Chitosan based adsorbents for the removal of phosphate and nitrate: A critical review

Activated carbon and their nanocomposites derived from vegetable and fruit residues for water treatment

Water pollution remains a pressing environmental issue, with diverse pollutants such as heavy metals, pharmaceuticals, dyes, and aromatic hydrocarbon compounds posing a significant threat to clean water access. Historically, biomass-derived activated carbons (ACs) have served as effective adsorbents for water treatment, owing to their inherent porosity and expansive surface area. Nanocomposites have emerged as a means to enhance the absorption properties of ACs, surpassing conventional AC performance. Biomass-based activated carbon nanocomposites (ACNCs) hold promise due to their high surface area and cost-effectiveness. This review explores recent advancements in biomass-based ACNCs, emphasizing their remarkable adsorption efficiencies and paving the way for future research in developing efficient and affordable ACNCs. Leveraging real-time communication for ACNC applications presents a viable approach to addressing cost concerns.

Sustainable adsorbent frameworks based on bio-resourced materials and biodegradable polymers in selective phosphate removal for waste-water remediation

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Crosslinked chitosan-montmorillonite composite and its magnetized counterpart for the removal of basic fuchsin from wastewater: Parametric optimization using Box-Behnken design

Treating wastewater polluted with organic dyestuffs is still a challenge. In that vein, facile synthesis of a structurally simple composite of chitosan with montmorillonite (CS-MMT) using glutaraldehyde as a crosslinker and the magnetized analogue (MAG@CS-MMT) was proposed as versatile adsorbents for the cationic dye, basic Fuchsin (FUS). Statistical modeling of the adsorption process was mediated using Box-Behnken (BB) design and by varying the composite dose, pH, [FUS], and contact time. Characterization of both composites showed an enhancement of surface features upon magnetization, substantiating a better FUS removal of the MAG@CS-MMT (%R = 98.43 %) compared to CS-MMT (%R = 68.02 %). The surface area analysis demonstrates that MAG@CS-MMT possesses a higher surface area, measuring 41.54 m2/g, and the surface analysis of the magnetized nanocomposite, conducted using FT-IR and Raman spectroscopies, proved the presence of FeO peaks. In the same context, adsorption of FUS onto MAG@CS-MMT fitted-well to the Langmuir isotherm model and the maximum adsorption capacities (qm) were 53.11 mg/g for CS-MMT and 88.34 mg/g for MAG@CS-MMT. Kinetics investigation shows that experimental data fitted well to the pseudo-second order (PSO) model. Regeneration study reveals that MAG@CS-MMT can be recovered effectively for repeated use with a high adsorption efficiency for FUS.

Production of safe cyanobacterial biomass for animal feed using wastewater and drinking water treatment residuals

The growing interest in microalgae and cyanobacteria biomass as an alternative to traditional animal feed is hindered by high production costs. Using wastewater (WW) as a cultivation medium could offer a solution, but this approach risks introducing harmful substances into the biomass, leading to significant safety concerns. In this study, we addressed these challenges by selectively extracting nitrates and phosphates from WW using drinking water treatment residuals (DWTR) and chitosan. This method achieved peak adsorption capacities of 4.4 mg/g for nitrate and 6.1 mg/g for phosphate with a 2.5 wt% chitosan blend combined with DWTR-nitrogen. Subsequently, these extracted nutrients were employed to cultivate Spirulina platensis, yielding a biomass productivity rate of 0.15 g/L/d, which is comparable to rates achieved with commercial nutrients. By substituting commercial nutrients with nitrate and phosphate from WW, we can achieve a 18 % reduction in the culture medium cost. While the cultivated biomass was initially nitrogen-deficient due to low nitrate levels, it proved to be protein-rich, accounting for 50 % of its dry weight, and contained a high concentration of free amino acids (1260 mg/g), encompassing all essential amino acids. Both in vitro and in vivo toxicity tests affirmed the biomass's safety for use as an animal feed component. Future research should aim to enhance the economic feasibility of this alternative feed source by developing efficient adsorbents, utilizing cost-effective reagents, and implementing nutrient reuse strategies in spent mediums.

Phosphorus removal from water by the metal-organic frameworks (MOFs)-based adsorbents: A review for structure, mechanism, and current progress

Efficacious phosphate removal is essential for mitigating eutrophication in aquatic ecosystems and complying with increasingly stringent phosphate emission regulations. Chemical adsorption, characterized by simplicity, prominent treatment efficiency, and convenient recovery, is extensively employed for profound phosphorus removal. Metal-organic frameworks (MOFs)-derived metal/carbon composites, surpassing the limitations of separate components, exhibit synergistic effects, rendering them tremendously promising for environmental remediation. This comprehensive review systematically summarizes MOFs-based materials' properties and their structure-property relationships tailored for phosphate adsorption, thereby enhancing specificity towards phosphate. Furthermore, it elucidates the primary mechanisms influencing phosphate adsorption by MOFs-based composites. Additionally, the review introduces strategies for designing and synthesizing efficacious phosphorus capture and regeneration materials. Lastly, it discusses and illuminates future research challenges and prospects in this field. This summary provides novel insights for future research on superlative MOFs-based adsorbents for phosphate removal.

A review on chitosan/metal oxide nanocomposites for applications in environmental remediation

A cleaner and safer environment is one of the most important requirements in the future. It has become increasingly urgent and important to fabricate novel environmentally-friendly materials to remove various hazardous pollutants. Compared with traditional materials, chitosan is a more environmentally friendly material due to its abundance, biocompatibility, biodegradability, film-forming ability and hydrophilicity. As an abundant of -NH2 and -OH groups on chitosan molecular chain could chelate with all kinds of metal ions efficiently, chitosan-based materials hold great potential as a versatile supporting matrix for metal oxide nanomaterials (MONMs) (TiO2, ZnO, SnO2, Fe3O4, etc.). Recently, many chitosan/metal oxide nanomaterials (CS/MONMs) have been reported as adsorbents, photocatalysts, heterogeneous Fenton-like agents, and sensors for potential and practical applications in environmental remediation and monitoring. This review analyzed and summarized the recent advances in CS/MONMs composites, which will provide plentiful and meaningful information on the preparation and application of CS/MONMs composites for wastewater treatment and help researchers to better understand the potential of CS/MONMs composites for environmental remediation and monitoring. In addition, the challenges of CS/MONM have been proposed.

Alginate-Moroccan Clay, New Bio-Nanocomposite for Removal of H2PO4-, HPO42-, and NO3- Ions from Aqueous Solutions

The aim of this work is to synthesize and characterize alginate-Moroccan clay bio-composite in order to improve our understanding of the adsorption of inorganic pollutants found in textile effluents. Characterization of the bio-composite used was carried out using a variety of techniques (IR-TF, SEM, DRX, and pHZPC). The influence of the medium's physico-chemical parameters (temperature, pH, initial concentration, etc.) on the retention of inorganic pollutants was also studied. Studies of adsorption and inorganic pollutants such as orthophosphate (H2PO4- and HPO42-) and nitrate (NO3-) ions were carried out, using simple solutions from the laboratory, in a batch system. This study explored the impact of adsorbent dose, contact time, solution pH, and temperature on the adsorption process. Various kinetic models, including pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich models, were tested and evaluated, to illustrate the adsorption kinetics. This study's findings demonstrated that the adsorption process follows second-order kinetics, with associated rate constants successfully determined. The correlation coefficient for the pseudo-second-order kinetic model is nearly equal to 1 (>0.98), and the value of theoretical adsorption capacity (qe,the) is comparable to the experimental one (qe,the = 58.14 mg/g for H2PO4-, qe,the = 54.64 mg/g for HPO42-, and qe,the = 52.63 mg/g for NO3-). Additionally, the adsorption equilibrium was investigated through the application of various mathematical models, including the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, to assess the mechanistic parameters associated with the adsorption process. Among these models, the Langmuir isotherm emerged as the most suitable one for characterizing the adsorption of H2PO4-, HPO42-, and NO3- ions using bio-nanocomposite beads. The maximum adsorbed amounts of metal ions by the bio-nanocomposite used were 625 mg/g for H2PO4-, 909.09 mg/g for HPO42-, and 588.23 mg/g for NO3- from the batch system. The endothermic and physical nature of the adsorption is suggested by the positive values of ΔH°, which is consistent with experimental findings. The adsorption process is spontaneous, as evidenced by the negative ΔG° values. Positive ΔS° values indicate increased randomness at the solid/liquid interface during adsorption of ion-organic ions onto the engineered bio-nanocomposite. The obtained results demonstrated that, from a scientific perspective, alginate-Moroccan clay bio-nanocomposites exhibit a highly significant adsorption capability for the removal of oxyanions in aqueous environments.

Konjac glucomannan/pectin/Ca-Mg hydrogel with self-releasing alkalinity to recover phosphate in aqueous solution

The combination of polysaccharides can obtain stable, degradable, and environmentally friendly hydrogels, which have broad application prospects in adsorbents assembly. With Ca2+ and Mg2+ as crosslinkers, a new pectin/Konjac glucomannan/Ca-Mg composite hydrogel was prepared for phosphate adsorption by the alkali-thermal co-reaction method. Since Mg(OH)2 can create a suitable pH condition for phosphate adsorption by Ca, Ca and Mg synergistically promoted phosphate adsorption and remained stable in the pH range of 4 to 10. FTIR, SEM-EDS, XRD, XPS, and zero potential analysis corroborated that the hydrogel used Ca and Mg as active sites to trap pollutants by electrostatic adsorption and fix phosphate through complexation to form Mg3(PO4)2·8H2O and CaPO3(OH)2·H2O. Furthermore, it is unnecessary to separate the recovered phosphate from the hydrogel, and it can be used directly as a fertilizer. By being reused in the soil, it promoted seed germination and seedling growth. This adsorbent has the potential for recovery as a phosphorus-containing organic fertilizer after phosphorus adsorption.

Recent advances in green technology and Industrial Revolution 4.0 for a sustainable future

This review gives concise information on green technology (GT) and Industrial Revolution 4.0 (IR 4.0). Climate change has begun showing its impacts on the environment, and the change is real. The devastating COVID-19 pandemic has negatively affected lives and the world from the deadly consequences at a social, economic, and environmental level. In order to balance this crisis, there is a need to transition toward green, sustainable forms of living and practices. We need green innovative technologies (GTI) and Internet of Things (IoT) technologies to develop green, durable, biodegradable, and eco-friendly products for a sustainable future. GTI encompasses all innovations that contribute to developing significant products, services, or processes that lower environmental harm, impact, and worsening while augmenting natural resource utilization. Sensors are typically used in IoT environmental monitoring applications to aid ecological safety by nursing air or water quality, atmospheric or soil conditions, and even monitoring species' movements and habitats. The industries and the governments are working together, have come up with solutions-the Green New Deal, carbon pricing, use of bio-based products as biopesticides, in biopharmaceuticals, green building materials, bio-based membrane filters for removing pollutants, bioenergy, biofuels and are essential for the green recovery of world economies. Environmental biotechnology, Green Chemical Engineering, more bio-based materials to separate pollutants, and product engineering of advanced materials and environmental economies are discussed here to pave the way toward the Sustainable Development Goals (SDGs) set by the UN and achieve the much-needed IR 4.0 for a greener-balanced environment and a sustainable future.

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

A critical review of enzymes immobilized on chitosan composites: characterization and applications

Enzymes with industrial significance are typically used in biological processes. However, instability, high sensitivity, and impractical recovery are the major drawbacks of enzymes in practical applications. In recent years, the immobilization technology has attracted wide attention to overcoming these restrictions and improving the efficiency of enzyme applications. Chitosan (CS) is a unique functional substance with biocompatibility, biodegradability, non-toxicity, and antibacterial properties. Chitosan composites are anticipated to be widely used in the near future for a variety of purposes, including as supports for enzyme immobilization, because of their advantages. Therefor this review explores the effects of the chitosan's structure, molecular weight, degree of deacetylation on the enzyme immobilized, effect of key factors, and the enzymes immobilized on chitosan based composites for numerous applications, including the fields of biosensor, biomedical science, food industry, environmental protection, and industrial production. Moreover, this study carefully investigates the advantages and disadvantages of using these composites as well as their potential in the future.

Polymer-based nanocomposite adsorbents for resource recovery from wastewater

Developing mitigation mechanisms for eutrophication caused by the uncontrolled release of nutrients is in the interest of the scientific community. Adsorption, being operationally simple and economical with no significant secondary pollution, has proven to be a feasible technology for resource recovery. However, the utility of adsorption often lies in the availability of effective adsorbents. In this regard, polymer-based nanocomposite (PNC) adsorbents have been highly acclaimed by researchers because of their high surface area, multiple functional groups, biodegradability, and ease of large-scale production. This review paper elaborates on the functionality, adsorption mechanisms, and factors that affect the adsorption and adsorption-desorption cycles of PNC adsorbents toward nutrient resources. Moreover, this review gives insight into the application of recovered nutrient resources in soil amendment.

Bioinspired, Robust, and Absorbable Cellulose Nanofibrils/Chitosan Filament with Remarkable Cytocompatibility and Wound Healing Properties

Surgical threads are of great importance to prevent wound infection and accelerate tissue healing in surgical treatment. Cellulose nanofibrils (CNF) and chitosan (CS) are attracting increasing attention to be employed as biomedicine materials due to their nontoxicity, cytocompatibility, and biodegradability. However, a robust and absorbable cellulose-based surgical thread has not been explored. Therefore, in this work, a bioinspired CNF/CS composite thread containing 5% cationic polyacrylamide (CPAM) by the mass of CS was prepared, and the obtained CNF/CS-5C thread exhibited excellent mechanical properties and low swelling ratio in water due to the high cross-link degree. Especially, the tensile strength (1877 ± 107 MPa) of this thread was much higher than that of most reported CNF-based threads. Meanwhile, compared with commercial silk and Vicryl surgical threads, the CNF/CS-5C thread exhibited better in vitro cytocompatibility toward endothelial and fibroblast cells and lower inflammatory response in vivo to subcutaneous tissues of rats. In addition, the obtained thread could be regarded as a promising absorbable suture, which exhibited excellent wound healing performances in vivo. Therefore, the prepared absorbable thread will open a new window to prepare novel and advanced cellulose-based threads for medical applications.

Cerium(IV) chitosan-based hydrogel composite for efficient adsorptive removal of phosphates(V) from aqueous solutions

The excess presence of phosphate(V) ions in the biosphere is one of the most serious problems that negatively affect aqueous biocenosis. Thus, phosphates(V) separation is considered to be important for sustainable development. In the presented study, an original cerium(IV)-modified chitosan-based hydrogel (Ce-CTS) was developed using the chemical co-precipitation method and then used as an adsorbent for efficient removal of phosphate(V) ions from their aqueous solutions. From the scientific point of view, it represents a completely new physicochemical system. It was found that the adsorptive removal of phosphate(V) anions by the Ce-CTS adsorbent exceeded 98% efficiency which is ca. 4-times higher compared with the chitosan-based hydrogel without any modification (non-cross-linked CTS). The best result of the adsorption capacity of phosphates(V) on the Ce-CTS adsorbent, equal to 71.6 mg/g, was a result of adsorption from a solution with an initial phosphate(V) concentration 9.76 mg/dm3 and pH 7, an adsorbent dose of 1 g/dm3, temperature 20 °C. The equilibrium interphase distribution data for the Ce-CTS adsorbent and aqueous solution of phosphates(V) agreed with the theoretical Redlich-Peterson and Hill adsorption isotherm models. From the kinetic point of view, the pseudo-second-order model explained the phosphates(V) adsorption rate for Ce-CTS adsorbent the best. The specific effect of porous structure of adsorbent influencing the diffusional mass transfer resistances was identified using Weber-Morris kinetic model. The thermodynamic study showed that the process was exothermic and the adsorption ran spontaneously. Modification of CTS with cerium(IV) resulted in the significant enhancement of the chitosan properties towards both physical adsorption (an increase of the point of zero charge of adsorbent), and chemical adsorption (through the presence of Ce(IV) that demonstrates a chemical affinity for phosphate(V) anions). The elaborated and experimentally verified highly effective adsorbent can be successfully applied to uptake phosphates(V) from aqueous systems. The Ce-CTS adsorbent is stable in the conditions of the adsorption process, no changes in the adsorbent structure or leaching of the inorganic filling were observed.

Recovery of Phosphate(V) Ions from Water and Wastewater Using Chitosan-Based Sorbents Modified-A Literature Review

Over the past two decades, there has been increasing interest in the use of low-cost and effective sorbents in water treatment. Hybrid chitosan sorbents are potential materials for the adsorptive removal of phosphorus, which occurs in natural waters mainly in the form of orthophosphate(V). Even though there are numerous publications on this topic, the use of such sorbents in industrial water treatment and purification is limited and controversial. However, due to the explosive human population growth, the ever-increasing global demand for food has contributed to the consumption of phosphorus compounds and other biogenic elements (such as nitrogen, potassium, or sodium) in plant cultivation and animal husbandry. Therefore, the recovery and reuse of phosphorus compounds is an important issue to investigate for the development and maintenance of a circular economy. This paper characterizes the problem of the presence of excess phosphorus in water reservoirs and presents methods for the adsorptive removal of phosphate(V) from water matrices using chitosan composites. Additionally, we compare the impact of modifications, structure, and form of chitosan composites on the efficiency of phosphate ion removal and adsorption capacity. The state of knowledge regarding the mechanism of adsorption is detailed, and the results of research on the desorption of phosphates are described.

Peroxymonosulfate activation by Fe-N-S co-doped tremella-like carbocatalyst for degradation of bisphenol A: Synergistic effect of pyridine N, Fe-Nx, thiophene S

Bisphenol A (BPA) has received increasing attention due to its long-term industrial application and persistence in environmental pollution. Iron-based carbon catalyst activation of peroxymonosulfate (PMS) shows a good prospect for effective elimination of recalcitrant contaminants in water. Herein, considering the problem about the leaching of iron ions and the optimization of heteroatoms doping, the iron, nitrogen and sulfur co-doped tremella-like carbon catalyst (Fe-NS@C) was rationally designed using very little iron, S-C₃N₄ and low-cost chitosan (CS) via the impregnation-calcination method. The as-prepared Fe-NS@C exhibited excellent performance for complete removal of BPA (20 mg/L) by activating PMS with the high kinetic constant (1.492 min^-1) in 15 min. Besides, the Fe-NS@C/PMS system not only possessed wide pH adaptation and high resistance to environmental interference, but also maintained an excellent degradation efficiency on different pollutants. Impressively, increased S-C₃N₄ doping amount modulated the contents of different N species in Fe-NS@C, and the catalytic activity of Fe-NS@C-1-x was visibly enhanced with increasing S-C₃N₄ contents, verifying pyridine N and Fe-N_x as main active sites in the system. Meanwhile, thiophene sulfur (C-S-C) as active sites played an auxiliary role. Furthermore, quenching experiment, EPR analysis and electrochemical test proved that surface-bound radicals (^·OH and SO₄^⋅-) and non-radical pathways worked in the BPA degradation (the former played a dominant role). Finally, possible BPA degradation route were proposed. This work provided a promising way to synthesize the novel Fe, N and S co-doping carbon catalyst for degrading organic pollutants with low metal leaching and high catalytic ability.

Adsorption Characterization of Cu(II) and Cd(II) by a Magnetite-Chitosan Composite: Kinetic, Thermodynamic and Equilibrium Studies

Optimizing the use of magnetite-chitosan composites for heavy metal adsorption has been of great interest due to their environmental friendliness. To gain insights into their potential with green synthesis, this study analyzed one of these composites through X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. Adsorption properties were then explored via static experiments to evaluate the pH dependence, isotherms, kinetics, thermodynamics and regeneration adsorption of Cu(II) and Cd(II). Results disclosed that the optimum pH of adsorption was 5.0, the equilibrium time was about 10 min, and the capacity for Cu(II) and Cd(II) reached 26.28 and 18.67 mg/g, respectively. The adsorption amount of cations increased with temperature from 25 °C to 35 °C and decreased with further increase in temperature from 40 °C to 50 °C, which might be related to the unfolding of chitosan; the adsorption capacity was above 80% of the initial value after two regenerations and about 60% after five regenerations. The composite has a relatively rough outer surface, but its inner surface and porosity are not obvious; it has functional groups of magnetite and chitosan, and chitosan might dominate the adsorption. Consequently, this research proposes the value of maintaining green synthesis research to further optimize the composite system of heavy metal adsorption.

High reusability and adsorption capacity of acid washed calcium alginate/chitosan composite hydrogel spheres in the removal of norfloxacin

Calcium alginate (CA) hydrogel spheres were widely used as adsorbents to remove organics, but their adsorption capacities and reusability to some antibiotics are unsatisfactory. In this study, calcium alginate/chitosan (CA/CTS) hydrogel spheres were prepared as precursors. Acid-washed CA/CTS (CA/CTS-M) hydrogel spheres (310.6 mg/g) behaved much better adsorption capacity of norfloxacin (NOR) than CA (69.5 mg/g) and CA/CTS (87.7 mg/g) hydrogel spheres. Astonishingly, after being reused for 15 cycles, CA/CTS-M has no loss of NOR adsorption capacity. In the original idea, acid wash was expected to remove the chitosan in CA/CTS hydrogel spheres for obtaining a larger specific surface area. Both scanning electron microscopy and Brunauer-Emmett-Teller test showed that acid wash can remove CTS from CA/CTS hydrogel spheres to increase the specific surface area. However, part of the chitosan remained in CA/CTS-M, having a role to enhance the structural stability of the material, because the acid-washed CA (about 2 mm) has a significantly smaller diameter than CA/CTS-M (about 3 mm). According to the influence of pH and density functional theory calculations, electrostatic attraction is the key driving force of NOR adsorption. Importantly, acid wash led to more negative-charged surface characterized by Zeta potential, which is the main reason of the significantly enhanced adsorption capacity of CA/CTS-M in removal of NOR. In short, CA/CTS-M hydrogel spheres are environment friendly and highly stable adsorbents with high adsorption capacity in the removal of NOR.

Titanium dioxide nanoparticles functionalized chitosan toward bio-based antibacterial adsorbent for enhanced phosphate capture

Developing an eco-friendly, sustainable and antibacterial adsorbent is significant for actual water treatment. Herein, a new bio-based antibacterial adsorbent based on titanium dioxide (TiO₂) nanoparticles functionalized chitosan (CS) was prepared through an in-situ hydrolysis strategy using titanium oxysulfate as the source of TiO₂. The as-obtained CS/TiO₂ nanocomposite was characterized by a variety of analytical techniques. According to the Langmuir mode, the adsorption capacity of CS/TiO₂ reached 23.64 mg P g^-1, almost 8 times higher than that of CS. In addition, the normalized adsorption capacity (adsorption value per Ti) of CS/TiO₂ was calculated to be 102.68 mg P g^-1 Ti^-1, much higher than pure TiO₂ (60.11 mg P g^-1 Ti^-1). Moreover, CS/TiO₂ exhibited a highly selective capacity for phosphate removal in the presence of competing anions, and showed high stability in a wide pH range of 3.0-9.0. When the phosphate concentration was 2.0 mg P L^-1, the removal efficiency of phosphate reached 99.5 % and the residual concentration was only 10 μg P L^-1, which meets the USEPA standards for eutrophication prevention and control. In addition, after treatment by CS/TiO₂, the phosphate concentration of two sewage water samples decreased from 1.50 and 1.0 mg P L^-1 to <0.010 mg P L^-1, meeting the standard of level II water based on the Environmental Quality Standard of China (GB3838-2002). Ligand exchange and electrostatic interactions are mainly responsible for phosphate adsorption by CS/TiO₂. Furthermore, the CS/TiO₂ nanocomposites exhibited excellent antibacterial activity, which could avoid biofouling contamination caused by microorganisms. Benefiting from the above advantages, the as-designed CS/TiO₂ nanocomposite has great potential as a bio-based antibacterial adsorbent for phosphate removal or capture from wastewater.

Optimization of Removal of Phosphate from Water by Adsorption Using Biopolymer Chitosan Beads

The need for clean water is the most basic human right. Water scarcity will be one important environmental problem of all countries in the future. Phosphate is a harmful matter for public health and the environment. In this study, the removal of phosphate from water by chitosan, which is an environmentally friendly material, was investigated. Chitosan adsorbent spheres were prepared for phosphate separation from water by adsorption, which is a feasible method. The effects of phosphate concentration, adsorbent dosage, and operation time on the removal were investigated. The removal increased with acid concentration and adsorbent amount. The maximum adsorption capacity of chitosan beads is 87.26 mg/g. Adsorption behavior of the chitosan beads were examined by Langmuir and Freundlich isotherms and pseudo-first and second-order kinetic models. The adsorption process was optimized by the response surface method (RSM). Trial version of Design Expert® 12.0 was used in the study. It has been understood as a result of the RSM statistical analysis that higher phosphate removal values would be obtained by increasing the amount of adsorbent. ANOVA analysis showed that adsorbent dosage had the biggest effect on removal of phosphate using chitosan beads prepared for adsorption.

Graphene oxide incorporated cellulose acetate beads for efficient removal of methylene blue dye; isotherms, kinetic, mechanism and co-existing ions studies

In this investigation, new porous adsorbent beads were formulated via the incorporation of graphene oxide (GO) into cellulose acetate beads (CA) for the adsorptive removal of methylene blue (MB) dye. The experimental results signified that the adsorption of MB dye increased with the increase in the GO ratio from 10 to 25%. In addition, the adsorption process obeyed PSO kinetic model and Langmuir isotherm model with a maximum adsorption capacity reaching 369.85 mg/g. More importantly, it was proposed that the adsorption mechanism of MB dye onto GO@CA proceeded via electrostatic interactions, H-bonding, van der Waals forces, n-π and π -π interactions. Besides, the fabricated beads exhibited an excellent ability to recycle and reuse after five successive cycles. In addition, there was a high selectivity of GO@CA beads towards MB molecules in the presence of co-existing cations such as Fe2+, Zn2+, Cu2+ and Ni2+.

Recent Application Prospects of Chitosan Based Composites for the Metal Contaminants Wastewater Treatment

Heavy metals, known for their toxic nature and ability to accumulate and magnify in the food chain, are a major environmental concern. The use of environmentally friendly adsorbents, such as chitosan (CS)—a biodegradable cationic polysaccharide, has gained attention for removing heavy metals from water. This review discusses the physicochemical properties of CS and its composites and nanocomposites and their potential application in wastewater treatment.

Poly β-Cyclodextrin/Quaternary Ammoniated Chitosan Cryogel with a Porous Structure for Effective Hemostasis

Uncontrolled bleeding is one of the most important causes threatening human health, but quick hemostasis remains a challenge. We prepared porous cryogels with poly β-cyclodextrin (Pβ-CD) and quaternary ammoniated chitosan (QCs). Pβ-CD acts as a "water-grabbing agent" to assist QCs' ability to absorb and concentrate blood rapidly. The rat-tail amputation model and liver injury model exhibited that cryogels had excellent hemostatic performance. Moreover, cryogels showed good antibacterial activity and biocompatibility. Therefore, these cryogels can be used as potential hemostatic materials.

Co3O4 anchored on biochar derived from chitosan (Co3O4@BCC) as a catalyst to efficiently activate peroxymonosulfate (PMS) for degradation of phenacetin

Chitosan, as a bio-friendly and abundant biochar precursor, was employed to prepare cobalt-based catalyst (Co₃O₄@BCC) by calcination for activating peroxymonosulfate (PMS) to degrade phenacetin (PNT). Various characterization technologies and experimental designs were performed to investigate the physicochemical properties and catalytic performance of Co₃O₄@BCC. Approximately 99.0% of phenacetin (10 mg/L) was degraded in the system of Co₃O₄@BCC (0.05 g/L)/PMS (1.0 mM) within 15 min and the rate constant was 6 times higher than that in the system of Co₃O₄ (0.05 g/L)/PMS (1.0 mM). The results demonstrated that BCC as a carrier not only dispersed Co₃O₄ nanoparticles and improved the stability of catalyst, but also provided abundant electron-rich groups to facilitate the activation of PMS and the production of reactive oxygen species (ROS). Co₃O₄@BCC composite also exhibited good universality and reusability. More than 90% of BPA, SIZ and CAP was degraded by Co₃O₄@BCC activated PMS within 15 min at pH 7. The degradation rate of PNT was recovered from 90% to 98.0% via the regeneration of the used catalyst after the third run (calcination at 400 °C for 5 min). SO₄^•-, •OH and ¹O₂ were identified to be responsible for PNT degradation. Furthermore, the activation mechanism of PMS and the possible pathways of PNT degradation were reasonably speculated according to the results of electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), quenching experiments and HPLC-TOF-MS². This study explored the application of chitosan as a recycled material and provides a feasible strategy for designing and fabricating environmentally friendly and efficient catalysts for PMS activation to degrade organic pollutants.

Polymer-based nanocomposite adsorbents for resource recovery from wastewater

Adsorption is alternative technique for recovery of nutrient resources with no/less secondary pollution. PNC adsorbents are effective for removal and recovery of nutrient resources, and reusing nutrients as fertilizer could prevent eutrophication.

Role of emerging chitosan and zeolite-modified adsorbents in the removal of nitrate and phosphate from an aqueous medium: A comprehensive perspective

Due to industrialization and population growth, freshwater supplies are diminishing and becoming impure with high organic pollutant concentrations such as nitrate and phosphate, which shows a high adverse impact on aquatic and human lives. In drinking water sources, particularly groundwater, nitrate is considered as one of the major pollutants which causes methemoglobinemia (in newborn infants), carcinogenic activities and diabetes. Excess concentration of phosphate leads to eutrophication and death of aquatic species due to reduced dissolved oxygen content. Therefore, all countries must implement highly effective technologies for treating wastewater. Chitosan and zeolite are naturally occurring and cost-effective adsorbent materials with a higher surface area that exhibit greater nitrate and phosphate adsorption. Surface modification of chitosan and zeolite increases the adsorption capacity of adsorbents for the removal of both anions selectively. This paper reviews the current development of modified chitosan and zeolite adsorbents for anion adsorption, with an emphasis on modification by zero and multivalent metals and metal oxides, different surfactants, biomass-derived carbon, and natural and synthetic polymers. Multiple adsorption parameters, optimum adsorption condition, adsorption mechanism, regeneration study, research gap and future aspects have been explained for further research work.

Phosphorus-Rich Ruthenium Phosphide Embedded on a 3D Porous Dual-Doped Graphitic Carbon for Hydrogen Evolution Reaction

Metal phosphides have recently emerged as promising electrocatalysts for hydrogen evolution reaction (HER). Herein, we report the synthesis of ruthenium diphosphide embedded on a dual-doped graphitic carbon by pyrolyzing chitosan beads impregnated with ruthenium chloride and phosphorus pentoxide. The as-synthesized RuP₂@N-P-C displays a good electrocatalytic activity in acidic, neutral and alkaline media. We show that the HER activity of the electrocatalyst can be tuned by varying the concentration of Li⁺ cations. Co-diffusion effects on H⁺ exerted by Li⁺ on HER in the porous carbon matrix have been observed.

Mechanistic study of Hg(II) interaction with three different α-aminophosphonate adsorbents: Insights from batch experiments and theoretical calculations

Herein, efficient and potential chelating α-aminophosphonate based sorbents (AP-) derived from three different amine origins (aniline/anthranilic acid/O-phenylenediamine) to form AP-H, carboxylated and aminated enhanced aminophosphonate as AP-H, AP-COOH, and AP-NH₂ were synthesized via a facile method. The structure of the synthesized sorbents was elucidated using different techniques; elemental analysis (CHNP/O), FT-IR, NMR (¹H-, ¹³C and ³¹P NMR), TGA and BET. The fabricated sorbents were exploited for Hg(II) removal from aqueous solution via sorption properties. Isotherm fitted by Langmuir equation: the maximum sorption capacities at optimum pH 5.5, and T:25 ± 1 °C, were found to be 1.33, 1.23, and 1.15 mmol Hg g^-1 for AP-COOH, AP-NH₂, AP-H, respectively, which is roughly correlated with the active sites density and the hard/soft characteristics of adsorbents' reactive groups. Metal-ligand binding affinities are qualitatively rationalized in terms of hard and soft acids and bases (HSAB) theory. The interaction of Hg(II) (soft) has a stronger affinity to AP-COOH can be considered a softer base compared with reference material (AP-H) over than AP-NH₂ (hard). This sequence result showed opposite trends consistent with their reciprocal properties according to the steric effect modulates and the specific surface area. Thermodynamics analysis for absolute values of ΔH°, ΔS° and ΔG° afford the selectivity towards Hg(II) sorption with the following order: AP-COOH > AP-NH₂ >AP-H. Elution and regeneration was carried out by HCl solution and recycled for a minimum of five cycles, the sorption and desorption efficiencies are greater than 91%. Such sorbents exhibit good durability, stability and promising potential for Hg(II) removal. Finally, a new modelling technique for quantitative non-linear description and comparison of equivalent geographical positions in 3D space of extended relationships. Exothermic and spontaneous behavior were observed using a proposed Floatotherm that included the Van't Hoff parameters model.

Efficient removal of noxious methylene blue and crystal violet dyes at neutral conditions by reusable montmorillonite/NiFe2O4@amine-functionalized chitosan composite

The jeopardy of the synthetic dyes effluents on human health and the environment has swiftly aggravated, threatening human survival. Hence, sustained studies have figured out the most acceptable way to eliminate this poisonous contaminant. Thereby, our investigation aimed to fabricate montmorillonite/magnetic NiFe₂O₄@amine-functionalized chitosan (MMT-mAmCs) composite as a promising green adsorbent to remove the cationic methylene blue (MB) and crystal violet (CV) dyes from the wastewater in neutral conditions. Interestingly, MMT-mAmCs composite carries high negative charges at a wide pH range from 4 to 11 as clarified from zeta potential measurements, asserting its suitability to adsorb the cationic contaminants. In addition, the experimental study confirmed that the optimum pH to adsorb both MB and CV was pH 7, inferring the ability of MMT-mAmCs to adsorb both cationic dyes in simple process conditions. Furthermore, the ferromagnetic behavior of the MMT-mAmCs composite is additional merit to our adsorbent that provides facile, fast, and flawless separation. Notably, the as-fabricated composite revealed an auspicious adsorbability towards the adsorptive removal of MB and CV, since the maximum adsorption capacity of MB and CV were 137 and 118 mg/g, respectively. Moreover, the isotherm and kinetic investigatins depicted that the adsorption of both cationic dyes fitted Langmuir and Pseudo 2nd order models, respectively. Besides, the advanced adsorbent preserved satisfactory adsorption characteristics with maximal removal efficacy exceeding 87% after reuse for ten consecutive cycles. More importantly, MMT-mAmCs efficiently adsorbed MB and CV from real agricultural water, Nile river water and wastewater samples at the neutral pH medium, reflecting its potentiality to be a superb reusable candidate for adsorptive removal cationic pollutants from their aquatic media.

Synthesis of a new magnetic Sulfacetamide-Ethylacetoacetate hydrazone-chitosan Schiff-base for Cr(VI) removal

In this study, a novel magnetic organic-inorganic composite was fabricated. Where, Chitosan, sulfacetamide and ethylacetoacetae were used to prepare a new Sulfacetamide-Ethylacetoacetate hydrazone-chitosan Schiff-base (SEH-CSB) with a variety of active sites that capable of forming coordinate covalent bonds with Cr(VI). This was followed by modification of the formed SHE-CSB with NiFe₂O₄ to obtain the magnetic Chitosan-Schiff-base (NiFe₂O₄@SEH-CSB). NiFe₂O₄@SEH-CSB was characterized using FTIR, zeta potential, SEM, VSM and XPS. Results clarified that SHE played a crucial role in the removal of Cr(VI). The removal of Cr(VI) on NiFe₂O₄@SEH-CSB was found to be more fitted to pseudo-2nd order kinetics model and Freundlich isotherm. Besides, the maximum adsorption capacity of NiFe₂O₄@SEH-CSB for Cr(VI) was found to be 373.61 mg/g. The plausible mechanism for the removal of Cr(VI) on NiFe₂O₄@SEH-CSB composite suggested coulombic interaction, outer-sphere complexation, ion-exchange, surface complexation and coordinate-covalent bond pathways. The magnetic property enabled easy recycling of NiFe₂O₄@SEH-CSB composite.

Reusable kaolin impregnated aminated chitosan composite beads for efficient removal of Congo red dye: isotherms, kinetics and thermodynamics studies

In this investigation, Kaolin (K) impregnated aminated chitosan (AM-CTS) composite beads were fabricated with multi-features including low-cost, high performance, renewable and ease of separation for adsorption of anionic Congo red (CR) dye. Characterization tools such as FTIR, XRD, SEM, TGA, BET, XPS and Zeta potential were thoroughly employed to confirm the successful formulation process. The results revealed that K@ AM-CTS composite beads displayed higher specific surface area (128.52 m²/g), while the thermal stability was prominently improved compared to pure AM-CTS. In addition, the adsorption equilibrium of CR dye was accomplished rapidly and closely gotten within 45 min. The removal efficiency was significantly enriched and reached 90.7% with increasing kaolin content up to 0.75%, compared to 20.3 and 58% for pristine kaolin and AM-CTS, respectively. Moreover, the adsorption process obeyed the pseudo-first order kinetic model, while data were agreed with the Freundlich isotherm model with a maximum adsorption capacity reached 104 mg/g at pH 6. Furthermore, D–R isotherm model demonstrated the physical adsorption process of CR dye, which includes the electrostatic interactions, ion exchange and H-bonding. Thermodynamics evidenced the spontaneous and endothermic nature of the adsorption process. Interestingly, the developed K@AM-CTS composites beads showed better reusability for eight consecutive cycles, suggesting their feasible applicability for adsorptive removal anionic dyes from polluted aquatic bodies.

Removal of Phosphate from Wastewater with a Recyclable La-Based Particulate Adsorbent in a Small-Scale Reactor

It is crucial to develop an effective and easily recoverable phosphate absorbent for the control of eutrophication problems in polluted rivers. In this study, a stable particulate adsorbent with a diameter of 5 mm synthesized from lanthanum, activated carbon, and zeolite (La-CZ) was developed, characterized, and tested for the removal of phosphate from wastewater in a small-scale reactor, which was designed to easily recycle La-CZ with a basket. Batch studies showed that La-CZ could reach adsorption equilibrium within 2 h and the maximum phosphate sorption capacity was 18.2 mg g−1. The experimental data showed good compliance with the Langmuir isotherm model and pseudo-second-order kinetic model, implying that chemisorption dominates the phosphate uptake process. La-CZ exhibited a stable adsorption capacity over a wide pH range (3–7), while the adsorption capacity decreased slightly under alkaline conditions. Although Nitrates (NO3−) and Carbonate (CO32−) had some effects, normal coexisting ions such as Chloride (Cl−), Sulfate (SO42−), and Fluorine (F−) had no significant effects on the phosphate adsorption capacity of La-CZ. The main form of phosphate removed from the reaction system was HCl-P (77.68%), as determined through phosphorus fractionation. In particular, this study designed a replaceable filler-type reactor integrating a reflux and aeration system, 98.8% of phosphorus could be removed from actual wastewater, and La-CZ could be reclaimed easily. This work provides an excellent reference for particulate adsorbents that can efficiently remove phosphate in practical applications in the future.

In situ synthesis and characterization of colloidal AuNPs capped nano-chitosan containing poly(2,5-dimethoxyaniline) nanocomposites for biomedical applications

Herein, we have successfully synthesized a novel nCS-PDMA/AuNPs nanocomposite based on nano-chitosan containing poly(2,5-dimethoxyaniline) capped gold nanoparticle in situ synthesis is reported. The AuNPs were synthesized using the green method without using any harmful chemicals, reducing and stabilizing agents to generate AuNPs, is not needed because these roles are played by nCS. The synthesized nCS-PDMA/AuNPs nanocomposite were characterized by UV-Vis, FT-IR, XRD, SEM, and TEM analysis. The polydispersed nCS-PDMA/AuNPs nanocomposite was observed approximately 25 nm. Furthermore, nCS-PDMA/AuNPs nanocomposite was showed significant antibacterial activity against S. aureus and E. coli. The nCS-PDMA/AuNPs nanocomposite showed strong antioxidant activity by inhibiting the DPPH radicals. In addition, the cytotoxicity of nCS-PDMA/AuNPs nanocomposite was tested in HeLa cells and found to be high toxicity than nCS-PDMA. This work suggests that green synthesized nCS-PDMA/AuNPs nanocomposite may be utilized as an effective antibacterial, antioxidant, and anticancer activity.[Figure: see text]Research highlightsnCS-PDMA capped gold nanoparticles (nCS-PDMA/AuNPs) were prepared.Physical characterization of nCS-PDMA/AuNPs by UV-vis, FTIR, XRD, SEM, and TEM.nCS-PDMA/AuNPs displayed promising inhibitory activity against both bacteria.nCS-PDMA/AuNPs showed significant DPPH radical scavenging activities.nCS-PDMA/AuNPs showed an excellent anticancer activity against HeLa cells.

Onsite Wastewater Treatment Upgrade for Water Reuse in Cooling Towers and Toilets

The increasing population size and housing density are responsible for greater consumption of water resources, causing drinking water shortages in many regions. To reduce water consumption, it is essential to perform wastewater treatment, particularly in onsite non-potable water systems (ONWS). This article discusses the performance of a wastewater treatment system in a shopping mall in Brazil (City of Guarulhos, São Paulo State, Brazil), using data collected over 3 years (2015–2018) that resulted in water reuse ranging from 12 to 42 m³ per day. The strategy used for this wastewater treatment and further reuse in cooling towers and toilets initially included nine steps; after adjustments, an additional step (tertiary decanter) was added. All steps were named as follows: (1) railing; (2) fats boxes; (3) aerobic reactors with selector tank; (4) denitrification; (5) flocculation; (6) secondary decanter; (7) ultrafiltration; (8) disinfection; (9) filtration by zeolites; and (10) tertiary decanter. Based on using FeCl3 as a flocculant followed by filtration by zeolites (SFM) for ion adsorption and removing above 99% of the biological oxygen demand (BOD5), generating a final BOD5 of <2.0 mg/L, total dissolved solids of 130 to 594 mg/L, pH ranging from 6.75 to 7.79, and remaining pathogen-free. This treatment demonstrated the feasibility of reusing water in air conditioning cooling towers and toilets, generating up to 797 m³/month of treated water for reuse with savings of up to 27% in drinking water consumption at the mall.

Lightweight and anisotropic cellulose nanofibril/rectorite composite sponges for efficient dye adsorption and selective separation

Constructing lightweight and porous adsorbents which can effectively remove dye contaminants is of great significance in the field of the sewage treatment. In this work, anisotropic cellulose nanofibril (CNF) composite sponges assisted by rectorites are fabricated through directional freeze-drying. The resulted composite sponge exhibits the superior saturated adsorption capacity and removal efficiency of 120.0 mg/g and 96.1% for methylene blue (MB), respectively, which is better than the pure CNF sponge and rectorite powders. This is attributed to the strong electrostatic interaction between CNFs and MB, and good cation exchange property of rectorites inside the three-dimensional (3D) highly porous composite sponge. The MB adsorption process of the composite sponge fits to the pseudo-second-order kinetic model and the Langmuir isotherm model well, which is affected by both boundary layer and intraparticle diffusion, resulting in a theoretical maximum adsorption capacity of 214.6 mg/g. Moreover, it also possesses a selective adsorption capacity for anionic and cationic dyes, which is expected to realize the separation treatment of different dyes according to actual application requirements.

Sustainable adsorptive removal of antibiotic residues by chitosan composites: An insight into current developments and future recommendations

During COVID-19 crisis, water pollution caused by pharmaceutical residuals have enormously aggravated since millions of patients worldwide are consuming tons of drugs daily. Antibiotics are the preponderance pharmaceutical pollutants in water bodies that surely cause a real threat to human life and ecosystems. The excellent characteristics of chitosan such as nontoxicity, easy functionality, biodegradability, availability in nature and the abundant hydroxyl and amine groups onto its backbone make it a promising adsorbent. Herein, we aimed to provide a comprehensive overview of recent published research papers regarding the removal of antibiotics by chitosan composite-based adsorbents. The structure, ionic form, optimum removal pH and λ_max of the most common antibiotics including Tetracycline, Ciprofloxacin, Amoxicillin, Levofloxacin, Ceftriaxone, Erythromycin, Norfloxacin, Ofloxacin, Doxycycline, Cefotaxime and Sulfamethoxazole were summarized. The development of chitosan composite-based adsorbents in order to enhance their adsorption capacity, reusability and validity were presented. Moreover, the adsorption mechanisms of these antibiotics were explored to provide more information about adsorbate-adsorbent interactions. Besides the dominant factors on the adsorption process including pH, dosage, coexisting ions, etc. were discussed. Moreover, conclusions and future recommendations are provided to inspire for further researches.

Environmental Valorization of Rice Waste as Adsorbent Material for the Removal of Nitrates from Water

An innovative water-treatment process consisting in reducing the nitrate concentration by using an active silica filter obtained from ashes produced during rice-straw thermal treatment has been developed by the LIFE LIBERNITRATE project. A life-cycle assessment (LCA) was carried out to evaluate the environmental impacts of this innovative process, from the production of ashes and extraction and activation of silica to the water treatment. These results were compared to the environmental impact derived from the use of bottled water, instead of tap water, where traditional water treatments (i.e., reverse osmosis) may not be available due to the high installation and operating costs. The comparison showed that the proposed innovative process could contribute to reducing the environmental impact in almost all analyzed impact categories (from 20% for photochemical oxidation to 90% for abiotic depletion) with respect to the use of bottled water. In addition, if conveniently optimized (for example reducing the amount of active silica used per day), the innovative process could further reduce the ecological footprint and be more eco-friendly than the use of bottled water and could be applied to treating water in small towns where reverse osmosis may not be installed. The LCA proved that the innovative process could contribute to reducing the environmental impact of water-treatment technologies resulting in lower environmental indicators with respect to the use of bottled water.

Novel reusable amine-functionalized cellulose acetate beads impregnated aminated graphene oxide for adsorptive removal of hexavalent chromium ions

In this study, a multi-featured adsorbent was developed for the adsorptive removal of hexavalent chromium (Cr⁶⁺) ions. Herein, aminated graphene oxide (GO-NH₂) was firstly synthetized and incorporated into cellulose acetate beads (CA) which were followed by surface amine-functionalization process. Varies characterization tools such as FT-IR spectroscopy, SEM, TGA, XRD, BET, XPS and zeta potential were employed to ensure the successful fabrication of GO-NH₂@CA-NH₂ composite beads. An enhancement in the adsorption performance was attained, while the adsorption equilibrium was closely gotten within only 60 min. Therefore, the adsorption capacity was boosted with increasing GO-NH₂ ratio in the beads matrix from 10 to 25%. Furthermore, the adsorption process agreed with Freundlich isotherm model with a supreme adsorption capacity of 410.21 mg/g at pH 2, while data followed the pseudo-second-order kinetic model. Besides, thermodynamic studies denoted that the adsorption process was endothermic, randomness and spontaneous. The composite beads retained better adsorption characteristics for seven sequential cycles with ease of separation. The proposed adsorption of Cr⁶⁺ onto GO-NH₂@CA-NH₂ surface occurred via the electrostatic interactions, reduction process and coordinate-covalent bonds. These findings hypothesize that the fabricated GO-NH₂@CA-NH₂ beads could be act as easy-separable and reusable adsorbent for efficient adsorption of Cr⁶⁺ ions.

Xanthate-Modified Magnetic Fe3O4@SiO2-Based Polyvinyl Alcohol/Chitosan Composite Material for Efficient Removal of Heavy Metal Ions from Water

Chitosan has several shortcomings that limit its practical application for the adsorption of heavy metals: mechanical instability, a challenging separation and recovery process, and low equilibrium capacity. This study describes the synthesis of a magnetic xanthate-modified polyvinyl alcohol and chitosan composite (XMPC) for the efficient removal and recovery of heavy metal ions from aqueous solutions. The XMPC was synthesized from polyvinyl alcohol, chitosan, and magnetic Fe₃O₄@SiO₂ nanoparticles. The XMPC was characterized, and its adsorption performance in removing heavy metal ions was studied under different experimental conditions. The adsorption kinetics fit a pseudo-second-order kinetic model well. This showed that the adsorption of heavy metal ions by the XMPC is a chemical adsorption and is affected by intra-particle diffusion. The equilibrium adsorption isotherm was well described by the Langmuir and Freundlich equations. The XMPC reached adsorption equilibrium at 303 K after approximately 120 min, and the removal rate of Cd(II) ions was 307 mg/g. The composite material can be reused many times and is easily magnetically separated from the solution. This makes the XMPC a promising candidate for widespread application in sewage treatment systems for the removal of heavy metals.

Novel Biogenic Synthesis of a Ag@Biochar Nanocomposite as an Antimicrobial Agent and Photocatalyst for Methylene Blue Degradation

The conventional synthesis of nanomaterials employing physical and chemical methods usually requires high cost and toxic chemicals. Thus, a facile, ecofriendly, cost-effective, novel, and sustainable route for the synthesis of a silver-loaded biochar nanocomposite (Ag@biochar) using Chenopodium ambrosioides leaf extract and biomass is reported for the first time in this study to advocate many of the principles of green chemistry such as safer solvents and auxiliaries. UV spectroscopic analysis at 420 nm indicated the formation of silver nanoparticles (AgNPs). The band gap energy of Ag@biochar was 1.9 eV, confirming its potential use as a photocatalyst. Ag@biochar was found to be photoluminescent at 425 nm. AgNPs on the surface of biochar were predominantly spherical with a size range of 25-35 nm and a surface area of 47.61 m²/g. A zeta potential of -5.87 mV designated the stability of Ag@biochar. Testing the photocatalytic potential of Ag@biochar to remove methylene blue from wastewater demonstrated its high removal efficiency that reached 88.4% due to its high efficiency of electron transfer confirmed via electrochemical impedance spectroscopy analysis and retained 70.65% after six cycles of reuse. Ag@biochar was shown to be a powerful broad-spectrum antimicrobial agent as it completely prevented the growth of Escherichia coli and also inhibited the growth of Pseudomonas aeruginosa, Klebsiella pneumoniae, Bacillus subtilis, and Candida albicans with the inhibition zones of 19, 18, 22, and 16 mm, respectively.

Recent developments in alginate-based adsorbents for removing phosphate ions from wastewater: a review

The huge development of the industrial sector has resulted in the release of large quantities of phosphate anions which adversely affect the environment, human health, and aquatic ecosystems. Naturally occurring biopolymers have attracted considerable attention as efficient adsorbents for phosphate anions due to their biocompatibility, biodegradability, environmentally-friendly nature, low-cost production, availability in nature, and ease of modification. Amongst them, alginate-based adsorbents are considered one of the most effective adsorbents for removing various types of pollutants from industrial wastewater. The presence of active COOH and OH^- groups along the alginate backbone facilitate its physical and chemical modifications and participate in various possible adsorption mechanisms of phosphate anions. Herein, we focus our attention on presenting a comprehensive overview of recent advances in phosphate removal by alginate-based adsorbents. Modification of alginate by various materials, including clays, magnetic materials, layered double hydroxides, carbon materials, and multivalent metals, is addressed. The adsorption potentials of these modified forms for removing phosphate anions, in addition to their adsorption mechanisms are clearly discussed. It is concluded that ion exchange, complexation, precipitation, Lewis acid-base interaction and electrostatic interaction are the most common adsorption mechanisms of phosphate removal by alginate-based adsorbents. Pseudo-2^nd order and Freundlich isotherms were figured out to be the major kinetic and isotherm models for the removal process of phosphate. The research findings revealed that some issues, including the high cost of production, leaching, and low efficiency of recyclability of alginate-based adsorbents still need to be resolved. Future trends that could inspire further studies to find the best solutions for removing phosphate anions from aquatic systems are also elaborated, such as the synthesis of magnetic-based alginate and various-shaped alginate nanocomposites that are capable of preventing the leaching of the active materials.

Synthesis of MgAl-LDH@ZIF-8 composites by in situ growth method for highly efficient phosphate removal

Removal of phosphate from wastewater by adsorption has become one of the effective ways to mitigate the negative effects of eutrophication in water bodies, and efficient adsorbent is the key....

Fabrication of easy separable and reusable MIL-125(Ti)/MIL-53(Fe) binary MOF/CNT/Alginate composite microbeads for tetracycline removal from water bodies

In this investigation, we aimed to fabricate easy separable composite microbeads for efficient adsorption of tetracycline (TC) drug. MIL-125(Ti)/MIL-53(Fe) binary metal organic framework (MOF) was synthetized and incorporated with carbon nanotube (CNT) into alginate (Alg) microbeads to form MIL-125(Ti)/MIL-53(Fe)/CNT@Alg composite microbeads. Various tools including FTIR, XRD, SEM, BET, Zeta potential and XPS were applied to characterize the composite microbeads. It was found that the specific surface area of MIL-125(Ti)/MIL-53(Fe)/CNT@Alg microbeads was 273.77 m2/g. The results revealed that the adsorption of TC augmented with rising CNT proportion up to 15 wt% in the microbeads matrix. In addition, the adsorption process followed the pseudo-second-order and well-fitted to Freundlich and Langmuir models with a maximum adsorption capacity of 294.12 mg/g at 25 ◦C and pH 6. Furthermore, thermodynamic study clarified that the TC adsorption process was endothermic, random and spontaneous. Besides, reusability test signified that MIL-125(Ti)/MIL-53(Fe)/CNT@Alg composite microbeads retained superb adsorption properties for six consecutive cycles, emphasizing its potentiality for removing of pharmaceutical residues.