Exploring highly active and inexpensive bifunctional electrocatalysts for water‐splitting is considered to be one of the prerequisites for developing hydrogen energy technology. Here, an efficient ...simultaneous etching‐doping sedimentation equilibrium (EDSE) strategy is proposed to design and prepare hollow Rh‐doped CoFe‐layered double hydroxides for overall water splitting. The elaborate electrocatalyst with optimized composition and typical hollow structure accelerates the electrochemical reactions, which can achieve a current density of 10 mA cm−2 at an overpotential of 28 mV (600 mA cm−2 at 188 mV) for hydrogen evolution reaction (HER) and 100 mA cm−2 at 245 mV for oxygen evolution reaction (OER). The cell voltage for overall water splitting of the electrolyzer assembled by this electrocatalyst is only 1.46 V, a value far lower than that of commercial electrolyzer constructed by Pt/C and RuO2 and most reported bifunctional electrocatalysts. Furthermore, the existence of Fe vacancies introduced by Rh doping and the typical hollow structure are demonstrated to optimize the entire HER and OER processes. EDSE associates doping with template‐directed hollow structures and paves a new avenue for developing bifunctional electrocatalysts for overall water splitting. It is also believed to be practical in other catalysis fields as well.
Etching‐doping sedimentation equilibrium induces the conversion of zeolitic imidazolate framework‐67 nanotriangles into template‐directed hollow Rh‐doped CoFe‐layered double hydroxides, which can combine the effects of doping and the synthesis method of etching precursor to accelerate the kinetics for water splitting. These findings provide a new avenue for the combination of doping and template‐directed hollow structures.
The Cu2O/ZnTi-LDH (Cu2O/LDH) composite was synthesized via Cu-doping into the ZnTi-LDH followed by in-situ reduction strategy for Cr(VI) reduction and tetracycline (TC) degradation under ...visible-light, where the Cu2O nanoparticles (NPs) were homogeneously embedded onto the LDH host layers through in-situ reducing the Cu-doped ZnTi-LDH (CuZnTi-LDH). The optical, photoelectric and photocatalytic performances of the Cu2O/LDH could be adjusted by changing the Cu-doping amount in the CuZnTi-LDH. As expected, the optimal Cu2O/LDH0.10 exhibited high photocatalytic activities for the Cr(VI) reduction (95.5% Cr(VI) removal) and TC degradation (71.6% TC removal) after 120 min. Based on the experimental and density functional theory (DFT) calculation results, a possible p-n heterostructure formation between Cu2O and ZnTi-LDH as well as the transfer route of photogenerated electron-hole pairs toward for Cr(VI) reduction and TC degradation were proposed. This work may provide a rational and facile strategy for improving the LDH-based materials in catalytic oxidation-reduction reactions.
The schematic diagram of the evolution process of the Cu2O/ZnTi-LDH, and photocatalytic of Cr(VI) reduction and TC degradation under visible-light. Display omitted
•Cu2O NPs were evenly embedded onto the LDH host layers by in-situ reduction strategy.•Cu2O self-photooxidation was restrained due to the high dispersion of Cu2O NPs.•The p-n heterostructure provided a new path for transfer and separation of electron-hole pairs.•Cu2O/ZnTi-LDH displayed excellent Cr(VI) reduction and TC degradation performances.
The concept of thin film nanocomposite membranes incorporated with CoAl LDH via interfacial polymerization has been explored for the first time to desalinate brackish water. With sizes in the range ...of 50–100 nm and high aspect ratio of the as synthesized LDH particles, they can be utilized as effective nanofillers for formulation of hydrophilic membranes. Consequentially, by incorporating the LDH particles as nanofillers, as compared to the pristine membrane, the modified membrane showed an increase in the hydrophilicity which was reflected by the relative decrease in the static water contact angle values. The modified membranes with 0.2 wt% of LDH particles exhibited excellent NaCl rejection of saline particles up to 99.03% at which the water flux corresponded to a value of 55 LMH. The flux enhancement can be attributed to (1) the increased hydrophilic character of the modified membranes due to the intercalated hydroxyl ions that enhances the solution-diffusion process (2) the structural change on the top surface of the membrane that creates channels for water transport and (3) the preferential sorption of water molecules due to the 2-dimensional unique structure and increased roughness induced by the LDH. This study may provide a new direction to design next-generation RO membranes because of the wide tunability of LDH with different intercalated ions, metal cations and composition ratios for seawater desalination.
•Synthesis of novel layered double hydroxide (LDH) particles with a sub-atomic interlayer spacing.•Successful incorporation of LDH into thin-film nanocomposite polyamide RO membranes.•Enhanced performance of the TFN membranes for brackish water desalination with superior flux and a rejection of 99.05%.•Significant performance enhancement due to the improved hydrophilicity and morphology of the modified membranes.•Preferential sorption of water molecules by the modified membranes due to the unique 2D structure of LDH particles.
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•Two types of membranes decorated with CoCu-LDH nanoparticles was fabricated.•LDH-based membranes exhibited excellent activity in PMS activation process.•The practical applicability ...of LDH@PVDF membrane was investigated.•The reactive mechanism of LDH@PVDF/PMS system was proposed.
In this study, we prepared two types of composite membranes decorated with CoCu layered double hydroxide (LDH) nanoparticles, i.e. LDH@Calotropis gigantean fiber (LDH@CGF) and LDH@polyvinylidene fluoride (LDH@PVDF) for the first time. Besides, the application potential of different types of composite functional membranes based on LDH in PMS activation system was compared. Both of the LDH-based composite membranes exhibited excellent activity in peroxymonosulfate (PMS) activation process. More importantly, the composite membrane could be separated from the treated water to meet the need of practical application. The superior composite membrane was identified as LDH@PVDF, which was with excellent PMS activation capability and pretty lower metal ions leaching concentration (cobalt 0.044 mg L−1, copper 0.026 mg L−1). And then, LDH@PVDF was employed to investigate the PMS activation performance in various pharmaceutical pollutants removal processes. Besides, the activity of LDH@PVDF for SMX degradation in real aquatic environment (tap water and wastewater) was detected, proving the wide practical applicability of LDH@PVDF membrane. Finally, the possible SMX degradation pathway and PMS activation mechanism occurring in LDH-based composite membrane/PMS system were proposed. Hence, this study for LDH-based membranes construction may provide new insights into the environmentally-friendly catalytic membranes preparation and practical application in wastewater treatment.
Layered Double Hydroxides (LDHs) are a group of hydrotalcite-like nano-sized materials with cationic layers and exchangeable interlayer anions. The wide range of divalent and trivalent cationic ...metals and anionic compounds are employed in the synthesis of LDH materials, which have improved their importance among the researchers. Because of their high anion exchange property, memory effect, tunable behavior, bio-friendly, simple preparation, and their affordability, these nano-materials are essentially interested today. Modification of LDHs improves their behaviours to make them appropriate in industrial fields, including biological, adsorbent, mechanical, optical, thermal, electrical fields, etc. This review has critically discussed the structural features, main properties, and also clarified the most important methods of modification and intercalation of LDH nano-materials. Moreover, some novel reported researches related to the successful modification of LDH materials have been characterized and briefly the advantages, disadvantages, and applications are presented in the industrial fields.
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•Constructional aspects and properties of LDHs are comprehensively argued.•The most important methods of modified LDH preparation are presented.•Modified LDHs are characterized by different analyses such as XRD, FT-IR, and TEM.•The recent applications and future challenges of modified LDHs are discussed.
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•A novel three-dimensional hierarchical structure by vermiculite supported LDH.•Higher removal efficiency of heavy metals by LDH@VMT from soil.•Removal mechanism of isomorphic ...substitution for Zn/Ni and precipitation for Cu/Pb.•Favorable interception function of LDH@VMT in soil by column leaching experiments.
Vermiculite supported Mg-Al layered double hydroxide (LDH@VMT) with three-dimensional hierarchical structure was successfully synthesized and the removal performance of LDH@VMT in soil was investigated for heavy metals removal (Cu2+, Pb2+, Zn2+ and Ni2+). Kinetics studies of heavy metals removal were well described by intraparticle diffusion and pseudo-second-order model. Adsorption isotherm data of Cu2+ and Pb2+ yielded a better accordance of Freundlich model, however, data of Zn2+ and Ni2+ were fitted Langmuir model well. Moreover, the different mechanisms of heavy metals removal by precipitation (Cu2+, Pb2+) and isomorphous replacement (Zn2+, Ni2+) were investigated and proposed, respectively. The effect of coexistence cations and column leaching experiments for practical performance assessment were also examined. The excellent removal performance suggested a promising strategy in heavy metals contaminated soil.
2D/2D interface heterostructures of g-C3N4 and NiAl-LDH are synthesized utilizing strong electrostatic interactions between positively charged 2D NiAl-LDH sheets and negatively charged 2D g-C3N4 ...nanosheets. This new 2D/2D interface heterojunction showed remarkable performance for photocatalytic CO2 reduction to produce renewable fuels such as CO and H2 under visible-light irradiation, far superior to that of either single phase g-C3N4 or NiAl-LDH nanosheets. The enhancement of photocatalytic activity could be attributed mainly to the excellent interfacial contact at the heterojunction of g-C3N4/NiAl-LDH, which subsequently results in suppressed recombination, and improved transfer and separation of photogenerated charge carriers. In addition, the optimal g-C3N4/NiAl-LDH nanocomposite possessed high photostability after successive experimental runs with no obvious change in the production of CO from CO2 reduction. Our findings regarding the design, fabrication and photophysical properties of 2D/2D heterostructure systems may find use in other photocatalytic applications including H2 production and water purification.
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•PMS activation by CoFe-LDH was improved by compounding with biochar.•Biochar acted as the catalyst carrier and electron mediator.•Reducing functional groups in biochar facilitated ...Co(III) and Fe(III) reduction.
Efficient and low-cost catalysts for peroxymonosulfate (PMS) activation are needed for pollution prevention and environmental remediation. In this work, PMS activation by CoFe layered double hydroxide (CoFe-LDH) was promoted by compositing with biochar (BC). The characterization and catalytic performance of BC, CoFe-LDH, and BC@CoFe-LDH composite (BC-LDH) were investigated. The results indicated that BC could act as a catalyst carrier and electron mediator, which improved the physicochemical properties of CoFe-LDH and promoted the redox cycle of transition metals. The redox-active moieties (RAMs) of BC, especially the reduced functional groups (e.g., phenolic –OH), played an important role in the reduction of Co(III) and Fe(III). Remarkably, benefiting from the synergistic effect between BC and CoFe-LDH, the resulting BC-LDH exhibited excellent catalytic activity and stability for PMS activation. More reactive oxygen species (ROS) were produced in BC-LDH/PMS system. As a result, 100% of dimethyl phthalate (DMP, 10 mg L−1) degradation efficiency was achieved within 60 min in BC-LDH/PMS system, while only 62% in CoFe-LDH/PMS system. The intermediates of DMP degradation were identified and the degradation pathways were proposed. Our findings are expected to provide new insights into the rational design and application of BC materials and transition metals/PMS system for environmental remediation.
The increasing concentration of nitroimidazoles antibiotics (NIs) in the water environment has great threat to human and ecosystem security. Herein, the degradation rates of four NIs were found to ...vary with their molecular structures using Co3Mn–layered double hydroxide (LDH) catalyzed peroxymonosulfate oxidation process. Specifically, the degradation efficiency of secnidazole (SNZ) was determined to be the highest with a reaction rate of 0.24 min−1, which was 3.6, 2.3 and 1.8 times to that of menidazole (MZ), metronidazole (MTZ) and ornidazole (ONZ), respectively. During the reaction, 8.3% of Co2+ and 8.4% of Mn3+ transformed to Co3+ and Mn4+ after reaction, respectively. The conversion of bimetallic valence in Co3Mn–LDH donated electrons (e–) for PMS activation, resulting in the production of 1O2, OH, SO4− and O2−. Density functional theory (DFT) calculation showed that the presence of electron–donating groups (–CH3 and –OH) and the absence of electron–withdrawing atom (Cl) leaded to the richest active sites in the molecular structure of SNZ, which thus contributed to the highest degradation efficiency of SNZ. By deducing the structure–dependent degradation pathways of four NIs, the carbon chain of SNZ was found to be more easily attacked to form MTZ and MZ because of its unique active sites, resulting in the faster degradation rate of SNZ than MTZ and MZ. This study may provide a valuable insight into the effects of molecular structures on the degradation rates and transformation pathways of NIs.
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•The degradation rates and pathways of NIs varied with their molecular structures.•The conversion of bimetallic valence donated e– for PMS activation.•The Co3Mn–LDH/PMS process possessed application potential for NIs removal.•DFT calculation was used to reveal the effects of active sites on NIs degradation.
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Low-cost, highly active and earth-abundant bifunctional electrocatalyst is very important for the large-scale hydrogen production by water splitting. In the present work, we report a ...novel two-step method to fabricate three-dimensional (3D) porous catalyst for water splitting. The Ni3Se2 nanowires are in-situ formed on Ni foam (NF) by simple hydrothermal method, subsequently NiFe layered double hydroxid (NiFe-LDH) nanosheets vertically grow on the nanowires to form core-shell structure. The as-formed Ni3Se2@NiFe-LDH/NF catalyst shows 3D porous structure, which can provide large specific surface area and effective substance transfers. The tight bonding between Ni3Se2 nanowires and NiFe-LDH nanosheets ensures good electron transfer. The Ni3Se2@NiFe-LDH/NF catalyst exhibits outstanding electrocatalytic property for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. The overpotentianls for HER and OER at the current density of 10 mA cm−2 in 1 M KOH are 68 mV and 222 mV, respectively. For overall water splitting, a small cell voltage of 1.55 V can achieve a current density of 10 mA cm−2 in 1 M KOH. This work provides a guidance for the rational design and development of heterostructure electrocatalysts for overall water splitting.
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