Porous Carbon–Carbon Composite Materials Obtained by Alkaline Dehydrochlorination of Polyvinyl Chloride

Porous carbon–carbon composite materials (PCCCM) were synthesized by the alkaline dehydrochlorination of polyvinyl chloride solutions in dimethyl sulfoxide containing the modifying additives of a nanostructured component (NC): graphite oxide (GO), reduced graphite oxide (RGO) or nanoglobular carbon (NGC), with subsequent two-step thermal treatment of the obtained polyvinylene–NC composites (carbonization at 400 °C and carbon dioxide activation at 900 °C). The focus of the study was on the analysis and digital processing of transmission electron microscopy images to study local areas of carbon composite materials, as well as to determine the distances between graphene layers. TEM and low-temperature nitrogen adsorption studies revealed that the structure of the synthesized PCCCM can be considered as a porous carbon matrix in which either carbon nanoglobules (in the case of NGC) or carbon particles with the “crumpled sheet” morphology (in the case of GO or RGO used as the modifying additives) are distributed. Depending on the features of the introduced 5–7 wt.% nanostructured component, the fraction of mesopores was shown to vary from 11% to 46%, and SBET—from 791 to 1115 m2 g−1. The synthesis of PCCNC using graphite oxide and reduced graphite oxide as the modifying additives can be considered as a method for synthesizing a porous carbon material with the hierarchical structure containing both the micro- and meso/macropores. Such materials are widely applied and can serve as adsorbents, catalyst supports, elements of power storage systems, etc

Temperature Dependences of Conductivity and Magnetoconductivity of Multiwall Carbon Nanotubes Annealed at Different Temperatures

Представлены температурные зависимости проводимости (в диапазоне 4.2-300 K) и магнето- проводимость (в полях до 10 кГ при 4.2 K) многослойных углеродных нанотрубок со средним внешним диаметром 8-10 и 20-22 нм, отожженных при различных температурах (1600, 2200, 2600, 2800◦C). Показано, что зависимость проводимости для нанотрубок со средним диаметром 20-22 нм характерна для квантовых поправок к проводимости взаимодействующих электронов в двумерных проводниках с локальным беспорядком. Для нанотрубок со средним диаметром 8- 10 нм имеет место одномерная прыжковая проводимость с переменной длиной прыжка. Показано, что при температурной обработке многослойных углеродных нанотрубок изменяется вклад квантовых поправок в проводимость, а также параметры прыжковой проводимости, что отжиг образцов влияет на магнетопроводимость. Многослойные углеродные нанотрубки со средним диаметром 20-22 нм имеют положительную магнетопроводимость.Temperature (in range 4.2-300 K) and magnetic field (in fields up to 10 kG at 4.2 K) dependences of the conductivity of two sets of multiwall carbon nanotubes with different average diameters (8-10 nm and 20-22 nm) heated at various temperatures (1600, 2200, 2600, 2800◦C) were investigated. Temperature dependences for nanotubes with average diameter 20-22 nm is typical for quantum corrections to conduc- tivity of the systems with interaction electrons in two dimensional conductors with local disorder. For nanotubes with average diameter 8-10 nm temperature dependences corresponds to one-dimensional variable range hopping conductivity (VRHC). The variation of annealing temperature of MWNTs influence on the contribution of corrections to conductivity and parameters of VRHC. The magnetoconductivity of MWNTs also depends on the annealing temperature and is less than that of highly oriented pyrographite. Annealed MWNTs with average diameter 20-22 nm has a positive magnetoconductivity

Temperature Dependences of Conductivity and Magnetoconductivity of Multiwall Carbon Nanotubes Annealed at Different Temperatures

Представлены температурные зависимости проводимости (в диапазоне 4.2-300 K) и магнето- проводимость (в полях до 10 кГ при 4.2 K) многослойных углеродных нанотрубок со средним внешним диаметром 8-10 и 20-22 нм, отожженных при различных температурах (1600, 2200, 2600, 2800◦C). Показано, что зависимость проводимости для нанотрубок со средним диаметром 20-22 нм характерна для квантовых поправок к проводимости взаимодействующих электронов в двумерных проводниках с локальным беспорядком. Для нанотрубок со средним диаметром 8- 10 нм имеет место одномерная прыжковая проводимость с переменной длиной прыжка. Показано, что при температурной обработке многослойных углеродных нанотрубок изменяется вклад квантовых поправок в проводимость, а также параметры прыжковой проводимости, что отжиг образцов влияет на магнетопроводимость. Многослойные углеродные нанотрубки со средним диаметром 20-22 нм имеют положительную магнетопроводимость.Temperature (in range 4.2-300 K) and magnetic field (in fields up to 10 kG at 4.2 K) dependences of the conductivity of two sets of multiwall carbon nanotubes with different average diameters (8-10 nm and 20-22 nm) heated at various temperatures (1600, 2200, 2600, 2800◦C) were investigated. Temperature dependences for nanotubes with average diameter 20-22 nm is typical for quantum corrections to conduc- tivity of the systems with interaction electrons in two dimensional conductors with local disorder. For nanotubes with average diameter 8-10 nm temperature dependences corresponds to one-dimensional variable range hopping conductivity (VRHC). The variation of annealing temperature of MWNTs influence on the contribution of corrections to conductivity and parameters of VRHC. The magnetoconductivity of MWNTs also depends on the annealing temperature and is less than that of highly oriented pyrographite. Annealed MWNTs with average diameter 20-22 nm has a positive magnetoconductivity

Influence of the Dielectric Matrix on the Electrical Nanocomposites Based on Oxidized Multi-Walled Carbon Nanotubes

В данной работе рассмотрено влияние окислительных обработок на свойства многослойных углеродных нанотрубок (МУНТ). Рассмотрены экспериментальные температурные зависимости электропроводности (в диапазоне температур 4,2-293 К) и полевые зависимости магнетосопротивления (в полях до 9 Тл при температуре 10 К) образцов МУНТ с модифицированными окислением поверхностными слоями, а также композитов на их основе. Установлено, что окисление поверхностных слоев МУНТ в растворах кислот ведет к изменению температурных зависимостей электропроводности. Введение МУНТ в диэлектрическую матрицу полиметилметакрилата (ПММА) приводит к температурной зависимости проводимости, близкой к типичной для прыжковой проводимости с переменной длиной прыжка для трехмерного случая.In this paper we consider the effect of oxidative treatments on the properties of multiwalled carbon nan- otubes (MWNT). The experimental temperature dependence of electrical conductivity (in the temperature range 4,2-293 K) and field dependence of magnetoresistance (in fields up to 9 Tl at 10 K) of the samples with MWCNT modified by oxidation of the surface layers, as well as the composites based on them. It was established that the oxidation of the surface layers of MWCNTs in acid solutions leads to a change in the temperature dependence of electrical conductivity. Introduction of MWCNTs in a dielectric matrix of polymethylmethacrylate (PMMA) leads to the dependence of the conductivity close to that typical for hopping conductivity with variable hopping length, three-dimensional case

Influence of the Dielectric Matrix on the Electrical Nanocomposites Based on Oxidized Multi-Walled Carbon Nanotubes

В данной работе рассмотрено влияние окислительных обработок на свойства многослойных углеродных нанотрубок (МУНТ). Рассмотрены экспериментальные температурные зависимости электропроводности (в диапазоне температур 4,2-293 К) и полевые зависимости магнетосопротивления (в полях до 9 Тл при температуре 10 К) образцов МУНТ с модифицированными окислением поверхностными слоями, а также композитов на их основе. Установлено, что окисление поверхностных слоев МУНТ в растворах кислот ведет к изменению температурных зависимостей электропроводности. Введение МУНТ в диэлектрическую матрицу полиметилметакрилата (ПММА) приводит к температурной зависимости проводимости, близкой к типичной для прыжковой проводимости с переменной длиной прыжка для трехмерного случая.In this paper we consider the effect of oxidative treatments on the properties of multiwalled carbon nan- otubes (MWNT). The experimental temperature dependence of electrical conductivity (in the temperature range 4,2-293 K) and field dependence of magnetoresistance (in fields up to 9 Tl at 10 K) of the samples with MWCNT modified by oxidation of the surface layers, as well as the composites based on them. It was established that the oxidation of the surface layers of MWCNTs in acid solutions leads to a change in the temperature dependence of electrical conductivity. Introduction of MWCNTs in a dielectric matrix of polymethylmethacrylate (PMMA) leads to the dependence of the conductivity close to that typical for hopping conductivity with variable hopping length, three-dimensional case

Atomistic Description of Thiostannate-Capped CdSe Nanocrystals: Retention of Four-Coordinate SnS4 Motif and Preservation of Cd-Rich Stoichiometry

Colloidal semiconductor nanocrystals (NCs) are widely studied as building blocks for novel solid-state materials. Inorganic surface functionalization, used to displace native organic capping ligands from NC surfaces, has been a major enabler of electronic solid-state devices based on colloidal NCs. At the same time, very little is known about the atomistic details of the organic-to-inorganic ligand exchange and binding motifs at the NC surface, severely limiting further progress in designing all-inorganic NCs and NC solids. Taking thiostannates (K4SnS4, K4Sn2S6, K6Sn2S7) as typical examples of chalcogenidometallate ligands and oleate-capped CdSe NCs as a model NC system, in this study we address these questions through the combined application of solution 1H NMR spectroscopy, solution and solid-state 119Sn NMR spectroscopy, far-infrared and X-ray absorption spectroscopies, elemental analysis, and by DFT modeling. We show that through the X-type oleate-to-thiostannate ligand exchange, CdSe NCs retain their Cd-rich stoichiometry, with a stoichiometric CdSe core and surface Cd adatoms serving as binding sites for terminal S atoms of the thiostannates ligands, leading to all-inorganic (CdSe)core[Cdm(Sn2S7)yK(6y-2m)]shell (taking Sn2S76- ligand as an example). Thiostannates SnS44- and Sn2S76- retain (distorted) tetrahedral SnS4 geometry upon binding to NC surface. At the same time, experiments and simulations point to lower stability of Sn2S64- (and SnS32-) in most solvents and its lower adaptability to the NC surface caused by rigid Sn2S2 rings. © 2015 American Chemical Society