Photoelectrochemical Catalysis toward Selective Anaerobic Oxidation of Alcohols.

Selective oxidation of alcohols to aldehydes plays an important role in perfumery, pharmaceuticals, and agrochemicals industry. Different from traditional catalysis or photocatalytic process, here we report an effective photoelectrochemical (PEC) approach for selective anaerobic oxidation of alcohols accompanied with H2 production by means of solar energy. By using TiO2 nanowires modified with graphitic carbon layer as photoanode, benzyl alcohol (BA) has been oxidized to benzaldehyde with high efficiency and selectivity (>99 %) in aqueous media at room temperature, superior to individual electrocatalytic or photocatalytic processes. Moreover, this PEC synthesis method can be effectively extended to the oxidation of several other aryl alcohols to their corresponding aldehydes under mild conditions. The electron spin resonance (ESR) results indicate the formation of intermediate active oxygen (O2.- ) on the photoanode, which further reacts with alcohols to produce final aldehyde compounds.

Active Site Dependent Reaction Mechanism over Ru/CeO2 Catalyst toward CO2 Methanation.

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 Ce(3+), 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).

DFT-Based Simulation and Experimental Validation of the Topotactic Transformation of MgAl Layered Double Hydroxides.

The thermal topotactic transformation mechanism of MgAl layered double hydroxides (LDHs) is investigated by a combined theoretical and experimental study. Thermogravimetric differential thermal analysis (TG-DTA) results reveal that the LDH phase undergoes four key endothermic events at 230, 330, 450, and 800 °C. DFT calculations show that the LDH decomposes into CO2 and residual O atoms via a monodentate intermediate at 330 °C. At 450 °C, the metal cations almost maintain their original distribution within the LDH(001) facet during the thermal dehydration process, but migrate substantially along the c-axis direction perpendicular to the (001) facet; this indicates that the metal arrangement/dispersion in the LDH matrix is maintained two-dimensionally. A complete collapse of the layered structure occurs at 800 °C, which results in a totally disordered cation distribution and many holes in the final product. The structures of the simulated intermediates are highly consistent with the observed in situ powder XRD data for the MgAl LDH sample calcined at the corresponding temperatures. Understanding the structural topotactic transformation process of LDHs would provide helpful information for the design and preparation of metal/metal oxides functional materials derived from LDH precursors.

Hierarchical Conducting Polymer@Clay Core-Shell Arrays for Flexible All-Solid-State Supercapacitor Devices.

A sophisticated hierarchical nanoarray consisting of a conducting polymer (polypyrrole, PPy) core and layered double hydroxide (LDH) shell are synthesized via a facile two-step electrosynthesis method. The obtained PPy@LDH-based flexible all-solid-state supercapacitor meets the requirements of both high energy/power output and long-term endurance, which can be potentially used in highly-efficient and stable energy storage.

Catalytic applications of layered double hydroxides: recent advances and perspectives.

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.

Transparent, Ultrahigh-Gas-Barrier Films with a Brick-Mortar-Sand Structure.

Transparent and flexible gas-barrier materials have shown broad applications in electronics, food, and pharmaceutical preservation. Herein, we report ultrahigh-gas-barrier films with a brick-mortar-sand structure fabricated by layer-by-layer (LBL) assembly of XAl-layered double hydroxide (LDH, X=Mg, Ni, Zn, Co) nanoplatelets and polyacrylic acid (PAA) followed by CO2 infilling, denoted as (XAl-LDH/PAA)n-CO2. The near-perfectly parallel orientation of the LDH "brick" creates a long diffusion length to hinder the transmission of gas molecules in the PAA "mortar". Most significantly, both the experimental studies and theoretical simulations reveal that the chemically adsorbed CO2 acts like "sand" to fill the free volume at the organic-inorganic interface, which further depresses the diffusion of permeating gas. The strategy presented here provides a new insight into the perception of barrier mechanism, and the (XAl-LDH/PAA)n-CO2 film is among the best gas barrier films ever reported.

Layered double hydroxide-based nanomaterials as highly efficient catalysts and adsorbents.

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.

Omidenepag Isopropyl Versus Timolol in Patients With Glaucoma or Ocular Hypertension: Two Randomized Phase 3 Trials (SPECTRUM 4 and 3).

PURPOSE: The SPECTRUM 4 and 3 studies assessed the intraocular pressure (IOP)-lowering efficacy and safety of omidenepag isopropyl (OMDI) 0.002% vs timolol 0.5% in patients with glaucoma or ocular hypertension (OHT). DESIGN: Phase 3, randomized, controlled, double-masked, noninferiority studies. METHODS: Multicenter studies in the US. Inclusion criteria for adults ≥ 18 years (SPECTRUM 4 [N = 409] and 3 [N = 413]) were open-angle glaucoma or OHT, and IOP ≥ 22 mm Hg and ≤ 34 mm Hg; and for pediatric patients < 18 years (N = 13, SPECTRUM 3) were pediatric glaucoma or OHT. The primary objective in both studies was OMDI noninferiority to timolol in reducing IOP (3 months). SPECTRUM 3 included an additional 9 months of OMDI treatment. Safety evaluations were of ocular/non-ocular adverse events (AEs). RESULTS: The IOP-lowering range of OMDI remained consistent in SPECTRUM 4 and 3 (-5.6 to -5.9 vs -5.3 to -5.7 mm Hg, respectively); however, timolol efficacy varied (-5.4 to -6.1 vs -6.4 to -7.0 mm Hg, respectively). OMDI noninferiority was achieved in SPECTRUM 4. Efficacy was maintained with 12-month treatment in SPECTRUM 3. Both studies reported more ocular AEs with OMDI, but lower rates of appearance-altering AEs vs timolol. No new safety concerns were identified. Rates of macular edema in pseudophakic patients increased with prolonged OMDI exposure. CONCLUSIONS: SPECTRUM 4 and 3 demonstrated consistent 3-month IOP-lowering efficacy and safety of OMDI vs timolol in patients with glaucoma or OHT. The 12-month data from SPECTRUM 3 suggest OMDI may have long-term benefits in patients with glaucoma or OHT.

Flexible CoAl LDH@PEDOT core/shell nanoplatelet array for high-performance energy storage.

A CoAl-layered double hydroxide (LDH)@poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell nanoplatelet array (NPA) is grown on a flexible Ni foil substrate as a high-performance pseudocapacitor. The LDH@PEDOT core/shell NPA shows a maximum specific capacitance of 649 F/g (based on the total mass) by cyclic voltammetry (scan rate: 2 mV/s) and 672 F/g by galvanostatic discharge (current density: 1 A/g). Furthermore, the hybrid NPA electrode also exhibits excellent rate capability with a specific energy of 39.4 Wh/kg at a current density of 40 A/g, as well as good long-term cycling stability (92.5% of its original capacitance is retained after 5000 cycles). These performances are superior to those of conventional supercapacitors and LDH NPA without the PEDOT coating. The largely enhanced pseudocapacitor behavior of the LDH@PEDOT NPA electrode is related to the synergistic effect of its individual components: the LDH nanoplatelet core provides abundant energy-storage capacity, while the highly conductive PEDOT shell and porous architecture facilitate the electron/mass transport in the redox reaction.

Hierarchical structures based on functionalized magnetic cores and layered double-hydroxide shells: concept, controlled synthesis, and applications.

The combination of magnetic particles and layered double hydroxide (LDHs) materials leads to the formation of hierarchical composites that can take full advantages of each component; this is an effective approach for achieving multifunctional materials with intriguing properties. This Concept article summarizes several important strategies for the fabrication of magnetic-core/LDH-shell hierarchical nanocomposites, including direct coprecipitation, layer-by-layer assembly, and in situ growth methods. The obtained nanocomposites exhibit excellent performance as multifunctional materials for promising applications in targeted drug delivery, efficient separation, and catalysis. The fabrication and application of magnetic-core/LDH-shell nanocomposite materials represent a new direction in the development of LDH-based multifunctional materials, which will contribute to the progress of chemistry and material science.

Study on UV-shielding mechanism of layered double hydroxide materials.

The development of UV-shielding materials has attracted considerable attention in the field of coatings and sunscreen. This paper reports the UV-shielding mechanism of layered double hydroxide (LDH) materials in terms of chemical composition, structure and morphology, by using (LDH/PAA)n films (n stands for bilayer number) through alternate LBL assembly of LDH nanoparticles and poly(acrylic acid) (PAA) on quartz substrates as a model system. A combination investigation based on experimental and theoretical study demonstrates that the maximum UV scattering can be achieved when λ/d ≈ 1.98; the introduction of Zn element is an effective way to tune the electron structure, band gap, transition mode and resulting UV-shielding property of LDH materials. A UV-shielding efficiency as high as 95% can be obtained by modulating the particle size, composition and thickness of the LDHs. Furthermore, the UV anti-aging capacity of LDH-modified bitumen was studied, which demonstrates a large improvement in UV-resistance performance of bitumen by the incorporation of LDH materials. Therefore, this work systematically discloses the relationship between UV-shielding property and chemical/structural parameters of LDH materials, which can be potentially used as anti-aging agents in various organic matrices and polymer areas.

A review of the first anti-evaporative prescription treatment for dry eye disease: perfluorohexyloctane ophthalmic solution.

Dry eye disease (DED) is one of the most common ocular surface disorders. All DED involves an imbalance between tear production and evaporation. Most cases of DED are driven by excessive evaporation, which is often associated with meibomian gland dysfunction (MGD). In evaporative DED, a deficient tear film lipid layer is believed to lead to increased tear evaporation, inflammation, and ocular surface damage. Most prescription treatments for DED address signs and symptoms by targeting tear production and/or inflammation, but they do not address excessive evaporation. Perfluorohexyloctane (PFHO) ophthalmic solution (MIEBO™; Bausch + Lomb) is a water-free, single-ingredient, preservative-free prescription eye drop that directly targets tear evaporation and is approved by the FDA to treat the signs and symptoms of DED. Results from preclinical studies indicate that PFHO has a high oxygen carrying capacity, may reduce friction on blinking, and spreads quickly over the tear film surface to form a monolayer that inhibits evaporation. These effects can lead to stabilization of the tear film to promote ocular surface healing. Further, PFHO was detected in tears for at least 6 hours in a rabbit pharmacokinetic study, and results indicate that it may improve lipid layer thickness and quality. In 2 pivotal phase 3 trials in patients with DED and clinical signs of MGD (GOBI [NCT04139798] and MOJAVE [NCT04567329]), treatment with PFHO consistently met primary efficacy end points related to DED signs and symptoms (total corneal fluorescein staining and eye dryness, respectively) and was well tolerated. Compared with use of hypotonic saline solution, instillation of PFHO led to significant improvements in signs and symptoms in as early as 2 weeks. In a long-term, open-label safety extension study, efficacy of PFHO was sustained over 12 months, and the safety profile was consistent with those of previous studies. Clinical trial results indicate that treatment with PFHO effectively and consistently reduces the signs and symptoms of DED.

Preparation of Fe3O4@SiO2@layered double hydroxide core-shell microspheres for magnetic separation of proteins.

Three-component microspheres containing an SiO(2)-coated Fe(3)O(4) magnetite core and a layered double hydroxide (LDH) nanoplatelet shell have been synthesized via an in situ growth method. The resulting Fe(3)O(4)@SiO(2)@NiAl-LDH microspheres display three-dimensional core-shell architecture with flowerlike morphology, large surface area (83 m(2)/g), and uniform mesochannels (4.3 nm). The Ni(2+) cations in the NiAl-LDH shell provide docking sites for histidine and the materials exhibit excellent performance in the separation of a histidine (His)-tagged green fluorescent protein, with a binding capacity as high as 239 µg/mg. The microspheres show highly selective adsorption of the His-tagged protein from Escherichia coli lysate, demonstrating their practical applicability. Moreover, the microspheres possess superparamagnetism and high saturation magnetization (36.8 emu/g), which allows them to be easily separated from solution by means of an external magnetic field and subsequently reused. The high stability and selectivity of the Fe(3)O(4)@SiO(2)@NiAl-LDH microspheres for the His-tagged protein were retained over several separation cycles. Therefore, this work provides a promising approach for the design and synthesis of multifunctional LDH microspheres, which can be used for the practical purification of recombinant proteins, as well as having other potential applications in a variety of biomedical fields including drug delivery and biosensors.

Highly dispersed TiO6 units in a layered double hydroxide for water splitting.

A family of photocatalysts for water splitting into hydrogen was prepared by distributing TiO(6) units in an MTi-layered double hydroxide matrix (M = Ni, Zn, Mg) that displays largely enhanced photocatalytic activity with an H(2)-production rate of 31.4 µmol h(-1) as well as excellent recyclable performance. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) mapping and XPS measurement reveal that a high dispersion of TiO(6) octahedra in the layered doubled hydroxide (LDH) matrix was obtained by the formation of an M(2+)-O-Ti network, rather different from the aggregation state of TiO(6) in the inorganic layered material K(2)Ti(4)O(9). Both transient absorption and photoluminescence spectra demonstrate that the electron-hole recombination process was significantly depressed in the Ti-containing LDH materials relative to bulk Ti oxide, which is attributed to the abundant surface defects that serve as trapping sites for photogenerated electrons verified by positron annihilation and extended X-ray absorption fine structure (EXAFS) techniques. In addition, a theoretical study on the basis of DFT calculations demonstrates that the electronic structure of the TiO(6) units was modified by the adjacent MO(6) octahedron by means of covalent interactions, with a much decreased bandgap of 2.1 eV, which accounts for its superior water-splitting behavior. Therefore, the dispersion strategy for TiO(6) units within a 2D inorganic matrix can be extended to fabricate other oxide or hydroxide catalysts with greatly enhanced performance in photocatalysis and energy conversion.

Gold nanoparticle-embedded porous graphene thin films fabricated via layer-by-layer self-assembly and subsequent thermal annealing for electrochemical sensing.

A uniform three-dimensional (3D) gold nanoparticle (AuNP)-embedded porous graphene (AuEPG) thin film has been fabricated by electrostatic layer-by-layer assembly of AuNPs and graphene nanosheets functionalized with bovine serum albumin and subsequent thermal annealing in air at 340 °C for 2 h. Scanning electron microscopy (SEM) investigations for the AuEPG film indicate that an AuNP was embedded in every pore of the porous graphene film, something that was difficult to achieve with previously reported methods. The mechanism of formation of the AuEPG film was initially explored. Application of the AuEPG film in electrochemical sensing was further demonstrated by use of H(2)O(2) as a model analyte. The AuEPG film-modified electrode showed improved electrochemical performance in H(2)O(2) detection compared with nonporous graphene-AuNP composite film-modified electrodes, which is mainly attributed to the porous structure of the AuEPG film. This work opens up a new and facile way for direct preparation of metal or metal oxide nanoparticle-embedded porous graphene composite films, which will enable exciting opportunities in highly sensitive electrochemical sensors and other advanced applications based on graphene-metal composites.

Resettable fluorescence logic gate based on calcein/layered double hydroxide ultrathin films.

A fluorescent logic gate was fabricated based on calcein/layered double hydroxide ultrathin films (UTFs) via alternate assembly technique, which exhibits high stability, reversibility, and resettability. The logic gate was manipulated by utilizing pH value, Hg(2+) and Cl(-) ion as inputs, and the fluorescence emission of the (calcein/LDH)(16) UTF as output, serving as a three-input logic gate that combines the YES and INHIBIT operation.

Temperature-controlled electrochemical switch based on layered double hydroxide/poly(N-isopropylacrylamide) ultrathin films fabricated via layer-by-layer assembly.

In this paper we report the fabrication of layered double hydroxide (LDH) nanoparticles/poly(N-isopropylacrylamide) (pNIPAM) ultrathin films (UTFs) via the layer-by-layer assembly technique, and their switchable electrocatalytic performance in response to temperature stimuli was demonstrated. X-ray diffraction and UV-vis absorption spectroscopy indicate a periodic layered structure with uniform and regular growth of the (LDH/pNIPAM)(n) UTFs; an interaction based on hydrogen bonding between LDH nanoparticles and pNIPAM was confirmed by X-ray-photoelectron spectroscopy and Fourier transform infrared spectroscopy. Temperature-triggered cyclic voltammetry and electrochemical impedance spectroscopy switch for the UTFs was obtained between 20 and 40 °C, accompanied by reversible changes in surface topography and film thickness revealed by atomic force microscopy and ellipsometry, respectively. The electrochemical on-off property of the temperature-controlled (LDH/pNIPAM)(n) UTFs originates from the contraction-expansion configuration of pNIPAM with low-high electrochemical impedance. In addition, a switchable electrocatalytic behavior of the (LDH/pNIPAM)(n) UTFs toward the oxidation of glucose was observed, resulting from the temperature-controlled charge transfer rate. Therefore, this work provides a facile approach for the design and fabrication of a well-ordered command interface with a temperature-sensitive property, which can be potentially applied in electrochemical sensors and switching.

Luminescent ultrathin film of anionic styrylbiphenyl derivative-layered double hydroxide and its reversible sensing for heavy metal ions.

Ordered ultrathin films (UTFs) with blue luminescence based on a styrylbiphenyl derivative (BTBS) and Mg-Al-layered double hydroxide (LDH) nanosheets have been constructed employing the layer-by-layer assembly technique. UV-visible absorption and fluorescence spectroscopy showed a stepwise and regular growth of the films upon increasing the number of deposition cycles. XRD, AFM and SEM indicated that the films possess a periodic layered structure with a period of ca. 1.5 nm, and uniform surface morphology. The film thickness can be precisely controlled in the range ca. 15-53 nm. The BTBS-LDH UTFs exhibit improved UV-light resistance capability compared with the pristine BTBS and show well-defined polarized photoemission, with anisotropy of ca. 0.24. The UTFs show a fast, selective and reversible luminescent response to aqueous solutions containing different heavy metal ions, with the most significant luminescent quenching occurring for the Hg(2+) solution, shedding light on the fact that these films can serve as a new type of selective solid luminescent metal-ion sensor.