Multiwalled Carbon Nanotube Oxygen Sensor: Enhanced Oxygen Sensitivity at Room Temperature and Mechanism of Sensing.
A pyrolysis assisted method was applied for the synthesis of defect controlled carbon nanotubes (CNTs) by varying different growth temperatures. The fabricated resistive devices containing a random network of CNTs were tested for oxygen sensing under standard room-temperature and pressure conditions. Nanotubes grown at moderate growth temperatures (870 °C), when exposed to different concentrations of oxygen, displayed a higher sensitivity (3.6%), with fast response and recovery times of about 60 and 180 s, respectively, compared to nanotubes grown at higher and lower temperatures. A room-temperature oxygen detection concentration as low as 0.3% is achieved. The fast response and recovery of CNTs are explained in terms of physisorption of oxygen molecules at (i) carboxyl functional sites and (ii) graphitic carbon sites (pristine CNT) rather than chemisorption at (iii) defected sites. Interestingly, the density functional theory simulated interaction energies (Eads) of oxygen molecules with defected CNTs (-3.381 eV) and pristine CNTs (-0.753 eV) are higher than that of the carboxyl functional sites (-0.551 eV) and are well correlated with the observed sensing response and recovery times of CNT sensors. Our results show that the carboxyl sites provide lower activation energy or shorter time for desorption of oxygen molecules to yield higher response and fast recovery of the CNT sensors.
Advanced Materials and Devices Laboratory, Department of Physics, Bharathiar University , Coimbatore - 641046, India.
Krishnamoorthy
K
Rajavel
Department of Physics, Bharathiar University , Coimbatore - 641046, India.
Murugan
M
Lalitha
Defence Bioengineering and Electrochemical Laboratory, DRDO , Bangalore - 560093, India.
Joghee Kullan
JK
Radhakrishnan
Department of Physics, Bharathiar University , Coimbatore - 641046, India.
Lakshmipathi
L
Senthilkumar
Advanced Materials and Devices Laboratory, Department of Physics, Bharathiar University , Coimbatore - 641046, India.|Department of NanoScience and Technology, Bharathiar University , Coimbatore - 641046, India.|DRDO-BU Center for Life Sciences, Bharathiar University , Coimbatore - 641046, Tamil Nadu, India.
Ramasamy Thangavelu
RT
Rajendra Kumar
carbon nanotubes; chemisorption; defect controlled; oxygen sensing; physisorption; pyrolysis