This review surveys recent advances in the applications of layered double hydroxides (LDHs) in heterogeneous catalysis. By virtue of the flexible tunability and uniform distribution of metal cations ...in the brucite-like layers and the facile exchangeability of intercalated anions, LDHs-both as directly prepared or after thermal treatment and/or reduction-have found many applications as stable and recyclable heterogeneous catalysts or catalyst supports for a variety of reactions with high industrial and academic importance. A major challenge in this rapidly growing field is to simultaneously improve the activity, selectivity and stability of these LDH-based materials by developing ways of tailoring the electronic structure of the catalysts and supports. Therefore, this Review article is mainly focused on the most recent developments in smart design strategies for LDH materials and the potential catalytic applications of the resulting materials.
This review article presents the most recent developments in the use of layered double hydroxide materials for catalytic applications.
Oxygen vacancy on the surface of metal oxides is one of the most important defects which acts as the reactive site in a variety of catalytic reactions. In this work, operando spectroscopy methodology ...was employed to study the CO2 methanation reaction catalyzed by Ru/CeO2 (with oxygen vacancy in CeO2) and Ru/α-Al2O3 (without oxygen vacancy), respectively, so as to give a thorough understanding on active site dependent reaction mechanism. In Ru/CeO2 catalyst, operando XANES, IR, and Raman were used to reveal the generation process of Ce3+, surface hydroxyl, and oxygen vacancy as well as their structural evolvements under practical reaction conditions. The steady-state isotope transient kinetic analysis (SSITKA)-type in situ DRIFT infrared spectroscopy undoubtedly substantiates that CO2 methanation undergoes formate route over Ru/CeO2 catalyst, and the formate dissociation to methanol catalyzed by oxygen vacancy is the rate-determining step. In contrast, CO2 methanation undergoes CO route over Ru surface in Ru/α-Al2O3 with the absence of oxygen vacancy, demonstrating active site dependent catalytic mechanism toward CO2 methanation. In addition, the catalytic activity evaluation and the oscillating reaction over Ru/CeO2 catalyst further prove that the oxygen vacancy catalyzes the rate-determining step with a much lower activation temperature compared with Ru surface in Ru/α-Al2O3 (125 vs 250 °C).
Layered double hydroxides (LDHs) are a class of anion clays consisting of brucite‐like host layers and interlayer anions, which have attracted increasing interest in the fields of ...catalysis/adsorption. By virtue of the versatility in composition, morphology, and architecture of LDH materials, as well as their unique structural properties (intercalation, topological transformation, and self‐assembly with other functional materials), LDHs display great potential in the design and fabrication of nanomaterials applied in photocatalysis, heterogeneous catalysis, and adsorption/separation processes. Taking advantage of the structural merits and various control synthesis strategies of LDHs, the active center structure (e.g., crystal facets, defects, geometric and electronic states, etc.) and macro–nano morphology can be facilely manipulated for specific catalytic/adsorbent processes with largely enhanced performances. In this review, the latest advancements in the design and preparation of LDH‐based functional nanomaterials for sustainable development in catalysis and adsorption are summarized.
Layered double hydroxides (LDHs) possess important unique features including versatility in composition, morphology and architecture, topological transformation, as well as self‐assembly with other functional materials. In this review, the latest advancements in the design and preparation of LDH‐based functional nanomaterials for sustainable development in catalysis and adsorption are summarized.
The ever-increasing demand for renewable and clean power sources has triggered the development of novel materials for photoelectrochemical (PEC) water splitting, but how to improve the solar ...conversion efficiency remains a big challenge. In this work, we report a conceptual strategy in a ternary material system to simultaneously enhance the charge separation and water oxidation efficiency of photoanodes by introducing reduced graphite oxide (rGO) and NiFe-layered double hydroxide (LDH) on TiO2 nanorod arrays (NAs). An experimental-computational combination study reveals that rGO with a high work function and superior electron mobility accepts photogenerated electrons from TiO2 and enables fast electron transportation; while NiFe-LDH acts as a cocatalyst which accelerates the surface water oxidation reaction. This synergistic effect in this ternary TiO2/rGO/NiFe-LDH photoanode gives rise to a largely enhanced photoconversion efficiency (0.58% at 0.13 V) and photocurrent density (1.74 mA cm-2 at 0.6 V). It is worth mentioning that the photocurrent density of TiO2/rGO/NiFe-LDH, to the best of our knowledge, is superior to previously reported TiO2-based photoanodes in benign and neutral media. In addition, the method presented here can be extended to the preparation of other efficient photoanodes (WO3/rGO/NiFe-LDH and alpha -Fe2O3/rGO/NiFe-LDH) toward high level PEC performance.
This study estimated the prevalence, severity, and extent of periodontitis in the adult U.S. population, with data from the 2009 and 2010 National Health and Nutrition Examination Survey (NHANES) ...cycle. Estimates were derived from a sample of 3,742 adults aged 30 years and older, of the civilian non-institutionalized population, having 1 or more natural teeth. Attachment loss (AL) and probing depth (PD) were measured at 6 sites per tooth on all teeth (except the third molars). Over 47% of the sample, representing 64.7 million adults, had periodontitis, distributed as 8.7%, 30.0%, and 8.5% with mild, moderate, and severe periodontitis, respectively. For adults aged 65 years and older, 64% had either moderate or severe periodontitis. Eighty-six and 40.9% had 1 or more teeth with AL ≥ 3 mm and PD ≥ 4 mm, respectively. With respect to extent of disease, 56% and 18% of the adult population had 5% or more periodontal sites with ≥ 3 mm AL and ≥ 4 mm PD, respectively. Periodontitis was highest in men, Mexican Americans, adults with less than a high school education, adults below 100% Federal Poverty Levels (FPL), and current smokers. This survey has provided direct evidence for a high burden of periodontitis in the adult U.S. population.
A hierarchical CoNi‐sulfide nanosheet array is fabricated via an in situ reduction of CoNi‐layered double hydroxide (LDH) nanosheets, then a vulcanization process. The material inherits the ...morphology of the LDH precursor, consisting of well‐distributed CoNi‐alloy@CoNi‐sulfide nanoparticles with a core–shell structure, and demonstrates promising performance toward hydrazine electrooxidation.
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•Ru0 at the metal–support interface facilitates the formation of oxygen vacancies on CeO2.•The oxygen vacancy concentration/type depends on the morphology/facet of ...CeO2.•Ru/CeO2-NCs{100} catalyst possesses the highest concentration of surface oxygen vacancy.•Ru/CeO2-NCs{100} catalyst exhibits the highest reaction rate toward CO2 methanation.•The surface oxygen vacancy in Ru/CeO2-NCs serves as the active site for CO2 activation.
The existence of oxygen vacancies in heterogeneous catalysis plays an essential role in determining the catalytic reactivity of metal catalysts. In this work, Ru nanoparticles were immobilized onto the CeO2 nanocubes (NCs), nanorods (NRs), and nanopolyhedrons (NPs) with the dominantly exposed {100}, {110}, and {111} facet of CeO2 support, respectively. Their catalytic behavior toward CO2 methanation was studied in detail, and the highest catalytic rate per gram of catalyst was obtained over the Ru(3%)/CeO2-NCs catalyst (reaction rate: 4.85×10−8molgcat−1s−1; selectivity: 99%; 150°C). The temperature-programmed reduction (TPR), Raman spectra, and oxygen storage capacity (OSC) test confirm that the Ru(3%)/CeO2-NCs catalyst possesses the highest concentration of oxygen vacancies owing to the Ru-promoted formation of oxygen vacancy on the CeO2-NCs. In addition, in situ infrared spectroscopy measurements demonstrate that the abundant oxygen vacancy in Ru(3%)/CeO2-NCs serves as the active site for CO2 activation, accounting for the significantly enhanced low-temperature reaction rate per gram of Ru/CeO2 catalyst.
Inorganic nanomaterials including gold nanoparticles, mesoporous silica nanoparticles, graphene, magnetic nanoparticles, quantum dots and layered double hydroxides have become one of the most active ...research fields in biochemistry, biotechnology and biomedicine. Benefiting from the facile synthesis/modification, intrinsically physicochemical properties and good biocompatibility, inorganic nanomaterials have shown great potential in bioimaging, targeted drug delivery and cancer therapies. This
Feature Article
summarizes recent progress on various inorganic nanocarriers, including the background, synthesis, modification, cytotoxicity, physicochemical properties as well as their applications in biomedicine.
This paper summarizes recent progress on various inorganic nanocarriers, including the background, synthesis, modification, cytotoxicity, physicochemical properties and biomedical applications.
Two-dimensional (2D) materials have attracted increasing interest in electrochemical energy storage and conversion. As typical 2D materials, layered double hydroxides (LDHs) display large potential ...in this area due to the facile tunability of their composition, structure and morphology. Various preparation strategies, including
in situ
growth, electrodeposition and layer-by-layer (LBL) assembly, have been developed to directly modify electrodes by using LDH materials. Moreover, several composite materials based on LDHs and conductive matrices have also been rationally designed and employed in supercapacitors, batteries and electrocatalysis with largely enhanced performances. This feature article summarizes the latest developments in the design, preparation and evaluation of LDH materials toward electrochemical energy storage and conversion.
This Feature Article summarizes the latest developments in LDH materials toward electrochemical energy storage and conversion.
This study evaluates the accuracy of periodontitis prevalence determined by the National Health and Nutrition Examination Survey (NHANES) partial-mouth periodontal examination protocols. True ...periodontitis prevalence was determined in a new convenience sample of 454 adults ≥ 35 years old, by a full-mouth “gold standard” periodontal examination. This actual prevalence was compared with prevalence resulting from analysis of the data according to the protocols of NHANES III and NHANES 2001-2004, respectively. Both NHANES protocols substantially underestimated the prevalence of periodontitis by 50% or more, depending on the periodontitis case definition used, and thus performed below threshold levels for moderate-to-high levels of validity for surveillance. Adding measurements from lingual or interproximal sites to the NHANES 2001-2004 protocol did not improve the accuracy sufficiently to reach acceptable sensitivity thresholds. These findings suggest that NHANES protocols produce high levels of misclassification of periodontitis cases and thus have low validity for surveillance and research.
