- Formation of monodisperse and shape-controlled MnO nanocrystals in non-injection synthesis: Self-focusing via ripening
-
Formation of nearly monodiperse MnO nanocrystals by simple heating of Mn stearate in octadecene was studied systematically and quantitatively as a model for non-injection synthesis of nanocrystals. For controlling the shape of the nanocrystals, that is, rice, rods, peanuts, needles, and dots, either an activation reagent (ocadecanol) or an inhibitor (stearic acid) might be added prior to heating. The quantitative results of this typical non-injection system reveal that the formation of nearly monodisperse nanocrystals did not follow the well-known focusing of size distribution mechanism. A new growth mechanism, self-focusing enabled by inter-particle diffusion, is proposed. Different from the traditional focusing of size distribution , self-focusing not only affects the growth process of the nanocrystals, but may also play a role in controlling nucleation. Because of the simplicity of the reaction system, it was possible to also identify the chemical reactions associated with the growth and ripening of MnO nanocrystals with a variety of shapes. Through a recycling reaction path, water was identified as a decisive component in determining the kinetics for both growth and ripening in this system, although the reaction occurred at around 300°C.
- Chen, Yongfen,Johnson, Eric,Peng, Xiaogang
-
-
Read Online
- Facile synthesis of highly luminescent Mn-doped ZnS nanocrystals
-
Manganese-doped zinc sulfide quantum dots (Mn:ZnS d-dots) with high optical quality, pure dopant emission of 55-65% photoluminescence quantum yield, were synthesized in octadecene media with generic starting materials, namely, zinc (manganese) carboxylic acid salts, S powder, and dodecanethiol (DDT) based on a nucleation doping strategy. The optical properties and structure of the obtained Mn:ZnS d-dots have been characterized by UV-vis, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The resulting nearly monodisperse d-dots were found to be of spherical shape with a zinc-blende crystal structure. The influences of various experimental variables, including the reaction temperature for the MnS core nanocluster and ZnS host material, the amount of octadecene (ODE)-S, DDT, as well as Zn/Mn ratio have been systematically investigated. The use of DDT as capping ligand ensured the reproducible access to a stable small-sized MnS core. This paves the way for reproducibly obtaining highly luminescent d-dots. Programmed overcoating temperature for growth of ZnS shell was employed to realize balanced diffusion of the Mn ions in the d-dots.
- Zhang, Wenjin,Li, Yan,Zhang, Hua,Zhou, Xinggui,Zhong, Xinhua
-
-
Read Online
- Manganese doped fluorescent paramagnetic nanocrystals for dual-modal imaging
-
In this work, dual-modal (fluorescence and magnetic resonance) imaging capabilities of water-soluble, low-toxicity, monodisperse Mn-doped ZnSe nanocrystals (NCs) with a size (6.5 nm) below the optimum kidney cutoff limit (10 nm) are reported. Synthesizing Mn-doped ZnSe NCs with varying Mn2+ concentrations, a systematic investigation of the optical properties of these NCs by using photoluminescence (PL) and time resolved fluorescence are demonstrated. The elemental properties of these NCs using X-ray photoelectron spectroscopy and inductive coupled plasma-mass spectroscopy confirming Mn2+ doping is confined to the core of these NCs are also presented. It is observed that with increasing Mn2+ concentration the PL intensity first increases, reaching a maximum at Mn2+ concentration of 3.2 at% (achieving a PL quantum yield (QY) of 37%), after which it starts to decrease. Here, this high-efficiency sample is demonstrated for applications in dual-modal imaging. These NCs are further made water-soluble by ligand exchange using 3-mercaptopropionic acid, preserving their PL QY as high as 18%. At the same time, these NCs exhibit high relaxivity (≈2.95 mM-1 s-1) to obtain MR contrast at 25°C, 3 T. Therefore, the Mn2+ doping in these water-soluble Cd-free NCs are sufficient to produce contrast for both fluorescence and magnetic resonance imaging techniques.
- Sharma, Vijay Kumar,Gokyar, Sayim,Kelestemur, Yusuf,Erdem, Talha,Unal, Emre,Demir, Hilmi Volkan
-
-
Read Online
- Efficient and color-tunable Mn-doped ZnSe nanocrystal emitters: Control of optical performance via greener synthetic chemistry
-
Formation of Mn-doped ZnSe quantum dots (Mm:ZnSe d-dots) using nucleation-doping strategy was studied systematically and optimized through greener approaches. The resulting d-dots were with high (~50%) photoluminescence (PL) quantum yield (QY), which was achieved by the controlled formation of small-sized MnSe nanoclusters as the core and a diffused interface between the nanocluster core and the ZnSe overcoating layers. Synthesis of the d-dots under high temperatures (240-300 °C) was achieved by varying the structure of the metal carboxylate precursors, concentration of the inhibitors, free fatty acid, and concentration of the activation reagents, fatty amines. Highly emissive d-dots synthesized under desired conditions were found to be extremely stable upon thermal treatment up to the boiling point of the solvent (about 300 °C), which was quantitatively studied using in situ measurements. The PL peak of the d-dots was controllably tuned in a surprisingly large optical window, from 565 to 610 nm. These highly emissive and stable d-dots possess characteristics of practical emissive materials, especially for applications requiring high power, high concentration of emitters, and under tough conditions.
- Pradhan, Narayan,Peng, Xiaogang
-
-
Read Online
- ANTIFERROMAGNETISM OF QUASI TWO-DIMENSIONAL MANGANESE STEARATE.
-
The magnetic properties of manganese stearate, a highly two-dimensional magnetic material, are found to change considerably when it is synthesized by a new procedure. Whereas earlier samples behaved like weak-ferromagnets with ordering temperatures about 5 K, the new material is an antiferromagnet with T//n equals 10 K. The reasons may be a change in the crystal structure.
- Aviram,Pomerantz
-
-
Read Online
- Tailoring Catalytic Properties of Copper Manganese Oxide Nanoparticles (Hopcalites-2G) via Flame Spray Pyrolysis
-
Humidity tolerant copper manganese oxide catalysts of the second generation (“Hopcalites-2G”) were produced by flame spray pyrolysis process (FSP) and their catalytic activity for carbon monoxide oxidation under dry and humid conditions was evaluated. The effects of synthesis parameters such as flame specific variables (OFR=oxygen to fuel ratio, sheath gas, reactor) and the precursor specifications (composition, concentration, solvent) were investigated systematically. From the findings of the synthesis variations, it was possible to identify key factors decisive to achieve a high catalytic activity for CO oxidation under humid conditions. The most important characteristics are phase composition, specific surface area and the carbon content to achieve increased long-term stability of the flame made catalysts under humid conditions. A high productivity in the flame-based Hopcalite synthesis was achieved with catalysts performances similar or better than that of the commercial Hopcalite catalyst Carulite 300 (CARUS). The most active catalyst showed 50 % higher CO conversion after one hour on stream at 50 °C and humid conditions compared with the reference. The latter is a crucial step towards an improved humidity tolerance of Hopcalite catalysts in respiratory filter applications.
- Wegner, Karl,Medicus, Maximilian,Schade, Elke,Grothe, Julia,Kaskel, Stefan
-
p. 3914 - 3922
(2018/08/06)
-
- Characterisation of metal carboxylates by Raman and infrared spectroscopy in works of art
-
This work introduces the complementary use of μ-Raman and μ-Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples. Metal carboxylates (metal soaps) form naturally when free fatty acids react with metal cations and may also be found as additives or degradation products. Twenty-two metal carboxylates were synthesised, and their spectra assembled in a reference database. Metal salts of cations commonly present in oil paintings were used, including lead, zinc, calcium, cadmium, copper and manganese. The fatty acids selected were the saturated acids palmitic (C1 6:0) and stearic (C18:0) and the polyunsaturated oleic acid (C1 8:1). Azelaic acid (C9 diacid), a product resulting from autoxidation of polyunsaturated acids, was also included. Metal carboxylates were characterised by Raman and IR spectroscopy, and their structures were confirmed by X-ray diffraction. Raman and IR spectroscopy proved to be complementary techniques for a full identification of the metal carboxylates in complex aged paint. Raman enables the differentiation of the carbon chain length in the C-C stretching region (1120-1040 cm-1), and IR distinguishes the metal cation in the COO- stretching absorption region (1650-1380cm-1). Principal component analysis was applied to the spectra in order to facilitate a fast and accurate method to discriminate between the different metal carboxylates and to aide in their identification. Finally, spectra from case studies were successfully projected in the principal component analysis models built, enabling a higher confidence level for the identification of copper palmitate and copper azelate in two 19th-century Portuguese oil paintings.
- Otero, Vanessa,Sanches, Diogo,Montagner, Cristina,Vilarigues, Mrcia,Carlyle, Leslie,Lopes, Joo A.,Melo, Maria J.
-
p. 1197 - 1206
(2015/02/19)
-
- Influence of doping on semiconductor nanocrystals mediated charge transfer and photocatalytic organic reaction
-
Doped and undoped ZnS semiconductor nanocrystals having different recombination pathways are explored to study the charge transfer reaction between the nanocrystals and the 4-nitrophenol/sodium borohydride redox couple.
- Sarkar, Suresh,Guria, Amit K.,Pradhan, Narayan
-
supporting information
p. 6018 - 6020
(2013/07/27)
-
- Wet-chemical catalyst deposition for scalable synthesis of vertical aligned carbon nanotubes on metal substrates
-
A scalable process for carbon nanotube (CNT) growth on metallic substrates has been developed including dip-coating steps for the wet-chemical catalyst and co-catalyst layer deposition and a subsequent chemical vapor deposition step. Organic metal salt/2-propanol solutions were applied as precursors for alumina co-catalyst thin films and the actual Fe (Co, Mo) catalyst layer. Vertical aligned carbon nanotube forests were obtained on catalyst-coated nickel foil in a thermal CVD process at atmospheric pressure and 730 °C using ethene as carbon source. The influence of the catalyst composition on growth rate, density and structure of resulting CNT films was investigated.
- Doerfler,Meier,Thieme,Nemeth,Althues,Kaskel
-
p. 288 - 293
(2011/10/06)
-
- Phosphine-free synthesis of high quality ZnSe, ZnSe/ZnS, and Cu-, Mn-doped ZnSe nanocrystals
-
High quality zinc blende ZnSe and ZnSe/ZnS core/shell nanocrystals have been synthesized by two converse injection methods (i.e. zinc precursor injection or selenium precursor injection) when Se-ODE complex was chosen as the phosphine-free selenium precur
- Shen, Huaibin,Wang, Hongzhe,Li, Xiaomin,Niu, Jin Zhong,Wang, Hua,Chen, Xia,Li, Lin Song
-
p. 10534 - 10540
(2010/04/04)
-
- Catalytic oxidative cleavage of terminal olefins by chromium(III) stearate
-
A new synthetic methodology for the preparation of carbonyl compounds from the oxidative cleavage of terminal olefins has been developed. With the use of TBHP in combination with chromium(III) stearate, selective oxidation of double bonds conjugated with aromatic ring or carbonyl group could be achieved at ambient temperature in moderate to excellent yield. The oxidative cleavage of electron rich α-methylstyrene derivatives proceeded in good to excellent yield whereas lower yields were observed in α-methylstyrene derivatives containing an electron withdrawing group. This developed oxidation reaction was believed to undergo via free radical process and high valent chromium oxo species.
- Jarupinthusophon, Suekanya,Thong-In, Uthumporn,Chavasiri, Warinthorn
-
p. 289 - 294
(2008/10/09)
-
- Synthesis of biodiesel via homogeneous Lewis acid catalyst
-
Nowadays, most biodiesel (fatty acids methyl esters, FAME) is produced by the transesterification of triglycerides (TG) of refined/edible type oils using methanol and an homogeneous alkaline catalyst. However, production costs are still rather high compared with the ones of petroleum-based diesel fuel. To lower costs and make biodiesel competitive less-expensive feedstocks such as waste fats or non-edible type oils could be used. The use of homogeneous alkaline catalysts in the transesterification of such types of fats and oils poses great difficulties due to the presence of large amounts of free fatty acids (FFA). This paper studies the use of carboxylic salts as a possible alternative, because these catalysts are active also in the presence of high FFA concentrations. The most active catalyst (Cd, Mn, Pb, Zn carboxylic salts) have been individuated and a correlation of the activities with the cation acidity has been found.
- Di Serio,Tesser,Dimiccoli,Cammarota,Nastasi,Santacesaria
-
p. 111 - 115
(2008/10/09)
-
- Liquid Phase Oxidation of s-Butyltoluene
-
Oxidation of s-butyltoluene (SBT) to its hydroperoxide (ROOH) by oxygen has been studied in the presence and absence of catalysts in aqueous suspension at 80 deg to 116 deg C and 1 to 8.5 kg/cm2 O2 pressure.The oxidation rate is higher at higher pressures and the selectivity to ROOH formation is the highest when no catalyst is used.Effects of various reaction parameters have been studied in the absence of catalyst.A reaction temperature of 100 deg, SBT-water ratio of 1:2 and oxygen pressure of more than 3 kg/cm2 are found to be the most suitable for ROOH formation.Oxidation above 11.5percent ROOH level leads mainly to byproducts including s-butylbenzoic acid.
- Kulsrestha, Girendra N.,Pathania, Bikram S.,Sharma, Krishna G.,Sharma, Jaipal S.,Negi, Janaki,Bhattacharyya, Kshitindra K.
-
p. 636 - 638
(2007/10/02)
-