Abstract
The role of acid treatment of Taunit carbon nanotubes in the formation of oxygen-containing functional groups on its surface as well as morphological and textural properties was studied. Acid treatment was carried out in an HNO3 solution or its mixture with H2SO4 under mild conditions (85 °C/1 h) with subsequent washing with distilled water or without washing. Properties of the initial and oxidized samples were investigated using elemental carbon, hydrogen, nitrogen, oxygen (CHNO) analysis, BET (Brunauer-Emmett-Teller) determination of surface area, X-ray diffraction, Raman and Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, and hydrogen temperature-programmed reduction. Treatment with HNO3 and HNO3/H2SO4 mixture was shown to be efficient for the formation of various oxygen-containing groups on the Taunit surface; therewith, the water washing step also contributed to functionalization of the surface. Depending on the oxidant, acid treatment increased graphite and oxygen content in the samples by a factor of 3‒4.5. Treatment with HNO3 without water washing exerted a weak effect on the graphite structure ordering, the concentration of aliphatic groups was high as compared to other oxidation conditions. Treatment of Taunit with the HNO3/H2SO4 mixture, on the contrary, increased the number of defects in graphite layers and decreased the concentration of aliphatic structures.
Highlights
Carbon materials are widely used as catalyst supports, adsorbents, electrodes for supercapacitors, reinforcing fillers of polymers, fuel cell electrodes, biosensors, for the delivery of therapeutic preparations in cells, etc. [1,2,3,4]
Investigation of the composition of Carbon nanotubes (CNTs) samples by CHNSO analysis (Table 1) before oxidation (T1) and after the oxidation with acids (T1N, T1Nwash, T1NSwash) revealed that acid treatment of the carbon material increases the content of carbon and decreases the content of hydrogen, which is accompanied by a decrease in the [H]/[C] ratio
Carbon nanotubes Taunit were treated with concentrated acids, nitric acid and a mixture of nitric and sulfuric acids taken in the volume ratio 1/1 at a temperature of 85 °C for 1 h
Summary
Carbon materials are widely used as catalyst supports, adsorbents, electrodes for supercapacitors, reinforcing fillers of polymers, fuel cell electrodes, biosensors, for the delivery of therapeutic preparations in cells, etc. [1,2,3,4]. [1,2,3,4] Such a wide application of carbon materials is based on the variety of their morphological structures (nanotubes, nanofibers, amorphous carbon, and others), electronic properties, chemical stability in aggressive media, inertness toward the supported catalytically active component, the possibility of recovering the deposited noble metals by burning of the support, etc. Carbon nanotubes (CNTs) consist of coaxial carbon layers, the number of which varies from 1 to 50, and have a cavity inside the tube [10]. In CNFs, in distinction to carbon nanotubes, multiple cuts or partially closed edges of graphenes terminate at the external surface of the fiber, which makes it possible to use CNFs in catalysis. The CNT surface can readily be functionalized, opening a way for selective deposition of active metals [15]
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