Highly efficient and rapid removal of arsenic(iii) from aqueous solutions by nanoscale zero-valent iron supported on a zirconium 1,4-dicarboxybenzene metal–organic framework (UiO-66 MOF)

A zirconium 1,4-dicarboxybenzene metal–organic framework (UiO-66 MOF) was successfully used as a template to enhance the distribution and activity of nanoscale zero-valent iron (NZVI). MOF-NZVI showed good anti-interference ability to co-existing ions (Ca²⁺, Mn²⁺, Cu²⁺, H₂PO₄⁻ and SO₄²⁻) and organic acids (oxalic acid and citric acid). SEM and TEM analyses indicated that the MOF as a support efficiently prevent NZVI from aggregation for quick and effective removal of As(iii). Through the non-linear least-squares (NLLS) adjustment, As(iii) removal by MOF-NZVI could be well fitted by pseudo first and second order reaction kinetics, as well as the Freundlich isotherm. FTIR, XRD and XPS results verified that NZVI and iron oxyhydroxides (Fe₃O₄, γ-Fe₂O₃, γ-FeOOH and α-FeOOH) might be responsible for the effective removal of As(iii) and its oxidized product As(v) with an adsorption capacity of 360.6 mg As per g NZVI through chemical oxidation and physical adsorption. This work indicates that MOF-NZVI with good reusability and high efficiency is promising for application in As(iii)-polluted wastewater treatment.

A zirconium 1,4-dicarboxybenzene metal–organic framework (UiO-66 MOF) was successfully used as a template to enhance the distribution and activity of nanoscale zero-valent iron (NZVI).     

Preparation of hyper-cross-linked hydroxylated polystyrene for adsorptive removal of methylene blue

A series of hydroxylated polystyrene (PS-OH) resins were prepared from macroporous poly(styrene-co-divinylbenzene) by nitration, reductive amination, diazotation and hydrolysis in sequence, and then a series of hyper-cross-linked hydroxylated polystyrene (HCPS-OH) resins were successfully prepared from the PS-OH resins by the Friedel–Crafts post-cross-linking using dichloromethane as an external cross-linker. Benefiting from the synthetic protocol, the HCPS-OH resins showed better adsorption performance for methylene blue in aqueous solution as compared with the corresponding PS-OH resins. HCPS-OH-4, one of the fabricated HCPS-OH resins which had the hydroxyl content of 5.0 mmol g⁻¹ and BET specific surface area of 69.0 m² g⁻¹, showed the highest adsorption capacity and selectivity for methylene blue. Higher temperature, higher pH, and higher ionic strength were beneficial to adsorption of methylene blue from aqueous solution. HCPS-OH-4 could be regenerated by treatment with 1.0 M HCl methanol solution and deionized water sequentially. Moreover, HCPS-OH-4 retained good adsorption performance for methylene blue even after 5 cycles of adsorption and regeneration, which implied that it was a good candidate for adsorptive removal of methylene blue dye in waste water.

This study presents the preparation of hyper-cross-linked hydroxylated polystyrene (HCPS-OH) resins using dichloromethane as an external cross-linker for the adsorption of methylene blue.     

One-pot preparation of MnOx impregnated cotton fibers for methylene blue dye removal

Using natural cotton fibers (CF) as a matrix, a series of novel MnO_x impregnated cotton fibers (designated as Mn-X@BCF) were prepared in this study through a one-pot sono-assisted KMnO₄ reduction process with no additional reducers. The as-prepared Mn-X@BCF was covered by a uniform and dense layer of MnO_x nanospheres (10–30 nm), the amount of which was significantly improved by CF pretreatment and linearly correlated with KMnO₄ concentration. Specifically, when KMnO₄ concentrations increased from 5 mmol L⁻¹ to 100 mmol L⁻¹, the impregnation ratios of MnO_x on BCF increased from 0.34% to 14.98% accordingly. Mn-X@BCF showed substantial removal for the typical dye MB. Under the studied conditions, MB removal equilibrium was reached within 10 minutes and solution pH showed no significant influence over a wide pH range (2–11). MB adsorption by Mn-25@BCF obeyed the pseudo-second-order kinetic model and Langmuir model well. The calculated maximum adsorption capacity (Q_m) of Mn-25@BCF was 46.3 mg g⁻¹, close to the cumulative adsorption capacity (Q_c 45 mg g⁻¹) of MB determined during the eight cycles of adsorption. It was proposed that adsorption followed by partial oxidation was the main mechanism of MB removal by Mn-X@BCF. The as-prepared Mn-25@BCF has great potential as an efficient and low-cost material for dye wastewater treatment because of its inexpensive and renewable source of raw materials, fast MB removal kinetics, wide working pH range and easy solid–liquid separation.

Mn-X@BCF, prepared by one-pot sono-assisted KMnO₄ reduction, could remove methylene blue efficiently by a proposed adsorption-partial oxidation mechanism.     

Fast removal of methylene blue from aqueous solution using coal-based activated carbon

Coal-based activated carbons (CACs) were prepared from three long flame coals with different ash and volatile matter content. CACs prepared by coal with high ash (6.74%) and volatile matter content (34.31%) showed better adsorption efficiency towards MB (547.35 mg g⁻¹) due to higher surface area and pore volume. The effect of coal to activating agent ratio (CAR) was also investigated in a batch reactor. The porosity development is closely related to the CAR. The calculated monolayer adsorption amount (714.29 mg g⁻¹) was found on YLC-AC-3 with a surface area of 1212.50 m² g⁻¹. The equilibrium data were favorably described by the Langmuir and Freundlich isotherm models, and adsorption kinetics fitted well to the pseudo-second order model. The removal efficiency remains at 98.21% after five runs. The results of the present study suggest that CACs are potential and effective adsorbents in fast removal of dyes from aqueous solution.

A monolayer adsorption amount of MB (714.29 mg g⁻¹) was found on a coal-based activated carbon prepared by a simple method.     

Hybrid MIL-101(Cr)@MIL-53(Al) composite for carbon dioxide capture from biogas

In this study, hybrids of nanoporous MIL-101(Cr) and MIL-53(Al) were synthesized using a hydrothermal method for various time periods, ranging from 8 to 40 h. The prepared materials were characterized by powder X-ray diffraction (PXRD) and elemental analysis, and their specific surface areas were measured by N₂ sorption at 77 K using the Brunauer–Emmett–Teller (BET) method. To investigate the practical application of these materials, the pure carbon dioxide and methane adsorption capacities of the samples were determined using the volumetric method. The Langmuir model was used to fit the CO₂ and CH₄ isotherms. Extended Langmuir (EL) equations and the ideal adsorbed solution theory (IAST) models were used to obtain the CO₂/CH₄ selectivity. The sample with the highest BET specific surface area was selected as a candidate for further investigations. The thermal stability of the selected sample was investigated by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to characterize the sample morphology. XRD results showed that the sample synthesized over the shortest time corresponded to MIL-101(Cr), while the sample synthesized over the longest time was in agreement with MIL-53(Al). Samples synthesized for time periods between these two limits were assumed to be composites of both MIL-53(Al) and MIL-101(Cr). TGA results indicated that the hybrid materials were thermally stable at temperatures about 100 °C higher than for pure MIL-101(Cr). The BET specific surface area (1746 m² g⁻¹) and CO₂ adsorption capacity (16 mmol g⁻¹) of the selected hybrid sample were about 50% and 35% higher, respectively, compared with those of pure MIL-53(Al), but 30% and 20% lower, respectively, compared with those of pure MIL-101(Cr). Binary adsorption modeling showed the high selectivity of the MIL-101(Cr) and MIL-53(Al) hybrid material for CO₂ with a minimum separation factor of about 60 at 298 K. This value was much higher than those reported previously and those observed in this work for the original MIL-101(Cr) or MIL-53(Al). These results demonstrated that the hybrid of MIL-101(Cr) and MIL-53(Al) was a promising material for selective CO₂ capture from natural and biogas.

In this study, hybrids of nanoporous MIL-101(Cr) and MIL-53(Al) were synthesized using a hydrothermal method for various time periods, ranging from 8 to 40 h.     

Recyclable magnetic carbonaceous porous composites derived from MIL-100(Fe) for superior adsorption and removal of malachite green from aqueous solution

Development of novel porous materials for efficient adsorption and removal of environmental pollutants from aqueous solution is of great importance and interest in environmental science and chemistry. Herein, we reported a facile synthesis of recyclable magnetic carbonaceous porous composite derived from iron-based metal–organic framework MIL-100(Fe) for superior adsorption and removal of malachite green (MG) from aqueous solution. Because of large surface area and high porosity, the synthesized magnetic carbonaceous porous material presented a superior adsorption capacity of 2090 mg g⁻¹ for MG. The adsorption of MG on magnetic carbonaceous porous composite is endothermic and spontaneous. The prepared magnetic carbonaceous porous composite could be separated easily and rapidly from the solution matrix by an external magnet. The rapid adsorption, large adsorption capacity and good reusability make it attractive for practical use in the adsorption and removal of dyes from aqueous solutions.

Magnetic carbonaceous porous composites (MCPCs) showed excellent adsorption capacity (up to 2090 mg g⁻¹) for malachite green with good reusability and stability.     

Glauconite clay-functionalized chitosan nanocomposites for efficient adsorptive removal of fluoride ions from polluted aqueous solutions

We herein have developed a mild approach for the fabrication of glauconite clay (G)-modified chitosan (CS) nanocomposites by the combination of a simple blending and crosslinking method. The chitosan was modified with ethylenediaminetetraacetic acid (EDTA), glutaraldehyde (GL), sodium dodecyl sulfate (SDS), and cetyltrimethyl ammonium bromide (CTAB). The as-prepared composites were identified using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), nitrogen physical adsorption (BET), atomic absorption spectrophotometry (AA), and thermal gravimetric analysis (TGA). The adsorption activities of the as-prepared materials were assessed for the removal of fluoride ions from aqueous media using a batch technique. Raw glauconite (G), GL-CS/G, SDS-CS/G, EDTA-GL-CS/G, and CTAB-CS/G adsorbents displayed maximum adsorption capacity values of 1.15, 4.31, 4.55, 6.90, and 9.03 mg g⁻¹, respectively. The adsorption results were well described by employing the pseudo-second-order kinetic and Langmuir isotherm models. The estimated thermodynamic constants indicated that the F⁻ ion adsorption was a spontaneous, physisorption process. Furthermore, the modified chitosan adsorbents are good candidates for the adsorptive elimination of F⁻ ions from aqueous solutions, according to their reusability, high stability, good adsorption capacity, and applicability for actual field water samples.

We herein have developed a mild approach for the fabrication of glauconite clay (G)-modified chitosan (CS) nanocomposites by the combination of a simple blending and crosslinking method.     

Magnetic GO/Fe3O4 for rapid malachite green (MG) removal from aqueous solutions: a reversible adsorption

Magnetic GO/Fe₃O₄ was synthesized using co-precipitation of Fe²⁺ and Fe³⁺ composited with graphene oxide (GO) in alkaline conditions. SEM, XPS, FTIR, N₂ adsorption and VSM techniques were employed to characterize the surface peculiarities of GO/Fe₃O₄ and it was then used for removal of malachite green (MG). The key influencing factors on adsorption, such as mass ratio of GO, pH value and dosage of GO/Fe₃O₄, were investigated. The Freundlich isotherm was well fitted to the experimental data, suggesting GO/Fe₃O₄ has more than one type of reactive site. By comparing the adsorption of anionic dyes and cationic dyes onto GO/Fe₃O₄, it was concluded that GO/Fe₃O₄ could be extensively applied to take up cationic dyes mainly for electrostatic interaction. In addition, the spent GO/Fe₃O₄ was almost 100% recovered in a water bath at 80 °C. An ultraviolet-visible (UV-vis) spectrophotometer and an atom adsorption spectrophotometer (AAS) were used to determine leached GO and Fe ions discharged into the treated solutions. Low leaching showed that magnetic GO/Fe₃O₄ is a stable environmentally-friendly material.

MG adsorbed onto magnetic GO/Fe₃O₄ by electrostatic interaction and π–π band.     

Cellulose citrate: a convenient and reusable bio-adsorbent for effective removal of methylene blue dye from artificially contaminated water

In the present work, we proved the efficacy of cellulose citrate to remove methylene blue (MB) from artificially contaminated water. MB is a widely used dye, but because of its chemical aromatic structure, it is significantly stable with quite slow biodegradation, causing consequent serious health problems for people and significant environmental pollution. Cellulose citrate, the bio-adsorbent proposed and studied by us to remediate water polluted by MB, is produced by a green, cheap and fast procedure that makes use of two abundant natural products, cellulose and citric acid. The average of two citrate groups for each glucose unit of cellulose chains allows this material to have many carboxylic groups available for interaction with the cationic dye. The characterization was carried out through FT-IR, SEM, specific surface area, pore structure parameters and zeta potential. The negative value of the zeta potential at neutral pH is consistent with the affinity of this material for the adsorption of cationic compounds like MB. The activity of the adsorbent at different times, temperatures, pH and concentrations was investigated. The process followed monolayer adsorption typical of the Langmuir model, with a maximum adsorption capacity of 96.2 mg g⁻¹, while for the kinetic studies the process followed a pseudo-second order model. The highest levels of adsorption were reported using solutions of dye with concentrations under 100 mg L⁻¹. The adsorbent can be regenerated several times without a significant loss in the adsorption capacity, and it is not strongly affected by temperature and pH, giving rise to a simple and eco-sustainable procedure for water remediation. Therefore, we conclude that cellulose citrate can be considered as a promising bio-adsorbent for the removal of MB and other cationic pollutants from the environment.

In the present work, we proved the efficacy of cellulose citrate to remove methylene blue (MB) from artificially contaminated water.     

A multifunctional composite Fe3O4/MOF/l-cysteine for removal,magnetic solid phase extraction and fluorescence sensing of Cd(ii)

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater. The adsorption kinetics and isotherms were investigated, and the results indicated that the adsorption obeyed the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity was calculated to be 248.24 mg g⁻¹. Fe₃O₄/MOF/l-cysteine was further applied to determine trace amounts of Cd(ii) in real water samples using ICP-AES (inductively coupled plasma-atomic emission spectroscopy) based on magnetic solid-phase extraction (MSPE). The determination limit was 10.6 ng mL⁻¹. Additionally, Fe₃O₄/MOF/l-cysteine can also be used as a fluorescent sensor for “turn-off” detection of Cd(ii), and the detection limit was 0.94 ng mL⁻¹.

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater.     

Preparation of Mn2O3/MIL-100(Fe) composite and its mechanism for enhancing the photocatalytic removal of rhodamine B in water

In this study, Mn₂O₃/MIL-100(Fe) composite was successfully synthesized by the hydrothermal method and applied for photocatalytic removal of rhodamine B (RhB) in water. The physical and chemical properties of the synthesized materials were characterized by XRD, FTIR, SEM, UV-visible, and BET analyses. Experimental results showed a great enhancement in the photocatalytic ability of the Mn₂O₃/MIL-100(Fe) composite as compared to individual Mn₂O₃ or MIL-100(Fe) under visible light and persulfate activation. The affecting factors such as pH, photocatalyst dose, RhB concentration, and Na₂S₂O₈ concentration were investigated to find out the best conditions for efficient photocatalysis. By conducting a radical quenching test, all radicals of HO˙, SO₄˙⁻, ¹O₂, and O₂˙⁻ were found to be important in photocatalytic decomposition. The mechanism was proposed for the enhancement of photocatalytic RhB removal via band potential calculation, charge separation, surface redox reaction, and key reactive oxidation species. With its durability, reusability, and high efficiency, the Mn₂O₃/MIL-100(Fe) composite emerges as a potential photocatalyst working under visible light for application in wastewater treatment.

Effective charge transfer enhances the persulfate activation of Mn₂O₃/MIL-100(Fe) for photocatalytic removal of RhB under LED-generated visible light.     

Chitosan-derived three-dimensional porous carbon for fast removal of methylene blue from wastewater

Despite much progress in modifying chitosan as an absorbent for wastewater treatment, it is still difficult for current chitosan-based adsorbents to achieve the desired removal effects towards basic dyes. In this study, chitosan-derived three-dimensional porous carbon (CTC) consisting of large-diameter channels and mesopores was prepared to remove methylene blue (MB) from wastewater. The results indicate that CTC has excellent performance for MB removal, and the maximum adsorption capacity was 925.93 mg g⁻¹ at 318 K. The adsorption isotherm and kinetics models of MB on CTC could be described well by the Langmuir isotherms and the pseudo-second-order rate model. An experiment to study the CTC removal of MB from a flowing aqueous solution was performed using a homemade device. The water treatment rate of CTC reached 250 L g⁻¹ h⁻¹, with high MB removal efficiency (>93.4%). Furthermore, the desorption–adsorption experiments indicate that CTC is also a reusable adsorbent that can be applied to recover MB from wastewater. The obtained CTC is a promising alternative for the current expensive absorbents and provides a concept for designing the three-dimensional (3D) structures of raw materials to improve adsorption capability.

The chitosan-derived three-dimensional porous carbon (CTC) consisting of large-diameter channels and mesopores was prepared by two steps activation and used for the removal of methylene blue (MB) from wastewater.     

Activation of persulfates by ferrocene–MIL-101(Fe) heterogeneous catalyst for degradation of bisphenol A

In this study, a novel and high-performance catalyst was prepared and used as the heterogeneous catalyst to activate persulfate for bisphenol A (BPA) degradation. Ferrocene was anchored to NH₂-MIL-101(Fe) post-synthetically by the condensation of amine group from NH₂-MIL-101(Fe) with the carbonyl group of ferrocenecarboxaldehyde. The synthesized ferrocene tethered MIL-101(Fe)–ferrocene was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photo-electron spectra, cyclic voltammetry and electrochemical impedance spectroscopy. The ferrocene acts as a redox mediator, which makes the ferrocene functionalized NH₂-MIL-101(Fe) highly active in the degradation of BPA by accelerating the rate of the charge-transfer processes in aqueous solution. MIL-101(Fe)–Fc was proved to be the most effective catalyst, removing more than 99.9% of BPA. In addition, the catalyst can be reused without significant loss in activity.

In this study, a novel and high-performance catalyst ferrocene-MIL-101(Fe) was prepared and used as the heterogeneous catalyst to activate persulfate for bisphenol A degradation.     

High removal of thiophene from model gasoline by porous MIL-101(Cr)/SA hybrid membrane

Membrane separation technologies have great promising potential for applications in several industries. Metal–organic frameworks (MOFs), for their large surface areas, low framework densities, transition-metal ions in the skeleton and high pore volumes relative to other porous matrices, have great potential for the removal of sulfur from gasoline with high efficiency. In the present study, a novel porous membrane adsorbent MIL-101(Cr)/SA was prepared by immobilizing MIL-101(Cr) onto sodium alginate (SA) matrix, which can combine the size/shape selectivity of MIL-101(Cr) with the processability and mechanical stability of SA polymer. The physico-chemical properties of MIL-101(Cr)/SA were investigated by FT-IR, SEM, BET, XRD and EDX methods. To investigate the effects of some important factors on the adsorption behavior for thiophene, a batch of experiments were performed by changing the concentration of porogen polyethylene glycol in the MIL-101(Cr)/SA, solution temperature, initial thiophene concentration and contact time. Meanwhile, benzothiophene, thiophene and 3-methyl thiophene were used to test the selectivity of MIL-101(Cr)/SA. The MIL-101(Cr)/SA showed an excellent uptake capacity of 671 mg g⁻¹ under the optimal adsorption conditions. Selectivity testing indicated that the uptake capacity of MIL-101(Cr)/SA follows the order of benzothiophene > thiophene > 3-methyl thiophene. Kinetics experiments indicated the pseudo-second-order model displayed good correlation with adsorption kinetics data. The Crank model showed that the intraparticle solute diffusion is the rate-controlling adsorption step. Regeneration experiment result shows that the prepared MIL-101(Cr)/SA has excellent adsorption and desorption efficiencies.

Membrane separation technologies have great promising potential for applications in several industries.     

New titania-based photocatalysts for hydrogen production from aqueous-alcoholic solutions of methylene blue

A series of CuO_x–TiO₂ photocatalysts were prepared using fresh and thermally activated Evonik Aeroxide P25 titanium dioxide. The photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, XANES, diffuse reflectance spectroscopy, and N₂ adsorption technique. Photocatalytic activity of the samples was tested in hydrogen production from aqueous-alcoholic solutions of methylene blue under UV radiation (λ = 386 nm). It was found for the first time the synergistic effect of hydrogen production from two substrates—dye and ethanol. The maximum hydrogen production rate in the system water–ethanol–methylene blue was 1 μmol min⁻¹, which is 25 times higher than a value measured in a 10% solution of ethanol in water. The thermal activation of titania also leads to a change in the rate of hydrogen production. The highest catalytic activity was observed for a CuO_x–TiO₂ photocatalyst based on titania thermally-activated at 600 °C in air. A mechanism of the photocatalytic reaction is discussed.

Simultaneous presence of ethanol and methylene blue was shown to provide the most efficient hydrogen production and methylene blue removal.     

Polyoxometalate supported on a magnetic Fe3O4/MIL-88A rod-like nanocomposite as an adsorbent for the removal of ciprofloxacin,tetracycline and cationic organic dyes from aqueous solutions

In this work, a magnetic H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) rod-like nanocomposite as a stable and effective ternary adsorbent was fabricated by the hydrothermal method and utilized for the removal of ciprofloxacin (CIP), tetracycline (TC) and organic dyes from aqueous solution. Characterization of the magnetic nanocomposite was accomplished by FT-IR, XRD, Raman spectroscopy, SEM, EDX, TEM, VSM, BET specific surface area and zeta potential analyses. The influencing factors on the adsorption potency of the H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) rod-like nanocomposite including initial dye concentration, temperature and adsorbent dose were studied. The maximum adsorption capacities of H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) for TC and CIP were 370.37 mg g⁻¹ and 333.33 mg g⁻¹ at 25 °C, respectively. In addition, the H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) adsorbent had high regeneration and reusability capacity after four cycles. In addition, the adsorbent was recovered through magnetic decantation and reused for three consecutive cycles without a considerable reduction in its performance. The adsorption mechanism was mainly ascribed to electrostatic and π–π interactions. According to these results, H₃PW₁₂O₄₀/Fe₃O₄/MIL-88A (Fe) can act as a reusable effective adsorbent for the fast elimination of tetracycline (TC), ciprofloxacin (CIP) and cationic dyes from aqueous solutions.

A magnetic Fe₃O₄/MIL-88A Fe rod-like nanocomposite containing H₃PW₁₂O₄₀ was fabricated and applied as a new magnetically recoverable ternary adsorbent to remove antibiotics and dyes from aqueous solutions.     

The preparation of a novel iron/manganese binary oxide for the efficient removal of hexavalent chromium [Cr(vi)] from aqueous solutions

To remove hexavalent chromium Cr(vi) efficiently, a novel Fe–Mn binary oxide adsorbent was prepared via a “two-step method” combined with a co-precipitation method and hydrothermal method. The as-prepared Fe–Mn binary oxide absorbent was characterized via transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), thermogravimetric analysis (TGA), zeta potential, BET and X-ray photoelectron spectroscopy (XPS). The results indicated that the morphology of the adsorbent was rod-like with length of about 100 nm and width of about 50–60 nm, specific surface area was 63.297 m² g⁻¹, has the composition of α-Fe₂O₃, β-MnO₂ and MnFe₂O₄ and isoelectric point was observed at pH value of 4.81. The removal of Cr(vi) was chosen as a model reaction to evaluate the adsorption capacity of the Fe–Mn binary oxide adsorbent, indicating that the Fe–Mn binary oxide adsorbent showed high adsorption performance (removal rate = 99%) and excellent adsorption stability (removal rate > 90% after six rounds of adsorption). The adsorption behavior of the Fe–Mn binary oxide was better represented by the Freundlich model (adsorption isotherm) and the pseudo-second-order model (adsorption kinetic), suggesting that the adsorption process was multi-molecular layer chemical adsorption. The possible adsorption mechanism of the Fe–Mn binary oxide for the removal of Cr(vi) included the protonation process and the electrostatic attraction interactions.

A novel Fe–Mn binary oxide adsorbent prepared via “co-precipitation and hydrothermal” method, for the efficient and fast removal of Cr(vi).     

Mxene/alginate composites for lead and copper ion removal from aqueous solutions

Mxene has been widely used as a sorbent to remove heavy metal ions from sewage due to its unique two-dimensional layered structure and abundant oxygen-containing groups. However, Mxene has a relatively limited adsorption capacity for metal ions possibly due to the limited adsorption active sites. Herein, we reported novel Mxene/alginate composites for lead and copper ion removal from wastewater. The Mxene/alginate composites prepared in this study not only enhance the chelation ability of the lead and copper ions, but also accelerate the ion transport efficiency. The combined advantages of high adsorption capacity and short equilibrium time enable the Mxene/alginate composites to achieve the maximum adsorption capacity for Pb²⁺ and Cu²⁺ at 382.7 and 87.6 mg g⁻¹, respectively, and reach the adsorption equilibrium in 15 min. We believe that the composites developed in this study can open a new avenue for designing high adsorption capacity and high efficiency adsorbents.

Studies on Mxene/alginate composite adsorption have opened up a new avenue for designing adsorbents possessing high adsorption capacity and high efficiency.     

Preparation of new adsorbent-supported Fe/Ni particles for the removal of crystal violet and methylene blue by a heterogeneous Fenton-like reaction

Prepared material-supported Fe/Ni particles (PM-Fe/Ni) were produced and applied as an adsorbent, reductant and Fenton-like catalyst for removing methylene blue (MB) and crystal violet (CV) from aqueous solutions. Fe/Ni particles were prepared by reducing ferric chloride with sodium borohydride and supported on the produced porous material. Various techniques including X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy analysis (SEM) were employed to characterize the crystal phase, surface area, surface morphology and functional groups. Removal experiments were conducted to study the effects of different factors such as PM-Fe/Ni dosage, initial pH, H₂O₂ concentration, initial concentrations and temperature on MB and CV removal. The removal efficiency of CV and MB by PM-Fe/Ni/H₂O₂ were 91.86% and 61.41% under the conditions of dye concentration of 1000 mg L⁻¹, H₂O₂ concentration of 50 mM, PM-Fe/Ni dosage of 0.20 g and temperature of 293 K. The analysis of the degradation kinetics showed that the degradation of MB and CV followed well pseudo-first-order kinetics. A possible mechanism of removal of MB and CV was proposed, including the adsorption, reduction and dominating Fenton oxidation. The regeneration experiments of PM-Fe/Ni demonstrated that PM-Fe/Ni with H₂O₂ still showed a high removal efficiency after six reaction cycles.

Possible reaction mechanism for CV and MB removal by the PM-Fe/Ni with H₂O₂ system.     

Amine-functionalized MOF-derived carbon materials for efficient removal of Congo red dye from aqueous solutions: simulation and adsorption studies

In this study, a novel polyethyleneimine (PEI) modified MOF-derived carbon adsorbent (PEI@MDC) was proposed, which exhibited significant adsorption capacity for Congo Red (CR) in aqueous solutions. FT-IR and XPS results showed that PEI was successfully grafted onto MDC, increasing the content of amine groups on the surface of MDC. The adsorption process conformed to the Langmuir isotherm adsorption model and pseudo-second-order kinetic equation, indicating that the adsorption of CR on PEI@MDC was covered by a single layer, and the adsorption process was controlled by chemical processes. According to the Langmuir model, the maximum adsorption capacity at 30 °C was 1723.86 mg g⁻¹. Hydrogen bonding and electrostatic interactions between CR and PEI@MDC surface functional groups were the main mechanisms controlling the adsorption process. After five adsorption–desorption cycles, PEI@MDC still showed a high adsorption capacity for CR, indicating that the adsorbent had an excellent regeneration ability.

Schematic diagram on the preparation of polyethyleneimine-modified MOF-derived carbon (PEI@MDC) samples and the Congo red dye adsorption process.