SciCombinator

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Metal-organic frameworks (MOFs) have proven to be an interesting class of sacrificial precursors of functional inorganic materials for catalysis, energy storage and conversion applications. However, the controlled synthesis of MOF-derived materials with desirable compositions, structures and properties still remains a big challenge. Herein, we propose a post-solvothermal route for the outer-to-inner loss of organic linkers from MOF, which is simple, rapid, controllable and can be operated at temperature much lower than that of the commonly adopted pyrolysis method. By such a strategy, the MIL-125-NH2 particles coated by TiO2 nanosheets were produced and the thickness of TiO2 shell can be easily tuned. The MIL-125-NH2@TiO2 core-shell particles combine the advantages of highly active TiO2 nanosheets, MIL-125-NH2 photosensitizer, plenty of linker defects and oxygen vacancies and mesoporous structure, which have been utilized as photocatalysts for the visible-light-driven hydrogen production reaction. It is remarkable that the hydrogen evolution rate by MIL-125-NH2@TiO2 can be enhanced 70 times compared with the pristine MIL-125-NH2, and even much higher than those of the noble metal loaded MOF catalysts. Such a route can be easily applied to the synthesis of different kinds of MOF-derived functional materials.

Concepts: Oxygen, Ultraviolet, Chemical reaction, Hydrogen, Catalysis, Haber process, Carbon, Photocatalysis

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Rationally generating oxygen vacancies in electrocatalysts is an important approach to modulate the electrochemical activity of catalyst. Herein, we report a remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCo2O4 supported on hollow carbon spheres achieved through generating abundant oxygen vacancies within the surface lattice. This catalyst exhibits enhanced ORR activity (larger limiting current density of ~-5.8 mA cm-2) and higher stability (~90% retention after 40,000 s) compared with those of NiCo2O4/HCS and NiCo2O4. The results of X-ray photoelectron spectroscopy (XPS) characterizations suggest that the introduction of oxygen vacancies optimizes valence state of active sites. Furthermore, we carried out density functional theory (DFT) calculations to further confirm the mechanism of oxygen vacancies, and results show that oxygen vacancies enhance the density of states (DOS) near Fermi level, decrease work function and lower the calculated overpotential of NiCo2O4.

Concepts: Photosynthesis, Carbon dioxide, Iron, Hydrogen, Redox, Electrochemistry, Nitrogen, Carbon

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It has long been documented in literature that, the lone-pair electrons (LPE) are generally thought to lead to low lattice thermal conductivity (κL) of bulk materials by inducing strong phonon anharmonicity. Herein, we show an exceptional case of two-dimensional (2D) penta-CN2 that possesses LPE but exhibits more than doubled κL (660.71 Wm-1K-1) than the LPE free counterpart of penta-graphene (252.95 Wm-1K-1), which is unexpected and contradictory to the traditional theory of LPE leading to low κL. Based on the comparative study of four 2D systems possessing LPE and their respective LPE free counterparts (planar C3N vs. graphene and penta-CN2 vs. penta-graphene), the underlying mechanism is found lying in the bonds homogenization in penta-CN2 due to the wide spatial extension of the non-symmetrically distributed LPE, which compensates the lattice anharmonicity due to LPE and is responsible for the opposite tendency of LPE affected κL in the four 2D systems.

Concepts: Vector space, Thermal conductivity, Metaphysics, Counterparts

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High tech applications, primarily photovoltaics, have greatly increased demand for the rare and versatile but toxic element tellurium (Te). Here we examine dated lake sediment Te concentration profiles collected near potential point sources (metal smelters, coal mining/combustion facilities, oil sands operations) and from rural regions and remote natural areas of Canada. Te contamination was most prevalent near a Cu/Zn smelter where observed deposition infers 21 g Te released per metric ton (t) of Cu processed. Globally, 9,500 t is predicted to have been atmospherically deposited near Cu smelters post-1900. In a remote area of central Canada (Experimental Lakes Area; ELA), preindustrial Te deposition rates were equivalent to the estimated average global mass flux supplied from natural sources; however more surprisingly, modern Te deposition rates were 6-fold higher and comparable with Te measurements in precipitation. We therefore suggest that sediment cores reliably record atmospheric Te deposition and that anthropogenic activities have significantly augmented atmospheric Te levels, making it an emerging contaminant of potential concern. Lake water residence time was found to influence lake sediment Te inventories among lakes within a region. The apparent settling rate for Te was comparable to macronutrients (C, N, P), likely indicative of significant biological processing of Te.

Concepts: Lake, Sediment, Water pollution, Copper, Canada, Tellurium, Region, Smelting

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Owing to the need for portable and sustainable energy sources and the development trend for microminiaturization and multifunctionalization in the electronic components, the study of integrated self-charging power packs has attracted increasing attention. A new self-charging power pack consisting of a silicon nanowire array/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hybrid solar cell and a laser-scribed graphene (LSG) supercapacitor has been fabricated. The Si nanowire array/PEDOT:PSS hybrid solar cell structure exhibited a high power conversion efficiency (PCE) of 12.37%. The LSG demonstrated excellent energy storage capability for the power pack, with high current density, energy density, and cyclic stability when compared to other supercapacitor electrodes such as active carbon and conducting polymers. The overall efficiency of the power unit is 2.92%.

Concepts: Energy, Density, Electric current, Carbon, Solar cell, Energy conversion, Energy conversion efficiency, Capacitor

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The carbon intensity of economic activity, or CO2 emissions per unit GDP, is a key indicator of the climate impacts of a given activity, business, or region. Although it is well-known that the carbon intensity of countries varies widely according to their level of economic development and dominant industries, few studies have assessed disparities in carbon intensity at the level of cities due to limited availability of data. Here, we present a detailed new inventory of emissions for 337 Chinese cities (every city in mainland China including 333 prefecture-level divisions and 4 province-level cities, Beijing, Tianjin, Shanghai, and Chongqing) in 2013, which we use to evaluate differences of carbon intensity between cities and the causes of those differences. We find that cities' average carbon intensity is 0.84 kg of CO2 per dollar of gross domestic product (kgCO2 per $GDP), but individual cities span a large range: from 0.09 to 7.86 kgCO2 per $GDP (coefficient of variation of 25%). Further analysis of economic and technological drivers of variations in cities' carbon intensity reveals that the differences are largely due to disparities in cities' economic structure that can in turn be traced to past investment-led growth. These patterns suggest that “carbon lock-in” via socio-economic and infrastructural inertia may slow China’s efforts to reduce emissions from activities in urban areas. Policy instruments targeted to accelerate the transition of urban economies from investment-led to consumption-led growth may thus be crucial to China meeting both its economic and climate targets.

Concepts: Carbon dioxide, Economics, China, People's Republic of China, Economic growth, Global warming, Beijing, Economy

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Capillary open microsystems are attractive and increasingly used in biotechnology, biology, and diagnostics as they allow simple and reliable control of fluid flows. In contrast to closed microfluidic systems, however, two-phase capillary flows in open microfluidics have remained largely unexplored. In this work, we present the theoretical basis and experimental demonstration of a spontaneous capillary flow (SCF) of two-phase systems in open microchannels. Analytical results show that an immiscible plug placed in an open channel can never stop the SCF of a fluid in a uniform cross-section microchannel. Numerical investigations of the morphologies of immiscible plugs in a capillary flow reveal three different possible behaviors. Finally, the predicted behaviors of the plugs are demonstrated experimentally, revealing an effect of inertial forces on the plug behavior. A model for predicting plug behaviors in SCFs is proposed, enabling the design of open microfluidic droplet-based systems that are simple to fabricate and use. The open-channel approach to droplet-based microfluidics has the potential to enable applications in which each drop can be accessed at any time and any location with simple pipettes or other fluid dispensing systems.

Concepts: Scientific method, Fluid dynamics, Force, Liquid, Surface tension, Motivation, Capillary action, Inertia

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In this work, the self-assembled behaviors of zwitterionic copolymer docosahexaenoic acid-b-poly(γ-benzyl-L-glutamate)-b-poly(carboxybetaine methacrylate) (DHA- PBLG-PCB) and the loading and release mechanism of the anti-cancer drug doxorubicin (DOX) was investigated via computer simulations. The effects of polymer concentration, drug content and pH on polymeric micelles were explored by dissipative particle dynamics (DPD) simulations. Simulation results show that DHA-PBLG15-PCB10 can self-assemble into core-shell micelles; in addition, the drug-loaded micelles have a pH-responsive feature. DOX can be encapsulated into the core-shell micelle at the normal physiological pH condition; whereas it can be released at the acidic pH condition. The self-assembled behaviors of copolymer DHA-PBLG-PEG were also studied to have a comparison with those of DHA-PBLG-PCB. The DHA-PBLG15-PCB10 system has a stable structure and it has a great potential to serve as drug delivery vehicles for targeted drug delivery.

Concepts: Psychology, Chemotherapy, PH, Computer graphics, Monte Carlo method, Computer simulation, Mathematical model, AnyLogic

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Two California heavy-duty fleets have been measured in 2013, 2015, and 2017 using the On-Road Heavy-Duty Measurement System. The Port of Los Angeles drayage fleet has increased in age by 3.3 model years (4.2-7.5 years old) since 2013, with little fleet turnover. Large increases in fuel-specific particle emissions (PM) observed in 2015 were reversed in 2017, returning to near 2013 levels, suggesting repairs and or removal of high emitting vehicles. Fuel-specific oxides of nitrogen (NO x) emissions of this fleet have increased, and NO x after-treatment systems do not appear to perform ideally in this setting. At the Cottonwood weigh station in northern California, the fleet age has declined (7.8 to 6 years old) since 2013 due to fleet turnover, significantly lowering the average fuel-specific emissions for PM (-87%), black carbon (-76%), and particle number (-64%). Installations of retrofit-diesel particulate filters in model year 2007 and older vehicles have further decreased particle emissions. Cottonwood fleet fuel-specific NO x emissions have decreased slightly (-8%) during this period; however, newer technology vehicles with selective catalytic reduction systems (SCR) promise an additional factor of 4-5 further reductions in the long-haul fleet emissions as California transitions to an all SCR-equipped fleet.

Concepts: Measurement, Systems of measurement, Fleet, The Fleet, Spanish missions in California

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High ionic conductivity, satisfactory mechanical properties, and wide electrochemical windows are crucial factors for composite electrolytes employed in solid-state lithium-ion batteries (SSLIBs). Based on these considerations, we fabricate Mg2B2O5 nanowire enabled poly(ethylene oxide) (PEO)-based solid-state electrolytes (SSEs). Notably, these SSEs have enhanced ionic conductivity and a large electrochemical window. The elevated ionic conductivity is attributed to the improved motion of PEO chains and the increased Li migrating pathway on the interface between Mg2B2O5 and PEO-LiTFSI. Moreover, the interaction between Mg2B2O5 and -SO2- in TFSI- anions could also benefit the improvement of conductivity. In addition, the SSEs containing Mg2B2O5 nanowires exhibit improved the mechanical properties and flame-retardant performance, which are all superior to the pristine PEO-LiTFSI electrolyte. When these multifunctional SSEs are paired with LiFePO4 cathodes and lithium metal anodes, the SSLIBs show better rate performance and higher cyclic capacity of 150, 106, and 50 mAh g-1 under 0.2 C at 50, 40, and 30 °C. This strategy of employing Mg2B2O5 nanowires provides the design guidelines of assembling multifunctional SSLIBs with high ionic conductivity, excellent mechanical properties, and flame-retardant performance at the same time.

Concepts: Cathode, Electrochemistry, Battery, Electrolyte, Lithium-ion battery, Lithium, Nanowire battery, Lithium iron phosphate battery