Experimental and DFT calculation study on the efficient removal of high fluoride wastewater from metallurgical wastewater by kaolinite

Fluoride pollution and water scarcity are urgent issues. Reducing fluoride concentration in water is crucial. Kaolinite has been used to study adsorption and fluoride removal in water and to characterize material properties. The experimental results showed that the adsorption capacity of kaolinite decreased with increasing pH. The highest adsorption of fluoride occurred at pH 2, with a capacity of 11.1 mg/g. The fluoride removal efficiency remained high after four regeneration cycles. The fitting results with the Freundlich isotherm model and the external diffusion model showed that the non-homogeneous adsorption of kaolinite fit the adsorption behavior better. Finally, the adsorption mechanism was analyzed by FT-IR and XPS. The binding energies of various adsorption sites and the chemical adsorption properties of atomic states were discussed in relation to DFT calculations. The results showed that Al and H sites were the main binding sites, and the bonding stability for different forms of fluoride varies, with the size of Al-F (-7.498 eV) > H-F (-6.04 eV) > H-HF (-3.439 eV) > Al-HF (-3.283 eV). Furthermore, the density of states and Mulliken charge distribution revealed that the 2p orbital of F was found to be active in the adsorption process and was the main orbital for charge transfer.

Adsorption of BiOBr microspheres to rhodamine B and its influence on photocatalytic reaction

Adsorption and its influence are often neglected during photocatalytic degradation of organic pollutants. To call attention to these issues, a novel bismuth oxybromide (BiOBr) microsphere with hierarchical flower-like structure was fabricated through a facile hydrothermal process using polyvinyl pyrrolidone (PVP) as additive in this work, and then the adsorption of the BiOBr microspheres to RhB and its influence on the photocatalytic degradation of RhB were investigated in detail. Experimental results show that the BiOBr microspheres have a very strong adsorption capacity to RhB. The adsorption behavior follows the Langmuir model and the quasi second order kinetic equation. Tests of the photocatalytic degradation of RhB under visible irradiation verify that the adsorption of the BiOBr microspheres to RhB greatly boosts the degradation of RhB due to the "enriching effect", and a complete degradation of 20 mg L^-1 RhB only requires 37 min.

High efficient arsenic removal by In-layer sulphur of layered double hydroxide

High-risk arsenic contamination found in aqueous system is reported across the world and causing severe environmental issues. In this study, the Mg-Al Layered Double Hydroxide (LDH) modified by sulphur species (LDH-S) was found exhibiting high effectivity and selectivity in As(V) removal owing to the strong interaction between embedded HS^- and AsO₄^3-. The LDH-S with Mg to Al ratio 2-1 give the best performance with As(V) adsorption capacity 40.8 mg/g, which is 715% higher than that of pristine LDH (2-1). The adsorbent exhibits a high tolerance to concentrated competitive anions. In the continuous flow test, the adsorbent can reduce the As(V) concentration from 20 ppm to below-ppb-level indicating the potential in industry application. The adsorption mechanism is experimentally investigated and examined by Density Function Theory (DFT) calculation. The result illustrates that, differ from the traditional ion exchange mechanism of LDH, the enhanced removal capacity and selectivity of LDH-S for As(V) is attributed to the strong affinity between H atom from HS- ion (in the interlayer region of LDH) and the O atom from AsO₄^3-.

Kinetic, thermodynamic and isotherm investigations of Cu2+ and Zn2+ adsorption on LiAl hydrotalcite-like compound

LiAl hydrotalcite-like compound (LiAl HTlc) was synthesized via a hydrothermal method and used to adsorb Cu²⁺ and Zn²⁺ for investigating the adsorption characteristics of heavy metal cations. The X-Raydiffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscopy (TEM) characterizations revealed the interconnecting flower-like layered structure of LiAl HTlc. The adsorption kinetics and isotherms of Cu²⁺ and Zn²⁺ on LiAl HTlc agreed with the pseudo-second-order model and the Langmuir model at a given sorbent concentration (C_s), respectively. The C_s-effect on the adsorption kinetics and isotherms was observed, and the Langmuir-surface component activity (SCA) equation could be utilized to characterize the effect of C_s in the adsorption isotherms. The adsorption process was spontaneous and endothermic. The adsorption mechanism denoted that the adsorption process was controlled using two main mechanisms, i.e., surface complexation and isomorphic substitution. This is the first report, to the best of our knowledge, on the usage of LiAl HTlc for the removal of heavy metal cations Cu²⁺ and Zn²⁺ from a solution. LiAl HTlc is a promising sorbent for treating water containing heavy metal cations.

Self-templated microwave-assisted hydrothermal synthesis of two-dimensional holey hydroxyapatite nanosheets for efficient heavy metal removal

Heavy metals have caused serious environmental problems and threat to human health. Ultrathin and holey two-dimensional (2D) nanosheets have recently drawn significant attention as superb adsorbent material to remove heavy metal ions due to their unique physicochemical properties. Herein, we report a self-template-directed ultrafast reaction route to synthesis porous hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanosheets via a microwave-assisted hydrothermal method using poly(allylamine hydrochloride) as an additive. The resulting hydroxyapatite nanosheets showed a high specific surface area (92.9 m² g^-1) and excellent adsorption performance for various heavy metal ions including Pb(II), Cu(II), and Cd(II), with maximum adsorption capacities of 210.5, 31.6, and 24.9 mg g^-1, respectively. The adsorption kinetics fitted well with the pseudo-second-order equation and the equilibrium data showed a high correlation coefficient with the Langmuir model. Based on the experimental results and analysis, we can conclude that the sorption of heavy metal ions with the hydroxyapatite nanosheets mainly attributes to surface complexation and cation exchange. The present synthetic strategy allows the fast and massive production of porous hydroxyapatite ultrathin nanosheets and may also potentially be applicable to the fabrication of other metal phosphates with assembled or hierarchical porous structures towards various applications such as water purification.

Synthesis of NiAl- layered double hydroxide with nitrate intercalation: Application in cyanide removal from steel industry effluent

Cyanide contamination in steel plant wastewater is a challenge. Nitrate intercalated nickel aluminum layered double hydroxide (LDH) is specially designed and synthesized for adsorption of cyanide from wastewater. The LDH was characterized by Field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and BET surface analyzer. Formation of nanosized plate like LDH particles was confirmed by FESEM analysis. FTIR analysis confirmed the intercalation of nitrate ions in the interlayer space of nickel-aluminum layered double hydroxide. Adsorption of cyanide in the LDH matrix was identified by FTIR study. Ion exchange was the prevalent mechanism of cyanide adsorption. The specific surface area of LDH was 142 m²/g with average pore size of 1.9 nm. The spent LDH could be regenerated using a chemical method and was reused up to five cycles. The efficiency of the LDH was evaluated using real life cyanide containing wastewater from steel plant.

Visible light photocatalytic degradation of MB using UiO-66/g-C3N4 heterojunction nanocatalyst

A unique hybrid of Zr-based metal-organic framework (UiO-66) with graphitic carbon nitride (g-C₃N₄) nanosheets was synthesized by a facile annealing method. Photocatalytic effect was measured by the photodegradation of methylene blue (MB) under visible light irradiation. The morphology, structure, and porous properties of the as-synthesized composites were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the thermogravimetric and differential scanning calorimetry analysis (TG-DSC), diffuse reflectance UV-vis spectroscopy (UV-vis DRS), photoluminescence (PL), and N₂ sorption-desorption isotherms (BET). The results showed that about 100% of MB (200 mL of 10 mg L^-1) photodegradation was achieved by the UiO-66/g-C₃N₄ hybrids (UC 10:10) in 240 min under visible light. The enhanced photocatalytic activity could be attributed to the heterojunction between UiO-66 and g-C₃N₄ therefore the photoelectron transfers efficiently from the conduction band (CB) of g-C₃N₄ to the CB of UiO-66 through the inner electric field generated by the heterojunction resulting the decreasing of recombination of electron/hole and the porous structures which enhance adsorption of the dye molecules on the catalyst surface thereby facilitates the electron/hole transfer within the framework. The trapping experiment and electron spin resonance (ESR) results showed that superoxide radicals (•O₂^-) was the main oxidative species in the photodegradation of MB and the enhanced photocatalytic mechanism of UiO-66/g-C₃N₄ heterojunction hybrids was also proposed.

l-cysteine intercalated layered double hydroxide for highly efficient capture of U(VI) from aqueous solutions

l-cysteine intercalated Mg/Al layered double hydroxide (Cys-LDH) composites were fabricated and applied for treating the U(VI) contaminated wastewater under various conditions. Interaction mechanisms and adsorption properties were investigated by using batch experiments with spectroscopy analysis. The adsorption isotherms and kinetics were fitted perfectly with the Langmuir isotherm and the pseudo-second-order model, respectively. The significant maximum adsorption capacity of Cys-LDH (211.58 mg/g) compared to LDH was attributed to the larger number of functional groups on Cys-LDH. The presence of humic acid (HA) decreased U(VI) elimination on Cys-LDH at high pH but increased U(VI) removal at low pH. Typically, the presence of various anions (such as NO₃^-, Cl^-, ClO₄^- and SO₄^2-) did not obviously affect U(VI) adsorption on Cys-LDH, while the coexisted CO₃^2- significantly affected U(VI) elimination. The predominate adsorption were determined to be the formation of Cys-U(VI)-Cys complexes with cysteine in the Cys-LDH interlayers. The results demonstrated that the Cys-LDH are promising adsorbents for efficient elimination and extraction of radionuclides in actual environmental contamination management.

3D assembly based on 2D structure of Cellulose Nanofibril/Graphene Oxide Hybrid Aerogel for Adsorptive Removal of Antibiotics in Water

Cellulose nanofibril/graphene oxide hybrid (CNF/GO) aerogel was fabricated via a one-step ultrasonication method for adsorptive removal of 21 kinds of antibiotics in water. The as-prepared CNF/GO aerogel possesses interconnected 3D network microstructure, in which GO nanosheets with 2D structure were intimately grown along CNF through hydrogen bonds. The aerogel exhibited superior adsorption capacity toward the antibiotics. The removal percentages (R%) of the antibiotics were more than 69% and the sequence of six categories antibiotics according to the adsorption efficiency was as follows: Tetracyclines > Quinolones > Sulfonamides > Chloramphenicols > β-Lactams > Macrolides. The adsorption mechanism was proposed to be electrostatic attraction, p-π interaction, π-π interaction and hydrogen bonds. In detail, the adsorption capacities of CNF/GO aerogel were 418.7 mg·g-1 for chloramphenicol, 291.8 mg·g-1 for macrolides, 128.3 mg·g-1 for quinolones, 230.7 mg·g-1 for β-Lactams, 227.3 mg·g-1 for sulfonamides, and 454.6 mg·g-1 for tetracyclines calculated by the Langmuir isotherm models. Furthermore, the regenerated aerogels still could be repeatedly used after ten cycles without obvious degradation of adsorption performance.

Superb adsorption capacity of hierarchical calcined Ni/Mg/Al layered double hydroxides for Congo red and Cr(VI) ions

The preparation of hierarchical porous materials as catalysts and sorbents has attracted much attention in the field of environmental pollution control. Herein, Ni/Mg/Al layered double hydroxides (NMA-LDHs) hierarchical flower-like hollow microspheres were synthesized by a hydrothermal method. After the NMA-LDHs was calcined at 600°C, NMA-LDHs transformed into Ni/Mg/Al layered double oxides (NMA-LDOs), which maintained the hierarchical flower-like hollow structure. The crystal phase, morphology, and microstructure of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy elemental mapping, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption methods. Both the calcined and non-calcined NMA-LDHs were examined for their performance to remove Congo red (CR) and hexavalent chromium (Cr(VI)) ions in aqueous solution. The maximum monolayer adsorption capacities of CR and Cr(VI) ions over the NMA-LDOs sample were 1250 and 103.4mg/g at 30°C, respectively. Thermodynamic studies indicated that the adsorption process was endothermic in nature. In addition, the addition of coexisting anions negatively influenced the adsorption capacity of Cr(VI) ions, in the following order: CO₃^2->SO₄^2->H₂PO₄^->Cl^-. This work will provide new insight into the design and fabrication of advanced adsorption materials for water pollutant removal.

Preparation of diethylenetriamine-modified magnetic chitosan nanoparticles for adsorption of rare-earth metal ions

The development of a sustainable method to conveniently separate rare-earth metal ions remains a challenge waiting for breakthrough in numerous of advanced technologies.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

A comprehensive review of the recent progress in the applications of hierarchically structured porous materials is given.

Polyaniline-intercalated layered double hydroxides: synthesis and properties for humidity sensing

A series of polyaniline and sodium dodecanesulfonate co-intercalated layered double hydroxides (LDH/PANI/SDS) with high humidity sensitivity, rapid response and good stability.

Magnetic Ni/PPy nanocomposite as effective reusable adsorbent for removal of arsenite and fluoride from contaminated water

Magnetic nickel/polypyrrole nanostructure has been in situ synthesized at room temperature and characterized. It acts as an effective reusable adsorbent for removal of arsenite and fluoride from contaminated water as well as ground water.

Synthesis and properties of a clean and sustainable deicing additive for asphalt mixture

A clean and sustainable deicing additive was prepared via the adsorption of acetate anions (Ac^-) by magnesium (Mg) and aluminum (Al) calcined layered double hydroxide (Mg/Al-CLDH). Fourier transform infrared spectroscopy spectrums proved that Ac^- had intercalated into LDH structure. X-ray diffraction patterns, scanning electron microscopy and transmission electron microscopy images showed that the intercalation spacing and platelet thickness of Mg and Al layered double hydroxide containing Ac^- anions (Mg/Al-Ac^- LDH) had been enlarged due to substitution of divalent CO₃^2- anions by a larger quantity of monovalent Ac^– anions. Differential scanning calorimetry tests testified that the insoluble Mg2/Al-Ac^- LDH evidently decreased the freeze point (FP) of water to -10.68°C. X-ray photoelectron spectroscopy analyses confirmed that the Ac- were strongly confined by the metal layers of LDHs. FP test of asphalt mixtures confirmed that Mg/Al-Ac^- LDHs reduced FP to -5.5°C. Immersion test results indicated that Mg/Al-Ac^- LDH had a good deicing durability and Ac^- did not released from asphalt mixture. Snow melting observation was conducted further testified that Mg/Al-Ac^- LDH melted snow or ice sustainably.

An insight into thermodynamics of adsorptive removal of fluoride by calcined Ca–Al–(NO3) layered double hydroxide

A framework for determination of thermodynamic equilibrium constant and Gibbs free surface energy change was presented. The interactive effect of temperature on adsorption process was addressed by RSM. Endothermic, spontaneous reaction was observed.

Fluoride removal from water using high-activity aluminum hydroxide prepared by the ultrasonic method

Ultrasonically prepared Al(OH)₃ has a high defluoridation capacity and a low residual aluminum concentration in drinking water after defluoridation.

Adsorption removal of Congo red over flower-like porous microspheres derived from Ni/Al layered double hydroxide

Flower-like porous microspheres of Ni/Al mixed oxide, consisting of a hollow core and mesoporous shell, can achieve a superior adsorption and regeneration capacity toward Congo red.

MgAl layered double hydroxides with chloride and carbonate ions as interlayer anions for removal of arsenic and fluoride ions in water

Flower-like MgAl layered double hydroxides (MgAl-LDHs) with chloride and carbonate ions as interlayer anions showed excellent adsorption capacities for As(v) and F⁻ ions under neutral conditions.

Sacrificial template-directed synthesis of mesoporous magnesium oxide architectures with superior performance for organic dye adsorption [corrected]

Mesoporous MgO architectures were successfully synthesized by the direct thermal transformation of the sacrificial oxalate template. The as-prepared mesoporous architectures were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption-desorption techniques. The MgO architectures showed extraordinary adsorption capacity and rapid adsorption rate for removal of Congo red (CR) from water. The maximum adsorption capacity of the MgO architectures toward CR reached 689.7 mg g⁻¹, much higher than most of the previously reported hierarchical adsorbents. The CR removal process was found to obey the Langmuir adsorption model and its kinetics followed pseudo-second-order rate equation. The superior adsorption performance of the mesoporous MgO architectures could be attributed to the unique mesoporous structure, high specific surface area as well as strong electrostatic interaction.

Nitrate-ion-selective exchange ability of layered double hydroxide consisting of MgII and FeIII

In this study, layered double hydroxide (LDH) consisting of Mg(II) and Fe(III) (Mg/Fe-LDH) was synthesized by using a combination of coprecipitation with hydrothermal aging, and its anion-exchange properties were investigated. Through various analyses, the chemical formula of the proposed Mg/Fe-LDH was determined to be [Mg(0.76)Fe(0.24)(OH)(2)](Cl(-))(0.21)(CO(3)(2-))(0.02)·0.76H(2)O. Furthermore, amorphous Fe(III) impurities were contained in the present Mg/Fe-LDH. The proposed Mg/Fe-LDH exhibited clear selectivity for nitrate ions dissolved in water. This selectivity for nitrate ions can be explained by an anion-sieve effect by the existence of amorphous Fe(III) impurities. Our findings suggest that it is possible to synthesize LDHs with high selectivity for various anions by effective hybridizing Fe(III) impurities.

Rattle-type carbon-alumina core-shell spheres: synthesis and application for adsorption of organic dyes

Porous micro- and nanostructured materials with desired morphologies and tunable pore sizes are of great interests because of their potential applications in environmental remediation. In this study, novel rattle-type carbon-alumina core-shell spheres were prepared by using glucose and metal salt as precursors via a simple one-pot hydrothermal synthesis followed by calcination. The microstructure, morphology, and chemical composition of the resulting materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N(2) adsorption-desorption techniques. These rattle-type spheres are composed of a porous Al(2)O(3) shell (thickness ≈ 80 nm) and a solid carbon core (diameter ≈ 200 nm) with variable space between the core and shell. Furthermore, adsorption experiments indicate that the resulting carbon-alumina particles are powerful adsorbents for the removal of Orange-II dye from water with maximum adsorption capacity of ~210 mg/g. It is envisioned that these rattle-type composite particles with high surface area and large cavities are of particular interest for adsorption of pollutants, separation, and water purification.