oxidation, filtration, disinfection may be used in combination with one or more conventional treatment stages, but technical and environmental criteria are important to assess their application. Natural and synthetic polyelectrolytes combined with some inorganic materials or other organic or inorganic polymers create new materials (composites) that are currently used in sorption of toxic pollutants. The recent developments on the synthesis and characterization of composites based on polyelectrolytes, divided according to their macroscopic shape-beads, core-shell, gels, nanofibers, membranes-are discussed, and a correlation of their actual structure and properties with the adsorption mechanisms and removal efficiencies of various pollutants in aqueous media (priority and emerging pollutants or other model pollutants) are presented.

Organic Dyes versus Adsorption Processing

Even in the first quarter of the XXI century, the presence of organic dyes in wastewaters was a normal occurrence in a series of countries. As these compounds are toxic, their removal from these waters is a necessity. Among the separation technologies, adsorption processing appeared as one of the most widely used to reach this goal. The present work reviewed the most recent approaches (first half of the 2021 year) regarding the use of a variety of adsorbents in the removal of a variety of organic dyes of different natures.

Recent Advances in Biopolymer-Based Dye Removal Technologies

Synthetic dyes have become an integral part of many industries such as textiles, tannin and even food and pharmaceuticals. Industrial dye effluents from various dye utilizing industries are considered harmful to the environment and human health due to their intense color, toxicity and carcinogenic nature. To mitigate environmental and public health related issues, different techniques of dye remediation have been widely investigated. However, efficient and cost-effective methods of dye removal have not been fully established yet. This paper highlights and presents a review of recent literature on the utilization of the most widely available biopolymers, specifically, cellulose, chitin and chitosan-based products for dye removal. The focus has been limited to the three most widely explored technologies: adsorption, advanced oxidation processes and membrane filtration. Due to their high efficiency in dye removal coupled with environmental benignity, scalability, low cost and non-toxicity, biopolymer-based dye removal technologies have the potential to become sustainable alternatives for the remediation of industrial dye effluents as well as contaminated water bodies.

Application of Chitosan/Alginate Nanocomposite Incorporated with Phycosynthesized Iron Nanoparticles for Efficient Remediation of Chromium

Biopolymers and nanomaterials are ideal candidates for environmental remediation and heavy metal removal. As hexavalent chromium (Cr⁶⁺) is a hazardous toxic pollutant of water, this study innovatively aimed to synthesize nanopolymer composites and load them with phycosynthesized Fe nanoparticles for the full Cr⁶⁺ removal from aqueous solutions. The extraction of chitosan (Cht) from prawn shells and alginate (Alg) from brown seaweed (Sargassum linifolium) was achieved with standard characteristics. The tow biopolymers were combined and cross-linked (via microemulsion protocol) to generate nanoparticles from their composites (Cht/Alg NPs), which had a mean diameter of 311.2 nm and were negatively charged (−23.2 mV). The phycosynthesis of iron nanoparticles (Fe-NPs) was additionally attained using S. linifolium extract (SE), and the Fe-NPs had semispherical shapes with a 21.4 nm mean diameter. The conjugation of Cht/Alg NPs with SE-phycosynthesized Fe-NPs resulted in homogenous distribution and stabilization of metal NPs within the polymer nanocomposites. Both nanocomposites exhibited high efficiency as adsorbents for Cr⁶⁺ at diverse conditions (e.g., pH, adsorbent dose, contact time and initial ion concentration) using batch adsorption evaluation; the most effectual conditions for adsorption were a pH value of 5.0, adsorbent dose of 4 g/L, contact time of 210 min and initial Cr⁶⁺ concentration of 75 ppm. These factors could result in full removal of Cr⁶⁺ from batch experiments. The composited nanopolymers (Cht/Alg NPs) incorporated with SE-phycosynthesized Fe-NPs are strongly recommended for complete removal of Cr⁶⁺ from aqueous environments.