Construction of ZnxCdyS with a 3D Hierarchical Structure for Enhanced Photocatalytic Hydrogen Production from Water Splitting.

The ZnxCdyS has been proven to have unique photoelectric properties, but its synthesis method and photocatalytic water cracking performance need to be further improved. In this paper, Cd-MOF@ZIF-8 with a MOF-on-MOF (MOF = metal-organic framework) structure was prepared by a simple ion adsorption method. Then, a CdS/ZnxCdyS heterojunction with a 3D hierarchical structure was formed by solvothermal sulfidation. The prepared catalysts with different Zn/Cd ratios show an improved hydrogen production performance for photocatalytic water splitting, and the hydrogen evolution rate of Zn1Cd1S can reach up to 29.2 mmol·g-1·h-1. The excellent photocatalytic activity not only benefits from ZnxCdyS strong light conversion ability but also is closely related to the hierarchical structure and large specific surface area. A type II heterojunction also plays an important role in the spatial separation of photogenerated carriers. This paper provides a simple and feasible idea for the synthesis of a photocatalyst with a large specific surface area using a MOF-on-MOF synthesis strategy.

Magnetic mesoporous material derived from MIL-88B modified by l-alanine as modified QuEChERS adsorbent for the determination of 6 pesticide residues in 4 vegetables by UPLC-MS/MS.

More and more attention has been paid to the improved QuEChERS (quick, easy, cheap, effective, rugged and safe) method in dealing complex sample matrices, especially for the study of QuEChERS adsorbents. In this study, a magnetic mesoporous material, which was derived from MIL-88B modified by l-alanine, was synthesized as modified QuEChERS adsorbents for the simultaneous determination of multiple pesticides (Methomyl, Isoprocarb, Carbofuran, 3-Hydroxycarbofuran, Acetamiprid, Imidacloprid) in Chinese cabbage, celery, long bean and leek. The prepared magnetic adsorbents can effectively remove interfering substances from the sample, and the proposed modified QuEChERS method can reduce sample pretreatment time via an external magnetic field. To achieve the best performance of QuEChERS method, the clean-up time and amount of QuEChERS adsorbents were investigated. Under the optimized conditions, a simple, rapid and sensitive method for the determination of 6 pesticide residues in vegetables was established by coupling the modified QuEChERS to ultrahigh-performance liquid chromatography-tandem mass spectrometry. Excellent sensitivity (The limit of detection for the 6 pesticides ranged from 0.001 to 0.020 µg kg-1), satisfactory linearity (r2 ≥ 0.9952), good recovery (73.9-107.7%) and good precision (3.6-16.9% for intraday relative standard deviation, 0.5-15.0% for interday relative standard deviation) were obtained. Compared with traditional QuEChERS method, the proposed method is simple, cost-effective, and efficient, which indicates that the method can be used to detect carbamate and neonicotinoid pesticides in real samples and provide an excellent pretreatment technique for the detection of trace multi-analytes from complex substrates.

Bamboo-like nitrogen-doped porous carbon nanofibers encapsulated nickel-cobalt alloy nanoparticles composite material derived from the electrospun fiber of a bimetal-organic framework as efficient bifunctional oxygen electrocatalysts.

The development of low-cost bifunctional electrocatalysts with both a high activity and long durability is critical for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The reasonable design and construction of bifunctional electrocatalysts is the key to energy storage and energy conversion technologies. In this study, transition metal carbon nitrides were used as a substitute for the precious metal catalyst, the Ni-Co-BTC (metal organic framework (MOF)) mixed with polyacrylonitrile (PAN) using electrostatic spinning technology to prepare the bamboo-like nanofibers precursor (Ni-Co-BTC@PAN). A series of electrocatalytic materials (NiCo-X@N-CNFs-Ts, T = 700, 800, 900 °C) were synthesized with nitrogen-doped carbon nanofibers coated with NiCo alloy nanoparticles using high temperature carbonization at different temperatures. We studied the effects of different calcination temperatures and different Ni/Co molar ratios of NiCo-X@N-CNFs-Ts (T = 700, 800, 900 °C) on the bifunctional catalytic performance of the ORR/OER. The composite, NiCo-0.8@N-CNFs-800, exhibited a highly doped-N level, uniform NiCo alloy nanoparticle dispersion and decentralized NiCo-Nx active sites, therefore affording an excellent bifunctional electrocatalytic performance. The ORR onset potential on NiCo-0.8@N-CNFs-800 was 0.91 V and the half-wave potential (E1/2) was 0.82 V, the NiCo-0.8@N-CNFs-800 corresponded to the minimum potential of 1.61 V at the current density of 10 mA cm-2 among all of the NiCo-X@N-CNFs-Ts hybrids under the OER condition. The NiCo-0.8@N-CNFs-800 catalyst exhibited a low reversible overpotential of 0.79 V between the ORR (E1/2) and OER (Ej = 10 mA cm-2) with excellent stability, durability and methanol tolerance, even surprisingly superior to the commercial Pt/C and RuO2 catalysts. This work provides a general strategy and useful guidance for the design and development of a variety of multifunctional non-noble metal catalysts for energy applications.

A general and efficient approach for tuning the crystal morphology of classical MOFs.

This communication introduces a general approach toward the size/morphology-controlled synthesis of classical MOFs with 2-methylimidazole (2-MI) as a competitive ligand and a base to accelerate the nucleation of crystallization. A higher concentration of 2-MI and a suitable polarity and solubility of the solvent will accelerate the nucleation of the crystal, resulting in nanometer size particles. However, larger crystals can be obtained via the further growth of nanoparticles with prolonging the reaction time. Such a serendipitous discovery may inspire future researchers to design new MOF materials with desired structures.

Zn 1,3,5-benzenetricarboxylate as an efficient catalyst for the synthesis of cyclic carbonates from CO2.

Development of heterogeneous catalysts for the cycloaddition of CO2 with epoxides to produce cyclic carbonates is a hot issue in the field of chemical fixation of carbon dioxide. It is fairly promising as production of by-products is quite low. In this study, the [Zn3(BTC)2]/n-Bu4NBr catalytic system was investigated for the solventless cycloaddition of carbon dioxide with epoxides and had an excellent synergetic effect in promoting the reaction. The reaction parameters were moderate i.e. (130 °C and 13 bar CO2 pressure) and were selected by a study of the catalytic system. Under the optimal reaction conditions, the yield of cyclic carbonate reached 99%. A decrease in the yield of cyclic carbonate was not apparent after [Zn3(BTC)2] was reused three times, indicating that [Zn3(BTC)2] was stable. At the same time, the catalytic activity of the catalyst for other epoxides was also verified. The acidic and alkaline nature of the [Zn3(BTC)2] catalyst did not change obviously after recycling the catalyst three times. In this study it is also verified that the [Zn3(BTC)2] catalytic cycloaddition reaction was closely related to the Lewis acid/base distribution. In addition, a plausible mechanism for the synergistic effect of the catalyst (Lewis acid and base properties) and the co-catalyst was suggested.