High-valence metal sites induced by heterostructure engineering for promoting 5-hydroxymethylfurfural electrooxidation and hydrogen generation.

The electrocatalytic 5-hydroxymethylfurfural (HMF) oxidation reaction coupling with hydrogen evolution reaction (HER) serves as a promising strategy to generate both high-value-added products and clean energy, which is limited by the poor catalytic efficiency of bifunctional electrocatalysts and unclear electrocatalytic mechanism for HMF oxidation reaction. Herein, we fabricate a bifunctional NiSe2-NiMoO4 heterostructure nanowire electrocatalyst for the conversion of HMF to 2,5-furandicarboxylic acid (FDCA) and simultaneous H2 production. As expected, the NiSe2-NiMoO4 exhibits outstanding activity and selectivity toward HMF oxidation reaction. In particular, at a potential of 1.50 V, the yield of FDCA could reach 98 % with a faradaic efficiency of 96.5 %, as well as excellent stability. Density functional theory calculation results demonstrate that the NiSe2-NiMoO4 heterostructure could tune the adsorption energy of HMF, facilitate high-valence active species formation, and enhance electronic conductivity. Furthermore, a two-electrode electrolyzer assembled using NiSe2-NiMoO4 as a bifunctional catalyst requires 1.53 V to acquire a current density of 50 mA cm-2, which is 201 mV lower than that of water electrolysis. This work provides new insights for designing multifunctional catalysts for biomass upgrading coupled with hydrogen evolution.

Engineering Single Cu Sites into Covalent Organic Framework for Selective Photocatalytic CO2 Reduction.

Photocatalytic CO2 conversion into value-added chemicals is a promising route but remains challenging due to poor product selectivity. Covalent organic frameworks (COFs) as an emerging class of porous materials are considered as promising candidates for photocatalysis. Incorporating metallic sites into COF is a successful strategy to realize high photocatalytic activities. Herein, 2,2'-bipyridine-based COF bearing non-noble single Cu sites is fabricated by chelating coordination of dipyridyl units for photocatalytic CO2 reduction. The coordinated single Cu sites not only significantly enhance light harvesting and accelerate electron-hole separation but also provide adsorption and activation sites for CO2 molecules. As a proof of concept, the Cu-Bpy-COF as a representative catalyst exhibits superior photocatalytic activity for reducing CO2 to CO and CH4 without photosensitizer, and impressively, the product selectivity of CO and CH4 can be readily modulated only by changing reaction media. Experimental and theoretical results reveal the crucial role of single Cu sites in promoting photoinduced charge separation and solvent effect in regulating product selectivity, which provides an important sight onto the design of COF photocatalysts for selective CO2 photoreduction.

Acetylene/Vinylene-Bridged π-Conjugated Covalent Triazine Polymers for Photocatalytic Aerobic Oxidation Reactions under Visible Light Irradiation.

Solar-driven photocatalytic chemical transformation provides a sustainable strategy to produce valuable feedstock, but designing photocatalysts with high efficiency remains challenging. Herein, two acetylene- or vinylene-bridged π-conjugated covalent triazine polymers, A-CTP-DPA and V-CTP-DPE, were successfully fabricated toward metal-free photocatalytic oxidation under visible light irradiation. Compared to the one without acetylene or vinylene bridge, both resulting polymers exhibited superior activity in photocatalytic selective oxidation of sulfides and oxidative coupling of amines; in particular, A-CTP-DPA delivered an optimal photocatalytic performance. The superior activity was attributed to the broadened spectral response range, effective separation, rapid transportation of photogenerated charge carriers, and abundant active sites for photogenerated electrons due to the existence of the acetylene bridge in the framework. This work highlights the potential of acetylene and vinylene bridges in tuning catalytic efficiency of organic semiconductors, providing a guideline for the design of efficient photocatalysts.

Structural and Morphological Engineering of Benzothiadiazole-Based Covalent Organic Frameworks for Visible Light-Driven Oxidative Coupling of Amines.

Covalent organic frameworks (COFs) are appealing platforms for photocatalysts because of their structural diversity and adjustable optical band gaps. The construction of efficient COFs for heterogeneous photocatalysis of organic transformations is highly desirable. Herein, we constructed a photoactive COF containing benzothiadiazole and triazine (BTDA-TAPT), for which the morphology and crystallinity might be easily tuned by slight synthetic variation. To unveil the relationship of photocatalytic properties between the structure and morphology, analogous COFs were synthesized by precisely tailoring building blocks. Systematic investigations indicated that tuning the structure and morphology might greatly impact photoelectric properties. The BTDA-TAPT featuring ordered alignment and perfect crystalline nature was more beneficial for promoting charge transfer and separation, which exhibited superior photocatalytic activity for visible light-driven oxidative coupling of amines. Outcomes from this study reveal the intrinsic synergy effects between the structure and morphology of COFs for photocatalysis.

Copper(i) iodide cluster-based lanthanide organic frameworks: synthesis and application as efficient catalysts for carboxylative cyclization of propargyl alcohols with CO2 under mild conditions.

Two metal-organic frameworks (MOFs), namely, [Dy2Cu4I4(NA)6(DMF)2]n (1) and [Gd2Cu2I2(IN)6(DMF)4]·5DMF (2) (HNA = nicotinic acid, HIN = isonicotinic acid), constructed based on lanthanide ions and copper iodide clusters ([Cu4I4] and [Cu2I2]) were successfully synthesized and characterized. Compound 1 has a three-dimensional framework and compound 2 displays a two-dimensional plane with sql topology, respectively. Both of them exhibit high thermostability and solvent stabilities. Additionally, catalytic explorations reveal that 1 displays higher catalytic activity than 2 for the carboxylic cyclization of propargyl alcohols. More importantly, 1 also exhibits excellent catalytic performance in the carboxylation reactions of CO2 and terminal propargylic alcohols with various substituents. To the best of our knowledge, this is the first example of non-noble metal based MOF catalysts for the carboxylative cyclization of propargyl alcohols with CO2 under atmospheric pressure and at room temperature, which provides a highly promising approach for MOFs in the catalytic conversion of CO2 to valuable chemicals.

Porous Carbon Nitride Frameworks Derived from Covalent Triazine Framework Anchored Ag Nanoparticles for Catalytic CO2 Conversion.

Porous carbon nitride frameworks (PCNFs) with uniform and rich nitrogen dopants and abundant porosity were successfully fabricated through the direct carbonization of the covalent triazine frameworks (CTFs) at different pyrolysis temperatures and used as supports to anchor and stabilize Ag nanoparticles (NPs) for catalytic CO2 conversion. Importantly, the pyrolysis temperature plays a crucial role in the properties of porous carbon nitride frameworks. The material carbonized at 700 °C showed the highest surface area and micro- and mesoporous structure with a certain interlayer distance. Taking advantage of their unique surface characteristics, PCNF-supported Ag NP catalysts (Ag/PCNF-T, T=pyrolysis temperature) were prepared by a simple chemical method. A series of characterizations revealed that Ag NPs are embedded in the porous carbon nitride frameworks and confined to a relatively small size with high dispersion owing to the assistance of the abundant surface groups and porous structures. The as-obtained Ag/PCNF-T catalysts, especially Ag/PCNF-700, showed excellent catalytic activity, selectivity, and stability for the carboxylation of CO2 with terminal alkynes under mild conditions. This can be due to the existence of abundant nitrogen atoms and diverse porosity, which resulted in highly efficient catalytic activity and stability.

Ultrafine Ag Nanoparticles Encapsulated by Covalent Triazine Framework Nanosheets for CO2 Conversion.

This paper describes the fabrication of covalent triazine framework nanosheet-encapsulated Ag nanoparticles (Ag0@CTFN) via a simple combination of the ultrasonic exfoliation and solution infiltration method. The as-prepared Ag0@CTFN displays an order layered-sheet structure with abundant micropores and mesopores, whereas ultrafine Ag nanoparticles are confined and stabilized in their interlayers through the interaction between N sites of triazine units and Ag nanoparticles. Considering that the Ag0@CTFN possesses the merits of high nitrogen, low density, and abundant basic sites, it was thus believed to have enough abilities to adsorb and activate CO2 in the CO2 conversion and catalysis. Importantly, the Ag0@CTFN, as a heterogeneous catalyst, showed highly catalytic activity in the carboxylation of various alkynes with CO2 at ambient pressure and low temperature. This catalyst also exhibited good functional group tolerance and excellent stability without any significant loss of its activity after six recycles. This work not only achieves valuable and novel composite material but also provides the first application of covalent triazine framework nanosheets in chemical conversion of CO2, opening a new field in preparing recyclable heterogeneous catalysts to accelerate the utilization of CO2.

Preparation of a H3PW12O40 Deposited Chitosan Coated Iron Oxide Magnetic Core-Shell Nanocomposite for Friedel-Crafts Acylation.

A novel H3PW12O40 deposited chitosan coated iron oxide magnetic core-shell nanocomposite (Fe3O4@CS@HPW) was prepared via a facile approach. Fe3O4 nanoparticles were first coated with crosslinking-agent-free chitosan, and then H3PW12O40 was loaded onto the surface of chitosan as an outer shell. The resultant nanocomposite was well characterized by Brunauer-Emmett-Teller surface area analysis (BET), inductively coupled plasma analysis (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and elemental mappings. Fe3O4@CS@HPW showed better catalytic performance than its counterpart with a chitosan-crosslinked shell in the Friedel-Crafts acylation of anisole to 4-methoxyacetophenone under solvent-free conditions, and can be easily separated by an external magnetic field and recycled effectively.

Biomass-Derived N-doped Carbon Materials with Silica-Supported Ultrasmall ZnO Nanoparticles: Robust Catalysts for the Green Synthesis of Benzimidazoles.

Ultrasmall ZnO nanoparticles anchored on N-doped carbon materials with a silica support (ZnO/SiO2 -NC) were fabricated from chitosan and metal ions by using a one-pot self-assembly strategy and were successfully applied to the synthesis of 2-arylbenzimidazoles under mild conditions. These catalysts showed excellent stability and could be used six times without any loss of conversion and selectivity. The use of silica gel and the biomass chitosan as a source of hydrophilic N-doped carbon materials facilitated the uniform dispersion of the ZnO nanoparticles in methanol and therefore the contact of these nanoparticles with reactants, thus contributing to a high catalytic performance. TEM analysis showed that the ZnO nanoparticles were around 2.55 nm in diameter and uniformly distributed on the support surface. The binding behavior of ZnO and N-doped carbon materials affected the catalytic activity. Interestingly, temperature-programmed NH3 desorption indicated that the interactions between ZnO and N-doped carbon materials might induce the presence of more acidic sites in these catalysts, thus resulting in enhanced activity and hence promoting this transformation.

Ligand-free nickel-catalyzed semihydrogenation of alkynes with sodium borohydride: a highly efficient and selective process for cis-alkenes under ambient conditions.

We report a low-cost and efficient catalytic system, involving in situ generated ligand-free Ni NPs, methanol and sodium borohydride, for the semihydrogenation of alkynes under ambient conditions. This catalytic system exhibits remarkably high activity, satisfactory cis-selectivity for internal alkynes, good stability and general applicability.

Sedimentation field-flow fractionation for characterization of citric acid-modified Hß zeolite particles: Effect of particle dispersion and carrier composition.

In this study, sedimentation field-flow fractionation (SdFFF) was, for the first time, applied for determination of size distribution of Hß zeolite particles modified by citric acid (CA-Hß). Effects of the particle dispersion and the carrier liquid composition (type of dispersing reagent (surfactant) and salt added in the carrier liquid, ionic strength, and pH) on SdFFF elution behavior of CA-Hß zeolite particles were systematically investigated. Also the SdFFF separation efficiency of the particles was discussed in terms of the forces such as van der Waals, hydrophobic, and induced-dipole interactions. Results reveal that the type of salt and pH of the carrier liquid significantly affect the SdFFF separation efficiency of the zeolite particles. It was found that addition of a salt (NaN3) into the carrier liquid affects the characteristic of the SdFFF channel surface. It was found that the use of an acidic medium (pH 3.2) leads to a particle-channel interaction, while the use of a basic medium (pH 10.6) promotes an inter-particle hydrophobic interaction. Result from SdFFF was compared with those from scanning electron microscopy (SEM) and dynamic light scattering (DLS). It seems that, once the experimental conditions are optimized, SdFFF becomes a valuable tool for size characterization of the zeolite particles.

A novel sodium iodide and ammonium molybdate co-catalytic system for the efficient synthesis of 2-benzimidazoles using hydrogen peroxide under ultrasound irradiation.

The reaction of aldehydes and o-phenylenediamine for the preparation of 2-benzimidazoles has been studied using hydrogen peroxide as an oxidant under ultrasound irradiation at room temperature in this paper. The combination of substoichiometric sodium iodide and ammonium molybdate as co-catalysts, together with using small amounts of hydrogen peroxide, makes this transformation very efficient and attractive under ultrasound. Thus, a mild, green and efficient method is established to carry out this reaction in high yield.

Preparation of nanoscale Ni-B amorphous alloys and their application in the selective hydrogenation of cinnamic acid.

A series of metal modified nanoscale Ni-B amorphous alloys was prepared by chemical reduction and tested in the selective hydrogenation of cinnamic acid. A Co modified Ni-B amorphous alloy (Ni-Co-B) exhibited excellent catalytic performance in this reaction with both 100.0% conversion of cinnamic acid and 100.0% selectivity for hydrocinnamic acid under the optimized reaction conditions. X-ray diffraction (XRD) results indicated that the addition of Co had not changed the amorphous structure of Ni-B; whereas, its addition was believed not only to favor decreased agglomeration of the active Ni species, as proven by transmission electron microscopy (TEM), but also to contribute to adsorption of hydrogen itself. Thus, Ni-Co-B showed a larger BET surface area, smaller particle size, and greater number of active species resulting in optimum H2-chemisorption compared to Ni-B and accounting for its excellent catalytic performance in cinnamic acid hydrogenation.