Complete Synthesis of Germanium Nanocrystal Encrusted Carbon Colloids in Supercritical CO₂ and their Superhydrophobic Properties

Abstract

RECEIVED DATEColloidal carbon spheres were synthesized by the carbonization of squalane, a nonvolatile hydrocarbon solvent, in supercritical carbon dioxide. Precise pressure modulation of the fluid medium led to size controlled growth of carbon spheres ranging from 300-1500 nm in diameter. This unique synthetic approach of carbonizing a hydrocarbon suspension in supercritical fluid is found to suppress any particle aggregation, resulting in excellent sphere monodispersity. Core-shell hybrid structures of C-Ge were subsequently formed by inducing the growth of 10-40 nm sized germanium nanocrystals from the spheres in a hierarchical bottom-up approach. Extensive characterization of the spheres and nanocrystals was conducted using transmission and scanning electron microscopy, X-ray diffraction, X-ray 2 photoelectron spectroscopy, Raman and thermogravametric analysis. Assemblies of nanocrystal modified carbon colloids impart outstanding superhydrophobic properties due to the combined nano-and micro-structuring of the particle arrays.

Pd Clusters Supported on Amorphous, Low-Porosity Carbon Spheres for Hydrogen Production from Formic Acid

“…This value is about two times higher than the geometric surface area of these spheres calculated accepting a density of 1.8 g cm –3 . This relatively small difference between the geometric and BET surface areas indicates that the studied carbon spheres are low-porosity materials in accordance with our earlier consideration …”

“…The details for synthesis of carbon spheres can be found elsewhere . Experiments were conducted using liquid carbon dioxide from BOC (99.85%).…”

“…The details for synthesis of carbon spheres can be found elsewhere. 19 Experiments were conducted using liquid carbon dioxide from BOC (99.85%). A Teledyne model 260D computer controlled syringe pump was used to pressurize the system.…”

“…2−4,16−18 Wu et al 17 showed that carbon spheres of 0.2−0.5 μm size prepared from acetylene at 1273 K consist of heavily distorted graphene layers. Recently, we have reported that low-porosity uniform amorphous carbon spheres (0.3−1.5 μm) with superhydrophobic properties can be synthesized by pyrolysis of squalane (C 30 H 62 ) in supercritical CO 2 at temperatures as low as 773 K. 19 In the present paper, we study further the structure and composition of these original spheres and the spheres treated by HNO 3 , prior to using them as catalysts' supports for Pd clusters (2−4 nm) to produce hydrogen effectively from vapor phase formic acid decomposition at low temperatures (<423 K).…”

Scalable Solution-Grown High-Germanium-Nanoparticle-Loading Graphene Nanocomposites as High-Performance Lithium-Ion Battery Electrodes: An Example of a Graphene-Based Platform toward Practical Full-Cell Applications

“…For example, in an 18650 cell, if graphite is replaced with an anode material having a capacity greater than 1000 mAh/g, then more than a 20% increase in total capacity can be obtained . Therefore, Li-alloy-based materials with high degrees of lithiation, especially for Si and Ge, are considered to be attractive alternatives to graphite. − However, bulk Li-alloy-based anodes exhibit rapid capacity fading after several cycles because of dramatic volume changes (e.g., ∼300% for Si and Ge) resulting from the insertion/extraction of Li ions. , Although nanoparticles of Li-alloy-based materials can tolerate mechanical stress to exhibit improved performance, they usually suffer from poor capacity retention after tens of cycles.…”