The detection of explosives is one of the current pressing concerns in global security. In the past few decades, a large number of emissive sensing materials have been developed for the detection of ...explosives in vapor, solution, and solid states through fluorescence methods. In recent years, great efforts have been devoted to develop new fluorescent materials with various sensing mechanisms for detecting explosives in order to achieve super-sensitivity, ultra-selectivity, as well as fast response time. This review article starts with a brief introduction on various sensing mechanisms for fluorescence based explosive detection, and then summarizes in an exhaustive and systematic way the state-of-the-art of fluorescent materials for explosive detection with a focus on the research in the recent 5 years. A wide range of fluorescent materials, such as conjugated polymers, small fluorophores, supramolecular systems, bio-inspired materials and aggregation induced emission-active materials, and their sensing performance and sensing mechanism are the centerpiece of this review. Finally, conclusions and future outlook are presented and discussed.
In quantum field theory, we learn that fermions come in three varieties: Majorana, Weyl, and Dirac. Here, we show that in solid-state systems this classification is incomplete, and we find several ...additional types of crystal symmetry-protected free fermionic excitations. We exhaustively classify linear and quadratic three-, six-, and eight-band crossings stabilized by space group symmetries in solid-state systems with spin-orbit coupling and time-reversal symmetry. Several distinct types of fermions arise, differentiated by their degeneracies at and along high-symmetry points, lines, and surfaces. Some notable consequences of these fermions are the presence of Fermi arcs in non-Weyl systems and the existence of Dirac lines. Ab initio calculations identify a number of materials that realize these exotic fermions close to the Fermi level.
With the increase of tunnel length, the air volume imbalance among the outlets for the central exhaust system is serious. Which causes the actual air volume of the end outlet is small. Combined with ...the design of an urban road tunnel, even air distributor (EAD) groups are installed in the exhaust duct. For different EAD groups setting, the air volume imbalance among the outlets and the resistance characteristics of exhaust system are analyzed. The results show that EAD groups improve the air exhaust uniformity significantly, which is less affected by the exhaust air volume. Furthermore, the flow impedance of the exhaust duct presents a two-stage increase distribution corresponding to the augment of exhaust air rate for a given duct width. For the central exhaust system equipped with EAD groups, closing the 1#-3# outlets can further reduce the CO concentration in the middle section of tunnel.
In recent years, the development of optical probes to analyse trace palladium ions (Pd
2+
) has attracted great attention because of the residual palladium released by catalytic converters or from ...various Pd-catalysed reactions. These residual palladium ions may cause potential health hazards. This review provides a brief introduction to the new methods used to determine trace amounts of Pd
2+
, which then mainly focuses on the different reporting systems and unique mechanisms of the colourimetric and fluorescent probes used to detect Pd
2+
, including Pd
2+
complex formation or Pd-catalysed reactions.
This review focuses on the colourimetric and fluorescent probes used for the optical sensing of palladium ions, discussed according to their different sensing mechanisms.
The proton exchange membrane fuel cell (PEMFC) as an attractive clean power source can promise a carbon-neutral future, but the widespread adoption of PEMFCs requires a substantial reduction in the ...usage of the costly platinum group metal (PGM) catalysts. Ultrafine nanocatalysts are essential to provide sufficient catalytic sites at a reduced PGM loading, but are fundamentally less stable and prone to substantial size growth in long-term operations. Here we report the design of a graphene-nanopocket-encaged platinum cobalt (PtCo@Gnp) nanocatalyst with good electrochemical accessibility and exceptional durability under a demanding ultralow PGM loading (0.070 mgPGM cm–2) due to the non-contacting enclosure of graphene nanopockets. The PtCo@Gnp delivers a state-of-the-art mass activity of 1.21 A mgPGM–1, a rated power of 13.2 W mgPGM–1 and a mass activity retention of 73% after an accelerated durability test. With the greatly improved rated power and durability, we project a 6.8 gPGM loading for a 90 kW PEMFC vehicle, which approaches that used in a typical catalytic converter.Ultrafine catalysts are desirable for the reduction of fuel cell costs but are intrinsically unstable. Here the authors report graphene-nanopocket-encaged PtCo catalysts with exceptional durability under the demanding ultralow-Pt-loading condition while delivering a satisfactory fuel cell performance.
Abstract
In order to study the influence of the positive slope of the fire source on the smoke control effect of the lateral smoke exhaust system of the tunnel, this paper established a tunnel fire ...model, reasonably divided the grid, and controlled variables such as the scale of the fire source, the amount of smoke, and the smoke outlet. Using FDS simulation software, by changing the forward slope of the fire source, study the temperature distribution, CO concentration, and smoke settlement height of the tunnel fire. The simulation shows that the effect of the tunnel lateral smoke exhaust system is different when the fire source is located on different slopes.
Platinum (Pt)-based materials are important components of microelectronic sensors, anticancer drugs, automotive catalytic converters and electrochemical energy conversion devices
. Pt is currently ...the most common catalyst used for the oxygen reduction reaction (ORR) in devices such as fuel cells and metal-air batteries
, although a scalable use is restricted by the scarcity, cost and vulnerability to poisoning of Pt (refs
). Here we show that nanoparticulate zirconium nitride (ZrN) can replace and even surpass Pt as a catalyst for ORR in alkaline environments. As-synthesized ZrN nanoparticles (NPs) exhibit a high oxygen reduction performance with the same activity as that of a widely used Pt-on-carbon (Pt/C) commercial catalyst. Both materials show the same half-wave potential (E
= 0.80 V) and ZrN has a higher stability (ΔE
= -3 mV) than the Pt/C catalyst (ΔE
= -39 mV) after 1,000 ORR cycles in 0.1 M KOH. ZrN is also shown to deliver a greater power density and cyclability than Pt/C in a zinc-air battery. Replacement of Pt by ZrN is likely to reduce costs and promote the usage of electrochemical energy devices, and ZrN may also be useful in other catalytic systems.
Beyond fossil fuel-driven nitrogen transformations Chen, Jingguang G; Crooks, Richard M; Seefeldt, Lance C ...
Science (American Association for the Advancement of Science),
05/2018, Volume:
360, Issue:
6391
Journal Article
Peer reviewed
Open access
Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals ...is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.
Abstract
Due to its potential to develop new added value products, a staggering number of nanoparticles (NPs) is already available on the market. Moreover, this increase is expected to continue in ...the future. However, there is a lack of knowledge on the level of exposure to nanoparticles, and the information related to possible adverse health effects is scarce. Furthermore, there is very little studies concerning the effect of risk management measures (RMMs) on the levels of exposure to nanoparticles at workplaces, compared to the number of exposure situations that can be distinguished.
This study focuses on 5 case studies covering different types of materials, assessing the effectiveness of targeted mitigation strategies applied during the production process. Customized mitigation measures were applied in each industrial scenario to minimize exposure levels. The effects on the particle concentration levels using source enclosure, partial or full, combined with local exhaust ventilation systems (LEVs), was evaluated to generate new knowledge to support the definition of informed safe by process design approaches when dealing with NPs. This study demonstrates that technological advancements can significantly reduce work-related exposures. The findings underscore the importance of tailored mitigation measures due to the diverse range of potential sources and activities in industrial scenarios.
•Backfire origins of hydrogen fuelled engines are comprehensively reviewed.•Backfire control technologies of hydrogen engines are detailed discussed.•Correlations between various backfire origins are ...analyzed.•Different backfire control technologies are recommended adopting jointly.
Hydrogen fuel applications in internal combustion engines have attracted increasing attention due to zero carbon emission and excellent combustion characteristics in terms of thermal efficiency. Internal combustion engines fuelled with hydrogen are demonstrated to have higher brake thermal efficiency than other fossil fuel cases. However, abnormal combustion such as backfire in port hydrogen injection engines limits the improvement of internal combustion engine performance resulting from low ignition energy and high flame propagation velocity of hydrogen fuel. Volumetric efficiency drops significantly if backfire occurs; moreover, it brings about damages to the intake systems and fuel injection systems. Backfire is induced by high temperature residual exhaust gas, hot spots, and abnormal discharge of spark plugs; all the factors causing pre-ignition of hydrogen-air mixture promote the backfire occurrences. This paper reviews the factors tending to induce backfire, such as improper intake valve timing and fuel injection timing, and high fuel-air equivalence ratios; additionally, the corresponding backfire control strategies are analyzed with advantages and disadvantages being discussed. The factors leading to backfire are mainly caused by large amounts of residual exhaust gas, extremely slow combustion, and improper hydrogen distributions around intake valve seats. Backfire control strategies have specific application conditions to ensure their effectiveness, beyond which they will generate negative impacts on backfire control effectiveness. Power loss is nearly inevitable for naturally aspirated engines when backfire control strategies are adopted. Multiple control strategies are recommended to ease the engine performance drop caused by backfire control; meantime, multi-objective optimizations are suggested to achieve the optimal global performance.
PDF
