In Situ Anodic Oxidation Tuning of NiFeV Diselenide to the Core-Shell Heterojunction for Boosting Oxygen Evolution.

Developing non-noble metal-based core-shell heterojunction electrocatalysts with high catalytic activity and long-lasting stability is crucial for the oxygen evolution reaction (OER). Here, we prepared novel core-shell Fe,V-NiSe2@NiFe(OH)x heterostructured nanoparticles on hydrophilic-treated carbon paper with high electronic transport and large surface area for accelerating the oxygen evolution rate via high-temperature selenization and electrochemical anodic oxidation procedures. Performance testing shows that Fe,V-NiSe2@NiFe(OH)x possesses the highest performance for OER compared to as-prepared diselenide core-derived heterojunctions, which only require an overpotential of 243 mV at 10 mA cm-2 and a low Tafel slope of 91.6 mV decade-1 under basic conditions. Furthermore, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) confirm the morphology and elementary stabilities of Fe,V-NiSe2@NiFe(OH)x after long-term chronopotentiometric testing. These advantages are largely because of the strong synergistic effect between the Fe,V-NiSe2 core with high conductivity and the amorphous NiFe(OH)x shell with enriched defects and vacancies. This study also presents a general approach to designing and synthesizing more active core-shell heterojunction electrocatalysts for OER.

Research progress of CO2 oxidative dehydrogenation of propane to propylene over Cr-free metal catalysts.

CO2-assisted oxidative dehydrogenation of propane (CO2-ODHP) is an attractive strategy to offset the demand gap of propylene due to its potentiality of reducing CO2 emissions, especially under the demands of peaking CO2 emissions and carbon neutrality. The introduction of CO2 as a soft oxidant into the reaction not only averts the over-oxidation of products, but also maintains the high oxidation state of the redox-active sites. Furthermore, the presence of CO2 increases the conversion of propane by coupling the dehydrogenation of propane (DHP) with the reverse water gas reaction (RWGS) and inhibits the coking formation to prolong the lifetime of catalysts via the reverse Boudouard reaction. An effective catalyst should selectively activate the C-H bond but suppress the C-C cleavage. However, to prepare such a catalyst remains challenging. Chromium-based catalysts are always applied in industrial application of DHP; however, their toxic properties are harmful to the environment. In this aspect, exploring environment-friendly and sustainable catalytic systems with Cr-free is an important issue. In this review, we outline the development of the CO2-ODHP especially in the last ten years, including the structural information, catalytic performances, and mechanisms of chromium-free metal-based catalyst systems, and the role of CO2 in the reaction. We also present perspectives for future progress in the CO2-ODHP.

Construction of Bi2WO6 with double active sites of tunable metallic Bi and oxygen vacancies for photocatalytic oxidation of cyclohexane to cyclohexanone.

Oxygen-containing organics, which are generated from the selective oxidation of their corresponding hydrocarbons, have high value in the chemical and pharmaceutical industries. However, their oxidation reactions are very challenging as the products are more active than the substrates, especially for the oxidation of cyclohexane (CHA). Herein, we focused on the one-step preparation of Bi2WO6 with double active sites of tunable metallic Bi and oxygen vacancies (OV-Bi/Bi2WO6) by a facile solvothermal treatment. Then, OV-Bi/Bi2WO6 was used as an efficient photocatalyst for the partial oxidation of CHA to cyclohexanone (CHA-one) for the first time in air as an oxidant under solvent-free and room temperature conditions. The Bi : Bi2WO6 ratio in the as-prepared OV-Bi/Bi2WO6 heterojunction could be tailored from 0.08 to 8.43 by controlling the solvothermal temperature, and the synergistic effect between DMF and EG could increase the reduction of MDF/EG and promote the production of Bi. Moreover, OV-Bi/Bi2WO6-160 yielded 4.4 and 8.8 times more CHA-one (128.8 µmol) than pure Bi2WO6 and metallic Bi, respectively, and achieved 93.6% selectivity to CHA-one in air as an oxidant under solvent-free conditions. The results revealed that the highly enhanced photocatalytic activity was mainly attributed to the superior specific surface area, outstanding photo-absorption, abundant oxygen vacancies, and efficient electron-hole separation. Moreover, for the unique double active sites in OV-Bi/Bi2WO6, oxygen vacancies can enhance the adsorption and activation capacity of Bi2WO6 for O2, while metallic Bi can improve the adsorption and activation capacity of Bi2WO6 for CHA. Meanwhile, OV-Bi/Bi2WO6 also exhibited excellent durability due to the strong interaction between metallic Bi and Bi2WO6. The present work provides a flexible approach for tailoring the Bi : Bi2WO6 ratio and outlines an effective method for producing CHA-one from CHA under mild conditions.

Photoluminescence study of low density InAs quantum clusters grown by molecular beam epitaxy.

We report a systematic optical spectroscopy study of low density InAs quantum clusters (QCs) grown by molecular beam epitaxy. The photoluminescence (PL) spectra show emission features of a wetting layer (WL) which contains hybridized quantum well states. The low-energy tail of the QCs' PL profile is actually an ensemble of some sharp lines, originating from the emission of different exciton states (e.g. X, X*, XX*) in a single quasi-three-dimensional (Q3D) cluster as detailed in the micro-PL spectra. The temperature dependence of PL spectra indicates photocarrier distribution and transport in the QC-WL system. Furthermore, this small InAs Q3D cluster is integrated with a distributed Bragg reflector structure, and using optical excitation creates a single photon source with the second-order correlation function of g((2))(0) = 0.31 at 16 K.

Cationic Nonporous Macrocyclic Organic Compounds for Multimedia Iodine Capture.

Over the past two decades, progress in chemistry has generated various types of porous materials for removing iodine (129 I or 131 I) that can be formed during nuclear energy generation or nuclear waste storage. However, most studies for iodine capture are based on the weak host-guest interactions of the porous materials. Here, we present two cationic nonporous macrocyclic organic compounds, namely, MOC-1 and MOC-2, in which 6I- and 8I- were as counter anions, for highly efficient iodine capture. MOC-1 and MOC-2 were formed by reacting 1,1'-diamino-4,4'-bipyridylium di-iodide with 1,2-diformylbenzene or 1,3-diformylbenzene, respectively. The presence of a large number of I- anions results in high I2 affinity with uptake capacities up to 2.15 g ⋅ g-1 for MOC-1 and 2.25 g ⋅ g-1 for MOC-2.