Highly Dispersed TiO(6) 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.     

Facile Fabrication of Highly‐Dispersed Nickel Nanoparticles with Largely Enhanced Electrocatalytic Activity

Supported nickel nanoparticles with high dispersion have been prepared by partial reduction of NiAl‐layered double hydroxide (NiAl‐LDH) precursors, which exhibit significant electrocatalytic behavior towards glucose. XRD and XPS results confirm that the nickel nanoparticles are successfully synthesized. TEM images reveal that the nickel nanoparticles are highly dispersed in the NiAl‐LDH matrix with a size of 6±0.3 nm. The resulting nanocomposite modified electrode displays significant electrocatalytic performance to glucose with a broad linear response range (8.0×10^?5–2.0×10^?3 M), low detection limit (3.6 µM), high sensitivity (339.2 µA/mM), selectivity and excellent reproducibility as well as repeatability.     

Synthesis of ionic liquid intercalated layered double hydroxides of magnesium and aluminum: A greener catalyst of Knoevenagel condensation

Due to their structural merits that arise from their stability and high surface area, the layered double hydroxide (LDH) materials have caused strong attention. These characteristics provided intriguing possibilities with improved efficiency for catalytic applications. In this work, the preparation of 1-butyl-3-methylimidazolium hydroxide ([BMIM]⁺OH⁻) intercalated by a facile approach in a layered double hydroxide (LDH) matrix is reported and its implementation as a greener catalyst is shown. Different physico-chemical techniques such as XRD, FTIR, TGA, and N₂-physisorption, HRTEM, and CO₂ adsorption are implemented to characterize the structure of the fabricated catalysts. The [BMIM]⁺OH⁻/LDH exhibit outstanding catalytic performance in Knoevenagel condensation, resulting from the high LDH surface area and synergistic effects between both the intercalated ionic liquid and LDHs matrix. Knoevenagel’s fabricated catalysts can be exploited to catalyze different condensations and can be reused well. This work therefore generates good opportunities in the field of catalysis for the preparing and implementation of LDH-based catalysts.     

催化剂Pd/TiO2-Al2O3低温下催化甲烷燃烧活性及18O同位素交换性能

Pd supported on TiO2-Al2O3 binary oxides prepared by coprecipitation method has been investigated for the total oxidation of methane. All Pd/TiO2-Al2O3 catalysts show higher activity than Pd/Al2O3 and Pd/TiO2. Among them, Pd/2Ti-3Al with a Ti/Al ratio of 2 to 3 has a T90% of 395 ℃ at a gas hourly mass velocity of 33000 mL/（h＊g）, which is at least 50 ℃ lower than that of Pd supported on single metal oxide Al2O3 or TiO2. The results of TPR and ^180-isotope exchange experiments demonstrated that the excellent activity of Pd/2Ti-3Al was due to its high oxygen mobility and moderate reducibility, which is in accordance with our previous work, XPS results indicated that the dispersion of Pd was not the key factor to influence the catalytic activity.     

Improving Thermal and Flame Retardant Properties of Epoxy Resin with Organic NiFe‐Layered Double Hydroxide‐Carbon Nanotubes Hybrids

To improve the dispersion of carbon nanotubes (CNTs) and flame retardancy of layered double hydroxide (LDH) in epoxy resin (EP), organic nickel‐iron layered double hydroxide (ONiFe‐LDH‐CNTs) hybrids were assembled through co‐precipitation. These hybrids were further used as reinforcing filler in EP. EP/ONiFe‐LDH‐CNTs nanocomposites containing 4 wt% of ONiFe‐LDH‐CNTs with different ratios of ONiFe‐LDH and CNTs were prepared by ultrasonic dispersion and program temperature curing. The structure and morphology of the obtained hybrids were characterized by different techniques. The dispersion of nanofillers in the EP matrix was observed by transmission electron microscopy (TEM). The results revealed a coexistence of exfoliated and intercalated ONiFe‐LDH‐ CNTs in polymer matrix. Strong combination of the above nanofillers with the EP matrix provided an efficient thermal and flame retardant improvement for the nanocomposites. It showed that EP/ONiFe‐LDH‐CNTs nanocomposites exhibited superior flame retardant and thermal properties compared with EP. Such improved thermal properties could be attributed to the better homogeneous dispersion, stronger interfacial interaction, excellent charring performance of ONiFe‐LDH and synergistic effect between ONiFe‐LDH and CNTs.     

Thermal and photocatalytic behavior of Ti/LDH nanocomposites

The development of nanocomposite photocatalyst based on layered double hydroxides (LDHs) associated with TiO₂ was the subject of this research. The thermally activated Zn–Al LDHs were selected as catalyst support precursor because of their proven photocatalytic activity and therefore their possible contribution to overall activity of novel Ti–Zn–Al nanocomposite. The catalyst precursor (Zn–Al LDH) was synthesized by low supersaturation coprecipitation method, and its association with active TiO₂ component targeting the formation of novel Ti–Zn–Al nanocomposite was achieved by wet impregnation. Simultaneous thermal analysis (TG–DTA) was used to investigate the thermal behavior of Zn–Al LDH and Ti–Zn–Al LDHs. Complementary, morphology, texture, and structure characterization was carried out. The photocatalytic test reaction was performed under UV light using the methylene blue degradation. The results confirmed a successful impregnation of TiO₂ on catalyst support precursor Zn–Al–LDH followed by considerable change in morphology and structure of Zn–Al LDH precursor. It was concluded that the synergic effect between TiO₂ and Zn–Al LDH precursor contributes to the overall photocatalytic activity.     

Sorption of Pb(Ⅱ) on Mg-Fe Layered Double Hydroxide

Mg‐Fe layered double hydroxide (LDH) with a Mg/Fe molar ratio of 3:1 was synthesized by using a coprecipitation method and the sorption removal of Pb(II) by the LDH sample from Pb(NO₃)₂ solution was investigated. It was found that Mg‐Fe LDH showed a good sorption ability for Pb(II) from Pb(NO₃)₂ solution, indicating that the use of LDH as a promising inorganic sorbent for the removal of heavy metal ions is possible. The sorption kinetics and the sorption isotherm of Pb(II) on the LDH sample obeyed the pseudo‐second order kinetic model and Aranovich‐Donohue equation, respectively. The sorption mechanism of Pb(II) on the LDH may be attributed to the surface‐induced precipitation and the chemical binding adsorption, and the removal ability arising from the surface‐induced precipitation is much higher than that from the chemical binding adsorption.     

Heterostructures of NiFe LDH hierarchically assembled on MoS2 nanosheets as high-efficiency electrocatalysts for overall water splitting

Typically, rational interfacial engineering can effectively modify the adsorption energy of active hydrogen molecules to improve water splitting efficiency. NiFe layered double hydroxide (NiFe LDH) composite, an efficient oxygen evolution reaction (OER) catalyst, suffers from slow hydrogen evolution reaction (HER) kinetics, restricting its application for overall water splitting. Herein, we construct the hierarchical MoS₂/NiFe LDH nanosheets with a heterogeneous interface used for HER and OER. Benefiting the hierarchical heterogeneous interface optimized hydrogen Gibbs free energy, tens of exposed active sites, rapid mass- and charge-transfer processes, the MoS₂/NiFe LDH displays a highly efficient synergistic electrocatalytic effect. The MoS₂/NiFe LDH electrode in 1 mol/L KOH exhibits excellent HER activity, only 98 mV overpotential at 10 mA/cm². Significantly, when it assembled as anode and cathode for overall water splitting, only 1.61 V cell voltage was required to achieve 10 mA/cm² with excellent durability (50 h).     

Effect of Electrolytes and Polymers on the Thixotropy of Mg‐Al‐Layered Double Hydroxides/Kaolinite Dispersions

The effect of electrolytes (NaCl and CaCl₂) and polymers (CPAM and HPAM) on the thixotropy of Mg‐Al‐layered double hydroxide (LDHs)/kaolinite dispersions has been investigated. It was observed that the type of thixotropy in LDH/kaolinite dispersions may be affected by NaCl, but not by CaCl₂ in range of concentration of interest. The type of thixotropy in LDH/kaolinite dispersion with R=0 transformed from positive thixotropy to complex thixotropy and at last positive thixotropy again with the concentration of NaCl in range of 0.00–0.10 mol·L⁻¹; the type of thixotropy in LDHs/kaolinite dispersions with R=0.25 transformed from complex thixotropy to positive thixotropy and then complex thixotropy again with the concentration of NaCl in range of 0.00–0.10 mol·L⁻¹. The type of thixotropy in LDH/kaolinite dispersion with R=0 may be not affected by cationic polyacrylamide (CPAM) and hydrolyzed polyacrylamide (HPAM); but the LDHs/kaolinite dispersions with R=0.25 transformed from complex thixotropy to positive thixotropy with the both polymers concentration in range of interest, which indicated that the microstructure of the dispersion changed from weak folc sediments structure to steric network structure.     

Synthesis and Characterization of PE-g-MA／MgAI-LDH Exfoliation Nanocomposite via Solution Intercalation

An organo‐modified MgAl‐layered double hydroxide (OMgAl‐LDH) was successfully exfoliated in the xylene solution of polyethylene‐grafted‐maleic anhydride (PE‐g‐MA) under re‐fluxing condition. A PE‐g‐MA/MgAl‐LDH exfoliation nanocomposite was formed after the precipitation of PE‐g‐MA from the dispersion system. The structure and thermal property of the PE‐g‐MA/MgAl‐LDH exfoliation nanocomposite were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry analysis (TGA). The disappearance of d₀₀₁ XRD peak of OMgAl‐LDH at 20 = 3.2° suggests that the MgAl hydroxide sheets are exfoliated in the nanocomposite. The TEM image shows that the MgAl hydroxide sheets of less than 70 nm in length or width are exfoliated and dispersed disorderly in PE‐g‐MA matrix. TGA profiles indicate that the PE‐g‐MA/MgAl‐LDH nanocomposite with 5 wt% OMgAl‐LDH loading shows a faster charring process in temperature range from 210 to 390 °C and a greater thermal stability beyond 390 °C than PE‐g‐MA does. The decomposition temperature of the nanocomposite is 25 °C higher than that of PE‐g‐MA as measured at 50% weight loss. The PE‐g‐MA/MgAl‐LDH nanocomposite is promising for application of flame‐retardant polymeric materials.     

Visible Light Photocatalytic Activity of Pt/N‐TiO2 towards Enhanced H2 Production from Water Splitting

Present work mainly focuses on experimental investigation to improvement of hydrogen production by water photoelectrolysis. An experimental facility was designed and constructed for visible light photocatalysis. A series of N‐TiO₂ photocatalysts impregnated with platinum on the surface of N‐TiO₂ were prepared. Hydrogen production upon irradiating aqueous Pt/N‐TiO₂ suspension with visible light was investigated. The shift in excitation wavelength of TiO₂ was 380 nm improved the yield of hydrogen production by N‐TiO₂ and Pt/N‐TiO₂. We used a 400 W mercury arc lamp combined with a 400 nm cutoff filter eliminating all the wavelengths under 400 nm. Pt/N‐TiO₂ material was characterized with TPR, reflective UV/Visible spectroscopy and TEM. The best hydrogen production rate obtained for this setup for N/Ti = 10, 0.05 wt% Pt/N‐TiO₂, through water splitting was about 772 μmolh^?1g^?1.     

Studies on Mechanochemical Method to Synthesize LDH Nanoparticles

Magnesium‐ferrum layered double hydroxide (Mg‐Fe‐LDH) and zinic‐aluminum layered double hydroxide (Zn‐Al‐LDH) compounds were prepared through a mechanochemical method. The influence of molar ratio of M²⁺ to M³⁺ (R value) on the property of LDH nanoparticles has been studied and the results showed that R=3:1 is the optimum value for the both samples. Besides pure water, the mixture of water and ethanol with the volume ratio of 3:1 is also used to wash the precipitates and used as suspending agent during the peptization process and our results showed that the addition of ethanol can improve the monodispersity of LDH nanoparticles greatly.     

Graphene Nanosheets as a Platform for the 2D Ordering of Metal Oxide Nanoparticles: Mesoporous 2D Aggregate of Anatase TiO2 Nanoparticles with Improved Electrode Performance

Graphene nanosheets are successfully applied as an effective platform for the 2D ordering of metal oxide nanoparticles. Mesoporous 2D aggregates of anatase TiO₂ nanoparticles are synthesized by the heat treatment of the uniformly hybridized nanocomposite of layered titanate–reduced graphene oxide (RGO) at elevated temperatures. The precursor layered titanate–RGO nanocomposite is prepared by self‐assembly of anionic RGO nanosheets and cationic TiO₂ nanosols. The calcination of the as‐prepared layered titanate–RGO nanocomposite at 500 °C induces a structural and morphological change of layered titanate nanoplates into anatase TiO₂ nanoparticles without significant modification of the RGO nanosheet. Increasing the heating temperature to 600 °C gives rise to elimination of the RGO component, leading to the formation of sheetlike porous aggregates of RGO‐free TiO₂ nanoparticles. The nanocomposites calcined at 500–700 °C display promising functionality as negative electrodes for lithium ion batteries. Among the present calcined derivatives, the 2D sheet‐shaped aggregate of TiO₂ nanoparticles obtained from calcination at 600 °C delivers the greatest specific discharge capacity with good capacity retention for all current density conditions applied. Such superior electrode performance of the nanocomposite calcined at 600 °C is attributable both to the improved stability of the crystal structure and crystal morphology of titania and to the enhancement of Li⁺ ion transport through the enlargement of mesopores. The present findings clearly demonstrate the usefulness of RGO nanosheets as a platform for 2D‐ordered superstructures of metal oxide nanoparticles with improved electrode performance.     

[Perfluorosulfonate ionomer]/[SiO2-TiO2] nanocomposites via polymer-in situ sol-gel chemistry: Sequential alkoxide procedure

In situ sol-gel chemistry was used to create inorganic/perfluoro-organic hybrids wherein titanium oxide outer regions of SiO_2[1—x/4](OH)_x nanoparticles, which were preformed in Nafion® membranes, were created by postreaction with tetrabutyltitanate (TBT). U-shaped Si and Ti distributions across the membrane thickness direction were determined via x-ray energy dispersive spectroscopy. Ti/Si ratio profiles are also U-shaped, indicating more Ti relative to Si in near-surface regions. IR spectroscopy verified structural bonding of TiO₄ units onto SiO₂ nanoparticles and indicated that alkoxide hydrolysis is not complete. Reacted silicon oxide nanophases retain the topological unconnectedness possessed by the corresponding unreacted phase. IR bands signifying molecular loops and linear fragments of Si(SINGLE BOND)O(SINGLE BOND)Si groups are seen. ²⁹Si solid-state NMR spectroscopy indicated that, for an inorganic uptake of 16.3 wt %, the Q³ state of SiO₄ is most populated although Q⁴ is only slightly less prominent and Q² and Q¹ are either small or absent. The silicon oxide component, although not being predominantly linear, retains a measure of uncondensed SiOH groups. Tensile stress vs. strain analyses suggested that TBT postreaction links nanoparticles, causing them to be contiguous over considerable distances. This percolative intergrowth occurs in near-surface regions generating a glassy zone. © 1996 John Wiley & Sons, Inc.     

Synthesis and Structural Analysis of Au-Doped TiO2/SiO2 Mixed Oxide Films Prepared by Sol-Gel Process

The systematic modifications of silica matrix as a function of modified Ti-alkoxide contents (Au nanocrystals doped TiO₂/SiO₂ mixed oxide thin films) have been investigated by the sol-gel process. A structural analysis on the various steps of the hydrolysis-condensation process as well as solid powder is determined by IR, UV-Visible, and ²⁹Si NMR spectroscopy. ²⁹Si MAS spectra are characterized by broad lines for the three types of sites. Different distributions (Q ², Q ³, and Q ⁴ units) observed in the TiO₂/SiO₂ (1 : 3) sample. Proper control of the process condition, modifying the Ti alkoxide as a less reactive precursor, improves the increase the amount of Ti–O–Si bonding in the silica network of TiO₂/SiO₂ mixed oxide matrices and the distribution of metal oxides. This method can be used for the preparation of homogeneous metal and metal-metal alloy nanocrystals deposition from mixed oxide thin films.     

Generalized Low‐Temperature Fabrication of Scalable Multi‐Type Two‐Dimensional Nanosheets with a Green Soft Template

Two‐dimensional nanosheets with high specific surface areas and fascinating physical and chemical properties have attracted tremendous interests because of their promising potentials in both fundamental research and practical applications. However, the problem of developing a universal strategy with a facile and cost‐effective synthesis process for multi‐type ultrathin 2 D nanostructures remains unresolved. Herein, we report a generalized low‐temperature fabrication of scalable multi‐type 2 D nanosheets including metal hydroxides (such as Ni(OH)₂, Co(OH)₂, Cd(OH)₂, and Mg(OH)₂), metal oxides (such as ZnO and Mn₃O₄), and layered mixed transition‐metal hydroxides (Ni‐Co LDH, Ni‐Fe LDH, Co‐Fe LDH, and Ni‐Co‐Fe layered ternary hydroxides) through the rational employment of a green soft‐template. The synthesized crystalline inorganic nanosheets possess confined thickness, resulting in ultrahigh surface atom ratios and chemically reactive facets. Upon evaluation as electrode materials for pseudocapacitors, the Ni‐Co LDH nanosheets exhibit a high specific capacitance of 1087 F g^?1 at a current density of 1 A g^?1, and excellent stability, with 103 % retention after 500 cycles. This strategy is facile and scalable for the production of high‐quality ultrathin crystalline inorganic nanosheets, with the possibility of extension to the preparation of other complex nanosheets.     

Development of air‐assisted dispersive micro‐solid‐phase extraction‐based supramolecular solvent‐mediated Fe3O4@Cu–Fe–LDH for the determination of tramadol in biological samples

A simple method, air‐assisted dispersive micro‐solid‐phase extraction‐based supramolecular solvent was developed for the preconcentration of tramadol in biological samples prior to gas chromatography–flame ionization detection. A new type of carrier liquid, supramolecular solvent based on a mixture of 1‐dodecanol and tetrahydrofuran was combined with layered double hydroxide coated on a magnetic nanoparticle (Fe₃O₄@SiO₂@Cu–Fe–LDH). The supramolecular solvent was injected into the solution containing Fe₃O₄@SiO₂@Cu–Fe–LDH in order to provide high stability and dispersion of the sorbent without any stabilizer agent. Air assisted was applied to enhance the dispersion of the sorbent and solvent. A number of analytical techniques such as Fourier transform‐infrared spectrometry, field emission scanning electron microscope, energy‐dispersive X‐ray spectroscopy and X‐ray diffraction measurements were applied to assess the surface chemical characteristics of Fe₃O₄@SiO₂@Cu–Fe–LDH nanoparticles. The effects of important parameters on the extraction recovery were also investigated. Under optimized conditions, the limits of detection and quantification were obtained in the range of 0.9–2.4 and 2.7–7.5 μg L^?1 with preconcentration factors in the range of 450–472 in biological samples. This method was used for the determination of tramadol in biological samples (plasma, urine and saliva samples) with good recoveries.     

超声化学技术合成MnO2/MoS2纳米交互积层材料

层状氧化锰在氢氧化四甲基胺溶液中超声处理20分钟后，层状氧化锰剥离成纳米层胶体分散液。层状LiMoS₂在超声条件下浸入到10^-4M HNO₃溶液中，随后将得到的处理液加入到层状氧化锰纳米层胶体分散液中，超声处理合成得到了MnO₂/MoS₂纳米交互积层材料，提出了相同电性无机纳米层间超声化学合成新型交互积层材料新技术。     

Preparation and Properties of Transparent Ultrathin Lanthanide‐Complex Films

Highly transparent ultrathin films (UTFs) based on alternative layer‐by‐layer assembly of Eu‐ and Tb‐based lanthanide complexes (LCs) and Mg–Al‐layered double hydroxide (LDH) nanosheets are reported herein. UV–visible absorption and fluorescence spectroscopy showed an orderly growth of the two types of ultrathin films upon increasing the number of deposition cycles. AFM and SEM measurements indicate that the films feature periodic layered structures as well as uniform surface morphology. Luminescent investigations reveal that (LCs/LDH)_n UTFs can detect Fe³⁺ with relative selectivity and high sensitivity (Stern–Volmer constant K_SV=8.43×10³ L mol^?1); this suggests that (LCs/LDH)_n UTFs could be a promising luminescent probe for selectively sensing Fe³⁺ ion.     

Thermal behavior of LDH 2CuAl.CO<Subscript>3</Subscript> and 2CuAl.CO<Subscript>3</Subscript>/Pd

Cu/Al layered double hydroxide (LDH) can be used as a catalyst for important processes such as cross-coupling reactions. This property may be improved by adding palladium by either impregnation or intercalation. Therefore, the LDH matrix and its composites with Pd⁰ or [PdCl₄]^2? have been prepared. By powder X-ray diffraction, FT-infrared spectroscopy, thermogravimetric and elemental analysis it was determined the LDH formula Cu₄Al₂(OH)₁₂CO₃.4H₂O, with malachite as the second phase. The LDH thermal decomposition occurs between 120 and 600 °C, having as intermediates the double oxi-hydroxide and the mixed oxide phases. At 800 °C the residue is composed of CuO and CuAl₂O₄. The composites were obtained employing [PdCl₄]^2? and Pd₂(dba)₃ as precursors, and the solvent choice for this process was shown to be of significant importance: the materials obtained using DMF had Pd impregnated in the surface, while the usage of water promoted the intercalation of [PdCl₄]^2? in the LDH matrix. The thermogravimetric analysis was able to distinguish the mode of supporting palladium between the composites being a reliable characterization for such task.