Unraveling Sequential Oxidation Kinetics and Determining Roles of Multi-Cobalt Active Sites on Co3O4 Catalyst for Water Oxidation.

The multi-redox mechanism involving multi-sites has great implications to dictate the catalytic water oxidation. Understanding the sequential dynamics of multi-steps in oxygen evolution reaction (OER) cycles on working catalysts is a highly important but challenging issue. Here, using quasi-operando transient absorption (TA) spectroscopy and a typical photosensitization strategy, we succeeded in resolving the sequential oxidation kinetics involving multi-active sites for water oxidation in OER catalytic cycle, with Co3O4 nanoparticles as model catalysts. When OER initiates from fast oxidation of surface Co2+ ions, both surface Co2+ and Co3+ ions are active sites of the multi-cobalt centers for water oxidation. In the sequential kinetics (Co2+ → Co3+ → Co4+), the key characteristic is fast oxidation and slow consumption for all the cobalt species. Due to this characteristic, the Co4+ intermediate distribution plays a determining role in OER activity and results in the slow overall OER kinetics. These insights shed light on the kinetic understanding of water oxidation on heterogeneous catalysts with multi-sites.

Identifying and Removing the Interfacial States in Metal-Oxide-Semiconductor Schottky Si Photoanodes for the Highest Fill Factor.

A critical bottleneck for realizing an efficient Schottky type Si photoelectrode is minimizing the charge extraction losses across the heterointerface via reducing the unfavorite defects. This requires a clear microscopic insight into the correlation between interfacial features and photoconversion. Herein, by taking the n-Si/oxide (MOx)/Ni as the prototype, the heterointerface with the different characteristics and its effects on charge transportation and the corresponding photoelectric/photoelectrochemical (PEC) behaviors were clarified. An ultra-thin AlOx layer can effectively diminish the interfacial pinning of n-Si/Ni and significantly facilitate the photoconversion; meanwhile, it results in some unexpected donor-like deep defects at around 0.59 eV below the conduction band of n-Si, which could be ionized under a reverse bias and cause about 10% photogenerated charge recombination. Fortunately, these deep defects can be further eliminated by cooperating AlOx with a thin Au layer. The AlOx/Au dual-interlayer can remove almost all unexpected defects and maximize the efficiency of the electric field for charge extraction from semiconductor Si for the surface catalytic reaction. Eventually, the n-Si/SiOx/AlOx/Au/Ni/NiFeOx photoanode exhibited a record fill factor of 0.75 for the corresponding photoelectric device and an applied bias photon-to-current efficiency of 3.71% for PEC water oxidation. This study provides definite insights into interfacial electronic states and elaborates their crucial role in solar photoelectric conversion.

Simultaneous separation and determination of five chlorogenic acid isomers in Honeysuckle by capillary electrophoresis using self-synthesized ionic liquid [N-methylimidazole-ß-cyclodextrin] [bromide] as separation selector.

A simple, comprehensive, and efficient capillary electrophoresis method using a self-synthesized ionic liquid [N-methylimidazole-ß-cyclodextrin] [bromide] as a separation selector was developed for the simultaneous separation and determination of five chlorogenic acid isomers (chlorogenic acid, cryptochlorogenic acid, neochlorogenic acid, isochlorogenic acid A, isochlorogenic acid B). After optimization of separation conditions, the electrolyte solution was 50 mM ammonium acetate buffer containing 0.7% (w/w) ionic liquid [N-methylimidazole-ß-cyclodextrin] [bromide] (pH 4.8), 15 kV of the electric field was applied at 25°C, and the detection wavelength was at 237 nm. Under the optimal separation conditions, good linearities were obtained with linear correlation coefficients of the five analytes of 0.9994-0.9998, and the limits of detection and the limits of quantification were 0.6-2.8 and 2.2-9.5 µg/ml. Excellent accuracy and precision were obtained for the five analytes. The intraday and interday precision of standards ranged from 0.5 to 1.3% and from 1.2 to 1.9%. The intraday and interday precision of samples ranged from 1.0 to 1.9% and from 1.2 to 2.6%. The sample recovery rates were between 98.0 and 101.8%. This method was successfully applied for the analysis of five components in Honeysuckle Chinese medicinal preparations. The mechanisms involved in the separation of five analytes by [N-methylimidazole-ß-cyclodextrin] [bromide] were discussed.

Metal-free iodine(iii)-promoted synthesis of 2,5-diaryloxazoles.

A nonmetal-catalyzed oxidative cyclization to achieve 2,5-disubstituted oxazoles from inexpensive and readily available substituted chalcone, (diacetoxyiodo)benzene (PIDA) and ammonium acetate (NH4OAc) at room temperature is described. The reaction forms a variety of 2,5-diaryloxazoles in good to excellent yields with broad substrate scope under mild conditions without the requirement of ligands and additional bases.

Approach for 2-(arylthio)imidazoles and imidazo[2,1-b]thiazoles from imidazo[2,1-b][1,3,4]thiadiazoles by ring-opening and -reconstruction.

A highly efficient one-pot synthesis of imidazo[2,1-b]thiazole derivatives has been developed and proceeds via a ring-opening and ring-closing reconstruction of imidazo[2,1-b][1,3,4]thiadiazoles with phenylacetylene in the presence of potassium tert-butoxide (t-BuOK) under very mild reaction conditions. A proposed mechanism is calculated computationally using a DFT method at the B3LYP/6-31+G(d,p) level. The imidazo[2,1-b][1,3,4]thiadiazoles are also successfully converted to a series of 2-(arylthio)-1H-imidazoles using aryl halide as a reactant and copper(ii) acetylacetonate (Cu(acac)2) as a catalyst under microwave irradiation conditions. The key features of these reactions are the use of readily available reagents, simple operation, the convenient utilization of new heterocyclic synthons, and a great variety of substrates with functional group compatibility.

Aza-crown ether complex cation ionic liquids: preparation and applications in organic reactions.

Aza-crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG-DTA), elemental analysis and physical properties. These new and room-temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO2 to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel-Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza-[18-C-6HK][HSO4]2 was the best acidic catalyst in the reactions of esterification and Friedel-Crafts alkylation under mild reaction conditions.

Combined use of [TBA][L-ASP] and hydroxypropyl-ß-cyclodextrin as selectors for separation of Cinchona alkaloids by capillary electrophoresis.

In this paper, a new capillary electrophoresis (CE) separation and detection method was developed for the chiral separation of the four major Cinchona alkaloids (quinine/quinidine and cinchonine/cinchonidine) using hydroxypropyl-ß-cyclodextrin (HP-ß-CD) and chiral ionic liquid ([TBA][L-ASP]) as selectors. Separation parameters such as buffer concentrations, pH, HP-ß-CD and chiral ionic liquid concentrations, capillary temperature, and separation voltage were investigated. After optimization of separation conditions, baseline separation of the three analytes (cinchonidine, quinine, cinchonine) was achieved in fewer than 7 min in ammonium acetate background electrolyte (pH 5.0) with the addition of HP-ß-CD in a concentration of 40 mM and [TBA][L-ASP] of 14 mM, while the baseline separation of cinchonine and quinidine was not obtained. Therefore, the first-order derivative electropherogram was applied for resolving overlapping peaks. Regression equations revealed a good linear relationship between peak areas in first-order derivative electropherograms and concentrations of the two diastereomer pairs. The results not only indicated that the first-order derivative electropherogram was effective in determination of a low content component and of those not fully separated from adjacent ones, but also showed that the ionic liquid appeared to be a very promising chiral selector in CE.

Palladium-catalyzed microwave-assisted direct arylation of imidazo[2,1-b]thiazoles with aryl bromides: synthesis and mechanistic study.

A palladium-catalyzed direct C-H arylation of various imidazo[2,1-b]thiazoles with a range of aryl bromides under microwave irradiation is described. 6-Phenyl substituted imidazo[2,1-b]thiazoles could be regioselectively C-5 arylated using the developed protocol. The utility of this method enables the representative coupling product to be achieved by a sequential one-pot reaction. Density functional theory (DFT) calculations show that this arylation proceeds via a concerted metalation-deprotonation (CMD) pathway, which is in agreement with our experimental results. This work provides a convenient access to a variety of biologically active imidazo[2,1-b]thiazole derivatives. Also, it enriches the mechanism study of site-selective C-H arylation in fused heterocycles, and offers a valuable guide to design highly efficient catalytic systems for the preparation of similar compounds.

Photoelectrothermocatalytic reduction of CO2 to glycol via Cu2S/MoS2-Vs octahedral heterostructure with synergistic mechanism.

The defects and interface engineering are efficient approaches to adjust the physical and chemical properties of nanomaterials to enhance catalytic performance. In this study, we report a new MOFs-driven porous Cu2S/MoS2-Vs octahedral semiconductor with heterostructure and photothermal effect. The introduction of sulfur vacancies directly improves the adsorption performance of CO2, and the formation of heterostructure significantly increases the charge transfer rate. The C-penetrating material obtained from MOFs not only acts as an octahedral skeleton support, but also gives photothermal effects under photoelectric conditions. The formation rate of sole C2 products in photoelectrocatalytic CO2 reduction by using Cu2S/MoS2-Vs heterostructure is up to 52 µM·h-1·cm-2 equal to the total electron transfer rate of 541 µM·h-1·cm-2. The carbene mechanism and reaction pathways were proposed and verified by 13CO2 isotopic labelling and operando Fourier transform infrared (FT-IR) spectra. The important intermediates of *CO2-, *CO, *CHO and *CHO-CHO were identified by operando FT-IR spectra. In the comparative experiments, the photothermal electrons are beneficial to C2 products. DFT calculations indicate that the presence of S vacancies (Vs) reduces the energy barrier for product generation.

Bipolar charge collecting structure enables overall water splitting on ferroelectric photocatalysts.

Ferroelectrics are considered excellent photocatalytic candidates for solar fuel production because of the unidirectional charge separation and above-gap photovoltage. Nevertheless, the performance of ferroelectric photocatalysts is often moderate. A few studies showed that these types of photocatalysts could achieve overall water splitting. This paper proposes an approach to fabricating interfacial charge-collecting nanostructures on positive and negative domains of ferroelectric, enabling water splitting in ferroelectric photocatalysts. The present study observes efficient accumulations of photogenerated electrons and holes within their thermalization length (~50 nm) around Au nanoparticles located in the positive and negative domains of a BaTiO3 single crystal. Photocatalytic overall water splitting is observed on a ferroelectric BaTiO3 single crystal after assembling oxidation and reduction cocatalysts on the positively and negatively charged Au nanoparticles, respectively. The fabrication of bipolar charge-collecting structures on ferroelectrics to achieve overall water splitting offers a way to utilize the energetic photogenerated charges in solar energy conversion.

Crown ether complex cation ionic liquids: preparation and applications in organic reactions.

A series of crown ether complex cation ionic liquids (CECILs) were designed, synthesised and characterised by NMR spectroscopy, HRMS, thermogravimetric differential thermal analysis (TG-DTA) and elemental analysis. Their applications in various organic reactions were investigated: [15-C-5Na][OH], [15-C-5Na][OAc], [18-C-6K][OH] and [18-C-6K][OAc] (15-C-5=[15]crown-5; 18-C-6=[18]crown-6) efficiently catalysed the Michael addition of alkenes and relevant nucleophiles; [18-C-6K][OH] and [15-C-5Na][OH] effectively catalysed the Henry reaction of nitromethane and aromatic aldehydes; [18-C-6K][OH] has excellent catalytic efficiency for Knoevenagel condensation of aromatic aldehydes and malononitrile; PdCl(2) /[18-C-6K](3)[PO(4)]/K(2)CO(3) efficaciously catalysed the Heck reaction of olefins and aromatic halides; [18-C-6K][BrO(3)] can be used as both oxidant and solvent in the oxidation reaction of aromatic alcohols. The CECIL catalysts [15-C-5Na][OH] (Michael addition) and [18-C-6K][OH] (Henry reaction) can be recycled and reused several times without obvious loss of activity and their recovery is very simple.

One approach to cyclic carbonates via a three-component cyclization of phenacyl bromide, CO2, and aldehyde.

A three-component cyclization reaction was designed for synthesizing cyclic carbonates in a single operation from phenacyl bromide, CO(2), and aldehyde in the presence of lithium diisopropylamide (LDA). These novel reactions were achieved under extremely mild conditions to generate the target products in moderate to good yields within 10 min.

Photoelectrocatalytic Reduction of CO2 to Paraffin Using p-n Heterojunctions.

Nowadays, photoelectrocatalytic (PEC) reduction of CO2 represents a very promising solution for storing solar energy in value-added chemicals, but so far it has been hampered by the lack of highly efficient catalyst of photocathode. Enlightened by the Calvin cycle of plants, here we show that a series of three-dimensional C/N-doped heterojunctions of Znx:Coy@Cu are successfully fabricated and applied as photocathodes in the PEC reduction of CO2 to generate paraffin product. These materials integrate semiconductors of p-type Co3O4 and n-type ZnO on Cu foam to construct fine heterojunctions with multiple active sites, which result in excellent C-C coupling control in reduction of CO2. The best catalyst of Zn0.2:Co1@Cu yields paraffin at a rate of 325 µg·h-1 under -0.4 V versus saturated calomel electrode without H2 release. The apparent quantum efficiency of PEC cell is up to 1.95%.

Internal-Field-Enhanced Charge Separation in a Single-Domain Ferroelectric PbTiO3 Photocatalyst.

Ferroelectric materials with spontaneous polarization-induced internal electric fields have drawn increasing attention in solar fuel production due to the intrinsic polarized structure. However, the origination of charge separation in these materials at the nano/microlevel is ambiguous owing to the complexity of the multielectric fields. Besides, the observed charge separation ability is far from theoretical expectation. Herein, by spatially resolved surface photovoltage spectroscopy, it is clearly demonstrated that the depolarization field in single-domain ferroelectric PbTiO3 (PTO) nanoplates is the main driving force for charge separation and it can effectively drive photogenerated electrons and holes to the positive and negative polarization facets, respectively. Moreover, the charge separation ability of PTO nanoplates increases with increasing particle size along the polarization direction, due to the increasing potential difference between the opposite polarization facets. Furthermore, this driving force for charge separation directly contributes to the enhancement of the photocatalytic hydrogen evolution reaction activity in ferroelectrics. Finally, it is proved that the screening field compensates part of the depolarization field and can be diminished by adding a dielectric layer on the ferroelectric surface. These findings demonstrate the importance of increasing the depolarization field and decreasing the screening field for efficient charge separation in ferroelectric semiconductor photocatalysts.

Artificial Photosynthesis of Alcohols by Multi-Functionalized Semiconductor Photocathodes.

Novel artificial photosynthesis systems are devised as cells of dye/Pd/NR-MOx (M=Ti, Zn)∥CoPi/W:BiVO4 that convert efficiently CO2 to alcohols. The photocathodes are aminofunctionalized, palladium-deposited, and in situ sensitized nano-TiO2 or ZnO/FTO (FTO: fluorine-doped tin oxide) electrodes that are characterized by X-ray photoelectron spectroscopy (XPS), TEM, XRD, UV/Vis spectra, and evaluated by electrochemical techniques. The cell of dye/Pd/S-TiO2 ∥CoPi/W:BiVO4 uniquely generates ethanol under irradiation of 200 mW cm-2 , reaching 0.56 % quantum efficiency (QE) at -0.56 V and 0.13 % QE without external electron supply. The cell of dye/Pd/ N-ZnO∥CoPi/W:BiVO4 produces solely methanol at a rate of 42.8 µm h-1 cm-2 at -0.56 V of a Si solar cell, which is far less than the electrochemical voltage of water splitting (1.23 V). Its QE reaches to 0.38 %, which is equal to plants. The isotopic labeling experiments confirm the carbon source and oxygen releasing. The selectivity for alcohols of multi-functionalized semiconductors is discussed.

Palladium-Catalyzed Intramolecular Dearomatization of Indoles via Decarboxylative Alkynyl Termination.

A highly diastereoselective dearomatization of indoles via palladium-catalyzed decarboxylative alkynyl termination was developed. This protocol provides dissimilar tetracyclic and tetrasubstituted indoline scaffolds bearing congested stereocenters, which led to operationally simple conditions, short time, and broad substrate scope. Additionally, this reaction system could be scaled to gram quantities in a satisfactory yield and diastereoselectivity.

Tunable catalytic activities and selectivities of metal ion doped TiO2 nanoparticles--oxidation of organic compounds.

A series of metal ion doped TiO2 nanoparticles (M-TiO2, M = Cr(3+), Mn(2+), Fe(3+), V(5+), Zn(2+), Ni(2+), Ag(+), Cu(2+) and Co(2+)) were prepared by a facile co-precipitation approach and characterized by means of ICP-AES, N2 adsorption-desorption isotherms, XRD, TEM and HRTEM. Their catalytic performance was investigated via the oxidation of organic compounds. The variation of metal ion species and doping contents allowed tuning the catalytic properties of the M-TiO2. Among them, the catalyst Cu-10 displayed excellent activity (97.5%) in the oxidation of styrene and the selectivity of benzaldehyde was as high as 99.4%. Surprisingly, the product distribution of styrene oxidation experienced a reverse trend over the Co-TiO2 catalysts with different doping amounts of cobalt ions: Co-10 was in favor of forming benzaldehyde (80.2% selectivity), in contrast with Co-15, which produced styrene oxide as the dominant product (84.7% selectivity). The M-TiO2 catalysts also showed catalytic activities for the oxidation of benzyl alcohol and toluene to generate chlorine-free benzaldehyde in excellent selectivities (>99%).

Strategy to improve photovoltaic performance of DSSC sensitized by zinc prophyrin using salicylic acid as a tridentate anchoring group.

Three new zinc porphyrin dyes attached to ethynyl benzoic acid as an electron transmission and anchoring group have been designed, synthesized, and well-characterized. The performances of their sensitized solar cells have been investigated by optical, photovoltaic, and electrochemical methods. The photoelectric conversion efficiency of the solar cells sensitized by the dye with salicylic acid as an anchoring group demonstrated obvious enhancement when compared with that sensitized by the dye with carboxylic acid as an anchoring group. The density functional theory calculations and the electrochemical impedance spectroscopies revealed that tridentate binding modes could increase the efficiency of electron injection from dyes to the TiO2 nanoparticles by more electron pathways.

Chiral separation and determination of amino acids in real samples by LE-MEKC using Cu(II)-L-proline as chiral selector.

This work reports that Cu(II) complexes with l-proline were used as chiral additives for the enantioseparations and determination of three underivatized amino acids by ligand-exchange micellar electrokinetic chromatography (LE-MEKC). Sodium dodecylsulfate (SDS) was shown to be necessary for simultaneous separation of the enantiomeric amino acids. Separation parameters such as SDS concentrations, the Cu(II)-l-proline ratio, the concentration of the copper(II) complex at a specific Cu(II)-l-proline ratio, pH and separation voltage were investigated for the enantioseparation in order to achieve the maximum possible resolution. A good separation was achieved in the BGE composing of 10mM ammonium acetate, 10mM Cu(II) and 20mM l-proline and 30 mM SDS at pH 5.0, and an applied voltage of 15 kV performed. Under above-mentioned optimum conditions, linearity was achieved within concentration ranges of up to two orders of magnitudes for the investigated amino acids with the correlation coefficients ranging from 0.9917 to 0.9984. The proposed method has been successfully applied to the determination of amino acid enantiomers in human urine, compound amino acids injection, and amino acid oral liquid.

Salicylic acid as a tridentate anchoring group for azo-bridged zinc porphyrin in dye-sensitized solar cells.

Two series dyes of azo-bridged zinc porphyrins have been devised, synthesized, and performed in dye-sensitized solar cells, in which salicylic acids and azo groups were introduced as a new anchoring group and π-conjugated bridge via a simple synthetic procedure. The representation of the new dyes has been investigated by optical, photovoltaic, and electrochemical means. The photoelectric conversion efficiency of their DSSC devices has been improved compared with other DSSC devices sensitized by symmetrical porphyrin dyes. The results revealed that tridentate binding modes between salicylic acid and TiO2 nanoparticles could enhance the efficiency of electron injection. The binding modes between salicylic acid and TiO2 nanoparticles may play a crucial role in the photovoltaic performance of DSSCs.