Fe-Ce/Layered Double Hydroxide Heterostructures and Their Derived Oxides: Electrochemical Characterization and Light-Driven Catalysis for the Degradation of Phenol from Water

Fe-Ce/layered double hydroxides (LDHs) were synthesized via a facile route by exploiting the "structural memory" of the LDH when the calcined MgAlLDH and ZnAlLDH were reconstructed in the aqueous solutions of FeSO₄/Ce(SO₄)₂. XRD analysis shows the formation of heterostructured catalysts that entangle the structural characteristics of the LDHs with those of Fe₂O₃ and CeO₂. Furthermore, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, TG/DTG, SEM/EDX and TEM results reveal a complex morphology defined by the large nano/microplates of the reconstructed LDHs that are tightly covered with nanoparticles of Fe₂O₃ and CeO₂. Calcination at 850 °C promoted the formation of highly crystallized mixed oxides of Fe₂O₃/CeO₂/ZnO and spinels. The photo-electrochemical behavior of Fe-Ce/LDHs and their derived oxides was studied in a three-electrode photo-electrochemical cell, using linear sweep voltammetry (LSV), Mott-Schottky (M-S) analysis and photo-electrochemical impedance spectroscopy (PEIS) measurements, in dark or under illumination. When tested as novel catalysts for the degradation of phenol from aqueous solutions, the light-driven catalytic heterojunctions of Fe-Ce/LDH and their derived oxides reveal their capabilities to efficiently remove phenol from water, under both UV and solar irradiation.

Facile Synthesis of Sulfate-Intercalated CoFe LDH Nanosheets Derived from Two-Dimensional ZIF-9(III) for Promoted Oxygen Evolution Reaction

Layered double hydroxide (LDH) has emerged as a promising electrocatalyst; however, the synthetic method usually requires high temperature and high pressure, and sulfate-intercalated LDH is rarely reported. Herein, the sulfate-intercalated CoFe LDH nanosheets were successfully fabricated at ambient temperature via a facile strategy, using two-dimensional ZIF-9(III) as a template and FeSO4 as both etchant and iron source. When the as-prepared sulfate-intercalated CoFe LDH acts as an electrocatalyst, it presents superior electrocatalytic performance for the oxygen evolution reaction (OER), requiring low overpotential (η@10 mA cm−2 = 218 mV) with a small Tafel slope of 59.9 mV dec−1 in 1.0 M KOH, which compares favorably with commercial RuO2 and most reported transition-metal electrocatalysts. The high catalytic activity of CoFe LDH might be ascribed to the large interlayer space distance originating from special SO42− ions and the strong synergistic effects between Fe and Co. This work provides a novel and feasible approach to designing highly efficient electrocatalysts based on advanced LDH materials for OER.

Preparation of Amine-Modified Cu-Mg-Al LDH Composite Photocatalyst

Cu-Mg-Al layered double hydroxides (LDHs) with amine modification were prepared by an organic combination of an anionic surfactant-mediated method and an ultrasonic spalling method using N-aminoethyl-γ-aminopropyltrimethoxysilane as a grafting agent. The materials were characterized by elemental analysis, XRD, SEM, FTIR, TGA, and XPS. The effects of the Cu²⁺ content on the surface morphology and the CO₂ adsorption of Cu-Mg-Al LDHs were investigated, and the kinetics of the CO₂ adsorption and the photocatalytic reduction of CO₂ were further analyzed. The results indicated that the amine-modified method and appropriate Cu²⁺ contents can improve the surface morphology, the increase amine loading and the free-amino functional groups of the materials, which were beneficial to CO₂ capture and adsorption. The CO₂ adsorption capacity of Cu-Mg-Al N was 1.82 mmol·g⁻¹ at 30 °C and a 0.1 MPa pure CO₂ atmosphere. The kinetic model confirmed that CO₂ adsorption was governed by both the physical and chemical adsorption, which could be enhanced with the increase of the Cu²⁺ content. The chemical adsorption was suppressed, when the Cu²⁺ content was too high. Cu-Mg-Al N can photocatalytically reduce CO₂ to methanol with Cu²⁺ as an active site, which can significantly improve the CO₂ adsorption and photocatalytic conversion.

Utilization of layered double hydroxides (LDHs) and their derivatives as photocatalysts for degradation of organic pollutants

Direct or indirect discharge of wastes containing organic pollutants have contributed to the environmental pollution globally. Decontamination of highly polluted natural resources such as water using an effective treatment is a great challenge for public health and environmental protection. Photodegradation of organic pollutants using efficient photocatalyst has attracted extensive interest due to their stability, effectiveness towards degradation efficiency, energy, and cost efficiency. Among various photocatalysts, layered double hydroxides (LDHs) and their derivatives have shown great potential towards photodegradation of organic pollutants. Herein, we review the mechanism, key factors, and performance of LDHs and their derivatives for the photodegradation of organic pollutants. LDH-based photocatalysts are classified into three different categories namely unmodified LDHs, modified LDHs, and calcined LDHs. Each LDH category is reviewed separately in terms of their photodegradation efficiency and kinetics of degradation. In addition, the effect of photocatalyst dose, pH, and initial concentration of pollutant as well as photocatalytic mechanisms are also summarized. Lastly, the stability and reusability of different photocatalysts are discussed. Challenges related to modeling the LDHs and its derivatives are addressed in order to improve their functional capacity.

State-of-the-art and prospects of Zn-containing layered double hydroxides (Zn-LDH)-based materials for photocatalytic water remediation

With the rapid worldwide development of industry and human activities, increasing amounts of multifarious contaminants have significantly threatened environmental ecosystems and human health. Solar photocatalytic decontamination, as an environmentally friendly technology, has been regarded as a good approach to eliminate water pollutants. To date, various photocatalysts have been developed for the purpose of water remediation. Zn-containing layered double hydroxides (Zn-LDHs) and their derivatives are promising candidates due to their suitable band edge positions (oxidation-reduction potentials) for high photocatalytic performances, flexible properties derived from adjustable components and tailorable electronic structures, chemical stabilities, and low toxicities. This review focuses on the fabrication and modification of Zn-LDHs and their photocatalytic applications for the elimination of contaminants in water, including the degradation of toxic organic pollutants, transfer of hazardous heavy metals to lower toxicity heavy metals, and bacterial inactivation. The mechanisms involved in the photocatalytic processes are also thoroughly reviewed. Finally, the emerging scientific and engineering opportunities and challenges in environmental photocatalysis are presented. This review provides basic insights into the construction of Zn-LDH-based materials with high photocatalytic activities and new perspectives on their applications for the photocatalytic elimination of contaminants, which is helpful for the development of photocatalysis for environmental remediation from the lab to industry.

Ultrasmall Ga-ICG nanoparticles based gallium ion/photodynamic synergistic therapy to eradicate biofilms and against drug-resistant bacterial liver abscess

Pyogenic liver abscess and keratitis are aggressive bacterial infections and the treatment has failed to eradicate bacteria in infectious sites completely owing to the currently severe drug resistance to existing antibiotics. Here, we report a simple and efficient one-step development of ultrasmall non-antibiotic nanoparticles (ICG-Ga NPs) containing clinically approved gallium (III) (Ga³⁺) and liver targeting indocyanine green (ICG) molecules to eradicate multi-drug resistant (MDR) bacteria thought the synergetic effect of photodynamic therapy and iron metabolism blocking. The ICG-Ga NPs induced photodynamic effect could destroy the bacterial membrane, further boost the endocytosis of Ga³⁺, then replace iron in bacteria cells to disrupt bacterial iron metabolism, and demonstrate the synergetic bacterial killing and biofilm disrupting effects. The ICG-Ga NPs show an excellent therapeutic effect against extended spectrum β-lactamases Escherichia coli (ESBL E. coli) and significantly improve treatment outcomes in infected liver abscess and keratitis. Meanwhile, the ultrasmall size of ICG-Ga NPs could be cleared rapid via renal clearance route, guaranteeing the biocompatibility. The protective effect and good biocompatibility of ICG-Ga NPs will facilitate clinical treatment of bacteria infected diseases and enable the development of next-generation non-antibiotic antibacterial agents.

Layered Double Hydroxides: A Toolbox for Chemistry and Biology

Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed for applications in organic catalysis, photocatalysis, sensors, drug delivery, and cell biology. Given the widespread contemporary interest in these topics, time-to-time it urges to review the recent progresses. This review aims to summarize the most recent cutting-edge reports appearing in the last years. It firstly focuses on the application of LDHs as catalysts in relevant chemical reactions and as photocatalysts for organic molecule degradation, water splitting reaction, CO2 conversion, and reduction. Subsequently, the emerging role of these materials in biological applications is discussed, specifically focusing on their use as biosensors, DNA, RNA, and drug delivery, finally elucidating their suitability as contrast agents and for cellular differentiation. Concluding remarks and future prospects deal with future applications of LDHs, encouraging researches in better understanding the fundamental mechanisms involved in catalytic and photocatalytic processes, and the molecular pathways that are activated by the interaction of LDHs with cells in terms of both uptake mechanisms and nanotoxicology effects.

Full-Spectrum Photocatalytic Activity of ZnO/CuO/ZnFe2O4 Nanocomposite as a PhotoFenton-Like Catalyst

Deriving photocatalysts by the calcination of hydrotalcite-like compounds has attracted growing interest for extending their photocatalytic activity to the visible and even near-infrared (NIR) light regions. Herein, we describe the acquisition of a ZnO/CuO/ZnFe2O4 nanocomposite with good photoFenton-like catalytic activity under UV, visible and near-infrared (NIR) light irradiation by optimizing the calcination temperature of the coprecipitation product of Zn2+, Cu2+ and Fe3+. The ZnO/CuO/ZnFe2O4 nanocomposite is composed of symbiotic crystals of ZnO, CuO and ZnFe2O4, which enable the nanocomposite to show absorption in the UV, visible and NIR light regions and to produce a transient photocurrent in the presence of H2O2 under NIR irradiation. The full-spectrum photoFenton-like catalyst shows improved performance for the degradation of methyl orange with an increasing amount of H2O2 and is very stable in the recycling process. We believe that the ZnO/CuO/ZnFe2O4 nanocomposite is a promising full-spectrum photoFenton-like catalyst for the degradation of organic pollutants.

Dynamics of Charge-Transfer Behavior in a Plasmon-Induced Quasi-Type-II p-n/n-n Dual Heterojunction in Ag@Ag3PO4/g-C3N4/NiFe LDH Nanocomposites for Photocatalytic Cr(VI) Reduction and Phenol Oxidation

In this work, a series of heterostructure Ag@Ag₃PO₄/g-C₃N₄/NiFe layered double hydroxide (LDH) nanocomposites were prepared by a combination of an electrostatic self-assembly and in situ photoreduction method. In this method, positively charged p-type Ag₃PO₄ was electrostatically bonded to the self-assembled negatively charged surface of the n-n-type g-C₃N₄/NiFe (CNLDH) LDH hybrid material with partial reduction of Ag⁺ to metallic Ag nanoparticles (NPs) by the photogenerated electrons and available surface -OH groups of LDH under visible light irradiation. The presence of Ag₃PO₄ as a p-type semiconductor, the surface plasmon resonance (SPR) effect of metallic Ag NPs, and oxygen vacancies as O_v-type defects in NiFe LDH could greatly achieve the quasi-type-II p-n/n-n dual heterojunctions, which was revealed by the shifted conduction band and valence band potentials in Mott-Schottky (M-S) analysis. Among all the optimized heterostructures, CNLDHAgP4 could achieve the highest photocatalytic Cr(VI) reduction rate of 97% and phenol oxidation rate of 90% in 2 h. The heterostructure CNLDHAgP4 photocatalyst possesses a unique morphology consisting of cubic phases of both Ag NPs and Ag₃PO₄, which adhered to the thin and curvy layers of the CNLDH hybrid for smooth electronic and ionic charge transport. Furthermore, the intimate Schottky barriers formed at the interface of quasi-type-II p-n/n-n dual heterojunctions were verified by the photoluminescence, linear sweep voltammetry, M-S, electrochemical impedance study, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy studies. The SPR effect of Ag NPs and oxygen vacancies as O_v-type defect in NiFe LDH can effectively accelerate the threshold of charge separation and be the main reason for the enhanced activity achieved by the as-fabricated heterostructure photocatalyst.

Designing a porous-crystalline structure of β-Ga2O3: a potential approach to tune its opto-electronic properties

β-Ga2O3 has drawn recent attention as a state-of-the-art electronic material due to its stability, optical transparency and appealing performance in power devices. However, it has also found a wider range of opto-electronic applications including photocatalysis, especially in its porous form. For such applications, a lower band gap must be obtained and an electron-hole spatial separation would be beneficial. Like many other metal oxides (e.g. Al2O3), Ga2O3 can also form various types of porous structure. In the present study, we investigate how its optical and electronic properties can be changed in a particular porous structure with stoichiometrically balanced and extended vacancy channels. We apply a set of first principles computational methods to investigate the formation and the structural, dynamic, and opto-electronic properties. We find that such an extended vacancy channel is mechanically stable and has relatively low formation energy. We also find that this results in a spatial separation of the electron and hole, forming a long-lived charge transfer state that has desirable characteristics for a photocatalyst. In addition, the electronic band gap reduces to the vis-region unlike the transparency in the pure β-Ga2O3 crystal. Thus, our systematic study is promising for the application of such a porous structure of β-Ga2O3 as a versatile electronic material.

Liquid-Metal-Based Super-Stretchable and Structure-Designable Triboelectric Nanogenerator for Wearable Electronics

The rapid advancement of intelligent wearable electronics imposes the emergent requirement for power sources that are deformable, compliant, and stretchable. Power sources with these characteristics are difficult and challenging to achieve. The use of liquid metals as electrodes may provide a viable strategy to produce such power sources. In this work, we propose a liquid-metal-based triboelectric nanogenerator (LM-TENG) by employing Galinstan as the electrode and silicone rubber as the triboelectric and encapsulation layer. The small Young's modulus of the liquid metal ensures the electrode remains continuously conductive under deformations, stretching to a strain as large as ∼300%. The surface oxide layer of Galinstan effectively prevents the liquid Galinstan electrode from further oxidization and permeation into silicone rubber, yielding outstanding device stability. Operating in the single-electrode mode at 3 Hz, the LM-TENG with an area of 6 × 3 cm² produces an open-circuit voltage of 354.5 V, transferred short-circuit charge of 123.2 nC, short-circuit current of 15.6 μA, and average power density of 8.43 mW/m², which represent outstanding performance values for TENGs. Further, the LM-TENG maintains stable performance under various deformations, such as stretching, folding, and twisting. LM-TENGs in different forms, such as bulk-shaped, bracelet-like, and textile-like, are all able to harvest mechanical energy from human walking, arm shaking, or hand patting to sustainably drive wearable electronic devices.

Synergistic effects of plasmon induced Ag@Ag3VO4/ZnCr LDH ternary heterostructures towards visible light responsive O2 evolution and phenol oxidation reactions

The SPR effect of monodisperse Ag nanoparticles in Ag@Ag₃VO₄/ZnCr LDH heterostructures exhibits high photocatalytic activity towards evolution of O₂ and oxidation of phenol.