Dispersion of metal nanoparticles on carbon nanotubes with few surface oxygen functional groups
Graphical Abstract
Uniform dispersion of metal oxide nanoparticles was achieved on carbon nanotubes (CNTs) even with a very small amount of surface oxygen functional groups (SOFGs), mediated by ethylene glycol and hydroxide.
Research Highlights
► Metal nanoparticles have been uniformly dispersed on carbon nanotube (CNT) surfaces ► Particle size distribution does not vary with the amount of SOFGs groups on CNTs. ► A similar particle size distribution has been achieved for several transition metal oxides. ► It was mediated by the co-presence of ethylene glycol and NaOH on CNT surface.
Introduction
Carbon nanotubes (CNTs) have evoked wide interest due to their potential applications in chemical sensors, energy storage, and catalysis [1], [2], [3]. Construction of these devices and catalysts requires decoration of CNT surfaces with metal nanoparticles. Extensive studies reveal that surface oxygen functional groups (SOFGs) on CNTs are essential for homogeneous dispersion of metal nanoparticles because they act as anchoring sites or nucleation sites for metal precursors [4], [5]. Although these SOFGs can be easily introduced via chemical oxidation of CNTs, this is unfortunately at the expenses of uniform graphene walls due to the damage and corrosion by oxidizing agents. Therefore, efforts to develop methods for homogeneous dispersion of metal nanoparticles on carbon surfaces without or with a very low amount of SOFGs have never stopped [6], [7].
We reported here a simple and versatile method for homogeneous dispersion of metal nanoparticles on CNT surfaces with varying amounts of SOFGs. The uniform dispersion of metal oxide nanoparticles likely relates to the presence of ethylene glycol (EG) and the addition sequence of NaOH and metal salt precursors.
Section snippets
Deposition of metal oxide particles
CNTs with varying amounts of SOFGs were obtained by treating pristine CNTs (Chengdu Organic Chemicals Co., LTD) in HNO3 under different conditions. The sample treated in 15 M HNO3 for 12 h at 130 °C was denoted as HCNT while those treated in 5 M HNO3 for 5 h at 110 °C as LCNT. HCNT-Ar was referred to the sample HCNT treated for 12 h at 1200 °C in Ar. For comparison, reduced graphene oxide was also used, which had been prepared according to a reported method [8].
The procedure of our novel method is
Results and discussion
The amounts and types of SOFGs are usually characterized by TPD in an inert atmosphere, which gives CO and CO2 signals resulting from thermal decomposition of the SOFGs. The TPD profiles in Fig. 1a and b show that HCNT, LCNT and HCNT-Ar all give CO and CO2 as products in similar temperature ranges. It indicates that similar types of SOFGs exist on these CNT surfaces. However, the integrated peak areas of CO and CO2 for HCNT are 2 and 5 times higher than those for LCNT respectively, indicating a
Summary
We have developed a facile method which enables homogeneous dispersion of metal oxide nanoparticles on carbon materials independence of the amounts of SOFGs. It involves homogeneous distribution of OH− on CNT surface, mediated by EG via hydrogen bonds. The experiments using carbon materials upon treatments in different concentration nitric acid and high temperature annealing as supports leading to a similar particle size distribution for iron, nickel and palladium verify the validity of our
Acknowledgement
We acknowledge the financial support from the Natural Science Foundation of China (project nos. 11079005 and 21033009).
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