Enhanced Photocatalytic Activity of a Molybdate-Intercalated Iron-Based Layered Double Hydroxide

Layered Double Hydroxide Catalysts Preparation, Characterization and Applications for Process Development: An Environmentally Green Approach

The adage of new generation of fine chemicals process is the best process applied in the absence of conventional methods. However, many methods use different reaction parameters, such as basic and acidic catalysts, for example oxidation, reduction, bromination, water splitting, cyanohydrin, ethoxylation, syngas, aldol condensation, Michael addition, asymmetric ring opening of epoxides, epoxidation, Wittig and Heck reaction, asymmetric ester epoxidation of fatty acids, combustion of methane, NOx reduction, biodiesel synthesis, propylene oxide polymerization. Layered Double Hydroxides (LDHs) have received considerable attention due their potential applications in flame retardant and has excellent medicinal property for reducing acidity. These catalysts are characterized using analytical techniques, such as: X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Raman spectroscopy, Thermogravimetric-Differential Thermal Analyzer (TG-DTA), Scanning electron microscope (SEM), Transmission electron microscopes (TEM), Brunauer-Emmett-Teller (BET) surface area, N2 Adsorption-desorption, Temperature programmed reduction (TPR), X-ray photoelectrons spectroscopy (XPS), which gives its overall picture of its structure, porosity, morphology, thermal stability, reusability, and activity of catalysts. LDHs catalysts have proven to be economic and environmentally friendly. The above discussed applications make these catalysts unique from Green Chemistry point of view since they are reusable, and eco-friendly catalysts. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Bifunctional iron molybdate as highly effective heterogeneous electro-Fenton catalyst and Li-ion battery anode

Three-dimensional materials have attracted considerable interest in energy and environmental remediation fields. Iron molybdate (FMO) materials have prepared via a facile hydrothermal technique with glycerol assistance, and their structural and chemical composition confirmed using various physico-chemical techniques. The prepared bi-functional material is a strong candidate for energy storage and electrocatalytic degradation of Methylene blue and Congo red. Experimental results confirmed the synthesized FMO-10 catalyst was extremely efficient for methylene blue and Congo red breakdown, achieving 91 % and 96 % degradation in 36 h, respectively. This high catalytic activity was attributed to FMO significant visible light absorption, and reactive OH formation from H₂O₂ synergistically triggered by both Fe³⁺ and MoO₄^2-. Prepared FMO samples demonstrated excellent potential as negative electrode material for lithium ion batteries. Electrode specific capacity initially dropped then rebounded to 1265 mAh g^-1 after 100 cycles at 100 mA g^-1 change rate between 0.01 and 3.0 V.

Heterogeneous Fenton Degradation of Organic Pollutants in Water Enhanced by Combining Iron-type Layered Double Hydroxide and Sulfate

Water pollution derived from organic pollutants is one of the global environmental problems. The Fenton reaction using Fe²⁺ as a homogeneous catalyst has been known as one of clean methods for oxidative degradation of organic pollutants. Here, a layered double hydroxide (Fe²⁺ Al³⁺ -LDH) containing Fe²⁺ and Al³⁺ in the structure was used to develop a "heterogeneous" Fenton catalyst capable of mineralizing organic pollutants. We found that sulfate ion (SO₄ ^2- ) immobilized on the Fe²⁺ Al³⁺ -LDH significantly facilitated oxidative degradation (mineralization) of phenol as a model compound of water pollutants to carbon dioxide (CO₂ ) in a heterogeneous Fenton process. The phenol conversion and mineralization efficiency to CO₂ reached >99% and ca. 50%, respectively, even with a reaction time of only 60 min.

Strong piezocatalysis in barium titanate/carbon hybrid nanocomposites for dye wastewater decomposition

In this work, the strong piezocatalysis is found in the two-step hydrothermally-synthesized barium titanate/carbon hybrid nanocomposites and is used for rhodamine B dye decomposition. As the carbon content increases from 0 to 5 wt%, the catalytic performance of hybrid nanocomposites first increases and then slightly decreases. When the carbon content increases to 2 wt%, the barium titanate/carbon hybrid nanocomposites exhibit the optimal piezocatalytic performance, which have the ~75.5% dye decomposition ratio and the ~0.04901 min^-1 reaction rate constant after the 40 min vibration stimulation, while that of the pure barium titanate are 48.4% and 0.01942 min^-1, respectively. The improvement of piezocatalytic performance in barium titanate/carbon hybrid nanocomposites can be ascribed to the action of carbon's charge transfer which promotes the effective separation of the piezoelectrically-induced electric charges. After three runs recycle utilization tests, the barium titanate/carbon hybrid nanocomposites still exhibit ~70% decomposition ratio of rhodamine B dye. The strong piezocatalytic performance and the good reusability make the barium titanate/carbon hybrid nanocomposites potential in the field of wastewater treatment through utilizing natural vibration energy in future.

Photocatalytic H2 Evolution from Ammonia Borane: Improvement of Charge Separation and Directional Charge Transmission

Co/M^II Fe layered double hydroxide (LDH) LDH photocatalysts have been designed from the aspect of employing stable half-filled Fe³⁺ to trap photogenerated electrons, adjusting the M^II -O-Fe oxo-bridged structure to optimize the short-range directional charge transmission and intercalating oxometallate anions into the LDH to further improve light absorption along with electron-hole separation and non-noble metal Co NP loading and reduction to form a heterojunction. These LDH-based photocatalysts are employed for photocatalytic H₂ evolution from ammonia borane in aqueous solution under visible light at 298 K. The photocatalytic H₂ evolution activity is greatly improved through adjustment of the M^II -O-Fe oxo-bridged structure and molybdate intercalation into the LDH. Turnover frequencies of up to 113.2 min^-1 are achieved with Co/CoFe-Mo. Alongside the experimental results and materials characterization, capture experiments and in situ DRIFTS analysis are carried out to study the photocatalytic hydrogen production mechanism.

Zn-Al Layered Double Hydroxide Film Functionalized by a Luminescent Octahedral Molybdenum Cluster: Ultraviolet-Visible Photoconductivity Response

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn₂Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low-cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo₆ cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo₆ cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

Superactive NiFe-LDH/graphene nanocomposites as competent catalysts for water splitting reactions

Adaptable strategies for the design of superactive NiFe-LDH/graphene nanocomposites for high-performance catalytic activity towards electrocatalytic, photoelectrocatalytic, and photocatalytic water splitting have been reviewed.

ZnFeAl-layered double hydroxides/TiO2 composites as photoanodes for photocathodic protection of 304 stainless steel

A series of ZnFeAl-layered double hydroxides/TiO₂ (ZnFeAl-LDHs/TiO₂) composites are synthesized by a combined anodization and hydrothermal method. The structure, surface morphology, photo absorption and photocathodic protection properties of these samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and electrochemical tests. The unique structure of the ZnFeAl-LDHs reduces the charge carriers recombination, and the visible photoresponse property increase the light harvesting. The XPS study reveals that the electrons in the ZnFeAl-LDHs travel to TiO₂, and the ZnFeAl-LDHs/TiO₂ composites generate and transfer more electrons to 304 stainless steel (304SS), and exhibits a better photocathodic protection performance than pure TiO₂. In addition, after intermittent visible-light illumination for four days, the photoanode still exhibits good stability and durability.

Precursor preparation of Zn–Al layered double hydroxide by ball milling for enhancing adsorption and photocatalytic decoloration of methyl orange

The higher photocatalytic decoloration efficiency of the precursor than that of LDH because of the synergistic effect of intercalation and catalysis.