The efficient use of natural gas will require catalysts that can activate the first C-H bond of methane while suppressing complete dehydrogenation and avoiding overoxidation. We report that single iron sites embedded in a silica matrix enable direct, nonoxidative conversion of methane, exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C-C coupling, further oligomerization, and hence, coke deposition. At 1363 kelvin, methane conversion reached a maximum at 48.1% and ethylene selectivity peaked at 48.4%, whereas the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The lattice-confined single iron sites delivered stable performance, with no deactivation observed during a 60-hour test.

Molybdenum disulphide is a novel two-dimensional semiconductor with potential applications in electronic and optoelectronic devices. However, the nature of charge transport in back-gated devices still remains elusive as they show much lower mobility than theoretical calculations and native n-type doping. Here we report a study of transport in few-layer molybdenum disulphide, together with transmission electron microscopy and density functional theory. We provide direct evidence that sulphur vacancies exist in molybdenum disulphide, introducing localized donor states inside the bandgap. Under low carrier densities, the transport exhibits nearest-neighbour hopping at high temperatures and variable-range hopping at low temperatures, which can be well explained under Mott formalism. We suggest that the low-carrier-density transport is dominated by hopping via these localized gap states. Our study reveals the important role of short-range surface defects in tailoring the properties and device applications of molybdenum disulphide.

In this work, spongy graphene (SG), a shape-mouldable and nanoporous kinds of sorbent also increases, and the material with a high specific surface area used as a versatile and recyclable environmental and ecological risk of these sorbent material, is proposed and studied. SG shows highly effi cient absorp-polymers in application remains unclear.As an alternative to polymer, expanded tion of not only petroleum products and fats, but also toxic solvents such graphite (EG) has also been used to as toluene and chloroform (up to 86 times of its own weight), requiring no remove oil. Applying EG as an oil sorbent further pretreatment, which is tens of times higher than that of conventional was first done by Toyoda and Inagaki. [12,13] absorbers. Moreover, SG can be regenerated ( >10 times) by heat treatment, EG is a good absorber for crude oil and yielding the full release of adsorbates (>99%). The present work suggests SG

Molybdenum disulfide is considered as one of the most promising two-dimensional semiconductors for electronic and optoelectronic device applications. So far, the charge transport in monolayer molybdenum disulfide is dominated by extrinsic factors such as charged impurities, structural defects and traps, leading to much lower mobility than the intrinsic limit. Here we develop a facile low-temperature thiol chemistry route to repair the sulfur vacancies and improve the interface, resulting in significant reduction of the charged impurities and traps. High mobility 480 cm 2 V À 1 s À 1 is achieved in backgated monolayer molybdenum disulfide field-effect transistors at room temperature. Furthermore, we develop a theoretical model to quantitatively extract the key microscopic quantities that control the transistor performances, including the density of charged impurities, short-range defects and traps. Our combined experimental and theoretical study provides a clear path towards intrinsic charge transport in two-dimensional dichalcogenides for future high-performance device applications.

A coordinatively unsaturated single iron site confined in a graphene matrix shows an ultrahigh activity for catalytic oxidation.

131wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat. de Being entangled in controlling the electronic properties of graphene for next-generation electronics, [ 1,2 ] monolayer transition metal dichalcogenides such as MS 2 (M = Mo, W) are attracting great interest as 2D semiconductors with a native direct-energy gap in the visible frequency range. [ 3,4 ] Monolayers of other layered materials such as h -BN, GaS, GaSe, TaSe 2 , and so on, have also attracted much attention because of their unique properties when scaled down to monolayers. [5][6][7][8] There are comprehensive and intensive studies on monolayer MoS 2 , including its optical and electronic properties, [9][10][11][12][13][14][15][16][17] valleytronics, [18][19][20][21] strain effects, [22][23][24] thermal effects, [ 25 ] and so on. However, investigations of WS 2 have just started. Similar to 2H-MoS 2 , monolayer 2H-WS 2 can be constructed by sandwiching two atomic layers of S and one atomic layer of W through covalent W-S bonds, where W locates at the body center of a trigonal-prismatic case formed by six S atoms. Confi nement of charge carriers inside the horizontal atomic plane gradually enlarges energy gaps when thinning WS 2 layers. [ 26 ] Instead of an indirect energy gap for multiple layers, a direct energy gap of ∼ 2 eV at the corners (K and K' points) of the Brillouin Zone could be formed in monolayer WS 2 as clearly demonstrated by both theoretical and experimental studies. [ 9,[27][28][29] The immediate consequence, also a benefi t of the existence of such direct bandgap, is the signifi cant enhancement of visible light emission. In WS 2 monolayers, breaking inversion symmetry leads to the strong spin-orbit coupling and the splitting of valence bands at K/K' points with a sub-gap of around 0.4 eV. [ 30 ] Furthermore, the split spins at the time-reversed K and K' valleys have the opposite signs. Thus, such spin-valley coupling offers an extra degree of freedom to charge carriers in WS 2 monolayers. Though it has not been reported in monolayer WS 2 , theory predicts and experiments have observed in monolayer MoS 2 a non-equilibrium charge carrier imbalance at two valleys, revealed by the remarkable difference of absorption of left-( σ -) and right-handed ( σ +) circular polarized lights at the two valleys. [ 9,[18][19][20][21]31 ] All these interesting and important properties, plus the newly revealed potential in the fl exible heterostructures of graphene-WS 2 stacks [ 32,33 ] guarantee a promising future of WS 2 as the candidate of nextgeneration nanoelectronics, spintronics, valleytronics, and optoelectronics. [ 34 ] However, compared to graphene, it is very diffi cult to prepare MS 2 monolayers, and atomically thin MS 2 fl akes made by mechanical exfoliation are much smaller, in fact too small to be well characterized and processed for devices. Most recently, chemical vapor deposition (CVD) has been used to successfully grow large-area single crystals of monolayer MoS 2 . [ 11,[35][36][37][38] However, the c...

The enhancement of power conversion efficiency (PCE) and the development of toxic Cd-, Pb-free quantum dots (QDs) are critical for the prosperity of QD-based solar cells. It is known that the properties (such as light harvesting range, band gap alignment, density of trap state defects, etc.) of QD light harvesters play a crucial effect on the photovoltaic performance of QD based solar cells. Herein, high quality ∼4 nm Cd-, Pb-free Zn-Cu-In-Se alloyed QDs with an absorption onset extending to ∼1000 nm were developed as effective light harvesters to construct quantum dot sensitized solar cells (QDSCs). Due to the small particle size, the developed QD sensitizer can be efficiently immobilized on TiO2 film electrode in less than 0.5 h. An average PCE of 11.66% and a certified PCE of 11.61% have been demonstrated in the QDSCs based on these Zn-Cu-In-Se QDs. The remarkably improved photovoltaic performance for Zn-Cu-In-Se QDSCs vs Cu-In-Se QDSCs (11.66% vs 9.54% in PCE) is mainly derived from the higher conduction band edge, which favors the photogenerated electron extraction and results in higher photocurrent, and the alloyed structure of Zn-Cu-In-Se QD light harvester, which benefits the suppression of charge recombination at photoanode/electrolyte interfaces and thus improves the photovoltage.

Evolution of growth/dissolution conductive filaments (CFs) in oxide-electrolyte-based resistive switching memories are studied by in situ transmission electron microscopy. Contrary to what is commonly believed, CFs are found to start growing from the anode (Ag or Cu) rather than having to reach the cathode (Pt) and grow backwards. A new mechanism based on local redox reactions inside the oxide-electrolyte is proposed.