Ultrasensitive Gas Detection with Boron-Doped Graphene
Ruitao Lv, Gugang Chen, Qing Li, Amber McCreary, Andrés Botello-Méndez, S. V. Morozov, Liangbo Liang, Xavier Declerck, Nestor Perea-López, David A. Cullen, Simin Feng, Ana Laura Elías, Rodolfo Cruz-Silva, Kazunori Fujisawa, Morinobu Endo, Feiyu Kang, Jean-Christophe Charlier, Vincent Meunier, Minghu Pan, Avetik R. Harutyunyan, Konstantin S. Novoselov, and Mauricio Terrones (2015).“Ultrasensitive gas detection of large-area boron-doped graphene”. PNAS, vol. 113, no. 3.
Heteroatom doping is an efficient way to modify the chemical and electronic properties of graphene. In particular, boron doping is expected to induce a p-type (boron)-conducting behavior to pristine (nondoped) graphene, which could lead to diverse applications. However, the experimental progress on atomic scale visualization and sensing properties of large-area boron-doped graphene (BG) sheets is still very scarce. This work describes the controlled growth of centimeter size, high-crystallinity BG sheets. Scanning tunneling microscopy and spectroscopy are used to visualize the atomic structure and the local density of states around boron dopants. It is confirmed that BG behaves as a p-type conductor and a unique croissant-like feature is frequently observed within the BG lattice, which is caused by the presence of boron-carbon trimers embedded within the hexagonal lattice. More interestingly, it is demonstrated for the first time that BG exhibits unique sensing capabilities when detecting toxic gases, such as NO2 and NH3, being able to detect extremely low concentrations (e.g., parts per trillion, parts per billion). This work envisions that other attractive applications could now be explored based on as-synthesized BG.
Nitrogen Doping Effects On Reverse Osmosis Performance
Josue Ortiz-Medina, Hiroki Kitano, Aaron Morelos-Gomez, Zhipeng Wang, Takumi Araki, Cheon-Soo Kang, Takuya Hayashi, Kenji Takeuchi, Takeyuki Kawaguchi, Akihiko Tanioka, Rodolfo Cruz-Silva, Mauricio Terrones, Morinobu Endo (2016). “Nanostructured carbon-based membranes: nitrogen doping effects on reverse osmosis performance”. NPG Asia Materials, 8, 4, e258.
“Ultrathin, flexible and highly water-permeable nanostructured carbon (NC)-based membranes are formed on porous polymer supports by plasma high-power impulse magnetron sputtering in order to fabricate carbon-based membranes for water desalination. The carbon membranes are produced at room temperature using mixtures of argon (Ar), nitrogen (N2) and methane (CH4) as precursors, and this procedure constitutes a simple solvent-free, waste-free scalable process. Structural characterization, molecular simulation, water permeation and salt rejection assessments are used to correlate the performance and membrane structure. Molecular simulations indicate that nitrogen doping on the carbon-based membranes drastically modifies the pore distribution and avoids the formation of clustered regions of high-density carbons. The optimum NC-based membrane has up to 96% salt rejection rate for 0.2 wt% NaCl saline water, with high water permeability ca. 25 l m−2 h−1 MPa−1. The NC-based membranes as active layers for desalination membranes exhibit attractive characteristics which render them a potential alternative to current polymeric technology used in reverse osmosis processes.”
The Local Interfacial Structure of Highly Photoresponsive Carbon Nanotubes/PbS-QDs
Kazunori Fujisawa, Ibrahima Ka, Vincent Le Borgne, Cheon-Soo Kang, Kensaku Kobayashi, Hiroyuki Muramatsu, Takuya Hayashi, Yoong Ahm Kim, Morinobu Endo, Mauricio Terrones, My Ali El Khakani (2016). “Elucidating the local interfacial structure of highly photoresponsive carbon nanotubes/PbS-QDs based nanohybrids grown by pulsed laser deposition”. Carbon, 96,145-152.
“Carbon nanotubes (CNTs)/lead sulfide (PbS) quantum dots (QDs) nanohybrids have been synthesized through the controlled decoration of CNTs by PbS-QDs by means of the pulsed laser deposition technique. The size of the PbS-QDs and their surface coverage of the CNTs’ surface are monitored through the number of laser ablation pulses. Here, while comparing both single-walled (SW) and double-walled (DW) CNTs based nanohybrids, focus is put on the investigation of their interfacial structure and the effect of inner tube. Anchoring PbS through direct sulfur-carbon chemical bonding between CNTs’ outer wall and PbS-QDs, which are thought to be profitable for efficient charge transfer but not for charge transport along CNT’s tube axis, are confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. In the case of double-walled CNTs (DWCNTs), inner tube remains unaffected by ablated PbS species, then it serves efficient conduction way for transferred photo-generated charges. This unique feature of the DWCNTs based nanohybrid, where the photocharges are generated by the chemically bonded PbS-QDs to the outer tube and then efficiently conveyed by the inner tube of the nanotubes, is highly likely at the origin of their significantly higher photo-activity (several hundred times than in SWCNTs-based nanohybrids).”
Temperature Dependence of Sensors Based On Silver-Decorated Nitrogen-Doped Multiwalled Carbon Nanotubes
Eduardo Gracia-Espino, Bernabé Rebollo-Plata, Hugo Martínez-Gutiérrez, Emilio Muñoz-Sandoval, Florentino López-Urías, Morinobu Endo, Humberto Terrones, Mauricio Terrones (2016). “Temperature Dependence of Sensors Based on Silver-Decorated Nitrogen-Doped Multiwalled Carbon Nanotubes”. Journal of Sensors, 2016, Article ID 4319498.
“Vapor sensors are easily fabricated onto alumina substrates using foils of silver-decorated nitrogen-doped multiwalled carbon nanotubes (CNX-MWNTs-Ag) as active sensing material. The vapor sensors are tested using carbon disulfide, acetone, ethanol, and chloroform vapors. The CNX-MWNTs are produced by chemical vapor deposition process and then decorated with 14 nm Ag nanoparticles (Ag-NPs). The samples are characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Our results demonstrate that Ag-decorated CNX-MWNTs exhibit a better response and sensitivity when compared with pristine CNX-MWNTs based sensors, making them promising candidates for air-pollutants environmental monitoring. The temperature effect on the sensor performance is also studied; we found that the detection mechanism could be tuned from physisorption, at room temperature, to chemisorption at higher working temperature. Finally, first-principles density functional calculations are carried out to understand the interactions between the systems involved in the sensors, finding good agreement between experimental results and the theoretical approach.”
Efficient Photovoltaic Conversion of Graphene-Carbon Nanotube Hybrid Films Grown From Solid Precursors
Xin Gan, Ruitao Lv, Junfei Bai, Zexia Zhang, Jinquan Wei, Zheng-Hong Huang, Hongwei Zhu, Feiyu Kang, Mauricio Terrones (2015). “Efficient photovoltaic conversion of graphene–carbon nanotube hybrid films grown from solid precursors”. 2D Materials, 2, 3, 034003.
“Large-area (e.g. centimeter size) graphene sheets are usually synthesized via pyrolysis of gaseous carbon precursors (e.g. methane) on metal substrates like Cu using chemical vapor deposition (CVD), but the presence of grain boundaries and the residual polymers during transfer deteriorates significantly the properties of the CVD graphene. If carbon nanotubes (CNTs) can be covalently bonded to graphene, the hybrid system could possess excellent electrical conductivity, transparency and mechanical strength. In this work, conducting and transparent CNT–graphene hybrid films were synthesized by a facile solid precursor pyrolysis method. Furthermore, the synthesized CNT–graphene hybrid films display enhanced photovoltaic conversion efficiency when compared to devices based on CNT membranes or graphene sheets. Upon chemical doping, the graphene–CNT/Si solar cells reveal power conversion efficiencies up to 8.50%.”
The Influence of Carbon Nanotubes Characteristics in their Performance as Positive Electrodes in Vanadium Redox Flow Batteries
Zoraida González, Patricia Álvarez, Clara Blanco, Sofía Vega-Díaz, Ferdinando Tristán-López, Lakshmy Pulickal Rajukumar, Rodolfo Cruz-Silva, Ana Laura Elías, Mauricio Terrones, Rosa Menéndez (2015). “The influence of carbon nanotubes characteristics in their performance as positive electrodes in vanadium redox flow batteries”. Sustainable Energy Technologies and Assessments, 9, 105-110.
“Three types of multi-walled carbon nanotubes are investigated as electrodes in the positive half-cell of a vanadium redox flow battery (VRFB). Pure (MWCNTs), nitrogen-doped (CNxMWNTs) and oxygen functionalized (MWCNT-Cs) carbon nanotubes exhibit significant structural differences at the nanoscale, as well as different chemical and physical properties. The influence of such different characteristics on the electrochemical behavior towards the VO2+/VO2+ redox reactions is investigated by cyclic voltammetry, electrochemical impedance spectroscopy and charge/discharge experiments. MWCNT-Cs exhibit the best performance despite not having the largest specific surface area, neither the greatest amount of oxygen nor nitrogen functional groups on their surface. Therefore, their enhanced performance in terms of electrochemical activity and kinetic reversibility towards the vanadium reactions and energy efficiency of the corresponding static battery, are attributed to the highest sp2 carbon content, which brings the highest electrical conductivity. These results represent a significant advance in the fundamental understanding and design of effective electrode materials that will lead to more efficient batteries.”