Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide Over ZrO<Subscript>2</Subscript>-based Composite Oxide Catalysts

We have been exploring various new catalyst systems for the utilization of carbon dioxide as a soft oxidant in the catalytic dehydrogenation of ethylbenzene (EB) to styrene. The utilization of CO₂ as a soft oxidant for the commercially important catalytic dehydrogenation of EB to styrene has received enormous attention recently due to its several attractive features. This review summarizes the results of our most recent findings on zirconia-based composite oxide catalyst systems exploited for this reaction. Under this systematic and comprehensive investigation various zirconia-based composite oxide catalysts namely, TiO₂-ZrO₂, MnO₂-ZrO₂, CeO₂-ZrO₂, K₂O/TiO₂-ZrO₂, B₂O₃/TiO₂-ZrO₂ and CeO₂-ZrO₂/SBA-15 have been synthesized, characterized by various techniques and evaluated for the title reaction. Most of these composite oxide catalysts were found to exhibit very interesting physicochemical characteristics and exceptionally better catalytic properties for this reaction. As revealed by characterization results, a large number of acid–base sites with moderate strength are essential for a high conversion and product selectivity of this reaction with CO₂ as the soft oxidant.     

Ab initio study of magnetic interactions of manganese-oxide clusters

The manganese clusters have attracted much attention in relation with the oxygen evolving center (OEC) in photosystem II (PS II) system, which catalyzes the water oxidation reaction. Previously, we examined various spin-structures of Mn(II)₄O₄ model clusters, of which all of magnetic interactions are antiferromagnetic. In this study, we investigated electronic and magnetic structures of simple model clusters, Mn₄O₄(OAc)₆ and Mn₃CaO₄(OAc)₆ using spin unrestricted B3LYP (UB3LYP) method. The UB3LYP method is a standard tool for this study and has been in fact employed by many researchers. However, several peculiar features are observed for these model clusters: for instance the most stable spin state becomes the highest spin state for Mn(IV)₄O₄(OAc)₆ although this model cluster consists of superexchange type of units, Mn(IV)₂O₂ that usually favors antiferromagnetic spin alignments. Implications of the comparative results are discussed in relation to the electrophilic (or radical) mechanism for the O-O bond formation in the OEC.     

Hydrogen sulfide conversion: How to capture hydrogen and sulfur by photocatalysis

H₂S is a notorious gas widely generated in the petrochemical industry. How to handle H₂S effectively and convert it into highly-valued products is vital. Photocatalysis is promising in this field, as it could directly utilize solar light and convert H₂S into H₂ and S. In this review, the properties of hydrogen sulfide (H₂S) is overviewed first, and conventional techniques (Claus process, thermolysis, non-thermal plasma, electrochemistry and other methods) for H₂S conversion are simply introduced. Basic knowledge of photocatalysis and general strategies for enhancing the activities of photocatalysts are presented as well. Then typical work for photocatalytic conversion of H₂S in gas phase and liquid phase are introduced case by case, with the generated H₂ as the main product in these systems. Furthermore, methods for extraction of elemental sulfur from H₂S by photocatalysis-related methods were discussed, with specific attention on photoelectrochemical cells and photovoltaic-electrochemical cells. In the end, current status of the research on photocatalytic conversion of H₂S is summarized, and challenges in this field is put forward. In addition, some other possible strategies for photocatalytic conversion of H₂S into highly-valued chemicals instead of hydrogen and elemental sulfur will be discussed, which is aimed to inspire researchers interested in this field.     

A Hierarchical Nanostructured Carbon Nanofiber–In2S3 Photocatalyst with High Photodegradation and Disinfection Abilities Under Visible Light

Photocatalytic degradation of pollutants under visible light provides a new door to solve the water contamination problem by utilizing free and renewable sunlight. The search for highly efficient photocatalysts with hierarchical nanostructures remains crucial for accessing this new door. In this work, a new hierarchical nanostructured photocatalyst is designed and synthesized, for the first time, by anchoring In₂S₃ flower‐like nanostructures on non‐woven carbon nanofiber (CNF). The nanostructures of these CNF–In₂S₃ composites were fine‐tuned, with the aim of achieving the highest photocatalytic activity under visible light. The formation mechanism of the hierarchical nanostructure is also investigated. The results indicate that the optimized hierarchical CNF–In₂S₃ photocatalyst is superior in photodegradation and disinfection efficiency to that of pure In₂S₃ under visible‐light irradiation. The prominent photocatalytic activities of these hierarchical CNF–In₂S₃ photocatalysts can be attributed to the excellent properties of enhanced light absorption, large surface area, and efficient charge separation, which are all derived from the special three‐dimensional hierarchical nanostructures. Therefore, this work presents the great potential of this hierarchical nanostructured CNF–In₂S₃ photocatalyst in practical environmental remediation fields.     

Competitive immunoassay for monitoring polybrominated diphenyl ethers in PM2.5 in Shanghai

In this paper, a sensitive biotin–streptavidin (BS)-ELISA was developed for determining the polybrominated diphenyl ethers in PM_2.5. For establishing this proposed BS-ELISA, we prepared the biotinylated antibody primarily. And for reducing the background interference, some in?uencing factors and procedures for this immunoassay were also discussed and optimised. Under the optimal conditions, the IC₅₀ = 0.53 ng/mL; IC₁₀ was 0.002 ng/mL; and the results were almost consistent with those using the gas chromatography and electron capture detection (GC-ECD). Less procedures and simpler sample preparation were required for this method compared with the GC-ECD. The results showed that the highest value of BDE-47 concentration occurred in December, which might re?ect the combination of heating and industrial pollution. In our analysis, we studied the Pearson correlations between BDE-47/PM_2.5 and gaseous pollutants (such as NO₂, SO₂, CO, O₃, PM₁₀ and PM_2.5). BDE-47 showed a higher correlation with NO₂ than that with PM₁₀, PM_2.5 and SO₂, which implied that the BDE-47 emission process might be accompanied by the emission of NO₂. Moreover, during the Spring Festival, the concentration of BDE-47 in PM_2.5 decreased significantly, whereas the PM_2.5 changed little. This suggested factories and vehicles might be the major contributors to BDE-47 emissions (but not to PM_2.5).     

Recent advances in strategies for highly selective electrocatalytic N2 reduction toward ambient NH3 synthesis

Industrial NH₃ production mainly relies on the Haber–Bosch process, which is energy-intensive, heavily dependent on fossil fuels with massive greenhouse gas emission. Electrochemical N₂-to-NH₃ conversion is an attractive method to address this issue. The great challenge for this process is its limited selectivity because of the competitive hydrogen evolution reaction and the sluggish kinetics of N₂ reduction reaction. In this review, we summarize recent progress in strategies in improving the NH₃ selectivity for the electrochemical N₂ reduction reaction, including electrocatalyst tuning, electrolyte choice, and cell configuration design.     

Selection of Microalgae and Cyanobacteria Strains for Bicarbonate-Based Integrated Carbon Capture and Algae Production System

Using microalgae to capture CO₂ from flue gas is an ideal way to reduce CO₂ emission, but this is challenged by the high cost of carbon capture and transportation. To address this problem, a bicarbonate-based integrated carbon capture and algae production system (BICCAPS) has been proposed, in which bicarbonate is used for algae culture, and the regenerated carbonate from this process can be used to capture more CO₂. High-concentration bicarbonate is obligate for the BICCAPS. Thus, different strains of microalgae and cyanobacteria were tested in this study for their capability to grow in high-concentration NaHCO₃. The highest NaHCO₃ concentrations they are tolerant to were determined as 0.30 M for Synechocystis sp. PCC6803, 0.60 M for Cyanothece sp., 0.10 M for Chlorella sorokiniana, 0.60 M for Dunaliella salina, and 0.30 M for Dunaliella viridis and Dunaliella primolecta. In further study, biomass production from culture of D. primolecta in an Erlenmeyer flask with either 0.30 M NaHCO₃ or 2 % CO₂ bubbling was compared, and no significant difference was detected. This indicates BICCAPS can reach the same biomass productivity as regular CO₂ bubbling culture, and it is promising for future application.     

Simultaneous Determination of Ten Estrogens and their Metabolites in Waters by Improved Two-Step SPE Followed by LC–MS

Ten highly potent estrogens including estrone (E₁), 17β-estradiol (E₂), estriol (E₃), 4-hydroxyestrone (4-OHE₁), 2-hydroxyestradiol (2-OHE₂), 16α-hydroxyestrone (16α-OHE₁), 2-methoxyestrone (2-MeO-E₁), 2-methoxyestradiol (2-MeO-E₂), diethylstilbestrol (DES), 17α-ethynylestradiol (EE₂) were identified and quantified by solid-phase extraction followed by liquid chromatography–mass spectrometry. An improved two-step SPE process was employed in this work. C18 cartridge was used for both enrichment of all target estrogens and retention of some nonpolar impurities, and then a polar florisil cartridge was subsequently used to separate the interested estrogens from the polar impurities. After this pretreatment for water samples, the results showed clean chromatograms without interference from matrix effects. Besides, this method was accurate (recovery percentages between 70.4 and 106.8% for river water and 73.4 and 101.3% for raw sewage, except 4-OHE₁ and 2-OHE₂), and precise (RSD varying between 1.3 and 17.8% for river water and 3.4 and 16.7% for raw sewage). In the optimized condition, this method was used to verify the presence of the target analytes in the Qinghe River and influent of sewage treatment plant in the northwest of Beijing, China. Some estrogens were detected in the river water and sewage water samples at a relatively high concentration. The developed method proved to be effective for analyzing estrogen compounds in complex matrices. Moreover, the achieved results demonstrated that a great concern should be addressed to the potential risk of the presence of estrogens in the aquatic environment.     

适用于汽油参比燃料TRF的多环芳香烃生成机理

构造了一个包括287种组分和1569个反应的汽油参比燃料TRF(toluene reference fuel)燃烧过程中多环芳香烃(PAHs)生成机理的详细化学反应动力学模型,引入四种PAH生长路径将多环芳香烃的生成机理发展到芘A4(C20H12)水平,并通过对PAH产率的分析,指出乙炔(C2H2)、丙炔(C3H3)、乙烯基乙炔(C4H4)以及含有奇数碳原子的环戊二烯自由基(C5H5)和茚基(C9H7)等物质对PAHs生成和生长起到重要作用.该机理可以较准确计算基础燃料(PRF)和TRF火焰的着火延迟期、燃烧火焰中小分子(PAH前驱体C2H2、C3H4等)和PAHs的物质浓度.通过与实验数据的比较表明,该机理在不同温度、压力、化学计量比下具有较好的性能.由此分析,该机理对碳烟前驱物PAHs的预测性能是可靠的.     

CO2还原反应二维电催化剂研究进展

二氧化碳(CO₂)电化学还原为高附加值化学品在解决CO₂过量排放上具有极好的应用前景,但这需要开发先进的电催化剂来降低CO₂活化能并提高还原产物的选择性。受益于独特的几何结构,二维材料在电催化CO₂还原反应中得到了广泛研究。本综述将系统介绍应用于CO₂还原反应的二维电催化剂上的最新进展。我们也将揭示特征结构与电催化性能之间的构效关系。我们希望本文可以为开发CO₂还原电催化剂提供有益的指导。     

Electrochemical polymerization of aniline in phosphoric acid

The electrochemical synthesis of common conductive polymers such as polyaniline in phosphoric acid is a little different from that in other acidic media such as sulfuric acid. Electropolymerization in phosphoric acid is difficult, and this electrolyte medium is not applicable for this purpose. However, it is possible to overcome this problem by the addition of a small amount of sulfuric acid. In this case, the electropolymerization process can be successfully performed when the phosphate ion is doped. For instance, polyaniline films electrodeposited from an electrolyte solution of phosphoric acid have good stabilities and useful morphologies. Interestingly, phosphate doping results in the formation of nanostructures, whereas the polymer surface is macroscopically smooth. In an appropriate ratio, a mixed electrolyte of H₃PO₄ and H₂SO₄ can be used for the electropolymerization of aniline; thus, H₂SO₄ acts as a required agent for successful polymer growth, and H₃PO₄ acts as a doping agent. In this case, a small amount of sulfate is incorporated into the polymer matrix, which does not participate in the electrochemical insertion/extraction process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3304–3311, 2006     

Topology and Equilibrium Analysis of the Monovalent Aluminum Compound Al4Cp*Ph4

The theoretical structure and thermochemistry of the tetrameric, low‐valence aluminum compound Al₄Cp*^Ph₄ (Cp*^Ph = C₅Me₄Ph) is discussed. The first synthesis of this compound was reported in 2005, but the compound failed to crystallize and experimental ²⁷Al NMR results were inconclusive in regard to the degree of association. Here density functional theory combined with a genetic algorithm is used to predict the expected structure and properties for Al₄Cp*^Ph₄. Synthesis efforts were repeated for this compound, resulting in a product with a ²⁷Al NMR chemical shift that differed from the previous report by nearly 20 ppm. However, calculated ²⁷Al NMR chemical shifts for the theoretically predicted structure are within one ppm of these new experimental results, strongly suggesting the tetrameric form has been synthesized. Previous work on five Al₄R₄ (R = C₅H₅, C₅Me₄H, C₅Me₅, C₅Me₄iPr, C₅Me₄Pr) compounds showed a general trend towards an increased likelihood of disassociation into monomeric species in solution as ligand bulk increased. Analysis of Al₄Cp*^Ph₄, the sixth and bulkiest compound in this series, indicates a departure from this trend. Bonding characteristics for monomer and tetramer forms in this series are examined in detail via topological analysis to understand this trend.     

Validation of pH-Metric Technique for Measurement of pKa and log Pow of Ionizable Herbicides

Abstract

Knowing the values of pK_a and partition coefficients between 1-octanol and water (P_ow) of ionizable herbicides helps us to understand the movement of these compounds in plants and soil. However, shake-flask and high-pressure liquid chromatography (HPLC) techniques. though valuable for measurement of log P_ow of herbicide molecules that do not ionize in aqueous solution, are difficult to use for ionizable molecules; this is especially so for molecules that form ion pairs having appreciable log P_ow values, those with multiple ionizations and for bases with high pK_a values. Our aim in this study was to validate the use of the pH-metric technique (based on potentiometric titration) for measurements of pK_a and log P_ow of ionizable standard substances and herbicides. The values obtained show good correlation with results from other techniques, including shake-flask and HPLC. The OECD Guideline for Testing of Chemicals 117, adopted 30th March 1989, describes the use of HPLC for the measurement of log P_ow. It is hoped that these studies and further testing of this technique will permit it to be included in these OECD guidelines.     

Halogen in materials design: Fluoroammonium lead triiodide (FNH3PbI3) perovskite as a newly discovered dynamical bandgap semiconductor in 3D

Methylammonium lead triiodide (CH₃NH₃PbI₃) has been recognized as one of the record‐breaking materials for photovoltaics since it can potentially convert light energy into electricity @ 23%. However, it has been suffering from serious stability and environmental issues for which it is not yet put on market. To this end, experimental and theoretical studies are underway to discover versatile halide‐based perovskite compounds. In this article, we report the polymorphic geometries, stabilities, band structures, density of states spectra, and carrier effective asses of a newly identified perovskite semiconductor called fluoroammonium lead triiodide (FNH₃PbI₃), obtained using compositional engineering combined with periodic density functional theory electronic structure calculations. We show that this compound is stable both in the orthorhombic and pseudocubic phases. We also show that the bandgap for this material oscillates between 1.62 eV (direct) and 1.79 (indirect) for the two polymorphs examined in the pseudocubic phase, with the former and latter values corresponding to the [111] and [110] orientations of the inorganic cation inside the perovskite cage, respectively. Contrariwise, it is direct at Γ‐point for the polymorph examined in the orthorhombic phase. The spin orbit coupling is displayed to have profound effect on the nature and magnitude of the bandgap for this material. This, together with the very small effective masses calculated for the charge carriers comparable with those of CH₃NH₃PbI₃, allows us to propose that FNH₃PbI₃ could be a possible candidate for photovoltaics, as well as for other optoelectronic applications.     

High Dielectric Constant in the Charge‐ordered Manganese Oxide CaMn7O12

The dielectric properties of mixed‐oxide CaMn₇O₁₂ are reported. This compound exhibits a high dielectric constant at room temperature (ε′_r> 10⁴), for frequencies up to 10⁴ Hz, values that make it very attractive for potential applications provided that its rather high losses can be minimized. Complex plane analysis of the obtained data reveal an important extrinsic contribution to these high ε′_r values; and also that the intrinsic dielectric constant of this material is ε′_r,∞ ≈ 30, a value rather high for this type of compounds, that could be related to the electronic process of charge‐ordering present in this oxide below 440 K.     

A Novel Method for Fixed‐node Quantum Monte Carlo

In this paper, a novel method for fixed‐node quantum Monte Carlo is given. By comparing this method with the traditional fixed‐node one, this novel method can be applied to calculate molecular energy more exactly. An expansion of the eigenvalue of the energy for a system has been derived. It is proved that the value of the energy calculated using the traditional fixed‐node method is only the zeroth order approximation of the eigenvalue of the energy. But when using this novel method, in the case of only increasing less computing amounts ( < 1%), the first order approximation, the second order approximation, and so on can be obtained conveniently with the detailed equations and steps in the practical calculation to calculate the values of the zeroth, first and second approximation of the energies of 1 ¹A, state of CH₂, ¹A₂(C_4h, acet) state of C₈ and the ground‐states of H₂, LiH, Li₂, and H₂O The results indicate that for these states it needs only the second order approximation to obtain over 97% of electronic correlation energy, which demonstrates that this novel method is very excellent in both the computing accuracy and the amount of calculation required.     

Production of Hydrogen Peroxide by Photocatalytic Processes

Hydrogen peroxide (H₂O₂) has received increasing attention because it is not only a mild and environmentally friendly oxidant for organic synthesis and environmental remediation but also a promising new liquid fuel. The production of H₂O₂ by photocatalysis is a sustainable process, since it uses water and oxygen as the source materials and solar light as the energy. Encouraging processes have been developed in the last decade for the photocatalytic production of H₂O₂. In this Review we summarize research progress in the development of processes for the photocatalytic production of H₂O₂. After a brief introduction emphasizing the superiorities of the photocatalytic generation of H₂O₂, the basic principles of establishing an efficient photocatalytic system for generating H₂O₂ are discussed, highlighting the advanced photocatalysts used. This Review is concluded by a brief summary and outlook for future advances in this emerging research field.     

Solid triphenylmethanol: A molecular material that undergoes multiple internal reorientational processes on different timescales

In solid triphenylmethanol, the molecules are arranged in hydrogen-bonded tetramers, and it is already well established that the hydrogen bonding in this material undergoes a dynamic switching process between different hydrogen bonding arrangements. In addition to this motion, we show here, from solid-state ²H NMR studies of the deuterated material (C₆D₅)₃COH, that each phenyl ring in this material undergoes a 180°-jump reorientation about the C₆D₅-C(OH) bond, with an activation energy of ca. 50 kJ mol⁻¹. The timescale for the phenyl ring dynamics is several orders of magnitude longer than the timescale for the hydrogen bond dynamics in this material, and is uncorrelated with the dynamics of the hydrogen bonding arrangement.     

Extraction of aflatoxins from food samples using graphene‐based magnetic nanosorbents followed by high‐performance liquid chromatography: A simple solution to overcome the problems of immunoaffinity columns

In this research, magnetic graphene nanoparticles were prepared and used as adsorbents for preconcentrating the aflatoxins in rice, wheat, and sesame samples. For this purpose, graphene was synthesized by Hummer's method. Magnetically modified graphene formed by the deposition of magnetite (Fe₃O₄) on graphene was used for the separation of aflatoxins B₁, B₂, G₁, and G₂ from the samples. The extractants were subsequently analyzed with high‐performance liquid chromatography and fluorescence detection. Parameters affecting the efficiency of the method were thoroughly investigated. The measurements were done under the optimized conditions. For aflatoxins B₁, B₂, G₁, and G₂, limits of detection were 0.025, 0.05, 0.05, and 0.075 ng/g and limits of quantification were 0.083, 0.16, 0.16, and 0.23 ng/g, respectively. Accuracy was examined by the determination of the relative recovery of the aflatoxins. The relative recovery of aflatoxins B₁, B₂, G₁, and G₂ were quite satisfactory (between 64.38 and 122.21% for food samples). Relative standard deviations for within laboratory repeatability (n = 6) were in the range from 1.3 to 3.2. The application of this sorbent for the separation and concentration of the mentioned aflatoxins from food samples was examined.     

A thermodynamic study of H-D exchange in the hydrogen-difluoroborane system

The hydrogen-deuterium exchange reaction between D₂ and HBF₂ is unique in certain respects due to its unusually fast reaction rate at ordinary temperatures. For this reason it has been possible to observe H-D exchange equilibria for this system and evaluate the thermodynamic properties of HBF₂ and DBF₂. In this paper we present the results of those equilibrium measurements.