Development of Novel PET-PAN Electrospun Nanocomposite Membrane Embedded with Layered Double Hydroxides Hybrid for Efficient Wastewater Treatment

Layered double hydroxides (LDHs) with their unique structural chemistry create opportunities to be modified with polymers, making different nanocomposites. In the current research, a novel PET-PAN embedded with Mg-AI-LDH-PVA nanocomposite membrane was fabricated through electrospinning. SEM, EDX, FTIR, XRD, and AFM were carried out to investigate the structure and morphology of the nanocomposite membrane. The characterization of the optimized nanocomposite membrane showed a beadless, smooth structure with a nanofiber diameter of 695 nm. The water contact angle and tensile strength were 16° and 1.4 Mpa, respectively, showing an increase in the hydrophilicity and stability of the nanocomposite membrane by the addition of Mg-Al-LDH-PVA. To evaluate the adsorption performance of the nanocomposite membrane, operating parameters were achieved for Cr(VI) and methyl orange at pH 2.0 and pH 4.0, respectively, including contact time, adsorbate dose, and pollutant concentration. The adsorption data of the nanocomposite membrane showed the removal of 68% and 80% for Cr(VI) and methyl orange, respectively. The process of adsorption followed a Langmuir isotherm model that fit well and pseudo-2nd order kinetics with R2 values of 0.97 and 0.99, respectively. The recycling results showed the membrane's stability for up to five cycles. The developed membrane can be used for efficient removal of pollutants from wastewater.

Highly efficient Cr (VI) removal from electroplating wastewater by regenerable copper sulfides: Mechanism and magical induction effect for Cr resource recovery

The current sorbents used to remove Cr (VI) from electroplating wastewater are faced with some challenges including the difficulty in separating, regenerating, and safely disposing of adsorbed Cr species. To address these challenges, CuSx/TiO2 was developed to recover Cr (VI) from electroplating wastewater. CuSx/TiO2 had superior performance in removing Cr (VI), with the rate and capacity of approximately 9.36 mg g-1 h-1 and 68.8 mg g-1 at initial pH 4.0, respectively. Additionally, Cu2+ released from CuSx/TiO2 during Cr (VI) removal would come back to its external surface as the Cu(OH)2 precipitate at initial pH 4.0, which helped to prevent the generation of secondary pollution. The Cu(OH)2 precipitate would be decomposed into CuOx after calcination, which would then be transformed back into CuSx by re-sulfuration for regeneration. Hence, CuSx showed a magical induction effect on Cr (VI) recovery, and Cr (VI) from electroplating wastewater might be gradually enriched as Cr2O3 in the sandwich between CuSx and TiO2 through multiple regenerations and removals, which could be considered as a chromium ore resource for industrial applications when the amount of enriched Cr2O3 reached more than 30 wt%. Overall, CuSx/TiO2 showed great potential as a promising sorbent for Cr (VI) removal from electroplating wastewater.

Tubular Sediment-Water Electrolytic Fuel Cell for Dual-Phase Hexavalent Chromium Reduction

A novel tubular sediment-water electrolytic fuel cell (SWEFC) was fabricated for the reduction of Cr(VI) in a dual-phase system. The approach simulates a standing water body with Cr(VI)-contaminated overlying water (electrolyte) and bottom sediment phase with electrodes placed in both the phases, supplemented with urea as a potential electron donor. Cr(VI) reduction efficiency of 93.2 ± 1.3% from electrolyte (in 1.5 h) and 81.2 ± 1.3% from the sediment phase (in 8 h) with an initial Cr(VI) concentration of 1,000 mg/L was observed in a single-cell configuration. The effect of initial Cr(VI) concentration, variation in sediment salinity and pH, and different electron donors on the SWEFC performance were systematically investigated. SWEFC showed enhanced performance with 2.4-fold higher current (193.9 mA) at 400 mg/L Cr(VI) concentration when cow dung was used as a low-cost alternative to urea as an electron donor. Furthermore, reactor scalability studies were carried out with nine-anode and nine-cathode configuration (3 L electrolyte and 2 kg sediment), and reduction efficiencies of 98.9 ± 0.9% (in 1 h) and 97.6 ± 2.2% (in 8 h) were observed from the electrolyte and sediment phases, respectively. The proposed sediment-water electrolytic fuel cell can be an advanced and environmentally benign strategy for Cr(VI) remediation from contaminated sediment-water interfaces along with electricity generation.

Fast and Efficient Removal of Uranium onto a Magnetic Hydroxyapatite Composite: Mechanism and Process Evaluation

The exploration and rational design of easily separable and highly efficient sorbents with satisfactory capability of extracting radioactive uranium (U)-containing compound(s) are of paramount significance. In this study, a novel magnetic hydroxyapatite (HAP) composite (HAP@ CoFe2O4), which was coupled with cobalt ferrite (CoFe2O4), was rationally designed for uranium(VI) removal through a facile hydrothermal process. The U(VI) ions were rapidly removed using HAP@ CoFe2O4 within a short time (i.e., 10 min), and a maximum U(VI) removal efficiency of 93.7% was achieved. The maximum adsorption capacity (Qmax) of the HAP@CoFe2O4 was 338 mg/g, which demonstrated the potential of as-prepared HAP@CoFe2O4 in the purification of U(VI) ions from nuclear effluents. Autunite [Ca(UO2)2(PO4)2(H2O)6] was the main crystalline phase to retain uranium, wherein U(VI) was effectively extracted and immobilized in terms of a relatively stable mineral. Furthermore, the reacted HAP@CoFe2O4 can be magnetically recycled. The results of this study reveal that the suggested process using HAP@CoFe2O4 is a promising approach for the removal and immobilization of U(VI) released from nuclear effluents.

Adsorption characteristics of Cr(VI) on microalgae immobilized by different carriers

To solve the problem of harvesting microalgae during heavy metal adsorption, six different carriers were selected in this study to compare the adsorption behavior of microalgae after immobilization. The results of the scanning electron microscope (SEM) and adsorption showed chitosan as a carrier showed the best immobilization effect and adsorption advantages after immobilizing microalgae. The optimal immobilized carrier-chitosan was obtained under the following conditions of chitosan: acetic acid (2:40), microalgae concentration (10⁸ cells mL^-1), and immobilization time (18 h). The optimal adsorption conditions were as follows: temperature: 30 °C, pH: 7.0, adsorption dose: 1.5 g L^-1, initial ion concentration: 40 mg L^-1. The adsorption capacity of metal ions can reach 37.1 mg g^-1 Cr(VI), 25.98 mg g^-1 Cu(II), 25.06 mg g^-1 Pb(II), and 24.62 mg g^-1 Cd(II), respectively. The desorption efficiency in 0.5 mol L^-1 NaOH desorption solution reached 90.01%. After five adsorption-desorption cycles, excluding chitosan (∼70%), the adsorption efficiency of other adsorbents decreased with an increase in the recycling times. Chitosan was a suitable carrier for the immobilization of Synechocystis sp. PCC6803. Fourier transform infrared spectroscopy and Raman spectra analysis showed that groups belonging to the microalgae were detected after the microalgae in different carriers, indicating that the microalgae were immobilized with the carriers. At the same time, the energy spectrum changed before and after adsorption indicated the specific functional groups of microalgae played an important role in the adsorption process. The kinetic and isothermal model data showed that the adsorption process was mainly chemical adsorption and homogeneous monolayer adsorption. Moreover, X-ray diffraction showed the interlayer peak strength decreased significantly, indicating that the interlayer structure was stretched after Cr(VI) ion exchange. X-ray photoelectron spectroscopy analysis showed that the Cr adsorption process involves the reduction of Cr(VI) to Cr(III).

Enhanced Removal of Sulfonated Lignite from Oil Wastewater with Multidimensional MgAl-LDH Nanoparticles

In this study, hierarchical MgAl-LDH (layered double hydroxide) nanoparticles with a flower-like morphology were prepared under a hydrothermal condition by employing worm-like micelles formed by cetyltrimethylammonium bromide (CTAB) and salicylic acid (SA) as templates. The morphology and structure of the materials were characterized by Brunauer-Emmett-Teller (BET), SEM, and XRD analyses. The performance for the adsorption of sulfonated lignite (SL) was also investigated in detail. FTIR was used to detect the presence of active functional groups and determine whether they play important roles in adsorption. The results showed that the hierarchical MgAl-LDH nanoparticles with a specific surface area of 126.31 m2/g possessed a flower-like morphology and meso-macroporous structures. The adsorption capacity was high-its value was 1014.20 mg/g at a temperature of 298 K and an initial pH = 7, which was higher than traditional MgAl-LDH (86 mg/g). The adsorption process of sulfonated lignite followed the pseudo-second-order kinetics model and conformed to Freundlich isotherm model with a spontaneous exothermic nature. In addition, the hierarchical MgAl-LDH could be regenerated and used, and the adsorption was high after three adsorption cycles. The main adsorption mechanisms were electrostatic attraction and ion exchange between the hierarchical MgAl-LDH and sulfonated lignite.

A Revised Pseudo-Second-Order Kinetic Model for Adsorption, Sensitive to Changes in Adsorbate and Adsorbent Concentrations

The development of new adsorbent materials for the removal of toxic contaminants from drinking water is crucial toward achieving the United Nations Sustainable Development Goal 6 (clean water and sanitation). The characterization of these materials includes fitting models of adsorption kinetics to experimental data, most commonly the pseudo-second-order (PSO) model. The PSO model, however, is not sensitive to parameters such as adsorbate and adsorbent concentrations (C₀ and C_s) and consequently is not able to predict changes in performance as a function of operating conditions. Furthermore, the experimental conditionality of the PSO rate constant, k₂, can lead to erroneous conclusions when comparing literature results. In this study, we analyze 103 kinetic experiments from 47 literature sources to develop a relatively simple modification of the PSO rate equation, yielding dqtdt=k'Ct(1-qtqe)2. Unlike the original PSO model, this revised rate equation (rPSO) provides the first-order and zero-order dependencies upon C₀ and C_s that we observe empirically. Our new model reduces the residual sum of squares by 66% when using a single rate constant to model multiple adsorption experiments with varying initial conditions. Furthermore, we demonstrate how the rPSO rate constant k' is more appropriate for comparing literature studies, highlighting faster kinetics in the adsorption of arsenic onto alumina versus iron oxides. This revised rate equation should find applications in engineering studies, especially since the rPSO rate constant k' does not show a counter-intuitive inverse relationship with increasing reaction rates when C₀ is increased, unlike the PSO rate constant k₂.

Unexpected effect of magnetic nanoparticles on the performance of aqueous removal of toxic Cr(VI) using modified biopolymer chitosan

Modified biopolymer chitosan namely 2-hydroxy-1-naphthaldehyde chitosan (CTS-Nap) has been synthesized for the removal of toxic chromium from aqueous solutions. In an attempt to enhance the adsorption capacity of toxic chromium on the prepared modified biopolymer, magnetic Fe₃O₄ nanoparticles have been loaded on the modified adsorbent to form the magnetite adsorbent (Fe₃O₄@CTS-Nap). The adsorption mechanism of both adsorbents is explored by batch experiments, FT-IR, SEM, TEM, XRD, VSM, and EDS. The optimum adsorption is achieved at pH 1.5 for CTS-Nap and 1.0 for Fe₃O₄@CTS-Nap. Pseudo second order illustrated the best description for the adsorption process with correlation coefficient R² = 0.999 and the film diffusion or chemisorption is the rate-limiting step. The equilibrium data is analyzed using five isotherm models, the experimental data agreed well with the Freundlich model with a maximum adsorption capacity of 78.12 mg g-1 and 57.14 mg g-1 for CTS-Nap and Fe₃O₄@CTS-Nap, respectively. However, this unexpected result revealed that the presence of magnetic nanoparticles does not always enhance the adsorption process and many other factors could control the adsorption process. Generally, these outcomes revealed that the unmagnetite modified adsorbent CTS-Nap have practical greater influence on wastewater treatment management rather than the magnetic modified chitosan Fe₃O₄@CTS-Nap.

Improved accuracy in multicomponent surface complexation models using surface-sensitive analytical techniques: Adsorption of arsenic onto a TiO2/Fe2O3 multifunctional sorbent

Novel composite materials are increasingly developed for water treatment applications with the aim of achieving multifunctional behaviour, e.g. combining adsorption with light-driven remediation. The application of surface complexation models (SCM) is important to understand how adsorption changes as a function of pH, ionic strength and the presence of competitor ions. Component additive (CA) models describe composite sorbents using a combination of single-phase reference materials. However, predictive adsorption modelling using the CA-SCM approach remains unreliable, due to challenges in the quantitative determination of surface composition. In this study, we test the hypothesis that characterisation of the outermost surface using low energy ion scattering (LEIS) improves CA-SCM accuracy. We consider the TiO₂/Fe₂O₃ photocatalyst-sorbents that are increasingly investigated for arsenic remediation. Due to an iron oxide surface coating that was not captured by bulk analysis, LEIS significantly improves the accuracy of our component additive predictions for monolayer surface processes: adsorption of arsenic(V) and surface acidity. We also demonstrate non-component additivity in multilayer arsenic(III) adsorption, due to changes in surface morphology/porosity. Our results demonstrate how surface-sensitive analytical techniques will improve adsorption models for the next generation of composite sorbents.

Fast and efficient removal of Cr(VI) to ppb level together with Cr(III) sequestration in water using layered double hydroxide interclated with diethyldithiocarbamate

It is still a great challenge to find an eco-friendly, easy-to-synthesize, and cheap adsorbent to rapidly remove Cr(VI) to ppb level in the Cr(VI)-polluted water. Herein, a new layered double hydroxide nanocage intercalated with diethyldithiocarbamate (DDTC-LDH) was fabricated via a facile calcination-rehydration method. The DDTC-LDH rapidly decreased Cr(VI) concentration from 5 to <0.05 mg/L within 35 min, and only a few seconds were required to completely remove it at an initial concentration of 0.5-1 mg/L, primarily attributed to the effective adsorption-reduction of Cr(VI) to Cr(III) by sulfur atoms in CS and CS groups. Attractively, the generated Cr(III) was also quickly removed to below 0.1 mg/L via an opportune Lewis hard-hard interaction with C-SO_x groups produced through CS oxidation. Additionally, Cr(VI) could be removed by DDTC-LDH at a wide pH application range (3.17-10.78) and with weak effects by coexisting anions (Cl^-, NO₃^-, CO₃^2-, SO₄^2-, and PO₄^3-). We systematically analyzed and proposed the mechanisms for Cr(VI) removal by the DDTC-LDH, orderly containing electrostatic attraction, Cr(VI) complexation by sulfur atoms in CS and CS groups, reduction of the Cr(VI) to Cr(III) by the CS and CS groups, and Cr(III) complexation by sulfur atoms in C-SOx groups. Our results provide new insights into the Cr(VI) removal using organosulfur compounds, that is to say, the organosulfur group Lewis hardness increased (from C-S to C-SOx) as the Cr species Lewis hardness increased (from Cr(VI) to Cr(III)), so as to opportunely ensure fast and efficient capture of both Cr(VI) and Cr(III) via Lewis acid-base interactions.

Fabrication of core@shell structural Fe-Fe2O3@PHCP nanochains with high saturation magnetization and abundant amino groups for hexavalent chromium adsorption and reduction

The rational design of novel adsorption materials is imperative to remove toxic metal species from the polluted water. Herein, a core@shell structural Fe-Fe₂O₃@poly (hexachlorocyclotriphosphazene-co-polyethylenimine) (Fe-Fe₂O₃@PHCP) magnetic nanochain with high saturation magnetization was fabricated and used for effective adsorption and reduction of hexavalent chromium. The morphology and microstructure of Fe-Fe₂O₃@PHCP were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The effects of concentration, pH, contact time, temperature and coexisting ions on Cr (VI) removal were studied. Four kinetic models (pseudo-first-order, pseudo-second-order, Bangham and intraparticle diffusion models) and two isotherm models (Freundlich and Langmuir) were used to fit experimental data. Results show the adsorption capacity of Fe-Fe₂O₃@PHCP for Cr (VI) is up to 229.0 mg g^-1. The excellent performance was ascribed to the favorable reduction of Cr (VI) to Cr (III), followed by the chelation of Cr (III) with imino groups. Meanwhile, the residual Cr (VI) were adsorbed on protonated amino and imino groups. The adsorption process is exothermic and spontaneous and nicely follows pseudo-second-order kinetics, intraparticle diffusion model and Langmuir isotherm model. These results indicated that easily separable Fe-Fe₂O₃@PHCP magnetic nanochains could be a promising adsorbent to remediate chromate wastewater.

Adsorption mechanism of hexavalent chromium onto layered double hydroxides-based adsorbents: A systematic in-depth review

An attempt has been made in this review to provide some insights into the possible adsorption mechanisms of hexavalent chromium onto layered double hydroxides-based adsorbents by critically examining the past and present literature. Layered double hydroxides (LDH) nanomaterials are typical dual-electronic adsorbents because they exhibit positively charged external surfaces and abundant interlayer anions. A high positive zeta potential value indicates that LDH has a high affinity to Cr(VI) anions in solution through electrostatic attraction. The host interlayer anions (i.e., Cl^-, NO₃^-, SO₄^2-, and CO₃^2-) provide a high anion exchange capacity (53-520 meq/100 g) which is expected to have an excellent exchangeable capacity to Cr(VI) oxyanions in water. Regarding the adsorption-coupled reduction mechanism, when Cr(VI) anions make contact with the electron-donor groups in the LDH, they are partly reduced to Cr(III) cations. The reduced Cr(III) cations are then adsorbed by LDH via numerous interactions, such as isomorphic substitution and complexation. Nonetheless, the adsorption-coupled reduction mechanism is greatly dependent on: (1) the nature of divalent and trivalent salts utilized in LDH preparation, and the types of interlayer anions (i.e., guest intercalated organic anions), and (3) the adsorption experiment conditions. The low Brunauer-Emmett-Teller specific surface area of LDH (1.80-179 m²/g) suggests that pore filling played an insignificant role in Cr(VI) adsorption. The Langmuir maximum adsorption capacity of LDH (Q^o_max) toward Cr(VI) was significantly affected by the natures of used inorganic salts and synthetic methods of LDH. The Q^o_max values range from 16.3 mg/g to 726 mg/g. Almost all adsorption processes of Cr(VI) by LDH-based adsorbent occur spontaneously (ΔG° <0) and endothermically (ΔH° >0) and increase the randomness (ΔS° >0) in the system. Thus, LDH has much potential as a promising material that can effectively remove anion pollutants, especially Cr(VI) anions in industrial wastewater.

Synthesis of C@Ni-Al LDH HSS for efficient U-entrapment from seawater

In this paper, a double hollow spherical shell composite modified with layered double hydroxide (C@Ni-Al LDH HSS) was fabricated for uranium(VI) (U(VI)) adsorption. Various batch experiments were carried out to investigate the influence of pH, concentration, time and coexistence ion on extraction. The results showed that the adsorption processes of U(VI) onto C@Ni-Al LDH HSS were spontaneous and endothermic and closely followed pseudo-second-order and Langmuir isotherm models. The equilibrium time and maximum adsorption capacity of C@Ni-Al LDH HSS was 360 min and 545.9 mg g^-1. FT-IR and XPS analyses proved that the adsorption behavior was primarily attributed to the strong interaction between oxygen-containing functional groups and U(VI). Moreover, the extraction of trace U(VI) (μg L^-1) in artificial and natural seawater was also studied. The results showed that C@Ni-Al LDH HSS provided a promising application for the efficient extraction of U(VI) from seawater.

Removal of chromium (VI) from aqueous solutions using Diospyros discolor seed activated with nitric acid: isotherm and kinetic studies

Diospyros discolor seed activated with nitric acid was investigated for removing Cr(VI) from aqueous solutions. Batch experiments were used to determine the adsorption efficiency, effect of pH, adsorption isotherm, and kinetics. Langmuir and Freundlich adsorption models were used to analyze data of Cr(VI) uptake. Fourier transform infrared spectroscopy was used to investigate the functional groups and surface morphology was checked using a scanning electron microscope, coupled with energy dispersive spectroscopy. The optimum pH in Cr(VI) uptake was 3.5 and the maximum adsorption efficiency reached 100% at 60 min.

Retracted Article: A layered double hydroxide assembled on a g-C3N4-modified hollow carbon sphere as an adsorbent for the removal of uranium(vi)

A layered double hydroxide assembled on a g-C₃N₄-modified hollow carbon sphere with unique flower-like morphology was prepared to capture U(vi).

Synthesis and characterization of citrate intercalated layered double hydroxide as a green adsorbent for Ni2+ and Pb2+ removal

Recently, a considerable attention has been paid on the preparation of layered double hydroxide (LDH) as a green adsorbent. This research presents a study on nickel and lead removal by Ca/Fe layered double hydroxides intercalate with citrate anions (Ca-Fe/LDH-Cit) which was successfully prepared through the co-precipitation and hydrothermal method. The as-synthesized Ca-Fe/LDH-Cit was characterized by various techniques including FT-IR, XRD, TGA, FE-SEM, and TEM techniques. The maximum uptake capacities of Ca-Fe/LDH-Cit were 2.26 mg/g for Ni(II) and 61.73 mg/g for Pb(II) inferred from the Langmuir model at the contact time of 30 min and pH of 7. Based on the results, the adsorption and kinetic isotherms were in good agreement with the Langmuir model and the pseudo-second-order equation, respectively. The results suggested that the composite adsorbent has the good ability to remove the Ni²⁺ and Pb²⁺ ions from aqueous solutions. The results reveal that the composite adsorbent can be considered as a high-capacity absorbent for Ni(II) and Pb(II) removal and also as a potential candidate for practical applications.

One-pot synthesis of layered double hydroxide hollow nanospheres with ultrafast removal efficiency for heavy metal ions and organic contaminants

Herein, Mg/Fe layered double hydroxide (MF-LDH) hollow nanospheres were successfully prepared by a one-step thermal method. After the thermal treatment of MF-LDH nanospheres at 400 °C, the MF-LDH was converted into the corresponding oxide, Mg/Fe layered double oxide (MF-LDO), which maintained the hollow nanosphere structure. The MF-LDO hollow nanospheres exhibited excellent adsorption efficiency for both As(V) and Cr(VI), showing 99% removal within 5 min and providing maximum removal capacities of 178.6 mg g^-1 [As(VI)] and 148.7 mg g^-1 [Cr(VI)]. Moreover, it met the maximum contaminant level requirements recommended by World Health Organization (WHO); 10 ppm for As(V) and 50 ppm for Cr(VI) in 10 and 20 min, respectively. Furthermore, Au nanoparticles were successfully introduced in the MF-LDO hollow nanospheres, and the products showed a conversion rate of 100% for the reduction of 4-nitrophenol into 4-aminophenol within 5 min. It is believed that these excellent and versatile abilities integrated with a facile synthetic strategy will facilitate the practical application of this material in cost-effective wastewater purification.

Aminated EVOH nanofiber membranes for Cr(vi) adsorption from aqueous solution

Ethylene vinyl alcohol (EVOH) nanofiber membranes were prepared by melt-blending extrusion with cellulose acetate butyrate ester (CAB) as the matrix and a high-speed flow deposition process. Then, aminated-EVOH (l-Lys/EVOH, Cy/l-Lys/EVOH and DETA/EVOH) nanofiber membranes were prepared for hexavalent chromium [Cr(vi)] removal by facile chemical modification on the surface of EVOH nanofiber membranes. Scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were carried out to test the morphology and structure of aminated-EVOH nanofiber membranes. Adsorption experiments suggested that amination was beneficial to adsorption, and the optimal pH for prepared membranes to Cr removal was 2.0. Adsorption kinetics analysis revealed that the adsorption process was successfully fitted with a Pseudo-second-order model. The Freundlich isothermal model well described the adsorption isotherm data. A thermodynamic study suggested that the adsorption process was endothermic and spontaneous. Aminated-EVOH nanofiber membranes exhibited excellent reusability for Cr removal. The Cr adsorption efficiency of DETA/EVOH nanofiber membranes retained up to 98.73% of the initial adsorption after 6 successive adsorption-desorption cycles.

Structure-enhanced removal of Cr(vi) in aqueous solutions using MoS2 ultrathin nanosheets

Molybdenum disulfide (MoS₂) ultrathin nanosheets with enlarged interlayer spacing and defects enables the structure-enhanced removal of Cr(vi), in which the synergistic effects of adsorption and reduction not only captured Cr(vi) from aqueous solutions, but also alleviated the toxicity of chromium to some degree.

[MoS4]2- Cluster Bridges in Co-Fe Layered Double Hydroxides for Mercury Uptake from S-Hg Mixed Flue Gas

[MoS₄]^2- clusters were bridged between CoFe layered double hydroxide (LDH) layers using the ion-exchange method. [MoS₄]^2-/CoFe-LDH showed excellent Hg⁰ removal performance under low and high concentrations of SO₂, highlighting the potential for such material in S-Hg mixed flue gas purification. The maximum mercury capacity was as high as 16.39 mg/g. The structure and physical-chemical properties of [MoS₄]^2-/CoFe-LDH composites were characterized with FT-IR, XRD, TEM&SEM, XPS, and H₂-TPR. [MoS₄]^2- clusters intercalated into the CoFe-LDH layered sheets; then, we enlarged the layer-to-layer spacing (from 0.622 to 0.880 nm) and enlarged the surface area (from 41.4 m²/g to 112.1 m²/g) of the composite. During the adsorption process, the interlayer [MoS₄]^2- cluster was the primary active site for mercury uptake. The adsorbed mercury existed as HgS on the material surface. The absence of active oxygen results in a composite with high sulfur resistance. Due to its high efficiency and SO₂ resistance, [MoS₄]^2-/CoFe-LDH is a promising adsorbent for mercury uptake from S-Hg mixed flue gas.

Magnetite and cobalt ferrite nanoparticles used as seeds for acid mine drainage treatment

In this study, magnetite and cobalt ferrite nanoparticles were used as seeds for acid mine drainage (AMD) treatment at pH of 7.05±0.35. Duplicate samples of AMD, one without heating and another with heating at 60°C was treated under continuous stirring for 1h. The filtrate analysis results from ICP-OES have shown complete removal of Al, Mg, and Mn, while for Fe, Ni and Zn over 90% removals were recorded. Particularly, settling time has significant effect on the removal of Mg, Ca and Na. The results from SQUID have shown superparamagnetic properties of the synthesised magnetic nanoparticles and ferrite sludge. The recovered nanoparticles from AMD are economically important and reduce the cost of waste disposal.

Highly efficient removal of Cu(ii) from aqueous solution using a novel magnetic EDTA functionalized CoFe2O4

CoFe₂O₄ exhibits excellent chemical stability and saturation magnetization; consequently, it has been prepared for and applied to contaminant adsorption.

Preparation of PEI/CS aerogel beads with a high density of reactive sites for efficient Cr(vi) sorption: batch and column studies

PEI/CS aerogel beads with a high density of reactive amino groups, with the aim of efficient Cr(vi) removal from aqueous solutions under column conditions, were easily prepared via combinational yet controllable sol–gel and freeze drying processes.

Composites of Quasi-Colloidal Layered Double Hydroxide Nanoparticles and Agarose Hydrogels for Chromate Removal

Composite hydrogels were prepared that consisted of quasi-colloidal layered double hydroxide (LDH) nanoparticles and agarose via the electrophoretic method, starting from three different agarose concentrations of 0.5, 1, and 2 wt/v%. The composite hydrogel was identified to have a uniform distribution of LDH nanoparticles in agarose matrix. Microscopic studies revealed that the composite hydrogel had a homogeneous quasi-colloidal state of LDHs, while the simple mixture of LDH powder and agarose hydrogels did not. It was determined that agarose concentration of the starting hydrogel did not significantly influence the amount of LDH that developed in the composite. The chromate scavenging efficiency of the composite hydrogel and corresponding agarose or mixture hydrogel was evaluated with respect to time, and chromate concentration. In general, the composite hydrogels exhibited much higher chromate removal efficacy compared with agarose or mixture hydrogels. Through estimating chromate adsorption by LDH moiety in the composite or mixture hydrogel, it was suggested that the agarose component facilitated the stability and dispersibility of the quasi-colloidal state of LDH nanoparticles in the composite resulting in high adsorption efficacy. From Freundlich isotherm adsorption fitting, composites were determined to possess beneficial cooperative adsorption behavior with a high adsorption coefficient.

Removal of chromium(vi) from wastewater using weakly and strongly basic magnetic adsorbents: adsorption/desorption property and mechanism comparative studies

Two novel strongly basic magnetic adsorbents were prepared, and the adsorption/desorption property and mechanism of weakly and strongly basic magnetic adsorbents were compared.

Adsorption–reduction of chromium(vi) from aqueous solution by phenol–formaldehyde resin microspheres

A novel adsorbent of phenol–formaldehyde resin (PF) microspheres was prepared at a low temperature, and had an excellent performance for the adsorption–reduction of Cr(vi).

Monolithic magnetic carbonaceous beads for efficient Cr(vi) removal from water

Alginate-derived magnetic monolithic carbonaceous beads were synthesized for the first time, aiming for efficient Cr(vi) removal, easy recovery and reusability.

Cost effective nanofiber composite membranes for Cr(vi) adsorption with high durability

PANI/EVOH composite nanofiber membranes were prepared though melt-blending extrusion, high-speed flow deposition and in situ chemical oxidative polymerization for the removal of hexavalent chromium [Cr(vi)].

Adsorption and intercalation of organic pollutants and heavy metal ions into MgAl-LDHs nanosheets with high capacity

The adsorption of MgAl-LDH nanosheets involves precipitation, surface complexation, isomorphic substitution and ion exchange in the interlayer space.​ Based on the efficient removal of heavy metal ions by the nanosheets a filter-type water purification device was designed.

Biosorption of Pb(ii) and Fe(iii) from aqueous co-solutions using chemically pretreated oil palm fronds

The removal of Pb(ii) and Fe(iii) from aqueous solutions using specially pretreated oil palm fronds (OPF) as biosorbents was investigated.