Layered double hydroxides (LDHs), also known as anionic clays, are lamellar inorganic solids with a brucite-like structure and consist of positively charged metal hydroxide sheets intercalated by ...anions and water molecules. Choice of LDH is beneficial as it displays properties like simple synthesis procedures, adjustable structure, stability, large surface area, homogeneous positive charge distribution over the surface, interplanar spacing, and versatility to synthesize a variety of composites. Due to these properties LDHs act as efficient adsorbents for wastewater treatment. This review presents a detailed overview of the removal of hazardous organic dyes using different LDHs and LDH-hybrids/composites. The review also incorporates methods of synthesis of various LDHs and composites and the effect of their morphology on dye removal capacity. The effects of adsorption variables such as pH, adsorbent dosage, initial concentration of dye, contact time on the adsorption of these materials are also explained along with adsorption isotherms, kinetics and operative mechanisms. This article incorporates 156 references, majority of which have been taken from the available literature of last 5 years.
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•Article summarizes the recent research on adsorptive performance of Layered Double Hydroxides and their hybrids/composites.•Methods of synthesis of LDHs and their hybrids/composites are presented in text as well as tabular form.•Applicable parameters for the removal of various dyes using LDHs are also presented in text as well as tabular form.•Review contains 156 references and provides in-depth knowledge on the role of LDHs as adsorbents for wastewater treatment.
Pesticides are common pollutants that cause detriment to the ecological environmental safety and health of human due to their toxicity, volatility and bioaccumulation. In this work, an ultra-thin ...polymetallic layered double hydroxide (FeCoNi-LDH) with hollow nanoflower structure composite was synthesized using ZIF-67 as a self-sacrificial template, which was used as solid-phase microextraction (SPME) coating for the targeted capture pesticides, which could be combined with high-performance liquid chromatography (HPLC) to sensitive inspection pesticides in real water samples. Orthogonal experimental design (OAD) was applied to ensure the best SPME condition. Additionally, the adsorption properties were evaluated by chemical thermodynamics and kinetics. Under the optimized conditions, high adsorption capacity was obtained (117.0–21.5 mg g−1). A wide linear range (0.020–1000.0 μg L−1), low detection limit (0.008–0.172 μg L−1) and excellent reproducibility were obtained under the established method. This research provided a new strategy for designing hollow materials with multiple cations for the adsorption of anion or organic pollutants.
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•Ultra-thin polymetallic layered double hydroxide (FeCoNi-LDH) with hollow nanoflower structure was designed.•FeCoNi-LDH were applied to fiber coating of SPME to enrichment of pesticides.•FeCoNi-LDH as fiber coating exhibit excellent stability and durability.•FeCoNi-LDH were used for targeted capture of pesticides in real water samples.
The design of high-efficiency electrocatalysts for water electrolysis has attracted much attention. A crucial half-reaction in electrochemical water splitting is the oxygen evolution reaction (OER), ...which suffers from sluggish reaction kinetics due to the high-energy barrier of the complex electron transfer process. This study presents a MoSe2@CoAl-layered double hydroxide (LDH) hybrid nanostructure prepared using the facile hydrothermal method and investigated as a potential OER electrocatalyst. Morphological analysis indicated that the MoSe2 formed in very thin nanosheet structures containing multiple defects on the LDH platelets, increasing the number of catalytic active sites. Compared with pristine MoSe2 and CoAl-LDH, the obtained MoSe2@CoAl-LDH catalyst exhibited enhanced electrocatalytic activity for the OER in an alkaline solution. The MoSe2@CoAl-LDH electrocatalyst showed an overpotential of 360 mV at a current density of 10 mA cm−2 and a small Tafel slope of 53 mV dec−1. In addition, it demonstrated good electrochemical stability. The MoSe2@CoAl-LDH exhibited a lower Tafel slope than commercial RuO2, indicating faster electron transfer on the MoSe2@CoAl-LDH electrode.
•MoSe2 nanosheets were grown on the surface of CoAl-layered double hydroxide using hydrothermal method.•Hydrothermal synthesis resulted in the formation of defect sites on MoSe2@CoAl-LDH.•The MoSe2@CoAl-LDH hybrid nanostructure exhibits improved catalytic active sites.•The MoSe2@CoAl-LDH catalyst improved the performance of the oxygen evolution reaction in an alkaline solution.
Herein, highly efficient composite photocatalysts comprising black Cu-doped TiO
nanoparticles (BCT) encapsulated within hierarchical flower-like NiAl-layered double hydroxide (LDH) microspheres were ...fabricated via a one-step hydrothermal route. Cu-doping and subsequent reduction treatment led to extended visible-light absorption of TiO
in the resulting composites, as confirmed by ultraviolet-visible diffuse reflectance spectral analysis. Moreover, thorough investigations confirmed the strong interactions between LDH and BCT in the resulting BCT/LDH composites. Notably, the BCT/LDH composites exhibited remarkable performance in the degradation of hazardous materials (methyl orange and isoniazid), superior to that of the individual components, reference P25, and P25/LDH under visible-light irradiation. Moreover, the BCT/LDH composite containing 30 wt% of BCT displayed the highest photocatalytic performance among the synthesized photocatalysts and also exhibited high stability during recycling tests with no obvious change in the activity. The superior photodegradation activity of the BCT/LDH composites was primarily attributed to efficient transfer and separation of the photoinduced charge carriers, resulting from the intimate contact interfaces between LDH and BCT. This approach represents a promising route for the rational design of highly efficient and visible-light-active LDH-based composite photocatalysts for application in energy harvesting and environmental protection.
Layered double hydroxides (LDHs), also known as anionic clays or hydrotalcite-like compounds, are a class of nanomaterials that attained great attention as a carrier for drug delivery applications. ...The lamellar structure of this compound exhibits a high surface-to-volume ratio which enables the intercalation of therapeutic agents and releases them at the target site, thereby reducing the adverse effect. Moreover, the intercalated drug can be released in a sustained manner, and hence the frequency of drug administration can be decreased. The co-precipitation, ion exchange, manual grinding, and sol-gel methods are the most employed for their synthesis. The unique properties like the ease of synthesis, low cost, high biocompatibility, and low toxicity render them suitable for biomedical applications. This review presents the advances in the structure, properties, method of preparation, types, functionalization, and drug delivery applications of LDH. Also, this review provides various new conceptual insights that can form the basis for new research questions related to the drug delivery applications of LDH.
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In order to achieve an economical CO2-mediated hydrogen energy cycle, the development of heterogeneous catalysts for CO2 hydrogenation to formic acid is an urgent and challenging task. In this study, ...a stable and well-defined single-site Ru catalyst on the surface of a layered double hydroxide (LDH) in a basic medium is proven to be efficient for selective hydrogenation of CO2 to formic acid under mild reaction conditions (2.0 MPa, 100 °C). The electron-donating ability of triads of basic hydroxyl ligands with a particular location is crucial for an active electron-rich Ru center. There is a strong correlation between catalytic activity and adjustable CO2 adsorption capacity in the vicinity of the Ru center. Such electronic metal–support interactions and a CO2 concentration effect result in a significant positive influence on the catalytic activity.
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•Chloride pre-intercalated CoFe-layered double hydroxide (CoFeCl-LDH) was prepared.•CoFeCl-LDH was used as Cl--capturing electrode for rocking-chair CDI system.•The system exhibits an ...ultrahigh desalination capacity and fast desalination rate.
Faradic electrochemical deionization (EDI), as the next generation of capacitive deionization (CDI), was considered one of the most promising solutions to address the global fresh-water shortage, while rationalizing its cell architecture and developing suitable electrode material are of equal importance to the desalination performance of EDI. In this work, chloride pre-intercalated CoFe-layered double hydroxides (LDH) (CoFeCl-LDHs) were fabricated through coprecipitation and further used as Cl- capturing electrodes for rocking-chair CDI (RCDI) system. By coupling the advantages of both rational cell architecture (symmetric RCDI system with balanced ion storage) and suitable electrode material (reversible Cl- intercalation and fast charge transfer), the CoFeCl-LDH-based RCDI system exhibits an ultrahigh desalination capacity (100.2 mg g−1) and fast desalination rate (0.38 mg g−1 s−1), which outpperform those of the other LDH-based CDI systems. The outstanding desalination performance of the CoFeCl-LDH-based RCDI further demonstrates the critical importance of both electrode material and cell architecture to the EDI system, which could shed light on the future design of highly efficient EDI systems.
The NiFeW-LDHs with W-doping and oxygen vacancies via electrodeposition and corrosion exhibit remarked OER performance.
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•W-doped NiFe-LDHs electrocatalyst is successfully prepared by ...electrodeposition and chemical corrosion.•The concentration of oxygen vacancies in NiFe-LDHs is increased via W-doping.•The low overpotential and excellent stability for OER of NiFeW-LDHs are the synergy of W-doping and oxygen vacancies.
Electrochemical water splitting requires efficient electrocatalysts to accelerate the sluggish kinetics of the oxygen evolution reaction (OER). A promising nanoporous W-doped oxygen vacancy-containing NiFe layered double hydroxides (NiFeW-LDHs) electrocatalyst is directly grown on nickel foam via electrodeposition combined with chemical corrosion. With an appropriate amount of W dopant in NiFe-LDHs, the electronic structures of Ni and Fe are modulated by the changes in local environment, and the oxygen vacancy concentration is further optimized, resulting in abundant OER electrocatalytic active centers on the electrocatalyst surface. Due to the excellent electronic conductivity and three-dimensional nanoporous configuration, the representative NiFeW3-LDHs exhibit remarkable OER electrocatalytic activity with a low overpotential (211 mV at 10 mA cm−2), a small Tafel slope (36.44 mV dec–1), and fine stability (more than 120 h at 10 mA cm−2). The oxygen vacancy effectively modifies the intrinsic electronic structure of NiFe-LDHs, optimizes the adsorption energy of intermediates, and accelerates the OER.
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•Oxygen vacancies enriched CoAl-LDH@CoSx hollow flowers was synthesized.•CoAl-LDH@CoSx exhibited excellent catalytic activity for sulfamethoxazole degradation.•1O2 was identified as ...the primary reactive species in the oxidation process.
In this study, oxygen vacancies enriched cobalt aluminum hydroxide@hydroxysulfide (CoAl-LDH@CoSx) hollow flowers was synthesized by in-situ etching of CoAl-LDH using sodium sulfide solution. The analysis of SEM, EDS, XRD, and XPS were used to characterize the samples. The as-synthesized 0.2CoAl-LDH@CoSx displayed higher catalysis performance of sulfamethoxazole (SMX) degradation via the activation of PMS than the pristine CoAl-LDH. 98.5 % of SMX (40 μM) was eliminated with 0.1 g/L 0.2CoAl-LDH@CoSx and 0.3 mM PMS at pH 6.0 in 4 min. The degradation fitted with the pseudo-first-order reaction kinetics well with rate constant of 0.89 min−1 for 0.2CoAl-LDH@CoSx/PMS system and 0.55 min−1 for CoAl-LDH/PMS system. Singlet oxygen (1O2) was verified as dominant reactive oxygen species responsible for SMX degradation via quenching tests. Mechanism investigation suggested that the oxygen vacancies, redox cycles of Co(II)/Co(III) and S22−/(S2− and sulfate species) on the surface of 0.2CoAl-LDH@CoSx were crucial for PMS activation. In addition, the plausible degradation pathways of SMX were proposed by analysis of the SMX degradation intermediates. This study not only reveals that 0.2CoAl-LDH@CoSx is an efficient catalyst to activate PMS for SMX degradation, but also shed a novel insight into development of heterogeneous catalysts with oxygen vacancies.
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•Cu-rGO LDH nanohybrid fabricated by intercalating rGO inside the LDH galleries.•Cu-rGO LDH exhibited higher surface area and electrical conductivity.•Cu-rGO LDH/PMS induced ...nonradical pathway.•1O2 generated through SO5− owing to electron conduction between PMS and Cu2+.
A new strategy was applied by periodic stacking of active sites of Cu and reduced graphene oxide (rGO) in the form of Cu-rGO LDH nanohybrid material. The experimental results revealed that newly prepared Cu-rGO LDH nanohybrid material was extremely reactive in PMS activation as evident from the degradation rate of 0.115 min−1, much higher than Mn-rGO LDH (0.071 min−1), Zn-rGO LDH (0.023 min−1) or other benchmarked material used during the degradation of bisphenol A (BPA). This excellent activity of Cu-rGO LDH nanohybrid was attributed to the better PMS utilization efficiency as compared to the other catalysts. Additionally, the characterization techniques disclosed that the layer by layer arrangement of active sites in the Cu-rGO LDH catalyst promotes interfacial electron mobility owing to the synergistic association between Cu in LDH and interlayered rGO. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR) and chemical scavengers, singlet oxygen (1O2) was unveiled as dominant reactive species for pollutant removal, resulting from the recombination of superoxides (O2−) or reduction of active Cu centers. We believe that this novel Cu-rGO LDH/PMS system will open up a new avenue to design efficient metal-carbon nanohybrid catalysts for the degradation of emerging aquatic pollutants in a real application.
