Gabriele Ilari

Growth and characterization of CNT–TiO2 heterostructures

Summary A thriving field in nanotechnology is to develop synergetic functions of nanomaterials by taking full advantages of unique properties of each component. In this context, combining TiO2 nanocrystals and carbon nanotubes (CNTs) offers enhanced photosensitivity and improved photocatalytic efficiency, which is key to achieving sustainable energy and preventing environmental pollution. Hence, it has aroused a tremendous research interest. This report surveys recent research on the topic of synthesis and characterization of the CNT–TiO2 interface. In particular, atomic layer deposition (ALD) offers a good control of the size, crystallinity and morphology of TiO2 on CNTs. Analytical transmission electron microscopy (TEM) techniques such as electron energy loss spectroscopy (EELS) in scanning transmission mode provides structural, chemical and electronic information with an unprecedented spatial resolution and increasingly superior energy resolution, and hence is a necessary tool to characterize the CNT–TiO2 interface, as well as other technologically relevant CNT–metal/metal oxide material systems.

Carbon–metal interfaces analyzed by aberration-corrected TEM: How copper and nickel nanoparticles interact with MWCNTs

Experimental confirmation for the stronger interaction of Ni with multi-walled carbon nanotubes (MWCNTs) compared to Cu with MWCNTs is presented. The interfaces between Cu (Ni) nanoparticles side-on oriented onto MWCNTs are analyzed with high spatial resolution electron energy-loss spectroscopy (EELS) of the carbon K-edge. The EEL spectra reveal a rehybridization from sp(2) to sp(3) hybridized carbon of the outermost MWCNT layer at the Ni interface, but no such rehybridization can be observed at the Cu interface. The EELS results are supported by transmission electron microscopy (TEM) images, which show a better wetting behavior of Ni and a smaller gap at the Ni-MWCNT interface, as compared to the corresponding Cu interfaces. The different behavior of Cu and Ni can be explained in terms of differing valence d-orbital occupancy. For the successful experimental demonstration of this effect the use of a soft chemical metal deposition technique is crucial.

Processing of Cr doped SrTiO3 nanoparticles into high surface area aerogels and thin films

We present the nonaqueous sol–gel synthesis of crystalline SrTi1−xCrxO3 (x = 0, 0.3, 2, 5, 10%) nanoparticles and their processing into highly concentrated dispersions in ethanol by surface functionalization with 2-[2-(2-methoxyethoxy) ethoxy] acetic acid (MEEAA). These stable nanoparticle dispersions can then be assembled into 2- and 3-dimensional architectures such as films and aerogels. Homogeneous transparent films with a compact microstructure and a thickness of 140 nm are prepared from the dispersion by dip coating, while efficient destabilization and supercritical drying results in nanostructured bulk aerogels with a high surface area of up to 370 m2 g−1.

Electron energy loss spectroscopy analysis of the interaction of Cr and V with MWCNTs

The presented scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) results show the strong reaction of Cr and V with the graphitic walls of MWCNTs. For Vanadium, an interfacial VC layer could be observed at the interface between VN and MWCNTs, when the samples were heated in situ to 750°C. Knowledge about this interfacial VC layer is important for the formation of VN-MWCNT hybrid materials, used in supercapacitor electrodes, often synthesized at high temperatures. Chromium reacts at 500°C with the MWCNTs to form Cr3C2 and in some cases, dissolved the MWCNT completely. Together with the previously published results about the interaction of MWCNTs with Cu (no interaction) and Ni (a slight rehybridisation trend for the outermost MWCNT-wall observed with EELS) (Ilari et al., 2015) the influence of the valence d-orbital occupancy of 3d transition metals on the interaction strength with CNTs is shown experimentally. For a transition metal to form chemical bonds towards CNT-walls, unoccupied states in its valence d-orbitals are needed. While Ni (2 unoccupied states) interacts only slightly, Cr (5 unoccupied states) and V (7 unoccupied states) react much stronger and can dissolve the MWCNTs, at least partially.