Organic–Inorganic Ternary Nanohybrids of Single-Walled Carbon Nanohorns for Room Temperature Chemiresistive Ethanol Detection

Abstract

Organic–inorganic ternary nanohybrids consisting of oxidized-single walled carbon nanohorns-SnO2-polyvinylpyrrolidone (ox-SWCNH/SnO2/PVP) with stoichiometry 1/1/1 and 2/1/1 and ox-SWCNH/ZnO/PVP = 5/2/1 and 5/3/2 (all mass ratios) were synthesized and characterized as sensing films of chemiresistive test structures for ethanol vapor detection in dry air, in the range from 0 up to 50 mg/L. All the sensing films had an ox-SWCNH concentration in the range of 33.3–62.5 wt%. A comparison between the transfer functions and the response and recovery times of these sensing devices has shown that the structures with ox-SWCNH/SnO2/PVP = 1/1/1 have the highest relative sensitivities of 0.0022 (mg/L)−1, while the devices with ox-SWCNH/SnO2/PVP = 2/1/1 have the lowest response time (15 s) and recovery time (50 s) for a room temperature operation, proving the key role of carbonic material in shaping the static and dynamic performance of the sensor. These response and recovery times are lower than those of “heated” commercial sensors. The sensing mechanism is explained in terms of the overall response of a p-type semiconductor, where ox-SWCNH percolated between electrodes of the sensor, shunting the heterojunctions made between n-type SnO2 or ZnO and p-type ox-SWCNH. The hard–soft acid–base (HSAB) principle supports this mechanism. The low power consumption of these devices, below 2 mW, and the sensing performances at room temperature may open new avenues towards ethanol sensors for passive samplers of environment monitoring, alcohol test portable instruments and wireless network sensors for Internet of Things applications.

Ternary Nanocomposites Based on Oxidized Carbon Nanohorns as Sensing Layers for Room Temperature Resistive Humidity Sensing

“…cm −1 which are characteristic for carbon nanomaterials. The Raman band from about 3202.7 cm −1 may be associated with the so-called 2D' band and this may come from the vibration spectrum of graphite, the most important impurity from oxidized carbon nanohorns [43].…”

“…For the simplicity of our description, we use the folowing abbreviations: Sensor 111-resisitive sensor which employed sensing layer based on GO/CNHox/PVP at 1/1/1 ratio (w/w/w); Sensor 121-resisitive sensor which employed sensing layer based on GO/CNHox/PVP at 1/2/1 ratio (w/w/w); The recorded spectrum exhibits the typical D (~1338.8 cm −1 ), G (~1584.1 cm −1 ), D' (1601 cm −1 ), and second-order bands of 2D and D + D' band localized at 2655.5 and 2915.9 cm −1 which are characteristic for carbon nanomaterials. The Raman band from about 3202.7 cm −1 may be associated with the so-called 2D' band and this may come from the vibration spectrum of graphite, the most important impurity from oxidized carbon nanohorns [43].…”

“…The recorded spectrum exhibits the typical D (~1338.8 cm −1 ), G (~1584.1 cm −1 ), D’ (1601 cm −1 ), and second-order bands of 2D and D + D’ band localized at 2655.5 and 2915.9 cm −1 which are characteristic for carbon nanomaterials. The Raman band from about 3202.7 cm −1 may be associated with the so-called 2D’ band and this may come from the vibration spectrum of graphite, the most important impurity from oxidized carbon nanohorns [ 43 ].…”

“…Moreover, the well-known peaks belonging to PVP (854, 1429, 1665, 2925, and 2997 cm −1 ) [ 60 ] overlapped with the bands of nanocarbonic components. The Raman band from about 920 cm −1 , which is not assigned in the spectrum of the carbonaceous nanocomposite, may come from the overlapping of the Raman bands of the silicon substrate and PVP [ 43 ]. Some of the small Raman shifts of the peaks associated to nanocarbonic materials [ 45 ] are a consequence, most probably, of the multiple chemical interactions such as stacking interactions, hydrogen bond between oxidized carbon nanohorns, graphene oxide, and polyvinylpyrrolidone.…”

“…Different nanocomposites and nanohybrids based on oxidized carbon nanohorns (CNHox) were also used in the design and manufacturing of chemiresistive sensors for ethanol vapor detection [ 43 , 44 ].…”