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1wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Uniform water-soluble monolayer MoS 2 quantum dots (MQDs) with lateral sizes of ≈2.1 nm, a clearly zigzag-terminated edge, and a hexagonal lattice structure are achieved using ammonium molybdate, thiourea, and N-acetyl-L -cysteine (NAC) as precursors and the capping reagent in a facile one-pot hydrothermal approach. MQDs have good dispersity and high stability in aqueous suspension and exhibit a signifi cantly larger direct bandgap (3.96 eV) compared to monolayer MoS 2 nanosheets (1.89 eV). Pronounced blue-shifts in the wavelengths of both the excitonic absorption and intrinsic state emission with activated strong luminescence at room temperature beyond monolayer MoS 2 nanosheets is demonstrated. Unusual upconversion photoluminescence is also observed and is caused by two successive transfers of energy from the near-infrared (NIR) absorption generated by the NAC capping reagent to the hexagonal structure of MQDs. Additional optical properties of MQDs may provide numerous exciting technological applications. Here, MQDs are demonstrated as a highly selective fl uorescent reagent for detecting tetracycline hydrochloride under UV and NIR irradiation. hydrogen storage, [ 10 ] nano-lubrication, [ 11 ] lithium ion batteries, [ 12 ] and biomedical imaging. [ 13 ] Few works emerged very recently concerning isolation and deposition of high-quality monolayer MoS 2 nanosheets by the top-down [ 14 ] and bottomup [ 9a , 15 ] approaches. Dramatic changes in the electronic structure and optical properties compared to the bulk counterparts were observed in these 2D ultrathin atomic layer structures. [ 16 ] When the lateral size of monolayer MoS 2 nanosheets further reduces to less than 10 nm leading to monolayer MoS 2 quantum dots (MQDs), extra fl uorescent property beyond singlelayer MoS 2 nanosheets might be obtained, since pronounced sizable bandgap in semiconducting TMDs has already been predicted. [ 17 ] However, rigorous control of the thickness and lateral size of these nanosheets is still a huge challenge. Exploitation of monolayer MQDs with extra optical properties has not been reported. In this paper, effective fabrication of uniform water-soluble monolayer MQDs of lateral size ≈2.1 nm by using a facile one-pot hydrothermal procedure is reported. These single-layer MQDs have good dispersity and high stability in aqueous suspension and possess unusual fl uorescence (especially near-infrared (NIR) excitation behavior). These attributes distinguish monolayer MQDs from single-layer MoS 2 nanosheets, which may offer going beyond fundamental pathways and open up numerous technological applications in catalysis, sensing, hydrogen storage, lithium ion batteries, photovoltaic devices, and microelectronics. Here, the fl uorescent properties of monolayer MQDs are demonstrated to be useful for highly selective detection of tetracycline hydrochloride under UV and NIR irradiation. Results and Discussion Synthesis and Characterization of MQDsMonolayer MQDs wer...

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Controllable engineering of high-electronegativity oxygen (O)-heteroatoms into MoS2 ultrathin nanosheets is realized via a facile post-modification process.

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Two types of gold nanoclusters (GNCs), one covered by self-assembled monolayers (SAMs) of mercaptoundecanoic acid (MUA), hexanethiol (C 6 SH), and ferrocenylhexanethiol (FcC 6 SH), MHF-GNC, and the other with MUA and C 6 SH, MH-GNC, were used for the construction of ten GNC layers of two different sequences on an MUA modified Au (111) surface based on the carboxylate/polycation (poly(allylamine hydrochloride) :PAH)/carboxylate electrostatic interaction. MHF-GNC was placed either as the layer closest to the gold electrode, i.e., the first layer, or as the outermost layer with MH-GHC in the other layers. A quasi-reversible redox peak with a constant charge corresponding to the redox of the ferrocene moiety of the MHF-GNC monolayer was observed at both electrodes, showing electrons and perchlorate ions could be transferred through the MH-GNC/PAH multilayers.Cross-sectional transmission electron microscopy revealed that the size of the immobilized GNC was almost same as that in solution and well-separated GNCs were dispersed rather uniformly within the polymeric matrix. The incorporation of perchlorate ion upon the oxidation of the ferrocene moiety of the MHF-GNC was demonstrated by electrochemical quartz microbalance measurement. Based on the above results, the charge transfer mechanism in the GNC multilayers was discussed.2

As one of promising catalysts that contain high density of active sites, N doped carbons have been extensively researched, while the reports for N, S dual-doped carbon materials are far less exhaustive. Herein, devoid of activation process and template, N, S dual-doped porous carbon (N-S-PC) was prepared for the first time via one-step pyrolysis of sodium citrate and cysteine. Possessing unique porous structure and large pore volume as well as good accessibility, N-S-PC demonstrates significantly improved electrocatalytic activity toward oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA). In the coexisting system, the peak potential separation between AA and DA is up to 251 mV, which is much larger than for most of the other carbons. On the basis of large potential separation and high current response, selective and sensitive simultaneous determination of AA, DA, and UA was successfully accomplished by differential pulse voltammetry, displaying a linear response from 50 to 2000 μM, from 0.1 to 50 μM, and from 0.1 to 50 μM with a detection limit (S/N = 3) of 0.78, 0.02, and 0.06 μM. This work highlights the importance of N, S dual doping and hierarchical porous carbons for efficient catalysis.