Dynamic and static adsorption and desorption of Hg(II) ions on chitosan membranes and spheres

Modeling and Optimization of the Adsorption of Cr (VI) in a Chitosan-Resole Aerogel Using Response Surface Methodology

In this paper, a model for Cr (VI) removal and optimization was made using a novel aerogel material, chitosan-resole CS/R aerogel, where a freeze-drying and final thermal treatment was employed to fabricate the aerogel. This processing ensures a network structure and stability for the CS, despite the non-uniform ice growth promoted by this process. Morphological analysis indicated a successful aerogel elaboration process., FTIR spectroscopy corroborated the aerogel precursor’s identity and ascertained chemical bonding after adsorption. Owing to the variability of formulations, the adsorption capacity was modeled and optimized using computational techniques. The response surface methodology (RSM), based on the Box–Behnken design using three levels, was used to calculate the best control parameters for the CS/R aerogel: the concentration at %vol (50–90%), the initial concentration of Cr (VI) (25–100 mg/L), and adsorption time (0.3–4 h). Analysis of variance (ANOVA) and 3D graphs reveal that the CS/R aerogel concentration and adsorption time are the main parameters that influence the initial concentration of CS/R aerogel metal-ion uptake. The developed model successfully describes the process with a correlation coefficient of R2 = 0.96 for the RSM. The model obtained was optimized to find the best material design proposal for Cr (VI) removal. Numerical optimization was used and showed superior Cr (VI) removal (94.4%) under conditions of a CS/R aerogel concentration of 87/13 %vol, with an initial concentration of Cr (VI) of 31 mg/L, and an adsorption time of 3.02 h. These results suggest that the proposed computational model can obtain an effective and viable model for CS material processing and for optimization of the uptake of this metal.

Magnetic chitosan/TiO2 composite for vanadium(v) adsorption simultaneously being transformed to an enhanced natural photocatalyst for the degradation of rhodamine B

A magnetic chitosan/TiO₂ composite material (MCT) was developed. MCT was successfully synthesized by a one-pot method using chitosan, TiO₂, and Fe₃O₄. The absorption equilibrium time of MCT was 40 min in absorbing vanadium(v), the optimal adsorption pH was 4, and the maximum adsorption capacity of vanadium(v) was 117.1 mg g^-1. The spent MCT was applied to photocatalytic reactions for reutilization. The decolorization rates for the degradation of rhodamine B (RhB) by new and spent MCT were 86.4% and 94.3%, respectively. The new and spent MCT exhibited absorption bands at 397 and 455 nm, respectively, which showed that the spent MCT was red-shifted to the cyan light region. These results indicated that the forbidden band widths of the new and spent MCT were about 3.12 and 2.72 eV, respectively. The mechanism of the degradation reaction showed that the hydroxyl radicals as oxidants in the spent MCT mediated the photocatalytic degradation of RhB. In addition, the superoxide anion radical formation of hydroxyl radicals was the main reaction, and the hole generation of hydroxyl radicals was the subordinate reaction. The N-de-ethylated intermediates and organic acids were monitored by MS and HPLC.

Environmental application of amine functionalised magnetite nanoparticles grafted graphene oxide chelants

This study proposed a two-step method involving hydrothermal and electrostatic self-assembly processes for synthesising an amine-functionalised magnetic ligand graphene oxide-based nanocomposite (EDTA@Fe₃O₄@GO). The amine groups were successfully attached to the surface of iron (II, III) oxide (Fe₃O₄), which were embedded on the surface of graphene oxide (GO) (Fe₃O₄@GO). This EDTA@ Fe₃O₄@GO nanocomposite was used as a chelating agent to bind the toxic heavy metal ions. EDTA@Fe₃O₄@GO demonstrated the synergistic effect between the large surface area and magnetic behaviour of Fe₃O₄@GO and the chelating effect of EDTA, and it showed higher efficiency than the individual GO and Fe₃O₄. The possible structural and compositional characteristics were proposed based on Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) and Raman spectroscopy analysis. The outcomes revealed the mechanism behind the excellent As(V) adsorption onto EDTA@Fe₃O₄@GO. The adsorption process was studied by fitting the experimental data obtained into various kinetic and isotherm models. The pseudo-second-order (PSO) kinetic model and the Freundlich isotherm model (FIM) were found to be the best fit models for the removal of As(V) by EDTA@Fe₃O₄@GO. EDTA@Fe₃O₄@GO has the utmost adsorption capacity of 178.4 mg/g. Furthermore, the EDTA@Fe₃O₄@GO nanocomposite is reusable, and it showed excellent adsorption capacity up to 5 cycles. This study has provided insight into the potential of EDTA@Fe₃O₄@GO and its applications in large-scale wastewater treatment.

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.

Multifunctional β-Cyclodextrin-EDTA-Chitosan polymer adsorbent synthesis for simultaneous removal of heavy metals and organic dyes from wastewater

Heavy metals and organic dyes are the major source of water pollution. Herein, a trifunctional β-cyclodextrin-ethylenediaminetetraacetic acid-chitosan (β-CD-EDTA-CS) polymer was synthesized using an easy and simple chemical route by the reaction of activated β-CD with CS through EDTA as a cross-linker (amidation reaction) for the removal of inorganic and organic pollutants from aqueous solution under different parameters such as pH, time effect, initial concentration, reusability, etc. The synthesized adsorbent was characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, field scanning electron microscopy, energy dispersive spectroscopy, Brunauer-Emmett-Teller (BET), thermogravimetric analyzer techniques to investigate their structural, functional, morphological, elemental compositions, surface area and thermal properties, respectively. Two types of heavy metals, i.e., mercury (Hg²⁺) and cadmium (Cd²⁺), and three organic dyes, i.e., methylene blue (MB), crystal violet (CV) and safranin O (SO) were chosen as inorganic and organic pollutants, respectively, to study the adsorption capacity of β-CD-EDTA-CS in aqueous solution. The β-CD-EDTA-CS shows monolayer adsorption capacity 346.30 ± 14.0 and 202.90 ± 13.90 mg g^-1 for Hg²⁺ and Cd²⁺, respectively, and a heterogeneous adsorption capacity 107.20 ± 5.70, 77.40 ± 5.30 and 55.30 ± 3.60 mg g^-1 for MB, CV and SO, respectively. Kinetics results followed pseudo-second order (PSO) kinetics behavior for both metal ions and dyes, and higher rate constants values (0.00161-0.00368 g mg^-1 min^-1) for dyes confirmed the cavitation of organic dyes (physisorption). In addition, we have also demonstrated the performance of β-CD-EDTA-CS for the of four heavy metals Hg²⁺, Cd²⁺, Ni²⁺, and Cu²⁺ and three dyes MB, CV, and SO in secondary treated wastewater. Findings of this study indicate that β-CD-EDTA-CS simple and essay to synthesize and can be use in wastewater treatment.

Efficient removal of Hg2+ from aqueous solution by a novel composite of nano humboldtine decorated almandine (NHDA): Ion exchange, reducing-oxidation and adsorption

Efficient removal of Hg²⁺ from aqueous solution is key for environmental protection and human health. Herein, a novel composite of nano humboldtine decorated almandine was synthesized from almandine for the removal of Hg²⁺. Results showed that the Hg²⁺ removal process followed pseudo-second-order kinetic model and Langmuir equation, and the maximum adsorption capacity was 575.17 mg/g. Furthermore, Hg²⁺ removal by the composite was pH-dependent and low pH value facilitated the removal of Hg²⁺. SEM and HADDF-STEM results suggested a new rod morphology was generated and the adsorbed mercury was mainly enriched into this structure after reaction with Hg²⁺ solution. The removal mechanisms of Hg²⁺ by the composite was pH dependent, and included ion exchange, surface complexation, reduction and oxidation. Our results demonstrated that the composite was an ideal material for Hg²⁺ removal and the transformation ways of mercury related species could be a significant but currently underestimated pathway in natural and engineered systems.

Fabrication of thiophene-chitosan hydrogel-trap for efficient immobilization of mercury (II) from aqueous environs

The fabrication of thiophene-chitosan (TCS) hydrogel has been carried out to show the excellent binding performance of Hg(II) from an aqueous solution of heavy metal ions in presence of thiophene moiety within the hydrogel network. Thiophene moiety has been implanted within chitosan, a wild bio-resources, through a facile Schiff base condensation strategy with 2-thiophenecarboxaldehyde to develop a three-dimensional network of TCS hydrogel. The parameters influencing adsorption capacity such as pH, volume of functional agent, contact time, amount of the hydrogel are included to broaden the in-depth study for the adsorption window of Hg(II) followed by the desorption and reusability performance of TCS. The results indicate that the TCS hydrogel for Hg(II) followed pseudo-second-order kinetics. Ethylenediaminetetraacetic acid (EDTA), acts as a better eluent compared to HCl to desorb Hg(II) and even after recurring adsorption/desorption cycles, removal efficacy of TCS hydrogel could be retained.

Enhanced adsorption/photocatalytic removal of Cu(Ⅱ) from wastewater by a novel magnetic chitosan@ bismuth tungstate coated by silver (MCTS-Ag/Bi2WO6) composite

An easily separation composite, magnetic chitosan@bismuth tungstate coated by silver (MCTS-Ag/Bi₂WO₆), was successfully synthesized by the simple hydrothermal method. Moreover, the MCTS-Ag/Bi₂WO₆ demonstrated excellent adsorption/photocatalytic removal of Cu(II) in aqueous solution. Adsorption played a leading role in the synergistic reaction. The catalysts were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The effects on adsorption of Cu(II) were investigated, which included illumination, pH, and initial concentration. The experimental results showed that the theoretical maximum adsorption capacity of Cu(II) (181.8 mg/g) was achieved under simulated solar light irradiation with the optimal pH value of 6.0, indicating that illumination could enhance the adsorption of Cu(II) by MCTS-Ag/Bi₂WO₆. Meanwhile, the composite exhibited desirable adsorption ability of Cu(II) after 5 cycles. The copper ion adsorption fitted well with pseudo-second-order kinetic model and its isotherm followed Freundlich model.

One-dimensional graphene for efficient aqueous heavy metal adsorption: Rapid removal of arsenic and mercury ions by graphene oxide nanoribbons (GONRs)

There is a knowledge gap for the application of one-dimensional graphene in the adsorption process. Our hypothesis was based on the fact that graphene oxide nanoribbons (GONRs) as one-dimensional graphene with more desired edges and specific surface area than other carbonaceous nanomaterials have more oxygen containing functional groups (active sites) on their edges and basal planes and therefore are more capable in adsorption of pollutants. In this regard, we synthesized GONRs by unzipping of multi-walled carbon nanotubes (MWCNTs) and investigated the adsorption behavior of GONRs by ultrasonic-assisted adsorptive removal of As(V) and Hg(II) ions from aqueous solution. The obtained results showed that As(V) ions are more favorably adsorbed onto the GONRs than Hg(II) ions and with increasing initial As(V) and Hg(II) ions concentration to 300 ppm, the equilibrium adsorption uptake of the synthesized GONRs increases to 155.61 and 33.02 mg/g for As(V) and Hg(II) ions, respectively through a rapid separation process in just 12 min. Also, three kinetic models and Freundlich and Langmuir adsorption isotherms were applied to evaluate the obtained experimental results. Our findings highlight the potential application of GONRs as one-dimensional graphene adsorbent with more desired edges than MWCNTs and graphene oxide (GO) and high adsorption capacity for selective removal of heavy metals.

Mercury Removal from Aqueous Solutions Using Modified Pyrite: A Column Experiment

Modified pyrite (MPy), which was obtained from calcination in an N2 atmosphere, was used as a sorbent for removing Hg(II) from aqueous solutions. Fixed-bed column experiments were conducted to determine the Hg(II) removal ability of MPy from aqueous solutions. MPy was found to be much better than natural pyrite for mercury removal. The concentration of Hg(II) in effluents was much lower than that of the emission standard used for Hg wastewater in China (0.05 mg/L), and the removal efficiency of Hg(II) was greater than 99% before breakthrough. When the capacity was 3274 times the column bed volume (1 bed volume = 25.12 cm3), the column breakthrough and the sorption amount of Hg(II) were 54.44 mg/g. The Hg(II) content in the used MPy sorbent was up to 24.79%. The mechanism was analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM), and X-ray Photoelectron Spectroscopy (XPS). The main mechanism of Hg(II) removal by MPy was the chemical reactions between mercury ions and mineral fillers, and HgS precipitated on the surface of MPy to remove Hg(II). The reaction was also accompanied by surface complexation and adsorption. The results of this work show that MPy can be used as a sorbent for continuous Hg(II) removal.

Hydrogel applications for adsorption of contaminants in water and wastewater treatment

During the last decade, hydrogels have been used as potential adsorbents for removal of contaminants from aqueous solution. To improve the adsorption efficiency, there are numerous different particles that can be chosen to encapsulate into hydrogels and each particle has their respective advantages. Depending on the type of pollutants and approaching method, the particles will be used to prepare hydrogels. The hydrogels commonly applied in water/wastewater treatment was mainly classified into three classes according to their shape included hydrogel beads, hydrogel films, and hydrogel nanocomposites. In review of many recently research papers, we take a closer look at hydrogels and their applications for removal of contaminants, such as heavy metal ion, dyes, and radionuclides from water/wastewater in order to elucidate the reactions between contaminants and particles and potential for recycling and regeneration of the post-treatment hydrogels. Graphical abstract ᅟ.

Towards a better understanding on mercury adsorption by magnetic bio-adsorbents with γ-Fe2O3 from pinewood sawdust derived hydrochar: Influence of atmosphere in heat treatment

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m²/g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe₂O₃ with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg₄Fe₈O₁₆C₅₆H₄₀ were also formed.

Sorption of Hg(II) and Pb(II) Ions on Chitosan-Iron(III) from Aqueous Solutions: Single and Binary Systems

The present work describes the study of mercury Hg(II) and lead Pb(II) removal in single and binary component systems into easily prepared chitosan-iron(III) bio-composite beads. Scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and point of zero charge (pHpzc) analysis were carried out. The experimental set covered pH study, single and competitive equilibrium, kinetics, chloride and sulfate effects as well as sorption⁻desorption cycles. In single systems, the Langmuir nonlinear model fitted the experimental data better than the Freundlich and Sips equations. The sorbent material has more affinity to Hg(II) rather than Pb(II) ions, the maximum sorption capacities were 1.8 mmol·g-1 and 0.56 mmol·g-1 for Hg(II) and Pb(II), respectively. The binary systems data were adjusted with competitive Langmuir isotherm model. The presence of sulfate ions in the multicomponent system [Hg(II)-Pb(II)] had a lesser impact on the sorption efficiency than did chloride ions, however, the presence of chloride ions improves the selectivity towards Hg(II) ions. The bio-based material showed good recovery performance of metal ions along three sorption⁻desorption cycles.

Nitrogen-containing amino compounds functionalized graphene oxide: Synthesis, characterization and application for the removal of pollutants from wastewater: A review

Nowadays, using graphene oxide (GO) as an adsorbent for removing pollutants from wastewater has attracted increasing attention due to its unique physic-chemical properties. Nitrogen-containing amino (NA) compounds have excellently complexing properties due to their abundant amino functional groups. In order to obtain an innovative adsorbent, functionalized GO (NAGO) has been developed by combining the properties of GO with the advantages of NA compounds. The obtained NAGO composites usually exhibit great improvement in adsorption properties and can be used as a promising adsorbent for decontamination of wastewater. This paper reviewed recent progress of synthetic technologies about fabricating various NAGOs, and their morphologies, structures and functional characteristics. Meanwhile, important applications of NAGOs for different kind of pollutants and theory of the adsorption phenomena are discussed based on the isothermal and kinetic adsorption models. Furthermore, the affecting factors, underlying mechanisms and comparison with other adsorbents for the removal of pollutants are reviewed. Conclusively, the perspectives and challenges involved in the application of NAGOs for decontamination of wastewater have also been proposed to promote sustainable development of this new exciting field.

Novel polyvinylidene fluoride nanofiltration membrane blended with functionalized halloysite nanotubes for dye and heavy metal ions removal

Membrane separation is an effective method for the removal of hazardous materials from wastewater. Halloysite nanotubes (HNTs) were functionalized with 3-aminopropyltriethoxysilane (APTES), and novel polyvinylidene fluoride (PVDF) nanofiltration membranes were prepared by blending with various concentrations of APTES grafted HNTs (A-HNTs). The morphology structure of the membranes were characterized by scanning electron microscope (SEM) and atomic force microscopy (AFM). The contact angle (CA), pure water flux (PWF) and antifouling capacity of membranes were investigated in detail. In addition, the separation performance of membranes were reflected by the removal of dye and heavy metal ions in simulated wastewater. The results revealed that the hydrophilicity of A-HNTs blended PVDF membrane (A-HNTs@PVDF) was enhanced significantly. Owing to the electrostatic interaction between membrane surface and dye molecules, the dye rejection ratio of 3% A-HNTs@PVDF membrane reached 94.9%. The heavy metal ions rejection ratio and adsorption capacity of membrane were also improved with the addition of A-HNTs. More importantly, A-HNTs@PVDF membrane exhibited excellent rejection stability and reuse performances after several times fouling and washing tests. It can be expected that the present work will provide insight into a new method for membrane modification in the field of wastewater treatment.

Nanoarchitectures of self-assembled poly(styrene-b-4-vinyl pyridine) diblock copolymer blended with polypeptide for effective adsorption of mercury(ii) ions

The crosslinked PS-b-P4VP/PTyr materials possesses superior adsorbed mercur since mercury ions tend to bind to the pyridyl rings of P4VP and the amido groups of PTyr through ionic dipole interactions.

Al-Doped chitosan nonwoven in a novel adsorption reactor with a cylindrical sleeve for dye removal: performance and mechanism of action

To overcome the inconvenience of solid/liquid separation of powdered adsorbents, a novel adsorption reactor with a cylinder sleeve was designed to match the textile-pattern of chitosan nonwoven for the sake of easy separation and simple operation.