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•Periodic shifts in pH can drive reversible uptake and release of phosphate by LDH.•The layered crystal structure of LDH remains stable in multi-rounds of regulation.•The regenerated ...LDH in pH regulation can work continuously without drying.•Surface coordination and electrostatic attraction are alternated in the regulation.•Ion-exchanged phosphate amount changes synchronously with apparent adsorption.
Layered double hydroxides (LDH) are potentially industry-producible adsorption materials for phosphate removal from wastewater. However, the sustainable desorption strategy to support its application in practical scenarios is still lacking. In this study, we proposed to control the phosphate uptake and release behavior of LDH through periodic pH regulation. After twelve stages of regulation, the restoration rates of phosphate and pH were maintained at 86.5 % and 96.2 %, respectively, indicating that LDH was robust to resist multiple rounds of pH shock. But extremely acidic or alkaline conditions can accelerate metal ion loss from LDH laminates, so the regulation needs to be in a mild pH range (4.0–11.0). Under this condition, an alternating pattern appeared in the surface interaction of LDH and phosphate. Spectroscopic data showed that the formation of metal-phosphate coordination complexes (MOP) was the dominant mode of phosphate adsorption at high pH, while the formation of electrostatic attraction complexes dominated at low pH. For the interlayer interaction, it is interesting to find the exchanged Cl− ions would not re-enter the interlayer of LDH, suggesting that the charge-balancing anions were almost entirely composed of phosphate. Quantitative analysis revealed that the ion-exchanged phosphate amount kept increasing/decreasing in parallel with the total adsorbed amount, implying the driving effect of ion exchange on the periodic uptake/release of phosphate. Overall, the switching mechanism and reversibility of the binding state of phosphate-LDH were revealed during pH regulation. These findings may provide new insights for the development of sustainable desorption options for LDH.
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•Powerful biomaterial LDH modified biochar combined with SA were prepared.•Adsorption kinetics, isotherm and response surface characterized material.•Biological method combined with ...chemisorption to remove nitrogen and phosphorus.•Bioreactor remove nitrogen and phosphorus efficiently under oligotrophic condition.•High-throughput showed that strain FYF8 might play a leading role in bioreactor.
A novel layered double hydroxide (LDH)-orange peel (OP) biochar/sodium alginate (SA) (LBSA) synthetic material was prepared as an immobilized carrier for Acinetobacter sp. FYF8 to improve the removal of nitrogen and phosphorus in the bioreactor. Results demonstrated that under optimum conditions, the nitrate and phosphate removal efficiency reached 95.32 and 86.11%, respectively. The response surface methodology was used to illustrate the adsorption properties of the material and obtained optimal conditions for the removal of nitrate. The adsorption kinetics and isotherm were well fitted with the pseudo-second-order and Langmuir isotherm model, respectively, indicating that the adsorption process was mainly controlled by chemical adsorption and was favorable. Moreover, the morphology and composition of LBSA immobilized bacteria were analyzed and the mechanism of removing nitrate and phosphate was the synergistic effect of biological metabolism and adsorption. Community structure analysis and microbial distribution showed that FYF8 might was the dominant strain in bioreactors.
Developing effective photocatalysts for CO2 reduction to high value-added chemicals or fuels is a promising strategy for alleviating serious environmental problems and energy crisis. Currently, the ...photocatalytic efficiency is still too slow to arouse industrial interest for most semiconductor photocatalysts due to their low CO2 uptake, limited visible light capture capacity, and serious recombination of electron–hole. Herein, we successfully synthesized a high-density ultrafine Au cluster (∼0.7 nm)-doped cobalt-layered double hydroxide nanocage (Au/Co-LDH) photocatalyst through an in situ redox strategy to explore the structure–activity relationship in the CO2 reduction system. A series of experimental characterizations showed that CO2 adsorption, visible light capture capacity, and charge transfer rate are significantly enhanced due to the highly dispersed and ultrafine Au cluster doping. Density functional theory calculations indicate that Au doping also promoted charge redistribution at the active site, increased the density of states near the Fermi energy level, stabilized the *COOH intermediate, and reduced the energy barrier of the rate-determining step. As a result, Au/Co-LDH delivers a CO evolution rate of 5610 μmol g–1 h–1 toward CO2 reduction under visible light (λ > 420 nm), which is 4 times and 22 times more active than the undoped one and Au nanoparticles, respectively. We believe that this work will provide an important implication for the development and optimization of photocatalysts for CO2 reduction.
Fouling is a common challenge to all membrane-based separation technologies. The current study demonstrated an antifouling membrane with a superhydrophilic but oleophobic (in air) characteristic, ...which was achieved through covalently tethering heterogeneously tailored two-dimensional layered double hydroxide (LDH) nanosheets to a polyvinylidene fluoride membrane surface. The nanosheets were in situ grafted with alternately arranged sodium 1-dodecanesulfonate (SDS) and 3-aminopropyltriethoxysilane (APTS) chains during preparation. Poly(methacrylic acid) (PMAA) was previously grafted on the membrane via plasma induced graft copolymerization as anchor sites for nanosheet binding. With a simple dip-coating operation, the surface-tailored LDH nanosheets could be bound to the membrane via cross-linking between the amine groups of APTS and carboxyl groups of PMAA. Ultimately, the long hydrophobic SDS and short hydrophilic APTS chains on the nanosheets formed a heterogeneous and infiltration selective (due to steric exclusion) surface on the membrane. As a result, the hydrophilic moieties on the membrane surface were much more accessible to water than to liquids of larger molecular size, thereby bringing about the superhydrophilic but oleophobic characteristic. The functionalization gave rise to both significantly enhanced wettability and hydrophilicity of the membrane, mainly owing to the increase of the electron donor component of surface energy (γAB−). Additionally, the functionalized membrane obtained a greater permeability without compromising its selectivity. Furthermore, as verified in both filtration tests with synthetic and practical foulant solutions, the superhydrophilic and oleophobic characteristic endowed the functionalized membrane with conspicuously greater cleaning efficiency and excellent capability in resisting irreversible fouling, suggesting promising applications in various fields.
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•A unique superhydrophilic but oleophobic (in air) PVDF membrane was fabricated.•The rationale behind the unique wetting behavior was elucidated.•The modified membrane achieved dramatically improved filtration performance.•The modified membrane obtained a remarkable antifouling behavior.
Metal–organic frameworks (MOFs) have shown great potential in gas storage and separation, energy storage and conversion, vapor sensing, and catalysis. Nevertheless, rare attention has been paid to ...their anticorrosion performances. At present, substantial hydrophobic and water stable MOFs (like ZIF-8), which are potentially favorable for their applications in anticorrosion industry, have been successfully designed and prepared. In this study, a facile ligand-assisted conversion strategy was employed to fully convert ZnAl-CO3 layered double hydroxide (LDH) precursor buffer layers to well intergrown ZIF-8 coatings. DC Polarization tests indicated that prepared ZIF-8 coatings showed the corrosive current 4 orders of magnitude lower than that of bare Al substrates, demonstrating that MOF materials were superb candidates for high-performance anticorrosion coatings.
The magnetite humic acid-decorated MgAl layered double hydroxide (MgAl-MHA) was prepared for this investigation. After five adsorption-desorption cycles, MgAl-MHA showed remarkable reusability and an ...adsorption rate of about 57% without suffering appreciable loss. The MgAl-MHA's magnetic properties further improve the process of adsorption and less the possibility of the surface being harmed. The influence of temperature, initial concentration of procion red, contact time, pH value, and pHpzc on procion red removal percentage of the MgAl-MHA was investigated in detail. The pseudo-second-order kinetic model and the Langmuir isotherm model were well-fitted by the adsorption kinetics and equilibrium adsorption isotherm, respectively. The thermodynamics analysis indicated that procion red adsorption onto the MgAl-MHA was endothermic and spontaneous. Procion red has a maximum adsorption capacity of 192.037 mg/g at 303 K. In light of the findings mentioned above, MgAl-MHA presents a viable adsorbent option with high recyclability and cheap cost for the removal of procion red.
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•Preparation of MgAl-Magnetite Humic Acid (MHA) was successful.•MgAl-MHA improved the adsorption of procion red.•MgAl-MHA has easily separated the adsorbent and adsorbate using an external magnet.•The highest maximum adsorption capacity is MgAl-MHA (192.037 mg/g).•MgA-MHA regeneration efficiency from 100% to 57.89% in the fifth cycle.
The integration of multiple degradation pathways in a single catalyst has been proposed as a promising strategy for environmental remediation. The successful transition process from MnO2 to ...alpha-Fe2O3 is used to prepare 1D/2D/3D alpha-Fe2O3 @NiFe LDH@diatomite (FENFD) nanocomposite for improving conversion efficiency during pollutant degradation. The effects of initial pH, pollutant concentration, persulfate (PS) dosage, and catalyst dosage on the degradation rate were systematically investigated. FENFD demonstrated favorable PS activation performance and high degradation efficiency for Rhodamine B, azo dyes, and tetracycline over a broad pH range. Comparative experiments with quenching catalytically active radicals and analysis of electron spin resonance (ESR) spectra reveal that the sulfate radical generated by PS photocatalytic activation has a synergistic effect with superoxide radical and hydroxyl radical to degrade pollutants. Biotemplate-diatomite effectively achieves the dispersion of magnetic nano Fe2O3 and LDH and increases light utilization. Meanwhile, density functional theory (DFT) calculations demonstrate that the in situ grow Fe2O3 @NiFe LDH heterojunctions can efficiently transform the interface band structure to inhibit the recombination of photogenerated electron-hole pairs. The stability and reusability of the magnetic nanocomposites were also evaluated, and the degradation efficiency reached 96.4% even after five cycles, which provides new insight into designing single catalysts with different degradation mechanisms.
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•Magnetic Fe2O3@NiFe LDH@diaotomite nanocomposite was synthesised via a dual template strategy.•FENFD possessed high catalytic activity and TOC removal by PS activation for organic pollutant elimination.••OH \SO4.‐andO2.‐, which were generated by interface reaction accounted for the removal of organic pollutants.•The Z-scheme mechanism is determined by DFT calculation to further elucidate the mechanism.•FENFD exhibits superior stability and favorable magnetic recovery.
Nanofluidic membranes formed by reassembling two-dimensional (2D) materials have attracted extensive research interest due to their simple fabrication process and wide application prospects for ion ...separation, fluid transport, flow detection and energy conversion, etc. Currently, most of the 2D nanofluidic channels reconstructed by graphene oxide and MXenes exhibit cationic transport behavior. Herein, we report reconstructed nanofluidic membranes based on totally delaminated nanosheets of layered double hydroxides (LDHs), achieving a high anion conductivity of 10−2 S cm−1. This high ion flux, approximately one order of magnitude higher than that comprised of multilayered LDHs, is mainly attributed to the large interlayer gallery of the membranes reassembled from monolayer nanosheets. In addition, the ion flux shows strong dependence on the interlayer spacing associated with the ionic species, which can be readily tuned by simple anion exchange method. Furthermore, anionic current rectification or nanofluidic diode behavior can be realized in membranes of geometric asymmetrical shape. A directional anion transport against 1000-fold concentration gradient has been demonstrated in isosceles trapezoidal-shaped membrane devices. The high-flux nanofluidic membranes and asymmetric transport devices reconstructed from LDH nanosheets hold great potential for various applications such as ion filtration, chemical sensing and biomimetic energy conversion.
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•Rare anion transport behavior of LDH monolayer nanosheet membranes.•Surface-charge-governed transport leading to an exceptionally high ion flux.•Diode-like ionic current rectification in geometric asymmetrical membranes.•Asymmetric anion transport against up to 1000-fold concentration gradient.
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•HE-MgAlO catalyst show excellent catalytic performance in bi-reforming of biogas.•HE-MgAlO catalyst was more active and stable than mono/bi-metallic counterparts.•The oxophilic ...property and medium-strong basic sites inhibit the coking.•The spinel structure and strong metal-support interaction prevent the sintering.
The bi-reforming of biogas is of great significance for the consumption of greenhouse gases and the generation of valuable syngas. In this study, porous high-entropy spinel-type HE-MgAlO (up to quinary metals: Ni, Co, Zn, Ga, Mn,) catalysts derived from layered double hydroxide were prepared by the one-step co-precipitation method. The catalysts were characterized comprehensively via XRD, XRF, H2-TPR, CO2-TPD, XPS, SEM, HR-TEM, STEM-EDS, CH4-TPSR/CO2-TPO, TG-DSC, Raman, and so on. Compared to the monometallic Ni/MgAlO and binary NiCo/MgAlO catalysts, the HE-MgAlO catalyst exhibits higher initial CH4 (∼98 %) and CO2 (∼55 %) conversion and high stability up to 100 h under certain reaction conditions. The homogeneously-dispersed and electronically-enriched Ni sites, the oxophilic property and medium-strong basic sites of HE-MgAlO catalyst, lead to efficient activation of CH4 and CO2 (H2O), respectively, and high catalytic activity ultimately. The generation of reactive O* from CO2 (H2O) over oxophilic and medium-strong alkaline sites of HE-MgAlO catalyst prompts the rapid removal of coke precursors, leads to satisfying coke-resistant behavior. The spinel structure and strong metal-support interaction in HE-MgAlO catalyst enhances the thermal stability and results in satisfying anti-sintering performance.
The Ni-Co LDH nanowires, directly grown on three-dimensional graphene nickel foam as binder free electrode with enhanced electrochemical performance, have been successfully fabricated through a ...three-step method. Meanwhile, an asymmetric supercapacitor device based on Ni-Co/3D ROG NF and active carbon as positive electrode and negative electrode respectively, exhibits a maximum energy density of 38.6Whkg−1 and a maximum power density of 7231.6Wkg−1, demonstrating its potential utilization for energy storage-conversion applications.
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In this paper, three dimensional reduced graphene oxide skeleton onto nickel foam (3D RGO NF) was fabricated by a facile dip-coating method combined with alkaline reduction. The as-prepared skeleton was used as a substrate to immobilize Ni-Co layered double hydroxide (Ni-Co LDH) with special morphology of nanowires to effectively prevent the agglomeration of material. The Ni-Co LDH/3D RGO NF electrode exhibited an enhanced specific capacitance of 1054Fg−1 compared with Ni-Co LDH/NF, excellent rate capability (60% capacitance retention with a ten-fold increase in current density) as well as long cyclic life (95% capacity retention after 2000 cycles). In addition, an aqueous asymmetric supercapacitor was composed of Ni-Co LDH/3D RGO NF as positive electrode and activated carbon as negative electrode, which exhibited a specific capacitance of 108.7Fg−1 at 2mAcm−2 in a potential range from 0 to 1.6V; it showed maximum energy density of 38.6 Wh kg−1 at 69.5Wkg−1. Moreover, the Ni-Co LDH/3D RGO NF//AC has an outstanding cycling stability (about 70% capacitance retention after 4000 cycles), which makes it a potential candidate for electrochemical energy storage devices.
