Carbon Nanotubes and Graphene - Research and Applications

We investigate the impact of the tailored load of gold (Au) nanoclusters functionalizing the sidewalls of the carbon nanotubes (CNTs) networks on gas sensing performance of a chemiresistor, operating at a working temperature in the range of 20–250 °C. CNTs networked films have been grown by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) technology onto low-cost alumina substrate, provided with 6 nm nominally thick cobalt (Co) growth-catalyst. Nanoclusters of Au have been deposited by sputtering onto CNTs networks with a controlled loading of equivalent thickness of 2.5, 5 and 10 nm. Microstructure and morphology of the CNTs have been characterized by FE-SEM and TEM with diameter of the bundles of nanotubules of 10–40 nm. CNTs and Au-modified CNTs exhibit a p-type response with a decrease in electrical resistance upon exposure to oxidizing NO₂ gas and an increase in resistance upon exposure to reducing gases (NH₃, CO, N₂O, H₂S, SO₂). Negligible response has been found for CNTs and Au-modified CNTs sensors exposed to CO, N₂O, SO₂. In the contrast, significantly enhanced gas response of NO₂, H₂S and NH₃, up to a low limit of sub-ppm level, has been measured for Au-functionalized CNTs-chemiresistors. Highest gas sensitivity to NO₂, H₂S and NH₃ has been found by CNTs functionalized with Au loading of 5 nm, at 200 °C. An optimal operating temperature for each Au-modified CNTs-sensor exposed to NO₂ gas has been recorded. Good repeatability of the electrical response to 200 ppb NO₂ is also reported, at 200 °C. These results demonstrate the efficiency of the CNTs-chemiresistors functionalized with Au nanoclusters for selective air-pollutants environmental monitoring applications.

(M. Penza, R. Rossi, M. Alvisi, G. Cassano and E. Serra, Sensors and Actuators B: Chemical, Article in Press, 2009, doi:10.1016/j.snb.2009.04.008)

The comparison of two deposition techniques, screen-printing and dip-coating, to cover non-conductive glass substrates with TiO₂:Multiwall Carbon Nanotubes (MWCNT), and its application as chemical sensors are reported. A sol–gel solution containing Ti-isopropoxide and acid treated MWCNT was either precipitated or kept as a sol by adjusting the pH and surfactant concentration. In the first case, screen-printing and annealing techniques were used to coat the substrates, while in the second case the substrates were dip coated and annealed several times. XRD data show the abundance of oriented rutile and anatase planes in the TiO₂ dip-coated films, when compared to the screen-printed films. For the TiO₂:MWCNT composites, the presence of carbon induces the growth of rutile in both screen-printed and dip-coated films. Additionally, dip-coated composite films are more crystalline and compact than screen-printed films, showing an average carbon content of 5–7 wt%, which is close to the 7 wt% of screen-printed films. Dip-coated composite films show n-type behaviour when sensing ammonia (NH₃), similar to the one observed for dip-coated TiO₂ but opposite to the p-type behaviour of screen-printed composites. The abundance of Ti³⁺ in dip-coating films, and/or differences in the coordination environment around the surface Ti sites, is proposed to be responsible for the differences in p/n conductivity of the composite films.
(M. Sánchez and M.E. Rincón, Sensors and Actuators B: Chemical, Article in Press, 2009, doi:10.1016/j.snb.2009.04.006)

In this work, chemical vapour deposition (CVD) synthesis of carbon nanotubes (CNT) and nanofibers on the surface of expanded vermiculite (EV) was used to produce a highly hydrophobic floatable absorvent to remove oil spilled on water. XRD, SEM, TG and Raman spectroscopy showed that the carbon nanotubes and nanofibers grow on FeMo catalyst impregnated on the EV surface to form a “sponge structure”. As a result of these carbonaceous nanosponges the absorption of different oils remarkably increased ca. 600% with a concomitant strong decrease of the undesirable water absorption.

(Flávia C.C. Moura and Rochel M. Lago, Applied Catalysis B: Environmental (2009), article in press).

Purified carboxylated multiwalled carbon nanotubes (MWCNTs) with different agglomeration propensities were evaluated in mice following a single dose intravenous injection. Both agglomerated and the well suspended MWCNTs were taken up by mononuclear phagocyte system organs. MWCNTs with higher degree of agglomeration were retained in lungs and later in the liver and were not eliminated completely in 28 days, while the well-dispersed ones remained well dispersed and formed fewer aggregates in the lungs and liver, and seemed to be easily eliminated. Persistent accumulation of agglomerated MWCNTs in the lungs caused inflammatory responses while the well-suspended ones did not. Although the elimination of MWCNTs is still to be evaluated quantitatively, the formation of a stable suspension is one of the key requirements for safe applications in medicine.
(Guangbo Qu, Yuhong Bai, Yi Zhang, Qing Jia, Weidong Zhang and Bing Yan, doi:10.1016/j.carbon.2009.03.056)

Purified carboxylated multiwalled carbon nanotubes (MWCNTs) with different agglomeration propensities were evaluated in mice following a single dose intravenous injection. Both agglomerated and the well suspended MWCNTs were taken up by mononuclear phagocyte system organs. MWCNTs with higher degree of agglomeration were retained in lungs and later in the liver and were not eliminated completely in 28 days, while the well-dispersed ones remained well dispersed and formed fewer aggregates in the lungs and liver, and seemed to be easily eliminated. Persistent accumulation of agglomerated MWCNTs in the lungs caused inflammatory responses while the well-suspended ones did not. Although the elimination of MWCNTs is still to be evaluated quantitatively, the formation of a stable suspension is one of the key requirements for safe applications in medicine.
(Guangbo Qu, Yuhong Bai, Yi Zhang, Qing Jia, Weidong Zhang, and Bing Yan, Carbon, Article in press, doi:10.1016/j.carbon.2009.03.056)

A heated composite electrode consisted of multi-wall carbon nanotube (MWNT) and ionic liquids (ILs) was designed and fabricated. The non-conductive binders were replaced by a conductive IL, n-octylpyridinum hexafluorophosphate (OPFP). This heated OPFP/MWNT composite electrode was applied for electrochemiluminescent (ECL) sensor, and the performance of ECL sensor was evaluated by ascorbic acid (AA)/lucigenin ECL system. The new heated electrode combines the advantages of ILs/CNT and heated electrode, showing high thermal stability and conductivity, simple heating setups, improved reproducibility, renewable surface, simplicity of fabrication and enhanced sensitivity with detection limit (S/N = 3) of 0.01 μmol/L for AA.

(Yiting Chen, Xiaoping Chen, Zhenyu Lin, Hong Dai, Bin Qiu, Jianjun Sun, Lan Zhang and Guonan Chen, Electrochemistry Communications, Article in Press, doi:10.1016/j.elecom.2009.03.033 )