(4R,5R,10S)-N-(4-Bromo­phen­yl)dehydro­abietamide

The title compound, C26H32BrNO, the ring with the amide unit possesses a chair conformation with the two methyl groups in axial positions.

Study on the Structure Optimization and the Operation Scheme Design of a Double-Tube Once-Through Steam Generator

AbstractA double-tube once-through steam generator (DOTSG) consisting of an outer straight tube and an inner helical tube is studied in this work. First, the structure of the DOTSG is optimized by considering two different objective functions. The tube length and the total pressure drop are considered as the first and second objective functions, respectively. Because the DOTSG is divided into the subcooled, boiling, and superheated sections according to the different secondary fluid states, the pitches in the three sections are defined as the optimization variables. A multi-objective optimization model is established and solved by particle swarm optimization. The optimization pitch is small in the subcooled region and superheated region, and large in the boiling region. Considering the availability of the optimum structure at power levels below 100% full power, we propose a new operating scheme that can fix the boundaries between the three heat-transfer sections. The operation scheme is proposed on the basis of data for full power, and the operation parameters are calculated at low power level. The primary inlet and outlet temperatures, as well as flow rate and secondary outlet temperature are changed according to the operation procedure

Heterostructures Based on 2D Materials: A Versatile Platform for Efficient Catalysis

The unique structural and electronic properties of 2D materials, including the metal and metal-free ones, have prompted intense exploration in the search for new catalysts. The construction of different heterostructures based on 2D materials offers great opportunities for boosting the catalytic activity in electo(photo)chemical reactions. Particularly, the merits resulting from the synergism of the constituent components and the fascinating properties at the interface are tremendously interesting. This scenario has now become the state-of-the-art point in the development of active catalysts for assisting energy conversion reactions including water splitting and CO2 reduction. Here, starting from the theoretical background of the fundamental concepts, the progressive developments in the design and applications of heterostructures based on 2D materials are traced. Furthermore, a personal perspective on the exploration of 2D heterostructures for further potential application in catalysis is offered

High-performance, multifunctional devices based on asymmetric van der Waals heterostructures

Two-dimensional materials are of interest for the development of electronic devices due to their useful properties and compatibility with silicon-based technology. Van der Waals heterostructures, in which two-dimensional materials are stacked on top of each other, allow different materials and properties to be combined and for multifunctional devices to be created. Here we show that an asymmetric van der Waals heterostructure device, which is composed of graphene, hexagonal boron nitride, molybdenum disulfide and molybdenum ditelluride, can function as a high-performance diode, transistor, photodetector and programmable rectifier. Due to the asymmetric structure of the device, charge-carrier injection can be switched between tunnelling and thermal activation under negative and positive bias conditions, respectively. As a result, the device exhibits a high current on/off ratio of 6 × 108 and a rectifying ratio of 108. The device can also function as a programmable rectifier with stable retention and continuously tunable memory states, as well as a high program/erase current ratio of 109 and a rectification ratio of 107

Selenium-Enriched Nickel Selenide Nanosheets as a Robust Electrocatalyst for Hydrogen Generation

To address the urgent need for clean and sustainable energy, the rapid development of hydrogen-based technologies has started to revolutionize the use of earth-abundant noble-metal-free catalysts for the hydrogen evolution reaction (HER). Like the active sites of hydrogenases, the cation sites of pyrite-type transition-metal dichalcogenides have been suggested to be active in the HER. Herein, we synthesized electrodes based on a Se-enriched NiSe2nanosheet array and explored the relationship between the anion sites and the improved hydrogen evolution activity through theoretical and experimental studies. The free energy for atomic hydrogen adsorption is much lower on the Se sites (0.13 eV) than on the Ni sites (0.87 eV). Notably, this electrode benefits from remarkable kinetic properties, with a small overpotential of 117 mV at 10 mA cm-2, a low Tafel slope of 32 mV per decade, and excellent stability. Control experiments showed that the efficient conversion of H+into H2is due to the presence of an excess of selenium in the NiSe2nanosheet surface. Excess selenium: Although the undercoordinated surface metal centers of pyrite-type transition-metal dichalcogenides have been suggested to be the main active sites for H2production, the ligand composition also plays a decisive role. The Se sites and excessive Se atoms on the surface of pyrite-type NiSe2are now corroborated to be the active sites for electrochemical H2evolution

Carbon Nanotube Addition to Cement-Sand Based Piezoelectric Composites

UROP paper, 2016, Mechanical and Industrial EngineeringCarbon Nanotubes (CNTs) were added to a cement-sand based piezoelectric composite with consideration of Structural Health Monitoring (SHM) to improve conductivity and poling efficiency, increasing piezoelectric effects. The addition of CNTs to the composite structure formed continuous electric networks between the Lead Zirconate Titanate (PZT) particles, allowing more effective poling. Samples of 50 volume percent PZT were fabricated with a mixture of PZT powder, white Portland cement, graded silica sand, CNTs and a superplasticizer, and cured at room temperature. The properties of the composite, including piezoelectric coefficient and sensing effects were characterized for a range of CNT inclusion from 0 to 0.9 vol %. Results showed that CNT inclusion allowed for effective room temperature poling, improving piezoelectric properties of the composite. The modified composite was optimal at 0.6 vol % CNTs.Undergraduate Research Opportunities Program, University of Minnesota Dulut

Efficient Photocatalytic Hydrogen Evolution via Band Alignment Tailoring: Controllable Transition from Type-I to Type-II

Considering the sizable band gap and wide spectrum response of tin disulfide (SnS2), ultrathin SnS2 nanosheets are utilized as solar-driven photocatalyst for water splitting. Designing a heterostructure based on SnS2 is believed to boost their catalytic performance. Unfortunately, it has been quite challenging to explore a material with suitable band alignment using SnS2 nanomaterials for photocatalytic hydrogen generation. Herein, a new strategy is used to systematically tailor the band alignment in SnS2 based heterostructure to realize efficient H2 production under sunlight. A Type-I to Type-II band alignment transition is demonstrated via introducing an interlayer of Ce2S3, a potential photocatalyst for H2 evolution, between SnS2 and CeO2. Subsequently, this heterostructure demonstrates tunability in light absorption, charge transfer kinetics, and material stability. The optimized heterostructure (SnS2–Ce2S3–CeO2) exhibits an incredibly strong light absorption ranging from deep UV to infrared light. Significantly, it also shows superior hydrogen generation with the rate of 240 µmol g−1 h−1 under the illumination of simulated sunlight with a very good stability

Hierarchical MnO2/activated carbon cloth electrode prepared by synchronized electrochemical activation and oxidation for flexible asymmetric supercapacitors

Despite appealing supercapacitive properties, the flexible asymmetric supercapacitor devices (FASCs) are still suffering from low mass loading and limited operating voltage, leading to unsatisfactory energy densities. Herein, we introduced a high-voltage anodic electro-deposition process (AED) which is a novel avenue enabling the synthesis of hierarchical MnO2 on activated carbon cloth (H-MnO2/ACC). Interestingly, the concomitant activation of carbon cloth substrate is found to be beneficial to improve the conductivity and hydrophilic nature of our novel electrode. A FASC based on H-MnO2/ACC-300 and reduced carbon cloth (RCC) was assembled using a mixed ionic liquid gel (ionogel) electrolyte. Benefiting from highly conductive paths derived from intimately attached fiber-MnO2 interfaces, hierarchically interpenetrated lamella MnO2 porosity and concentric MnO2 interlayer voids, as well as the merits of ionic liquid, the resultant FASC delivers an output voltage as high as 4 V and an impressive volumetric energy density of 3.82 mWh/cm3. Furthermore, the optimized H-MnO2/ACC-300 electrode with high mass loading can even retain 94.2% of initial capacitance upon 5000 cycles in 1 M Na2SO4. The unique H-MnO2/ACC can aid in the rational design towards flexible electronic devices with high mass loading and this synthetic strategy opens up enormous possibilities for the fabrication of electrodeposited materials