Sergei Smirnov

New Mexico State University, Las Cruces, New Mexico, United States

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Publications (54)292.32 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The controllable synthesis of strongly coupled inorganic materials/carbon nanotubes (CNTs) hybrids represents a long-standing challenge for developing advanced catalysts and energy-storage materials. Here we report a simple sol-gel method for facile synthesis of TiO2/CNTs hybrid. The porous anatase TiO2 nanoparticles are uniformly coated on the CNTs conducting network, which leads to remarkably improved electrochemical performances such as exceptional cycling stability, good high rate durability, and reduced resistance. This hybrid exhibits a reversible capacity as high as 200 mA·h g−1 at a current density of 0.1 A g−1 as an anode in lithium-ion battery (LIB). As a supercapacitor (SC), it shows a specific supercapacitance of 145 F g−1 in 0.5 M H2SO4 electrolyte, higher than that of the previously reported TiO2 based supercapacitors. Moreover, this hybrid also exhibits excellent durability after 1000 cycles for both LIBs and SCs. Such superior performance and cycling durability demonstrate the reinforced synergistic effects between the porous TiO2 and interweaved CNTs network, indicating a great application potential for such hybrid materials in high power LIBs and SCs.
    Electrochimica Acta 07/2015; 169:73-81. DOI:10.1016/j.electacta.2015.04.061 · 4.09 Impact Factor
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    ABSTRACT: Graphene presents an ideal candidate for lightweight, high strength composite materials given its superior mechanical properties (specific strength of 130GPa and stiffness of 1 TPa). To date, easily scalable graphene-like materials in a form of separated flakes (exfoliated graphene, graphene oxide and reduced graphene oxide) have been investigated as candidates for large-scale applications such as material reinforcement. These graphene-like materials do not fully exhibit all the capabilities of graphene in composite materials. In the current study, we show that macro (2''x 2'') graphene laminates and fibers can be produced using large continuous sheets of single layer graphene grown by chemical vapor deposition (CVD). The resulting composite structures have potential to outperform the current state of the art composite materials in both mechanical properties and electrical conductivities (>8 S/cm with only 0.13% volumetric graphene loading and 5·10(3) S/cm for pure graphene fibers) with estimated graphene contribution >10 GPa in strength and 1TPa in stiffness.
    ACS Applied Materials & Interfaces 04/2015; 7(20). DOI:10.1021/acsami.5b01367 · 5.90 Impact Factor
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    ABSTRACT: Recently it has been reported that palladium nanocubes (PdNC) are capable of generating singlet oxygen without photo-excitation simply via chemisorption of molecular oxygen on its surface. Such a trait would make PdNC a highly versatile catalyst suitable in organic synthesis and a Reactive Oxygen Species (ROS) inducing cancer treatment reagent. Here we thoroughly investigated the catalytic activity of PdNC with respect to their ability to produce singlet oxygen and to oxidize 3,5,3',5'-tetramethyl-benzidine (TMB), as well as, analyzed the cytotoxic properties of PdNC on HeLa cells. Our findings showed no evidence of singlet oxygen production by PdNC. The nanocubes' activity is not necessarily linked to activation of oxygen. The oxidation of substrate on PdNC can be a first step followed by PdNC regeneration with oxygen or other oxidant. The catalytic activity of PdNC towards oxidation of TMB is very high and shows direct two-electrons oxidation when the surface of PdNC is clean and the ratio of TMB/PdNC is not very high. Sequential one electron oxidation is observed when the pristine quality of PdNC surface is compromised by serum or uncontrolled impurities and/or the ratio of TMB/PdNC is high. Clean PdNC in serum-free media efficiently induce apoptosis of HeLa cells. It is the primary route of cell death and is associated with hyperpolarization of mitochondria, contrary to a common mitochondrial depolarization initiated by ROS. Again, the effects are very sensitive to how well the pristine surface of PdNC is preserved, suggesting that PdNC can be used as an apoptosis inducing agent but only with appropriate drug delivery system.
    ACS Applied Materials & Interfaces 04/2015; 7(18). DOI:10.1021/am509124x · 5.90 Impact Factor
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    ABSTRACT: By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 10(6) g m(-2) s(-1) at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m(-2) s(-1) atm(-1).
    Nature Nanotechnology 03/2015; 10(5). DOI:10.1038/nnano.2015.37 · 33.27 Impact Factor
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    ABSTRACT: Direct growth of mesoporous TiO2 on Ni foam via a one-step soft template synthesis was directly used for a binder-free anode for lithium-ion batteries. The mesoporous TiO2 with a high specific surface area of 158.8 m2 g-1 and average pore size of 5.4 nm formed network-like sheets on the surface of the Ni foam. The binder-free TiO2/Ni anode shows improved electrochemical performance with a capacity as high as 341 mA h g-1 at a current density of 100 mA g-1 after 10 cycles and 82.4 mA h g-1 at a current density of 1000 mA g-1 after 30 cycles. The enhanced electrochemical performance is attributed to the mesoporous structure that shortens the lithium ion diffusion path and facilitates the transport of lithium ions.
    RSC Advances 10/2014; 4(90-90):48938-48942. DOI:10.1039/C4RA08395D · 3.71 Impact Factor
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    ABSTRACT: We report a facile hydrothermal route for the synthesis of Fe2O3 nanoparticles and their composites with conductive additives, reduced graphite oxide (rGO) and conductive polymer PEDOT:PSS, as anode materials for lithium ion batteries (LIBs). The addition of conductive polymer layer on Fe2O3 nanoparticles may facilitate the electron transport but hinders the Li+ ion insertion at higher current density. On the other hand, Fe2O3@rGO prepared by growing Fe2O3 nanoparticles directly on rGO sheets shows the best electrochemical behavior due to a beneficial combination of the rGO nanosheets partially wrapped around Fe2O3 which facilitates both the electron transport and the Li+ ion insertion. The enhanced conductivity of the composites was proved. The high specific capacity and stable rate performance of Fe2O3@rGO composites encourages their further study to be potential candidate for the anode materials in LIBs. These results will be helpful in further elucidation of the role of conductive additives in improving the electrochemical performance of Fe2O3 based composite anodes and this simple synthetic strategy can be applied for the large scale production of metal oxides with conductive additives for LIBs.
    Journal of Power Sources 03/2014; 259:227-232. DOI:10.1016/j.jpowsour.2014.02.096 · 5.21 Impact Factor
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    ABSTRACT: Three-dimensional (3D) nanoporous architectures, possessing high surface area, massive pores, and excellent structural stability, are highly desirable for many applications including catalysts and electrode materials in lithium ion batteries. However, the preparation of such materials remains a major challenge. Here, we introduce a novel method, instant gelation, for the synthesis of such materials. The as-prepared porous 3D MoS2@C nanocomposites, with layered MoS2 clusters or strips ingrained in porous and conductive 3D carbon matrix, indeed showed excellent electrochemical performance when applied as anode materials for lithium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, and mesoporous nature effectively shortens the lithium ion diffusion path and provides room necessary for volume expansion. The large specific surface area is beneficial for a better contact between electrode materials and electrolyte.
    Nanoscale 01/2014; DOI:10.1039/C3NR05815H · 6.74 Impact Factor
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    ABSTRACT: Studies of DNA translocation through graphene nanopores have revealed their potential for DNA sequencing. Here we report a study of protein translocation through chemically modified graphene nanopores. A transmission electron microscope (TEM) was used to cut nanopores with diameters between 5 and 20 nm in multilayer graphene prepared by chemical vapor deposition (CVD). After oxygen plasma treatment, the dependence of the measured ionic current on salt concentration and pH was consistent with a small surface charge induced by the formation of carboxyl groups. While translocation of gold nanoparticles (10 nm) was readily detected through such treated pores of a larger diameter, translocation of the protein ferritin was not observed either for oxygen plasma treated pores, or for pores modified with mercaptohexadecanoic acid. Ferritin translocation events were reliably observed after the pores were modified with the phospholipid-PEG (DPPE-PEG750) amphiphile. The ion current signature of translocation events was complex, suggesting that a series of interactions between the protein and pores occurs during the process.
    Nanotechnology 11/2013; 24(49):495102. DOI:10.1088/0957-4484/24/49/495102 · 3.67 Impact Factor
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    ABSTRACT: Bismuth oxide directly grown on nickel foam (p-Bi2O3/Ni) was prepared by a facile polymer-assisted solution approach and was used directly as a lithium-ion battery anode for the first time. The Bi2O3 particles were covered with thin carbon layers, forming network-like sheets on the surface of the Ni foam. The binder-free p-Bi2O3/Ni shows superior electrochemical properties with a capacity of 668 mAh/g at a current density of 800 mA/g, which is much higher than that of commercial Bi2O3 powder (c-Bi2O3) and Bi2O3 powder prepared by the polymer-assisted solution method (p-Bi2O3). The good performance of p-Bi2O3/Ni can be attributed to higher volumetric utilization efficiency, better connection of active materials to the current collector, and shorter lithium ion diffusion path.
    Journal of Materials Chemistry A 10/2013; 1(39). DOI:10.1039/C3TA12655B · 7.44 Impact Factor
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    ABSTRACT: Unlike most conventional anode materials, the newly developed TiNb2O7 (TNO) does not form a solid electrolyte interface (SEI) layer, which makes it safe for high power requiring lithium-ion batteries. In this paper, we demonstrated an SBA-15 confined synthetic approach to prepare TNO nanoparticles (S-TNO) with a small particle size around 10 nm and a large BET surface area of 79.5 m(2) g(-1). It is worth mentioning that this is the smallest size reported so far for TNO. In contrast, the TNO (L-TNO) synthesized without SBA-15 has a particle size above 100 nm and a BET surface area of only 4.3 m(2) g(-1). The S-TNO shows better lithium-ion storage properties than L-TNO. The excellent electrochemical performance of S-TNO is attributed to its small crystalline size, which not only provides a larger effective area for better contact between the electrode material and the electrolyte, but also reduces the rate-limiting Li diffusion path. Moreover, S-TNO shows a high Coulombic efficiency (above 98% over 300 cycles) and negligible increase of impedance after cycling, which confirms no SEI layer formation in the operational voltage (1-3 V) of TNO.
    Nanoscale 09/2013; 5(22). DOI:10.1039/c3nr03594h · 6.74 Impact Factor
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    ABSTRACT: In this paper we discuss the effect of background pressure and synthesis temperature on the graphene crystal sizes in chemical vapor deposition (CVD) on copper catalyst. For the first time, we quantitatively demonstrate a fundamental role of the background pressure and provide the activation energy for graphene nucleation in atmospheric pressure CVD (9 eV), which is substantially higher than for the low pressure CVD (4 eV). We attribute the difference to a greater importance of copper sublimation in the low pressure CVD, where severe copper evaporation likely dictates the desorption rate of active carbon from the surface. At atmospheric pressure, where copper evaporation is suppressed, the activation energy is assigned to the desorption energy of carbon clusters instead. The highest possible temperature, close to the melting point of copper, should be used for large single crystal graphene synthesis. Using these conditions, we have synthesized graphene single crystals with sizes over 0.5 mm. Single cry
    The Journal of Physical Chemistry C 08/2013; 117(37). DOI:10.1021/jp4047648 · 4.84 Impact Factor
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    ABSTRACT: New nanocomposite formulation of the FeS based anode for lithium-ion batteries is proposed, where FeS nanoparticles wrapped in reduced graphene oxide (RGO) are produced via a facile direct-precipitation approach. The resulting nanocomposite FeS@RGO structure has better lithium ion storage properties exceeding those of FeS prepared without RGO sheets. The enhanced electrochemical performance is attributed to the robust sheet-wrapped structure with smaller FeS nanoparticles and synergetic effects between FeS and RGO sheets, such as increased conductivity, shortened lithium ion diffusion path, and the effective prevention of polysulfide dissolution.
    ACS Applied Materials & Interfaces 05/2013; 5(11). DOI:10.1021/am401239f · 5.90 Impact Factor
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    ABSTRACT: We demonstrate that large scale high quality graphene synthesis can be performed using atmospheric pressure chemical vapor deposition (CVD) on Cu and illustrate how this procedure eliminates major difficulties associated with the low pressure CVD approach while allowing straightforward expansion of this technology to the roll-to-roll industrial scale graphene production. The detailed recipes evaluating the effects of copper foil thicknesses, purity, morphology and crystallographic orientation on the graphene growth rates and the number of graphene layers were investigated and optimized. Various foil cleaning protocols and growth conditions were evaluated and optimized to be suitable for production of large scale single layer graphene that was subsequently transferred on transparent flexible polyethylene terephthalate (PET) polymer substrates. Such "ready to use" graphene-PET sandwich structures were as large as 40 '' in diagonal and >98% single layer, sufficient for many commercial and research applications. Synthesized large graphene film consists of domains exceeding 100 mu m. Some curious behavior of high temperature graphene etching by oxygen is described that allows convenient visualization of interdomain boundaries and internal stresses. Published by Elsevier Ltd.
    Carbon 04/2013; 54:58-67. DOI:10.1016/j.carbon.2012.11.003 · 6.16 Impact Factor
  • Sergei N Smirnov, Ivan V Vlassiouk, Nickolay V Lavrik
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    ABSTRACT: Hydrophobicity is a fundamental property that is responsible for numerous physical and biophysical aspects of molecular interactions in water. Peculiar behavior is expected for water in the vicinity of hydrophobic structures, such as nanopores. Indeed, hydrophobic nanopores can be found in two distinct states, dry and wet, even though the latter is thermodynamically unstable. Transitions between these two states are kinetically hindered in long pores but can be much faster in shorter pores. As it is demonstrated for the first time in this paper, these transitions can be induced by applying a voltage across a membrane with a single hydrophobic nanopore. Such voltage-induced gating in single nanopores can be realized in a reversible manner through electrowetting of inner walls of the nanopores. The resulting I-V curves of such artificial hydrophobic nanopores mimic biological voltage-gated channels.
    ACS Nano 08/2011; 5(9):7453-61. DOI:10.1021/nn202392d · 12.03 Impact Factor
  • Fabian Rios, Sergei N. Smirnov
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    ABSTRACT: pH switchable valves were constructed using nanoporous membranes, the surface of which was modified by mixtures of aminopropyl trimethoxy silane and butyl trimethoxy silane. The modified membranes are dry at neutral and basic conditions because of their hydrophobicity but open to flux of aqueous solutions at slightly acidic pH because of protonation of amino groups. The resulting high contrast between the open and the closed states and a high flux in the open state because of large pore size make the approach attractive in applications where pH switching is employed, for example, in drug delivery applications.Keywords: pH sensitive valve; hydrophobicity
    Chemistry of Materials 07/2011; 23(16). DOI:10.1021/cm200501e · 8.54 Impact Factor
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    ABSTRACT: We show that graphene chemical vapor deposition growth on copper foil using methane as a carbon source is strongly affected by hydrogen, which appears to serve a dual role: an activator of the surface bound carbon that is necessary for monolayer growth and an etching reagent that controls the size and morphology of the graphene domains. The resulting growth rate for a fixed methane partial pressure has a maximum at hydrogen partial pressures 200-400 times that of methane. The morphology and size of the graphene domains, as well as the number of layers, change with hydrogen pressure from irregularly shaped incomplete bilayers to well-defined perfect single layer hexagons. Raman spectra suggest the zigzag termination in the hexagons as more stable than the armchair edges.
    ACS Nano 06/2011; 5(7):6069-76. DOI:10.1021/nn201978y · 12.03 Impact Factor
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    ABSTRACT: In this paper we present a study of graphene produced by chemical vapor deposition (CVD) under different conditions with the main emphasis on correlating the thermal and electrical properties with the degree of disorder. Graphene grown by CVD on Cu and Ni catalysts demonstrates the increasing extent of disorder at low deposition temperatures as revealed by the Raman peak ratio, IG/ID. We relate this ratio to the characteristic domain size, La, and investigate the electrical and thermal conductivity of graphene as a function of La. The electrical resistivity, ρ, measured on graphene samples transferred onto SiO2/Si substrates shows linear correlation with La − 1. The thermal conductivity, K, measured on the same graphene samples suspended on silicon pillars, on the other hand, appears to have a much weaker dependence on La, close to K ~ La1/3. It results in an apparent ρ ~ K3 correlation between them. Despite the progressively increasing structural disorder in graphene grown at lower temperatures, it shows remarkably high thermal conductivity (102–103 W K − 1 m − 1) and low electrical (103–3 × 105 Ω) resistivities suitable for various applications.
    Nanotechnology 05/2011; 22(27):275716. DOI:10.1088/0957-4484/22/27/275716 · 3.67 Impact Factor
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    ABSTRACT: Wetting and drying of hydrophobic pores with diameters lower than 0.2 μm by aqueous solutions at different hydrostatic pressures is investigated by measuring the ionic conductance variation through the nanopores. The critical pressure for water intrusion into the nanopores increases with lowering the pore diameter and the surface tension of the hydrophobic modification, in agreement with the Laplace equation. Nevertheless, restoring the pressure to the atmospheric one does not result in spontaneous pore dewetting unless bubbles are left inside the pores. Such bubbles can appear at the regions of narrowing cross section and/or varying quality of the hydrophobic modification and thus can be engineered to control water expulsion.
    ACS Nano 09/2010; 4(9):5069-75. DOI:10.1021/nn101080k · 12.03 Impact Factor
  • Areen Khattabi, Sergei N. Smirnov
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    ABSTRACT: Monolayer assemblies of stearic, elaidic and oleic acids on alumina (flat surfaces and nanoporous membranes) and aminated glass were characterized by IR and the contact angle with water and organic solvents. The saturated (stearic) acid has the highest density of the surface bound molecules due to its good packing while the unsaturated elaidic (the trans isomer) and the oleic (the cis isomer) acids have their packing densities lower because of a kink due to the double bond. As a result, such modified surfaces have the contact angles decreasing in the same order not only with water but also with long hydrocarbons such as hexadecane. The effect is less pronounced with short hydrocarbons. We propose to employ these experiments in undergraduate laboratory as illustration of the molecular nature of the effect of unsaturated fatty acids on the density/fluidity of bilipid membranes.
    64th American Chemical Society Southwest Regional Meeting; 11/2009
  • Conference Paper: Nanoporous Sensors
    Sergei N. Smirnov
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    ABSTRACT: Nanoporous membranes and single nanopores have found a broad range of applications in material science and sensor design. We demonstrate here such applications in biochemical and chemical sensors, where surface of the nanopores is modified to achieve their specificity to physical stimuli and/or binding desired biochemical and chemical analytes. Various detection methods can be utilized but we will focus on measuring ionic conductance through the pores as the most convenient; different mechanisms affecting the condcutance will be reviewed.
    64th American Chemical Society Southwest Regional Meeting; 11/2009

Publication Stats

1k Citations
292.32 Total Impact Points

Institutions

  • 2001–2015
    • New Mexico State University
      • Department of Chemistry and Biochemistry
      Las Cruces, New Mexico, United States
  • 2011
    • Oak Ridge National Laboratory
      • Measurement Science and Systems Engineering Division
      Oak Ridge, FL, United States
  • 1993–2003
    • Dartmouth College
      • Department of Chemistry
      Hanover, New Hampshire, United States
  • 2002
    • Universität Bremen
      Bremen, Bremen, Germany