Sn Precursor Research Articles

Synthesis of chelating diamido Sn(IV) compounds from oxidation of Sn(II) and directly from Sn(IV) precursors.

Three dimethyltindiamides containing chelating diamide ligands were synthesised from the reaction of the dilithiated diamine and Me2SnCl2; [SnMe2(L1)] 1 (L1 = κ(2)-N(Dipp)C2H4N(Dipp)), [SnMe2(L2)] 2 (L2 = κ(2)-N(Dipp)C3H6N(Dipp)) and [SnMe2(L3)] 3 (L3 = κ(2)-N(Dipp)SiPh2N(Dipp)), Dipp = 2,6-(i)Pr2C6H3. Reaction of (L2)H2 with SnCl4 and NEt3 led to the formation of the diamidotin dichloride [SnCl2(L2)] 4 whereas reaction of (L1)H2 with SnCl4 and NEt3, or [Sn(L1)] with SnCl4, led to the exclusive formation of the amidotin trichloride [SnCl3{κ(2)-DippN(H)C2H4N(Dipp)}] 5. Reactions of [Sn(L1)] with sulfur and selenium formed [{Sn(L1)(μ-E)}2] (E = S 10 and Se )11. MeI reacted with N-heterocyclic stannylenes to generate the Sn(iv) addition products [Sn(Me)I(L1)] 12, [Sn(Me)I(L2)] 13, [Sn(Me)I(L3)] 14 and [Sn(Me)I(L4)] 15 (L4 = κ(3)-N(Dipp)C2H4OC2H4N(Dipp)), and subsequent reaction with AgOTf (OTf = OSO2CF3) generated the corresponding Sn(iv) triflates [Sn(Me)OTf(L1)] 16, [Sn(Me)OTf(L2)] 17 and [Sn(Me)OTf(L4)] 19 with [Sn(Me)OTf(L3)] 18 formed only as a mixture with unidentified by-products. All of the compounds were characterised by single crystal X-ray diffraction.

Thin-walled SnO₂ nanotubes functionalized with Pt and Au catalysts via the protein templating route and their selective detection of acetone and hydrogen sulfide molecules.

Bio-inspired Pt (∼2 nm) and Au (∼2.7 nm) catalysts encapsulated by a protein shell, i.e., Pt-apoferritin (Pt@AF) and Au-apoferriten (Au@AF), were synthesized via the hollow protein nanocage (apoferritin) templating route and directly functionalized on the interior and exterior walls of electrospun SnO2 nanotubes (NTs) during controlled single-nozzle electrospinning followed by high temperature calcination with heating rate control. Fast crystallization of the exterior shell and outward diffusion of the interior Sn precursors and crystallites result in the continued growth of a tubular wall, which is related to rapid heating driven Ostwald-ripening behavior. Very importantly, the Pt and Au nanoparticles (NPs) were immobilized onto thin-walled SnO2 NTs with a diameter of ∼350 nm and a shell thickness of ∼40 nm without any aggregation of catalysts due to high dispersibility, which originated from repulsive electrostatic (Coulombic) forces acting on the surface charged protein shells, leading to an enhanced catalytic effect and outstanding gas sensing properties. Pt-loaded SnO2 NTs exhibited superior acetone response (R(air)/R(gas) = 92 at 5 ppm) compared to pure SnO2 NFs (R(air)/R(gas) = 4.8 at 5 ppm) and SnO2 NTs (Rair/Rgas = 11 at 5 ppm) while Au-loaded SnO2 NTs showed a high response when exposed to hydrogen sulfide (R(air)/R(gas) = 34 at 5 ppm), offering selective gas detection with minimal cross-sensitivity against other interfering gases such as NH3, CO, NO, C6H5CH3, and C5H12. Our results provide a new insight into facile, cost-effective, and highly dispersible catalyst loading on the interior and exterior walls of hollow metal oxide NTs via simple electrospinning as a potential breath analyzer.

Early-time spectra of supernovae and their precursor winds

We present the first quantitative spectroscopic modeling of an early-time supernova that interacts with its progenitor wind. Using the radiative transfer code CMFGEN, we investigate the recently-reported 15.5 h post-explosion spectrum of the type IIb SN 2013cu. For the first time, we are able to directly measure the chemical abundances of a SN progenitor and find a relatively H-rich wind, with H and He abundances (by mass) of X=0.46 +- 0.2 and Y=0.52 +- 0.2, respectively. The wind is enhanced in N and depleted in C relative to solar values (mass fractions of 8.2e-3 and 1e-5). We obtain that a dense wind/circumstellar medium, with a mass-loss rate of Mdot= 3e-3 Msun/yr and wind velocity vwind=100 km/s, surrounds the star at the pre-SN stage. These values are lower than previous analytical estimates, although we find Mdot/vinf consistent with previous work. We also compute a CMFGEN model to constrain the progenitor spectral type and find that the high Mdot and low vwind imply that the star had an effective temperature of ~8000 K immediately before the SN explosion. Our models suggest that the progenitor was either an unstable luminous blue variable or a yellow hypergiant undergoing an eruptive phase, and rule out a WR star. We classify the post-explosion spectra at 15.5 h as XWN5(h) and advocate for the use of the prefix `X' (eXplosion) to avoid confusion between post-explosion, non-stellar spectra with those of massive stars. We show that the progenitor spectral type is significantly different than the early post-explosion spectral type owing to the huge differences in the ionization structure before and after the SN event. We find the following temporal evolution: LBV/YHG -> XWN5(h) -> SN IIb. Future early-time spectroscopy in the UV will give access to additional spectroscopic diagnostics and further constrain the properties of SN precursors, such as their metallicities.

Effect of selenization conditions on the growth and properties of Cu2ZnSn(S,Se)4 thin films

The opto-electronic properties of copper zinc tin sulfide can be tuned to achieve better cell efficiencies by controlled incorporation of selenium. In this paper we report the growth of Cu2ZnSn(S,Se)4 (CZTSSe) using a hybrid process involving the sequential evaporation of Zn and sputtering of the sulfide precursors of Cu and Sn, followed by a selenization step. Two approaches for selenization were followed, one using a tubular furnace and the other using a rapid thermal processor. The effects of annealing conditions on the morphological and structural properties of the films were investigated. Scanning electron microscopy and energy dispersive spectroscopy were employed to investigate the morphology and composition of the films. Structural analyses were done using X-ray diffraction (XRD) and Raman spectroscopy. Structural analyses revealed the formation of CZTSSe. This study shows that regardless of the selenization method a temperature above 450 °C is required for conversion of precursors to a compact CZTSSe layer. XRD and Raman analysis suggests that the films selenized in the tubular furnace are selenium rich whereas the samples selenized in the rapid thermal processor have higher sulfur content.

Characterization of Cu2ZnSnS4 thin films on flexible metal foil substrates

The vacuum-based magnetron sputtering was utilized to the fabrication of Cu2ZnSnS4 (CZTS) thin films on flexible Al, Mo, and stainless steel foil substrates. The structural, compositional, and morphological properties of prepared thin films were investigated. According to the XRD and Raman results, for Al and Mo foil substrates, the structures of thin films are major CZTS and tiny secondary phase of Cu2SnS3. The preferred orientation of CZTS is along the (112) plane. The XRD peaks and Raman peaks of CZTS on Mo foil substrate are stronger than those on Al foil substrate. The calculated grain sizes are 33.6 and 39.0 nm for the thin films on Al and Mo foil substrates, respectively, indicating the higher crystallinity for Mo foil substrate samples. The compositions of thin films are near the stoichiometry of CZTS and show Cu-poor and Zn-rich properties. The surfaces of thin films are composed of compact grains. When using stainless steel foil as substrate, the fabricated thin films are composed of Cu2SnS3, FeS, and Zn, revealing the existence of sulfurization of Fe. The reaction between Fe and S inhibits the full sulfurization of Cu–Zn–Sn precursor, resulting in the absence of CZTS in the fabricated thin films. The composition of thin films is far from the stoichiometry of CZTS. In order to get desired properties of CZTS thin films, the inhibition of reaction between Fe and S is needed for stainless steel foil substrate.

Thermoelectric Properties of Sn-Doped Bi0.4Sb1.6Te3 Thin Films

The effect of Sn doping on the thermoelectric properties of p-type Bi0.4Sb1.6Te3 (BST) thin films was studied. Sn-doped BST films were grown on 4° tilted GaAs (001) substrates by metal–organic chemical vapor deposition. To control the Sn ion concentration in the films, we systematically controlled the dose of the Sn precursor by varying the H2 flow rate from 0 sccm to 100 sccm. The hole carrier concentration increased as the H2 flow rate was increased. Interestingly, the Seebeck coefficient of the films simultaneously increased with the carrier concentration when the H2 flow rate was increased up to 60 sccm. This might be attributed to the formation of virtual bound states in the valence band by Sn doping. Consequently, the Sn ion doping contributed to the thermopower enhancement of the BST films.

Galvanostatically-electrodeposited Cu–Zn–Sn multilayers as precursors for crystallising kesterite Cu2ZnSnS4 thin films

Metallic stacked layers containing Cu, Zn and Sn on Mo-coated glass substrates were prepared by galvanostatic electrodeposition as precursors for crystallising kesterite Cu2ZnSnS4 films. Due to the nature of the MoOx passivating layer on the Mo surface, initial trials were particularly addressed to deposit strong adhesive precursors by firstly depositing Cu layers on Mo-coated substrates from acidic as well as alkaline solutions. It was found that the acidic Cu solutions were not appropriate for the Cu deposition on Mo-coated glass substrates, since they led to an inhomogeneous coverage of the Cu deposits in addition to extremely poor adhesion. In contrast, utilising an alkaline Cu solution yielded a homogeneous coverage of the Cu deposits, having strong adhesion to the Mo-coated glass substrates, which was essential for the subsequent acidic Zn or Sn galvanostatic electrodepositions. The crystallisation of kesterite Cu2ZnSnS4 from metallic stacked Cu/Sn/Zn precursors was investigated as well. The sulfurisation process crystallises the Cu–Zn–Sn precursor films into films exhibiting predominant kesterite phase. This result demonstrates that the established galvanostatic electrodeposition technique for metals has a technological potential for preparing kesterite precursors.

Transparent conducting aerogels of antimony-doped tin oxide.

Bulk antimony-doped tin oxide aerogels are prepared by epoxide-initiated sol-gel processing. Tin and antimony precursors are dissolved in ethanol and water, respectively, and propylene oxide is added to cause rapid gelation of the sol, which is then dried supercritically. The Sb:Sn precursor mole ratio is varied from 0 to 30% to optimize the material conductivity and absorbance. The materials are characterized by electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), nitrogen physisorption analysis, a four-point probe resistivity measurement, and UV-vis diffuse reflectance spectroscopy. The samples possess morphology typical of aerogels without significant change with the amount of doping. Calcination at 450 °C produces a cassiterite crystal structure in all aerogel samples. Introduction of Sb at 15% in the precursor (7.6% Sb by XPS) yields a resistivity more than 3 orders of magnitude lower than an undoped SnO2 aerogel. Calcination at 800 °C reduces the resistivity by an additional 2 orders of magnitude to 30 Ω·cm, but results in a significant decrease in surface area and pore volume.

SnO2 thin films grown by atomic layer deposition using a novel Sn precursor

SnO2 thin films were grown by atomic layer deposition (ALD) with dimethylamino-2-methyl-2-propoxy-tin(II) (Sn(dmamp)2) and O3 in a temperature range of 100–230°C. The ALD window was found to be in the range of 100–200°C. The growth per cycle of the films in the ALD window increased with temperature in the range from 0.018 to 0.042nm/cycle. Above 230°C, the self-limiting behavior which is a unique characteristic of ALD, was not observed in the growth because of the thermal decomposition of the Sn(dmamp)2 precursor. The SnO2 films were amorphous in the ALD window and exhibited quite a smooth surface. Sn ions in all films had a single binding state corresponding to Sn4+ in SnO2. The concentration of carbon and nitrogen in the all SnO2 films was below the detection limit of the auger electron spectroscopy technique and a very small amount of carbon, nitrogen, and hydrogen was detected by secondary ions mass spectroscopy only. The impurity contents decreased with increasing the growth temperature. This is consistent with the increase in the density of the SnO2 films with respect to the growth temperature. The ALD process with Sn(dmamp)2 and O3 shows excellent conformality on a hole structure with an aspect ratio of ∼9. This demonstrates that the ALD process with Sn(dmamp)2 and O3 is promising for growth of robust and highly pure SnO2 films.

Characterization of Cu2ZnSnSe4 solar cells prepared from electrochemically co-deposited Cu–Zn–Sn alloy

Cu–Zn–Sn (CZT) precursors for Cu2ZnSnSe4 (CZTSe) solar cell were prepared by electrochemical co-deposition method with different metals composition. CZT precursors were preliminary annealed in three different atmospheres in order to obtain homogenous, without pores Cu–Zn–Sn layers. A high crystalline quality CZTSe absorber was synthesised as has been determined by X-ray diffraction and Raman spectroscopy methods. CZTSe based solar cells were fabricated and champion cell demonstrated 2.7% efficiency and reached as high as 70% of external quantum efficiency. Scanning electron microscope investigations of CZTSe solar cells cross-section revealed that Mo/CZTSe interface exhibits large voids and local delamination from Mo layer. The back contact issues are detrimental to solar cell performance reducing shunt resistance and open circuit voltage.

Ge1-xSnx Epitaxial Growth on Ge Substrate by MOCVD

Introduction Ge1-xSnx is recognized as one of the post scaling materials, which can be used as a channel material and a stressor for Ge MOSFETs. For instance, it was reported that a hole mobility of pMOSFET with Ge1-xSnx channel was improved comparing to the pure Ge channel [1]. Moreover, Ge1-xSnx can be used as an optical devices because the band structure changes from indirect to direct as Sn composition increasing more than 10 at.%. Ge1-xSnx is a very attractive material, and therefore often fabricated by epitaxial growth on the Ge substrate using CVD technique. However, the precursors used for CVD so far have a safety problem. GeH4 or Ge2H6 for Ge and SnH4 for Sn are very dangerous because they have a pyrophoric and explosive nature [2, 3]. In this paper, we succeeded in performing Ge1-xSnx epitaxial film growth by MOCVD (metal-organic chemical vapor deposition) using tertiary-butyl-german (t-C4H9GeH3) and tetra-ethyl-tin ((C2H5)4Sn) which have neither a pyrophoric nor explosive nature. Experiments We synthesized and used t-C4H9GeH3 and (C2H5)4Sn as Ge and Sn precursors, respectively. Ge precursor has a high vapor pressure and can be decomposed at low temperature. Furthermore, it has few residual carbon impurities in the deposited film [4]. Our selected Sn precursor also has high vapor pressure. Moreover, these precursors are sufficiently safe. In this experiment, we used Ge(100) wafer as a substrate. After the chemical cleaning of the substrates using NH4OH, HCl and HF, residual native oxide on the substrate was removed by thermal treatment at 450 ºC in the CVD process chamber. Then, the precursor vapor was injected into the chamber. The precursor supply was controlled by the flow rate of N2 carrier gas, and the temperatures of precursor bottles and pressure. In the experiment, the injected rates were estimated to be 1.4E-04 mol/min for both Ge and Sn precursors. The deposition temperature and chamber pressure were 360 ºC and 30 torr. The deposited films were investigated by transmission electron microscopy (TEM; JEM-2100, JEOL Ltd.) and X-ray diffractometry (XRD; Rigaku SmartLab). Results and Discussion Figure 1 (a) shows cross-sectional TEM (XTEM) image, here the film thickness is approximately 50 nm. Figure 1 (b) is the close-up image with enhanced brightness at the epitaxial interface indicated by the rectangle in Fig. 1 (a). No obvious defect was observed at the interface and in the film. The electron diffraction patterns taken from the Ge1-xSnx film (Fig. 2 (a)) and Ge substrate (Fig. 2 (b)) showed the same crystalline orientations, implying successful epitaxial growth. Figure 3 shows the X-ray diffraction reciprocal space mapping (XRD-2DRSM) around -2-24 diffraction. The lattice constant was expanded approximately 0.6 % in the epitaxial film from the Ge substrate. This corresponds to approximately 2 at.% Sn incorporation in the film, which exceeds solid solubility limit of 1 at.% reported in the literature [5]. In summary, we have succeeded in the Ge0.98Sn0.02 heteroepitaxial film growth on the Ge substrate by MOCVD for the first time.

Effects of Sn doping on the morphology, structure, and electrical property of In2O3 nanofiber networks

This paper studies the effect of Sn doping on the morphological, structural, and electrical properties of the Sn-doping In2O3 nanofiber networks. In2O3-based nanofibers with various relative concentration of Sn precursor (0–20 mol%) were fabricated through the electrospinning method. Scanning electron microscopy observations show that, depending on the relative concentration of SnCl4 in the starting materials, the doped nanofibers with different morphologies, from smooth to corn-like and then to accidented, are fabricated. Transmission electron microscopy and X-ray diffraction analyses reveal that the Sn dopants influence the growth direction of seeds, resulting in doped nanoparticles having diverse shapes and sizes, which are critical for the formation of doped nanofiber with different morphology. From these nanofiber networks, we fabricated several thin sheets to characterize the effect of Sn concentration on the electrical resistivity. The resistivity of thin sheets decreased significantly before the doping concentration up to 12.5 mol%, and then increased slightly at a larger addition. This work will assist further understanding the formation of Sn-doped In2O3 nanofibers and is expected to be extended to other transparent conductive oxides.

Effect of the thickness on the optoelectronic properties of SnS films and photovoltaic performance of SnS/i-a-Si/n-a-Si solar cells

Different thick orthorhombic SnS films were successfully fabricated by sulfurization of various sputtered different thick Sn precursor layers. All the absorption coefficients of different thick SnS films are higher than 2 × 104 cm−1 in the visible light region of 400–800 nm, and the direct band gaps of these SnS films were estimated to be about 1.2 eV. Furthermore, SnS/i-a-Si/n-a-Si solar cells with 205-, 420-, 635-, 845- and 1,060-nm-thick SnS-absorber layers were fabricated, and the 845-nm-thick SnS-absorber-based SnS/i-a-Si/n-a-Si solar cell shows the highest conversion efficiency of 0.42 %, a short-circuit current density of 2.4 mA/cm2, and an open-circuit voltage of 362 mV.

Precursor Stack Ordering Effects in Cu2ZnSnSe4 Thin Films Prepared by Rapid Thermal Processing

Solar cells based on Cu2ZnSnSe4 thin film absorber layers have shown promise as an alternative to more mature thin film technologies because they are composed of more earth abundant elements. To increase device efficiencies there is still much to be investigated about its properties, and film and device processing. Rapid thermal processing is a more industrially viable method of forming thin film absorber layers than time intensive conventional thermal processing. However, optimized conditions for conventional processing are not readily transferable to rapid thermal processing. Thermal processing of this material is complicated through loss of volatile components such as Zn and Sn–Se, in addition to decomposition at elevated temperatures. In this study the effect of stack order has been investigated for Cu–Zn(O)–Sn precursor stacks selenized by rapid thermal processing to form Cu2ZnSnSe4 thin films. Precursor stack ordering is shown to have significant effects on the film properties, including precursor alloy formation, composition and elemental loss, morphology, and secondary phase formation and distribution. Optoelectronic properties of devices prepared from these films also show a dependence on precursor stack order. Most notable is the poor performance of devices with Zn as a bottom layer, due to excessive ZnSe formation at the back contact region. The viability of ZnO as a precursor layer—in place of volatile Zn—is also investigated, and shown to not completely react in the Se atmosphere, leaving residual oxygen in the Cu2ZnSnSe4 films. The best performing device has a conversion efficiency of 4.3%, and uses a stack order of glass/Mo/Sn/Zn/Cu.

One pot direct synthesis of mesoporous SnO2/SBA-15 nanocomposite by the hydrothermal method

We report a novel one step route for direct loading of SnO2 into the mesoporous framework of SBA-15 by simultaneous co-condensation of Sn precursor and silica source using the hydrothermal method. HRTEM images confirm that co-condensation of both Sn and silica species leads to uniform distribution of SnO2 nanoparticles in the framework of SBA-15 whereby retaining the mesoporous characteristics as confirmed using X-ray diffraction (XRD), N2 adsorption–desorption and energy-dispersive X-ray (EDX) spectroscopy. The mesoporous framework of SBA-15 does not collapse although the efficiency of SnO2 loading decreases with increment of SnO2 content in SBA-15.

The conducting tin oxide thin films deposited via atomic layer deposition using Tetrakis-dimethylamino tin and peroxide for transparent flexible electronics

Abstract The ALD SnO 2 thin films were investigated as a function of growth temperature to obtain optimized process and film properties using tetrakis(dimethylamino)tin as a Sn precursor, and hydrogen peroxide as reactant. The film growth shows 1.2 A/cycle in the 100–200 °C temperature range and follows typical ALD window behavior. ALD SnO 2 thin films show low resistivity (9.7 × 10 −4 Ω cm) at 200 °C, and high carrier mobility (22 cm 2 /V sec). The transmittance of 40 nm ALD SnO 2 films was over 80% at all of temperatures. The growth behavior, film composition, chemical bonding states, film crystallinity, electronic structure, and optical properties were investigated in order to verify the origin of the electrical properties as a function of growth temperature. These data show that the favorable properties of ALD SnO 2 are due to the electronic band structure change associated with poly-crystalline formation.

Phase and microstructural evolution of Sn particles embedded in amorphous carbon nanofibers and their anode properties in Li-ion batteries

Phase and microstructural evolution of Sn-Carbon composite nanofibers (NFs) under various heat treatment conditions was clearly demonstrated in this work. Amorphous carbon nanofibers (a-CNFs) that contained metallic Sn nanoparticles were prepared via electrospinning and subsequent calcination under a reducing atmosphere. The sizes of the metallic Sn particles, which were decorated inside and outside of a-CNFs, were precisely manipulated by varying the Sn precursor content and introducing a reinforced quenching step, i.e., controlling the cooling rate after high-temperature processing. Because of the low melting temperature of metallic Sn (231.9 °C), the nucleation and growth rates of the Sn nanoparticles were significantly influenced by the high-temperature processing and cooling condition. In particular, the stresses that originated from volume changes of the Sn nanoparticles during the lithium alloying and dealloying processes were effectively compensated by amorphous carbon containing Sn particles, which led to reduced structural damage. The morphologies of the fibers with incorporated Sn nanoparticles provided efficient permeability to allow the penetration of the electrolyte into the inner fiber structure while maintaining a high-capacity (950 mAh g−1 at 0.5 C-rate) characteristics due to enhanced surface activity.

Sn(1−x)LaxO2 thin films deposited on AISI 304 stainless steel substrates

To minimize the corrosive processes that affect metal structures, this work involved the synthesis of Sn(1−x)LaxO2 ceramic thin film deposited on AISI 304 steel. The polymeric precursor method was used here to obtain resin precursors of Sn(1−x)LaxO2 films with x=1, 3 and 5mol%. The films were deposited using dip-coating and spin-coating techniques to ensure better packing, and were then heat-treated in a muffle furnace at temperatures of 400, 450 and 500°C for two hours. The SnO2 samples and the organic precursors were morphologically and structurally characterized by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG–DTA), Raman spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). These characterizations revealed crack-free, single-phase, dense thin films with good adhesion to the metal substrate in the entire temperature range employed in this study.

Well-Dispersed Pt Catalysts Supported on Porous Carbon Nanofibers for Improved Methanol Oxidation in Direct Methanol Fuel Cells

CNFs with embedded SnO2 nanoparticles were synthesized using the carbonization at 800 ◦ Ci n aN 2. Subsequently, in order to obtain porous CNFs, SnO2-embedded CNFs were subjected to a H2reductionmethod(N2:H2 =9:1;v/v)at600 ◦ Cfor15h.Thistreatment caused the Sn nanoparticles to agglomerate outside the porous CNFs. In order to simultaneously remove the agglomerated Sn particles from the CNF surface and form functional groups on the surface instead, an acid treatment using a mixture (1:1 (v/v)) of HF (52%) and HNO3 (66%) was performed. To fabricate Pt catalysts supported on porous CNFs, a reduction method was employed. Porous CNFs were dispersed in a 1.12 mM H2PtCl6 ·xH2 O( ≥99.9%) solution in de-ionized (DI) water. Then, concentrated NaBH4 solution (100 mg/mL), used as a reducing agent, was added into the above-mentioned solution. The resultant samples were washed several times using DI water, and then freeze-dried at −50 ◦ C to maintain metallic Pt phases. Also, for comparison, Pt electrocatalysts supported on conventional CNFs were prepared using electrospinning followed by a reduction method. Conventional CNFs were synthesized using only PAN and PVP without the addition of Sn precursors. 5 We prepared 40 wt% Pt catalysts supported on conventional CNFs, 40 wt% Pt catalysts supported on porous CNFs synthesized using 4 wt% Sn precursor, and 40 wt% Pt catalysts supported on porous CNFs synthesized using 8 wt% Sn precursor(referredtoasPt/CNF,sampleA,andsampleBhenceforth). The morphological and structural properties of the samples were examined by field emission-scanning electron microscopy (FESEM; Hitachi S-4800) and transmission electron microscopy (TEM; JEOL 2100F, KBSI Suncheon Center). The specific surface areas and pore volumes of the samples were performed using the Brunauer-EmmettTeller (BET) measurements by N2 adsorption at 77 K. The crystal structures of the samples were characterized by X-ray diffractometry (XRD, Rigaku D/MAX2500 V). Electrochemical performance tests were performed by means of a potentiostat/galvanostat (PGST302N by Eco Chemie, Netherlands), set up using a conventional threeelectrode system comprising a glassy carbon electrode (0.07 cm 2 , a working electrode), a Pt gauze (a counter electrode), and Ag/AgCl (saturated KCl, a reference electrode). The electrolyte used was a mixture of 0.5 M H2SO4 and 2MC H3OH aqueous solutions. The electrocatalytic oxidation of methanol was characterized by cyclic voltammetry (CV) at a scan rate of 50 mV/s in the range −0.2−1.0V. The chronoamperometric curves were obtained in a 0.5 M H2SO4 + 2MC H3OH solutions at a constant voltage of 0.5 V for 2,000s. For comparison, the commercial Pt/C (40 wt% Pt on Vulcan carbon, E-TEK) was prepared and tested using above-mentioned same procedures.

Extra-small porous Sn-silicate nanoparticles as catalysts for the synthesis of lactates

A series of Sn-MCM-41 nanoparticles (XS-Sn-MCM-41) with a diameter ranging from 20 to 140nm and very high specific surface area were successfully prepared and tested as heterogeneous catalysts for the conversion of the triose sugar dihydroxyacetone to ethyl lactate. Characterization of the materials indicated that the physicochemical properties of the nanoparticles can be significantly affected by different synthesis parameters, including the metal loading, the sequence of adding the Si and Sn precursors into the synthesis mixture, the preparation time and temperature. Most of the XS-Sn-MCM-41 catalysts displayed higher activity compared to conventional Sn-MCM-41 with large particle size in the conversion of dihydroxyacetone into ethyl lactate. The superiority of the best XS-Sn-MCM-41 catalyst in terms of conversion and turnover number is correlated to its high amount of accessible acid sites, which in turn is ascribed to a combination of different physicochemical features such as high surface area, particles morphology and coordination of the tin atoms in tetrahedral framework sites. The best catalyst can be reused in consecutive runs without loss of activity.